Export of internal Abseil changes.

--
906c47420646d510edd2479d5542c56f5fa31b65 by CJ Johnson <johnsoncj@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 216573923

--
74560d4afd2b605909e677c6fc3076049fb3010a by Eric Fiselier <ericwf@google.com>:

Avoid -Wformat-pedantic in benchmark.

PiperOrigin-RevId: 216523769

--
9bcc9da8b03e6d1ea43ee78931256c5541cb9686 by Eric Fiselier <ericwf@google.com>:

Delete unused CityHash functions.

PiperOrigin-RevId: 216464492

--
a42563b394c89fbb4c55cb5a6a5edbf96d271eea by Abseil Team <absl-team@google.com>:

Introduce new Abseil interfaces for converting between civil
times and absolute times.s

Deprecates absl::ConvertDateTime() and absl::FromDateTime().

PiperOrigin-RevId: 216424948

--
088e11235124267517d7f137854fa5554679c24f by Eric Fiselier <ericwf@google.com>:

Remove unneeded break statements in test.

PiperOrigin-RevId: 216403321
GitOrigin-RevId: 906c47420646d510edd2479d5542c56f5fa31b65
Change-Id: Idb44420be623e369c66f5a9c92bdc9ab46d3ec92

16 files changed, 2524 insertions, 891 deletions

diff --git a/absl/time/BUILD.bazel b/absl/time/BUILD.bazel
index c7c16d4376c7..969ddd2e6acf 100644
--- a/absl/time/BUILD.bazel
+++ b/absl/time/BUILD.bazel
@@ -27,6 +27,7 @@ licenses(["notice"])  # Apache 2.0
 cc_library(
     name = "time",
     srcs = [
+        "civil_time.cc",
         "clock.cc",
         "duration.cc",
         "format.cc",
@@ -35,6 +36,7 @@ cc_library(
         "time.cc",
     ],
     hdrs = [
+        "civil_time.h",
         "clock.h",
         "time.h",
     ],
@@ -72,10 +74,10 @@ cc_library(
 cc_test(
     name = "time_test",
     srcs = [
+        "civil_time_test.cc",
         "clock_test.cc",
         "duration_test.cc",
         "format_test.cc",
-        "time_norm_test.cc",
         "time_test.cc",
         "time_zone_test.cc",
     ],
@@ -94,6 +96,7 @@ cc_test(
 cc_test(
     name = "time_benchmark",
     srcs = [
+        "civil_time_benchmark.cc",
         "clock_benchmark.cc",
         "duration_benchmark.cc",
         "format_benchmark.cc",
diff --git a/absl/time/CMakeLists.txt b/absl/time/CMakeLists.txt
index 06272364f14e..53216cda055b 100644
--- a/absl/time/CMakeLists.txt
+++ b/absl/time/CMakeLists.txt
@@ -15,6 +15,7 @@
 #
 
 list(APPEND TIME_PUBLIC_HEADERS
+  "civil_time.h"
   "clock.h"
   "time.h"
 )
@@ -29,6 +30,7 @@ list(APPEND TIME_INTERNAL_HEADERS
 )
 
 list(APPEND TIME_SRC
+  "civil_time.cc"
   "time.cc"
   "clock.cc"
   "duration.cc"
@@ -74,11 +76,11 @@ absl_library(
 
 # test time_test
 list(APPEND TIME_TEST_SRC
+  "civil_time_test.cc"
   "time_test.cc"
   "clock_test.cc"
   "duration_test.cc"
   "format_test.cc"
-  "time_norm_test.cc"
   "time_test.cc"
   "time_zone_test.cc"
   "internal/test_util.cc"
diff --git a/absl/time/civil_time.cc b/absl/time/civil_time.cc
new file mode 100644
index 000000000000..56541799fca3
--- /dev/null
+++ b/absl/time/civil_time.cc
@@ -0,0 +1,88 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/time/civil_time.h"
+
+#include <cstdlib>
+#include <string>
+
+#include "absl/strings/str_cat.h"
+#include "absl/time/time.h"
+
+namespace absl {
+
+namespace {
+
+// Since a civil time has a larger year range than absl::Time (64-bit years vs
+// 64-bit seconds, respectively) we normalize years to roughly +/- 400 years
+// around the year 2400, which will produce an equivalent year in a range that
+// absl::Time can handle.
+inline civil_year_t NormalizeYear(civil_year_t year) {
+  return 2400 + year % 400;
+}
+
+// Formats the given CivilSecond according to the given format.
+std::string FormatYearAnd(string_view fmt, CivilSecond cs) {
+  const CivilSecond ncs(NormalizeYear(cs.year()), cs.month(), cs.day(),
+                        cs.hour(), cs.minute(), cs.second());
+  const TimeZone utc = UTCTimeZone();
+  // TODO(absl-team): Avoid conversion of fmt std::string.
+  return StrCat(cs.year(), FormatTime(std::string(fmt), FromCivil(ncs, utc), utc));
+}
+
+}  // namespace
+
+std::string FormatCivilTime(CivilSecond c) {
+  return FormatYearAnd("-%m-%dT%H:%M:%S", c);
+}
+std::string FormatCivilTime(CivilMinute c) {
+  return FormatYearAnd("-%m-%dT%H:%M", c);
+}
+std::string FormatCivilTime(CivilHour c) {
+  return FormatYearAnd("-%m-%dT%H", c);
+}
+std::string FormatCivilTime(CivilDay c) {
+  return FormatYearAnd("-%m-%d", c);
+}
+std::string FormatCivilTime(CivilMonth c) {
+  return FormatYearAnd("-%m", c);
+}
+std::string FormatCivilTime(CivilYear c) {
+  return FormatYearAnd("", c);
+}
+
+namespace time_internal {
+
+std::ostream& operator<<(std::ostream& os, CivilYear y) {
+  return os << FormatCivilTime(y);
+}
+std::ostream& operator<<(std::ostream& os, CivilMonth m) {
+  return os << FormatCivilTime(m);
+}
+std::ostream& operator<<(std::ostream& os, CivilDay d) {
+  return os << FormatCivilTime(d);
+}
+std::ostream& operator<<(std::ostream& os, CivilHour h) {
+  return os << FormatCivilTime(h);
+}
+std::ostream& operator<<(std::ostream& os, CivilMinute m) {
+  return os << FormatCivilTime(m);
+}
+std::ostream& operator<<(std::ostream& os, CivilSecond s) {
+  return os << FormatCivilTime(s);
+}
+
+}  // namespace time_internal
+
+}  // namespace absl
diff --git a/absl/time/civil_time.h b/absl/time/civil_time.h
new file mode 100644
index 000000000000..a1f553059939
--- /dev/null
+++ b/absl/time/civil_time.h
@@ -0,0 +1,487 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: civil_time.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines abstractions for computing with "civil time".
+// The term "civil time" refers to the legally recognized human-scale time
+// that is represented by the six fields `YYYY-MM-DD hh:mm:ss`. A "date"
+// is perhaps the most common example of a civil time (represented here as
+// an `absl::CivilDay`).
+//
+// Modern-day civil time follows the Gregorian Calendar and is a
+// time-zone-independent concept: a civil time of "2015-06-01 12:00:00", for
+// example, is not tied to a time zone. Put another way, a civil time does not
+// map to a unique point in time; a civil time must be mapped to an absolute
+// time *through* a time zone.
+//
+// Because a civil time is what most people think of as "time," it is common to
+// map absolute times to civil times to present to users.
+//
+// Time zones define the relationship between absolute and civil times. Given an
+// absolute or civil time and a time zone, you can compute the other time:
+//
+//   Civil Time = F(Absolute Time, Time Zone)
+//   Absolute Time = G(Civil Time, Time Zone)
+//
+// The Abseil time library allows you to construct such civil times from
+// absolute times; consult time.h for such functionality.
+//
+// This library provides six classes for constructing civil-time objects, and
+// provides several helper functions for rounding, iterating, and performing
+// arithmetic on civil-time objects, while avoiding complications like
+// daylight-saving time (DST):
+//
+//   * `absl::CivilSecond`
+//   * `absl::CivilMinute`
+//   * `absl::CivilHour`
+//   * `absl::CivilDay`
+//   * `absl::CivilMonth`
+//   * `absl::CivilYear`
+//
+// Example:
+//
+//   // Construct a civil-time object for a specific day
+//   const absl::CivilDay cd(1969, 07, 20);
+//
+//   // Construct a civil-time object for a specific second
+//   const absl::CivilSecond cd(2018, 8, 1, 12, 0, 1);
+//
+// Note: In C++14 and later, this library is usable in a constexpr context.
+//
+// Example:
+//
+//   // Valid in C++14
+//   constexpr absl::CivilDay cd(1969, 07, 20);
+//
+
+#ifndef ABSL_TIME_CIVIL_TIME_H_
+#define ABSL_TIME_CIVIL_TIME_H_
+
+#include <string>
+
+#include "absl/base/port.h"  // Needed for string vs std::string
+#include "absl/strings/string_view.h"
+#include "absl/time/internal/cctz/include/cctz/civil_time.h"
+
+namespace absl {
+
+namespace time_internal {
+struct second_tag : cctz::detail::second_tag {};
+struct minute_tag : second_tag, cctz::detail::minute_tag {};
+struct hour_tag : minute_tag, cctz::detail::hour_tag {};
+struct day_tag : hour_tag, cctz::detail::day_tag {};
+struct month_tag : day_tag, cctz::detail::month_tag {};
+struct year_tag : month_tag, cctz::detail::year_tag {};
+}  // namespace time_internal
+
+// -----------------------------------------------------------------------------
+// CivilSecond, CivilMinute, CivilHour, CivilDay, CivilMonth, CivilYear
+// -----------------------------------------------------------------------------
+//
+// Each of these civil-time types is a simple value type with the same
+// interface for construction and the same six accessors for each of the civil
+// time fields (year, month, day, hour, minute, and second, aka YMDHMS). These
+// classes differ only in their alignment, which is indicated by the type name
+// and specifies the field on which arithmetic operates.
+//
+// CONSTRUCTION
+//
+// Each of the civil-time types can be constructed in two ways: by directly
+// passing to the constructor up to six integers representing the YMDHMS fields,
+// or by copying the YMDHMS fields from a differently aligned civil-time type.
+// Omitted fields are assigned their minimum valid value. Hours, minutes, and
+// seconds will be set to 0, month and day will be set to 1. Since there is no
+// minimum year, the default is 1970.
+//
+// Examples:
+//
+//   absl::CivilDay default_value;               // 1970-01-01 00:00:00
+//
+//   absl::CivilDay a(2015, 2, 3);               // 2015-02-03 00:00:00
+//   absl::CivilDay b(2015, 2, 3, 4, 5, 6);      // 2015-02-03 00:00:00
+//   absl::CivilDay c(2015);                     // 2015-01-01 00:00:00
+//
+//   absl::CivilSecond ss(2015, 2, 3, 4, 5, 6);  // 2015-02-03 04:05:06
+//   absl::CivilMinute mm(ss);                   // 2015-02-03 04:05:00
+//   absl::CivilHour hh(mm);                     // 2015-02-03 04:00:00
+//   absl::CivilDay d(hh);                       // 2015-02-03 00:00:00
+//   absl::CivilMonth m(d);                      // 2015-02-01 00:00:00
+//   absl::CivilYear y(m);                       // 2015-01-01 00:00:00
+//
+//   m = absl::CivilMonth(y);                    // 2015-01-01 00:00:00
+//   d = absl::CivilDay(m);                      // 2015-01-01 00:00:00
+//   hh = absl::CivilHour(d);                    // 2015-01-01 00:00:00
+//   mm = absl::CivilMinute(hh);                 // 2015-01-01 00:00:00
+//   ss = absl::CivilSecond(mm);                 // 2015-01-01 00:00:00
+//
+// Each civil-time class is aligned to the civil-time field indicated in the
+// class's name after normalization. Alignment is performed by setting all the
+// inferior fields to their minimum valid value (as described above). The
+// following are examples of how each of the six types would align the fields
+// representing November 22, 2015 at 12:34:56 in the afternoon. (Note: the
+// string format used here is not important; it's just a shorthand way of
+// showing the six YMDHMS fields.)
+//
+//   absl::CivilSecond   : 2015-11-22 12:34:56
+//   absl::CivilMinute   : 2015-11-22 12:34:00
+//   absl::CivilHour     : 2015-11-22 12:00:00
+//   absl::CivilDay      : 2015-11-22 00:00:00
+//   absl::CivilMonth    : 2015-11-01 00:00:00
+//   absl::CivilYear     : 2015-01-01 00:00:00
+//
+// Each civil-time type performs arithmetic on the field to which it is
+// aligned. This means that adding 1 to an absl::CivilDay increments the day
+// field (normalizing as necessary), and subtracting 7 from an absl::CivilMonth
+// operates on the month field (normalizing as necessary). All arithmetic
+// produces a valid civil time. Difference requires two similarly aligned
+// civil-time objects and returns the scalar answer in units of the objects'
+// alignment. For example, the difference between two absl::CivilHour objects
+// will give an answer in units of civil hours.
+//
+// ALIGNMENT CONVERSION
+//
+// The alignment of a civil-time object cannot change, but the object may be
+// used to construct a new object with a different alignment. This is referred
+// to as "realigning". When realigning to a type with the same or more
+// precision (e.g., absl::CivilDay -> absl::CivilSecond), the conversion may be
+// performed implicitly since no information is lost. However, if information
+// could be discarded (e.g., CivilSecond -> CivilDay), the conversion must
+// be explicit at the call site.
+//
+// Examples:
+//
+//   void UseDay(absl::CivilDay day);
+//
+//   absl::CivilSecond cs;
+//   UseDay(cs);                  // Won't compile because data may be discarded
+//   UseDay(absl::CivilDay(cs));  // OK: explicit conversion
+//
+//   absl::CivilDay cd;
+//   UseDay(cd);                  // OK: no conversion needed
+//
+//   absl::CivilMonth cm;
+//   UseDay(cm);                  // OK: implicit conversion to absl::CivilDay
+//
+// NORMALIZATION
+//
+// Normalization takes invalid values and adjusts them to produce valid values.
+// Within the civil-time library, integer arguments passed to the Civil*
+// constructors may be out-of-range, in which case they are normalized by
+// carrying overflow into a field of courser granularity to produce valid
+// civil-time objects. This normalization enables natural arithmetic on
+// constructor arguments without worrying about the field's range.
+//
+// Examples:
+//
+//   // Out-of-range; normalized to 2016-11-01
+//   absl::CivilDay d(2016, 10, 32);
+//   // Out-of-range, negative: normalized to 2016-10-30T23
+//   absl::CivilHour h1(2016, 10, 31, -1);
+//   // Normalization is cumulative: normalized to 2016-10-30T23
+//   absl::CivilHour h2(2016, 10, 32, -25);
+//
+// Note: If normalization is undesired, you can signal an error by comparing
+// the constructor arguments to the normalized values returned by the YMDHMS
+// properties.
+//
+// COMPARISON
+//
+// Comparison between civil-time objects considers all six YMDHMS fields,
+// regardless of the type's alignment. Comparison between differently aligned
+// civil-time types is allowed.
+//
+// Examples:
+//
+//   absl::CivilDay feb_3(2015, 2, 3);  // 2015-02-03 00:00:00
+//   absl::CivilDay mar_4(2015, 3, 4);  // 2015-03-04 00:00:00
+//   // feb_3 < mar_4
+//   // absl::CivilYear(feb_3) == absl::CivilYear(mar_4)
+//
+//   absl::CivilSecond feb_3_noon(2015, 2, 3, 12, 0, 0);  // 2015-02-03 12:00:00
+//   // feb_3 < feb_3_noon
+//   // feb_3 == absl::CivilDay(feb_3_noon)
+//
+//   // Iterates all the days of February 2015.
+//   for (absl::CivilDay d(2015, 2, 1); d < absl::CivilMonth(2015, 3); ++d) {
+//     // ...
+//   }
+//
+// ARITHMETIC
+//
+// Civil-time types support natural arithmetic operators such as addition,
+// subtraction, and difference. Arithmetic operates on the civil-time field
+// indicated in the type's name. Difference operators require arguments with
+// the same alignment and return the answer in units of the alignment.
+//
+// Example:
+//
+//   absl::CivilDay a(2015, 2, 3);
+//   ++a;                              // 2015-02-04 00:00:00
+//   --a;                              // 2015-02-03 00:00:00
+//   absl::CivilDay b = a + 1;         // 2015-02-04 00:00:00
+//   absl::CivilDay c = 1 + b;         // 2015-02-05 00:00:00
+//   int n = c - a;                    // n = 2 (civil days)
+//   int m = c - absl::CivilMonth(c);  // Won't compile: different types.
+//
+// ACCESSORS
+//
+// Each civil-time type has accessors for all six of the civil-time fields:
+// year, month, day, hour, minute, and second.
+//
+// civil_year_t year()
+// int          month()
+// int          day()
+// int          hour()
+// int          minute()
+// int          second()
+//
+// Recall that fields inferior to the type's aligment will be set to their
+// minimum valid value.
+//
+// Example:
+//
+//   absl::CivilDay d(2015, 6, 28);
+//   // d.year() == 2015
+//   // d.month() == 6
+//   // d.day() == 28
+//   // d.hour() == 0
+//   // d.minute() == 0
+//   // d.second() == 0
+//
+// CASE STUDY: Adding a month to January 31.
+//
+// One of the classic questions that arises when considering a civil time
+// library (or a date library or a date/time library) is this:
+//   "What is the result of adding a month to January 31?"
+// This is an interesting question because it is unclear what is meant by a
+// "month", and several different answers are possible, depending on context:
+//
+//   1. March 3 (or 2 if a leap year), if "add a month" means to add a month to
+//      the current month, and adjust the date to overflow the extra days into
+//      March. In this case the result of "February 31" would be normalized as
+//      within the civil-time library.
+//   2. February 28 (or 29 if a leap year), if "add a month" means to add a
+//      month, and adjust the date while holding the resulting month constant.
+//      In this case, the result of "February 31" would be truncated to the last
+//      day in February.
+//   3. An error. The caller may get some error, an exception, an invalid date
+//      object, or perhaps return `false`. This may make sense because there is
+//      no single unambiguously correct answer to the question.
+//
+// Practically speaking, any answer that is not what the programmer intended
+// is the wrong answer.
+//
+// The Abseil time library avoids this problem by making it impossible to
+// ask ambiguous questions. All civil-time objects are aligned to a particular
+// civil-field boundary (such as aligned to a year, month, day, hour, minute,
+// or second), and arithmetic operates on the field to which the object is
+// aligned. This means that in order to "add a month" the object must first be
+// aligned to a month boundary, which is equivalent to the first day of that
+// month.
+//
+// Of course, there are ways to compute an answer the question at hand using
+// this Abseil time library, but they require the programmer to be explicit
+// about the answer they expect. To illustrate, let's see how to compute all
+// three of the above possible answers to the question of "Jan 31 plus 1
+// month":
+//
+// Example:
+//
+//   const absl::CivilDay d(2015, 1, 31);
+//
+//   // Answer 1:
+//   // Add 1 to the month field in the constructor, and rely on normalization.
+//   const auto normalized = absl::CivilDay(d.year(), d.month() + 1, d.day());
+//   // normalized == 2015-03-03 (aka Feb 31)
+//
+//   // Answer 2:
+//   // Add 1 to month field, capping to the end of next month.
+//   const auto next_month = absl::CivilMonth(d) + 1;
+//   const auto last_day_of_next_month = absl::CivilDay(next_month + 1) - 1;
+//   const auto capped = std::min(normalized, last_day_of_next_month);
+//   // capped == 2015-02-28
+//
+//   // Answer 3:
+//   // Signal an error if the normalized answer is not in next month.
+//   if (absl::CivilMonth(normalized) != next_month) {
+//     // error, month overflow
+//   }
+//
+using CivilSecond =
+    time_internal::cctz::detail::civil_time<time_internal::second_tag>;
+using CivilMinute =
+    time_internal::cctz::detail::civil_time<time_internal::minute_tag>;
+using CivilHour =
+    time_internal::cctz::detail::civil_time<time_internal::hour_tag>;
+using CivilDay =
+    time_internal::cctz::detail::civil_time<time_internal::day_tag>;
+using CivilMonth =
+    time_internal::cctz::detail::civil_time<time_internal::month_tag>;
+using CivilYear =
+    time_internal::cctz::detail::civil_time<time_internal::year_tag>;
+
+// civil_year_t
+//
+// Type alias of a civil-time year value. This type is guaranteed to (at least)
+// support any year value supported by `time_t`.
+//
+// Example:
+//
+//   absl::CivilSecond cs = ...;
+//   absl::civil_year_t y = cs.year();
+//   cs = absl::CivilSecond(y, 1, 1, 0, 0 0);  // CivilSecond(CivilYear(cs))
+//
+using civil_year_t = time_internal::cctz::year_t;
+
+// civil_diff_t
+//
+// Type alias of the difference between two civil-time values.
+// This type is used to indicate arguments that are not
+// normalized (such as parameters to the civil-time constructors), the results
+// of civil-time subtraction, or the operand to civil-time addition.
+//
+// Example:
+//
+//   absl::civil_diff_t n_sec = cs1 - cs2;             // cs1 == cs2 + n_sec;
+//
+using civil_diff_t = time_internal::cctz::diff_t;
+
+// Weekday::monday, Weekday::tuesday, Weekday::wednesday, Weekday::thursday,
+// Weekday::friday, Weekday::saturday, Weekday::sunday
+//
+// The Weekday enum class represents the civil-time concept of a "weekday" with
+// members for all days of the week.
+//
+//   absl::Weekday wd = absl::Weekday::thursday;
+//
+using Weekday = time_internal::cctz::weekday;
+
+// GetWeekday()
+//
+// Returns the absl::Weekday for the given absl::CivilDay.
+//
+// Example:
+//
+//   absl::CivilDay a(2015, 8, 13);
+//   absl::Weekday wd = absl::GetWeekday(a);  // wd == absl::Weekday::thursday
+//
+inline Weekday GetWeekday(CivilDay cd) {
+  return time_internal::cctz::get_weekday(cd);
+}
+
+// NextWeekday()
+// PrevWeekday()
+//
+// Returns the absl::CivilDay that strictly follows or precedes a given
+// absl::CivilDay, and that falls on the given absl::Weekday.
+//
+// Example, given the following month:
+//
+//       August 2015
+//   Su Mo Tu We Th Fr Sa
+//                      1
+//    2  3  4  5  6  7  8
+//    9 10 11 12 13 14 15
+//   16 17 18 19 20 21 22
+//   23 24 25 26 27 28 29
+//   30 31
+//
+//   absl::CivilDay a(2015, 8, 13);
+//   // absl::GetWeekday(a) == absl::Weekday::thursday
+//   absl::CivilDay b = absl::NextWeekday(a, absl::Weekday::thursday);
+//   // b = 2015-08-20
+//   absl::CivilDay c = absl::PrevWeekday(a, absl::Weekday::thursday);
+//   // c = 2015-08-06
+//
+//   absl::CivilDay d = ...
+//   // Gets the following Thursday if d is not already Thursday
+//   absl::CivilDay thurs1 = absl::PrevWeekday(d, absl::Weekday::thursday) + 7;
+//   // Gets the previous Thursday if d is not already Thursday
+//   absl::CivilDay thurs2 = absl::NextWeekday(d, absl::Weekday::thursday) - 7;
+//
+inline CivilDay NextWeekday(CivilDay cd, Weekday wd) {
+  return CivilDay(time_internal::cctz::next_weekday(cd, wd));
+}
+inline CivilDay PrevWeekday(CivilDay cd, Weekday wd) {
+  return CivilDay(time_internal::cctz::prev_weekday(cd, wd));
+}
+
+// GetYearDay()
+//
+// Returns the day-of-year for the given absl::CivilDay.
+//
+// Example:
+//
+//   absl::CivilDay a(2015, 1, 1);
+//   int yd_jan_1 = absl::GetYearDay(a);   // yd_jan_1 = 1
+//   absl::CivilDay b(2015, 12, 31);
+//   int yd_dec_31 = absl::GetYearDay(b);  // yd_dec_31 = 365
+//
+inline int GetYearDay(CivilDay cd) {
+  return time_internal::cctz::get_yearday(cd);
+}
+
+// FormatCivilTime()
+//
+// Formats the given civil-time value into a string value of the following
+// format:
+//
+//  Type        | Format
+//  ---------------------------------
+//  CivilSecond | YYYY-MM-DDTHH:MM:SS
+//  CivilMinute | YYYY-MM-DDTHH:MM
+//  CivilHour   | YYYY-MM-DDTHH
+//  CivilDay    | YYYY-MM-DD
+//  CivilMonth  | YYYY-MM
+//  CivilYear   | YYYY
+//
+// Example:
+//
+//   absl::CivilDay d = absl::CivilDay(1969, 7, 20);
+//   string day_string = absl::FormatCivilTime(d);          // "1969-07-20"
+//
+std::string FormatCivilTime(CivilSecond c);
+std::string FormatCivilTime(CivilMinute c);
+std::string FormatCivilTime(CivilHour c);
+std::string FormatCivilTime(CivilDay c);
+std::string FormatCivilTime(CivilMonth c);
+std::string FormatCivilTime(CivilYear c);
+
+namespace time_internal {  // For functions found via ADL on civil-time tags.
+
+// Streaming Operators
+//
+// Each civil-time type may be sent to an output stream using operator<<().
+// The result matches the string produced by `FormatCivilTime()`.
+//
+// Example:
+//
+//   absl::CivilDay d = absl::CivilDay("1969-07-20");
+//   std::cout << "Date is: " << d << "\n";
+//
+std::ostream& operator<<(std::ostream& os, CivilYear y);
+std::ostream& operator<<(std::ostream& os, CivilMonth m);
+std::ostream& operator<<(std::ostream& os, CivilDay d);
+std::ostream& operator<<(std::ostream& os, CivilHour h);
+std::ostream& operator<<(std::ostream& os, CivilMinute m);
+std::ostream& operator<<(std::ostream& os, CivilSecond s);
+
+}  // namespace time_internal
+
+}  // namespace absl
+
+#endif  // ABSL_TIME_CIVIL_TIME_H_
diff --git a/absl/time/civil_time_benchmark.cc b/absl/time/civil_time_benchmark.cc
new file mode 100644
index 000000000000..567c2a33b12d
--- /dev/null
+++ b/absl/time/civil_time_benchmark.cc
@@ -0,0 +1,57 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/time/civil_time.h"
+
+#include "benchmark/benchmark.h"
+
+namespace {
+
+// Benchmark                            Time(ns)       CPU(ns)    Iterations
+// -------------------------------------------------------------------------
+// BM_Difference_Days                         20            20      34542508
+// BM_Step_Days                               15            15      48098146
+// BM_Format                                 688           687       1019803
+// BM_Parse                                  921           920        762788
+// BM_RoundTripFormatParse                  1766          1764        396092
+
+void BM_Difference_Days(benchmark::State& state) {
+  const absl::CivilDay c(2014, 8, 22);
+  const absl::CivilDay epoch(1970, 1, 1);
+  while (state.KeepRunning()) {
+    const absl::civil_diff_t n = c - epoch;
+    benchmark::DoNotOptimize(n);
+  }
+}
+BENCHMARK(BM_Difference_Days);
+
+void BM_Step_Days(benchmark::State& state) {
+  const absl::CivilDay kStart(2014, 8, 22);
+  absl::CivilDay c = kStart;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(++c);
+  }
+}
+BENCHMARK(BM_Step_Days);
+
+void BM_Format(benchmark::State& state) {
+  const absl::CivilSecond c(2014, 1, 2, 3, 4, 5);
+  while (state.KeepRunning()) {
+    const std::string s = absl::FormatCivilTime(c);
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_Format);
+
+}  // namespace
diff --git a/absl/time/civil_time_test.cc b/absl/time/civil_time_test.cc
new file mode 100644
index 000000000000..dc83d7a9668a
--- /dev/null
+++ b/absl/time/civil_time_test.cc
@@ -0,0 +1,1073 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/time/civil_time.h"
+
+#include <limits>
+#include <sstream>
+#include <type_traits>
+
+#include "absl/base/macros.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+TEST(CivilTime, DefaultConstruction) {
+  absl::CivilSecond ss;
+  EXPECT_EQ("1970-01-01T00:00:00", absl::FormatCivilTime(ss));
+
+  absl::CivilMinute mm;
+  EXPECT_EQ("1970-01-01T00:00", absl::FormatCivilTime(mm));
+
+  absl::CivilHour hh;
+  EXPECT_EQ("1970-01-01T00", absl::FormatCivilTime(hh));
+
+  absl::CivilDay d;
+  EXPECT_EQ("1970-01-01", absl::FormatCivilTime(d));
+
+  absl::CivilMonth m;
+  EXPECT_EQ("1970-01", absl::FormatCivilTime(m));
+
+  absl::CivilYear y;
+  EXPECT_EQ("1970", absl::FormatCivilTime(y));
+}
+
+TEST(CivilTime, StructMember) {
+  struct S {
+    absl::CivilDay day;
+  };
+  S s = {};
+  EXPECT_EQ(absl::CivilDay{}, s.day);
+}
+
+TEST(CivilTime, FieldsConstruction) {
+  EXPECT_EQ("2015-01-02T03:04:05",
+            absl::FormatCivilTime(absl::CivilSecond(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015-01-02T03:04:00",
+            absl::FormatCivilTime(absl::CivilSecond(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015-01-02T03:00:00",
+            absl::FormatCivilTime(absl::CivilSecond(2015, 1, 2, 3)));
+  EXPECT_EQ("2015-01-02T00:00:00",
+            absl::FormatCivilTime(absl::CivilSecond(2015, 1, 2)));
+  EXPECT_EQ("2015-01-01T00:00:00",
+            absl::FormatCivilTime(absl::CivilSecond(2015, 1)));
+  EXPECT_EQ("2015-01-01T00:00:00",
+            absl::FormatCivilTime(absl::CivilSecond(2015)));
+
+  EXPECT_EQ("2015-01-02T03:04",
+            absl::FormatCivilTime(absl::CivilMinute(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015-01-02T03:04",
+            absl::FormatCivilTime(absl::CivilMinute(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015-01-02T03:00",
+            absl::FormatCivilTime(absl::CivilMinute(2015, 1, 2, 3)));
+  EXPECT_EQ("2015-01-02T00:00",
+            absl::FormatCivilTime(absl::CivilMinute(2015, 1, 2)));
+  EXPECT_EQ("2015-01-01T00:00",
+            absl::FormatCivilTime(absl::CivilMinute(2015, 1)));
+  EXPECT_EQ("2015-01-01T00:00",
+            absl::FormatCivilTime(absl::CivilMinute(2015)));
+
+  EXPECT_EQ("2015-01-02T03",
+            absl::FormatCivilTime(absl::CivilHour(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015-01-02T03",
+            absl::FormatCivilTime(absl::CivilHour(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015-01-02T03",
+            absl::FormatCivilTime(absl::CivilHour(2015, 1, 2, 3)));
+  EXPECT_EQ("2015-01-02T00",
+            absl::FormatCivilTime(absl::CivilHour(2015, 1, 2)));
+  EXPECT_EQ("2015-01-01T00",
+            absl::FormatCivilTime(absl::CivilHour(2015, 1)));
+  EXPECT_EQ("2015-01-01T00",
+            absl::FormatCivilTime(absl::CivilHour(2015)));
+
+  EXPECT_EQ("2015-01-02",
+            absl::FormatCivilTime(absl::CivilDay(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015-01-02",
+            absl::FormatCivilTime(absl::CivilDay(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015-01-02",
+            absl::FormatCivilTime(absl::CivilDay(2015, 1, 2, 3)));
+  EXPECT_EQ("2015-01-02",
+            absl::FormatCivilTime(absl::CivilDay(2015, 1, 2)));
+  EXPECT_EQ("2015-01-01",
+            absl::FormatCivilTime(absl::CivilDay(2015, 1)));
+  EXPECT_EQ("2015-01-01",
+            absl::FormatCivilTime(absl::CivilDay(2015)));
+
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015, 1, 2, 3)));
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015, 1, 2)));
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015, 1)));
+  EXPECT_EQ("2015-01",
+            absl::FormatCivilTime(absl::CivilMonth(2015)));
+
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015, 1, 2, 3, 4, 5)));
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015, 1, 2, 3, 4)));
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015, 1, 2, 3)));
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015, 1, 2)));
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015, 1)));
+  EXPECT_EQ("2015",
+            absl::FormatCivilTime(absl::CivilYear(2015)));
+}
+
+TEST(CivilTime, FieldsConstructionLimits) {
+  const int kIntMax = std::numeric_limits<int>::max();
+  EXPECT_EQ("2038-01-19T03:14:07",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, 0, 0, kIntMax)));
+  EXPECT_EQ("6121-02-11T05:21:07",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, 0, kIntMax, kIntMax)));
+  EXPECT_EQ("251104-11-20T12:21:07",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, kIntMax, kIntMax, kIntMax)));
+  EXPECT_EQ("6130715-05-30T12:21:07",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, kIntMax, kIntMax, kIntMax, kIntMax)));
+  EXPECT_EQ("185087685-11-26T12:21:07",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, kIntMax, kIntMax, kIntMax, kIntMax, kIntMax)));
+
+  const int kIntMin = std::numeric_limits<int>::min();
+  EXPECT_EQ("1901-12-13T20:45:52",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, 0, 0, kIntMin)));
+  EXPECT_EQ("-2182-11-20T18:37:52",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, 0, kIntMin, kIntMin)));
+  EXPECT_EQ("-247165-02-11T10:37:52",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, 1, kIntMin, kIntMin, kIntMin)));
+  EXPECT_EQ("-6126776-08-01T10:37:52",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, 1, kIntMin, kIntMin, kIntMin, kIntMin)));
+  EXPECT_EQ("-185083747-10-31T10:37:52",
+            absl::FormatCivilTime(absl::CivilSecond(
+                1970, kIntMin, kIntMin, kIntMin, kIntMin, kIntMin)));
+}
+
+TEST(CivilTime, RangeLimits) {
+  const absl::civil_year_t kYearMax =
+      std::numeric_limits<absl::civil_year_t>::max();
+  EXPECT_EQ(absl::CivilYear(kYearMax),
+            absl::CivilYear::max());
+  EXPECT_EQ(absl::CivilMonth(kYearMax, 12),
+            absl::CivilMonth::max());
+  EXPECT_EQ(absl::CivilDay(kYearMax, 12, 31),
+            absl::CivilDay::max());
+  EXPECT_EQ(absl::CivilHour(kYearMax, 12, 31, 23),
+            absl::CivilHour::max());
+  EXPECT_EQ(absl::CivilMinute(kYearMax, 12, 31, 23, 59),
+            absl::CivilMinute::max());
+  EXPECT_EQ(absl::CivilSecond(kYearMax, 12, 31, 23, 59, 59),
+            absl::CivilSecond::max());
+
+  const absl::civil_year_t kYearMin =
+      std::numeric_limits<absl::civil_year_t>::min();
+  EXPECT_EQ(absl::CivilYear(kYearMin),
+            absl::CivilYear::min());
+  EXPECT_EQ(absl::CivilMonth(kYearMin, 1),
+            absl::CivilMonth::min());
+  EXPECT_EQ(absl::CivilDay(kYearMin, 1, 1),
+            absl::CivilDay::min());
+  EXPECT_EQ(absl::CivilHour(kYearMin, 1, 1, 0),
+            absl::CivilHour::min());
+  EXPECT_EQ(absl::CivilMinute(kYearMin, 1, 1, 0, 0),
+            absl::CivilMinute::min());
+  EXPECT_EQ(absl::CivilSecond(kYearMin, 1, 1, 0, 0, 0),
+            absl::CivilSecond::min());
+}
+
+TEST(CivilTime, ImplicitCrossAlignment) {
+  absl::CivilYear year(2015);
+  absl::CivilMonth month = year;
+  absl::CivilDay day = month;
+  absl::CivilHour hour = day;
+  absl::CivilMinute minute = hour;
+  absl::CivilSecond second = minute;
+
+  second = year;
+  EXPECT_EQ(second, year);
+  second = month;
+  EXPECT_EQ(second, month);
+  second = day;
+  EXPECT_EQ(second, day);
+  second = hour;
+  EXPECT_EQ(second, hour);
+  second = minute;
+  EXPECT_EQ(second, minute);
+
+  minute = year;
+  EXPECT_EQ(minute, year);
+  minute = month;
+  EXPECT_EQ(minute, month);
+  minute = day;
+  EXPECT_EQ(minute, day);
+  minute = hour;
+  EXPECT_EQ(minute, hour);
+
+  hour = year;
+  EXPECT_EQ(hour, year);
+  hour = month;
+  EXPECT_EQ(hour, month);
+  hour = day;
+  EXPECT_EQ(hour, day);
+
+  day = year;
+  EXPECT_EQ(day, year);
+  day = month;
+  EXPECT_EQ(day, month);
+
+  month = year;
+  EXPECT_EQ(month, year);
+
+  // Ensures unsafe conversions are not allowed.
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilSecond, absl::CivilMinute>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilSecond, absl::CivilHour>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilSecond, absl::CivilDay>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilSecond, absl::CivilMonth>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilSecond, absl::CivilYear>::value));
+
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilMinute, absl::CivilHour>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilMinute, absl::CivilDay>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilMinute, absl::CivilMonth>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilMinute, absl::CivilYear>::value));
+
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilHour, absl::CivilDay>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilHour, absl::CivilMonth>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilHour, absl::CivilYear>::value));
+
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilDay, absl::CivilMonth>::value));
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilDay, absl::CivilYear>::value));
+
+  EXPECT_FALSE(
+      (std::is_convertible<absl::CivilMonth, absl::CivilYear>::value));
+}
+
+TEST(CivilTime, ExplicitCrossAlignment) {
+  //
+  // Assign from smaller units -> larger units
+  //
+
+  absl::CivilSecond second(2015, 1, 2, 3, 4, 5);
+  EXPECT_EQ("2015-01-02T03:04:05", absl::FormatCivilTime(second));
+
+  absl::CivilMinute minute(second);
+  EXPECT_EQ("2015-01-02T03:04", absl::FormatCivilTime(minute));
+
+  absl::CivilHour hour(minute);
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(hour));
+
+  absl::CivilDay day(hour);
+  EXPECT_EQ("2015-01-02", absl::FormatCivilTime(day));
+
+  absl::CivilMonth month(day);
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(month));
+
+  absl::CivilYear year(month);
+  EXPECT_EQ("2015", absl::FormatCivilTime(year));
+
+  //
+  // Now assign from larger units -> smaller units
+  //
+
+  month = absl::CivilMonth(year);
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(month));
+
+  day = absl::CivilDay(month);
+  EXPECT_EQ("2015-01-01", absl::FormatCivilTime(day));
+
+  hour = absl::CivilHour(day);
+  EXPECT_EQ("2015-01-01T00", absl::FormatCivilTime(hour));
+
+  minute = absl::CivilMinute(hour);
+  EXPECT_EQ("2015-01-01T00:00", absl::FormatCivilTime(minute));
+
+  second = absl::CivilSecond(minute);
+  EXPECT_EQ("2015-01-01T00:00:00", absl::FormatCivilTime(second));
+}
+
+// Metafunction to test whether difference is allowed between two types.
+template <typename T1, typename T2>
+struct HasDiff {
+  template <typename U1, typename U2>
+  static std::false_type test(...);
+  template <typename U1, typename U2>
+  static std::true_type test(decltype(std::declval<U1>() - std::declval<U2>()));
+  static constexpr bool value = decltype(test<T1, T2>(0))::value;
+};
+
+TEST(CivilTime, DisallowCrossAlignedDifference) {
+  // Difference is allowed between types with the same alignment.
+  static_assert(HasDiff<absl::CivilSecond, absl::CivilSecond>::value, "");
+  static_assert(HasDiff<absl::CivilMinute, absl::CivilMinute>::value, "");
+  static_assert(HasDiff<absl::CivilHour, absl::CivilHour>::value, "");
+  static_assert(HasDiff<absl::CivilDay, absl::CivilDay>::value, "");
+  static_assert(HasDiff<absl::CivilMonth, absl::CivilMonth>::value, "");
+  static_assert(HasDiff<absl::CivilYear, absl::CivilYear>::value, "");
+
+  // Difference is disallowed between types with different alignments.
+  static_assert(!HasDiff<absl::CivilSecond, absl::CivilMinute>::value, "");
+  static_assert(!HasDiff<absl::CivilSecond, absl::CivilHour>::value, "");
+  static_assert(!HasDiff<absl::CivilSecond, absl::CivilDay>::value, "");
+  static_assert(!HasDiff<absl::CivilSecond, absl::CivilMonth>::value, "");
+  static_assert(!HasDiff<absl::CivilSecond, absl::CivilYear>::value, "");
+
+  static_assert(!HasDiff<absl::CivilMinute, absl::CivilHour>::value, "");
+  static_assert(!HasDiff<absl::CivilMinute, absl::CivilDay>::value, "");
+  static_assert(!HasDiff<absl::CivilMinute, absl::CivilMonth>::value, "");
+  static_assert(!HasDiff<absl::CivilMinute, absl::CivilYear>::value, "");
+
+  static_assert(!HasDiff<absl::CivilHour, absl::CivilDay>::value, "");
+  static_assert(!HasDiff<absl::CivilHour, absl::CivilMonth>::value, "");
+  static_assert(!HasDiff<absl::CivilHour, absl::CivilYear>::value, "");
+
+  static_assert(!HasDiff<absl::CivilDay, absl::CivilMonth>::value, "");
+  static_assert(!HasDiff<absl::CivilDay, absl::CivilYear>::value, "");
+
+  static_assert(!HasDiff<absl::CivilMonth, absl::CivilYear>::value, "");
+}
+
+TEST(CivilTime, ValueSemantics) {
+  const absl::CivilHour a(2015, 1, 2, 3);
+  const absl::CivilHour b = a;
+  const absl::CivilHour c(b);
+  absl::CivilHour d;
+  d = c;
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(d));
+}
+
+TEST(CivilTime, Relational) {
+  // Tests that the alignment unit is ignored in comparison.
+  const absl::CivilYear year(2014);
+  const absl::CivilMonth month(year);
+  EXPECT_EQ(year, month);
+
+#define TEST_RELATIONAL(OLDER, YOUNGER) \
+  do {                                  \
+    EXPECT_FALSE(OLDER < OLDER);        \
+    EXPECT_FALSE(OLDER > OLDER);        \
+    EXPECT_TRUE(OLDER >= OLDER);        \
+    EXPECT_TRUE(OLDER <= OLDER);        \
+    EXPECT_FALSE(YOUNGER < YOUNGER);    \
+    EXPECT_FALSE(YOUNGER > YOUNGER);    \
+    EXPECT_TRUE(YOUNGER >= YOUNGER);    \
+    EXPECT_TRUE(YOUNGER <= YOUNGER);    \
+    EXPECT_EQ(OLDER, OLDER);            \
+    EXPECT_NE(OLDER, YOUNGER);          \
+    EXPECT_LT(OLDER, YOUNGER);          \
+    EXPECT_LE(OLDER, YOUNGER);          \
+    EXPECT_GT(YOUNGER, OLDER);          \
+    EXPECT_GE(YOUNGER, OLDER);          \
+  } while (0)
+
+  // Alignment is ignored in comparison (verified above), so CivilSecond is
+  // used to test comparison in all field positions.
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 0, 0, 0),
+                  absl::CivilSecond(2015, 1, 1, 0, 0, 0));
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 0, 0, 0),
+                  absl::CivilSecond(2014, 2, 1, 0, 0, 0));
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 0, 0, 0),
+                  absl::CivilSecond(2014, 1, 2, 0, 0, 0));
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 0, 0, 0),
+                  absl::CivilSecond(2014, 1, 1, 1, 0, 0));
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 1, 0, 0),
+                  absl::CivilSecond(2014, 1, 1, 1, 1, 0));
+  TEST_RELATIONAL(absl::CivilSecond(2014, 1, 1, 1, 1, 0),
+                  absl::CivilSecond(2014, 1, 1, 1, 1, 1));
+
+  // Tests the relational operators of two different civil-time types.
+  TEST_RELATIONAL(absl::CivilDay(2014, 1, 1),
+                  absl::CivilMinute(2014, 1, 1, 1, 1));
+  TEST_RELATIONAL(absl::CivilDay(2014, 1, 1),
+                  absl::CivilMonth(2014, 2));
+
+#undef TEST_RELATIONAL
+}
+
+TEST(CivilTime, Arithmetic) {
+  absl::CivilSecond second(2015, 1, 2, 3, 4, 5);
+  EXPECT_EQ("2015-01-02T03:04:06", absl::FormatCivilTime(second += 1));
+  EXPECT_EQ("2015-01-02T03:04:07", absl::FormatCivilTime(second + 1));
+  EXPECT_EQ("2015-01-02T03:04:08", absl::FormatCivilTime(2 + second));
+  EXPECT_EQ("2015-01-02T03:04:05", absl::FormatCivilTime(second - 1));
+  EXPECT_EQ("2015-01-02T03:04:05", absl::FormatCivilTime(second -= 1));
+  EXPECT_EQ("2015-01-02T03:04:05", absl::FormatCivilTime(second++));
+  EXPECT_EQ("2015-01-02T03:04:07", absl::FormatCivilTime(++second));
+  EXPECT_EQ("2015-01-02T03:04:07", absl::FormatCivilTime(second--));
+  EXPECT_EQ("2015-01-02T03:04:05", absl::FormatCivilTime(--second));
+
+  absl::CivilMinute minute(2015, 1, 2, 3, 4);
+  EXPECT_EQ("2015-01-02T03:05", absl::FormatCivilTime(minute += 1));
+  EXPECT_EQ("2015-01-02T03:06", absl::FormatCivilTime(minute + 1));
+  EXPECT_EQ("2015-01-02T03:07", absl::FormatCivilTime(2 + minute));
+  EXPECT_EQ("2015-01-02T03:04", absl::FormatCivilTime(minute - 1));
+  EXPECT_EQ("2015-01-02T03:04", absl::FormatCivilTime(minute -= 1));
+  EXPECT_EQ("2015-01-02T03:04", absl::FormatCivilTime(minute++));
+  EXPECT_EQ("2015-01-02T03:06", absl::FormatCivilTime(++minute));
+  EXPECT_EQ("2015-01-02T03:06", absl::FormatCivilTime(minute--));
+  EXPECT_EQ("2015-01-02T03:04", absl::FormatCivilTime(--minute));
+
+  absl::CivilHour hour(2015, 1, 2, 3);
+  EXPECT_EQ("2015-01-02T04", absl::FormatCivilTime(hour += 1));
+  EXPECT_EQ("2015-01-02T05", absl::FormatCivilTime(hour + 1));
+  EXPECT_EQ("2015-01-02T06", absl::FormatCivilTime(2 + hour));
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(hour - 1));
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(hour -= 1));
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(hour++));
+  EXPECT_EQ("2015-01-02T05", absl::FormatCivilTime(++hour));
+  EXPECT_EQ("2015-01-02T05", absl::FormatCivilTime(hour--));
+  EXPECT_EQ("2015-01-02T03", absl::FormatCivilTime(--hour));
+
+  absl::CivilDay day(2015, 1, 2);
+  EXPECT_EQ("2015-01-03", absl::FormatCivilTime(day += 1));
+  EXPECT_EQ("2015-01-04", absl::FormatCivilTime(day + 1));
+  EXPECT_EQ("2015-01-05", absl::FormatCivilTime(2 + day));
+  EXPECT_EQ("2015-01-02", absl::FormatCivilTime(day - 1));
+  EXPECT_EQ("2015-01-02", absl::FormatCivilTime(day -= 1));
+  EXPECT_EQ("2015-01-02", absl::FormatCivilTime(day++));
+  EXPECT_EQ("2015-01-04", absl::FormatCivilTime(++day));
+  EXPECT_EQ("2015-01-04", absl::FormatCivilTime(day--));
+  EXPECT_EQ("2015-01-02", absl::FormatCivilTime(--day));
+
+  absl::CivilMonth month(2015, 1);
+  EXPECT_EQ("2015-02", absl::FormatCivilTime(month += 1));
+  EXPECT_EQ("2015-03", absl::FormatCivilTime(month + 1));
+  EXPECT_EQ("2015-04", absl::FormatCivilTime(2 + month));
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(month - 1));
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(month -= 1));
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(month++));
+  EXPECT_EQ("2015-03", absl::FormatCivilTime(++month));
+  EXPECT_EQ("2015-03", absl::FormatCivilTime(month--));
+  EXPECT_EQ("2015-01", absl::FormatCivilTime(--month));
+
+  absl::CivilYear year(2015);
+  EXPECT_EQ("2016", absl::FormatCivilTime(year += 1));
+  EXPECT_EQ("2017", absl::FormatCivilTime(year + 1));
+  EXPECT_EQ("2018", absl::FormatCivilTime(2 + year));
+  EXPECT_EQ("2015", absl::FormatCivilTime(year - 1));
+  EXPECT_EQ("2015", absl::FormatCivilTime(year -= 1));
+  EXPECT_EQ("2015", absl::FormatCivilTime(year++));
+  EXPECT_EQ("2017", absl::FormatCivilTime(++year));
+  EXPECT_EQ("2017", absl::FormatCivilTime(year--));
+  EXPECT_EQ("2015", absl::FormatCivilTime(--year));
+}
+
+TEST(CivilTime, ArithmeticLimits) {
+  const int kIntMax = std::numeric_limits<int>::max();
+  const int kIntMin = std::numeric_limits<int>::min();
+
+  absl::CivilSecond second(1970, 1, 1, 0, 0, 0);
+  second += kIntMax;
+  EXPECT_EQ("2038-01-19T03:14:07", absl::FormatCivilTime(second));
+  second -= kIntMax;
+  EXPECT_EQ("1970-01-01T00:00:00", absl::FormatCivilTime(second));
+  second += kIntMin;
+  EXPECT_EQ("1901-12-13T20:45:52", absl::FormatCivilTime(second));
+  second -= kIntMin;
+  EXPECT_EQ("1970-01-01T00:00:00", absl::FormatCivilTime(second));
+
+  absl::CivilMinute minute(1970, 1, 1, 0, 0);
+  minute += kIntMax;
+  EXPECT_EQ("6053-01-23T02:07", absl::FormatCivilTime(minute));
+  minute -= kIntMax;
+  EXPECT_EQ("1970-01-01T00:00", absl::FormatCivilTime(minute));
+  minute += kIntMin;
+  EXPECT_EQ("-2114-12-08T21:52", absl::FormatCivilTime(minute));
+  minute -= kIntMin;
+  EXPECT_EQ("1970-01-01T00:00", absl::FormatCivilTime(minute));
+
+  absl::CivilHour hour(1970, 1, 1, 0);
+  hour += kIntMax;
+  EXPECT_EQ("246953-10-09T07", absl::FormatCivilTime(hour));
+  hour -= kIntMax;
+  EXPECT_EQ("1970-01-01T00", absl::FormatCivilTime(hour));
+  hour += kIntMin;
+  EXPECT_EQ("-243014-03-24T16", absl::FormatCivilTime(hour));
+  hour -= kIntMin;
+  EXPECT_EQ("1970-01-01T00", absl::FormatCivilTime(hour));
+
+  absl::CivilDay day(1970, 1, 1);
+  day += kIntMax;
+  EXPECT_EQ("5881580-07-11", absl::FormatCivilTime(day));
+  day -= kIntMax;
+  EXPECT_EQ("1970-01-01", absl::FormatCivilTime(day));
+  day += kIntMin;
+  EXPECT_EQ("-5877641-06-23", absl::FormatCivilTime(day));
+  day -= kIntMin;
+  EXPECT_EQ("1970-01-01", absl::FormatCivilTime(day));
+
+  absl::CivilMonth month(1970, 1);
+  month += kIntMax;
+  EXPECT_EQ("178958940-08", absl::FormatCivilTime(month));
+  month -= kIntMax;
+  EXPECT_EQ("1970-01", absl::FormatCivilTime(month));
+  month += kIntMin;
+  EXPECT_EQ("-178955001-05", absl::FormatCivilTime(month));
+  month -= kIntMin;
+  EXPECT_EQ("1970-01", absl::FormatCivilTime(month));
+
+  absl::CivilYear year(0);
+  year += kIntMax;
+  EXPECT_EQ("2147483647", absl::FormatCivilTime(year));
+  year -= kIntMax;
+  EXPECT_EQ("0", absl::FormatCivilTime(year));
+  year += kIntMin;
+  EXPECT_EQ("-2147483648", absl::FormatCivilTime(year));
+  year -= kIntMin;
+  EXPECT_EQ("0", absl::FormatCivilTime(year));
+}
+
+TEST(CivilTime, Difference) {
+  absl::CivilSecond second(2015, 1, 2, 3, 4, 5);
+  EXPECT_EQ(0, second - second);
+  EXPECT_EQ(10, (second + 10) - second);
+  EXPECT_EQ(-10, (second - 10) - second);
+
+  absl::CivilMinute minute(2015, 1, 2, 3, 4);
+  EXPECT_EQ(0, minute - minute);
+  EXPECT_EQ(10, (minute + 10) - minute);
+  EXPECT_EQ(-10, (minute - 10) - minute);
+
+  absl::CivilHour hour(2015, 1, 2, 3);
+  EXPECT_EQ(0, hour - hour);
+  EXPECT_EQ(10, (hour + 10) - hour);
+  EXPECT_EQ(-10, (hour - 10) - hour);
+
+  absl::CivilDay day(2015, 1, 2);
+  EXPECT_EQ(0, day - day);
+  EXPECT_EQ(10, (day + 10) - day);
+  EXPECT_EQ(-10, (day - 10) - day);
+
+  absl::CivilMonth month(2015, 1);
+  EXPECT_EQ(0, month - month);
+  EXPECT_EQ(10, (month + 10) - month);
+  EXPECT_EQ(-10, (month - 10) - month);
+
+  absl::CivilYear year(2015);
+  EXPECT_EQ(0, year - year);
+  EXPECT_EQ(10, (year + 10) - year);
+  EXPECT_EQ(-10, (year - 10) - year);
+}
+
+TEST(CivilTime, DifferenceLimits) {
+  const absl::civil_diff_t kDiffMax =
+      std::numeric_limits<absl::civil_diff_t>::max();
+  const absl::civil_diff_t kDiffMin =
+      std::numeric_limits<absl::civil_diff_t>::min();
+
+  // Check day arithmetic at the end of the year range.
+  const absl::CivilDay max_day(kDiffMax, 12, 31);
+  EXPECT_EQ(1, max_day - (max_day - 1));
+  EXPECT_EQ(-1, (max_day - 1) - max_day);
+
+  // Check day arithmetic at the start of the year range.
+  const absl::CivilDay min_day(kDiffMin, 1, 1);
+  EXPECT_EQ(1, (min_day + 1) - min_day);
+  EXPECT_EQ(-1, min_day - (min_day + 1));
+
+  // Check the limits of the return value.
+  const absl::CivilDay d1(1970, 1, 1);
+  const absl::CivilDay d2(25252734927768524, 7, 27);
+  EXPECT_EQ(kDiffMax, d2 - d1);
+  EXPECT_EQ(kDiffMin, d1 - (d2 + 1));
+}
+
+TEST(CivilTime, Properties) {
+  absl::CivilSecond ss(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, ss.year());
+  EXPECT_EQ(2, ss.month());
+  EXPECT_EQ(3, ss.day());
+  EXPECT_EQ(4, ss.hour());
+  EXPECT_EQ(5, ss.minute());
+  EXPECT_EQ(6, ss.second());
+
+  absl::CivilMinute mm(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, mm.year());
+  EXPECT_EQ(2, mm.month());
+  EXPECT_EQ(3, mm.day());
+  EXPECT_EQ(4, mm.hour());
+  EXPECT_EQ(5, mm.minute());
+  EXPECT_EQ(0, mm.second());
+
+  absl::CivilHour hh(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, hh.year());
+  EXPECT_EQ(2, hh.month());
+  EXPECT_EQ(3, hh.day());
+  EXPECT_EQ(4, hh.hour());
+  EXPECT_EQ(0, hh.minute());
+  EXPECT_EQ(0, hh.second());
+
+  absl::CivilDay d(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, d.year());
+  EXPECT_EQ(2, d.month());
+  EXPECT_EQ(3, d.day());
+  EXPECT_EQ(0, d.hour());
+  EXPECT_EQ(0, d.minute());
+  EXPECT_EQ(0, d.second());
+
+  absl::CivilMonth m(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, m.year());
+  EXPECT_EQ(2, m.month());
+  EXPECT_EQ(1, m.day());
+  EXPECT_EQ(0, m.hour());
+  EXPECT_EQ(0, m.minute());
+  EXPECT_EQ(0, m.second());
+
+  absl::CivilYear y(2015, 2, 3, 4, 5, 6);
+  EXPECT_EQ(2015, y.year());
+  EXPECT_EQ(1, y.month());
+  EXPECT_EQ(1, y.day());
+  EXPECT_EQ(0, y.hour());
+  EXPECT_EQ(0, y.minute());
+  EXPECT_EQ(0, y.second());
+}
+
+TEST(CivilTime, Format) {
+  absl::CivilSecond ss;
+  EXPECT_EQ("1970-01-01T00:00:00", absl::FormatCivilTime(ss));
+
+  absl::CivilMinute mm;
+  EXPECT_EQ("1970-01-01T00:00", absl::FormatCivilTime(mm));
+
+  absl::CivilHour hh;
+  EXPECT_EQ("1970-01-01T00", absl::FormatCivilTime(hh));
+
+  absl::CivilDay d;
+  EXPECT_EQ("1970-01-01", absl::FormatCivilTime(d));
+
+  absl::CivilMonth m;
+  EXPECT_EQ("1970-01", absl::FormatCivilTime(m));
+
+  absl::CivilYear y;
+  EXPECT_EQ("1970", absl::FormatCivilTime(y));
+}
+
+TEST(CivilTime, FormatAndParseLenient) {
+  absl::CivilSecond ss;
+  EXPECT_EQ("1970-01-01T00:00:00", absl::FormatCivilTime(ss));
+
+  absl::CivilMinute mm;
+  EXPECT_EQ("1970-01-01T00:00", absl::FormatCivilTime(mm));
+
+  absl::CivilHour hh;
+  EXPECT_EQ("1970-01-01T00", absl::FormatCivilTime(hh));
+
+  absl::CivilDay d;
+  EXPECT_EQ("1970-01-01", absl::FormatCivilTime(d));
+
+  absl::CivilMonth m;
+  EXPECT_EQ("1970-01", absl::FormatCivilTime(m));
+
+  absl::CivilYear y;
+  EXPECT_EQ("1970", absl::FormatCivilTime(y));
+}
+
+TEST(CivilTime, OutputStream) {
+  absl::CivilSecond cs(2016, 2, 3, 4, 5, 6);
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilYear(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016.................X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilMonth(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016-02..............X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilDay(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016-02-03...........X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilHour(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016-02-03T04........X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilMinute(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016-02-03T04:05.....X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::CivilSecond(cs);
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..2016-02-03T04:05:06..X..", ss.str());
+  }
+  {
+    std::stringstream ss;
+    ss << std::left << std::setfill('.');
+    ss << std::setw(3) << 'X';
+    ss << std::setw(21) << absl::Weekday::wednesday;
+    ss << std::setw(3) << 'X';
+    EXPECT_EQ("X..Wednesday............X..", ss.str());
+  }
+}
+
+TEST(CivilTime, Weekday) {
+  absl::CivilDay d(1970, 1, 1);
+  EXPECT_EQ(absl::Weekday::thursday, absl::GetWeekday(d)) << d;
+
+  // We used to get this wrong for years < -30.
+  d = absl::CivilDay(-31, 12, 24);
+  EXPECT_EQ(absl::Weekday::wednesday, absl::GetWeekday(d)) << d;
+}
+
+TEST(CivilTime, NextPrevWeekday) {
+  // Jan 1, 1970 was a Thursday.
+  const absl::CivilDay thursday(1970, 1, 1);
+
+  // Thursday -> Thursday
+  absl::CivilDay d = absl::NextWeekday(thursday, absl::Weekday::thursday);
+  EXPECT_EQ(7, d - thursday) << d;
+  EXPECT_EQ(d - 14, absl::PrevWeekday(thursday, absl::Weekday::thursday));
+
+  // Thursday -> Friday
+  d = absl::NextWeekday(thursday, absl::Weekday::friday);
+  EXPECT_EQ(1, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::friday));
+
+  // Thursday -> Saturday
+  d = absl::NextWeekday(thursday, absl::Weekday::saturday);
+  EXPECT_EQ(2, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::saturday));
+
+  // Thursday -> Sunday
+  d = absl::NextWeekday(thursday, absl::Weekday::sunday);
+  EXPECT_EQ(3, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::sunday));
+
+  // Thursday -> Monday
+  d = absl::NextWeekday(thursday, absl::Weekday::monday);
+  EXPECT_EQ(4, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::monday));
+
+  // Thursday -> Tuesday
+  d = absl::NextWeekday(thursday, absl::Weekday::tuesday);
+  EXPECT_EQ(5, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::tuesday));
+
+  // Thursday -> Wednesday
+  d = absl::NextWeekday(thursday, absl::Weekday::wednesday);
+  EXPECT_EQ(6, d - thursday) << d;
+  EXPECT_EQ(d - 7, absl::PrevWeekday(thursday, absl::Weekday::wednesday));
+}
+
+// NOTE: Run this with --copt=-ftrapv to detect overflow problems.
+TEST(CivilTime, DifferenceWithHugeYear) {
+  absl::CivilDay d1(9223372036854775807, 1, 1);
+  absl::CivilDay d2(9223372036854775807, 12, 31);
+  EXPECT_EQ(364, d2 - d1);
+
+  d1 = absl::CivilDay(-9223372036854775807 - 1, 1, 1);
+  d2 = absl::CivilDay(-9223372036854775807 - 1, 12, 31);
+  EXPECT_EQ(365, d2 - d1);
+
+  // Check the limits of the return value at the end of the year range.
+  d1 = absl::CivilDay(9223372036854775807, 1, 1);
+  d2 = absl::CivilDay(9198119301927009252, 6, 6);
+  EXPECT_EQ(9223372036854775807, d1 - d2);
+  d2 = d2 - 1;
+  EXPECT_EQ(-9223372036854775807 - 1, d2 - d1);
+
+  // Check the limits of the return value at the start of the year range.
+  d1 = absl::CivilDay(-9223372036854775807 - 1, 1, 1);
+  d2 = absl::CivilDay(-9198119301927009254, 7, 28);
+  EXPECT_EQ(9223372036854775807, d2 - d1);
+  d2 = d2 + 1;
+  EXPECT_EQ(-9223372036854775807 - 1, d1 - d2);
+
+  // Check the limits of the return value from either side of year 0.
+  d1 = absl::CivilDay(-12626367463883278, 9, 3);
+  d2 = absl::CivilDay(12626367463883277, 3, 28);
+  EXPECT_EQ(9223372036854775807, d2 - d1);
+  d2 = d2 + 1;
+  EXPECT_EQ(-9223372036854775807 - 1, d1 - d2);
+}
+
+// NOTE: Run this with --copt=-ftrapv to detect overflow problems.
+TEST(CivilTime, DifferenceNoIntermediateOverflow) {
+  // The difference up to the minute field would be below the minimum
+  // int64_t, but the 52 extra seconds brings us back to the minimum.
+  absl::CivilSecond s1(-292277022657, 1, 27, 8, 29 - 1, 52);
+  absl::CivilSecond s2(1970, 1, 1, 0, 0 - 1, 0);
+  EXPECT_EQ(-9223372036854775807 - 1, s1 - s2);
+
+  // The difference up to the minute field would be above the maximum
+  // int64_t, but the -53 extra seconds brings us back to the maximum.
+  s1 = absl::CivilSecond(292277026596, 12, 4, 15, 30, 7 - 7);
+  s2 = absl::CivilSecond(1970, 1, 1, 0, 0, 0 - 7);
+  EXPECT_EQ(9223372036854775807, s1 - s2);
+}
+
+TEST(CivilTime, NormalizeSimpleOverflow) {
+  absl::CivilSecond cs;
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32, 59 + 1);
+  EXPECT_EQ("2013-11-15T16:33:00", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16, 59 + 1, 14);
+  EXPECT_EQ("2013-11-15T17:00:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 23 + 1, 32, 14);
+  EXPECT_EQ("2013-11-16T00:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 30 + 1, 16, 32, 14);
+  EXPECT_EQ("2013-12-01T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 12 + 1, 15, 16, 32, 14);
+  EXPECT_EQ("2014-01-15T16:32:14", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeSimpleUnderflow) {
+  absl::CivilSecond cs;
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32, 0 - 1);
+  EXPECT_EQ("2013-11-15T16:31:59", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16, 0 - 1, 14);
+  EXPECT_EQ("2013-11-15T15:59:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 0 - 1, 32, 14);
+  EXPECT_EQ("2013-11-14T23:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 1 - 1, 16, 32, 14);
+  EXPECT_EQ("2013-10-31T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 1 - 1, 15, 16, 32, 14);
+  EXPECT_EQ("2012-12-15T16:32:14", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeMultipleOverflow) {
+  absl::CivilSecond cs(2013, 12, 31, 23, 59, 59 + 1);
+  EXPECT_EQ("2014-01-01T00:00:00", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeMultipleUnderflow) {
+  absl::CivilSecond cs(2014, 1, 1, 0, 0, 0 - 1);
+  EXPECT_EQ("2013-12-31T23:59:59", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeOverflowLimits) {
+  absl::CivilSecond cs;
+
+  const int kintmax = std::numeric_limits<int>::max();
+  cs = absl::CivilSecond(0, kintmax, kintmax, kintmax, kintmax, kintmax);
+  EXPECT_EQ("185085715-11-27T12:21:07", absl::FormatCivilTime(cs));
+
+  const int kintmin = std::numeric_limits<int>::min();
+  cs = absl::CivilSecond(0, kintmin, kintmin, kintmin, kintmin, kintmin);
+  EXPECT_EQ("-185085717-10-31T10:37:52", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeComplexOverflow) {
+  absl::CivilSecond cs;
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32, 14 + 123456789);
+  EXPECT_EQ("2017-10-14T14:05:23", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32 + 1234567, 14);
+  EXPECT_EQ("2016-03-22T00:39:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16 + 123456, 32, 14);
+  EXPECT_EQ("2027-12-16T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15 + 1234, 16, 32, 14);
+  EXPECT_EQ("2017-04-02T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11 + 123, 15, 16, 32, 14);
+  EXPECT_EQ("2024-02-15T16:32:14", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeComplexUnderflow) {
+  absl::CivilSecond cs;
+  cs = absl::CivilSecond(1999, 3, 0, 0, 0, 0);  // year 400
+  EXPECT_EQ("1999-02-28T00:00:00", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32, 14 - 123456789);
+  EXPECT_EQ("2009-12-17T18:59:05", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16, 32 - 1234567, 14);
+  EXPECT_EQ("2011-07-12T08:25:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15, 16 - 123456, 32, 14);
+  EXPECT_EQ("1999-10-16T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11, 15 - 1234, 16, 32, 14);
+  EXPECT_EQ("2010-06-30T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11 - 123, 15, 16, 32, 14);
+  EXPECT_EQ("2003-08-15T16:32:14", absl::FormatCivilTime(cs));
+}
+
+TEST(CivilTime, NormalizeMishmash) {
+  absl::CivilSecond cs;
+  cs = absl::CivilSecond(2013, 11 - 123, 15 + 1234, 16 - 123456, 32 + 1234567,
+                         14 - 123456789);
+  EXPECT_EQ("1991-05-09T03:06:05", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11 + 123, 15 - 1234, 16 + 123456, 32 - 1234567,
+                         14 + 123456789);
+  EXPECT_EQ("2036-05-24T05:58:23", absl::FormatCivilTime(cs));
+
+  cs = absl::CivilSecond(2013, 11, -146097 + 1, 16, 32, 14);
+  EXPECT_EQ("1613-11-01T16:32:14", absl::FormatCivilTime(cs));
+  cs = absl::CivilSecond(2013, 11 + 400 * 12, -146097 + 1, 16, 32, 14);
+  EXPECT_EQ("2013-11-01T16:32:14", absl::FormatCivilTime(cs));
+}
+
+// Convert all the days from 1970-1-1 to 1970-1-146097 (aka 2369-12-31)
+// and check that they normalize to the expected time.  146097 days span
+// the 400-year Gregorian cycle used during normalization.
+TEST(CivilTime, NormalizeAllTheDays) {
+  absl::CivilDay expected(1970, 1, 1);
+  for (int day = 1; day <= 146097; ++day) {
+    absl::CivilSecond cs(1970, 1, day, 0, 0, 0);
+    EXPECT_EQ(expected, cs);
+    ++expected;
+  }
+}
+
+TEST(CivilTime, NormalizeWithHugeYear) {
+  absl::CivilMonth c(9223372036854775807, 1);
+  EXPECT_EQ("9223372036854775807-01", absl::FormatCivilTime(c));
+  c = c - 1;  // Causes normalization
+  EXPECT_EQ("9223372036854775806-12", absl::FormatCivilTime(c));
+
+  c = absl::CivilMonth(-9223372036854775807 - 1, 1);
+  EXPECT_EQ("-9223372036854775808-01", absl::FormatCivilTime(c));
+  c = c + 12;  // Causes normalization
+  EXPECT_EQ("-9223372036854775807-01", absl::FormatCivilTime(c));
+}
+
+TEST(CivilTime, LeapYears) {
+  const absl::CivilSecond s1(2013, 2, 28 + 1, 0, 0, 0);
+  EXPECT_EQ("2013-03-01T00:00:00", absl::FormatCivilTime(s1));
+
+  const absl::CivilSecond s2(2012, 2, 28 + 1, 0, 0, 0);
+  EXPECT_EQ("2012-02-29T00:00:00", absl::FormatCivilTime(s2));
+
+  const absl::CivilSecond s3(1900, 2, 28 + 1, 0, 0, 0);
+  EXPECT_EQ("1900-03-01T00:00:00", absl::FormatCivilTime(s3));
+
+  const struct {
+    int year;
+    int days;
+    struct {
+      int month;
+      int day;
+    } leap_day;  // The date of the day after Feb 28.
+  } kLeapYearTable[]{
+      {1900, 365, {3, 1}},
+      {1999, 365, {3, 1}},
+      {2000, 366, {2, 29}},  // leap year
+      {2001, 365, {3, 1}},
+      {2002, 365, {3, 1}},
+      {2003, 365, {3, 1}},
+      {2004, 366, {2, 29}},  // leap year
+      {2005, 365, {3, 1}},
+      {2006, 365, {3, 1}},
+      {2007, 365, {3, 1}},
+      {2008, 366, {2, 29}},  // leap year
+      {2009, 365, {3, 1}},
+      {2100, 365, {3, 1}},
+  };
+
+  for (int i = 0; i < ABSL_ARRAYSIZE(kLeapYearTable); ++i) {
+    const int y = kLeapYearTable[i].year;
+    const int m = kLeapYearTable[i].leap_day.month;
+    const int d = kLeapYearTable[i].leap_day.day;
+    const int n = kLeapYearTable[i].days;
+
+    // Tests incrementing through the leap day.
+    const absl::CivilDay feb28(y, 2, 28);
+    const absl::CivilDay next_day = feb28 + 1;
+    EXPECT_EQ(m, next_day.month());
+    EXPECT_EQ(d, next_day.day());
+
+    // Tests difference in days of leap years.
+    const absl::CivilYear year(feb28);
+    const absl::CivilYear next_year = year + 1;
+    EXPECT_EQ(n, absl::CivilDay(next_year) - absl::CivilDay(year));
+  }
+}
+
+TEST(CivilTime, FirstThursdayInMonth) {
+  const absl::CivilDay nov1(2014, 11, 1);
+  const absl::CivilDay thursday =
+      absl::PrevWeekday(nov1, absl::Weekday::thursday) + 7;
+  EXPECT_EQ("2014-11-06", absl::FormatCivilTime(thursday));
+
+  // Bonus: Date of Thanksgiving in the United States
+  // Rule: Fourth Thursday of November
+  const absl::CivilDay thanksgiving = thursday +  7 * 3;
+  EXPECT_EQ("2014-11-27", absl::FormatCivilTime(thanksgiving));
+}
+
+TEST(CivilTime, DocumentationExample) {
+  absl::CivilSecond second(2015, 6, 28, 1, 2, 3);  // 2015-06-28 01:02:03
+  absl::CivilMinute minute(second);                // 2015-06-28 01:02:00
+  absl::CivilDay day(minute);                      // 2015-06-28 00:00:00
+
+  second -= 1;                    // 2015-06-28 01:02:02
+  --second;                       // 2015-06-28 01:02:01
+  EXPECT_EQ(minute, second - 1);  // Comparison between types
+  EXPECT_LT(minute, second);
+
+  // int diff = second - minute;  // ERROR: Mixed types, won't compile
+
+  absl::CivilDay june_1(2015, 6, 1);  // Pass fields to c'tor.
+  int diff = day - june_1;            // Num days between 'day' and June 1
+  EXPECT_EQ(27, diff);
+
+  // Fields smaller than alignment are floored to their minimum value.
+  absl::CivilDay day_floor(2015, 1, 2, 9, 9, 9);
+  EXPECT_EQ(0, day_floor.hour());  // 09:09:09 is floored
+  EXPECT_EQ(absl::CivilDay(2015, 1, 2), day_floor);
+
+  // Unspecified fields default to their minium value
+  absl::CivilDay day_default(2015);  // Defaults to Jan 1
+  EXPECT_EQ(absl::CivilDay(2015, 1, 1), day_default);
+
+  // Iterates all the days of June.
+  absl::CivilMonth june(day);  // CivilDay -> CivilMonth
+  absl::CivilMonth july = june + 1;
+  for (absl::CivilDay day = june_1; day < july; ++day) {
+    // ...
+  }
+}
+
+}  // namespace
diff --git a/absl/time/format_benchmark.cc b/absl/time/format_benchmark.cc
index ee53d71c6854..766f1b39a55b 100644
--- a/absl/time/format_benchmark.cc
+++ b/absl/time/format_benchmark.cc
@@ -38,7 +38,8 @@ void BM_Format_FormatTime(benchmark::State& state) {
   const absl::TimeZone lax =
       absl::time_internal::LoadTimeZone("America/Los_Angeles");
   const absl::Time t =
-      absl::FromDateTime(1977, 6, 28, 9, 8, 7, lax) + absl::Nanoseconds(1);
+      absl::FromCivil(absl::CivilSecond(1977, 6, 28, 9, 8, 7), lax) +
+      absl::Nanoseconds(1);
   while (state.KeepRunning()) {
     benchmark::DoNotOptimize(absl::FormatTime(fmt, t, lax).length());
   }
@@ -50,8 +51,8 @@ void BM_Format_ParseTime(benchmark::State& state) {
   state.SetLabel(fmt);
   const absl::TimeZone lax =
       absl::time_internal::LoadTimeZone("America/Los_Angeles");
-  absl::Time t =
-      absl::FromDateTime(1977, 6, 28, 9, 8, 7, lax) + absl::Nanoseconds(1);
+  absl::Time t = absl::FromCivil(absl::CivilSecond(1977, 6, 28, 9, 8, 7), lax) +
+                 absl::Nanoseconds(1);
   const std::string when = absl::FormatTime(fmt, t, lax);
   std::string err;
   while (state.KeepRunning()) {
diff --git a/absl/time/format_test.cc b/absl/time/format_test.cc
index 7c84c33f1eb5..40f4c24633cc 100644
--- a/absl/time/format_test.cc
+++ b/absl/time/format_test.cc
@@ -118,7 +118,7 @@ TEST(FormatTime, RFC1123FormatPadsYear) {  // locale specific
   absl::TimeZone tz = absl::UTCTimeZone();
 
   // A year of 77 should be padded to 0077.
-  absl::Time t = absl::FromDateTime(77, 6, 28, 9, 8, 7, tz);
+  absl::Time t = absl::FromCivil(absl::CivilSecond(77, 6, 28, 9, 8, 7), tz);
   EXPECT_EQ("Mon, 28 Jun 0077 09:08:07 +0000",
             absl::FormatTime(absl::RFC1123_full, t, tz));
   EXPECT_EQ("28 Jun 0077 09:08:07 +0000",
@@ -154,9 +154,9 @@ TEST(ParseTime, Basics) {
   EXPECT_TRUE(absl::ParseTime("%Y-%m-%d %H:%M:%S %z",
                               "2013-06-28 19:08:09 -0800", &t, &err))
       << err;
-  absl::Time::Breakdown bd = t.In(absl::FixedTimeZone(-8 * 60 * 60));
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 6, 28, 19, 8, 9, -8 * 60 * 60, false);
-  EXPECT_EQ(absl::ZeroDuration(), bd.subsecond);
+  const auto ci = absl::FixedTimeZone(-8 * 60 * 60).At(t);
+  EXPECT_EQ(absl::CivilSecond(2013, 6, 28, 19, 8, 9), ci.cs);
+  EXPECT_EQ(absl::ZeroDuration(), ci.subsecond);
 }
 
 TEST(ParseTime, NullErrorString) {
@@ -177,17 +177,17 @@ TEST(ParseTime, WithTimeZone) {
   EXPECT_TRUE(
       absl::ParseTime("%Y-%m-%d %H:%M:%S", "2013-06-28 19:08:09", tz, &t, &e))
       << e;
-  absl::Time::Breakdown bd = t.In(tz);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 6, 28, 19, 8, 9, -7 * 60 * 60, true);
-  EXPECT_EQ(absl::ZeroDuration(), bd.subsecond);
+  auto ci = tz.At(t);
+  EXPECT_EQ(absl::CivilSecond(2013, 6, 28, 19, 8, 9), ci.cs);
+  EXPECT_EQ(absl::ZeroDuration(), ci.subsecond);
 
   // But the timezone is ignored when a UTC offset is present.
   EXPECT_TRUE(absl::ParseTime("%Y-%m-%d %H:%M:%S %z",
                               "2013-06-28 19:08:09 +0800", tz, &t, &e))
       << e;
-  bd = t.In(absl::FixedTimeZone(8 * 60 * 60));
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 6, 28, 19, 8, 9, 8 * 60 * 60, false);
-  EXPECT_EQ(absl::ZeroDuration(), bd.subsecond);
+  ci = absl::FixedTimeZone(8 * 60 * 60).At(t);
+  EXPECT_EQ(absl::CivilSecond(2013, 6, 28, 19, 8, 9), ci.cs);
+  EXPECT_EQ(absl::ZeroDuration(), ci.subsecond);
 }
 
 TEST(ParseTime, ErrorCases) {
@@ -332,15 +332,15 @@ TEST(ParseTime, InfiniteTime) {
   EXPECT_TRUE(absl::ParseTime("infinite-future %H:%M", "infinite-future 03:04",
                               &t, &err));
   EXPECT_NE(absl::InfiniteFuture(), t);
-  EXPECT_EQ(3, t.In(tz).hour);
-  EXPECT_EQ(4, t.In(tz).minute);
+  EXPECT_EQ(3, tz.At(t).cs.hour());
+  EXPECT_EQ(4, tz.At(t).cs.minute());
 
   // "infinite-past" as literal std::string
   EXPECT_TRUE(
       absl::ParseTime("infinite-past %H:%M", "infinite-past 03:04", &t, &err));
   EXPECT_NE(absl::InfinitePast(), t);
-  EXPECT_EQ(3, t.In(tz).hour);
-  EXPECT_EQ(4, t.In(tz).minute);
+  EXPECT_EQ(3, tz.At(t).cs.hour());
+  EXPECT_EQ(4, tz.At(t).cs.minute());
 
   // The input doesn't match the format.
   EXPECT_FALSE(absl::ParseTime("infinite-future %H:%M", "03:04", &t, &err));
@@ -365,16 +365,17 @@ TEST(ParseTime, FailsOnUnrepresentableTime) {
 //
 
 TEST(FormatParse, RoundTrip) {
-  const absl::TimeZone gst =
+  const absl::TimeZone lax =
       absl::time_internal::LoadTimeZone("America/Los_Angeles");
-  const absl::Time in = absl::FromDateTime(1977, 6, 28, 9, 8, 7, gst);
+  const absl::Time in =
+      absl::FromCivil(absl::CivilSecond(1977, 6, 28, 9, 8, 7), lax);
   const absl::Duration subseconds = absl::Nanoseconds(654321);
   std::string err;
 
   // RFC3339, which renders subseconds.
   {
     absl::Time out;
-    const std::string s = absl::FormatTime(absl::RFC3339_full, in + subseconds, gst);
+    const std::string s = absl::FormatTime(absl::RFC3339_full, in + subseconds, lax);
     EXPECT_TRUE(absl::ParseTime(absl::RFC3339_full, s, &out, &err))
         << s << ": " << err;
     EXPECT_EQ(in + subseconds, out);  // RFC3339_full includes %Ez
@@ -383,7 +384,7 @@ TEST(FormatParse, RoundTrip) {
   // RFC1123, which only does whole seconds.
   {
     absl::Time out;
-    const std::string s = absl::FormatTime(absl::RFC1123_full, in, gst);
+    const std::string s = absl::FormatTime(absl::RFC1123_full, in, lax);
     EXPECT_TRUE(absl::ParseTime(absl::RFC1123_full, s, &out, &err))
         << s << ": " << err;
     EXPECT_EQ(in, out);  // RFC1123_full includes %z
diff --git a/absl/time/internal/cctz/src/time_zone_posix.h b/absl/time/internal/cctz/src/time_zone_posix.h
index 9ccd4a8b68bd..ef2a8c1647db 100644
--- a/absl/time/internal/cctz/src/time_zone_posix.h
+++ b/absl/time/internal/cctz/src/time_zone_posix.h
@@ -68,25 +68,35 @@ namespace cctz {
 // it would take us to another day, and perhaps week, or even month.
 struct PosixTransition {
   enum DateFormat { J, N, M };
-  struct {
+
+  struct Date {
+    struct NonLeapDay {
+      std::int_fast16_t day;  // day of non-leap year [1:365]
+    };
+    struct Day {
+      std::int_fast16_t day;  // day of year [0:365]
+    };
+    struct MonthWeekWeekday {
+      std::int_fast8_t month;    // month of year [1:12]
+      std::int_fast8_t week;     // week of month [1:5] (5==last)
+      std::int_fast8_t weekday;  // 0==Sun, ..., 6=Sat
+    };
+
     DateFormat fmt;
+
     union {
-      struct {
-        std::int_fast16_t day;  // day of non-leap year [1:365]
-      } j;
-      struct {
-        std::int_fast16_t day;  // day of year [0:365]
-      } n;
-      struct {
-        std::int_fast8_t month;    // month of year [1:12]
-        std::int_fast8_t week;     // week of month [1:5] (5==last)
-        std::int_fast8_t weekday;  // 0==Sun, ..., 6=Sat
-      } m;
+      NonLeapDay j;
+      Day n;
+      MonthWeekWeekday m;
     };
-  } date;
-  struct {
+  };
+
+  struct Time {
     std::int_fast32_t offset;  // seconds before/after 00:00:00
-  } time;
+  };
+
+  Date date;
+  Time time;
 };
 
 // The entirety of a POSIX-string specified time-zone rule. The standard
diff --git a/absl/time/internal/test_util.cc b/absl/time/internal/test_util.cc
index bbbef7da70c4..4483f2a977e5 100644
--- a/absl/time/internal/test_util.cc
+++ b/absl/time/internal/test_util.cc
@@ -26,12 +26,6 @@ namespace cctz = absl::time_internal::cctz;
 namespace absl {
 namespace time_internal {
 
-#if GTEST_USES_SIMPLE_RE
-extern const char kZoneAbbrRE[] = ".*";  // just punt
-#else
-extern const char kZoneAbbrRE[] = "[A-Za-z]{3,4}|[-+][0-9]{2}([0-9]{2})?";
-#endif
-
 TimeZone LoadTimeZone(const std::string& name) {
   TimeZone tz;
   ABSL_RAW_CHECK(LoadTimeZone(name, &tz), name.c_str());
diff --git a/absl/time/internal/test_util.h b/absl/time/internal/test_util.h
index 8fd5fb9fd038..d99402934c67 100644
--- a/absl/time/internal/test_util.h
+++ b/absl/time/internal/test_util.h
@@ -17,35 +17,11 @@
 
 #include <string>
 
-#include "gmock/gmock.h"
-#include "gtest/gtest.h"
 #include "absl/time/time.h"
 
-// This helper is a macro so that failed expectations show up with the
-// correct line numbers.
-//
-// This is for internal testing of the Base Time library itself. This is not
-// part of a public API.
-#define ABSL_INTERNAL_EXPECT_TIME(bd, y, m, d, h, min, s, off, isdst)     \
-  do {                                                                    \
-    EXPECT_EQ(y, bd.year);                                                \
-    EXPECT_EQ(m, bd.month);                                               \
-    EXPECT_EQ(d, bd.day);                                                 \
-    EXPECT_EQ(h, bd.hour);                                                \
-    EXPECT_EQ(min, bd.minute);                                            \
-    EXPECT_EQ(s, bd.second);                                              \
-    EXPECT_EQ(off, bd.offset);                                            \
-    EXPECT_EQ(isdst, bd.is_dst);                                          \
-    EXPECT_THAT(bd.zone_abbr,                                             \
-                testing::MatchesRegex(absl::time_internal::kZoneAbbrRE)); \
-  } while (0)
-
 namespace absl {
 namespace time_internal {
 
-// A regular expression that matches all zone abbreviations (%Z).
-extern const char kZoneAbbrRE[];
-
 // Loads the named timezone, but dies on any failure.
 absl::TimeZone LoadTimeZone(const std::string& name);
 
diff --git a/absl/time/time.cc b/absl/time/time.cc
index 71fd8ee6e743..0703856fa327 100644
--- a/absl/time/time.cc
+++ b/absl/time/time.cc
@@ -22,13 +22,14 @@
 // NOTE: To keep type verbosity to a minimum, the following variable naming
 // conventions are used throughout this file.
 //
-// cz: A cctz::time_zone
 // tz: An absl::TimeZone
+// ci: An absl::TimeZone::CivilInfo
+// ti: An absl::TimeZone::TimeInfo
+// cd: An absl::CivilDay or a cctz::civil_day
+// cs: An absl::CivilSecond or a cctz::civil_second
+// bd: An absl::Time::Breakdown
 // cl: A cctz::time_zone::civil_lookup
 // al: A cctz::time_zone::absolute_lookup
-// cd: A cctz::civil_day
-// cs: A cctz::civil_second
-// bd: An absl::Time::Breakdown
 
 #include "absl/time/time.h"
 
@@ -75,7 +76,7 @@ inline absl::Time::Breakdown InfiniteFutureBreakdown() {
   return bd;
 }
 
-inline Time::Breakdown InfinitePastBreakdown() {
+inline absl::Time::Breakdown InfinitePastBreakdown() {
   Time::Breakdown bd;
   bd.year = std::numeric_limits<int64_t>::min();
   bd.month = 1;
@@ -92,6 +93,26 @@ inline Time::Breakdown InfinitePastBreakdown() {
   return bd;
 }
 
+inline absl::TimeZone::CivilInfo InfiniteFutureCivilInfo() {
+  TimeZone::CivilInfo ci;
+  ci.cs = CivilSecond::max();
+  ci.subsecond = InfiniteDuration();
+  ci.offset = 0;
+  ci.is_dst = false;
+  ci.zone_abbr = "-00";
+  return ci;
+}
+
+inline absl::TimeZone::CivilInfo InfinitePastCivilInfo() {
+  TimeZone::CivilInfo ci;
+  ci.cs = CivilSecond::min();
+  ci.subsecond = -InfiniteDuration();
+  ci.offset = 0;
+  ci.is_dst = false;
+  ci.zone_abbr = "-00";
+  return ci;
+}
+
 inline absl::TimeConversion InfiniteFutureTimeConversion() {
   absl::TimeConversion tc;
   tc.pre = tc.trans = tc.post = absl::InfiniteFuture();
@@ -134,19 +155,6 @@ Time MakeTimeWithOverflow(const cctz::time_point<cctz::seconds>& sec,
   return time_internal::FromUnixDuration(time_internal::MakeDuration(hi));
 }
 
-inline absl::TimeConversion::Kind MapKind(
-    const cctz::time_zone::civil_lookup::civil_kind& kind) {
-  switch (kind) {
-    case cctz::time_zone::civil_lookup::UNIQUE:
-      return absl::TimeConversion::UNIQUE;
-    case cctz::time_zone::civil_lookup::SKIPPED:
-      return absl::TimeConversion::SKIPPED;
-    case cctz::time_zone::civil_lookup::REPEATED:
-      return absl::TimeConversion::REPEATED;
-  }
-  return absl::TimeConversion::UNIQUE;
-}
-
 // Returns Mon=1..Sun=7.
 inline int MapWeekday(const cctz::weekday& wd) {
   switch (wd) {
@@ -170,9 +178,13 @@ inline int MapWeekday(const cctz::weekday& wd) {
 
 }  // namespace
 
+//
+// Time
+//
+
 absl::Time::Breakdown Time::In(absl::TimeZone tz) const {
-  if (*this == absl::InfiniteFuture()) return absl::InfiniteFutureBreakdown();
-  if (*this == absl::InfinitePast()) return absl::InfinitePastBreakdown();
+  if (*this == absl::InfiniteFuture()) return InfiniteFutureBreakdown();
+  if (*this == absl::InfinitePast()) return InfinitePastBreakdown();
 
   const auto tp = unix_epoch() + cctz::seconds(time_internal::GetRepHi(rep_));
   const auto al = cctz::time_zone(tz).lookup(tp);
@@ -187,92 +199,18 @@ absl::Time::Breakdown Time::In(absl::TimeZone tz) const {
   bd.minute = cs.minute();
   bd.second = cs.second();
   bd.subsecond = time_internal::MakeDuration(0, time_internal::GetRepLo(rep_));
-  bd.weekday = MapWeekday(get_weekday(cd));
-  bd.yearday = get_yearday(cd);
+  bd.weekday = MapWeekday(cctz::get_weekday(cd));
+  bd.yearday = cctz::get_yearday(cd);
   bd.offset = al.offset;
   bd.is_dst = al.is_dst;
   bd.zone_abbr = al.abbr;
   return bd;
 }
 
-absl::Time FromTM(const struct tm& tm, absl::TimeZone tz) {
-  const auto cz = cctz::time_zone(tz);
-  const auto cs =
-      cctz::civil_second(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
-                         tm.tm_hour, tm.tm_min, tm.tm_sec);
-  const auto cl = cz.lookup(cs);
-  const auto tp = tm.tm_isdst == 0 ? cl.post : cl.pre;
-  return MakeTimeWithOverflow(tp, cs, cz);
-}
-
-struct tm ToTM(absl::Time t, absl::TimeZone tz) {
-  const absl::Time::Breakdown bd = t.In(tz);
-  struct tm tm;
-  std::memset(&tm, 0, sizeof(tm));
-  tm.tm_sec = bd.second;
-  tm.tm_min = bd.minute;
-  tm.tm_hour = bd.hour;
-  tm.tm_mday = bd.day;
-  tm.tm_mon = bd.month - 1;
-
-  // Saturates tm.tm_year in cases of over/underflow, accounting for the fact
-  // that tm.tm_year is years since 1900.
-  if (bd.year < std::numeric_limits<int>::min() + 1900) {
-    tm.tm_year = std::numeric_limits<int>::min();
-  } else if (bd.year > std::numeric_limits<int>::max()) {
-    tm.tm_year = std::numeric_limits<int>::max() - 1900;
-  } else {
-    tm.tm_year = static_cast<int>(bd.year - 1900);
-  }
-
-  tm.tm_wday = bd.weekday % 7;
-  tm.tm_yday = bd.yearday - 1;
-  tm.tm_isdst = bd.is_dst ? 1 : 0;
-
-  return tm;
-}
-
 //
-// Factory functions.
+// Conversions from/to other time types.
 //
 
-absl::TimeConversion ConvertDateTime(int64_t year, int mon, int day, int hour,
-                                     int min, int sec, TimeZone tz) {
-  // Avoids years that are too extreme for civil_second to normalize.
-  if (year > 300000000000) return InfiniteFutureTimeConversion();
-  if (year < -300000000000) return InfinitePastTimeConversion();
-  const auto cz = cctz::time_zone(tz);
-  const auto cs = cctz::civil_second(year, mon, day, hour, min, sec);
-  absl::TimeConversion tc;
-  tc.normalized = year != cs.year() || mon != cs.month() || day != cs.day() ||
-                  hour != cs.hour() || min != cs.minute() || sec != cs.second();
-  const auto cl = cz.lookup(cs);
-  // Converts the civil_lookup struct to a TimeConversion.
-  tc.pre = MakeTimeWithOverflow(cl.pre, cs, cz, &tc.normalized);
-  tc.trans = MakeTimeWithOverflow(cl.trans, cs, cz, &tc.normalized);
-  tc.post = MakeTimeWithOverflow(cl.post, cs, cz, &tc.normalized);
-  tc.kind = MapKind(cl.kind);
-  return tc;
-}
-
-absl::Time FromDateTime(int64_t year, int mon, int day, int hour, int min,
-                        int sec, TimeZone tz) {
-  if (year > 300000000000) return InfiniteFuture();
-  if (year < -300000000000) return InfinitePast();
-  const auto cz = cctz::time_zone(tz);
-  const auto cs = cctz::civil_second(year, mon, day, hour, min, sec);
-  const auto cl = cz.lookup(cs);
-  return MakeTimeWithOverflow(cl.pre, cs, cz);
-}
-
-absl::Time TimeFromTimespec(timespec ts) {
-  return time_internal::FromUnixDuration(absl::DurationFromTimespec(ts));
-}
-
-absl::Time TimeFromTimeval(timeval tv) {
-  return time_internal::FromUnixDuration(absl::DurationFromTimeval(tv));
-}
-
 absl::Time FromUDate(double udate) {
   return time_internal::FromUnixDuration(absl::Milliseconds(udate));
 }
@@ -281,10 +219,6 @@ absl::Time FromUniversal(int64_t universal) {
   return absl::UniversalEpoch() + 100 * absl::Nanoseconds(universal);
 }
 
-//
-// Conversion to other time types.
-//
-
 int64_t ToUnixNanos(Time t) {
   if (time_internal::GetRepHi(time_internal::ToUnixDuration(t)) >= 0 &&
       time_internal::GetRepHi(time_internal::ToUnixDuration(t)) >> 33 == 0) {
@@ -321,6 +255,23 @@ int64_t ToUnixSeconds(Time t) {
 
 time_t ToTimeT(Time t) { return absl::ToTimespec(t).tv_sec; }
 
+double ToUDate(Time t) {
+  return absl::FDivDuration(time_internal::ToUnixDuration(t),
+                            absl::Milliseconds(1));
+}
+
+int64_t ToUniversal(absl::Time t) {
+  return absl::FloorToUnit(t - absl::UniversalEpoch(), absl::Nanoseconds(100));
+}
+
+absl::Time TimeFromTimespec(timespec ts) {
+  return time_internal::FromUnixDuration(absl::DurationFromTimespec(ts));
+}
+
+absl::Time TimeFromTimeval(timeval tv) {
+  return time_internal::FromUnixDuration(absl::DurationFromTimeval(tv));
+}
+
 timespec ToTimespec(Time t) {
   timespec ts;
   absl::Duration d = time_internal::ToUnixDuration(t);
@@ -359,15 +310,6 @@ timeval ToTimeval(Time t) {
   return tv;
 }
 
-double ToUDate(Time t) {
-  return absl::FDivDuration(time_internal::ToUnixDuration(t),
-                            absl::Milliseconds(1));
-}
-
-int64_t ToUniversal(absl::Time t) {
-  return absl::FloorToUnit(t - absl::UniversalEpoch(), absl::Nanoseconds(100));
-}
-
 Time FromChrono(const std::chrono::system_clock::time_point& tp) {
   return time_internal::FromUnixDuration(time_internal::FromChrono(
       tp - std::chrono::system_clock::from_time_t(0)));
@@ -381,4 +323,141 @@ std::chrono::system_clock::time_point ToChronoTime(absl::Time t) {
          time_internal::ToChronoDuration<D>(d);
 }
 
+//
+// TimeZone
+//
+
+absl::TimeZone::CivilInfo TimeZone::At(Time t) const {
+  if (t == absl::InfiniteFuture()) return InfiniteFutureCivilInfo();
+  if (t == absl::InfinitePast()) return InfinitePastCivilInfo();
+
+  const auto ud = time_internal::ToUnixDuration(t);
+  const auto tp = unix_epoch() + cctz::seconds(time_internal::GetRepHi(ud));
+  const auto al = cz_.lookup(tp);
+
+  TimeZone::CivilInfo ci;
+  ci.cs = CivilSecond(al.cs);
+  ci.subsecond = time_internal::MakeDuration(0, time_internal::GetRepLo(ud));
+  ci.offset = al.offset;
+  ci.is_dst = al.is_dst;
+  ci.zone_abbr = al.abbr;
+  return ci;
+}
+
+absl::TimeZone::TimeInfo TimeZone::At(CivilSecond ct) const {
+  const cctz::civil_second cs(ct);
+  const auto cl = cz_.lookup(cs);
+
+  TimeZone::TimeInfo ti;
+  switch (cl.kind) {
+    case cctz::time_zone::civil_lookup::UNIQUE:
+      ti.kind = TimeZone::TimeInfo::UNIQUE;
+      break;
+    case cctz::time_zone::civil_lookup::SKIPPED:
+      ti.kind = TimeZone::TimeInfo::SKIPPED;
+      break;
+    case cctz::time_zone::civil_lookup::REPEATED:
+      ti.kind = TimeZone::TimeInfo::REPEATED;
+      break;
+  }
+  ti.pre = MakeTimeWithOverflow(cl.pre, cs, cz_);
+  ti.trans = MakeTimeWithOverflow(cl.trans, cs, cz_);
+  ti.post = MakeTimeWithOverflow(cl.post, cs, cz_);
+  return ti;
+}
+
+//
+// Conversions involving time zones.
+//
+
+absl::TimeConversion ConvertDateTime(int64_t year, int mon, int day, int hour,
+                                     int min, int sec, TimeZone tz) {
+  // Avoids years that are too extreme for CivilSecond to normalize.
+  if (year > 300000000000) return InfiniteFutureTimeConversion();
+  if (year < -300000000000) return InfinitePastTimeConversion();
+
+  const CivilSecond cs(year, mon, day, hour, min, sec);
+  const auto ti = tz.At(cs);
+
+  TimeConversion tc;
+  tc.pre = ti.pre;
+  tc.trans = ti.trans;
+  tc.post = ti.post;
+  switch (ti.kind) {
+    case TimeZone::TimeInfo::UNIQUE:
+      tc.kind = TimeConversion::UNIQUE;
+      break;
+    case TimeZone::TimeInfo::SKIPPED:
+      tc.kind = TimeConversion::SKIPPED;
+      break;
+    case TimeZone::TimeInfo::REPEATED:
+      tc.kind = TimeConversion::REPEATED;
+      break;
+  }
+  tc.normalized = false;
+  if (year != cs.year() || mon != cs.month() || day != cs.day() ||
+      hour != cs.hour() || min != cs.minute() || sec != cs.second()) {
+    tc.normalized = true;
+  }
+  return tc;
+}
+
+absl::Time FromTM(const struct tm& tm, absl::TimeZone tz) {
+  const CivilSecond cs(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+                       tm.tm_hour, tm.tm_min, tm.tm_sec);
+  const auto ti = tz.At(cs);
+  return tm.tm_isdst == 0 ? ti.post : ti.pre;
+}
+
+struct tm ToTM(absl::Time t, absl::TimeZone tz) {
+  struct tm tm = {};
+
+  const auto ci = tz.At(t);
+  const auto& cs = ci.cs;
+  tm.tm_sec = cs.second();
+  tm.tm_min = cs.minute();
+  tm.tm_hour = cs.hour();
+  tm.tm_mday = cs.day();
+  tm.tm_mon = cs.month() - 1;
+
+  // Saturates tm.tm_year in cases of over/underflow, accounting for the fact
+  // that tm.tm_year is years since 1900.
+  if (cs.year() < std::numeric_limits<int>::min() + 1900) {
+    tm.tm_year = std::numeric_limits<int>::min();
+  } else if (cs.year() > std::numeric_limits<int>::max()) {
+    tm.tm_year = std::numeric_limits<int>::max() - 1900;
+  } else {
+    tm.tm_year = static_cast<int>(cs.year() - 1900);
+  }
+
+  const CivilDay cd(cs);
+  switch (GetWeekday(cd)) {
+    case Weekday::sunday:
+      tm.tm_wday = 0;
+      break;
+    case Weekday::monday:
+      tm.tm_wday = 1;
+      break;
+    case Weekday::tuesday:
+      tm.tm_wday = 2;
+      break;
+    case Weekday::wednesday:
+      tm.tm_wday = 3;
+      break;
+    case Weekday::thursday:
+      tm.tm_wday = 4;
+      break;
+    case Weekday::friday:
+      tm.tm_wday = 5;
+      break;
+    case Weekday::saturday:
+      tm.tm_wday = 6;
+      break;
+  }
+  tm.tm_yday = GetYearDay(cd) - 1;
+  tm.tm_isdst = ci.is_dst ? 1 : 0;
+
+  return tm;
+}
+
 }  // namespace absl
diff --git a/absl/time/time.h b/absl/time/time.h
index 50bf971df0a2..2858da2955f6 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -25,18 +25,29 @@
 //  * `absl::TimeZone` defines geopolitical time zone regions (as collected
 //     within the IANA Time Zone database (https://www.iana.org/time-zones)).
 //
+// Note: Absolute times are distinct from civil times, which refer to the
+// human-scale time commonly represented by `YYYY-MM-DD hh:mm:ss`. The mapping
+// between absolute and civil times can be specified by use of time zones
+// (`absl::TimeZone` within this API). That is:
+//
+//   Civil Time = F(Absolute Time, Time Zone)
+//   Absolute Time = G(Civil Time, Time Zone)
+//
+// See civil_time.h for abstractions related to constructing and manipulating
+// civil time.
 //
 // Example:
 //
 //   absl::TimeZone nyc;
-//
 //   // LoadTimeZone() may fail so it's always better to check for success.
 //   if (!absl::LoadTimeZone("America/New_York", &nyc)) {
 //      // handle error case
 //   }
 //
 //   // My flight leaves NYC on Jan 2, 2017 at 03:04:05
-//   absl::Time takeoff = absl::FromDateTime(2017, 1, 2, 3, 4, 5, nyc);
+//   absl::CivilSecond cs(2017, 1, 2, 3, 4, 5);
+//   absl::Time takeoff = absl::FromCivil(cs, nyc);
+//
 //   absl::Duration flight_duration = absl::Hours(21) + absl::Minutes(35);
 //   absl::Time landing = takeoff + flight_duration;
 //
@@ -48,6 +59,7 @@
 //       "My flight will land in Sydney on %Y-%m-%d at %H:%M:%S",
 //       landing, syd);
 //
+
 #ifndef ABSL_TIME_TIME_H_
 #define ABSL_TIME_TIME_H_
 
@@ -66,6 +78,7 @@
 
 #include "absl/base/port.h"  // Needed for string vs std::string
 #include "absl/strings/string_view.h"
+#include "absl/time/civil_time.h"
 #include "absl/time/internal/cctz/include/cctz/time_zone.h"
 
 namespace absl {
@@ -348,11 +361,11 @@ constexpr Duration InfiniteDuration();
 // Factory functions for constructing `Duration` values from an integral number
 // of the unit indicated by the factory function's name.
 //
-// Note: no "Days()" factory function exists because "a day" is ambiguous. Civil
-// days are not always 24 hours long, and a 24-hour duration often does not
-// correspond with a civil day. If a 24-hour duration is needed, use
-// `absl::Hours(24)`.
-//
+// Note: no "Days()" factory function exists because "a day" is ambiguous.
+// Civil days are not always 24 hours long, and a 24-hour duration often does
+// not correspond with a civil day. If a 24-hour duration is needed, use
+// `absl::Hours(24)`. (If you actually want a civil day, use absl::CivilDay
+// from civil_time.h.)
 //
 // Example:
 //
@@ -371,6 +384,7 @@ constexpr Duration Hours(int64_t n);
 // factories, which should be preferred.
 //
 // Example:
+//
 //   auto a = absl::Seconds(1.5);        // OK
 //   auto b = absl::Milliseconds(1500);  // BETTER
 template <typename T, time_internal::EnableIfFloat<T> = 0>
@@ -546,7 +560,7 @@ std::string UnparseFlag(Duration d);
 //
 // `absl::Time` uses a resolution that is high enough to avoid loss in
 // precision, and a range that is wide enough to avoid overflow, when
-// converting between tick counts in most Google time scales (i.e., precision
+// converting between tick counts in most Google time scales (i.e., resolution
 // of at least one nanosecond, and range +/-100 billion years).  Conversions
 // between the time scales are performed by truncating (towards negative
 // infinity) to the nearest representable point.
@@ -556,7 +570,6 @@ std::string UnparseFlag(Duration d);
 //   absl::Time t1 = ...;
 //   absl::Time t2 = t1 + absl::Minutes(2);
 //   absl::Duration d = t2 - t1;  // == absl::Minutes(2)
-//   absl::Time::Breakdown bd = t1.In(absl::LocalTimeZone());
 //
 class Time {
  public:
@@ -590,7 +603,10 @@ class Time {
   // intended to represent an instant in time. So, rather than passing
   // a `Time::Breakdown` to a function, pass an `absl::Time` and an
   // `absl::TimeZone`.
-  struct Breakdown {
+  //
+  // Deprecated. Use `absl::TimeZone::CivilInfo`.
+  struct
+      Breakdown {
     int64_t year;          // year (e.g., 2013)
     int month;           // month of year [1:12]
     int day;             // day of month [1:31]
@@ -614,6 +630,8 @@ class Time {
   // Time::In()
   //
   // Returns the breakdown of this instant in the given TimeZone.
+  //
+  // Deprecated. Use `absl::TimeZone::At(Time)`.
   Breakdown In(TimeZone tz) const;
 
   template <typename H>
@@ -679,126 +697,6 @@ constexpr Time InfinitePast() {
       time_internal::MakeDuration(std::numeric_limits<int64_t>::min(), ~0U));
 }
 
-// TimeConversion
-//
-// An `absl::TimeConversion` represents the conversion of year, month, day,
-// hour, minute, and second values (i.e., a civil time), in a particular
-// `absl::TimeZone`, to a time instant (an absolute time), as returned by
-// `absl::ConvertDateTime()`. (Subseconds must be handled separately.)
-//
-// It is possible, though, for a caller to try to convert values that
-// do not represent an actual or unique instant in time (due to a shift
-// in UTC offset in the `absl::TimeZone`, which results in a discontinuity in
-// the civil-time components). For example, a daylight-saving-time
-// transition skips or repeats civil times---in the United States, March
-// 13, 2011 02:15 never occurred, while November 6, 2011 01:15 occurred
-// twice---so requests for such times are not well-defined.
-//
-// To account for these possibilities, `absl::TimeConversion` is richer
-// than just a single `absl::Time`. When the civil time is skipped or
-// repeated, `absl::ConvertDateTime()` returns times calculated using the
-// pre-transition and post-transition UTC offsets, plus the transition
-// time itself.
-//
-// Examples:
-//
-//   absl::TimeZone lax;
-//   if (!absl::LoadTimeZone("America/Los_Angeles", &lax)) {
-//     // handle error case
-//   }
-//
-//   // A unique civil time
-//   absl::TimeConversion jan01 =
-//       absl::ConvertDateTime(2011, 1, 1, 0, 0, 0, lax);
-//   // jan01.kind == TimeConversion::UNIQUE
-//   // jan01.pre    is 2011/01/01 00:00:00 -0800
-//   // jan01.trans  is 2011/01/01 00:00:00 -0800
-//   // jan01.post   is 2011/01/01 00:00:00 -0800
-//
-//   // A Spring DST transition, when there is a gap in civil time
-//   absl::TimeConversion mar13 =
-//       absl::ConvertDateTime(2011, 3, 13, 2, 15, 0, lax);
-//   // mar13.kind == TimeConversion::SKIPPED
-//   // mar13.pre   is 2011/03/13 03:15:00 -0700
-//   // mar13.trans is 2011/03/13 03:00:00 -0700
-//   // mar13.post  is 2011/03/13 01:15:00 -0800
-//
-//   // A Fall DST transition, when civil times are repeated
-//   absl::TimeConversion nov06 =
-//       absl::ConvertDateTime(2011, 11, 6, 1, 15, 0, lax);
-//   // nov06.kind == TimeConversion::REPEATED
-//   // nov06.pre   is 2011/11/06 01:15:00 -0700
-//   // nov06.trans is 2011/11/06 01:00:00 -0800
-//   // nov06.post  is 2011/11/06 01:15:00 -0800
-//
-// The input month, day, hour, minute, and second values can also be
-// outside of their valid ranges, in which case they will be "normalized"
-// during the conversion.
-//
-// Example:
-//
-//   // "October 32" normalizes to "November 1".
-//   absl::TimeZone tz = absl::LocalTimeZone();
-//   absl::TimeConversion tc =
-//       absl::ConvertDateTime(2013, 10, 32, 8, 30, 0, tz);
-//   // tc.kind == TimeConversion::UNIQUE && tc.normalized == true
-//   // tc.pre.In(tz).month == 11 && tc.pre.In(tz).day == 1
-struct TimeConversion {
-  Time pre;    // time calculated using the pre-transition offset
-  Time trans;  // when the civil-time discontinuity occurred
-  Time post;   // time calculated using the post-transition offset
-
-  enum Kind {
-    UNIQUE,    // the civil time was singular (pre == trans == post)
-    SKIPPED,   // the civil time did not exist
-    REPEATED,  // the civil time was ambiguous
-  };
-  Kind kind;
-
-  bool normalized;  // input values were outside their valid ranges
-};
-
-// ConvertDateTime()
-//
-// The full generality of a civil time to absl::Time conversion.
-TimeConversion ConvertDateTime(int64_t year, int mon, int day, int hour,
-                               int min, int sec, TimeZone tz);
-
-// FromDateTime()
-//
-// A convenience wrapper for `absl::ConvertDateTime()` that simply returns the
-// "pre" `absl::Time`.  That is, the unique result, or the instant that
-// is correct using the pre-transition offset (as if the transition
-// never happened). This is typically the answer that humans expected when
-// faced with non-unique times, such as near daylight-saving time transitions.
-//
-// Example:
-//
-//   absl::TimeZone seattle;
-//   if (!absl::LoadTimeZone("America/Los_Angeles", &seattle)) {
-//     // handle error case
-//   }
-//   absl::Time t =  absl::FromDateTime(2017, 9, 26, 9, 30, 0, seattle);
-Time FromDateTime(int64_t year, int mon, int day, int hour, int min, int sec,
-                  TimeZone tz);
-
-// FromTM()
-//
-// Converts the `tm_year`, `tm_mon`, `tm_mday`, `tm_hour`, `tm_min`, and
-// `tm_sec` fields to an `absl::Time` using the given time zone. See ctime(3)
-// for a description of the expected values of the tm fields. IFF the indicated
-// time instant is not unique (see `absl::ConvertDateTime()` above), the
-// `tm_isdst` field is consulted to select the desired instant (`tm_isdst` > 0
-// means DST, `tm_isdst` == 0 means no DST, `tm_isdst` < 0 means use the default
-// like `absl::FromDateTime()`).
-Time FromTM(const struct tm& tm, TimeZone tz);
-
-// ToTM()
-//
-// Converts the given `absl::Time` to a struct tm using the given time zone.
-// See ctime(3) for a description of the values of the tm fields.
-struct tm ToTM(Time t, TimeZone tz);
-
 // FromUnixNanos()
 // FromUnixMicros()
 // FromUnixMillis()
@@ -883,6 +781,340 @@ Time FromChrono(const std::chrono::system_clock::time_point& tp);
 //   // tp == std::chrono::system_clock::from_time_t(123);
 std::chrono::system_clock::time_point ToChronoTime(Time);
 
+// Support for flag values of type Time. Time flags must be specified in a
+// format that matches absl::RFC3339_full. For example:
+//
+//   --start_time=2016-01-02T03:04:05.678+08:00
+//
+// Note: A UTC offset (or 'Z' indicating a zero-offset from UTC) is required.
+//
+// Additionally, if you'd like to specify a time as a count of
+// seconds/milliseconds/etc from the Unix epoch, use an absl::Duration flag
+// and add that duration to absl::UnixEpoch() to get an absl::Time.
+bool ParseFlag(const std::string& text, Time* t, std::string* error);
+std::string UnparseFlag(Time t);
+
+// TimeZone
+//
+// The `absl::TimeZone` is an opaque, small, value-type class representing a
+// geo-political region within which particular rules are used for converting
+// between absolute and civil times (see https://git.io/v59Ly). `absl::TimeZone`
+// values are named using the TZ identifiers from the IANA Time Zone Database,
+// such as "America/Los_Angeles" or "Australia/Sydney". `absl::TimeZone` values
+// are created from factory functions such as `absl::LoadTimeZone()`. Note:
+// strings like "PST" and "EDT" are not valid TZ identifiers. Prefer to pass by
+// value rather than const reference.
+//
+// For more on the fundamental concepts of time zones, absolute times, and civil
+// times, see https://github.com/google/cctz#fundamental-concepts
+//
+// Examples:
+//
+//   absl::TimeZone utc = absl::UTCTimeZone();
+//   absl::TimeZone pst = absl::FixedTimeZone(-8 * 60 * 60);
+//   absl::TimeZone loc = absl::LocalTimeZone();
+//   absl::TimeZone lax;
+//   if (!absl::LoadTimeZone("America/Los_Angeles", &lax)) {
+//     // handle error case
+//   }
+//
+// See also:
+// - https://github.com/google/cctz
+// - http://www.iana.org/time-zones
+// - http://en.wikipedia.org/wiki/Zoneinfo
+class TimeZone {
+ public:
+  explicit TimeZone(time_internal::cctz::time_zone tz) : cz_(tz) {}
+  TimeZone() = default;  // UTC, but prefer UTCTimeZone() to be explicit.
+  TimeZone(const TimeZone&) = default;
+  TimeZone& operator=(const TimeZone&) = default;
+
+  explicit operator time_internal::cctz::time_zone() const { return cz_; }
+
+  std::string name() const { return cz_.name(); }
+
+  // TimeZone::CivilInfo
+  //
+  // Information about the civil time corresponding to an absolute time.
+  // This struct is not intended to represent an instant in time. So, rather
+  // than passing a `TimeZone::CivilInfo` to a function, pass an `absl::Time`
+  // and an `absl::TimeZone`.
+  struct CivilInfo {
+    CivilSecond cs;
+    Duration subsecond;
+
+    // Note: The following fields exist for backward compatibility
+    // with older APIs.  Accessing these fields directly is a sign of
+    // imprudent logic in the calling code.  Modern time-related code
+    // should only access this data indirectly by way of FormatTime().
+    // These fields are undefined for InfiniteFuture() and InfinitePast().
+    int offset;             // seconds east of UTC
+    bool is_dst;            // is offset non-standard?
+    const char* zone_abbr;  // time-zone abbreviation (e.g., "PST")
+  };
+
+  // TimeZone::At(Time)
+  //
+  // Returns the civil time for this TimeZone at a certain `absl::Time`.
+  // If the input time is infinite, the output civil second will be set to
+  // CivilSecond::max() or min(), and the subsecond will be infinite.
+  //
+  // Example:
+  //
+  //   const auto epoch = lax.At(absl::UnixEpoch());
+  //   // epoch.cs == 1969-12-31 16:00:00
+  //   // epoch.subsecond == absl::ZeroDuration()
+  //   // epoch.offset == -28800
+  //   // epoch.is_dst == false
+  //   // epoch.abbr == "PST"
+  CivilInfo At(Time t) const;
+
+  // TimeZone::TimeInfo
+  //
+  // Information about the absolute times corresponding to a civil time.
+  // (Subseconds must be handled separately.)
+  //
+  // It is possible for a caller to pass a civil-time value that does
+  // not represent an actual or unique instant in time (due to a shift
+  // in UTC offset in the TimeZone, which results in a discontinuity in
+  // the civil-time components). For example, a daylight-saving-time
+  // transition skips or repeats civil times---in the United States,
+  // March 13, 2011 02:15 never occurred, while November 6, 2011 01:15
+  // occurred twice---so requests for such times are not well-defined.
+  // To account for these possibilities, `absl::TimeZone::TimeInfo` is
+  // richer than just a single `absl::Time`.
+  struct TimeInfo {
+    enum CivilKind {
+      UNIQUE,    // the civil time was singular (pre == trans == post)
+      SKIPPED,   // the civil time did not exist (pre => trans > post)
+      REPEATED,  // the civil time was ambiguous (pre < trans <= post)
+    } kind;
+    Time pre;    // time calculated using the pre-transition offset
+    Time trans;  // when the civil-time discontinuity occurred
+    Time post;   // time calculated using the post-transition offset
+  };
+
+  // TimeZone::At(CivilSecond)
+  //
+  // Returns an `absl::TimeInfo` containing the absolute time(s) for this
+  // TimeZone at an `absl::CivilSecond`. When the civil time is skipped or
+  // repeated, returns times calculated using the pre-transition and post-
+  // transition UTC offsets, plus the transition time itself.
+  //
+  // Examples:
+  //
+  //   // A unique civil time
+  //   const auto jan01 = lax.At(absl::CivilSecond(2011, 1, 1, 0, 0, 0));
+  //   // jan01.kind == TimeZone::TimeInfo::UNIQUE
+  //   // jan01.pre    is 2011-01-01 00:00:00 -0800
+  //   // jan01.trans  is 2011-01-01 00:00:00 -0800
+  //   // jan01.post   is 2011-01-01 00:00:00 -0800
+  //
+  //   // A Spring DST transition, when there is a gap in civil time
+  //   const auto mar13 = lax.At(absl::CivilSecond(2011, 3, 13, 2, 15, 0));
+  //   // mar13.kind == TimeZone::TimeInfo::SKIPPED
+  //   // mar13.pre   is 2011-03-13 03:15:00 -0700
+  //   // mar13.trans is 2011-03-13 03:00:00 -0700
+  //   // mar13.post  is 2011-03-13 01:15:00 -0800
+  //
+  //   // A Fall DST transition, when civil times are repeated
+  //   const auto nov06 = lax.At(absl::CivilSecond(2011, 11, 6, 1, 15, 0));
+  //   // nov06.kind == TimeZone::TimeInfo::REPEATED
+  //   // nov06.pre   is 2011-11-06 01:15:00 -0700
+  //   // nov06.trans is 2011-11-06 01:00:00 -0800
+  //   // nov06.post  is 2011-11-06 01:15:00 -0800
+  TimeInfo At(CivilSecond ct) const;
+
+  template <typename H>
+  friend H AbslHashValue(H h, TimeZone tz) {
+    return H::combine(std::move(h), tz.cz_);
+  }
+
+ private:
+  friend bool operator==(TimeZone a, TimeZone b) { return a.cz_ == b.cz_; }
+  friend bool operator!=(TimeZone a, TimeZone b) { return a.cz_ != b.cz_; }
+  friend std::ostream& operator<<(std::ostream& os, TimeZone tz) {
+    return os << tz.name();
+  }
+
+  time_internal::cctz::time_zone cz_;
+};
+
+// LoadTimeZone()
+//
+// Loads the named zone. May perform I/O on the initial load of the named
+// zone. If the name is invalid, or some other kind of error occurs, returns
+// `false` and `*tz` is set to the UTC time zone.
+inline bool LoadTimeZone(const std::string& name, TimeZone* tz) {
+  if (name == "localtime") {
+    *tz = TimeZone(time_internal::cctz::local_time_zone());
+    return true;
+  }
+  time_internal::cctz::time_zone cz;
+  const bool b = time_internal::cctz::load_time_zone(name, &cz);
+  *tz = TimeZone(cz);
+  return b;
+}
+
+// FixedTimeZone()
+//
+// Returns a TimeZone that is a fixed offset (seconds east) from UTC.
+// Note: If the absolute value of the offset is greater than 24 hours
+// you'll get UTC (i.e., no offset) instead.
+inline TimeZone FixedTimeZone(int seconds) {
+  return TimeZone(
+      time_internal::cctz::fixed_time_zone(std::chrono::seconds(seconds)));
+}
+
+// UTCTimeZone()
+//
+// Convenience method returning the UTC time zone.
+inline TimeZone UTCTimeZone() {
+  return TimeZone(time_internal::cctz::utc_time_zone());
+}
+
+// LocalTimeZone()
+//
+// Convenience method returning the local time zone, or UTC if there is
+// no configured local zone.  Warning: Be wary of using LocalTimeZone(),
+// and particularly so in a server process, as the zone configured for the
+// local machine should be irrelevant.  Prefer an explicit zone name.
+inline TimeZone LocalTimeZone() {
+  return TimeZone(time_internal::cctz::local_time_zone());
+}
+
+// ToCivilSecond()
+// ToCivilMinute()
+// ToCivilHour()
+// ToCivilDay()
+// ToCivilMonth()
+// ToCivilYear()
+//
+// Helpers for TimeZone::At(Time) to return particularly aligned civil times.
+//
+// Example:
+//
+//   absl::Time t = ...;
+//   absl::TimeZone tz = ...;
+//   const auto cd = absl::ToCivilDay(t, tz);
+inline CivilSecond ToCivilSecond(Time t, TimeZone tz) {
+  return tz.At(t).cs;  // already a CivilSecond
+}
+inline CivilMinute ToCivilMinute(Time t, TimeZone tz) {
+  return CivilMinute(tz.At(t).cs);
+}
+inline CivilHour ToCivilHour(Time t, TimeZone tz) {
+  return CivilHour(tz.At(t).cs);
+}
+inline CivilDay ToCivilDay(Time t, TimeZone tz) {
+  return CivilDay(tz.At(t).cs);
+}
+inline CivilMonth ToCivilMonth(Time t, TimeZone tz) {
+  return CivilMonth(tz.At(t).cs);
+}
+inline CivilYear ToCivilYear(Time t, TimeZone tz) {
+  return CivilYear(tz.At(t).cs);
+}
+
+// FromCivil()
+//
+// Helper for TimeZone::At(CivilSecond) that provides "order-preserving
+// semantics." If the civil time maps to a unique time, that time is
+// returned. If the civil time is repeated in the given time zone, the
+// time using the pre-transition offset is returned. Otherwise, the
+// civil time is skipped in the given time zone, and the transition time
+// is returned. This means that for any two civil times, ct1 and ct2,
+// (ct1 < ct2) => (FromCivil(ct1) <= FromCivil(ct2)), the equal case
+// being when two non-existent civil times map to the same transition time.
+//
+// Note: Accepts civil times of any alignment.
+inline Time FromCivil(CivilSecond ct, TimeZone tz) {
+  const auto ti = tz.At(ct);
+  if (ti.kind == TimeZone::TimeInfo::SKIPPED) return ti.trans;
+  return ti.pre;
+}
+
+// TimeConversion
+//
+// An `absl::TimeConversion` represents the conversion of year, month, day,
+// hour, minute, and second values (i.e., a civil time), in a particular
+// `absl::TimeZone`, to a time instant (an absolute time), as returned by
+// `absl::ConvertDateTime()`. Lecacy version of `absl::TimeZone::TimeInfo`.
+//
+// Deprecated. Use `absl::TimeZone::TimeInfo`.
+struct
+    TimeConversion {
+  Time pre;    // time calculated using the pre-transition offset
+  Time trans;  // when the civil-time discontinuity occurred
+  Time post;   // time calculated using the post-transition offset
+
+  enum Kind {
+    UNIQUE,    // the civil time was singular (pre == trans == post)
+    SKIPPED,   // the civil time did not exist
+    REPEATED,  // the civil time was ambiguous
+  };
+  Kind kind;
+
+  bool normalized;  // input values were outside their valid ranges
+};
+
+// ConvertDateTime()
+//
+// Legacy version of `absl::TimeZone::At(absl::CivilSecond)` that takes
+// the civil time as six, separate values (YMDHMS).
+//
+// The input month, day, hour, minute, and second values can be outside
+// of their valid ranges, in which case they will be "normalized" during
+// the conversion.
+//
+// Example:
+//
+//   // "October 32" normalizes to "November 1".
+//   absl::TimeConversion tc =
+//       absl::ConvertDateTime(2013, 10, 32, 8, 30, 0, lax);
+//   // tc.kind == TimeConversion::UNIQUE && tc.normalized == true
+//   // absl::ToCivilDay(tc.pre, tz).month() == 11
+//   // absl::ToCivilDay(tc.pre, tz).day() == 1
+//
+// Deprecated. Use `absl::TimeZone::At(CivilSecond)`.
+TimeConversion ConvertDateTime(int64_t year, int mon, int day, int hour,
+                               int min, int sec, TimeZone tz);
+
+// FromDateTime()
+//
+// A convenience wrapper for `absl::ConvertDateTime()` that simply returns
+// the "pre" `absl::Time`.  That is, the unique result, or the instant that
+// is correct using the pre-transition offset (as if the transition never
+// happened).
+//
+// Example:
+//
+//   absl::Time t = absl::FromDateTime(2017, 9, 26, 9, 30, 0, lax);
+//   // t = 2017-09-26 09:30:00 -0700
+//
+// Deprecated. Use `absl::TimeZone::At(CivilSecond).pre`.
+inline Time FromDateTime(int64_t year, int mon, int day, int hour,
+                         int min, int sec, TimeZone tz) {
+  return ConvertDateTime(year, mon, day, hour, min, sec, tz).pre;
+}
+
+// FromTM()
+//
+// Converts the `tm_year`, `tm_mon`, `tm_mday`, `tm_hour`, `tm_min`, and
+// `tm_sec` fields to an `absl::Time` using the given time zone. See ctime(3)
+// for a description of the expected values of the tm fields. If the indicated
+// time instant is not unique (see `absl::TimeZone::At(absl::CivilSecond)`
+// above), the `tm_isdst` field is consulted to select the desired instant
+// (`tm_isdst` > 0 means DST, `tm_isdst` == 0 means no DST, `tm_isdst` < 0
+// means use the post-transition offset).
+Time FromTM(const struct tm& tm, TimeZone tz);
+
+// ToTM()
+//
+// Converts the given `absl::Time` to a struct tm using the given time zone.
+// See ctime(3) for a description of the values of the tm fields.
+struct tm ToTM(Time t, TimeZone tz);
+
 // RFC3339_full
 // RFC3339_sec
 //
@@ -929,12 +1161,8 @@ extern const char RFC1123_no_wday[];  // %d %b %E4Y %H:%M:%S %z
 //
 // Example:
 //
-//   absl::TimeZone lax;
-//   if (!absl::LoadTimeZone("America/Los_Angeles", &lax)) {
-//     // handle error case
-//   }
-//   absl::Time t = absl::FromDateTime(2013, 1, 2, 3, 4, 5, lax);
-//
+//   absl::CivilSecond cs(2013, 1, 2, 3, 4, 5);
+//   absl::Time t = absl::FromCivil(cs, lax);
 //   string f = absl::FormatTime("%H:%M:%S", t, lax);  // "03:04:05"
 //   f = absl::FormatTime("%H:%M:%E3S", t, lax);  // "03:04:05.000"
 //
@@ -985,7 +1213,7 @@ inline std::ostream& operator<<(std::ostream& os, Time t) {
 // in the conversion.
 //
 // Date and time fields that are out-of-range will be treated as errors
-// rather than normalizing them like `absl::FromDateTime()` does.  For example,
+// rather than normalizing them like `absl::CivilSecond` does.  For example,
 // it is an error to parse the date "Oct 32, 2013" because 32 is out of range.
 //
 // A leap second of ":60" is normalized to ":00" of the following minute
@@ -1012,121 +1240,11 @@ bool ParseTime(const std::string& format, const std::string& input, Time* time,
 // given TimeZone.  This means that the input, by itself, does not identify a
 // unique instant.  Being time-zone dependent, it also admits the possibility
 // of ambiguity or non-existence, in which case the "pre" time (as defined
-// for ConvertDateTime()) is returned.  For these reasons we recommend that
+// by TimeZone::TimeInfo) is returned.  For these reasons we recommend that
 // all date/time strings include a UTC offset so they're context independent.
 bool ParseTime(const std::string& format, const std::string& input, TimeZone tz,
                Time* time, std::string* err);
 
-// Support for flag values of type Time. Time flags must be specified in a
-// format that matches absl::RFC3339_full. For example:
-//
-//   --start_time=2016-01-02T03:04:05.678+08:00
-//
-// Note: A UTC offset (or 'Z' indicating a zero-offset from UTC) is required.
-//
-// Additionally, if you'd like to specify a time as a count of
-// seconds/milliseconds/etc from the Unix epoch, use an absl::Duration flag
-// and add that duration to absl::UnixEpoch() to get an absl::Time.
-bool ParseFlag(const std::string& text, Time* t, std::string* error);
-std::string UnparseFlag(Time t);
-
-// TimeZone
-//
-// The `absl::TimeZone` is an opaque, small, value-type class representing a
-// geo-political region within which particular rules are used for converting
-// between absolute and civil times (see https://git.io/v59Ly). `absl::TimeZone`
-// values are named using the TZ identifiers from the IANA Time Zone Database,
-// such as "America/Los_Angeles" or "Australia/Sydney". `absl::TimeZone` values
-// are created from factory functions such as `absl::LoadTimeZone()`. Note:
-// strings like "PST" and "EDT" are not valid TZ identifiers. Prefer to pass by
-// value rather than const reference.
-//
-// For more on the fundamental concepts of time zones, absolute times, and civil
-// times, see https://github.com/google/cctz#fundamental-concepts
-//
-// Examples:
-//
-//   absl::TimeZone utc = absl::UTCTimeZone();
-//   absl::TimeZone pst = absl::FixedTimeZone(-8 * 60 * 60);
-//   absl::TimeZone loc = absl::LocalTimeZone();
-//   absl::TimeZone lax;
-//   if (!absl::LoadTimeZone("America/Los_Angeles", &lax)) {
-//     // handle error case
-//   }
-//
-// See also:
-// - https://github.com/google/cctz
-// - http://www.iana.org/time-zones
-// - http://en.wikipedia.org/wiki/Zoneinfo
-class TimeZone {
- public:
-  explicit TimeZone(time_internal::cctz::time_zone tz) : cz_(tz) {}
-  TimeZone() = default;  // UTC, but prefer UTCTimeZone() to be explicit.
-  TimeZone(const TimeZone&) = default;
-  TimeZone& operator=(const TimeZone&) = default;
-
-  explicit operator time_internal::cctz::time_zone() const { return cz_; }
-
-  std::string name() const { return cz_.name(); }
-
-  template <typename H>
-  friend H AbslHashValue(H h, TimeZone tz) {
-    return H::combine(std::move(h), tz.cz_);
-  }
-
- private:
-  friend bool operator==(TimeZone a, TimeZone b) { return a.cz_ == b.cz_; }
-  friend bool operator!=(TimeZone a, TimeZone b) { return a.cz_ != b.cz_; }
-  friend std::ostream& operator<<(std::ostream& os, TimeZone tz) {
-    return os << tz.name();
-  }
-
-  time_internal::cctz::time_zone cz_;
-};
-
-// LoadTimeZone()
-//
-// Loads the named zone. May perform I/O on the initial load of the named
-// zone. If the name is invalid, or some other kind of error occurs, returns
-// `false` and `*tz` is set to the UTC time zone.
-inline bool LoadTimeZone(const std::string& name, TimeZone* tz) {
-  if (name == "localtime") {
-    *tz = TimeZone(time_internal::cctz::local_time_zone());
-    return true;
-  }
-  time_internal::cctz::time_zone cz;
-  const bool b = time_internal::cctz::load_time_zone(name, &cz);
-  *tz = TimeZone(cz);
-  return b;
-}
-
-// FixedTimeZone()
-//
-// Returns a TimeZone that is a fixed offset (seconds east) from UTC.
-// Note: If the absolute value of the offset is greater than 24 hours
-// you'll get UTC (i.e., no offset) instead.
-inline TimeZone FixedTimeZone(int seconds) {
-  return TimeZone(
-      time_internal::cctz::fixed_time_zone(std::chrono::seconds(seconds)));
-}
-
-// UTCTimeZone()
-//
-// Convenience method returning the UTC time zone.
-inline TimeZone UTCTimeZone() {
-  return TimeZone(time_internal::cctz::utc_time_zone());
-}
-
-// LocalTimeZone()
-//
-// Convenience method returning the local time zone, or UTC if there is
-// no configured local zone.  Warning: Be wary of using LocalTimeZone(),
-// and particularly so in a server process, as the zone configured for the
-// local machine should be irrelevant.  Prefer an explicit zone name.
-inline TimeZone LocalTimeZone() {
-  return TimeZone(time_internal::cctz::local_time_zone());
-}
-
 // ============================================================================
 // Implementation Details Follow
 // ============================================================================
diff --git a/absl/time/time_benchmark.cc b/absl/time/time_benchmark.cc
index e1009946cd58..9bbed6f81afe 100644
--- a/absl/time/time_benchmark.cc
+++ b/absl/time/time_benchmark.cc
@@ -169,32 +169,32 @@ void BM_Time_ToUnixSeconds(benchmark::State& state) {
 BENCHMARK(BM_Time_ToUnixSeconds);
 
 //
-// FromDateTime
+// FromCivil
 //
-// In each "FromDateTime" benchmark we switch between two YMDhms
-// values separated by at least one transition in order to defeat any
-// internal caching of previous results (e.g., see time_local_hint_).
+// In each "FromCivil" benchmark we switch between two YMDhms values
+// separated by at least one transition in order to defeat any internal
+// caching of previous results (e.g., see time_local_hint_).
 //
 // The "UTC" variants use UTC instead of the Google/local time zone.
 // The "Day0" variants require normalization of the day of month.
 //
 
-void BM_Time_FromDateTime_Absl(benchmark::State& state) {
+void BM_Time_FromCivil_Absl(benchmark::State& state) {
   const absl::TimeZone tz =
       absl::time_internal::LoadTimeZone("America/Los_Angeles");
   int i = 0;
   while (state.KeepRunning()) {
     if ((i & 1) == 0) {
-      absl::FromDateTime(2014, 12, 18, 20, 16, 18, tz);
+      absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz);
     } else {
-      absl::FromDateTime(2013, 11, 15, 18, 30, 27, tz);
+      absl::FromCivil(absl::CivilSecond(2013, 11, 15, 18, 30, 27), tz);
     }
     ++i;
   }
 }
-BENCHMARK(BM_Time_FromDateTime_Absl);
+BENCHMARK(BM_Time_FromCivil_Absl);
 
-void BM_Time_FromDateTime_Libc(benchmark::State& state) {
+void BM_Time_FromCivil_Libc(benchmark::State& state) {
   // No timezone support, so just use localtime.
   int i = 0;
   while (state.KeepRunning()) {
@@ -219,32 +219,32 @@ void BM_Time_FromDateTime_Libc(benchmark::State& state) {
     ++i;
   }
 }
-BENCHMARK(BM_Time_FromDateTime_Libc);
+BENCHMARK(BM_Time_FromCivil_Libc);
 
-void BM_Time_FromDateTimeUTC_Absl(benchmark::State& state) {
+void BM_Time_FromCivilUTC_Absl(benchmark::State& state) {
   const absl::TimeZone tz = absl::UTCTimeZone();
   while (state.KeepRunning()) {
-    FromDateTime(2014, 12, 18, 20, 16, 18, tz);
+    absl::FromCivil(absl::CivilSecond(2014, 12, 18, 20, 16, 18), tz);
   }
 }
-BENCHMARK(BM_Time_FromDateTimeUTC_Absl);
+BENCHMARK(BM_Time_FromCivilUTC_Absl);
 
-void BM_Time_FromDateTimeDay0_Absl(benchmark::State& state) {
+void BM_Time_FromCivilDay0_Absl(benchmark::State& state) {
   const absl::TimeZone tz =
       absl::time_internal::LoadTimeZone("America/Los_Angeles");
   int i = 0;
   while (state.KeepRunning()) {
     if ((i & 1) == 0) {
-      absl::FromDateTime(2014, 12, 0, 20, 16, 18, tz);
+      absl::FromCivil(absl::CivilSecond(2014, 12, 0, 20, 16, 18), tz);
     } else {
-      absl::FromDateTime(2013, 11, 0, 18, 30, 27, tz);
+      absl::FromCivil(absl::CivilSecond(2013, 11, 0, 18, 30, 27), tz);
     }
     ++i;
   }
 }
-BENCHMARK(BM_Time_FromDateTimeDay0_Absl);
+BENCHMARK(BM_Time_FromCivilDay0_Absl);
 
-void BM_Time_FromDateTimeDay0_Libc(benchmark::State& state) {
+void BM_Time_FromCivilDay0_Libc(benchmark::State& state) {
   // No timezone support, so just use localtime.
   int i = 0;
   while (state.KeepRunning()) {
@@ -269,7 +269,7 @@ void BM_Time_FromDateTimeDay0_Libc(benchmark::State& state) {
     ++i;
   }
 }
-BENCHMARK(BM_Time_FromDateTimeDay0_Libc);
+BENCHMARK(BM_Time_FromCivilDay0_Libc);
 
 //
 // To/FromTimespec
diff --git a/absl/time/time_norm_test.cc b/absl/time/time_norm_test.cc
deleted file mode 100644
index 4436242e4125..000000000000
--- a/absl/time/time_norm_test.cc
+++ /dev/null
@@ -1,306 +0,0 @@
-// Copyright 2017 The Abseil Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-// This file contains tests for FromDateTime() normalization, which is
-// time-zone independent so we just use UTC throughout.
-
-#include <cstdint>
-#include <limits>
-
-#include "gmock/gmock.h"
-#include "gtest/gtest.h"
-#include "absl/time/internal/test_util.h"
-#include "absl/time/time.h"
-
-namespace {
-
-TEST(TimeNormCase, SimpleOverflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc =
-      absl::ConvertDateTime(2013, 11, 15, 16, 32, 59 + 1, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 15, 16, 33, 0, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16, 59 + 1, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 15, 17, 0, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 23 + 1, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 16, 0, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 30 + 1, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 12, 1, 16, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 12 + 1, 15, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2014, 1, 15, 16, 32, 14, 0, false);
-}
-
-TEST(TimeNormCase, SimpleUnderflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc = ConvertDateTime(2013, 11, 15, 16, 32, 0 - 1, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 15, 16, 31, 59, 0, false);
-
-  tc = ConvertDateTime(2013, 11, 15, 16, 0 - 1, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 15, 15, 59, 14, 0, false);
-
-  tc = ConvertDateTime(2013, 11, 15, 0 - 1, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 14, 23, 32, 14, 0, false);
-
-  tc = ConvertDateTime(2013, 11, 1 - 1, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 10, 31, 16, 32, 14, 0, false);
-
-  tc = ConvertDateTime(2013, 1 - 1, 15, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2012, 12, 15, 16, 32, 14, 0, false);
-}
-
-TEST(TimeNormCase, MultipleOverflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-  absl::TimeConversion tc = ConvertDateTime(2013, 12, 31, 23, 59, 59 + 1, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2014, 1, 1, 0, 0, 0, 0, false);
-}
-
-TEST(TimeNormCase, MultipleUnderflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-  absl::TimeConversion tc = absl::ConvertDateTime(2014, 1, 1, 0, 0, 0 - 1, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 12, 31, 23, 59, 59, 0, false);
-}
-
-TEST(TimeNormCase, OverflowLimits) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-  absl::TimeConversion tc;
-  absl::Time::Breakdown bd;
-
-  const int kintmax = std::numeric_limits<int>::max();
-  tc = absl::ConvertDateTime(0, kintmax, kintmax, kintmax, kintmax, kintmax,
-                             utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 185085715, 11, 27, 12, 21, 7, 0, false);
-
-  const int kintmin = std::numeric_limits<int>::min();
-  tc = absl::ConvertDateTime(0, kintmin, kintmin, kintmin, kintmin, kintmin,
-                             utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, -185085717, 10, 31, 10, 37, 52, 0, false);
-
-  const int64_t max_year = std::numeric_limits<int64_t>::max();
-  tc = absl::ConvertDateTime(max_year, 12, 31, 23, 59, 59, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  EXPECT_EQ(absl::InfiniteFuture(), tc.pre);
-
-  const int64_t min_year = std::numeric_limits<int64_t>::min();
-  tc = absl::ConvertDateTime(min_year, 1, 1, 0, 0, 0, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  EXPECT_EQ(absl::InfinitePast(), tc.pre);
-}
-
-TEST(TimeNormCase, ComplexOverflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc =
-      ConvertDateTime(2013, 11, 15, 16, 32, 14 + 123456789, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2017, 10, 14, 14, 5, 23, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16, 32 + 1234567, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2016, 3, 22, 0, 39, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16 + 123456, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2027, 12, 16, 16, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15 + 1234, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2017, 4, 2, 16, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11 + 123, 15, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2024, 2, 15, 16, 32, 14, 0, false);
-}
-
-TEST(TimeNormCase, ComplexUnderflow) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc =
-      absl::ConvertDateTime(1999, 3, 0, 0, 0, 0, utc);  // year 400
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1999, 2, 28, 0, 0, 0, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16, 32, 14 - 123456789, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2009, 12, 17, 18, 59, 5, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16, 32 - 1234567, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2011, 7, 12, 8, 25, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15, 16 - 123456, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1999, 10, 16, 16, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11, 15 - 1234, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2010, 6, 30, 16, 32, 14, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11 - 123, 15, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2003, 8, 15, 16, 32, 14, 0, false);
-}
-
-TEST(TimeNormCase, Mishmash) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc =
-      absl::ConvertDateTime(2013, 11 - 123, 15 + 1234, 16 - 123456,
-                            32 + 1234567, 14 - 123456789, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1991, 5, 9, 3, 6, 5, 0, false);
-
-  tc = absl::ConvertDateTime(2013, 11 + 123, 15 - 1234, 16 + 123456,
-                             32 - 1234567, 14 + 123456789, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2036, 5, 24, 5, 58, 23, 0, false);
-
-  // Here is a normalization case we got wrong for a while.  Because the
-  // day is converted to "1" within a 400-year (146097-day) period, we
-  // didn't need to roll the month and so we didn't mark it as normalized.
-  tc = absl::ConvertDateTime(2013, 11, -146097 + 1, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1613, 11, 1, 16, 32, 14, 0, false);
-
-  // Even though the month overflow compensates for the day underflow,
-  // this should still be marked as normalized.
-  tc = absl::ConvertDateTime(2013, 11 + 400 * 12, -146097 + 1, 16, 32, 14, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 11, 1, 16, 32, 14, 0, false);
-}
-
-TEST(TimeNormCase, LeapYears) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-
-  absl::TimeConversion tc =
-      absl::ConvertDateTime(2013, 2, 28 + 1, 0, 0, 0, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  absl::Time::Breakdown bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2013, 3, 1, 0, 0, 0, 0, false);
-
-  tc = absl::ConvertDateTime(2012, 2, 28 + 1, 0, 0, 0, utc);
-  EXPECT_FALSE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2012, 2, 29, 0, 0, 0, 0, false);
-
-  tc = absl::ConvertDateTime(2000, 2, 28 + 1, 0, 0, 0, utc);
-  EXPECT_FALSE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 2000, 2, 29, 0, 0, 0, 0, false);
-
-  tc = absl::ConvertDateTime(1900, 2, 28 + 1, 0, 0, 0, utc);
-  EXPECT_TRUE(tc.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-  bd = tc.pre.In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1900, 3, 1, 0, 0, 0, 0, false);
-}
-
-// Convert all the days from 1970-1-1 to 1970-1-146097 (aka 2369-12-31)
-// and check that they normalize to the expected time.  146097 days span
-// the 400-year Gregorian cycle used during normalization.
-TEST(TimeNormCase, AllTheDays) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-  absl::Time exp_time = absl::UnixEpoch();
-
-  for (int day = 1; day <= 146097; ++day) {
-    absl::TimeConversion tc = absl::ConvertDateTime(1970, 1, day, 0, 0, 0, utc);
-    EXPECT_EQ(day > 31, tc.normalized);
-    EXPECT_EQ(absl::TimeConversion::UNIQUE, tc.kind);
-    EXPECT_EQ(exp_time, tc.pre);
-    exp_time += absl::Hours(24);
-  }
-}
-
-}  // namespace
diff --git a/absl/time/time_test.cc b/absl/time/time_test.cc
index 4f8f58a6ef36..feca45873814 100644
--- a/absl/time/time_test.cc
+++ b/absl/time/time_test.cc
@@ -28,6 +28,27 @@
 
 namespace {
 
+#if GTEST_USES_SIMPLE_RE
+const char kZoneAbbrRE[] = ".*";  // just punt
+#else
+const char kZoneAbbrRE[] = "[A-Za-z]{3,4}|[-+][0-9]{2}([0-9]{2})?";
+#endif
+
+// This helper is a macro so that failed expectations show up with the
+// correct line numbers.
+#define EXPECT_CIVIL_INFO(ci, y, m, d, h, min, s, off, isdst)      \
+  do {                                                             \
+    EXPECT_EQ(y, ci.cs.year());                                    \
+    EXPECT_EQ(m, ci.cs.month());                                   \
+    EXPECT_EQ(d, ci.cs.day());                                     \
+    EXPECT_EQ(h, ci.cs.hour());                                    \
+    EXPECT_EQ(min, ci.cs.minute());                                \
+    EXPECT_EQ(s, ci.cs.second());                                  \
+    EXPECT_EQ(off, ci.offset);                                     \
+    EXPECT_EQ(isdst, ci.is_dst);                                   \
+    EXPECT_THAT(ci.zone_abbr, testing::MatchesRegex(kZoneAbbrRE)); \
+  } while (0)
+
 // A gMock matcher to match timespec values. Use this matcher like:
 // timespec ts1, ts2;
 // EXPECT_THAT(ts1, TimespecMatcher(ts2));
@@ -84,10 +105,10 @@ TEST(Time, ValueSemantics) {
 }
 
 TEST(Time, UnixEpoch) {
-  absl::Time::Breakdown bd = absl::UnixEpoch().In(absl::UTCTimeZone());
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1970, 1, 1, 0, 0, 0, 0, false);
-  EXPECT_EQ(absl::ZeroDuration(), bd.subsecond);
-  EXPECT_EQ(4, bd.weekday);  // Thursday
+  const auto ci = absl::UTCTimeZone().At(absl::UnixEpoch());
+  EXPECT_EQ(absl::CivilSecond(1970, 1, 1, 0, 0, 0), ci.cs);
+  EXPECT_EQ(absl::ZeroDuration(), ci.subsecond);
+  EXPECT_EQ(absl::Weekday::thursday, absl::GetWeekday(absl::CivilDay(ci.cs)));
 }
 
 TEST(Time, Breakdown) {
@@ -95,26 +116,26 @@ TEST(Time, Breakdown) {
   absl::Time t = absl::UnixEpoch();
 
   // The Unix epoch as seen in NYC.
-  absl::Time::Breakdown bd = t.In(tz);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1969, 12, 31, 19, 0, 0, -18000, false);
-  EXPECT_EQ(absl::ZeroDuration(), bd.subsecond);
-  EXPECT_EQ(3, bd.weekday);  // Wednesday
+  auto ci = tz.At(t);
+  EXPECT_CIVIL_INFO(ci, 1969, 12, 31, 19, 0, 0, -18000, false);
+  EXPECT_EQ(absl::ZeroDuration(), ci.subsecond);
+  EXPECT_EQ(absl::Weekday::wednesday, absl::GetWeekday(absl::CivilDay(ci.cs)));
 
   // Just before the epoch.
   t -= absl::Nanoseconds(1);
-  bd = t.In(tz);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1969, 12, 31, 18, 59, 59, -18000, false);
-  EXPECT_EQ(absl::Nanoseconds(999999999), bd.subsecond);
-  EXPECT_EQ(3, bd.weekday);  // Wednesday
+  ci = tz.At(t);
+  EXPECT_CIVIL_INFO(ci, 1969, 12, 31, 18, 59, 59, -18000, false);
+  EXPECT_EQ(absl::Nanoseconds(999999999), ci.subsecond);
+  EXPECT_EQ(absl::Weekday::wednesday, absl::GetWeekday(absl::CivilDay(ci.cs)));
 
   // Some time later.
   t += absl::Hours(24) * 2735;
   t += absl::Hours(18) + absl::Minutes(30) + absl::Seconds(15) +
        absl::Nanoseconds(9);
-  bd = t.In(tz);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 1977, 6, 28, 14, 30, 15, -14400, true);
-  EXPECT_EQ(8, bd.subsecond / absl::Nanoseconds(1));
-  EXPECT_EQ(2, bd.weekday);  // Tuesday
+  ci = tz.At(t);
+  EXPECT_CIVIL_INFO(ci, 1977, 6, 28, 14, 30, 15, -14400, true);
+  EXPECT_EQ(8, ci.subsecond / absl::Nanoseconds(1));
+  EXPECT_EQ(absl::Weekday::tuesday, absl::GetWeekday(absl::CivilDay(ci.cs)));
 }
 
 TEST(Time, AdditiveOperators) {
@@ -550,67 +571,63 @@ TEST(Time, ToChronoTime) {
             absl::ToChronoTime(absl::UnixEpoch() - tick));
 }
 
-TEST(Time, ConvertDateTime) {
-  const absl::TimeZone utc = absl::UTCTimeZone();
-  const absl::TimeZone goog =
-      absl::time_internal::LoadTimeZone("America/Los_Angeles");
+TEST(Time, TimeZoneAt) {
   const absl::TimeZone nyc =
       absl::time_internal::LoadTimeZone("America/New_York");
   const std::string fmt = "%a, %e %b %Y %H:%M:%S %z (%Z)";
 
-  // A simple case of normalization.
-  absl::TimeConversion oct32 = ConvertDateTime(2013, 10, 32, 8, 30, 0, goog);
-  EXPECT_TRUE(oct32.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, oct32.kind);
-  absl::TimeConversion nov01 = ConvertDateTime(2013, 11, 1, 8, 30, 0, goog);
-  EXPECT_FALSE(nov01.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, nov01.kind);
-  EXPECT_EQ(oct32.pre, nov01.pre);
-  EXPECT_EQ("Fri,  1 Nov 2013 08:30:00 -0700 (PDT)",
-            absl::FormatTime(fmt, nov01.pre, goog));
+  // A non-transition where the civil time is unique.
+  absl::CivilSecond nov01(2013, 11, 1, 8, 30, 0);
+  const auto nov01_ci = nyc.At(nov01);
+  EXPECT_EQ(absl::TimeZone::TimeInfo::UNIQUE, nov01_ci.kind);
+  EXPECT_EQ("Fri,  1 Nov 2013 08:30:00 -0400 (EDT)",
+            absl::FormatTime(fmt, nov01_ci.pre, nyc));
+  EXPECT_EQ(nov01_ci.pre, nov01_ci.trans);
+  EXPECT_EQ(nov01_ci.pre, nov01_ci.post);
+  EXPECT_EQ(nov01_ci.pre, absl::FromCivil(nov01, nyc));
 
   // A Spring DST transition, when there is a gap in civil time
   // and we prefer the later of the possible interpretations of a
   // non-existent time.
-  absl::TimeConversion mar13 = ConvertDateTime(2011, 3, 13, 2, 15, 0, nyc);
-  EXPECT_FALSE(mar13.normalized);
-  EXPECT_EQ(absl::TimeConversion::SKIPPED, mar13.kind);
+  absl::CivilSecond mar13(2011, 3, 13, 2, 15, 0);
+  const auto mar_ci = nyc.At(mar13);
+  EXPECT_EQ(absl::TimeZone::TimeInfo::SKIPPED, mar_ci.kind);
   EXPECT_EQ("Sun, 13 Mar 2011 03:15:00 -0400 (EDT)",
-            absl::FormatTime(fmt, mar13.pre, nyc));
+            absl::FormatTime(fmt, mar_ci.pre, nyc));
   EXPECT_EQ("Sun, 13 Mar 2011 03:00:00 -0400 (EDT)",
-            absl::FormatTime(fmt, mar13.trans, nyc));
+            absl::FormatTime(fmt, mar_ci.trans, nyc));
   EXPECT_EQ("Sun, 13 Mar 2011 01:15:00 -0500 (EST)",
-            absl::FormatTime(fmt, mar13.post, nyc));
-  EXPECT_EQ(mar13.pre, absl::FromDateTime(2011, 3, 13, 2, 15, 0, nyc));
+            absl::FormatTime(fmt, mar_ci.post, nyc));
+  EXPECT_EQ(mar_ci.trans, absl::FromCivil(mar13, nyc));
 
   // A Fall DST transition, when civil times are repeated and
   // we prefer the earlier of the possible interpretations of an
   // ambiguous time.
-  absl::TimeConversion nov06 = ConvertDateTime(2011, 11, 6, 1, 15, 0, nyc);
-  EXPECT_FALSE(nov06.normalized);
-  EXPECT_EQ(absl::TimeConversion::REPEATED, nov06.kind);
+  absl::CivilSecond nov06(2011, 11, 6, 1, 15, 0);
+  const auto nov06_ci = nyc.At(nov06);
+  EXPECT_EQ(absl::TimeZone::TimeInfo::REPEATED, nov06_ci.kind);
   EXPECT_EQ("Sun,  6 Nov 2011 01:15:00 -0400 (EDT)",
-            absl::FormatTime(fmt, nov06.pre, nyc));
+            absl::FormatTime(fmt, nov06_ci.pre, nyc));
   EXPECT_EQ("Sun,  6 Nov 2011 01:00:00 -0500 (EST)",
-            absl::FormatTime(fmt, nov06.trans, nyc));
+            absl::FormatTime(fmt, nov06_ci.trans, nyc));
   EXPECT_EQ("Sun,  6 Nov 2011 01:15:00 -0500 (EST)",
-            absl::FormatTime(fmt, nov06.post, nyc));
-  EXPECT_EQ(nov06.pre, absl::FromDateTime(2011, 11, 6, 1, 15, 0, nyc));
+            absl::FormatTime(fmt, nov06_ci.post, nyc));
+  EXPECT_EQ(nov06_ci.pre, absl::FromCivil(nov06, nyc));
 
   // Check that (time_t) -1 is handled correctly.
-  absl::TimeConversion minus1 = ConvertDateTime(1969, 12, 31, 18, 59, 59, nyc);
-  EXPECT_FALSE(minus1.normalized);
-  EXPECT_EQ(absl::TimeConversion::UNIQUE, minus1.kind);
-  EXPECT_EQ(-1, absl::ToTimeT(minus1.pre));
+  absl::CivilSecond minus1(1969, 12, 31, 18, 59, 59);
+  const auto minus1_cl = nyc.At(minus1);
+  EXPECT_EQ(absl::TimeZone::TimeInfo::UNIQUE, minus1_cl.kind);
+  EXPECT_EQ(-1, absl::ToTimeT(minus1_cl.pre));
   EXPECT_EQ("Wed, 31 Dec 1969 18:59:59 -0500 (EST)",
-            absl::FormatTime(fmt, minus1.pre, nyc));
+            absl::FormatTime(fmt, minus1_cl.pre, nyc));
   EXPECT_EQ("Wed, 31 Dec 1969 23:59:59 +0000 (UTC)",
-            absl::FormatTime(fmt, minus1.pre, utc));
+            absl::FormatTime(fmt, minus1_cl.pre, absl::UTCTimeZone()));
 }
 
-// FromDateTime(year, mon, day, hour, min, sec, UTCTimeZone()) has
-// a specialized fastpath implementation which we exercise here.
-TEST(Time, FromDateTimeUTC) {
+// FromCivil(CivilSecond(year, mon, day, hour, min, sec), UTCTimeZone())
+// has a specialized fastpath implementation, which we exercise here.
+TEST(Time, FromCivilUTC) {
   const absl::TimeZone utc = absl::UTCTimeZone();
   const std::string fmt = "%a, %e %b %Y %H:%M:%S %z (%Z)";
   const int kMax = std::numeric_limits<int>::max();
@@ -618,65 +635,36 @@ TEST(Time, FromDateTimeUTC) {
   absl::Time t;
 
   // 292091940881 is the last positive year to use the fastpath.
-  t = absl::FromDateTime(292091940881, kMax, kMax, kMax, kMax, kMax, utc);
+  t = absl::FromCivil(
+      absl::CivilSecond(292091940881, kMax, kMax, kMax, kMax, kMax), utc);
   EXPECT_EQ("Fri, 25 Nov 292277026596 12:21:07 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-  t = absl::FromDateTime(292091940882, kMax, kMax, kMax, kMax, kMax, utc);
-  EXPECT_EQ("infinite-future", absl::FormatTime(fmt, t, utc));  // no overflow
-  t = absl::FromDateTime(
-      std::numeric_limits<int64_t>::max(), kMax, kMax, kMax, kMax, kMax, utc);
+  t = absl::FromCivil(
+      absl::CivilSecond(292091940882, kMax, kMax, kMax, kMax, kMax), utc);
   EXPECT_EQ("infinite-future", absl::FormatTime(fmt, t, utc));  // no overflow
 
   // -292091936940 is the last negative year to use the fastpath.
-  t = absl::FromDateTime(-292091936940, kMin, kMin, kMin, kMin, kMin, utc);
+  t = absl::FromCivil(
+      absl::CivilSecond(-292091936940, kMin, kMin, kMin, kMin, kMin), utc);
   EXPECT_EQ("Fri,  1 Nov -292277022657 10:37:52 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-  t = absl::FromDateTime(-292091936941, kMin, kMin, kMin, kMin, kMin, utc);
+  t = absl::FromCivil(
+      absl::CivilSecond(-292091936941, kMin, kMin, kMin, kMin, kMin), utc);
   EXPECT_EQ("infinite-past", absl::FormatTime(fmt, t, utc));  // no underflow
-  t = absl::FromDateTime(
-      std::numeric_limits<int64_t>::min(), kMin, kMin, kMin, kMin, kMin, utc);
-  EXPECT_EQ("infinite-past", absl::FormatTime(fmt, t, utc));  // no overflow
 
   // Check that we're counting leap years correctly.
-  t = absl::FromDateTime(1900, 2, 28, 23, 59, 59, utc);
+  t = absl::FromCivil(absl::CivilSecond(1900, 2, 28, 23, 59, 59), utc);
   EXPECT_EQ("Wed, 28 Feb 1900 23:59:59 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-  t = absl::FromDateTime(1900, 3, 1, 0, 0, 0, utc);
+  t = absl::FromCivil(absl::CivilSecond(1900, 3, 1, 0, 0, 0), utc);
   EXPECT_EQ("Thu,  1 Mar 1900 00:00:00 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-  t = absl::FromDateTime(2000, 2, 29, 23, 59, 59, utc);
+  t = absl::FromCivil(absl::CivilSecond(2000, 2, 29, 23, 59, 59), utc);
   EXPECT_EQ("Tue, 29 Feb 2000 23:59:59 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-  t = absl::FromDateTime(2000, 3, 1, 0, 0, 0, utc);
+  t = absl::FromCivil(absl::CivilSecond(2000, 3, 1, 0, 0, 0), utc);
   EXPECT_EQ("Wed,  1 Mar 2000 00:00:00 +0000 (UTC)",
             absl::FormatTime(fmt, t, utc));
-
-  // Check normalization.
-  const std::string ymdhms = "%Y-%m-%d %H:%M:%S";
-  t = absl::FromDateTime(2015, 1, 1, 0, 0, 60, utc);
-  EXPECT_EQ("2015-01-01 00:01:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 1, 0, 60, 0, utc);
-  EXPECT_EQ("2015-01-01 01:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 1, 24, 0, 0, utc);
-  EXPECT_EQ("2015-01-02 00:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 32, 0, 0, 0, utc);
-  EXPECT_EQ("2015-02-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 13, 1, 0, 0, 0, utc);
-  EXPECT_EQ("2016-01-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 13, 32, 60, 60, 60, utc);
-  EXPECT_EQ("2016-02-03 13:01:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 1, 0, 0, -1, utc);
-  EXPECT_EQ("2014-12-31 23:59:59", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 1, 0, -1, 0, utc);
-  EXPECT_EQ("2014-12-31 23:59:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, 1, -1, 0, 0, utc);
-  EXPECT_EQ("2014-12-31 23:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, 1, -1, 0, 0, 0, utc);
-  EXPECT_EQ("2014-12-30 00:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, -1, 1, 0, 0, 0, utc);
-  EXPECT_EQ("2014-11-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
-  t = absl::FromDateTime(2015, -1, -1, -1, -1, -1, utc);
-  EXPECT_EQ("2014-10-29 22:58:59", absl::FormatTime(ymdhms, t, utc));
 }
 
 TEST(Time, ToTM) {
@@ -684,8 +672,10 @@ TEST(Time, ToTM) {
 
   // Compares the results of ToTM() to gmtime_r() for lots of times over the
   // course of a few days.
-  const absl::Time start = absl::FromDateTime(2014, 1, 2, 3, 4, 5, utc);
-  const absl::Time end = absl::FromDateTime(2014, 1, 5, 3, 4, 5, utc);
+  const absl::Time start =
+      absl::FromCivil(absl::CivilSecond(2014, 1, 2, 3, 4, 5), utc);
+  const absl::Time end =
+      absl::FromCivil(absl::CivilSecond(2014, 1, 5, 3, 4, 5), utc);
   for (absl::Time t = start; t < end; t += absl::Seconds(30)) {
     const struct tm tm_bt = ToTM(t, utc);
     const time_t tt = absl::ToTimeT(t);
@@ -711,12 +701,12 @@ TEST(Time, ToTM) {
   // Checks that the tm_isdst field is correct when in standard time.
   const absl::TimeZone nyc =
       absl::time_internal::LoadTimeZone("America/New_York");
-  absl::Time t = absl::FromDateTime(2014, 3, 1, 0, 0, 0, nyc);
+  absl::Time t = absl::FromCivil(absl::CivilSecond(2014, 3, 1, 0, 0, 0), nyc);
   struct tm tm = ToTM(t, nyc);
   EXPECT_FALSE(tm.tm_isdst);
 
   // Checks that the tm_isdst field is correct when in daylight time.
-  t = absl::FromDateTime(2014, 4, 1, 0, 0, 0, nyc);
+  t = absl::FromCivil(absl::CivilSecond(2014, 4, 1, 0, 0, 0), nyc);
   tm = ToTM(t, nyc);
   EXPECT_TRUE(tm.tm_isdst);
 
@@ -808,8 +798,8 @@ TEST(Time, TMRoundTrip) {
       absl::time_internal::LoadTimeZone("America/New_York");
 
   // Test round-tripping across a skipped transition
-  absl::Time start = absl::FromDateTime(2014, 3, 9, 0, 0, 0, nyc);
-  absl::Time end = absl::FromDateTime(2014, 3, 9, 4, 0, 0, nyc);
+  absl::Time start = absl::FromCivil(absl::CivilHour(2014, 3, 9, 0), nyc);
+  absl::Time end = absl::FromCivil(absl::CivilHour(2014, 3, 9, 4), nyc);
   for (absl::Time t = start; t < end; t += absl::Minutes(1)) {
     struct tm tm = ToTM(t, nyc);
     absl::Time rt = FromTM(tm, nyc);
@@ -817,8 +807,8 @@ TEST(Time, TMRoundTrip) {
   }
 
   // Test round-tripping across an ambiguous transition
-  start = absl::FromDateTime(2014, 11, 2, 0, 0, 0, nyc);
-  end = absl::FromDateTime(2014, 11, 2, 4, 0, 0, nyc);
+  start = absl::FromCivil(absl::CivilHour(2014, 11, 2, 0), nyc);
+  end = absl::FromCivil(absl::CivilHour(2014, 11, 2, 4), nyc);
   for (absl::Time t = start; t < end; t += absl::Minutes(1)) {
     struct tm tm = ToTM(t, nyc);
     absl::Time rt = FromTM(tm, nyc);
@@ -826,8 +816,8 @@ TEST(Time, TMRoundTrip) {
   }
 
   // Test round-tripping of unique instants crossing a day boundary
-  start = absl::FromDateTime(2014, 6, 27, 22, 0, 0, nyc);
-  end = absl::FromDateTime(2014, 6, 28, 4, 0, 0, nyc);
+  start = absl::FromCivil(absl::CivilHour(2014, 6, 27, 22), nyc);
+  end = absl::FromCivil(absl::CivilHour(2014, 6, 28, 4), nyc);
   for (absl::Time t = start; t < end; t += absl::Minutes(1)) {
     struct tm tm = ToTM(t, nyc);
     absl::Time rt = FromTM(tm, nyc);
@@ -980,27 +970,27 @@ TEST(Time, ConversionSaturation) {
   EXPECT_EQ(min_timespec_sec, ts.tv_sec);
   EXPECT_EQ(0, ts.tv_nsec);
 
-  // Checks how Time::In() saturates on infinities.
-  absl::Time::Breakdown bd = absl::InfiniteFuture().In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, std::numeric_limits<int64_t>::max(), 12, 31, 23,
+  // Checks how TimeZone::At() saturates on infinities.
+  auto ci = utc.At(absl::InfiniteFuture());
+  EXPECT_CIVIL_INFO(ci, std::numeric_limits<int64_t>::max(), 12, 31, 23,
                             59, 59, 0, false);
-  EXPECT_EQ(absl::InfiniteDuration(), bd.subsecond);
-  EXPECT_EQ(4, bd.weekday);  // Thursday
-  EXPECT_EQ(365, bd.yearday);
-  EXPECT_STREQ("-00", bd.zone_abbr);  // artifact of absl::Time::In()
-  bd = absl::InfinitePast().In(utc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, std::numeric_limits<int64_t>::min(), 1, 1, 0, 0,
+  EXPECT_EQ(absl::InfiniteDuration(), ci.subsecond);
+  EXPECT_EQ(absl::Weekday::thursday, absl::GetWeekday(absl::CivilDay(ci.cs)));
+  EXPECT_EQ(365, absl::GetYearDay(absl::CivilDay(ci.cs)));
+  EXPECT_STREQ("-00", ci.zone_abbr);  // artifact of TimeZone::At()
+  ci = utc.At(absl::InfinitePast());
+  EXPECT_CIVIL_INFO(ci, std::numeric_limits<int64_t>::min(), 1, 1, 0, 0,
                             0, 0, false);
-  EXPECT_EQ(-absl::InfiniteDuration(), bd.subsecond);
-  EXPECT_EQ(7, bd.weekday);  // Sunday
-  EXPECT_EQ(1, bd.yearday);
-  EXPECT_STREQ("-00", bd.zone_abbr);  // artifact of absl::Time::In()
+  EXPECT_EQ(-absl::InfiniteDuration(), ci.subsecond);
+  EXPECT_EQ(absl::Weekday::sunday, absl::GetWeekday(absl::CivilDay(ci.cs)));
+  EXPECT_EQ(1, absl::GetYearDay(absl::CivilDay(ci.cs)));
+  EXPECT_STREQ("-00", ci.zone_abbr);  // artifact of TimeZone::At()
 
   // Approach the maximal Time value from below.
-  t = absl::FromDateTime(292277026596, 12, 4, 15, 30, 6, utc);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 15, 30, 6), utc);
   EXPECT_EQ("292277026596-12-04T15:30:06+00:00",
             absl::FormatTime(absl::RFC3339_full, t, utc));
-  t = absl::FromDateTime(292277026596, 12, 4, 15, 30, 7, utc);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 15, 30, 7), utc);
   EXPECT_EQ("292277026596-12-04T15:30:07+00:00",
             absl::FormatTime(absl::RFC3339_full, t, utc));
   EXPECT_EQ(
@@ -1008,21 +998,21 @@ TEST(Time, ConversionSaturation) {
 
   // Checks that we can also get the maximal Time value for a far-east zone.
   const absl::TimeZone plus14 = absl::FixedTimeZone(14 * 60 * 60);
-  t = absl::FromDateTime(292277026596, 12, 5, 5, 30, 7, plus14);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 5, 5, 30, 7), plus14);
   EXPECT_EQ("292277026596-12-05T05:30:07+14:00",
             absl::FormatTime(absl::RFC3339_full, t, plus14));
   EXPECT_EQ(
       absl::UnixEpoch() + absl::Seconds(std::numeric_limits<int64_t>::max()), t);
 
   // One second later should push us to infinity.
-  t = absl::FromDateTime(292277026596, 12, 4, 15, 30, 8, utc);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 15, 30, 8), utc);
   EXPECT_EQ("infinite-future", absl::FormatTime(absl::RFC3339_full, t, utc));
 
   // Approach the minimal Time value from above.
-  t = absl::FromDateTime(-292277022657, 1, 27, 8, 29, 53, utc);
+  t = absl::FromCivil(absl::CivilSecond(-292277022657, 1, 27, 8, 29, 53), utc);
   EXPECT_EQ("-292277022657-01-27T08:29:53+00:00",
             absl::FormatTime(absl::RFC3339_full, t, utc));
-  t = absl::FromDateTime(-292277022657, 1, 27, 8, 29, 52, utc);
+  t = absl::FromCivil(absl::CivilSecond(-292277022657, 1, 27, 8, 29, 52), utc);
   EXPECT_EQ("-292277022657-01-27T08:29:52+00:00",
             absl::FormatTime(absl::RFC3339_full, t, utc));
   EXPECT_EQ(
@@ -1030,14 +1020,15 @@ TEST(Time, ConversionSaturation) {
 
   // Checks that we can also get the minimal Time value for a far-west zone.
   const absl::TimeZone minus12 = absl::FixedTimeZone(-12 * 60 * 60);
-  t = absl::FromDateTime(-292277022657, 1, 26, 20, 29, 52, minus12);
+  t = absl::FromCivil(absl::CivilSecond(-292277022657, 1, 26, 20, 29, 52),
+                      minus12);
   EXPECT_EQ("-292277022657-01-26T20:29:52-12:00",
             absl::FormatTime(absl::RFC3339_full, t, minus12));
   EXPECT_EQ(
       absl::UnixEpoch() + absl::Seconds(std::numeric_limits<int64_t>::min()), t);
 
   // One second before should push us to -infinity.
-  t = absl::FromDateTime(-292277022657, 1, 27, 8, 29, 51, utc);
+  t = absl::FromCivil(absl::CivilSecond(-292277022657, 1, 27, 8, 29, 51), utc);
   EXPECT_EQ("infinite-past", absl::FormatTime(absl::RFC3339_full, t, utc));
 }
 
@@ -1051,38 +1042,97 @@ TEST(Time, ExtendedConversionSaturation) {
       absl::time_internal::LoadTimeZone("America/New_York");
   const absl::Time max =
       absl::FromUnixSeconds(std::numeric_limits<int64_t>::max());
-  absl::Time::Breakdown bd;
+  absl::TimeZone::CivilInfo ci;
   absl::Time t;
 
   // The maximal time converted in each zone.
-  bd = max.In(syd);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 292277026596, 12, 5, 2, 30, 7, 39600, true);
-  t = absl::FromDateTime(292277026596, 12, 5, 2, 30, 7, syd);
+  ci = syd.At(max);
+  EXPECT_CIVIL_INFO(ci, 292277026596, 12, 5, 2, 30, 7, 39600, true);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 5, 2, 30, 7), syd);
   EXPECT_EQ(max, t);
-  bd = max.In(nyc);
-  ABSL_INTERNAL_EXPECT_TIME(bd, 292277026596, 12, 4, 10, 30, 7, -18000, false);
-  t = absl::FromDateTime(292277026596, 12, 4, 10, 30, 7, nyc);
+  ci = nyc.At(max);
+  EXPECT_CIVIL_INFO(ci, 292277026596, 12, 4, 10, 30, 7, -18000, false);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 10, 30, 7), nyc);
   EXPECT_EQ(max, t);
 
   // One second later should push us to infinity.
-  t = absl::FromDateTime(292277026596, 12, 5, 2, 30, 8, syd);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 5, 2, 30, 8), syd);
   EXPECT_EQ(absl::InfiniteFuture(), t);
-  t = absl::FromDateTime(292277026596, 12, 4, 10, 30, 8, nyc);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 10, 30, 8), nyc);
   EXPECT_EQ(absl::InfiniteFuture(), t);
 
   // And we should stick there.
-  t = absl::FromDateTime(292277026596, 12, 5, 2, 30, 9, syd);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 5, 2, 30, 9), syd);
   EXPECT_EQ(absl::InfiniteFuture(), t);
-  t = absl::FromDateTime(292277026596, 12, 4, 10, 30, 9, nyc);
+  t = absl::FromCivil(absl::CivilSecond(292277026596, 12, 4, 10, 30, 9), nyc);
   EXPECT_EQ(absl::InfiniteFuture(), t);
 
   // All the way up to a saturated date/time, without overflow.
-  t = absl::FromDateTime(
-      std::numeric_limits<int64_t>::max(), 12, 31, 23, 59, 59, syd);
+  t = absl::FromCivil(absl::CivilSecond::max(), syd);
   EXPECT_EQ(absl::InfiniteFuture(), t);
-  t = absl::FromDateTime(
-      std::numeric_limits<int64_t>::max(), 12, 31, 23, 59, 59, nyc);
+  t = absl::FromCivil(absl::CivilSecond::max(), nyc);
   EXPECT_EQ(absl::InfiniteFuture(), t);
 }
 
+TEST(Time, FromCivilAlignment) {
+  const absl::TimeZone utc = absl::UTCTimeZone();
+  const absl::CivilSecond cs(2015, 2, 3, 4, 5, 6);
+  absl::Time t = absl::FromCivil(cs, utc);
+  EXPECT_EQ("2015-02-03T04:05:06+00:00", absl::FormatTime(t, utc));
+  t = absl::FromCivil(absl::CivilMinute(cs), utc);
+  EXPECT_EQ("2015-02-03T04:05:00+00:00", absl::FormatTime(t, utc));
+  t = absl::FromCivil(absl::CivilHour(cs), utc);
+  EXPECT_EQ("2015-02-03T04:00:00+00:00", absl::FormatTime(t, utc));
+  t = absl::FromCivil(absl::CivilDay(cs), utc);
+  EXPECT_EQ("2015-02-03T00:00:00+00:00", absl::FormatTime(t, utc));
+  t = absl::FromCivil(absl::CivilMonth(cs), utc);
+  EXPECT_EQ("2015-02-01T00:00:00+00:00", absl::FormatTime(t, utc));
+  t = absl::FromCivil(absl::CivilYear(cs), utc);
+  EXPECT_EQ("2015-01-01T00:00:00+00:00", absl::FormatTime(t, utc));
+}
+
+TEST(Time, LegacyDateTime) {
+  const absl::TimeZone utc = absl::UTCTimeZone();
+  const std::string ymdhms = "%Y-%m-%d %H:%M:%S";
+  const int kMax = std::numeric_limits<int>::max();
+  const int kMin = std::numeric_limits<int>::min();
+  absl::Time t;
+
+  t = absl::FromDateTime(std::numeric_limits<absl::civil_year_t>::max(),
+                         kMax, kMax, kMax, kMax, kMax, utc);
+  EXPECT_EQ("infinite-future",
+            absl::FormatTime(ymdhms, t, utc));  // no overflow
+  t = absl::FromDateTime(std::numeric_limits<absl::civil_year_t>::min(),
+                         kMin, kMin, kMin, kMin, kMin, utc);
+  EXPECT_EQ("infinite-past",
+            absl::FormatTime(ymdhms, t, utc));  // no overflow
+
+  // Check normalization.
+  EXPECT_TRUE(absl::ConvertDateTime(2013, 10, 32, 8, 30, 0, utc).normalized);
+  t = absl::FromDateTime(2015, 1, 1, 0, 0, 60, utc);
+  EXPECT_EQ("2015-01-01 00:01:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 1, 0, 60, 0, utc);
+  EXPECT_EQ("2015-01-01 01:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 1, 24, 0, 0, utc);
+  EXPECT_EQ("2015-01-02 00:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 32, 0, 0, 0, utc);
+  EXPECT_EQ("2015-02-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 13, 1, 0, 0, 0, utc);
+  EXPECT_EQ("2016-01-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 13, 32, 60, 60, 60, utc);
+  EXPECT_EQ("2016-02-03 13:01:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 1, 0, 0, -1, utc);
+  EXPECT_EQ("2014-12-31 23:59:59", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 1, 0, -1, 0, utc);
+  EXPECT_EQ("2014-12-31 23:59:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, 1, -1, 0, 0, utc);
+  EXPECT_EQ("2014-12-31 23:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, 1, -1, 0, 0, 0, utc);
+  EXPECT_EQ("2014-12-30 00:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, -1, 1, 0, 0, 0, utc);
+  EXPECT_EQ("2014-11-01 00:00:00", absl::FormatTime(ymdhms, t, utc));
+  t = absl::FromDateTime(2015, -1, -1, -1, -1, -1, utc);
+  EXPECT_EQ("2014-10-29 22:58:59", absl::FormatTime(ymdhms, t, utc));
+}
+
 }  // namespace