Add 'third_party/abseil_cpp/' from commit '768eb2ca2857342673fcd462792ce04b8bac3fa3' r/781

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diff --git a/third_party/abseil_cpp/absl/time/civil_time.h b/third_party/abseil_cpp/absl/time/civil_time.h
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+// 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
+//
+//      https://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/strings/string_view.h"
+#include "absl/time/internal/cctz/include/cctz/civil_time.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+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 alignment 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 (realigned) civil-time value.
+//
+// Example:
+//
+//   absl::CivilDay a(2015, 8, 13);
+//   absl::Weekday wd = absl::GetWeekday(a);  // wd == absl::Weekday::thursday
+//
+inline Weekday GetWeekday(CivilSecond cs) {
+  return time_internal::cctz::get_weekday(cs);
+}
+
+// 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::NextWeekday(d - 1, absl::Weekday::thursday);
+//   // Gets the previous Thursday if d is not already Thursday
+//   absl::CivilDay thurs2 = absl::PrevWeekday(d + 1, absl::Weekday::thursday);
+//
+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 (realigned) civil-time value.
+//
+// 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(CivilSecond cs) {
+  return time_internal::cctz::get_yearday(cs);
+}
+
+// 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);
+//   std::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);
+
+// absl::ParseCivilTime()
+//
+// Parses a civil-time value from the specified `absl::string_view` into the
+// passed output parameter. Returns `true` upon successful parsing.
+//
+// The expected form of the input string is as follows:
+//
+//  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;
+//   bool ok = absl::ParseCivilTime("2018-01-02", &d); // OK
+//
+// Note that parsing will fail if the string's format does not match the
+// expected type exactly. `ParseLenientCivilTime()` below is more lenient.
+//
+bool ParseCivilTime(absl::string_view s, CivilSecond* c);
+bool ParseCivilTime(absl::string_view s, CivilMinute* c);
+bool ParseCivilTime(absl::string_view s, CivilHour* c);
+bool ParseCivilTime(absl::string_view s, CivilDay* c);
+bool ParseCivilTime(absl::string_view s, CivilMonth* c);
+bool ParseCivilTime(absl::string_view s, CivilYear* c);
+
+// ParseLenientCivilTime()
+//
+// Parses any of the formats accepted by `absl::ParseCivilTime()`, but is more
+// lenient if the format of the string does not exactly match the associated
+// type.
+//
+// Example:
+//
+//   absl::CivilDay d;
+//   bool ok = absl::ParseLenientCivilTime("1969-07-20", &d); // OK
+//   ok = absl::ParseLenientCivilTime("1969-07-20T10", &d);   // OK: T10 floored
+//   ok = absl::ParseLenientCivilTime("1969-07", &d);   // OK: day defaults to 1
+//
+bool ParseLenientCivilTime(absl::string_view s, CivilSecond* c);
+bool ParseLenientCivilTime(absl::string_view s, CivilMinute* c);
+bool ParseLenientCivilTime(absl::string_view s, CivilHour* c);
+bool ParseLenientCivilTime(absl::string_view s, CivilDay* c);
+bool ParseLenientCivilTime(absl::string_view s, CivilMonth* c);
+bool ParseLenientCivilTime(absl::string_view s, 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, 7, 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
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_TIME_CIVIL_TIME_H_