Export of internal Abseil changes.

--
00d42e3d5433aaf29c2ed293520b2ba178ae8bdb by Greg Falcon <gfalcon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 238061818

--
867a7ca318fac2991ea9a4107dbae3cc9fbf974a by Abseil Team <absl-team@google.com>:

Added a IWYU export pragma when including a standard header for the purpose of aliasing its symbols.

PiperOrigin-RevId: 238022277

--
17047745058f2f151cd986ea9f649512542d3876 by Matt Armstrong <marmstrong@google.com>:

Clarify the comment discouraging WrapUnique<T>(x) calls.

PiperOrigin-RevId: 237873803

--
3dcb2e4968243d33ca0ce53280c445df50f4a7ec by Samuel Benzaquen <sbenza@google.com>:

Workaround clang bug https://bugs.llvm.org/show_bug.cgi?id=38289

PiperOrigin-RevId: 237873551

--
f348d2dc7087a990cbdfb95aa51fd7ff478ae40e by Samuel Benzaquen <sbenza@google.com>:

Reduce minimum capacity to 1.
This reduces memory usage for small tables.
A flat_hash_set<int> of 1 element goes from 92 bytes to 24.
A flat_hash_set<string> of 1 element goes from 512 bytes to 56.

PiperOrigin-RevId: 237859811

--
9c8125be5e4e5d22a7bb62bdec8c323338385c1b by Jon Cohen <cohenjon@google.com>:

Bump to CMake 3.5. This is the oldest modern cmake being included by default in most popular OS distributions according to https://repology.org/project/cmake/versions.  Specifically, Ubuntu LTS 16.04 uses cmake 3.5 (https://packages.ubuntu.com/xenial/cmake)

PiperOrigin-RevId: 237859345

--
07638d672e0a4dced986a62750cfd8318ed36ffa by Derek Mauro <dmauro@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 237714597
GitOrigin-RevId: 00d42e3d5433aaf29c2ed293520b2ba178ae8bdb
Change-Id: I5faecc45add4a5a774d4f9baf06e5519091f2ccc

37 files changed, 180 insertions, 128 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a56d238b64..571e48c5fa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,9 +14,12 @@
 # limitations under the License.
 #
 
-# We require 3.0 for modern, target-based CMake.  We require 3.1 for the use of
-# CXX_STANDARD in our targets.
-cmake_minimum_required(VERSION 3.1)
+# Most widely used distributions have cmake 3.5 or greater available as of March
+# 2019.  A notable exception is RHEL-7 (CentOS7).  You can install a current
+# version of CMake by first installing Extra Packages for Enterprise Linux
+# (https://fedoraproject.org/wiki/EPEL#Extra_Packages_for_Enterprise_Linux_.28EPEL.29)
+# and then issuing `yum install cmake3` on the command line.
+cmake_minimum_required(VERSION 3.5)
 
 # Compiler id for Apple Clang is now AppleClang.
 if (POLICY CMP0025)
diff --git a/absl/container/flat_hash_map_test.cc b/absl/container/flat_hash_map_test.cc
index 562305e4b9..bae5c15d48 100644
--- a/absl/container/flat_hash_map_test.cc
+++ b/absl/container/flat_hash_map_test.cc
@@ -141,6 +141,7 @@ TEST(FlatHashMap, LazyKeyPattern) {
   int conversions = 0;
   int hashes = 0;
   flat_hash_map<size_t, size_t, Hash, Eq> m(0, Hash{&hashes});
+  m.reserve(3);
 
   m[LazyInt(1, &conversions)] = 1;
   EXPECT_THAT(m, UnorderedElementsAre(Pair(1, 1)));
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index c4f198bb42..85e33344c7 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -446,9 +446,7 @@ using Group = GroupPortableImpl;
 template <class Policy, class Hash, class Eq, class Alloc>
 class raw_hash_set;
 
-inline bool IsValidCapacity(size_t n) {
-  return ((n + 1) & n) == 0 && n >= Group::kWidth - 1;
-}
+inline bool IsValidCapacity(size_t n) { return ((n + 1) & n) == 0 && n > 0; }
 
 // PRECONDITION:
 //   IsValidCapacity(capacity)
@@ -470,13 +468,9 @@ inline void ConvertDeletedToEmptyAndFullToDeleted(
   ctrl[capacity] = kSentinel;
 }
 
-// Rounds up the capacity to the next power of 2 minus 1 and ensures it is
-// greater or equal to Group::kWidth - 1.
+// Rounds up the capacity to the next power of 2 minus 1, with a minimum of 1.
 inline size_t NormalizeCapacity(size_t n) {
-  constexpr size_t kMinCapacity = Group::kWidth - 1;
-  return n <= kMinCapacity
-             ? kMinCapacity
-             : (std::numeric_limits<size_t>::max)() >> LeadingZeros(n);
+  return n ? ~size_t{} >> LeadingZeros(n) : 1;
 }
 
 // We use 7/8th as maximum load factor.
@@ -1507,6 +1501,7 @@ class raw_hash_set {
 
   void drop_deletes_without_resize() ABSL_ATTRIBUTE_NOINLINE {
     assert(IsValidCapacity(capacity_));
+    assert(!is_small());
     // Algorithm:
     // - mark all DELETED slots as EMPTY
     // - mark all FULL slots as DELETED
@@ -1572,7 +1567,7 @@ class raw_hash_set {
 
   void rehash_and_grow_if_necessary() {
     if (capacity_ == 0) {
-      resize(Group::kWidth - 1);
+      resize(1);
     } else if (size() <= CapacityToGrowth(capacity()) / 2) {
       // Squash DELETED without growing if there is enough capacity.
       drop_deletes_without_resize();
@@ -1619,17 +1614,15 @@ class raw_hash_set {
       auto mask = g.MatchEmptyOrDeleted();
       if (mask) {
 #if !defined(NDEBUG)
-        // We want to force small tables to have random entries too, so
-        // in debug build we will randomly insert in either the front or back of
+        // We want to add entropy even when ASLR is not enabled.
+        // In debug build we will randomly insert in either the front or back of
         // the group.
         // TODO(kfm,sbenza): revisit after we do unconditional mixing
-        if (ShouldInsertBackwards(hash, ctrl_))
+        if (!is_small() && ShouldInsertBackwards(hash, ctrl_)) {
           return {seq.offset(mask.HighestBitSet()), seq.index()};
-        else
-          return {seq.offset(mask.LowestBitSet()), seq.index()};
-#else
-        return {seq.offset(mask.LowestBitSet()), seq.index()};
+        }
 #endif
+        return {seq.offset(mask.LowestBitSet()), seq.index()};
       }
       assert(seq.index() < capacity_ && "full table!");
       seq.next();
@@ -1732,11 +1725,28 @@ class raw_hash_set {
     }
 
     ctrl_[i] = h;
-    ctrl_[((i - Group::kWidth) & capacity_) + Group::kWidth] = h;
+    ctrl_[((i - Group::kWidth) & capacity_) + 1 +
+          ((Group::kWidth - 1) & capacity_)] = h;
   }
 
   size_t& growth_left() { return settings_.template get<0>(); }
 
+  // The representation of the object has two modes:
+  //  - small: For capacities < kWidth-1
+  //  - large: For the rest.
+  //
+  // Differences:
+  //  - In small mode we are able to use the whole capacity. The extra control
+  //  bytes give us at least one "empty" control byte to stop the iteration.
+  //  This is important to make 1 a valid capacity.
+  //
+  //  - In small mode only the first `capacity()` control bytes after the
+  //  sentinel are valid. The rest contain dummy kEmpty values that do not
+  //  represent a real slot. This is important to take into account on
+  //  find_first_non_full(), where we never try ShouldInsertBackwards() for
+  //  small tables.
+  bool is_small() const { return capacity_ < Group::kWidth - 1; }
+
   hasher& hash_ref() { return settings_.template get<1>(); }
   const hasher& hash_ref() const { return settings_.template get<1>(); }
   key_equal& eq_ref() { return settings_.template get<2>(); }
diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index b684571feb..db0bb823b1 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -55,13 +55,16 @@ using ::testing::Pair;
 using ::testing::UnorderedElementsAre;
 
 TEST(Util, NormalizeCapacity) {
-  constexpr size_t kMinCapacity = Group::kWidth - 1;
-  EXPECT_EQ(kMinCapacity, NormalizeCapacity(0));
-  EXPECT_EQ(kMinCapacity, NormalizeCapacity(1));
-  EXPECT_EQ(kMinCapacity, NormalizeCapacity(2));
-  EXPECT_EQ(kMinCapacity, NormalizeCapacity(kMinCapacity));
-  EXPECT_EQ(kMinCapacity * 2 + 1, NormalizeCapacity(kMinCapacity + 1));
-  EXPECT_EQ(kMinCapacity * 2 + 1, NormalizeCapacity(kMinCapacity + 2));
+  EXPECT_EQ(1, NormalizeCapacity(0));
+  EXPECT_EQ(1, NormalizeCapacity(1));
+  EXPECT_EQ(3, NormalizeCapacity(2));
+  EXPECT_EQ(3, NormalizeCapacity(3));
+  EXPECT_EQ(7, NormalizeCapacity(4));
+  EXPECT_EQ(7, NormalizeCapacity(7));
+  EXPECT_EQ(15, NormalizeCapacity(8));
+  EXPECT_EQ(15, NormalizeCapacity(15));
+  EXPECT_EQ(15 * 2 + 1, NormalizeCapacity(15 + 1));
+  EXPECT_EQ(15 * 2 + 1, NormalizeCapacity(15 + 2));
 }
 
 TEST(Util, GrowthAndCapacity) {
@@ -72,10 +75,7 @@ TEST(Util, GrowthAndCapacity) {
     size_t capacity = NormalizeCapacity(GrowthToLowerboundCapacity(growth));
     // The capacity is large enough for `growth`
     EXPECT_THAT(CapacityToGrowth(capacity), Ge(growth));
-    if (growth < Group::kWidth - 1) {
-      // Fits in one group, that is the minimum capacity.
-      EXPECT_EQ(capacity, Group::kWidth - 1);
-    } else {
+    if (growth != 0 && capacity > 1) {
       // There is no smaller capacity that works.
       EXPECT_THAT(CapacityToGrowth(capacity / 2), Lt(growth));
     }
@@ -814,7 +814,7 @@ TEST(Table, EnsureNonQuadraticAsInRust) {
 TEST(Table, ClearBug) {
   IntTable t;
   constexpr size_t capacity = container_internal::Group::kWidth - 1;
-  constexpr size_t max_size = capacity / 2;
+  constexpr size_t max_size = capacity / 2 + 1;
   for (size_t i = 0; i < max_size; ++i) {
     t.insert(i);
   }
@@ -1741,80 +1741,74 @@ TEST(Nodes, ExtractInsert) {
   EXPECT_FALSE(node);
 }
 
-StringTable MakeSimpleTable(size_t size) {
-  StringTable t;
-  for (size_t i = 0; i < size; ++i) t.emplace(std::string(1, 'A' + i), "");
+IntTable MakeSimpleTable(size_t size) {
+  IntTable t;
+  while (t.size() < size) t.insert(t.size());
   return t;
 }
 
-std::string OrderOfIteration(const StringTable& t) {
-  std::string order;
-  for (auto& p : t) order += p.first;
-  return order;
+std::vector<int> OrderOfIteration(const IntTable& t) {
+  return {t.begin(), t.end()};
 }
 
+// These IterationOrderChanges tests depend on non-deterministic behavior.
+// We are injecting non-determinism from the pointer of the table, but do so in
+// a way that only the page matters. We have to retry enough times to make sure
+// we are touching different memory pages to cause the ordering to change.
+// We also need to keep the old tables around to avoid getting the same memory
+// blocks over and over.
 TEST(Table, IterationOrderChangesByInstance) {
-  // Needs to be more than kWidth elements to be able to affect order.
-  const StringTable reference = MakeSimpleTable(20);
-
-  // Since order is non-deterministic we can't just try once and verify.
-  // We'll try until we find that order changed. It should not take many tries
-  // for that.
-  // Important: we have to keep the old tables around. Otherwise tcmalloc will
-  // just give us the same blocks and we would be doing the same order again.
-  std::vector<StringTable> garbage;
-  for (int i = 0; i < 10; ++i) {
-    auto trial = MakeSimpleTable(20);
-    if (OrderOfIteration(trial) != OrderOfIteration(reference)) {
-      // We are done.
-      return;
+  for (size_t size : {2, 6, 12, 20}) {
+    const auto reference_table = MakeSimpleTable(size);
+    const auto reference = OrderOfIteration(reference_table);
+
+    std::vector<IntTable> tables;
+    bool found_difference = false;
+    for (int i = 0; !found_difference && i < 500; ++i) {
+      tables.push_back(MakeSimpleTable(size));
+      found_difference = OrderOfIteration(tables.back()) != reference;
+    }
+    if (!found_difference) {
+      FAIL()
+          << "Iteration order remained the same across many attempts with size "
+          << size;
     }
-    garbage.push_back(std::move(trial));
   }
-  FAIL();
 }
 
 TEST(Table, IterationOrderChangesOnRehash) {
-  // Since order is non-deterministic we can't just try once and verify.
-  // We'll try until we find that order changed. It should not take many tries
-  // for that.
-  // Important: we have to keep the old tables around. Otherwise tcmalloc will
-  // just give us the same blocks and we would be doing the same order again.
-  std::vector<StringTable> garbage;
-  for (int i = 0; i < 10; ++i) {
-    // Needs to be more than kWidth elements to be able to affect order.
-    StringTable t = MakeSimpleTable(20);
-    const std::string reference = OrderOfIteration(t);
+  std::vector<IntTable> garbage;
+  for (int i = 0; i < 500; ++i) {
+    auto t = MakeSimpleTable(20);
+    const auto reference = OrderOfIteration(t);
     // Force rehash to the same size.
     t.rehash(0);
-    std::string trial = OrderOfIteration(t);
+    auto trial = OrderOfIteration(t);
     if (trial != reference) {
       // We are done.
       return;
     }
     garbage.push_back(std::move(t));
   }
-  FAIL();
+  FAIL() << "Iteration order remained the same across many attempts.";
 }
 
-TEST(Table, IterationOrderChangesForSmallTables) {
-  // Since order is non-deterministic we can't just try once and verify.
-  // We'll try until we find that order changed.
-  // Important: we have to keep the old tables around. Otherwise tcmalloc will
-  // just give us the same blocks and we would be doing the same order again.
-  StringTable reference_table = MakeSimpleTable(5);
-  const std::string reference = OrderOfIteration(reference_table);
-  std::vector<StringTable> garbage;
-  for (int i = 0; i < 50; ++i) {
-    StringTable t = MakeSimpleTable(5);
-    std::string trial = OrderOfIteration(t);
-    if (trial != reference) {
-      // We are done.
-      return;
-    }
-    garbage.push_back(std::move(t));
-  }
-  FAIL() << "Iteration order remained the same across many attempts.";
+// Verify that pointers are invalidated as soon as a second element is inserted.
+// This prevents dependency on pointer stability on small tables.
+TEST(Table, UnstablePointers) {
+  IntTable table;
+
+  const auto addr = [&](int i) {
+    return reinterpret_cast<uintptr_t>(&*table.find(i));
+  };
+
+  table.insert(0);
+  const uintptr_t old_ptr = addr(0);
+
+  // This causes a rehash.
+  table.insert(1);
+
+  EXPECT_NE(old_ptr, addr(0));
 }
 
 // Confirm that we assert if we try to erase() end().
@@ -1857,6 +1851,7 @@ TEST(RawHashSamplerTest, Sample) {
 #ifdef ADDRESS_SANITIZER
 TEST(Sanitizer, PoisoningUnused) {
   IntTable t;
+  t.reserve(5);
   // Insert something to force an allocation.
   int64_t& v1 = *t.insert(0).first;
 
diff --git a/absl/memory/memory.h b/absl/memory/memory.h
index a0d0714fab..5a4a1a1dfe 100644
--- a/absl/memory/memory.h
+++ b/absl/memory/memory.h
@@ -47,19 +47,14 @@ namespace absl {
 //   X* NewX(int, int);
 //   auto x = WrapUnique(NewX(1, 2));  // 'x' is std::unique_ptr<X>.
 //
-// The purpose of WrapUnique is to automatically deduce the pointer type. If you
-// wish to make the type explicit, for readability reasons or because you prefer
-// to use a base-class pointer rather than a derived one, just use
+// Do not call WrapUnique with an explicit type, as in
+// `WrapUnique<X>(NewX(1, 2))`.  The purpose of WrapUnique is to automatically
+// deduce the pointer type. If you wish to make the type explicit, just use
 // `std::unique_ptr` directly.
 //
-// Example:
-//   X* Factory(int, int);
-//   auto x = std::unique_ptr<X>(Factory(1, 2));
+//   auto x = std::unique_ptr<X>(NewX(1, 2));
 //                  - or -
-//   std::unique_ptr<X> x(Factory(1, 2));
-//
-// This has the added advantage of working whether Factory returns a raw
-// pointer or a `std::unique_ptr`.
+//   std::unique_ptr<X> x(NewX(1, 2));
 //
 // While `absl::WrapUnique` is useful for capturing the output of a raw
 // pointer factory, prefer 'absl::make_unique<T>(args...)' over
diff --git a/absl/numeric/int128.cc b/absl/numeric/int128.cc
index 33f528ce9c..93b62c5290 100644
--- a/absl/numeric/int128.cc
+++ b/absl/numeric/int128.cc
@@ -123,6 +123,28 @@ uint128 MakeUint128FromFloat(T v) {
 
   return MakeUint128(0, static_cast<uint64_t>(v));
 }
+
+#if defined(__clang__) && !defined(__SSE3__)
+// Workaround for clang bug: https://bugs.llvm.org/show_bug.cgi?id=38289
+// Casting from long double to uint64_t is miscompiled and drops bits.
+// It is more work, so only use when we need the workaround.
+uint128 MakeUint128FromFloat(long double v) {
+  // Go 50 bits at a time, that fits in a double
+  static_assert(std::numeric_limits<double>::digits >= 50, "");
+  static_assert(std::numeric_limits<long double>::digits <= 150, "");
+  // Undefined behavior if v is not finite or cannot fit into uint128.
+  assert(std::isfinite(v) && v > -1 && v < std::ldexp(1.0L, 128));
+
+  v = std::ldexp(v, -100);
+  uint64_t w0 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+  v = std::ldexp(v - static_cast<double>(w0), 50);
+  uint64_t w1 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+  v = std::ldexp(v - static_cast<double>(w1), 50);
+  uint64_t w2 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+  return (static_cast<uint128>(w0) << 100) | (static_cast<uint128>(w1) << 50) |
+         static_cast<uint128>(w2);
+}
+#endif  // __clang__ && !__SSE3__
 }  // namespace
 
 uint128::uint128(float v) : uint128(MakeUint128FromFloat(v)) {}
diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
index 216ec50c54..5e1b5ec352 100644
--- a/absl/numeric/int128_test.cc
+++ b/absl/numeric/int128_test.cc
@@ -271,6 +271,20 @@ TEST(Uint128, ConversionTests) {
   EXPECT_EQ(static_cast<absl::uint128>(round_to_zero), 0);
   EXPECT_EQ(static_cast<absl::uint128>(round_to_five), 5);
   EXPECT_EQ(static_cast<absl::uint128>(round_to_nine), 9);
+
+  absl::uint128 highest_precision_in_long_double =
+      ~absl::uint128{} >> (128 - std::numeric_limits<long double>::digits);
+  EXPECT_EQ(highest_precision_in_long_double,
+            static_cast<absl::uint128>(
+                static_cast<long double>(highest_precision_in_long_double)));
+  // Apply a mask just to make sure all the bits are the right place.
+  const absl::uint128 arbitrary_mask =
+      absl::MakeUint128(0xa29f622677ded751, 0xf8ca66add076f468);
+  EXPECT_EQ(highest_precision_in_long_double & arbitrary_mask,
+            static_cast<absl::uint128>(static_cast<long double>(
+                highest_precision_in_long_double & arbitrary_mask)));
+
+  EXPECT_EQ(static_cast<absl::uint128>(-0.1L), 0);
 }
 
 TEST(Uint128, OperatorAssignReturnRef) {
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index 524dbebb66..bd894e1daa 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -32,7 +32,7 @@
 
 #ifdef ABSL_HAVE_STD_STRING_VIEW
 
-#include <string_view>
+#include <string_view>  // IWYU pragma: export
 
 namespace absl {
 using std::string_view;
diff --git a/absl/time/internal/cctz/BUILD.bazel b/absl/time/internal/cctz/BUILD.bazel
index 1fb33c20b9..903499be3a 100644
--- a/absl/time/internal/cctz/BUILD.bazel
+++ b/absl/time/internal/cctz/BUILD.bazel
@@ -4,7 +4,7 @@
 # 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
+#   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,
diff --git a/absl/time/internal/cctz/include/cctz/civil_time.h b/absl/time/internal/cctz/include/cctz/civil_time.h
index 0842fa4a46..f844182b1c 100644
--- a/absl/time/internal/cctz/include/cctz/civil_time.h
+++ b/absl/time/internal/cctz/include/cctz/civil_time.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/include/cctz/civil_time_detail.h b/absl/time/internal/cctz/include/cctz/civil_time_detail.h
index 1c5d097082..a5923f13c7 100644
--- a/absl/time/internal/cctz/include/cctz/civil_time_detail.h
+++ b/absl/time/internal/cctz/include/cctz/civil_time_detail.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/include/cctz/time_zone.h b/absl/time/internal/cctz/include/cctz/time_zone.h
index f28dad1755..ef6c4ba109 100644
--- a/absl/time/internal/cctz/include/cctz/time_zone.h
+++ b/absl/time/internal/cctz/include/cctz/time_zone.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
@@ -72,7 +72,7 @@ split_seconds(const time_point<seconds>& tp) {
 //
 // See also:
 // - http://www.iana.org/time-zones
-// - http://en.wikipedia.org/wiki/Zoneinfo
+// - https://en.wikipedia.org/wiki/Zoneinfo
 class time_zone {
  public:
   time_zone() : time_zone(nullptr) {}  // Equivalent to UTC
diff --git a/absl/time/internal/cctz/include/cctz/zone_info_source.h b/absl/time/internal/cctz/include/cctz/zone_info_source.h
index 20a7697937..2b898d182c 100644
--- a/absl/time/internal/cctz/include/cctz/zone_info_source.h
+++ b/absl/time/internal/cctz/include/cctz/zone_info_source.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/cctz_benchmark.cc b/absl/time/internal/cctz/src/cctz_benchmark.cc
index a00f47bf6f..445366eae5 100644
--- a/absl/time/internal/cctz/src/cctz_benchmark.cc
+++ b/absl/time/internal/cctz/src/cctz_benchmark.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/civil_time_detail.cc b/absl/time/internal/cctz/src/civil_time_detail.cc
index 780d5c96e8..cb40b6bc53 100644
--- a/absl/time/internal/cctz/src/civil_time_detail.cc
+++ b/absl/time/internal/cctz/src/civil_time_detail.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/civil_time_test.cc b/absl/time/internal/cctz/src/civil_time_test.cc
index faffde470a..e590ee3096 100644
--- a/absl/time/internal/cctz/src/civil_time_test.cc
+++ b/absl/time/internal/cctz/src/civil_time_test.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_fixed.cc b/absl/time/internal/cctz/src/time_zone_fixed.cc
index db9a475a9b..81ece72b79 100644
--- a/absl/time/internal/cctz/src/time_zone_fixed.cc
+++ b/absl/time/internal/cctz/src/time_zone_fixed.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_fixed.h b/absl/time/internal/cctz/src/time_zone_fixed.h
index 489b857d5d..9c1f5e7d7d 100644
--- a/absl/time/internal/cctz/src/time_zone_fixed.h
+++ b/absl/time/internal/cctz/src/time_zone_fixed.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_format.cc b/absl/time/internal/cctz/src/time_zone_format.cc
index a5c72df8c1..25850980b5 100644
--- a/absl/time/internal/cctz/src/time_zone_format.cc
+++ b/absl/time/internal/cctz/src/time_zone_format.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_format_test.cc b/absl/time/internal/cctz/src/time_zone_format_test.cc
index b99e1c6359..705ccdcdcc 100644
--- a/absl/time/internal/cctz/src/time_zone_format_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_format_test.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_if.cc b/absl/time/internal/cctz/src/time_zone_if.cc
index 380834a172..09aaee5fb4 100644
--- a/absl/time/internal/cctz/src/time_zone_if.cc
+++ b/absl/time/internal/cctz/src/time_zone_if.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_if.h b/absl/time/internal/cctz/src/time_zone_if.h
index e4bd3866a8..d000b7a5f7 100644
--- a/absl/time/internal/cctz/src/time_zone_if.h
+++ b/absl/time/internal/cctz/src/time_zone_if.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_impl.cc b/absl/time/internal/cctz/src/time_zone_impl.cc
index 3062ccd3ce..3cbc674653 100644
--- a/absl/time/internal/cctz/src/time_zone_impl.cc
+++ b/absl/time/internal/cctz/src/time_zone_impl.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_impl.h b/absl/time/internal/cctz/src/time_zone_impl.h
index 14965ef54b..b73fad9bb8 100644
--- a/absl/time/internal/cctz/src/time_zone_impl.h
+++ b/absl/time/internal/cctz/src/time_zone_impl.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_info.cc b/absl/time/internal/cctz/src/time_zone_info.cc
index 6aa80ff638..50f7de5401 100644
--- a/absl/time/internal/cctz/src/time_zone_info.cc
+++ b/absl/time/internal/cctz/src/time_zone_info.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
@@ -25,7 +25,7 @@
 // a grain of salt.
 //
 // For more information see tzfile(5), http://www.iana.org/time-zones, or
-// http://en.wikipedia.org/wiki/Zoneinfo.
+// https://en.wikipedia.org/wiki/Zoneinfo.
 //
 // Note that we assume the proleptic Gregorian calendar and 60-second
 // minutes throughout.
diff --git a/absl/time/internal/cctz/src/time_zone_info.h b/absl/time/internal/cctz/src/time_zone_info.h
index 958e9b6bd7..bff639f45c 100644
--- a/absl/time/internal/cctz/src/time_zone_info.h
+++ b/absl/time/internal/cctz/src/time_zone_info.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_libc.cc b/absl/time/internal/cctz/src/time_zone_libc.cc
index 2829170847..3ab1623cbd 100644
--- a/absl/time/internal/cctz/src/time_zone_libc.cc
+++ b/absl/time/internal/cctz/src/time_zone_libc.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_libc.h b/absl/time/internal/cctz/src/time_zone_libc.h
index 4e40c61ab2..0d18e9a7f3 100644
--- a/absl/time/internal/cctz/src/time_zone_libc.h
+++ b/absl/time/internal/cctz/src/time_zone_libc.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_lookup.cc b/absl/time/internal/cctz/src/time_zone_lookup.cc
index f2d151e4d5..4a68c7d588 100644
--- a/absl/time/internal/cctz/src/time_zone_lookup.cc
+++ b/absl/time/internal/cctz/src/time_zone_lookup.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
@@ -20,6 +20,11 @@
 #include <dlfcn.h>
 #endif
 #endif
+
+#if defined(__APPLE__)
+#include <CoreFoundation/CFTimeZone.h>
+#endif
+
 #include <cstdlib>
 #include <cstring>
 #include <string>
@@ -121,6 +126,11 @@ time_zone local_time_zone() {
   char* tz_env = nullptr;
 #if defined(_MSC_VER)
   _dupenv_s(&tz_env, nullptr, "TZ");
+#elif defined(__APPLE__)
+  CFTimeZoneRef system_time_zone = CFTimeZoneCopySystem();
+  CFStringRef tz_name = CFTimeZoneGetName(system_time_zone);
+  tz_env = strdup(CFStringGetCStringPtr(tz_name, CFStringGetSystemEncoding()));
+  CFRelease(system_time_zone);
 #else
   tz_env = std::getenv("TZ");
 #endif
@@ -153,6 +163,8 @@ time_zone local_time_zone() {
 #if defined(_MSC_VER)
   free(localtime_env);
   free(tz_env);
+#elif defined(__APPLE__)
+  free(tz_env);
 #endif
 
   time_zone tz;
diff --git a/absl/time/internal/cctz/src/time_zone_lookup_test.cc b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
index 2e49e48c2d..8068e2fc82 100644
--- a/absl/time/internal/cctz/src/time_zone_lookup_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_posix.cc b/absl/time/internal/cctz/src/time_zone_posix.cc
index 75ad8bcba9..993901acfa 100644
--- a/absl/time/internal/cctz/src/time_zone_posix.cc
+++ b/absl/time/internal/cctz/src/time_zone_posix.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/time_zone_posix.h b/absl/time/internal/cctz/src/time_zone_posix.h
index ef2a8c1647..6a60022fa7 100644
--- a/absl/time/internal/cctz/src/time_zone_posix.h
+++ b/absl/time/internal/cctz/src/time_zone_posix.h
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/src/zone_info_source.cc b/absl/time/internal/cctz/src/zone_info_source.cc
index 1bc16aecdb..132484628c 100644
--- a/absl/time/internal/cctz/src/zone_info_source.cc
+++ b/absl/time/internal/cctz/src/zone_info_source.cc
@@ -4,7 +4,7 @@
 // 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
+//   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,
diff --git a/absl/time/internal/cctz/testdata/zoneinfo/iso3166.tab b/absl/time/internal/cctz/testdata/zoneinfo/iso3166.tab
index c2e0f8eafc..4e4a5c3d1d 100644
--- a/absl/time/internal/cctz/testdata/zoneinfo/iso3166.tab
+++ b/absl/time/internal/cctz/testdata/zoneinfo/iso3166.tab
@@ -10,7 +10,7 @@
 #
 # 1.  ISO 3166-1 alpha-2 country code, current as of
 #     ISO 3166-1 N905 (2016-11-15).  See: Updates on ISO 3166-1
-#     http://isotc.iso.org/livelink/livelink/Open/16944257
+#     https://isotc.iso.org/livelink/livelink/Open/16944257
 # 2.  The usual English name for the coded region,
 #     chosen so that alphabetic sorting of subsets produces helpful lists.
 #     This is not the same as the English name in the ISO 3166 tables.
diff --git a/absl/types/any.h b/absl/types/any.h
index e750f485ab..f3a3281266 100644
--- a/absl/types/any.h
+++ b/absl/types/any.h
@@ -58,7 +58,7 @@
 
 #ifdef ABSL_HAVE_STD_ANY
 
-#include <any>
+#include <any>  // IWYU pragma: export
 
 namespace absl {
 using std::any;
diff --git a/absl/types/optional.h b/absl/types/optional.h
index 0c1213f4f2..a86dea92c4 100644
--- a/absl/types/optional.h
+++ b/absl/types/optional.h
@@ -40,7 +40,7 @@
 
 #ifdef ABSL_HAVE_STD_OPTIONAL
 
-#include <optional>
+#include <optional>  // IWYU pragma: export
 
 namespace absl {
 using std::bad_optional_access;
diff --git a/absl/types/variant.h b/absl/types/variant.h
index 9652e3b9c6..8d8b5dbd00 100644
--- a/absl/types/variant.h
+++ b/absl/types/variant.h
@@ -47,7 +47,7 @@
 
 #ifdef ABSL_HAVE_STD_VARIANT
 
-#include <variant>
+#include <variant>  // IWYU pragma: export
 
 namespace absl {
 using std::bad_variant_access;