Export of internal Abseil changes.

--
5f1ab09522226336830d9ea6ef7276d37f536ac5 by Abseil Team <absl-team@google.com>:

Clarify the documentation of ABSL_MUST_USE_RESULT.

PiperOrigin-RevId: 221663609

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af4c8359a20d56369fd1dce318220cf3be03ca66 by Greg Falcon <gfalcon@google.com>:

Internal change

PiperOrigin-RevId: 221538448

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487cd09bd1942bf607080deeae38fee6ce66f294 by Eric Fiselier <ericwf@google.com>:

Work around emscripten bugs and missing features in absl/time:time_test.

The emscripten toolchain has a couple of issues that cause time_test
to fail. Specifically:

1) emscripten doesn't support signals.
2) The javascript implementation of strftime/strptime use different expansions
of '%c' that mean it doesn't round-trip.

PiperOrigin-RevId: 221523701

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5823652e6a200b97b07334bc47128dfac40e20fc by Xiaoyi Zhang <zhangxy@google.com>:

Fix MSVC compiler warning by explicitly casting to char.
Currently our MSVC build breaks with the following error:
raw_hash_set.h(406): warning C4309: 'argument': truncation of constant value

PiperOrigin-RevId: 221492585

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c5806358320711a5efbe5c523df13e14ab53a17d by Greg Falcon <gfalcon@google.com>:

Replace calls to getpagesize() with the more portable sysconf(_SC_PAGESIZE); the latter is in POSIX 1.0 and is called out in the Linux `getpagesize` man page as a more portable spelling.

PiperOrigin-RevId: 221492471

--
19ffe82851072229bb7ce73f754ffe4c18e8c575 by Abseil Team <absl-team@google.com>:

Fix -Wundef error in absl/hash/internal/hash.h.

PiperOrigin-RevId: 221444120

--
b30f3d0a848563b6e4ec33f3dc085831dfabb748 by Jon Cohen <cohenjon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 221339736
GitOrigin-RevId: 5f1ab09522226336830d9ea6ef7276d37f536ac5
Change-Id: I96223d522d98bf6616dea88eb047c2d536eeddd0

absl/base/attributes.h

@@ -402,17 +402,28 @@
 
 // ABSL_MUST_USE_RESULT
 //
-// Tells the compiler to warn about unused return values for functions declared
-// with this macro. The macro must appear as the very first part of a function
-// declaration or definition:
+// Tells the compiler to warn about unused results.
 //
-// Example:
+// When annotating a function, it must appear as the first part of the
+// declaration or definition. The compiler will warn if the return value from
+// such a function is unused:
 //
 //   ABSL_MUST_USE_RESULT Sprocket* AllocateSprocket();
+//   AllocateSprocket();  // Triggers a warning.
+//
+// When annotating a class, it is equivalent to annotating every function which
+// returns an instance.
+//
+//   class ABSL_MUST_USE_RESULT Sprocket {};
+//   Sprocket();  // Triggers a warning.
+//
+//   Sprocket MakeSprocket();
+//   MakeSprocket();  // Triggers a warning.
+//
+// Note that references and pointers are not instances:
 //
-// This placement has the broadest compatibility with GCC, Clang, and MSVC, with
-// both defs and decls, and with GCC-style attributes, MSVC declspec, C++11
-// and C++17 attributes.
+//   Sprocket* SprocketPointer();
+//   SprocketPointer();  // Does *not* trigger a warning.
 //
 // ABSL_MUST_USE_RESULT allows using cast-to-void to suppress the unused result
 // warning. For that, warn_unused_result is used only for clang but not for gcc.

absl/base/config.h

@@ -274,7 +274,8 @@
 #error ABSL_HAVE_MMAP cannot be directly set
 #elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) ||   \
     defined(__ros__) || defined(__native_client__) || defined(__asmjs__) || \
-    defined(__wasm__) || defined(__Fuchsia__) || defined(__sun)
+    defined(__wasm__) || defined(__Fuchsia__) || defined(__sun) || \
+    defined(__ASYLO__)
 #define ABSL_HAVE_MMAP 1
 #endif
 
@@ -328,6 +329,8 @@
 #define ABSL_HAVE_ALARM 1
 #elif defined(_MSC_VER)
 // feature tests for Microsoft's library
+#elif defined(__EMSCRIPTEN__)
+// emscripten doesn't support signals
 #elif defined(__native_client__)
 #else
 // other standard libraries

absl/base/internal/direct_mmap.h

@@ -75,7 +75,7 @@ inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
   // On these architectures, implement mmap with mmap2.
   static int pagesize = 0;
   if (pagesize == 0) {
-    pagesize = getpagesize();
+    pagesize = sysconf(_SC_PAGESIZE);
   }
   if (offset < 0 || offset % pagesize != 0) {
     errno = EINVAL;

absl/base/internal/low_level_alloc.cc

@@ -208,7 +208,7 @@ struct LowLevelAlloc::Arena {
   int32_t allocation_count GUARDED_BY(mu);
   // flags passed to NewArena
   const uint32_t flags;
-  // Result of getpagesize()
+  // Result of sysconf(_SC_PAGESIZE)
   const size_t pagesize;
   // Lowest power of two >= max(16, sizeof(AllocList))
   const size_t roundup;
@@ -325,7 +325,7 @@ size_t GetPageSize() {
   GetSystemInfo(&system_info);
   return std::max(system_info.dwPageSize, system_info.dwAllocationGranularity);
 #else
-  return getpagesize();
+  return sysconf(_SC_PAGESIZE);
 #endif
 }
 

absl/container/internal/raw_hash_set.h

@@ -403,7 +403,7 @@ struct GroupSse2Impl {
   }
 
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
-    auto msbs = _mm_set1_epi8(0x80);
+    auto msbs = _mm_set1_epi8(static_cast<char>(-128));
     auto x126 = _mm_set1_epi8(126);
 #if SWISSTABLE_HAVE_SSSE3
     auto res = _mm_or_si128(_mm_shuffle_epi8(x126, ctrl), msbs);

absl/debugging/failure_signal_handler.cc

@@ -119,7 +119,7 @@ const char* FailureSignalToString(int signo) {
 #ifndef _WIN32
 
 static bool SetupAlternateStackOnce() {
-  const size_t page_mask = getpagesize() - 1;
+  const size_t page_mask = sysconf(_SC_PAGESIZE) - 1;
   size_t stack_size = (std::max(SIGSTKSZ, 65536) + page_mask) & ~page_mask;
 #if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
     defined(THREAD_SANITIZER)

absl/debugging/symbolize_elf.inc

@@ -333,7 +333,7 @@ static std::atomic<Symbolizer *> g_cached_symbolizer;
 }  // namespace
 
 static int SymbolizerSize() {
-  int pagesize = getpagesize();
+  int pagesize = sysconf(_SC_PAGESIZE);
   return ((sizeof(Symbolizer) - 1) / pagesize + 1) * pagesize;
 }
 

absl/hash/internal/hash.h

@@ -303,13 +303,13 @@ H hash_tuple(H hash_state, const Tuple& t, absl::index_sequence<Is...>) {
 
 // AbslHashValue for hashing tuples
 template <typename H, typename... Ts>
-#if _MSC_VER
+#if defined(_MSC_VER)
 // This SFINAE gets MSVC confused under some conditions. Let's just disable it
 // for now.
 H
-#else
+#else  // _MSC_VER
 typename std::enable_if<absl::conjunction<is_hashable<Ts>...>::value, H>::type
-#endif
+#endif  // _MSC_VER
 AbslHashValue(H hash_state, const std::tuple<Ts...>& t) {
   return hash_internal::hash_tuple(std::move(hash_state), t,
                                    absl::make_index_sequence<sizeof...(Ts)>());
@@ -545,7 +545,7 @@ hash_range_or_bytes(H hash_state, const T* data, size_t size) {
 // In MSVC we can't probe std::hash or stdext::hash because it triggers a
 // static_assert instead of failing substitution.
 #if defined(_MSC_VER)
-#undef ABSL_HASH_INTERNAL_CAN_POISON_
+#define ABSL_HASH_INTERNAL_CAN_POISON_ 0
 #else   // _MSC_VER
 #define ABSL_HASH_INTERNAL_CAN_POISON_ 1
 #endif  // _MSC_VER
@@ -553,6 +553,8 @@ hash_range_or_bytes(H hash_state, const T* data, size_t size) {
 #if defined(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE) && \
     ABSL_HASH_INTERNAL_CAN_POISON_
 #define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 1
+#else
+#define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 0
 #endif
 
 enum class InvokeHashTag {

absl/time/format_test.cc

@@ -394,7 +394,12 @@ TEST(FormatParse, RoundTrip) {
   // work. On Windows, `absl::ParseTime()` falls back to std::get_time() which
   // appears to fail on "%c" (or at least on the "%c" text produced by
   // `strftime()`). This makes it fail the round-trip test.
-#ifndef _MSC_VER
+  //
+  // Under the emscripten compiler `absl::ParseTime() falls back to
+  // `strptime()`, but that ends up using a different definition for "%c"
+  // compared to `strftime()`, also causing the round-trip test to fail
+  // (see https://github.com/kripken/emscripten/pull/7491).
+#if !defined(_MSC_VER) && !defined(__EMSCRIPTEN__)
   // Even though we don't know what %c will produce, it should roundtrip,
   // but only in the 0-offset timezone.
   {
@@ -403,7 +408,7 @@ TEST(FormatParse, RoundTrip) {
     EXPECT_TRUE(absl::ParseTime("%c", s, &out, &err)) << s << ": " << err;
     EXPECT_EQ(in, out);
   }
-#endif  // _MSC_VER
+#endif  // !_MSC_VER && !__EMSCRIPTEN__
 }
 
 TEST(FormatParse, RoundTripDistantFuture) {

absl/time/internal/cctz/include/cctz/civil_time_detail.h

@@ -506,9 +506,11 @@ enum class weekday {
 };
 
 CONSTEXPR_F weekday get_weekday(const civil_day& cd) noexcept {
-  CONSTEXPR_D weekday k_weekday_by_sun_off[7] = {
-      weekday::sunday,     weekday::monday,    weekday::tuesday,
-      weekday::wednesday,  weekday::thursday,  weekday::friday,
+  CONSTEXPR_D weekday k_weekday_by_mon_off[13] = {
+      weekday::monday,    weekday::tuesday,  weekday::wednesday,
+      weekday::thursday,  weekday::friday,   weekday::saturday,
+      weekday::sunday,    weekday::monday,   weekday::tuesday,
+      weekday::wednesday, weekday::thursday, weekday::friday,
       weekday::saturday,
   };
   CONSTEXPR_D int k_weekday_offsets[1 + 12] = {
@@ -517,7 +519,7 @@ CONSTEXPR_F weekday get_weekday(const civil_day& cd) noexcept {
   year_t wd = 2400 + (cd.year() % 400) - (cd.month() < 3);
   wd += wd / 4 - wd / 100 + wd / 400;
   wd += k_weekday_offsets[cd.month()] + cd.day();
-  return k_weekday_by_sun_off[(wd % 7 + 7) % 7];
+  return k_weekday_by_mon_off[wd % 7 + 6];
 }
 
 ////////////////////////////////////////////////////////////////////////