Export of internal Abseil changes

--
9c9eb300c95024ea4242bbb4835595f555cb1eed by Derek Mauro <dmauro@google.com>:

Sync string_view comments from the internal copy

PiperOrigin-RevId: 328582796

--
c0bc4e77a46889430a1a40d836a5ff426a4a5bc9 by Xiaoyi Zhang <zhangxy@google.com>:

Make `absl::allocator_traits` an alias to `std::allocator_traits` for C++17 or
above. `std::allocator_traits` should have all its members since C++17 so we
don't need a backport.

PiperOrigin-RevId: 328258154

--
5599a3c0f2d865128057b5e267a397011cd032d0 by Derek Mauro <dmauro@google.com>:

Fix an #endif comment

Reported at https://groups.google.com/g/abseil-io/c/GRUdB0bBrG8/m/852HrgchCQAJ

PiperOrigin-RevId: 328247093

--
abd7e98088267f436e6c10779e574153ece015be by Abseil Team <absl-team@google.com>:

Don't call win32 APIs for UWP builds

symbolize.cc is including symbolize_win32.inc for all Windows builds,
including UWP builds. However, UWP doesn't have access to win32 APIs, so
it should instead include symbolize_unimplemented.inc.

This allows the necessary functions to still exist and be called, but
the win32 calls are not made.

This is part of the effort to enable Abseil in ANGLE:
https://anglebug.com/4873

PiperOrigin-RevId: 328226766

--
f622d3dfb804a6f427c1fd86ee69f47785b49483 by Greg Falcon <gfalcon@google.com>:

Remove incorrect claims of HASH_NAMESPACE support in Abseil hash.

The documentation presently claims that absl::Hash will look for legacy hashers (e.g, in the __gnu_cxx namespace) as controlled by the HASH_NAMESPACE preprocessor define, but this has never been true.

(Vestigial support for this appears in the form `ABSL_INTERNAL_LEGACY_HASH_NAMESPACE`, but this is not a supported extension point, as indicated by the use of `INTERNAL` in the name.)

PiperOrigin-RevId: 328154123

--
32b40a25efe1f7f7da98ce8faf3482c825464ed4 by Abseil Team <absl-team@google.com>:

Switch ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED checks to defined().

PiperOrigin-RevId: 328151556
GitOrigin-RevId: 9c9eb300c95024ea4242bbb4835595f555cb1eed
Change-Id: Ib0686286f7889a976311e8cd2b35655765a8d033

8 files changed, 29 insertions, 18 deletions

diff --git a/absl/base/dynamic_annotations.h b/absl/base/dynamic_annotations.h
index c470c747..545f8cbc 100644
--- a/absl/base/dynamic_annotations.h
+++ b/absl/base/dynamic_annotations.h
@@ -83,12 +83,9 @@
 #define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 1
 #if !defined(SWIG)
 #define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 1
-#else
-#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 0
 #endif
 #else
 #define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 0
-#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 0
 #endif
 
 // Read/write annotations are enabled in Annotalysis mode; disabled otherwise.
@@ -271,19 +268,19 @@ ABSL_INTERNAL_END_EXTERN_C
 // -------------------------------------------------------------------------
 // Define IGNORE_READS_BEGIN/_END attributes.
 
-#if ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED == 1
+#if defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 #define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE \
   __attribute((exclusive_lock_function("*")))
 #define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE \
   __attribute((unlock_function("*")))
 
-#else  // ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED == 0
+#else  // !defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 #define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE  // empty
 #define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE    // empty
 
-#endif  // ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED
+#endif  // defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 // -------------------------------------------------------------------------
 // Define IGNORE_READS_BEGIN/_END annotations.
diff --git a/absl/base/internal/dynamic_annotations.h b/absl/base/internal/dynamic_annotations.h
index b69c1301..b23c5ec1 100644
--- a/absl/base/internal/dynamic_annotations.h
+++ b/absl/base/internal/dynamic_annotations.h
@@ -58,8 +58,6 @@
 
 #if defined(__clang__) && !defined(SWIG)
 #define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 1
-#else
-#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 0
 #endif
 
 #if DYNAMIC_ANNOTATIONS_ENABLED != 0
@@ -84,7 +82,7 @@
 
 // ANNOTALYSIS_ENABLED == 1 when IGNORE_READ_ATTRIBUTE_ENABLED == 1
 #define ABSL_INTERNAL_ANNOTALYSIS_ENABLED \
-  ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED
+  defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 // Read/write annotations are enabled in Annotalysis mode; disabled otherwise.
 #define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED \
   ABSL_INTERNAL_ANNOTALYSIS_ENABLED
@@ -247,19 +245,19 @@
 // -------------------------------------------------------------------------
 // Define IGNORE_READS_BEGIN/_END attributes.
 
-#if ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED == 1
+#if defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 #define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE \
   __attribute((exclusive_lock_function("*")))
 #define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE \
   __attribute((unlock_function("*")))
 
-#else  // ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED == 0
+#else  // !defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 #define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE  // empty
 #define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE    // empty
 
-#endif  // ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED
+#endif  // defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
 
 // -------------------------------------------------------------------------
 // Define IGNORE_READS_BEGIN/_END annotations.
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index 308119cf..e140ee00 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -186,7 +186,7 @@ class HashtablezInfoHandle {
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 extern ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
-#endif  // ABSL_PER_THREAD_TLS
+#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 // Returns an RAII sampling handle that manages registration and unregistation
 // with the global sampler.
diff --git a/absl/debugging/symbolize.cc b/absl/debugging/symbolize.cc
index eec7a6e8..5e4a25d6 100644
--- a/absl/debugging/symbolize.cc
+++ b/absl/debugging/symbolize.cc
@@ -14,9 +14,18 @@
 
 #include "absl/debugging/symbolize.h"
 
+#ifdef _WIN32
+#include <winapifamily.h>
+#if !(WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP)) || \
+    WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+// UWP doesn't have access to win32 APIs.
+#define ABSL_INTERNAL_HAVE_SYMBOLIZE_WIN32
+#endif
+#endif
+
 #if defined(ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE)
 #include "absl/debugging/symbolize_elf.inc"
-#elif defined(_WIN32)
+#elif defined(ABSL_INTERNAL_HAVE_SYMBOLIZE_WIN32)
 // The Windows Symbolizer only works if PDB files containing the debug info
 // are available to the program at runtime.
 #include "absl/debugging/symbolize_win32.inc"
diff --git a/absl/hash/hash.h b/absl/hash/hash.h
index d7386f6c..5de132ca 100644
--- a/absl/hash/hash.h
+++ b/absl/hash/hash.h
@@ -88,7 +88,6 @@ ABSL_NAMESPACE_BEGIN
 //  * T is an arithmetic or pointer type
 //  * T defines an overload for `AbslHashValue(H, const T&)` for an arbitrary
 //    hash state `H`.
-//  - T defines a specialization of `HASH_NAMESPACE::hash<T>`
 //  - T defines a specialization of `std::hash<T>`
 //
 // `absl::Hash` intrinsically supports the following types:
@@ -128,8 +127,6 @@ ABSL_NAMESPACE_BEGIN
 //   * Natively supported types out of the box (see above)
 //   * Types for which an `AbslHashValue()` overload is provided (such as
 //     user-defined types). See "Adding Type Support to `absl::Hash`" below.
-//   * Types which define a `HASH_NAMESPACE::hash<T>` specialization (aka
-//     `__gnu_cxx::hash<T>` for gcc/Clang or `stdext::hash<T>` for MSVC)
 //   * Types which define a `std::hash<T>` specialization
 //
 // The fallback to legacy hash functions exists mainly for backwards
diff --git a/absl/memory/memory.h b/absl/memory/memory.h
index 513f7103..2b5ff623 100644
--- a/absl/memory/memory.h
+++ b/absl/memory/memory.h
@@ -420,6 +420,9 @@ struct pointer_traits<T*> {
 //
 // A C++11 compatible implementation of C++17's std::allocator_traits.
 //
+#if __cplusplus >= 201703L
+using std::allocator_traits;
+#else  // __cplusplus >= 201703L
 template <typename Alloc>
 struct allocator_traits {
   using allocator_type = Alloc;
@@ -609,6 +612,7 @@ struct allocator_traits {
     return a;
   }
 };
+#endif  // __cplusplus >= 201703L
 
 namespace memory_internal {
 
diff --git a/absl/memory/memory_test.cc b/absl/memory/memory_test.cc
index 0d2e13bd..1990c7ba 100644
--- a/absl/memory/memory_test.cc
+++ b/absl/memory/memory_test.cc
@@ -555,7 +555,7 @@ TEST(AllocatorTraits, FunctionsMinimal) {
   EXPECT_CALL(mock, deallocate(&x, 7));
 
   EXPECT_EQ(&x, Traits::allocate(mock, 7));
-  Traits::allocate(mock, 7, static_cast<const void*>(&hint));
+  static_cast<void>(Traits::allocate(mock, 7, static_cast<const void*>(&hint)));
   EXPECT_EQ(&x, Traits::allocate(mock, 7, static_cast<const void*>(&hint)));
   Traits::deallocate(mock, &x, 7);
 
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index 8a9db8c3..5260b5b7 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -111,6 +111,11 @@ ABSL_NAMESPACE_BEGIN
 // example, when splitting a string, `std::vector<absl::string_view>` is a
 // natural data type for the output.
 //
+// For another example, a Cord is a non-contiguous, potentially very
+// long string-like object.  The Cord class has an interface that iteratively
+// provides string_view objects that point to the successive pieces of a Cord
+// object.
+//
 // When constructed from a source which is NUL-terminated, the `string_view`
 // itself will not include the NUL-terminator unless a specific size (including
 // the NUL) is passed to the constructor. As a result, common idioms that work
@@ -382,6 +387,7 @@ class string_view {
   // Returns a "substring" of the `string_view` (at offset `pos` and length
   // `n`) as another string_view. This function throws `std::out_of_bounds` if
   // `pos > size`.
+  // Use absl::ClippedSubstr if you need a truncating substr operation.
   constexpr string_view substr(size_type pos, size_type n = npos) const {
     return ABSL_PREDICT_FALSE(pos > length_)
                ? (base_internal::ThrowStdOutOfRange(