Export of internal Abseil changes.

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f6c627ce4470a814adc377947b58346eef69a4c9 by Jon Cohen <cohenjon@google.com>:

Don't create install rules when Abseil is used as a subdirectory.

Fix #287

PiperOrigin-RevId: 240559825

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a5d9b06fe736143068997988b654b5f66ec3266a by Matt Calabrese <calabrese@google.com>:

Make absl::nullopt an inline constexpr variable, as specified in the standard (with a workaround for pre-c++17 compilers).

PiperOrigin-RevId: 240552286

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d7bee50cff745fbb8d1cdf56a200d9073d311c80 by Abseil Team <absl-team@google.com>:

Internal Change

PiperOrigin-RevId: 240425622

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828dd49d392d83dbeecd9d3e9cb14551ab265905 by Jon Cohen <cohenjon@google.com>:

Add default link options to absl builds.

Currently all this does is add -ignore:4221 to Abseil msvc builds, but the structure is all in place to add more link options when necessary

Fix #277

Note: This CL changes tact for us in that it puts the default options in the helper function as opposed to the invocations of absl_cc_blah.  The original intent of keeping these out of the helper functions was to make generating the CMakeLists.txt files have a smaller diff, but looking now that is a problem for the future, and small compared to making maintenance and use of our CMake buildsystem easier
PiperOrigin-RevId: 240409463

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4aa120e9dcf76d29e9ca0008d0f6d4d9fa8abe8c by Matt Kulukundis <kfm@google.com>:

Reduce flake rate for non-determistic test to < 1/10,000

PiperOrigin-RevId: 240370938

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bc30e219531827bfbf90915b2067c7fb8160bb6d by Derek Mauro <dmauro@google.com>:

Add Bazel caching on Kokoro for new linux targets.

PiperOrigin-RevId: 240356556

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c4e06d79a50d7bb211312b7845c4bd92c0761747 by Jon Cohen <cohenjon@google.com>:

include AbseilInstallDirs instead of GNUInstallDirs.  It worked before because global_CMakeLists.txt also included AbseilInstallDirs

PiperOrigin-RevId: 240206409

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c254dc6cade8a263f3f97fb1417d92fe5235ff32 by Jon Cohen <cohenjon@google.com>:

Fix logic for when we create the variant_exception_safety_test in CMake.  Currently we are only running in on gcc > 4.9, when we want it run on every compiler except gcc <= 4.8

PiperOrigin-RevId: 240194174

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01518006b351d3670ba1d349cfbcb7dd6f3a8b84 by CJ Johnson <johnsoncj@google.com>:

Removes old implementation warning comment now that InlinedVector has an implementation detail file

PiperOrigin-RevId: 240167265

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eb05355ae8c7397752ab7a65afc9e0a99472ba9d by Jon Cohen <cohenjon@google.com>:

Remove the forward declaration of Span

PiperOrigin-RevId: 240156660

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b7e75aa3933d6e79dd086821cf58d15e72f476f4 by Jon Cohen <cohenjon@google.com>:

Prepare CMake install rule for LTS releases:
  * Remove the warning against installing in system install locations
  * Insert versioning to keep different LTS installs from colliding.  Headers are installed in <prefix>/absl_$version/include, .a files in <prefix>/absl_$version/lib, and config files in <prefix>/absl_$version/lib/cmake

PiperOrigin-RevId: 240153986

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de63488ab6236e041f08260794b0b634a2b8ed16 by CJ Johnson <johnsoncj@google.com>:

Reduce reader confusion by using std::addressof(...) even when the type is known to not overload operator&(...)

PiperOrigin-RevId: 240131902
GitOrigin-RevId: f6c627ce4470a814adc377947b58346eef69a4c9
Change-Id: I95dbbacaaf65aceeeca9e9bee5fd9ea456225f62

1 files changed, 13 insertions, 14 deletions

diff --git a/absl/types/optional.h b/absl/types/optional.h
index f0ae9a173c22..6806160dff7f 100644
--- a/absl/types/optional.h
+++ b/absl/types/optional.h
@@ -61,6 +61,7 @@ using std::nullopt;
 #include <utility>
 
 #include "absl/base/attributes.h"
+#include "absl/base/internal/inline_variable.h"
 #include "absl/meta/type_traits.h"
 #include "absl/types/bad_optional_access.h"
 
@@ -126,32 +127,30 @@ namespace absl {
 template <typename T>
 class optional;
 
+namespace optional_internal {
+
+// This tag type is used as a constructor parameter type for `nullopt_t`.
+struct init_t {
+  explicit init_t() = default;
+};
+
+}  // namespace optional_internal
+
 // nullopt_t
 //
 // Class type for `absl::nullopt` used to indicate an `absl::optional<T>` type
 // that does not contain a value.
 struct nullopt_t {
-  struct init_t {};
-  static init_t init;
-
   // It must not be default-constructible to avoid ambiguity for opt = {}.
-  // Note the non-const reference, which is to eliminate ambiguity for code
-  // like:
-  //
-  // struct S { int value; };
-  //
-  // void Test() {
-  //   optional<S> opt;
-  //   opt = {{}};
-  // }
-  explicit constexpr nullopt_t(init_t& /*unused*/) {}
+  explicit constexpr nullopt_t(optional_internal::init_t) noexcept {}
 };
 
 // nullopt
 //
 // A tag constant of type `absl::nullopt_t` used to indicate an empty
 // `absl::optional` in certain functions, such as construction or assignment.
-extern const nullopt_t nullopt;
+ABSL_INTERNAL_INLINE_CONSTEXPR(nullopt_t, nullopt,
+                               nullopt_t(optional_internal::init_t()));
 
 namespace optional_internal {