Export of internal Abseil changes.

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

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

Fix #287

PiperOrigin-RevId: 240559825

--
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

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

Internal Change

PiperOrigin-RevId: 240425622

--
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

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

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

PiperOrigin-RevId: 240370938

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

Add Bazel caching on Kokoro for new linux targets.

PiperOrigin-RevId: 240356556

--
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

--
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

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

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

PiperOrigin-RevId: 240167265

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

Remove the forward declaration of Span

PiperOrigin-RevId: 240156660

--
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

--
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, 42 insertions, 24 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3f4fbdc..ad55fa4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,13 +22,14 @@
 cmake_minimum_required(VERSION 3.5)
 
 # Compiler id for Apple Clang is now AppleClang.
-if (POLICY CMP0025)
-  cmake_policy(SET CMP0025 NEW)
-endif()
+cmake_policy(SET CMP0025 NEW)
 
 # if command can use IN_LIST
 cmake_policy(SET CMP0057 NEW)
 
+# Project version variables are the empty std::string if version is unspecified
+cmake_policy(SET CMP0048 NEW)
+
 project(absl)
 
 # when absl is included as subproject (i.e. using add_subdirectory(abseil-cpp))
@@ -44,7 +45,7 @@ list(APPEND CMAKE_MODULE_PATH
   ${CMAKE_CURRENT_LIST_DIR}/absl/copts
 )
 
-include(GNUInstallDirs)
+include(AbseilInstallDirs)
 include(CMakePackageConfigHelpers)
 include(AbseilHelpers)
 
@@ -85,6 +86,7 @@ if(${ABSL_RUN_TESTS})
   enable_testing()
 endif()
 
+# absl:lts-remove-begin(system installation is supported for LTS releases)
 # We don't support system-wide installation
 list(APPEND SYSTEM_INSTALL_DIRS "/usr/local" "/usr" "/opt/" "/opt/local" "c:/Program Files/${PROJECT_NAME}")
 if(NOT DEFINED CMAKE_INSTALL_PREFIX OR CMAKE_INSTALL_PREFIX IN_LIST SYSTEM_INSTALL_DIRS)
@@ -94,6 +96,7 @@ releases of Abseil.  Please set CMAKE_INSTALL_PREFIX to install Abseil in your \
 source or build tree directly.\
   ")
 endif()
+# absl:lts-remove-end
 
 ## check targets
 if(BUILD_TESTING)
@@ -118,25 +121,40 @@ endif()
 
 add_subdirectory(absl)
 
-# install as a subdirectory only
-install(EXPORT ${PROJECT_NAME}Targets
-  NAMESPACE absl::
-  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
-)
-
-configure_package_config_file(
-  CMake/abslConfig.cmake.in
-  "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
-  INSTALL_DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
-)
+if (ABSL_ENABLE_INSTALL)
+  # install as a subdirectory only
+  install(EXPORT ${PROJECT_NAME}Targets
+    NAMESPACE absl::
+    DESTINATION "${ABSL_INSTALL_CONFIGDIR}"
+  )
 
-install(FILES "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
-  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
-)
+  configure_package_config_file(
+    CMake/abslConfig.cmake.in
+    "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+    INSTALL_DESTINATION "${ABSL_INSTALL_CONFIGDIR}"
+  )
+  install(FILES "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+    DESTINATION "${ABSL_INSTALL_CONFIGDIR}"
+  )
 
-install(DIRECTORY absl
-  DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
-  FILES_MATCHING
-    PATTERN "*.inc"
-    PATTERN "*.h"
-)
+  # Abseil only has a version in LTS releases.  This mechanism is accomplished
+  # Abseil's internal Copybara (https://github.com/google/copybara) workflows and
+  # isn't visible in the CMake buildsystem itself.
+  if (absl_VERSION)
+    write_basic_package_version_file(
+      "${PROJECT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
+      COMPATIBILITY ExactVersion
+    )
+
+    install(FILES "${PROJECT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
+      DESTINATION ${ABSL_INSTALL_CONFIGDIR}
+    )
+  endif()  # absl_VERSION
+
+  install(DIRECTORY absl
+    DESTINATION ${ABSL_INSTALL_INCLUDEDIR}
+    FILES_MATCHING
+      PATTERN "*.inc"
+      PATTERN "*.h"
+  )
+endif()  # ABSL_ENABLE_INSTALL