From 308bbf300fe9332130f4784c7a91fa2ad707d6e4 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Tue, 6 Sep 2022 13:11:28 -0700
Subject: CMake: install artifacts reflect the compiled ABI

Change `absl/base/options.h` at install time to reflect the ABI used
to compile the libraries, i.e., if Abseil was compiled with
C++ >= 17 then the `ABSL_OPTION_USE_STD_*` macros are set to `1`,
because then the C++ 17 types are embedded in the ABI of the installed
artifacts.

Likewise, set the `target_compile_features()` of Abseil libraries
to reflect the C++ version used to compile them. If they the Abseil
libraries are compiled with C++ >= 17, then all downstream
dependencies must also be compiled with C++ >= 17.

Fixes #696

PiperOrigin-RevId: 472538165
Change-Id: Ic9e346ebe277c882a18ad96e1918c9e3511c91c3
---
 CMake/AbseilHelpers.cmake | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

(limited to 'CMake')

diff --git a/CMake/AbseilHelpers.cmake b/CMake/AbseilHelpers.cmake
index e3194bcf..e1196fd7 100644
--- a/CMake/AbseilHelpers.cmake
+++ b/CMake/AbseilHelpers.cmake
@@ -40,6 +40,27 @@ function(_target_compile_features_if_available TARGET TYPE FEATURE)
   endif()
 endfunction()
 
+include(CheckCXXSourceCompiles)
+
+check_cxx_source_compiles(
+  [==[
+#ifdef _MSC_VER
+#  if _MSVC_LANG < 201700L
+#    error "The compiler defaults or is configured for C++ < 17"
+#  endif
+#elif __cplusplus < 201700L
+#  error "The compiler defaults or is configured for C++ < 17"
+#endif
+int main() { return 0; }
+]==]
+  ABSL_INTERNAL_AT_LEAST_CXX17)
+
+if(ABSL_INTERNAL_AT_LEAST_CXX17)
+  set(ABSL_INTERNAL_CXX_STD_FEATURE cxx_std_17)
+else()
+  set(ABSL_INTERNAL_CXX_STD_FEATURE cxx_std_14)
+endif()
+
 # absl_cc_library()
 #
 # CMake function to imitate Bazel's cc_library rule.
@@ -279,7 +300,7 @@ Cflags: -I\${includedir}${PC_CFLAGS}\n")
       # Abseil libraries require C++14 as the current minimum standard.
       # Top-level application CMake projects should ensure a consistent C++
       # standard for all compiled sources by setting CMAKE_CXX_STANDARD.
-      _target_compile_features_if_available(${_NAME} PUBLIC cxx_std_14)
+      _target_compile_features_if_available(${_NAME} PUBLIC ${ABSL_INTERNAL_CXX_STD_FEATURE})
     else()
       # Note: This is legacy (before CMake 3.8) behavior. Setting the
       # target-level CXX_STANDARD property to ABSL_CXX_STANDARD (which is
@@ -327,7 +348,7 @@ Cflags: -I\${includedir}${PC_CFLAGS}\n")
       # Abseil libraries require C++14 as the current minimum standard.
       # Top-level application CMake projects should ensure a consistent C++
       # standard for all compiled sources by setting CMAKE_CXX_STANDARD.
-      _target_compile_features_if_available(${_NAME} INTERFACE cxx_std_14)
+      _target_compile_features_if_available(${_NAME} INTERFACE ${ABSL_INTERNAL_CXX_STD_FEATURE})
 
       # (INTERFACE libraries can't have the CXX_STANDARD property set, so there
       # is no legacy behavior else case).
@@ -439,7 +460,7 @@ function(absl_cc_test)
     # Abseil libraries require C++14 as the current minimum standard.
     # Top-level application CMake projects should ensure a consistent C++
     # standard for all compiled sources by setting CMAKE_CXX_STANDARD.
-    _target_compile_features_if_available(${_NAME} PUBLIC cxx_std_14)
+    _target_compile_features_if_available(${_NAME} PUBLIC ${ABSL_INTERNAL_CXX_STD_FEATURE})
   else()
     # Note: This is legacy (before CMake 3.8) behavior. Setting the
     # target-level CXX_STANDARD property to ABSL_CXX_STANDARD (which is
-- 
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