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Compile CMake as C++17 if supported by the compiler

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Add a check that a simple source file can compile as C++17 that uses
some of the features we need.  Do this only when hosted by CMake 3.8
or above because those versions are aware of C++17.

Check for unordered_map as we do in bootstrap since commit 375eca7881
(bootstrap: Check support for unordered_map from compiler mode,
2017-11-30).  Also maintain the existing C++14 cstdio check.
This commit is contained in:
Brad King 2017-12-06 11:06:12 -05:00
parent 31c6b9adbf
commit 31d59ff3b1
3 changed files with 56 additions and 4 deletions
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17
CMakeLists.txt
View File

@ -64,11 +64,20 @@ if(NOT DEFINED CMAKE_CXX_STANDARD AND NOT CMake_NO_CXX_STANDARD)
if (CMAKE_CXX_COMPILER_ID STREQUAL SunPro AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.14)
set(CMAKE_CXX_STANDARD 98)
else()
include(${CMake_SOURCE_DIR}/Source/Checks/cm_cxx14_check.cmake)
if(NOT CMake_CXX14_BROKEN)
set(CMAKE_CXX_STANDARD 14)
if(NOT CMAKE_VERSION VERSION_LESS 3.8)
include(${CMake_SOURCE_DIR}/Source/Checks/cm_cxx17_check.cmake)
else()
set(CMAKE_CXX_STANDARD 11)
set(CMake_CXX17_BROKEN 1)
endif()
if(NOT CMake_CXX17_BROKEN)
set(CMAKE_CXX_STANDARD 17)
else()
include(${CMake_SOURCE_DIR}/Source/Checks/cm_cxx14_check.cmake)
if(NOT CMake_CXX14_BROKEN)
set(CMAKE_CXX_STANDARD 14)
else()
set(CMAKE_CXX_STANDARD 11)
endif()
endif()
endif()
endif()

36
Source/Checks/cm_cxx17_check.cmake Normal file
View File

@ -0,0 +1,36 @@
set(CMake_CXX17_BROKEN 0)
if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
if(NOT CMAKE_CXX17_STANDARD_COMPILE_OPTION)
set(CMake_CXX17_WORKS 0)
endif()
if(NOT DEFINED CMake_CXX17_WORKS)
message(STATUS "Checking if compiler supports needed C++17 constructs")
try_compile(CMake_CXX17_WORKS
${CMAKE_CURRENT_BINARY_DIR}
${CMAKE_CURRENT_LIST_DIR}/cm_cxx17_check.cpp
CMAKE_FLAGS -DCMAKE_CXX_STANDARD=17
OUTPUT_VARIABLE OUTPUT
)
if(CMake_CXX17_WORKS AND "${OUTPUT}" MATCHES "error: no member named.*gets.*in the global namespace")
set_property(CACHE CMake_CXX17_WORKS PROPERTY VALUE 0)
endif()
if(CMake_CXX17_WORKS)
message(STATUS "Checking if compiler supports needed C++17 constructs - yes")
file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
"Determining if compiler supports needed C++17 constructs passed with the following output:\n"
"${OUTPUT}\n"
"\n"
)
else()
message(STATUS "Checking if compiler supports needed C++17 constructs - no")
file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
"Determining if compiler supports needed C++17 constructs failed with the following output:\n"
"${OUTPUT}\n"
"\n"
)
endif()
endif()
if(NOT CMake_CXX17_WORKS)
set(CMake_CXX17_BROKEN 1)
endif()
endif()

7
Source/Checks/cm_cxx17_check.cpp Normal file
View File

@ -0,0 +1,7 @@
#include <cstdio>
#include <unordered_map>
int main()
{
return 0;
}