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cmake: CMake compile features support

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Fixes: #36558 #32577

This commit introduces CMAKE_C_COMPILE_FEATURES and
CMAKE_CXX_COMPILE_FEATURES.

This allows users to use the `target_compile_features()` in their own
code.

In Zephyr, the CMAKE_C/CXX_COMPILE_FEATURES are defined based on the
compiler and the Kconfig / CSTD setting.
Doing so ensures that a user compiling Zephyr with c99 and specifies
`target_compile_features(<target> ... c_std_11)` will get an error.
And similar if building Zephyr with C++ support and c++11, but testing
for `target_compile_features(<target> ... cxx_std_17)`.

For example in the C++ case, the user must ensure that Zephyr is
compiled with C++17, that is: CPLUSPLUS=y and STD_CPP17=y, in which case
the CMAKE_CXX_COMPILE_FEATURES will contain support for C++17 and thus
the `target_compile_features(<target> ... cxx_std_17)` will succeed.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
This commit is contained in:
Torsten Rasmussen 2021-09-30 21:01:57 +02:00 • committed by Christopher Friedt
commit 917d5021d7
3 changed files with 40 additions and 0 deletions
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9
CMakeLists.txt
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@ -168,21 +168,29 @@ if(CONFIG_CPLUSPLUS)
# Kconfig choice ensures only one of these CONFIG_STD_CPP* is set.
if(CONFIG_STD_CPP98)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp98>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp98})
elseif(CONFIG_STD_CPP11)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp11>) # Default in kconfig
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp11})
elseif(CONFIG_STD_CPP14)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp14>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp14})
elseif(CONFIG_STD_CPP17)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp17>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp17})
elseif(CONFIG_STD_CPP2A)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp2a>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp20})
elseif(CONFIG_STD_CPP20)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp20>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp20})
elseif(CONFIG_STD_CPP2B)
set(STD_CPP_DIALECT_FLAGS $<TARGET_PROPERTY:compiler-cpp,dialect_cpp2b>)
list(APPEND CMAKE_CXX_COMPILE_FEATURES ${compile_features_cpp20})
else()
assert(0 "Unreachable code. Expected C++ standard to have been chosen. See Kconfig.zephyr.")
endif()
set(CMAKE_CXX_COMPILE_FEATURES ${CMAKE_CXX_COMPILE_FEATURES} PARENT_SCOPE)
zephyr_compile_options($<$<COMPILE_LANGUAGE:CXX>:${STD_CPP_DIALECT_FLAGS}>)
endif()
@ -979,6 +987,7 @@ set_ifndef(CSTD c99)
zephyr_compile_options(
$<$<COMPILE_LANGUAGE:C>:$<TARGET_PROPERTY:compiler,cstd>${CSTD}>
)
set(CMAKE_C_COMPILE_FEATURES ${compile_features_${CSTD}} PARENT_SCOPE)
# @Intent: Configure linker scripts, i.e. generate linker scripts with variables substituted
toolchain_ld_configure_files()