This was intended to be part of the initial MR (!6177), but accidentally went
missing when debugging nightly failures on less common systems. Noticed during
!6711 review as the comment about this behaviour didn't match the code.
Documentation for CMP0128 is updated to remove a false case and note the two
cases related to this.
Fixes#22224.
The changes are part of CMP0128.
When the standard level is unset:
* Flags are added if extension mode doesn't match the compiler's default.
Previously logic only worked if LANG_EXTENSIONS was ON. Fixes#22224.
* The full flag is used. Previously CMAKE_LANG_EXTENSION_COMPILE_OPTION was
used. This was only supported for IAR.
Otherwise:
* Avoid adding flags if not necessary per the detected compiler defaults.
* Fixed check for when the requested standard is older. It now matches the
nearby comments.
I reworded the fallback comment as its logic was a bit difficult to wrap my
head around.
Remove the Cuda/ConsumeCompileFeatures test as it only existed to
validate that using `cxx_std_XY` would cause the paired language (CUDA) to also build in mode XY.
The cmLocalGenerator::AddCompilerRequirementFlag was another
source of truth on what standard levels existed per language,
so fold that into cmStandardLevelResolver to make updating
CMake easier
