ee1396e29e CMP0128: Add flag in OLD mode even when standard matches the default
b2c25de8e0 CMP0128: Avoid test code duplication
3a089cd256 CMP0128: Prefix test names with mode
e13dd52535 XL: Detect default extensions mode for legacy compiler
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !6890
Commit 4a0485be (cmStandardLevelResolver: Avoid unnecessary flags, fix unset
level logic, 2021-04-29) unintentionally changed the behavior by modifying the
code to match a pre-existing comment. The resulting behavior change however
matches the intentions of CMP0128, so we simply need to guard it.
Fixes#23122.
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
