Although there is no `cl -std:c23` flag, the underlying Clang compiler
does have a C23 mode we can activate by passing `-std=c23` through a
`clang-cl` wrapper flag.
Also port the fix from commit 30139913e9 (VS: Restore support for mixing
C++23 and C in one target with clang-cl, 2024-12-09, v3.31.3~10^2).
Fixes: #27038
Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Co-authored-by: Brad King <brad.king@kitware.com>
Add a variable to indicate the latest standard known to be supported for
each language:
* `CMAKE_C_STANDARD_LATEST`
* `CMAKE_CXX_STANDARD_LATEST`
* `CMAKE_CUDA_STANDARD_LATEST`
* `CMAKE_HIP_STANDARD_LATEST`
* `CMAKE_OBJC_STANDARD_LATEST`
* `CMAKE_OBJCXX_STANDARD_LATEST`
These variables, more generally referred to as
`CMAKE_<LANG>_STANDARD_LATEST`, are assigned an integer value which
represents the minimum between the latest version of the associated
language standard supported by the current compiler and the latest
version supported by CMake.
Add documentation for these variables in a new page called
`CMAKE_<LANG>_STANDARD_LATEST` was added under the "Variables for
Languages" section of the `cmake-variables(7)` page.
Update each compiler-specific CMake script under
`${CMAKE_ROOT}\Modules\Compiler` to manually define the relevant
`CMAKE_<LANG>_STANDARD_LATEST` variable as necessary. This will
require updating and maintaining as newer compiler versions become
recognized by CMake.
Closes: #25717
C11 was made default in LLVM commit ab506adf7d3ced6abcaf42f92de3d6cd15fa19e8,
released in 3.5.2.
C99 was made default in LLVM commit 17f76e04d244c80e70f1c81c94d4524b53d9772d,
released in 2.1. It was flipped a few times between C89 and C99 during the 2.1
cycle, but the C89 default never made it into a release.
C89, C99 flags in LLVM commit ff43821d5380ee38aff421701f1d461242b524ee.
C90 flag in LLVM commit 229ce60fc9983df5f7e83e25fa6b5c0ca4d2b135.
C1x flag in LLVM commit a686b5f8bf7b5a2ab636c0c2de5ad4c174aa33e0.
C11 flag in LLVM commit 6784aeb9ef96e5735850fa7226ed0cb45cb82e75.
Mark C90, C99 full support since 2.1. Might've been possibly a little later,
but source spelunking that much back is difficult.
Mark C11 full support since 3.0, which added _Static_assert in LLVM commit
3d9cbdc3e66e274d5d3cb94ce81a65478d9baae0.
This change was originally made by commit 74b1c9fc8e (Explicitly specify
language flag when source LANGUAGE property is set, 2020-06-01,
v3.19.0-rc1~722^2), but it was reverted by commit 30aa715fac (Revert
"specify language flag when source LANGUAGE property is set",
2020-11-19) to restore compatibility with pre-3.19 behavior.
Implement the change again, but add policy CMP0119 to make this change
while preserving compatibility with existing projects.
Note that the `Compiler/{Clang,Intel,MSVC}-CXX` modules do not need to
specify `-TP` for their MSVC-like variants because we already use the
flag in `CMAKE_CXX_COMPILE_OBJECT`. Similarly for `Compiler/XL-CXX`
and `Platform/Windows-Embarcadero`.
Note also that this does not seem possible to implement for XL C.
Even with `-qsourcetype=c`, `xlc` complains about an unknown suffix:
`1501-218 (W) file /.../AltExtC.zzz contains an incorrect file suffix`.
It returns non-zero even with `-qsuppress=1501-218`.
Co-Author: Robert Maynard <robert.maynard@kitware.com>
Fixes: #14516, #20716
Each source compilation generates a dependencies file. These dependencies
files are consolidated in one file per target. This consolidation is done
as part of command 'cmake -E cmake_depends` launched before evaluation of
makefile dependency graph.
The consolidation uses the same approach as `CMake` dependencies management.
Fixes: #21321
Revert commit 74b1c9fc8e (Explicitly specify language flag when source
LANGUAGE property is set, 2020-06-01, v3.19.0-rc1~722^2) and the lookup
tables from its two immediate ancestors. The purpose of that change was
to convert an explicit `LANGUAGE` source file property into an explicit
language specification compiler flag like `-x c`. This seems reasonable
since the property is documented as meaning "indicate what programming
language the source file is". It is also needed to help compilers deal
with non-standard source file extensions they don't recognize.
However, some projects have been setting `LANGUAGE C` on `.S` assembler
source files to mean "use the C compiler". Passing `-x c` for them
breaks the build because the `.S` sources are not written in C. These
projects should be updated to use `enable_language(ASM)`, for which
CMake often chooses the C compiler as the assembler when using
toolchains that support it (which would have to be the case for projects
using the approach).
Revert the change for now to preserve the old behavior for such projects.
We can re-introduce it with a policy in a future version of CMake.
Fixes: #21469
Issue: #14516, #20716
`clang-tidy` does not infer driver mode if it is not provided with a
JSON compilation database. This is exactly the way cmake launches it.
Hence clang-tidy will only use the default driver mode. Add an explicit
driver mode argument to avoid this.
Use the infrastructure added by commit f92ccbc306
(CompileFeatures: memoize C compilers with full language level support)
to avoid using a `try_compile` to check for C 90/99/11 feature support when the running compiler is known to have a fixed set of feature support.
This was done for C++ by commit v3.5.0-rc1~69^2 (Record compile features
for MinGW Clang on Windows, 2016-01-11). Make the same change for C.
The `UNIX` condition on Clang C compiler features was already dropped by
refactoring in commit v3.9.0-rc1~17^2~4 (Compilers: Port to use default
cmake_record_lang_compile_features macros, 2017-05-10).
Our documentation already claims support for this combination. This
was simply an oversight when support was added for MinGW Clang C++.
Issue: #15897
Issue: #15943
Condition all calls to `_record_compiler_features_{c,cxx}` on
`_result EQUAL 0` so that adding new language standards later does
not need to update them. Avoid some duplicate compiler version
checks by conditioning C11 and CXX14 feature recording on the
existence of `CMAKE_{C11,CXX14}_STANDARD_COMPILE_OPTION` (whose
setting already used the version check).
Prior to commit v3.4.0-rc1~71^2 (Project: Determine default language
dialect for the compiler, 2015-09-15) we always guessed the default
language standard dialect based on the compiler version. This was not
reliable so that commit switched to computing the default language
standard dialect while detecting the compiler id.
When a toolchain file uses CMakeForceCompiler to set the compiler id
then the detection does not occur. Therefore commit v3.4.0-rc1~54^2
(Project: Don't require computed default dialect if compiler was forced,
2015-09-22) made the lack of detection an error only if the compiler was
not forced. However, this means that projects using CMakeForceCompiler
no longer even get the guess that we had before so <LANG>_COMPILER does
not work.
Due to the sophistication of CMake's compiler detection logic projects
should be ported away from using CMakeForceCompiler. In the meantime,
restore a guess of the default language standard dialect when the
compiler is forced.
Commit 7235334a (Project: Determine default language dialect for the
compiler., 2015-09-15) introduced a mechanism to determine the default
dialect used for the running compiler. If conditions in
the <CompilerId>-<Lang>.cmake file are such that compile features for
that version of the compiler should be supported, the _DEFAULT_STANDARD
is set to the computed value.
However, the CMakeForceCompiler module allows users to bypass execution of the
compiler by CMake. In that case, do not set the _DEFAULT_STANDARD variable at
all, which effectively disables the compile-features where the module is used.
No compile features have ever been recorded where the module is used so no
functionality is lost.
GNU-CXX already has complex logic and sets the _result to 0 before
tests which may set it to something else.
Change the other modules to be consistent with that.
Clang 3.4 uses C99 by default, and Clang 3.6 uses C11 by default:
http://thread.gmane.org/gmane.comp.compilers.clang.devel/39379
GNU 4.9 uses C90 by default, and GNU 5.0 uses C11 by default:
https://gcc.gnu.org/gcc-5/changes.html
Test that the default compiler settings result in the expected dialect
macros being defined for both C and CXX. Remove the unused main.c
file from the CompileFeatures unit test.
While Clang presents an almost identical interface to GNU there will be
some differences. Split the compiler information modules to allow
separate rules for Clang. Start by loading the GNU rules but leave a
place to add Clang-specific information.
Map to the platform and compiler information for GNU because the
compilers are command-line compatible for common operations. Later we
can add Clang-specific features as necessary. We honor the preferred
capitalization is "Clang", not the common mis-spelling "CLang".
