The `CMAKE_REQUIRED_FLAGS` variable, used by the various entry points to
`cmake_check_source_{compiles,runs}`, specifies that flags shall not be
separated by semicolons. This is because the way in which it is passed
to the child `cmake` process means that, when considered as a list (with
semicolon separated items), only the first item is actually used as
compile flags, with any additional items actually seen as arguments to
the child `cmake` process. While this usage is unsupported, if invoked
accidentally, flags starting with `-W` were silently ignored by CMake.
However, CMake 4.4 newly complains about unrecognized warning
categories, which means that uses which were silently broken now result
in a hard error.
In the longer term, it would be helpful to introduce a policy to repair
improper use of semicolons in `CMAKE_REQUIRED_FLAGS` in order to do what
the user probably meant. However, for various reasons, we do not want to
introduce a policy to CMake 4.4 at this time, and anyway, the policy
won't help users that haven't enabled it. Therefore, alter the 'check
source' functions to detect arguments being passed to `cmake` rather
than the compiler, and remove any such that start with `-W`. This
removes any arguments that newly cause errors starting with CMake 4.4,
while not otherwise altering behavior in case any users were abusing
this implementation quirk.
Strictly speaking, this means that users can no longer abuse this quirk
to alter CMake's diagnostics. However, the only case in which this
should be observable is if the user is already abusing the quirk to
inject their own CMake logic into the CMake-provided test projects.
Since this was never supported, anyone doing that can keep the pieces.
Issue: #27901Fixes: #27893
Cases for `CheckSource{Compiles,Runs}` and `Check{Compiler,Linker}Flag`
cover the modules with the language as a parameter, not the
language-specific modules.
Matthew Woehlke
Joseph Snyder
Evan Wilde
Brad King
Robert Maynard