The Swift wrapper uses a hook directly from cc-wrapper to set the
`-target` flag appropriately. This works because Clang and Swift use the
same syntax for `-target`, but there was never a guarantee that this
compatibility would be true for every option set in the hook. Indeed,
commit 369cc5c66b (PR #445119) made
availability warnings into errors by setting the
`-Werror=unguarded-availability` flag in this hook, which Swift doesn't
accept at the top level. This caused all invocations of Swift to fail
with the error `unknown argument: '-Werror=unguarded-availability'` -
including the bootstrap Swift, which meant that `swiftPackages.swift`
would fail.
This commit adds all `-Werror` flags to the list of flags that need to
be prefixed with `-Xcc`. I could have just dropped the flag, since Swift
already makes this an error, but you can have C/C++ targets in Swift
packages and we'd want to pass this flag on to them. (I'm not sure
whether the clang used for those targets is already wrapped, but if it
is there is no harm done.)
Swift needs Clang to link with. The linker patch breaks linking
when using Swift with a GCC‐based standard environment.
Similarly, the internal Clang headers in the resource directory are
coupled to the corresponding version of Clang. The resource root patch
caused Swift’s Clang to use the resource directory from the version
of Clang used in the build environment, which is only compatible if
the versions match.
Instead, hard‐code the Clang path in the patches and wrappers.
We already did this for -march in 12b0e8ac74 ("clang: don't set
-march for overridden target"), but it should have been done for all
machine flags, for the same reason.
Example bug this fixes:
nix-shell -E '
with import ./. {
crossSystem = {
system = "powerpc64le-linux";
gcc.cpu = "power10";
};
};
clangStdenv.mkDerivation { name = "test"; }
' --run '$CC -target wasm32-unknown-unknown -c /dev/null'
Which previously failed with:
clang: error: unsupported option '-mcpu=' for target 'wasm32-unknown-unknown'
David McFarland