fix: clang-cl detect warning on MacOS

[LinusChen-yf]

#1445

[NobodyXu]

I remember that there are some compiler that doesn't work with --

I think it's better to detect the clang-cl and use -- for it?

cc @madsmtm

[madsmtm]

I recall that too, see also discussion in #1328.

I feel like we're shooting ourselves in the foot here by not having better CI for this sort of stuff? At the very least, I'd expect a test to be added that doesn't work before the PR, and works after.

[NobodyXu]

While this will work for many cases, checking filename isn't very robust...

@madsmtm does clang-cl --version offer anything special that we can check here?

[LinusChen-yf]

# On Windows
> clang-cl --version
clang version 20.1.2
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Users\crash\scoop\apps\llvm\20.1.2\bin

# On MacOS
> clang-cl --version
Homebrew clang version 19.1.7
Target: arm64-pc-windows-msvc
Thread model: posix
InstalledDir: /opt/homebrew/Cellar/llvm/19.1.7_1/bin

# On Linux
> clang-cl --version
clang version 19.1.7
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: /usr/bin

It seems that the output of clang-cl --version is not a very reliable way to determine whether it is clang-cl?

Because I saw the logic of using the file name to judge clang-cl in the original code, I referred to this part of the code.

cc-rs/src/tool.rs

Lines 242 to 244 in 5f55b01

	match path.file_name().map(OsStr::to_string_lossy) {
	Some(fname) if fname.contains("clang-cl") => ToolFamily::Msvc { clang_cl: true },
	Some(fname) if fname.ends_with("cl") || fname == "cl.exe" => {

Or maybe it would be safer to use full characters to match clang-cl or clang-cl.exe?

[NobodyXu]

thanks, in that case I think it might be the only solution, cc @madsmtm wdyt

[PaulWagener]

With clang-cl the same warning about -Wslash-u-filename is still generated. The difference with normal clang is that the warning is output to stderr and the exit code is set to 1. Both things can be captured and checked for, allowing for a check without relying on the filename.

[LinusChen-yf]

When using clang-cl, you only need to add the parameter "--" before Path to avoid generating warnings, which is also the recommended way to deal with warnings.

In addition, is the reason why this PR has no follow-up now because there are not enough test cases in CI to ensure the safety of its code?

[NobodyXu]

Yes, detecting clang-cl via filename isn't very robust