[clangd] Detect GCC version for default C/C++ standard

[GreenYun]

GCC 15 changes the default language version for C compilation from -std=gnu17 to -std=gnu23. Will Clangd follow the change by detecting the GCC version on the machine?

[llvmbot]

@llvm/issue-subscribers-clangd

Author: None (GreenYun)

GCC 15 changes the default language version for C compilation from `-std=gnu17` to `-std=gnu23`. Will Clangd follow the change by detecting the GCC version on the machine?

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: None (GreenYun)

GCC 15 changes the default language version for C compilation from `-std=gnu17` to `-std=gnu23`. Will Clangd follow the change by detecting the GCC version on the machine?

[HighCommander4]

The current behaviour of clangd is that if a compile command does not contain an explicit -std flag, the default standard of the clang version corresponding to the clangd version (e.g. if using clangd 19 then clang 19) is used.

If this does not produce the desired result for a given project, an explicit -std flag can be added using https://clangd.llvm.org/config.html#compileflags.

Inferring the default standard version of a non-clang compiler is an interesting idea. I don't think I'd be opposed to it if someone wanted to implement it, but there are no current plans for such a feature.