[clangd] suppress warning originated in macros from system headers

[yshui]

i think warnings from system headers are already suppressed. but say i include a header that defines a macro, and i later use that macro. if the macro expands to something that trips clangd checks, i will still get the warning. but there is nothing i can do about those warnings.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Yuxuan Shui (yshui)

i think warnings from system headers are already suppressed. but say i include a header that defines a macro, and i later use that macro. if the macro expands to something that trips clangd checks, i will still get the warning. but there is nothing i can do about those warnings.

[HighCommander4]

Please provide information necessary to reproduce the issue:

• a complete code example
• your clangd version
• relevant configuration files like .clangd or .clang-tidy (in particular whatever enables the warning you're seeing, if not enabled by default)

[yshui]

@HighCommander4 if you don't need a minimal example, you can checkout picom. open, say src/picom.c, and you will see warnings on HASH_FIND_STR, HASH_DEL, etc.

clangd version is 20.1.6

[HighCommander4]

you can checkout picom. open, say src/picom.c

Can you also say how to generate a compilation database for this project?

[yshui]

@HighCommander4 meson

you do meson setup build and it's under build

[HighCommander4]

Ok, I got the project set up. However...

open, say src/picom.c, and you will see warnings on HASH_FIND_STR, HASH_DEL, etc.

... I do not get warnings here.

Can you attach clangd logs, taken with --log=verbose from a session where you open this file and get warnings?

[yshui]

in that case i suspect it's caused by how nix passes include paths. IIUC only -isystem headers are suppressed but not -I ones, right?

nix passes some include paths via the CPATH environment variable, i suspect that's being treated like a -I?

[HighCommander4]

IIUC only -isystem headers are suppressed but not -I ones, right?

That is correct.

nix passes some include paths via the CPATH environment variable, i suspect that's being treated like a -I?

It looks that way. This is handled by the clang driver, around here in the code.

[yshui]

Looks like I should be able to use C_INCLUDE_PATH to add system includes? I think I can make it work with nix.

[HighCommander4]

Closing as this is working as intended: clangd is successfully suppressing warnings originating in macros from system headers, as long as the directories containing the system headers are identified by using -isystem rather than -I.