I know, fortran is so clumsy that nobody want to use it. However it is widely used in scientific community. Fortran does not use any "standard" include path. Even if include files (headers or "modules") are in, e.g., /usr/include, it needs -I/usr/include when invoked.
A --fortran option that would turn pkg-config behaviour to return also "standard" locations would be useful.
You can set the environment variable PKG_CONFIG_ALLOW_SYSTEM_CFLAGS to keep pkg-config from stripping the standard include paths.
Still, I can see how it would be helpful to be able to specify a language specific behavior from pkg-config. Either with a --mode=fortran (a la libtool), or by specifying the language/mode in the .pc file. I'll keep this open as a possible future enhancement, but for now I'm OK with using environment variables to get the behavior you want.
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