It would be nice to be able to list all of the glsllib files included for a given input. Build systems can use this to then do dependency tracking/caching/etc. The compiler can hopefully get this information rather easily, where as doing it externally would require parsing all of the files. As the compiler inputs get more complex (with preprocessor logic/etc) it gets more difficult to do this from the outside.

e.g., glsl-compiler --input=foo.glsl --list-dependencies foo.glsl somelib.glsllib some/path/lib.glslib ...

If dumped on stdout it'd be possible to grab this and pipe it to another file or programmatically act on it.