Emit rerun-if-changed of used and included files

[chrysn]

When bindgen is used in build.rs, no cargo:rerun-if-changed lines are emitted that'd cause the build process to be rerun if any source file changed.

On projects where the C source and crates using the -sys crate are actively being developed, this leads to confusing error situations, and users that rm -rf target out of frustration.

I suggest adding an option to generate rerun-if-changed lines for all included files. If there is a danger to lead to long checking times due to lots of system libraries in practice, adding a filter function on the emitted header files could be an option. (That's inspired by gcc's distinction between -MD and MMD, where the latter ignores system header files).

[emilio]

Yeah, I agree that'd be nice. What Gecko does is not all that great either: https://searchfox.org/mozilla-central/rev/01d1011ca4a460f751da030d455d35c267c3e210/servo/components/style/build_gecko.rs#55

I think libclang exposes includes in the AST, so adding a ParseCallback for this would be the easiest, that way you can do whatever with them, not just printing them.

[highfive]

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[emilio]

Well I guess this is not E-easy as in trivial, but I don't expect it'd be all that hard.

[emilio]

In particular we'd need to poke at the InclusionDirective cursors. This code ignores them, there's probably a better place to poke at them, but maybe just calling a function from there would do the trick... All cursors should go through there.

[chrysn]

Thanks, I'll try to work from there.

@highfive: assign me

[highfive]

Hey @chrysn! Thanks for your interest in working on this issue. It's now assigned to you!

[emilio]

Awesome, thanks!