BINDGEN_EXTRA_CLANG_ARGS for command line mode

[BaoshanPang]

when option dump-preprocessed-input is used, BINDGEN_EXTRA_CLANG_ARGS is evaluated AFTER handling dump-preprocessed-input which result errors like "head files not found" etc in cross-compiling.

[emilio]

Ah, this should be relatively straight-forward to fix. Probably most of Bindings::generate should move to a common function that dump_preprocessed_input could reuse. We should make sure we only run it once though.

[highfive]

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[smurfd]

Hi, have looked at this abit and was wondering.

Would it be something like in impl Bindings { create a

fn generate_common(options: &mut BindgenOptions) {
// context from these lines : 
https://github.com/rust-lang/rust-bindgen/blob/b424c17608206166b98db0e1b7da752a1e560f54/src/lib.rs#L1884-L1956
}

then at :

rust-bindgen/src/lib.rs

Line 1957 in b424c17

we call Bindings::generate_common(&mut options);

Im abit fuzzy on where in dump_preprocessed_input we would call this generate_common()
Maby here?

rust-bindgen/src/lib.rs

Line 1374 in d794a08

Before we go through the self.options.clang_args that the BINDGEN_EXTRA_CLANG_ARGS is stored?!

And then for it to just be run once we have a boolean argument to Bindings::generate that is set to false as default, but if true then we dont run the generate_common()

Pretty much here, set a boolean to true

rust-bindgen/src/lib.rs

Line 1286 in b424c17

};

that we add to the Bindings::generate(self.option) abit lower down.

Thanks in advance :)

[smurfd]

Hey, if someone is interested in working on this, please please do.
Had completely forgot about this until last week when i got a mail about my pr conflicting with 67538b6

Will probably close my pr in a while if i don't see something easy i have missed.

[smurfd]

nevermind the above, have an actual patch that might be what is looked for in #1915