When only generating functions, type parameter is lost

[fitzgen]

We still have more issues like #835...

Input C/C++ Header

• TODO

Bindgen Invocation

• TODO

Actual Results

https://treeherder.mozilla.org/logviewer.html#?job_id=117196247&repo=try&lineNumber=6725

error[E0243]: wrong number of type arguments: expected 1, found 0
   --> /home/worker/workspace/build/src/obj-firefox/toolkit/library/x86_64-unknown-linux-gnu/release/build/style-077f5b469d68e8b7/out/gecko/bindings.rs:526:14
    |
526 |      -> *mut nsTArray;
    |              ^^^^^^^^ expected 1 type argument
error[E0243]: wrong number of type arguments: expected 1, found 0
   --> /home/worker/workspace/build/src/obj-firefox/toolkit/library/x86_64-unknown-linux-gnu/release/build/style-077f5b469d68e8b7/out/gecko/bindings.rs:529:65
    |
529 |     pub fn Gecko_DestroyAnonymousContentList(anon_content: *mut nsTArray);
    |                                                                 ^^^^^^^^ expected 1 type argument
error[E0243]: wrong number of type arguments: expected 1, found 0
    --> /home/worker/workspace/build/src/obj-firefox/toolkit/library/x86_64-unknown-linux-gnu/release/build/style-077f5b469d68e8b7/out/gecko/bindings.rs:1073:53
     |
1073 |     pub fn Gecko_ResizeTArrayForStrings(array: *mut nsTArray, length: u32);
     |                                                     ^^^^^^^^ expected 1 type argument
error: aborting due to 3 previous errors
error: Could not compile `style`.

Expected Results

nsTArray should have a type argument.

[fitzgen]

cc @emilio @Manishearth

[fitzgen]

This is really hard to reproduce. I've preprocessed all of nsTArray.h and added nsTArray_Simple and Gecko_ResizeTArrayForStrings to the bottom and it doesn't repro.

Trying reproducing with the full servo bindings next.

[fitzgen]

Blech I can't even reproduce with the full preprocessed servo bindings.

[upsuper]

OK, I eventually figured out a real way to reproduce it...

[upsuper]

And this is reproducible on Windows as well. I have no idea why it didn't cause any issue on other platforms when with Gecko...

[upsuper]

You need two files, in different directory. Let's say input.hpp and subdir/another.h, they have code:

// input.hpp
#include "another.h"

// subdir/another.h
template<typename T>
class nsTArray;

/**
 * <div rustbindgen replaces="nsTArray"></div>
 */
template<typename T>
class nsTArray_Simple {
  T* m;
};

extern "C" {
nsTArray<int>* func();
}

Then invoke bindgen with:

bindgen input.hpp -- -I subdir

[upsuper]

If you move all the code from subdir/another.h into input.hpp directly, then this bug wouldn't appear, that is why a fully preprocessed file doesn't trigger this bug.

[upsuper]

What seem to be necessary for triggering this bug are:

• The other header file need to be searched from a directory specified by -I. If you use "subdir/another.h" directly in input.hpp, it doesn't happen.
• The replacing type (nsTArray_Simple here) must be in the header file mentioned above.

What doesn't seem to be related:

• Where are other things, including the replaced type (nsTArray) and the function. They can be in either file and the result wouldn't change.
• Whether the replaced type is a definition or a declaration.
• The order of things, as far as nsTArray is declared before the function.

[emilio]

Thanks a lot for the investigation an the test-case Xidorn, trying to repro now.

[emilio]

So, I can repro, but the generated code is:

/* automatically generated by rust-bindgen */

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct nsTArray {
    pub mBuffer: *mut ::std::os::raw::c_void,
}
#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct nsTArray_Simple<T> {
    pub m: *mut T,
    pub _phantom_0: ::std::marker::PhantomData<::std::cell::UnsafeCell<T>>,
}
extern "C" {
    pub fn func() -> *mut nsTArray;
}

Which means that we're not managing to see the replacement. Does that match what you see @upsuper?

[emilio]

I think I know why this is...