Binding generation fails when generic struct is aliased

[awelkie]

It looks like this happens when there is a generic struct in one module and a non-generic struct in another module, and you want to generate bindings for that non-generic struct. I have an example project here with these contents:

───────┬───────────────────────────────────────────────────────────────────
       │ File: src/ffi.rs
───────┼───────────────────────────────────────────────────────────────────
   1   │ type SomeType = super::MyStruct<u32>;
   2   │
   3   │ #[repr(C)]
   4   │ pub struct MyStruct;
   5   │
   6   │ #[no_mangle]
   7   │ pub extern "C" fn use_mystruct(my_struct: *mut MyStruct) {
   8   │ }
───────┴───────────────────────────────────────────────────────────────────
───────┬───────────────────────────────────────────────────────────────────
       │ File: src/lib.rs
───────┼───────────────────────────────────────────────────────────────────
   1   │ pub mod ffi;
   2   │
   3   │ pub struct MyStruct<T> {
   4   │     t: T,
   5   │ }
───────┴───────────────────────────────────────────────────────────────────
───────┬───────────────────────────────────────────────────────────────────
       │ File: build.rs
───────┼───────────────────────────────────────────────────────────────────
   1   │ extern crate cbindgen;
   2   │
   3   │ use std::env;
   4   │ use cbindgen::Language;
   5   │
   6   │ fn main() {
   7   │     let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
   8   │
   9   │     cbindgen::Builder::new()
  10   │       .with_crate(crate_dir)
  11   │       .with_language(Language::C)
  12   │       .generate()
  13   │       .expect("Unable to generate bindings")
  14   │       .write_to_file("bindings.h");
  15   │ }
───────┴───────────────────────────────────────────────────────────────────

And I get this error:

allen@allen-XPS-13-9370 ~/s/cbindgen_bug> env RUST_BACKTRACE=1 cargo build
   Compiling cbindgen_bug v0.1.0 (/home/allen/scratch/cbindgen_bug)
error: failed to run custom build command for `cbindgen_bug v0.1.0 (/home/allen/scratch/cbindgen_bug)`
process didn't exit successfully: `/home/allen/scratch/cbindgen_bug/target/debug/build/cbindgen_bug-34f7bb810f197ece/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'MyStruct is not generic', /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/ir/structure.rs:290:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:211
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:491
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:398
   6: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:353
   7: <cbindgen::bindgen::ir::structure::Struct as cbindgen::bindgen::ir::item::Item>::instantiate_monomorph
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/ir/structure.rs:290
   8: cbindgen::bindgen::ir::ty::Type::add_monomorphs
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/ir/ty.rs:535
   9: cbindgen::bindgen::ir::typedef::Typedef::add_monomorphs
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/ir/typedef.rs:108
  10: cbindgen::bindgen::library::Library::instantiate_monomorphs::{{closure}}
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/library.rs:363
  11: <cbindgen::bindgen::ir::item::ItemMap<T>>::for_all_items
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/ir/item.rs:188
  12: cbindgen::bindgen::library::Library::instantiate_monomorphs
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/library.rs:362
  13: cbindgen::bindgen::library::Library::generate
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/library.rs:63
  14: cbindgen::bindgen::builder::Builder::generate
             at /home/allen/.cargo/registry/src/github.com-1ecc6299db9ec823/cbindgen-0.7.1/src/bindgen/builder.rs:345
  15: build_script_build::main
             at ./build.rs:9
  16: std::rt::lang_start::{{closure}}
             at /rustc/9fda7c2237db910e41d6a712e9a2139b352e558b/src/libstd/rt.rs:74
  17: std::panicking::try::do_call
             at src/libstd/rt.rs:59
             at src/libstd/panicking.rs:310
  18: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:102
  19: std::rt::lang_start_internal
             at src/libstd/panicking.rs:289
             at src/libstd/panic.rs:398
             at src/libstd/rt.rs:58
  20: std::rt::lang_start
             at /rustc/9fda7c2237db910e41d6a712e9a2139b352e558b/src/libstd/rt.rs:74
  21: main
  22: __libc_start_main
  23: _start

It's interesting that if I comment out line 1 of src/ffi.rs, then the bug doesn't occur and binding generation happens as I'd expect.

[emilio]

So this is because cbindgen isn't able to follow paths, so it gets confused, and your MyStruct in ffi.rs is indeed not generic...

[emilio]

I think you can hack around this, fwiw, with something like:

// ffi.rs
pub use super::MyStruct as MyGenericStruct;
type SomeType = MyGenericStruct<i32>;

[awelkie]

Yes, that seems to work. That'll be a good workaround for now. Thanks!

[PiDelport]

Underlying issue: #7