Panic when parsing a generic type with empty tuple as default type parameter #993
Description
#959 added support for default generic type parameters. This broke some existing use cases, in particular where a type is defined with a type parameter with a default, but where all usages specify the type parameter.
MRE:
#[repr(C)]
pub struct NeverUsedWithDefault<T = ()> {
field: T
}
#[no_mangle]
pub extern "c" fn with_i32(x: NeverUsedWithDefault<i32>) {}Running cbindgen against that produces the following:
thread 'main' panicked at src/bindgen/parser.rs:928:82:
called `Result::unwrap()` on an `Err` value: "unsupported generic type default: Some(Type::Tuple { paren_token: Paren, elems: [] })"
stack backtrace:
0: rust_begin_unwind
at /rustc/684b3553f70148ded97a80371c2405984d4f6aa7/library/std/src/panicking.rs:661:5
1: core::panicking::panic_fmt
at /rustc/684b3553f70148ded97a80371c2405984d4f6aa7/library/core/src/panicking.rs:74:14
2: core::result::unwrap_failed
at /rustc/684b3553f70148ded97a80371c2405984d4f6aa7/library/core/src/result.rs:1679:5
3: core::result::Result<T,E>::unwrap
at /rustc/684b3553f70148ded97a80371c2405984d4f6aa7/library/core/src/result.rs:1102:23
4: cbindgen::bindgen::parser::Parse::load_syn_struct
at ./src/bindgen/parser.rs:928:21
5: cbindgen::bindgen::parser::Parse::load_syn_crate_mod
at ./src/bindgen/parser.rs:524:21
6: cbindgen::bindgen::parser::Parser::process_mod
at ./src/bindgen/parser.rs:306:30
7: cbindgen::bindgen::parser::Parser::parse_mod
at ./src/bindgen/parser.rs:277:9
8: cbindgen::bindgen::parser::parse_src
at ./src/bindgen/parser.rs:59:5
9: cbindgen::bindgen::builder::Builder::generate
at ./src/bindgen/builder.rs:375:33
10: cbindgen::load_bindings
at ./src/main.rs:98:16
11: cbindgen::main
at ./src/main.rs:327:26
12: core::ops::function::FnOnce::call_once
at /rustc/684b3553f70148ded97a80371c2405984d4f6aa7/library/core/src/ops/function.rs:250:5