Cannot provide user-defined Debug implementation for enum

[gonzalobg]

Input C/C++ Header

typedef enum E {
  A = 0,
  B = 1
} ET;

Bindgen Invocation

fn main() {
    let bindings = bindgen::builder()
        .header("src/header.h")
        .default_enum_style(bindgen::EnumVariation::Rust { non_exhaustive: true })
        .derive_debug(false)  // Don't derive debug
        .parse_callbacks(Box::new(MyCallback))
        .generate()
        .expect("Unable to generate bindings");

    let out_path = std::path::Path::new("src/ffi.rs");
    bindings.write_to_file(out_path).expect("Couldn't write bindings");
}

#[derive(Debug)]
struct MyCallback;
impl core::panic::UnwindSafe for MyCallback {}

impl bindgen::callbacks::ParseCallbacks for MyCallback {
    fn add_derives(&self, name: &str) -> Vec<String> {
        let mut v: Vec<String> = Vec::new();
        if name == "E" {
            v = vec!["Debug".to_string()];  // Provide my own Debug impl somewhere
        }
        v
    }
}

Actual Results

The above fails with:

error[E0119]: conflicting implementations of trait `std::fmt::Debug` for type `E`
 --> src/ffi.rs:5:51
  |
5 | #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, Debug)]
  |          ----- first implementation here          ^^^^^ conflicting implementation for `E`

The .derive_debug(false) is set, but a Debug impl is still being added, which prevents me from providing my own implementation somewhere (not necessarily in a callback).

Expected Results

I'd like to be able to provide my own implementation of Debug for the type above, while still automatically adding the Debug trait to all other types.

[gonzalobg]

@emilio if you hint me towards the best way to achieve this I can submit a PR.

[emilio]

I believe this is a regression from 098b416. The:

+            if !item.annotations().disallow_debug() {
+                derives.insert(DerivableTraits::DEBUG);
+            }

there is causing this.

Without it we fail tests/headers/enum-no-debug-rust.h, but the result seems fair, I think, so we could just update the expectation I think.