`windows-bindgen` does not generate event registration method

[lifers]

Summary

Define a runtimeclass with an event (e.g. OnClicked) in an .idl file, then compile it to .winmd using midlrt.exe. Use windows-bindgen to generate Rust projection using --implement flag.

Expected: both OnClicked and RemoveOnClicked are generated
Seen: only RemoveOnClicked is generated

Crate manifest

[package]
name = "event-test"
version = "0.1.0"
edition = "2024"

[dependencies]


[build-dependencies]
windows-bindgen = "0.61.1"

Crate code

// definition.idl
namespace Definition
{
    runtimeclass ExampleClass
    {
        ExampleClass();

        event Windows.Foundation.TypedEventHandler<ExampleClass, String> OnClicked;
    }
}

// build.rs
fn main() {
    println!("cargo:rerun-if-changed=definition.idl");
    let metadata_dir = format!("{}\\System32\\WinMetadata", env!("windir"));
    let mut command = std::process::Command::new("midlrt.exe");

    command.args([
        "/winrt",
        "/nomidl",
        "/h",
        "nul",
        "/metadata_dir",
        &metadata_dir,
        "/reference",
        &format!("{metadata_dir}\\Windows.Foundation.winmd"),
        "/winmd",
        "definition.winmd",
        "definition.idl",
    ]);

    if !command.status().unwrap().success() {
        panic!("failed to run midlrt.exe");
    }

    windows_bindgen::bindgen([
        "--in",
        "definition.winmd",
        "default",
        "--out",
        "src/bindings.rs",
        "--filter",
        "Definition",
        "--implement"
    ]);
}

[kennykerr]

The bindgen function returns warnings for cases like this. I should add the must_use attribute to make that more obvious. The resulting Warnings struct should have information about the fact that the filter is omitting certain methods due to missing dependencies. You can either include the Windows.Foundation dependencies directly in the --filter to include them in the resulting bindings or --reference the windows crate.

See also #3514 and #3359

[kennykerr]

Warnings are described in #3498.