Add ImplParam GAT: use primitive types directly in _Impl trait methods

[Copilot]

Resolves the TODO in crates/tests/libs/implement/tests/map.rs that said // TODO: shouldn't require Ref for primitive.

Problem

When implementing IMap_Impl<i32, f32>, users had to write:

fn HasKey(&self, key: Ref<i32>) -> Result<bool> { ... }

even though i32 is a primitive copy type where Ref<T> adds no semantic value. The same issue affected event handler closures — EventHandler::<i32>::new(move |_, args: Ref<i32>| { assert_eq!(*args, 2); ... }) required unnecessary wrapping and dereferencing.

Solution

Added a Param<'a> generic associated type (GAT) to the Type<T, C> trait in windows-core:

• For CopyType (primitives, GUID, enums, etc.): Param<'a> = T — the type itself, no Ref wrapper
• For CloneType (HSTRING, etc.): Param<'a> = Ref<'a, T> — same as before
• For InterfaceType (COM interfaces): Param<'a> = Ref<'a, T> — same as before

Two helpers are added to Type<T, C>:

• abi_to_param(abi: &Self::Abi) -> Self::Param<'_> — used in generated vtable code to convert from raw ABI parameter to impl param type
• param_as_default(param: &Self::Param<'_>) -> &Self::Default — used in generic impl method bodies to get &K::Default from either K (copy) or Ref<K> (others)

A public type alias is exported:

pub type ImplParam<'a, T> = <T as Type<T>>::Param<'a>;

The bindgen code generator is updated to:

• Emit windows_core::ImplParam<'_, K> instead of windows_core::Ref<K> for generic type parameters in _Impl trait method signatures
• Use <K as windows_core::Type<K>>::abi_to_param(&key) instead of transmute_copy(&key) in vtable upcall code for generic parameters

All affected bindings are regenerated (windows-collections, windows-future, Windows/Foundation, test bindgen files, reference_custom/src/bindings.rs, reference_no_deps/src/bindings.rs). Hand-written impls (map_view.rs, vector_view.rs, test files) are updated to use the new API. Test files using event handler closures (events_client/src/lib.rs, event_core/tests/tests.rs) are updated to use primitive values directly instead of Ref<primitive> / *args. Two clippy::explicit_auto_deref lints in the param_as_default implementations are resolved by returning param directly instead of &**param. The delegates.rs test is updated to remove the now-resolved *port dereference of a primitive i32.

Result

Users can now write:

impl IMap_Impl<i32, f32> for Map_Impl {
    fn HasKey(&self, key: i32) -> Result<bool> { ... }    // i32 directly, no Ref!
    fn Insert(&self, key: i32, value: f32) -> Result<bool> { ... }
    fn Lookup(&self, key: i32) -> Result<f32> { ... }
    fn Remove(&self, key: i32) -> Result<()> { ... }
}

Event handler closures over primitive types are also simplified:

// Before
EventHandler::<i32>::new(move |_, args: Ref<i32>| { assert_eq!(*args, 2); Ok(()) });

// After
EventHandler::<i32>::new(move |_, args| { assert_eq!(args, 2); Ok(()) });

For non-primitive types like HSTRING and COM interfaces, Ref<T> is still used as before (which remains the correct approach for borrowed, non-owned types).

[kennykerr]

@copilot check the build failures

[Copilot]

@copilot check the build failures

Fixed in 70debcf. The CI failures were in events_client/src/lib.rs and event_core/tests/tests.rs — these test files had explicit args: Ref<i32> type annotations and *args dereferences in event handler closures. After the change, ImplParam<'_, i32> resolves to i32 directly (not Ref<i32>), so those were updated to use args: i32 and args directly. Also fixed generic_primitive.rs which had the same pattern.

[kennykerr]

@copilot fmt failed

[kennykerr]

@copilot more test failures

[Copilot]

@copilot more test failures

Fixed in 0d8c552. Two clippy::explicit_auto_deref errors in crates/libs/core/src/type.rs — the param_as_default implementations for InterfaceType and CloneType were returning &**param instead of param (auto-deref handles the coercion).

[kennykerr]

@copilot clippy failure

[Copilot]

@copilot clippy failure

Fixed in eb7a009. crates/tests/winrt/old/tests/delegates.rs line 50 had assert!(*port == 80) — port is now i32 directly (not Ref<i32>), so dereferencing it caused E0614. Changed to assert!(port == 80) and removed the stale TODO comment.

[kennykerr]

@copilot build failures

[Copilot]

@copilot build failures

Fixed in 7e3ed76. The "Tests changed code in the repo" check was failing because crates/tests/winrt/reference_custom/src/bindings.rs and crates/tests/winrt/reference_no_deps/src/bindings.rs were not regenerated — they still had windows_core::Ref<T> and transmute_copy(&value) patterns. Updated both files to use ImplParam<'_, T> in trait signatures and <T as windows_core::Type<T>>::abi_to_param(&value) in vtable code.