fahadnayyar 7b8b33eda0 [cxx-interop] Allow SWIFT_RETURNS_(UN)RETAINED on template class member functions returning T* (#84375) ...

When importing C++ template classes like`Ref<T>` that have methods
returning `T*`, we face the following situation when `T` is a
`SWIFT_SHARED_REFERENCE` type:

1. Without `SWIFT_RETURNS_(UN)RETAINED` annotation: Swift compiler would
emit a warning (currently under experimental-feature flag
`WarnUnannotatedReturnOfCxxFrt`) _"cannot infer the ownership of the
returned value" when T is a SWIFT_SHARED_REFERENCE type_
2. With annotation: Compiler rejects it with this error: _"cannot be
annotated... not returning a SWIFT_SHARED_REFERENCE type"_

This affects WebGPU's smart pointer types (`WTF::Ref<T>,
WTF::RefPtr<T>`) and similar patterns in other C++ codebases.

In this patch I am fixing the logic for diagnostic
`returns_retained_or_returns_unretained_for_non_cxx_frt_values`. I'm
also making it a warning instead of an error to minimize the risk, as
this diagnostic has been a hindrance to the adoption of these
annotations in real codebases when templated functions and types are
involved. (Refer to
[PR-78968](https://github.com/swiftlang/swift/pull/78968))

rdar://160862498

2025-09-19 12:09:05 -07:00

438 KiB

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