Make PinCoerceUnsized require Deref #149218
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Also, delete impls on non-Deref types. Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense. This is a breaking change, since stable code can observe the deleted `PinCoerceUnsized` impls by uselessly coercing between such types inside a `Pin`. There is still some strange behavior, such as `Pin<&mut i32>` being able to coerce to `Pin<&dyn Send>`, but not being able to coerce to `Pin<&i32>`. However, I don't think it's possible to fix this. Fixes rust-lang#145081
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Make PinCoerceUnsized require Deref
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Also, delete impls on non-Deref types.
Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense.
This is a breaking change, since stable code can observe the deleted
PinCoerceUnsizedimpls by uselessly coercing between such types inside aPin.There is still some strange behavior, such as
Pin<&mut i32>being able to coerce toPin<&dyn Send>, but not being able to coerce toPin<&i32>. However, I don't think it's possible to fix this.Fixes #145081