Fix issue with 'Self' metadata when class conforms to protocol with default implementations #12174
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@swift-ci Please test source compatibility |
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@swift-ci Please test compiler performance |
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Build comment file:Optimized (O)No Changes (333)
Unoptimized (Onone)Improvement (1)
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@graydon "Test compiler performance" failure you might want to look at |
…onstrained 'Self'
At this point, we already have a witness, so the requirement environment can depend on the witness as well as the requirement. Then, store the RequirementEnvironment inside the RequirementMatch.
…rotocol extension
…s conformances have an abstract 'Self'
Consider the following code:
protocol P {
func foo<A>(_: A)
}
extension P {
func foo<A>(_: A) {}
}
class C<T> : P {}
Before, the witness thunk for [C : P].foo() had the generic signature
<T, A>, and the witness P.foo() was called with a substitution
Self := C<T>.
This is incorrect because the caller might be using a subclass of C
as the 'Self' type, but this was being erased.
Now, the witness thunk for [C : P].foo() has the generic signature
<X : C<T>, T, A>, and the witness P.foo() is called with the
substitution Self := X.
Fixes <rdar://problem/33690383>, <https://bugs.swift.org/browse/SR-617>.
… resolveWitnessViaLookup()
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…t implementations returning 'Self' Now that we pass in the correct type metadata for 'Self', it is sound for a class to conform to a protocol with a default implementation for a method returning 'Self'. Fixes <rdar://problem/23671426>.
…ment-operator.swift, it was never being run
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This broke the simulator, reverting. |
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This builds upon #12118. Witness thunks for conformances of classes now have a generic parameter for
Self, constrained to the class. If the witness is defined in a protocol extension, we pass through theSelfparameter instead of using the static conforming type.This means we now allow the following:
Previously, we rejected this, to paper over the problem with passing
Selfmetadata. However this was an unsatisfactory fix, because not only does it ban a useful pattern, it also means adding a new protocol requirement is source breaking, even when there is a default implementation.Furthermore, even if your default implementation does not return
Self, it was possible to observe the incorrectSelfmetadata, as was shown in https://bugs.swift.org/browse/SR-617.Fixes rdar://problem/23671426, rdar://problem/33690383, https://bugs.swift.org/browse/SR-617.