[5.3] [SR-12486] T.self is Any.Protocol is broken
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* SR-12486: `T.self is Any.Protocol` is broken This turned out to be fallout from swiftlang#27572 which was in turn motivated by our confusing metatype syntax when generic variables are bound to protocols. In particular, the earlier PR was an attempt to make the expression `x is T.Type` (where `T` is a generic type variable bound to a protocol `P`) behave the same as `x is P.Type` (where `P` is a protocol). Unfortunately, the generic `T.Type` actually binds to `P.Protocol` in this case (not `P.Type`), so the original motivation was flawed, and as it happens, `x is T.Type` already behaved the same as `x is P.Protocol` in this situation. This PR reverts that earlier change and beefs up some of the tests around these behaviors. Resolves SR-12486 Resolves rdar://62201613 Reverts PR#27572
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airspeedswift
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Jul 7, 2020
AnthonyLatsis
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swift 5.3
🍒 release cherry pick
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Merge PR #31662 into release/5.3 branch
Description from original PR #31662
This turned out to be fallout from #27572 which was in turn motivated by our confusing metatype syntax when generic variables are bound to protocols.
In particular, the earlier PR was an attempt to make the expression
x is T.Type(whereTis a generic type variable bound to a protocolP) behave the same asx is P.Type(wherePis a protocol). Unfortunately, the genericT.Typeactually binds toP.Protocolin this case (notP.Type), so the original motivation was flawed, and as it happens,x is T.Typealready behaved the same asx is P.Protocolin this situation.This PR reverts that earlier change and beefs up some of the tests around these behaviors.
Resolves SR-12486
Resolves rdar://62201613
Reverts PR#27572
CCC Information
• Explanation: Reverts PR#27572 which broke several different runtime casts
• Scope of Issue: Restores the correct behavior from Swift 5.0
• Origination: PR#27572
• Risk: Some projects may have introduced dependencies on the Swift 5.1 or 5.2 behaviors (which were different from each other and different from the correct Swift 5.0 behavior)
• Reviewed By: Joe Groff, Mike Ash
• Automated Testing: Unit tests were augmented to clarify the correct behavior
• Impact: Runtime only