[4.2-04-30-2018] [SILGen] Ensure type params in witness method conformances match the witness method signatures. #16518
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…witness method signatures. A witness method of a class can have its generic parameters rephrased: a parameters of the class, like τ_0_0, get pushed to the next depth, like τ_1_0, to make way for a τ_0_0 parameter with a τ_0_0: Class<...> subclass constraint. When this wasn't accounted for, IRGen would find that it couldn't satisfy conditional requirements on the rewritten type parameters, and they'd incorrectly be passed as additional arguments of a witness method thunk rather than pulled out of the Self witness table's private area inside the thunk. Fixes rdar://problem/40078863.
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@swift-ci please test |
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@swift-ci please test source compatibility |
huonw
changed the title
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@swift-ci please nominate |
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@swift-ci please test source compatibility |
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I'm told that these the source compatibility failures haven't been set up for this branch. Merging. |
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Explanation: A class conditionally conforming to a protocol and using a default method for one of the requirements, would result in an incorrect signature (at the LLVM/asm level) for the thunk for the witness for that requirement. These are called dynamically, and so would result in crashes/undefined behaviour at runtime if things from the conditional requirements were used (e.g. calling a method on a
Tinextension Class: P where T: Q).Scope: Any class conforming to a protocol as above is at high risk of this.
Radar: rdar://problem/40078863.
Risk: Low: this is, essentially, just changing a type parameter from the incorrect default to the correct one, without modifying anything around it.
Testing: Test suite plus source compatibility suite
Reviewer: @DougGregor
#16493 #16514