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RequirementMachine: Fix concrete_contraction_unrelated_typealias test and add comments describing the hack #42005

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Mar 24, 2022
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RequirementMachine: Fix concrete_contraction_unrelated_typealias test and add comments describing the hack #42005

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25 changes: 21 additions & 4 deletions test/Generics/concrete_contraction_unrelated_typealias.swift
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Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
// R/UN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-inferred-signatures=on 2>&1 | %FileCheck %s
// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-inferred-signatures=on -disable-requirement-machine-concrete-contraction 2>&1 | %FileCheck %s
// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-inferred-signatures=on 2>&1 | %FileCheck %s

// Another GenericSignatureBuilder oddity, reduced from RxSwift.
//
Expand All @@ -19,6 +18,11 @@ class GenericDelegateProxy<P : AnyObject, D> {
typealias Parent = P
typealias Delegate = D

// Here if we resolve Proxy.Parent and Proxy.Delegate to the typealiases,
// we get vacuous requirements 'P == P' and 'D == D'. By keeping both
// the substituted and original requirement, we ensure that the
// unrelated associated type 'Parent' is constrained instead.

// CHECK-LABEL: .GenericDelegateProxy.init(_:)@
// CHECK-NEXT: <P, D, Proxy where P == Proxy.[DelegateProxyType]Parent, D == Proxy.[DelegateProxyType]Delegate, Proxy : GenericDelegateProxy<P, D>, Proxy : DelegateProxyType>
init<Proxy: DelegateProxyType>(_: Proxy.Type)
Expand All @@ -34,8 +38,21 @@ class ConcreteDelegateProxy {
typealias Parent = SomeClass
typealias Delegate = SomeStruct

// An even more esoteric edge case. Note that this one I made up; only
// the first one is relevant for compatibility with RxSwift.
//
// Here unfortunately we produce a different result from the GSB, because
// the hack for keeping both the substituted and original requirement means
// the substituted requirements become 'P == SomeClass' and 'D == SomeStruct'.
//
// The GSB does not constrain P and D in this way and instead produced the
// following minimized signature:
//
// <P, D, Proxy where P == Proxy.[DelegateProxyType]Parent, D == Proxy.[DelegateProxyType]Delegate, Proxy : ConcreteDelegateProxy, Proxy : DelegateProxyType>!

// CHECK-LABEL: .ConcreteDelegateProxy.init(_:_:_:)@
// CHECK-NEXT: <P, D, Proxy where P == Proxy.[DelegateProxyType]Parent, D == Proxy.[DelegateProxyType]Delegate, Proxy : ConcreteDelegateProxy, Proxy : DelegateProxyType>
// CHECK-NEXT: <P, D, Proxy where P == SomeClass, D == SomeStruct, Proxy : ConcreteDelegateProxy, Proxy : DelegateProxyType, Proxy.[DelegateProxyType]Delegate == SomeStruct, Proxy.[DelegateProxyType]Parent == SomeClass>

init<P, D, Proxy: DelegateProxyType>(_: P, _: D, _: Proxy.Type)
where Proxy: ConcreteDelegateProxy,
Proxy.Parent == P,
Expand All @@ -45,4 +62,4 @@ class ConcreteDelegateProxy {
protocol DelegateProxyType {
associatedtype Parent : AnyObject
associatedtype Delegate
}
}