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Sema: Workaround for broken existential opening behavior #84501

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Merged
slavapestov merged 1 commit into from
Sep 26, 2025
Merged

Sema: Workaround for broken existential opening behavior #84501

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6 changes: 5 additions & 1 deletion lib/Sema/CSSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13394,8 +13394,12 @@ bool ConstraintSystem::simplifyAppliedOverloadsImpl(
choiceType = objectType;
}

// FIXME: The !getSelfProtocolDecl() check is load-bearing, because
// this optimization interacts poorly with existential opening
// somehow. It should all be removed.
if (auto *choiceFnType = choiceType->getAs<FunctionType>()) {
if (isa<ConstructorDecl>(choice.getDecl())) {
if (isa<ConstructorDecl>(choice.getDecl()) &&
!choice.getDecl()->getDeclContext()->getSelfProtocolDecl()) {
auto choiceResultType = choice.getBaseType()
->getRValueType()
->getMetatypeInstanceType();
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30 changes: 30 additions & 0 deletions test/Constraints/opened_existentials_overload.swift
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
// RUN: %target-typecheck-verify-swift

protocol P {}

func g(_: some P) {}
// expected-note@-1 {{required by global function 'g' where 'some P' = 'any P'}}

// rdar://problem/160389221
func good(_ x: Array<any P>) {
Array(x).forEach { y in g(y) }
}

extension Array {
var ffirst: Element? { fatalError() }
func ffirst(wwhere: (Element) -> Bool) -> Element { fatalError() }
}

func bad(_ x: Array<any P>) {
let y = x.ffirst!
g(y) // ok

let yy = x.ffirst
g(yy!) // ok

// FIXME: This is broken

g(x.ffirst!)
// expected-error@-1 {{type 'any P' cannot conform to 'P'}}
// expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
}