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[Diagnostics] Fix a few issues with existential type mismatches #84715

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[Diagnostics] Fix a few issues with existential type mismatches #84715

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af90907
[CSSimplify] Look through `InstanceType` while attempting to diagnose…
xedin Oct 6, 2025
36fc1e6
[CSSimplify] Diagnose an attempt to match non-existential type to an …
xedin Oct 6, 2025
15c5662
[CSSimplify] Remove all `InstanceType` at the end of a locator to dia…
xedin Oct 6, 2025
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22 changes: 21 additions & 1 deletion lib/Sema/CSSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8750,7 +8750,27 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
return SolutionKind::Solved;
}

return matchExistentialTypes(type, protocol, kind, flags, locator);
auto result = matchExistentialTypes(type, protocol, kind, flags, locator);

if (shouldAttemptFixes() && result.isFailure()) {
auto *loc = getConstraintLocator(locator);

if (loc->isLastElement<LocatorPathElt::InstanceType>())
loc = getConstraintLocator(loc->getAnchor(), loc->getPath().drop_back());

ConstraintFix *fix = nullptr;
if (loc->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
fix = AllowArgumentMismatch::create(*this, type, protocol, loc);
} else if (loc->isLastElement<LocatorPathElt::ContextualType>()) {
fix = ContextualMismatch::create(*this, type, protocol, loc);
}

if (fix) {
return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
}
}

return result;
}

void ConstraintSystem::recordSynthesizedConformance(
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7 changes: 3 additions & 4 deletions test/Constraints/existential_metatypes.swift
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Expand Up @@ -120,6 +120,8 @@ func parameterizedExistentials() {
pt = ppt // expected-error {{cannot assign value of type 'any PP4<Int>.Type' to type 'any P4<Int>.Type'}}
}

// https://github.com/swiftlang/swift/issues/83991

func testNestedMetatype() {
struct S: P {}

Expand All @@ -131,8 +133,5 @@ func testNestedMetatype() {

// Make sure we don't crash.
foo2(bar(S.self))

// FIXME: Bad diagnostic
// https://github.com/swiftlang/swift/issues/83991
foo2(bar(0)) // expected-error {{failed to produce diagnostic for expression}}
foo2(bar(0)) // expected-error {{cannot convert value of type 'Int' to expected argument type 'any P.Type'}}
}