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[CS] Fix an overly strict assert #83992

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Merged
merged 1 commit into from
Aug 29, 2025
Merged

[CS] Fix an overly strict assert #83992

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2 changes: 1 addition & 1 deletion lib/Sema/Constraint.cpp
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Expand Up @@ -784,7 +784,7 @@ Constraint *Constraint::create(ConstraintSystem &cs, ConstraintKind kind,
assert((kind != ConstraintKind::ConformsTo &&
kind != ConstraintKind::NonisolatedConformsTo &&
kind != ConstraintKind::TransitivelyConformsTo) ||
second->isExistentialType());
second->isAnyExistentialType());
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Should we unwrap the metatype before we generate the constraint though, in the caller?

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I don't think we can since we rely on matchExistentialTypes to iteratively match each level of metatype, i.e if you have $T0 <> P.Type, we need to form an unsolved constraint with P.Type since we wouldn't want it to succeed if $T0 ends up being simply S rather than S.Type.


// Literal protocol conformances expect a protocol.
assert((kind != ConstraintKind::LiteralConformsTo) ||
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14 changes: 14 additions & 0 deletions test/Constraints/existential_metatypes.swift
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Expand Up @@ -119,3 +119,17 @@ func parameterizedExistentials() {
var ppt: any PP4<Int>.Type
pt = ppt // expected-error {{cannot assign value of type 'any PP4<Int>.Type' to type 'any P4<Int>.Type'}}
}

func testNestedMetatype() {
struct S: P {}

func bar<T>(_ x: T) -> T.Type { type(of: x) }
func foo(_ x: P.Type.Type) { }

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

// FIXME: Bad diagnostic
// https://github.com/swiftlang/swift/issues/83991
foo(bar(0)) // expected-error {{failed to produce diagnostic for expression}}
}
2 changes: 1 addition & 1 deletion ...ompiler_crashers_2/c5955772856ea0fa.swift → ...r_crashers_2_fixed/c5955772856ea0fa.swift
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@@ -1,3 +1,3 @@
// {"kind":"typecheck","signature":"swift::constraints::Constraint::create(swift::constraints::ConstraintSystem&, swift::constraints::ConstraintKind, swift::Type, swift::Type, swift::constraints::ConstraintLocator*, llvm::ArrayRef<swift::TypeVariableType*>)","signatureAssert":"Assertion failed: ((kind != ConstraintKind::ConformsTo && kind != ConstraintKind::NonisolatedConformsTo && kind != ConstraintKind::TransitivelyConformsTo) || second->isExistentialType()), function create"}
// RUN: not --crash %target-swift-frontend -typecheck %s
// RUN: not %target-swift-frontend -typecheck %s
protocol a let : a.Type.Type = b->c