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Sema: Relax diagnosis of implied marker protocol conformances with mismatched availability

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This logic was introduced in https://github.com/swiftlang/swift/pull/75135.
The intent was to prevent an implied conformance from overriding an
existing unavailable one, for example in the case of Sendable. Let's
relax this check a bit to only diagnose if the mismatch is in the
unconditional availability, and not OS version.

Fixes rdar://142873265.
This commit is contained in:
Slava Pestov
2025-06-16 16:20:58 -04:00
parent d22a24744f
commit dad358350a
4 changed files with 123 additions and 1 deletions
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9
lib/AST/ConformanceLookupTable.cpp
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@@ -599,6 +599,11 @@ ConformanceLookupTable::Ordering ConformanceLookupTable::compareConformances(
}
}
auto isUnavailable = [](DeclContext *dc) -> bool {
auto *ext = dyn_cast<ExtensionDecl>(dc);
return ext && ext->isUnavailable();
};
// If only one of the conformances is unconditionally available on the
// current deployment target, pick that one.
//
@@ -610,7 +615,9 @@ ConformanceLookupTable::Ordering ConformanceLookupTable::compareConformances(
rhs->getDeclContext()->isAlwaysAvailableConformanceContext()) {
// Diagnose conflicting marker protocol conformances that differ in
// un-availability.
diagnoseSuperseded = lhs->getProtocol()->isMarkerProtocol();
diagnoseSuperseded = (lhs->getProtocol()->isMarkerProtocol() &&
isUnavailable(lhs->getDeclContext()) !=
isUnavailable(rhs->getDeclContext()));
return (lhs->getDeclContext()->isAlwaysAvailableConformanceContext()
? Ordering::Before

8
test/Sema/Inputs/conformance_availability_implied_other.swift Normal file
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@@ -0,0 +1,8 @@
@available(macOS 200, *)
extension Conformer1: Derived2 {}
@available(macOS 100, *)
extension Conformer2: Derived1 {}
// expected-error@-1 {{conformance of 'Conformer2' to 'Base' is only available in macOS 200 or newer}}

59
test/Sema/conformance_availability_implied.swift Normal file
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@@ -0,0 +1,59 @@
// RUN: %target-typecheck-verify-swift -swift-version 6
// REQUIRES: OS=macosx
// Protocols:
protocol Base {
func f() // expected-note {{protocol requirement here}}
}
func takesBase<T: Base>(_: T.Type) {}
protocol Derived1: Base {}
protocol Derived2: Base {}
@_marker protocol MarkerBase {}
func takesMarkerBase<T: MarkerBase>(_: T.Type) {}
protocol MarkerDerived1: MarkerBase {}
protocol MarkerDerived2: MarkerBase {}
// Verify that the implied conformance is macOS 100:
struct Conformer1 {}
@available(macOS 100, *)
extension Conformer1: Derived1 {
func f() {} // okay!
}
@available(macOS 200, *)
extension Conformer1: Derived2 {}
takesBase(Conformer1.self)
// expected-error@-1 {{conformance of 'Conformer1' to 'Base' is only available in macOS 100 or newer}}
// expected-note@-2 {{add 'if #available' version check}}
// No warning about redundant MarkerBase conformance (rdar://142873265):
@available(macOS 100, *)
extension Conformer1: MarkerDerived1 {}
@available(macOS 200, *)
extension Conformer1: MarkerDerived2 {}
takesMarkerBase(Conformer1.self)
// expected-error@-1 {{conformance of 'Conformer1' to 'MarkerBase' is only available in macOS 100 or newer}}
// expected-note@-2 {{add 'if #available' version check}}
// Bad availability on the Base.f() witness:
struct Conformer2 {}
@available(macOS 100, *)
extension Conformer2: Derived1 {
// expected-error@-1 {{protocol 'Base' requires 'f()' to be available in macOS 100 and newer}}
}
@available(macOS 200, *)
extension Conformer2: Derived2 {
func f() {} // expected-note {{'f()' declared here}}
}

48
test/Sema/conformance_availability_implied_multifile.swift Normal file
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@@ -0,0 +1,48 @@
// RUN: %target-swift-frontend -typecheck -verify %s %S/Inputs/conformance_availability_implied_other.swift -swift-version 6
// RUN: %target-swift-frontend -typecheck -verify %S/Inputs/conformance_availability_implied_other.swift %s -swift-version 6
// REQUIRES: OS=macosx
protocol Base {
func f()
}
func takesBase<T: Base>(_: T.Type) {}
protocol Derived1: Base {}
protocol Derived2: Base {}
// Verify that the implied conformance is macOS 100:
struct Conformer1 {}
@available(macOS 100, *)
extension Conformer1: Derived1 {
func f() {} // okay!
}
// Note that Conformer1: Derived2 is in the other file
func check1() {
// expected-note@-1 {{add '@available' attribute to enclosing global function}}
takesBase(Conformer1.self)
// expected-error@-1 {{conformance of 'Conformer1' to 'Base' is only available in macOS 100 or newer}}
// expected-note@-2 {{add 'if #available' version check}}
}
// Verify that the implied conformance is macOS 200:
// FIXME: This appears to be unsound!
struct Conformer2 {}
@available(macOS 200, *)
extension Conformer2: Derived2 {
func f() {}
}
// Note that Conformer2: Derived1 is in the other file
func check2() {
// expected-note@-1 {{add '@available' attribute to enclosing global function}}
takesBase(Conformer2.self)
// expected-error@-1 {{conformance of 'Conformer2' to 'Base' is only available in macOS 200 or newer}}
// expected-note@-2 {{add 'if #available' version check}}
}