Merge pull request #76053 from tshortli/associated-conformance-availability

Sema: Relax associated conformance availability checking

Author: tshortli

lib/Sema/TypeCheckAvailability.cpp

@@ -295,6 +295,13 @@ ExportContext ExportContext::withExported(bool exported) const {
   return copy;
 }
 
+ExportContext ExportContext::withRefinedAvailability(
+    const AvailabilityContext &availability) const {
+  auto copy = *this;
+  copy.RunningOSVersion.intersectWith(availability);
+  return copy;
+}
+
 std::optional<PlatformKind> ExportContext::getUnavailablePlatformKind() const {
   if (Unavailable)
     return PlatformKind(Platform);

lib/Sema/TypeCheckAvailability.h

@@ -153,6 +153,11 @@ class ExportContext {
   /// That is, this will perform a 'bitwise and' on the 'exported' bit.
   ExportContext withExported(bool exported) const;
 
+  /// Produce a new context with the same properties as this one, except the
+  /// availability context is constrained by \p availability if necessary.
+  ExportContext
+  withRefinedAvailability(const AvailabilityContext &availability) const;
+
   DeclContext *getDeclContext() const { return DC; }
 
   AvailabilityContext getAvailabilityContext() const {

lib/Sema/TypeCheckProtocol.cpp

@@ -4987,9 +4987,21 @@ static void ensureRequirementsAreSatisfied(ASTContext &ctx,
       if (assocConf.isConcrete()) {
         auto *concrete = assocConf.getConcrete();
         auto replacementTy = dc->mapTypeIntoContext(concrete->getType());
-        diagnoseConformanceAvailability(conformance->getLoc(),
-                                        assocConf, where,
-                                        depTy, replacementTy);
+
+        // If this requirement has a dependent member type, only require the
+        // associated conformance to be as available as the requirement's
+        // associated type.
+        auto availability = AvailabilityContext::alwaysAvailable();
+        if (auto depMemberType = depTy->getAs<DependentMemberType>()) {
+          auto assocType = depMemberType->getAssocType();
+          availability.intersectWith(
+              TypeChecker::overApproximateAvailabilityAtLocation(
+                  assocType->getLoc(), assocType->getDeclContext()));
+        }
+
+        diagnoseConformanceAvailability(
+            conformance->getLoc(), assocConf,
+            where.withRefinedAvailability(availability), depTy, replacementTy);
       }
 
       return false;

test/Sema/conformance_availability.swift

@@ -279,6 +279,15 @@ func passAvailableConformance1a(x: HasAvailableConformance1) {
   _ = UsesHorse<HasAvailableConformance1>.self
 }
 
+// Always available conformance
+struct HasAvailableConformance2: Horse {}
+
+// Conformance available in macOS 200
+struct HasAvailableConformance3 {}
+
+@available(macOS 200, *)
+extension HasAvailableConformance3: Horse {}
+
 // Associated conformance with unavailability
 protocol Rider {
   associatedtype H : Horse
@@ -326,6 +335,58 @@ extension AssocConformanceAvailable4 : Rider {
   typealias H = HasAvailableConformance1
 }
 
+@available(macOS 100, *)
+protocol Saddle {
+  associatedtype H : Horse = HasAvailableConformance1
+}
+
+struct ConformsToSaddle1 : Saddle {}
+
+struct ConformsToSaddle2 : Saddle {
+  typealias H = HasAvailableConformance2
+}
+
+struct ConformsToSaddle3 : Saddle {
+  // expected-error@-1 {{conformance of 'HasAvailableConformance3' to 'Horse' is only available in macOS 200 or newer}}
+  // expected-note@-2 {{add @available attribute to enclosing struct}}
+  // expected-note@-3 {{in associated type 'Self.H' (inferred as 'HasAvailableConformance3'}}
+  typealias H = HasAvailableConformance3
+}
+
+struct ConformsToSaddle4 : Saddle {
+  // expected-error@-1 {{conformance of 'HasAvailableConformance3' to 'Horse' is only available in macOS 200 or newer}}
+  // expected-note@-2 {{add @available attribute to enclosing struct}}
+  // expected-note@-3 {{in associated type 'Self.H' (inferred as 'HasAvailableConformance3'}}
+  @available(macOS 200, *)
+  typealias H = HasAvailableConformance3
+}
+
+protocol Barn {
+  @available(macOS 100, *)
+  associatedtype H : Horse = HasAvailableConformance1
+}
+
+struct ConformsToBarn1 : Barn {}
+
+struct ConformsToBarn2 : Barn {
+  typealias H = HasAvailableConformance2
+}
+
+struct ConformsToBarn3 : Barn {
+  // expected-error@-1 {{conformance of 'HasAvailableConformance3' to 'Horse' is only available in macOS 200 or newer}}
+  // expected-note@-2 {{add @available attribute to enclosing struct}}
+  // expected-note@-3 {{in associated type 'Self.H' (inferred as 'HasAvailableConformance3'}}
+  typealias H = HasAvailableConformance3
+}
+
+struct ConformsToBarn4 : Barn {
+  // expected-error@-1 {{conformance of 'HasAvailableConformance3' to 'Horse' is only available in macOS 200 or newer}}
+  // expected-note@-2 {{add @available attribute to enclosing struct}}
+  // expected-note@-3 {{in associated type 'Self.H' (inferred as 'HasAvailableConformance3'}}
+  @available(macOS 200, *)
+  typealias H = HasAvailableConformance3
+}
+
 // Solution ranking should down-rank solutions involving unavailable conformances
 protocol First {}
 extension First {