Sema: Fix a regression in retroactive conformance diagnostic suppression.

Module qualifying a protocol name in an inheritance clause should suppress
retroactive conformance diagnostics for the protocol and any protocols it
inherits from, just like adding the `@retroactive` attribute. Fixes a
regression in Swift 6.2 introduced by
#81576.

Resolves rdar://162295268.

Author: tshortli

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1720,30 +1720,35 @@ static TypeRepr *unwrapAttributedRepr(TypeRepr *repr) {
   return repr;
 }
 
+struct ProtocolAndRetroactiveStatus {
+  ProtocolDecl *proto = nullptr;
+  bool isMarkedRetroactive = false;
+};
+
 static void collectProtocolsFromInheritedEntry(
-    const InheritedEntry &entry,
-    Type inheritedTy,
-    llvm::SmallPtrSetImpl<ProtocolDecl *> &protocolsWithRetroactiveAttr,
-    SmallVectorImpl<ProtocolDecl *> &protos) {
+    const InheritedEntry &entry, Type inheritedTy,
+    SmallVectorImpl<ProtocolAndRetroactiveStatus> &protos) {
+
+  bool isMarkedRetroactive = entry.isRetroactive();
 
   if (auto *protoTy = inheritedTy->getAs<ProtocolType>()) {
     auto *proto = protoTy->getDecl();
 
     // As a fallback, to support previous language versions, also allow
     // this through if the protocol has been explicitly module-qualified.
     TypeRepr *repr = unwrapAttributedRepr(entry.getTypeRepr());
-    if (isModuleQualified(repr, proto->getParentModule())) {
-      protocolsWithRetroactiveAttr.insert(proto);
-    }
+    if (isModuleQualified(repr, proto->getParentModule()))
+      isMarkedRetroactive = true;
 
-    protos.push_back(proto);
+    protos.push_back({proto, isMarkedRetroactive});
   } else if (auto *pct = inheritedTy->getAs<ProtocolCompositionType>()) {
     for (auto member : pct->getMembers()) {
-      collectProtocolsFromInheritedEntry(entry, member,
-                                         protocolsWithRetroactiveAttr, protos);
+      // FIXME: Check for module qualification on each composed protocol.
+      collectProtocolsFromInheritedEntry(entry, member, protos);
     }
   } else if (auto *ppt = inheritedTy->getAs<ParameterizedProtocolType>()) {
-    protos.push_back(ppt->getProtocol());
+    // FIXME: Check for module qualification.
+    protos.push_back({ppt->getProtocol(), isMarkedRetroactive});
   }
 }
 
@@ -1810,11 +1815,12 @@ static void diagnoseRetroactiveConformances(
       continue;
     }
 
-    SmallVector<ProtocolDecl *, 2> protos;
-    collectProtocolsFromInheritedEntry(entry, inheritedTy,
-                                       protocolsWithRetroactiveAttr, protos);
+    SmallVector<ProtocolAndRetroactiveStatus, 2> protosAndStatuses;
+    collectProtocolsFromInheritedEntry(entry, inheritedTy, protosAndStatuses);
+
+    for (auto protoAndStatus : protosAndStatuses) {
+      auto proto = protoAndStatus.proto;
 
-    for (auto *proto : protos) {
       proto->walkInheritedProtocols([&](ProtocolDecl *decl) {
         // If this isn't a retroactive conformance, skip it.
         auto found = protocols.find(proto);
@@ -1846,8 +1852,7 @@ static void diagnoseRetroactiveConformances(
           return TypeWalker::Action::Continue;
         }
 
-        // If it's marked @retroactive, no need to warn.
-        if (entry.isRetroactive()) {
+        if (protoAndStatus.isMarkedRetroactive) {
           // Note that we encountered this protocol through a conformance marked
           // @retroactive in case multiple clauses cause the protocol to be
           // inherited.

test/Sema/extension_retroactive_conformances.swift

@@ -24,15 +24,20 @@ public struct Sample3 {}
 public struct Sample4 {}
 public struct Sample5 {}
 public struct Sample6 {}
+public struct Sample6a {}
+public struct Sample6b {}
+public struct Sample6c {}
 public struct Sample7 {}
 public struct Sample8 {}
+public struct Sample8a {}
 
 public struct SampleAlreadyConforms: SampleProtocol1 {}
 
 public struct GenericSample1<T> {}
 
 public struct Sample9 {}
-public struct Sample10 {}
+public struct Sample9a {}
+public struct Sample9b {}
 
 #else
 
@@ -83,9 +88,13 @@ typealias MySample6 = Sample6
 extension MySample6: SampleProtocol1 {} // expected-warning {{extension declares a conformance of imported type 'Sample6' to imported protocol 'SampleProtocol1'}}
 // expected-note @-1 {{add '@retroactive' to silence this warning}} {{22-37=@retroactive SampleProtocol1}}
 
-// Ensure module-qualifying both types still silences the warning
+// Ensure module-qualifying the protocol silences the warning
 
-extension Library.Sample6: Library.SampleProtocol2 {} // ok, module-qualified.
+extension Library.Sample6: Library.SampleProtocol2 {} // ok, both types are module-qualified.
+extension Sample6a: Library.SampleProtocol2 {} // ok, protocol is module qualified.
+extension Library.Sample6b: SampleProtocol2 {} // expected-warning {{extension declares a conformance of imported type 'Sample6b' to imported protocol 'SampleProtocol2'; this will not behave correctly if the owners of 'Library' introduce this conformance in the future}}
+// expected-note @-1 {{add '@retroactive' to silence this warning}}
+extension Sample6c: Library.SampleProtocol1a {} // ok, protocol is module qualified.
 
 protocol ClientProtocol {}
 
@@ -125,10 +134,20 @@ extension Sample7: SampleProtocol1 & SampleProtocol2 {}
 
 extension Sample8: @retroactive SampleProtocol1 & SampleProtocol2 {}  // ok
 
+// FIXME: Module qualification should suppress this warning
+extension Sample8a: Library.SampleProtocol1 & Library.SampleProtocol2 {}  // ok
+// expected-warning@-1 {{extension declares a conformance of imported type 'Sample8a' to imported protocols 'SampleProtocol1', 'SampleProtocol2'; this will not behave correctly if the owners of 'Library' introduce this conformance in the future}}
+// expected-note@-2 {{add '@retroactive' to silence this warning}}
+
 extension Sample9: SampleProtocol3<Int> {}
 // expected-warning@-1 {{extension declares a conformance of imported type 'Sample9' to imported protocol 'SampleProtocol3'; this will not behave correctly if the owners of 'Library' introduce this conformance in the future}}
 // expected-note@-2 {{add '@retroactive' to silence this warning}}
 
-extension Sample10: @retroactive SampleProtocol3<Int> {}
+extension Sample9a: @retroactive SampleProtocol3<Int> {}
 
-#endif
+// FIXME: Module qualification should suppress this warning
+extension Sample9b: Library.SampleProtocol3<Int> {}
+// expected-warning@-1 {{extension declares a conformance of imported type 'Sample9b' to imported protocol 'SampleProtocol3'; this will not behave correctly if the owners of 'Library' introduce this conformance in the future}}
+// expected-note@-2 {{add '@retroactive' to silence this warning}}
+
+#endif