Sema: Fix @retroactive does not apply diags for same package conformance.

SE-0364 was amended to allow same-package conformances to be considered
non-retroactive. The logic for that ammendment was implemented in Swift 6.0,
but the diagnostics were not updated.

Resolves rdar://133423931.

Author: tshortli

include/swift/AST/DiagnosticsSema.def

@@ -2606,8 +2606,9 @@ ERROR(retroactive_not_in_extension_inheritance_clause,none,
       "extensions", ())
 
 ERROR(retroactive_attr_does_not_apply,none,
-      "'retroactive' attribute does not apply; %0 is declared in this module",
-      (Identifier))
+      "'retroactive' attribute does not apply; %0 is declared in "
+      "%select{the same package|this module}1",
+      (const ValueDecl *, bool))
 
 WARNING(extension_retroactive_conformance,none,
        "extension declares a conformance of imported type %0 to imported "

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1819,13 +1819,20 @@ static void diagnoseRetroactiveConformances(
         if (decl == proto && entry.isRetroactive()) {
           auto loc =
               entry.getTypeRepr()->findAttrLoc(TypeAttrKind::Retroactive);
+
+          bool typeInSamePackage = extTypeModule->inSamePackage(module);
           bool typeIsSameModule =
               extTypeModule->isSameModuleLookingThroughOverlays(module);
-          auto incorrectTypeName = typeIsSameModule ? 
-              extendedNominalDecl->getName() : proto->getName();
+
+          auto declForDiag = (typeIsSameModule || typeInSamePackage)
+                                 ? extendedNominalDecl
+                                 : proto;
+          bool isSameModule = declForDiag->getParentModule()
+                                  ->isSameModuleLookingThroughOverlays(module);
+
           diags
-              .diagnose(loc, diag::retroactive_attr_does_not_apply,
-                        incorrectTypeName)
+              .diagnose(loc, diag::retroactive_attr_does_not_apply, declForDiag,
+                        isSameModule)
               .warnUntilSwiftVersion(6)
               .fixItRemove(SourceRange(loc, loc.getAdvancedLoc(1)));
           return TypeWalker::Action::Stop;

test/Sema/extension_retroactive_conformances_package.swift

@@ -3,7 +3,8 @@
 
 // RUN: %target-swift-frontend -swift-version 5 %t/Library.swift -emit-module -module-name Library -o %t -package-name Library 
 // RUN: %target-swift-frontend -swift-version 5 %t/OtherLibrary.swift -emit-module -module-name OtherLibrary -o %t -package-name Library
-// RUN: %target-swift-frontend -typecheck %t/Client.swift -module-name Client -verify -swift-version 5 -I %t -package-name Library 
+// RUN: %target-swift-frontend -swift-version 5 %t/ExternalLibrary.swift -emit-module -module-name ExternalLibrary -o %t
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -module-name Client -verify -swift-version 5 -I %t -package-name Library
 
 //--- Library.swift
 
@@ -19,10 +20,16 @@ public protocol OtherLibraryProtocol {}
 package class PackageOtherLibraryClass {}
 package protocol PackageOtherLibraryProtocol {}
 
+//--- ExternalLibrary.swift
+
+public class ExternalLibraryClass {}
+public protocol ExternalLibraryProtocol {}
+
 //--- Client.swift
 
 public import Library
 public import OtherLibrary
+public import ExternalLibrary
 
 // These are all fine because all 3 of these modules are in the same package.
 
@@ -40,4 +47,13 @@ extension LibraryClass: PackageOtherLibraryProtocol {}
 
 extension PackageLibraryClass: PackageLibraryProtocol {}
 extension PackageOtherLibraryClass: PackageLibraryProtocol {}
-extension PackageLibraryClass: PackageOtherLibraryProtocol {}
+extension PackageLibraryClass: PackageOtherLibraryProtocol {}
+
+extension ExternalLibraryClass: ExternalLibraryProtocol {} // expected-warning {{extension declares a conformance of imported type 'ExternalLibraryClass' to imported protocol 'ExternalLibraryProtocol'; this will not behave correctly if the owners of 'ExternalLibrary' introduce this conformance in the future}}
+// expected-note @-1 {{add '@retroactive' to silence this warning}} {{33-56=@retroactive ExternalLibraryProtocol}}
+
+extension ExternalLibraryClass: LibraryProtocol {}
+extension LibraryClass: ExternalLibraryProtocol {}
+
+extension ExternalLibraryClass: @retroactive OtherLibraryProtocol {} // expected-warning {{'retroactive' attribute does not apply; 'OtherLibraryProtocol' is declared in the same package; this is an error in the Swift 6 language mode}}
+extension OtherLibraryClass: @retroactive ExternalLibraryProtocol {} // expected-warning {{'retroactive' attribute does not apply; 'OtherLibraryClass' is declared in the same package; this is an error in the Swift 6 language mode}}