Sema: Register the extended type of a package-level extension

The warnings on superfluously public/package imports has a hole where
it could report a package import as not being used by package decls
even if it provides a type extended by a package extension. This is
caused by the exportability checker not being enabled for package
decls, thus not triggering the usual logic registering this reference.

Address this issue by adding a check specifically for package extensions.
We can remove this check once we have exportability checking for package
decls.

rdar://126712864

Author: xymus

lib/Sema/TypeCheckAccess.cpp

@@ -2538,6 +2538,49 @@ void swift::diagnoseUnnecessaryPublicImports(SourceFile &SF) {
   }
 }
 
+/// Register the type extended by \p ED as being used in a package decl if
+/// any member is a package decl. This patches a hole in the warnings on
+/// superfluously public imports which usually relies on exportability checking
+/// that is not currently executed for package decls.
+void registerPackageAccessForPackageExtendedType(ExtensionDecl *ED) {
+  auto extendedType = ED->getExtendedNominal();
+  if (!extendedType)
+    return;
+
+  bool hasPackageMembers = llvm::any_of(ED->getMembers(),
+                                        [](const Decl *member) -> bool {
+    auto *VD = dyn_cast<ValueDecl>(member);
+    if (!VD)
+      return false;
+
+    AccessScope accessScope =
+        VD->getFormalAccessScope(nullptr,
+                                 /*treatUsableFromInlineAsPublic*/true);
+    return accessScope.isPackage();
+  });
+  if (!hasPackageMembers)
+    return;
+
+  DeclContext *DC = ED->getDeclContext();
+  ImportAccessLevel import = extendedType->getImportAccessFrom(DC);
+  if (import.has_value()) {
+    auto SF = DC->getParentSourceFile();
+    if (SF)
+      SF->registerAccessLevelUsingImport(import.value(),
+                                         AccessLevel::Package);
+
+    auto &ctx = DC->getASTContext();
+    if (ctx.LangOpts.EnableModuleApiImportRemarks) {
+      ModuleDecl *importedVia = import->module.importedModule,
+                 *sourceModule = ED->getModuleContext();
+      ED->diagnose(diag::module_api_import,
+                   ED, importedVia, sourceModule,
+                   importedVia == sourceModule,
+                   /*isImplicit*/false);
+    }
+  }
+}
+
 void swift::checkAccessControl(Decl *D) {
   if (isa<ValueDecl>(D) || isa<PatternBindingDecl>(D)) {
     bool allowInlineable =
@@ -2546,6 +2589,7 @@ void swift::checkAccessControl(Decl *D) {
     UsableFromInlineChecker().visit(D);
   } else if (auto *ED = dyn_cast<ExtensionDecl>(D)) {
     checkExtensionGenericParamAccess(ED);
+    registerPackageAccessForPackageExtendedType(ED);
   }
 
   if (isa<AccessorDecl>(D))

test/Sema/superfluously-public-imports.swift

@@ -17,6 +17,7 @@
 // RUN: %target-swift-frontend -emit-module %t/ExtendedDefinitionNonPublic.swift -o %t -I %t
 // RUN: %target-swift-frontend -emit-module %t/UnusedImport.swift -o %t -I %t
 // RUN: %target-swift-frontend -emit-module %t/UnusedPackageImport.swift -o %t -I %t
+// RUN: %target-swift-frontend -emit-module %t/ExtendedPackageTypeImport.swift -o %t -I %t
 // RUN: %target-swift-frontend -emit-module %t/ImportNotUseFromAPI.swift -o %t -I %t
 // RUN: %target-swift-frontend -emit-module %t/ImportUsedInPackage.swift -o %t -I %t
 // RUN: %target-swift-frontend -emit-module %t/ExportedUnused.swift -o %t -I %t
@@ -98,6 +99,9 @@ public struct NonPublicExtendedType {}
 //--- UnusedImport.swift
 
 //--- UnusedPackageImport.swift
+//--- ExtendedPackageTypeImport.swift
+
+public struct ExtendedPackageType {}
 
 //--- ImportNotUseFromAPI.swift
 public struct NotAnAPIType {}
@@ -145,6 +149,7 @@ package import UnusedImport // expected-warning {{package import of 'UnusedImpor
 // expected-warning @-1 {{module 'UnusedImport' is imported as 'public' from the same file; this 'package' access level will be ignored}}
 
 package import UnusedPackageImport // expected-warning {{package import of 'UnusedPackageImport' was not used in package declarations}} {{1-9=}}
+package import ExtendedPackageTypeImport
 public import ImportNotUseFromAPI // expected-warning {{public import of 'ImportNotUseFromAPI' was not used in public declarations or inlinable code}} {{1-8=}}
 public import ImportUsedInPackage // expected-warning {{public import of 'ImportUsedInPackage' was not used in public declarations or inlinable code}} {{1-7=package}}
 
@@ -243,6 +248,10 @@ public protocol Countable {
 extension Extended: Countable { // expected-remark {{struct 'Extended' is imported via 'RetroactiveConformance'}}
 }
 
+extension ExtendedPackageType { // expected-remark {{struct 'ExtendedPackageType' is imported via 'ExtendedPackageTypeImport'}}
+  package func useExtendedPackageType() { }
+}
+
 /// Tests for imports of clang modules.
 //--- module.modulemap
 module ClangSimpleUnused {