[cxx-interop] Allow import-as-member for types in namespaces

This adds support for `swift_name` attribute being used with C++ types that are declared within namespaces, e.g.
```
__attribute__((swift_name("MyNamespace.MyType.my_method()")))
```

Previously import-as-member would only accept a top-level unqualified type name.

rdar://138934888

lib/ClangImporter/SwiftLookupTable.cpp

@@ -219,7 +219,7 @@ bool SwiftLookupTable::contextRequiresName(ContextKind kind) {
 
 /// Try to translate the given Clang declaration into a context.
 static std::optional<SwiftLookupTable::StoredContext>
-translateDeclToContext(clang::NamedDecl *decl) {
+translateDeclToContext(const clang::NamedDecl *decl) {
   // Tag declaration.
   if (auto tag = dyn_cast<clang::TagDecl>(decl)) {
     if (tag->getIdentifier())
@@ -324,22 +324,46 @@ SwiftLookupTable::translateContext(EffectiveClangContext context) {
 
 /// Lookup an unresolved context name and resolve it to a Clang
 /// declaration context or typedef name.
-clang::NamedDecl *SwiftLookupTable::resolveContext(StringRef unresolvedName) {
+const clang::NamedDecl *
+SwiftLookupTable::resolveContext(StringRef unresolvedName) {
+  SmallVector<StringRef, 1> nameComponents;
+  unresolvedName.split(nameComponents, '.');
+
+  EffectiveClangContext parentContext;
+
   // Look for a context with the given Swift name.
-  for (auto entry :
-       lookup(SerializedSwiftName(unresolvedName),
-              std::make_pair(ContextKind::TranslationUnit, StringRef()))) {
-    if (auto decl = entry.dyn_cast<clang::NamedDecl *>()) {
-      if (isa<clang::TagDecl>(decl) ||
-          isa<clang::ObjCInterfaceDecl>(decl) ||
-          isa<clang::TypedefNameDecl>(decl))
-        return decl;
+  for (auto nameComponent : nameComponents) {
+    auto entries =
+        parentContext
+            ? lookup(SerializedSwiftName(nameComponent), parentContext)
+            : lookup(SerializedSwiftName(nameComponent),
+                     std::make_pair(ContextKind::TranslationUnit, StringRef()));
+    bool entryFound = false;
+    for (auto entry : entries) {
+      if (auto decl = entry.dyn_cast<clang::NamedDecl *>()) {
+        if (isa<clang::TagDecl>(decl) ||
+            isa<clang::ObjCInterfaceDecl>(decl) ||
+            isa<clang::NamespaceDecl>(decl)) {
+          entryFound = true;
+          parentContext = EffectiveClangContext(cast<clang::DeclContext>(decl));
+          break;
+        }
+        if (auto typedefDecl = dyn_cast<clang::TypedefNameDecl>(decl)) {
+          entryFound = true;
+          parentContext = EffectiveClangContext(typedefDecl);
+          break;
+        }
+      }
     }
+
+    // If we could not resolve this component of the qualified name, bail.
+    if (!entryFound)
+      return nullptr;
   }
 
-  // FIXME: Search imported modules to resolve the context.
-
-  return nullptr;
+  return parentContext.getAsDeclContext()
+             ? cast<clang::NamedDecl>(parentContext.getAsDeclContext())
+             : parentContext.getTypedefName();
 }
 
 void SwiftLookupTable::addCategory(clang::ObjCCategoryDecl *category) {

lib/ClangImporter/SwiftLookupTable.h

@@ -593,7 +593,7 @@ private:
 public:
   /// Lookup an unresolved context name and resolve it to a Clang
   /// named declaration.
-  clang::NamedDecl *resolveContext(StringRef unresolvedName);
+  const clang::NamedDecl *resolveContext(StringRef unresolvedName);
 
   /// Lookup the set of entities with the given base name.
   ///

test/APINotes/Inputs/broken-modules/BrokenAPINotes.apinotes

@@ -13,4 +13,4 @@ Functions:
   - Name: ZXSpectrumSetMisnamedRegister
     SwiftName: 'setter:ZXSpectrum.misnamedRegister(self:newValue:)'
   - Name: ZXSpectrumHelperReset
-    SwiftName: 'ZXSpectrum.Helper.reset()'
+    SwiftName: 'ZXSpectrum::Helper.reset()'

test/Interop/Cxx/namespace/Inputs/import-as-member.h

@@ -0,0 +1,26 @@
+#define SWIFT_NAME(name) __attribute__((swift_name(name)))
+
+namespace MyNS {
+struct NestedStruct {
+  int value = 123;
+};
+}
+
+int nestedStruct_method(MyNS::NestedStruct p) SWIFT_NAME("MyNS.NestedStruct.method(self:)") { return p.value; }
+int nestedStruct_methodConstRef(const MyNS::NestedStruct &p) SWIFT_NAME("MyNS.NestedStruct.methodConstRef(self:)") { return p.value + 1; }
+
+namespace MyNS {
+namespace MyDeepNS {
+struct DeepNestedStruct {
+  int value = 456;
+};
+}
+}
+
+int deepNestedStruct_method(MyNS::MyDeepNS::DeepNestedStruct p) SWIFT_NAME("MyNS.MyDeepNS.DeepNestedStruct.method(self:)") { return p.value; }
+int deepNestedStruct_methodConstRef(const MyNS::MyDeepNS::DeepNestedStruct &p) SWIFT_NAME("MyNS.MyDeepNS.DeepNestedStruct.methodConstRef(self:)") { return p.value + 2; }
+
+typedef MyNS::MyDeepNS::DeepNestedStruct DeepNestedStructTypedef;
+
+int deepNestedStructTypedef_method(DeepNestedStructTypedef p) SWIFT_NAME("DeepNestedStructTypedef.methodTypedef(self:)") { return p.value + 3; }
+int deepNestedStructTypedef_methodQualName(MyNS::MyDeepNS::DeepNestedStruct p) SWIFT_NAME("DeepNestedStructTypedef.methodTypedefQualName(self:)") { return p.value + 4; }

test/Interop/Cxx/namespace/Inputs/module.modulemap

@@ -60,6 +60,12 @@ module Enums {
   requires cplusplus
 }
 
+module ImportAsMember {
+  header "import-as-member.h"
+  export *
+  requires cplusplus
+}
+
 module MembersDirect {
   header "members-direct.h"
   requires cplusplus

test/Interop/Cxx/namespace/import-as-member-module-interface.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-ide-test -print-module -module-to-print=ImportAsMember -I %S/Inputs -source-filename=x -cxx-interoperability-mode=upcoming-swift | %FileCheck %s
+
+// CHECK:      extension MyNS.NestedStruct {
+// CHECK-NEXT:   func method() -> Int32
+// CHECK-NEXT:   func methodConstRef() -> Int32
+// CHECK-NEXT: }
+
+// CHECK:      extension MyNS.MyDeepNS.DeepNestedStruct {
+// CHECK-NEXT:   func method() -> Int32
+// CHECK-NEXT:   func methodConstRef() -> Int32
+// CHECK-NEXT:   func methodTypedef() -> Int32
+// CHECK-NEXT:   func methodTypedefQualName() -> Int32
+// CHECK-NEXT: }

test/Interop/Cxx/namespace/import-as-member-typechecker.swift

@@ -0,0 +1,19 @@
+// RUN: %target-typecheck-verify-swift -I %S/Inputs -cxx-interoperability-mode=upcoming-swift
+
+import ImportAsMember
+
+func takesNestedStruct(_ s: MyNS.NestedStruct) {
+  _ = s.method()
+  _ = s.methodConstRef()
+
+  _ = nestedStruct_method(s) // expected-error {{'nestedStruct_method' has been replaced by instance method 'MyNS.NestedStruct.method()'}}
+}
+
+func takesDeepNestedStruct(_ s: MyNS.MyDeepNS.DeepNestedStruct) {
+  _ = s.method()
+  _ = s.methodConstRef()
+  _ = s.methodTypedef()
+  _ = s.methodTypedefQualName()
+
+  _ = deepNestedStruct_method(s) // expected-error {{'deepNestedStruct_method' has been replaced by instance method 'MyNS.MyDeepNS.DeepNestedStruct.method()'}}
+}

test/Interop/Cxx/namespace/import-as-member.swift

@@ -0,0 +1,24 @@
+// RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -cxx-interoperability-mode=upcoming-swift)
+
+// REQUIRES: executable_test
+
+import StdlibUnittest
+import ImportAsMember
+
+var NamespacesTestSuite = TestSuite("Import as member of namespace")
+
+NamespacesTestSuite.test("Struct in a namespace") {
+  let s = MyNS.NestedStruct()
+  expectEqual(123, s.method())
+  expectEqual(124, s.methodConstRef())
+}
+
+NamespacesTestSuite.test("Struct in a deep namespace") {
+  let s = MyNS.MyDeepNS.DeepNestedStruct()
+  expectEqual(456, s.method())
+  expectEqual(458, s.methodConstRef())
+  expectEqual(459, s.methodTypedef())
+  expectEqual(460, s.methodTypedefQualName())
+}
+
+runAllTests()