When default @SwiftName rules are being applied, this update changes the Swift names of inner Java interfaces and of types declared within Java interfaces. Previously, if an interface Bar was declared within a type Foo or a concrete type Bar was declared within an interface Foo, they would be translated to a top-level type with Swift name Bar. This could cause problems if another inner type with the same name was also promoted. Now the Swift type name in each of these cases will be formed by concatenating the outer and inner type names: FooBar. This matches KMP's Swift naming of inner interfaces and of concrete types within interfaces.

translator/src/main/java/com/google/devtools/j2objc/gen/TypeDeclarationGenerator.java

@@ -226,7 +226,7 @@ private void printNativeEnum() {
       print("}");
 
       if (!printPrivateDeclarations()) {
-        String swiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement, true);
+        String swiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement);
         if (swiftName != null) {
           printf(" NS_SWIFT_NAME(%sEnum)", swiftName);
         }
@@ -337,7 +337,7 @@ private void printSwiftName() {
       return;
     }
 
-    String swiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement, true);
+    String swiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement);
     // We need to force NS_SWIFT_NAME in this case; otherwise swift confuses this with some kind
     // of legacy name that was not migrated and errors.
     if (swiftName == null && typeElement.getKind().isInterface() && needsCompanionClass()) {
@@ -493,7 +493,7 @@ protected void printCompanionClassDeclaration() {
       return;
     }
     if (hasCompanionSuffix()) {
-      String baseSwiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement, true);
+      String baseSwiftName = nameTable.getSwiftClassNameFromAnnotation(typeElement);
       String companionSwiftName = baseSwiftName != null ? baseSwiftName : typeName;
       printf("\nNS_SWIFT_NAME(%sCompanion)", companionSwiftName);
       printf("\n@interface %sCompanion : NSObject", typeName);

translator/src/main/java/com/google/devtools/j2objc/util/NameTable.java

@@ -634,31 +634,60 @@ private boolean hasMethodWithSelector(TypeElement clazz, String selector) {
     return Iterables.any(ElementUtil.getMethods(clazz), m -> getMethodSelector(m).equals(selector));
   }
 
-  public @Nullable String getSwiftClassNameFromAnnotation(TypeElement clazz, boolean getParents) {
+  public @Nullable String getSwiftClassNameFromAnnotation(TypeElement clazz) {
     String annotationName = swiftNameFromAnnotation(clazz);
     if (annotationName != null) {
       return annotationName;
     }
 
+    NestingKind nesting = clazz.getNestingKind();
+    if (nesting == NestingKind.MEMBER) {
+      Element parent = clazz.getEnclosingElement();
+      if (parent instanceof TypeElement parentElement) {
+        // Protocols are named by concatenating the interface name and names of the parent type
+        // hierarchy. Any types declared within an interface are also named by concatenating the
+        // inner type name to the parent interface name. E.g. FooBar rather than Foo.Bar.
+        if (clazz.getKind().isInterface() || parentElement.getKind().isInterface()) {
+          return getFlatSwiftClassName(clazz);
+        }
+        String parentName = getSwiftClassNameFromAnnotation(parentElement);
+        if (parentName != null) {
+          return (parentName + "." + clazz.getSimpleName()).replace("$", "");
+        }
+      }
+    }
+
     if (!packageHasSwiftNameAnnotation(clazz) && !elementHasSwiftNameAnnotation(clazz)) {
       return null;
     }
 
-    if (getParents) {
-      NestingKind nesting = clazz.getNestingKind();
-      if (nesting == NestingKind.MEMBER) {
-        Element parent = clazz.getEnclosingElement();
-        if (parent instanceof TypeElement parentElement && !parent.getKind().isInterface()) {
-          String parentName = getSwiftClassNameFromAnnotation(parentElement, false);
-          if (parentName != null) {
-            return (parentName + "." + clazz.getSimpleName()).replace("$", "");
-          }
-        }
+    String className = clazz.getSimpleName().toString();
+    return className.replace("$", "");
+  }
+
+  private @Nullable String getFlatSwiftClassName(TypeElement clazz) {
+    List<String> hierarchy = new ArrayList<>();
+    Element current = clazz;
+    boolean hasSwiftName = packageHasSwiftNameAnnotation(clazz);
+    while (current instanceof TypeElement typeElement) {
+      String annotationName = swiftNameFromAnnotation(typeElement);
+      if (annotationName != null && !annotationName.isEmpty()) {
+        hierarchy.add(annotationName);
+        hasSwiftName = true;
+        break;
       }
+      hierarchy.add(typeElement.getSimpleName().toString().replace("$", ""));
+      if (elementHasSwiftNameAnnotation(typeElement)) {
+        hasSwiftName = true;
+      }
+      current = typeElement.getEnclosingElement();
     }
 
-    String className = clazz.getSimpleName().toString();
-    return className.replace("$", "");
+    if (!hasSwiftName) {
+      return null;
+    }
+
+    return String.join("", hierarchy.reversed());
   }
 
   public @Nullable String getSwiftFunctionNameFromAnnotation(FunctionDeclaration function) {
@@ -686,7 +715,7 @@ private boolean hasMethodWithSelector(TypeElement clazz, String selector) {
       return null;
     }
 
-    String className = getSwiftClassNameFromAnnotation(owner, false);
+    String className = getSwiftClassNameFromAnnotation(owner);
     if (className == null) {
       // There isn't nice naming so fallback to the normal ObjC class name
       className = getObjCType(owner.asType()).replace(" *", "");

translator/src/test/java/com/google/devtools/j2objc/gen/ObjectiveCHeaderGeneratorTest.java

@@ -1849,9 +1849,128 @@ public void testSwiftNameInterfaceSubtype() throws IOException {
             + "  public final class NestedBar {}"
             + "}";
     String translation = translateSourceFile(sourceContent, "FooBar", "com/foo/bar/FooBar.h");
-    assertInTranslation(translation, "NS_SWIFT_NAME(MyEnumEnum)");
-    assertInTranslation(translation, "NS_SWIFT_NAME(MyEnum)");
-    assertInTranslation(translation, "NS_SWIFT_NAME(NestedBar)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBarMyEnumEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBarMyEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBarNestedBar)");
+  }
+
+  public void testSwiftNameDeepNestingInInterface() throws IOException {
+    addSourceFile(
+        "@SwiftName "
+            + "package com.foo.bar;"
+            + ""
+            + "import com.google.j2objc.annotations.SwiftName;",
+        "com/foo/bar/package-info.java");
+
+    String sourceContent =
+        """
+        package com.foo.bar;
+        public interface OuterInterface {
+          public class InnerClass {
+            public enum InnerEnum { A, B }
+          }
+        }
+        """;
+    String translation =
+        translateSourceFile(sourceContent, "OuterInterface", "com/foo/bar/OuterInterface.h");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterInterfaceInnerClass)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterInterfaceInnerClass.InnerEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterInterfaceInnerClass.InnerEnumEnum)");
+  }
+
+  public void testSwiftNameExplicitAnnotationOnNestedType() throws IOException {
+    addSourceFile(
+        "@SwiftName "
+            + "package com.foo.bar;"
+            + ""
+            + "import com.google.j2objc.annotations.SwiftName;",
+        "com/foo/bar/package-info.java");
+
+    String sourceContent =
+        """
+        package com.foo.bar;
+        import com.google.j2objc.annotations.SwiftName;
+        public interface OuterInterface {
+          @SwiftName("CustomName")
+          public class InnerClass {
+            public enum InnerEnum { A, B }
+          }
+        }
+        """;
+    String translation =
+        translateSourceFile(sourceContent, "OuterInterface", "com/foo/bar/OuterInterface.h");
+    assertInTranslation(translation, "NS_SWIFT_NAME(CustomName)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(CustomName.InnerEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(CustomName.InnerEnumEnum)");
+  }
+
+  public void testSwiftNameExplicitAnnotationOnInterface() throws IOException {
+    String sourceContent =
+        """
+        package com.foo.bar;
+        import com.google.j2objc.annotations.SwiftName;
+        @SwiftName("CustomInterface")
+        public interface OuterInterface {
+          public enum InnerEnum { A, B }
+        }
+        """;
+    String translation =
+        translateSourceFile(sourceContent, "OuterInterface", "com/foo/bar/OuterInterface.h");
+    assertInTranslation(translation, "NS_SWIFT_NAME(CustomInterfaceInnerEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(CustomInterfaceInnerEnumEnum)");
+  }
+
+  public void testSwiftNameInterfaceInsideClass() throws IOException {
+    addSourceFile(
+        "@SwiftName "
+            + "package com.foo.bar;"
+            + ""
+            + "import com.google.j2objc.annotations.SwiftName;",
+        "com/foo/bar/package-info.java");
+
+    String sourceContent =
+        """
+        package com.foo.bar;
+        public class Foo {
+          public interface Bar {
+            public enum Baz { A, B }
+          }
+          public class Biz {}
+        }
+        """;
+    String translation =
+        translateSourceFile(sourceContent, "Foo", "com/foo/bar/Foo.h");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBar)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBarBaz)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(FooBarBazEnum)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(Foo.Biz)");
+  }
+
+  public void testSwiftNameInterfaceInsideNestedClass() throws IOException {
+    addSourceFile(
+        "@SwiftName "
+            + "package com.foo.bar;"
+            + ""
+            + "import com.google.j2objc.annotations.SwiftName;",
+        "com/foo/bar/package-info.java");
+
+    String sourceContent =
+        """
+        package com.foo.bar;
+        public class Outer {
+          public class Middle {
+            public interface Inner {
+              public enum Baz { A, B }
+            }
+          }
+        }
+        """;
+    String translation =
+        translateSourceFile(sourceContent, "Outer", "com/foo/bar/Outer.h");
+    assertInTranslation(translation, "NS_SWIFT_NAME(Outer.Middle)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterMiddleInner)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterMiddleInnerBaz)");
+    assertInTranslation(translation, "NS_SWIFT_NAME(OuterMiddleInnerBazEnum)");
   }
 
   public void testMethodSorting() throws IOException {