Don't scan into nested enums in ClassInitializationDeadlock

#4378

PiperOrigin-RevId: 629452163

Author: cushon

core/src/main/java/com/google/errorprone/bugpatterns/ClassInitializationDeadlock.java

@@ -71,7 +71,7 @@ public Description matchClass(ClassTree tree, VisitorState state) {
       @Override
       public Void visitClass(ClassTree node, Void unused) {
         for (Tree member : node.getMembers()) {
-          if (member.getKind().equals(Tree.Kind.CLASS)) {
+          if (member instanceof ClassTree) {
             continue;
           }
           scan(member, null);

core/src/test/java/com/google/errorprone/bugpatterns/ClassInitializationDeadlockTest.java

@@ -266,4 +266,34 @@ public void negativeNonPrivateUnrelatedSuper() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void nestedEnum() {
+    testHelper
+        .addSourceLines(
+            "TestInterface.java", //
+            "public interface TestInterface {",
+            "  default Object foo() {",
+            "    return null;",
+            "  }",
+            "  enum TestEnum implements TestInterface {",
+            "    INSTANCE;",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void nestedInterface() {
+    testHelper
+        .addSourceLines(
+            "Foo.java", //
+            "interface Foo {",
+            "  default void foo() {}",
+            "  interface Sub extends Foo {",
+            "    final Sub INSTANCE = new Sub() {};",
+            "  }",
+            "}")
+        .doTest();
+  }
 }