Allow private or protected access flags for inner classes.

asm-util/src/main/java/org/objectweb/asm/util/CheckClassAdapter.java

@@ -215,8 +215,7 @@ public class CheckClassAdapter extends ClassVisitor {
     }
     visitCalled = true;
     checkState();
-    checkAccess(
-        access,
+    int validAccessFlags =
         Opcodes.ACC_PUBLIC
             | Opcodes.ACC_FINAL
             | Opcodes.ACC_SUPER
@@ -227,10 +226,14 @@ public class CheckClassAdapter extends ClassVisitor {
             | Opcodes.ACC_ENUM
             | Opcodes.ACC_DEPRECATED
             | Opcodes.ACC_RECORD
-            | Opcodes.ACC_MODULE);
+            | Opcodes.ACC_MODULE;
     if (name == null) {
       throw new IllegalArgumentException("Illegal class name (null)");
     }
+    if (name.contains("$")) {
+      validAccessFlags |= Opcodes.ACC_PROTECTED | Opcodes.ACC_PRIVATE;
+    }
+    checkAccess(access, validAccessFlags);
     if (!name.endsWith("package-info") && !name.endsWith("module-info")) {
       CheckMethodAdapter.checkInternalName(version, name, "class name");
     }

asm-util/src/test/java/org/objectweb/asm/util/CheckClassAdapterTest.java

@@ -6,13 +6,13 @@
 // modification, are permitted provided that the following conditions
 // are met:
 // 1. Redistributions of source code must retain the above copyright
-//    notice, this list of conditions and the following disclaimer.
+// notice, this list of conditions and the following disclaimer.
 // 2. Redistributions in binary form must reproduce the above copyright
-//    notice, this list of conditions and the following disclaimer in the
-//    documentation and/or other materials provided with the distribution.
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution.
 // 3. Neither the name of the copyright holders nor the names of its
-//    contributors may be used to endorse or promote products derived from
-//    this software without specific prior written permission.
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
@@ -78,6 +78,30 @@ public class CheckClassAdapterTest extends AsmTest implements Opcodes {
     assertEquals("Invalid access flags: 1048576", exception.getMessage());
   }
 
+  @Test
+  public void testVisit_illegalPrivateClassAccessFlagForNonInnerClass() {
+    CheckClassAdapter checkClassAdapter = new CheckClassAdapter(null);
+
+    Executable visit =
+        () ->
+            checkClassAdapter.visit(V1_1, Opcodes.ACC_PRIVATE, "C", null, "java/lang/Object", null);
+
+    Exception exception = assertThrows(IllegalArgumentException.class, visit);
+    assertEquals("Invalid access flags: 2", exception.getMessage());
+  }
+
+  @Test
+  public void testVisit_legalPrivateClassAccessFlagForInnerClass() {
+    CheckClassAdapter checkClassAdapter = new CheckClassAdapter(null);
+
+    Executable visit =
+        () ->
+            checkClassAdapter.visit(
+                V1_1, Opcodes.ACC_PRIVATE, "C$Inner", null, "java/lang/Object", null);
+
+    assertDoesNotThrow(visit);
+  }
+
   @Test
   public void testVisit_illegalClassName() {
     CheckClassAdapter checkClassAdapter = new CheckClassAdapter(null);