8347562: javac crash due to type vars in permits clause

Reviewed-by: vromero

Author: SirYwell

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -875,7 +875,7 @@ public Object attribLazyConstantValue(Env<AttrContext> env,
         }
     }
 
-    /** Attribute type reference in an `extends' or `implements' clause.
+    /** Attribute type reference in an `extends', `implements', or 'permits' clause.
      *  Supertypes of anonymous inner classes are usually already attributed.
      *
      *  @param tree              The tree making up the type reference.
@@ -5407,6 +5407,10 @@ void attribClass(ClassSymbol c) throws CompletionFailure {
                     Set<Symbol> permittedTypes = new HashSet<>();
                     boolean sealedInUnnamed = c.packge().modle == syms.unnamedModule || c.packge().modle == syms.noModule;
                     for (Type subType : c.getPermittedSubclasses()) {
+                        if (subType.isErroneous()) {
+                            // the type already caused errors, don't produce more potentially misleading errors
+                            continue;
+                        }
                         boolean isTypeVar = false;
                         if (subType.getTag() == TYPEVAR) {
                             isTypeVar = true; //error recovery

test/langtools/tools/javac/sealed/SealedCompilationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,7 +25,7 @@
  * SealedCompilationTests
  *
  * @test
- * @bug 8246353 8273257 8294550
+ * @bug 8246353 8273257 8294550 8347562
  * @summary Negative compilation tests, and positive compilation (smoke) tests for sealed classes
  * @library /lib/combo /tools/lib
  * @modules
@@ -41,6 +41,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -61,6 +62,7 @@
 import toolbox.Task;
 import toolbox.Task.OutputKind;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
 
 class SealedCompilationTests extends CompilationTestCase {
@@ -560,6 +562,13 @@ sealed class C permits T  {}
             """)) {
             assertFail("compiler.err.invalid.permits.clause", s);
         }
+        assertFail("compiler.err.illegal.forward.ref", _ -> {
+                assertEquals(Collections.nCopies(2, "compiler.err.illegal.forward.ref"), diags.keys());
+            },
+            """
+            sealed class Permits<X, Y> permits X, Y {}
+            """
+        );
     }
 
     @Test