8258972: unexpected compilation error with generic sealed interface

Reviewed-by: jlahoda

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java

@@ -1667,11 +1667,11 @@ public class Types {
     }
     // where
         private boolean areDisjoint(ClassSymbol ts, ClassSymbol ss) {
-            if (isSubtype(ts.type, ss.type)) {
+            if (isSubtype(erasure(ts.type), erasure(ss.type))) {
                 return false;
             }
             // if both are classes or both are interfaces, shortcut
-            if (ts.isInterface() == ss.isInterface() && isSubtype(ss.type, ts.type)) {
+            if (ts.isInterface() == ss.isInterface() && isSubtype(erasure(ss.type), erasure(ts.type))) {
                 return false;
             }
             if (ts.isInterface() && !ss.isInterface()) {

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

@@ -1247,6 +1247,17 @@ public class SealedCompilationTests extends CompilationTestCase {
                      a = (A)c;
                   }
                 }
+                """,
+                """
+                sealed interface A<T> {
+                    final class B implements A<Object> { }
+                }
+
+                class Test {
+                    void f(A.B a, A<Object> b) {
+                        a = (A.B)b;
+                    }
+                }
                 """
         )) {
             assertOK(s);