6880344: Recursive type parameters do not compile

Issue in type-variable substitution causes valid code to be rejected

Reviewed-by: jjg

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

@@ -588,10 +588,21 @@ public class Types {
                 case BYTE: case CHAR: case SHORT: case INT: case LONG: case FLOAT:
                 case DOUBLE: case BOOLEAN: case VOID: case BOT: case NONE:
                     return t.tag == s.tag;
-                case TYPEVAR:
+                case TYPEVAR: {
-                    return s.isSuperBound()
+                    if (s.tag == TYPEVAR) {
-                        && !s.isExtendsBound()
+                        //type-substitution does not preserve type-var types
-                        && visit(t, upperBound(s));
+                        //check that type var symbols and bounds are indeed the same
+                        return t.tsym == s.tsym &&
+                                visit(t.getUpperBound(), s.getUpperBound());
+                    }
+                    else {
+                        //special case for s == ? super X, where upper(s) = u
+                        //check that u == t, where u has been set by Type.withTypeVar
+                        return s.isSuperBound() &&
+                                !s.isExtendsBound() &&
+                                visit(t, upperBound(s));
+                    }
+                }
                 default:
                     throw new AssertionError("isSameType " + t.tag);
                 }

langtools/src/share/classes/com/sun/tools/javac/comp/Check.java

@@ -915,7 +915,7 @@ public class Check {
                 List<Type> actuals = tree.type.allparams();
                 List<JCExpression> args = tree.arguments;
                 List<Type> forms = tree.type.tsym.type.getTypeArguments();
-                ListBuffer<TypeVar> tvars_buf = new ListBuffer<TypeVar>();
+                ListBuffer<Type> tvars_buf = new ListBuffer<Type>();
 
                 // For matching pairs of actual argument types `a' and
                 // formal type parameters with declared bound `b' ...
@@ -946,12 +946,15 @@ public class Check {
                 }
 
                 args = tree.arguments;
-                List<TypeVar> tvars = tvars_buf.toList();
+                List<Type> tvars = tvars_buf.toList();
 
                 while (args.nonEmpty() && tvars.nonEmpty()) {
+                    Type actual = types.subst(args.head.type,
+                        tree.type.tsym.type.getTypeArguments(),
+                        tvars_buf.toList());
                     checkExtends(args.head.pos(),
-                                 args.head.type,
+                                 actual,
-                                 tvars.head);
+                                 (TypeVar)tvars.head);
                     args = args.tail;
                     tvars = tvars.tail;
                 }

langtools/test/tools/javac/generics/typevars/T6880344.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2009 Sun Microsystems, Inc.  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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * @test
+ * @bug     6880344
+ * @summary Recursive type parameters do not compile
+ * @author  mcimadamore
+ * @compile T6880344.java
+ */
+
+class T6880344 {
+    static class A<X1 extends G<X1>> {
+        public A<N<X1>> xyz;
+    }
+
+    static class N<X2 extends G<X2>> implements G<N<X2>> { }
+
+    interface G<X3 extends G<X3>> { }
+}