6835428: regression: return-type inference rejects valid code

Redundant subtyping test during type-inference ends up in rejecting legal code

Reviewed-by: jjg

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

@@ -158,8 +158,7 @@ public class Infer {
                 that.inst = types.glb(that.hibounds);
         }
         if (that.inst == null ||
-            that.inst.isErroneous() ||
+            that.inst.isErroneous())
-            !types.isSubtypeUnchecked(that.inst, that.hibounds, warn))
             throw ambiguousNoInstanceException
                 .setMessage("no.unique.maximal.instance.exists",
                             that.qtype, that.hibounds);

langtools/test/tools/javac/generics/inference/T6835428.java

@@ -0,0 +1,38 @@
+/*
+ * 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 6835428
+ * @author mcimadamore
+ * @summary regression: return-type inference rejects valid code
+ * @compile T6835428.java
+ */
+
+class T6835428<T> {
+    interface X<T> {}
+   <T extends Comparable<? super T>> T6835428<X<T>> m() { return null; }
+   <T extends Comparable<? super T>> void test() {
+      T6835428<X<T>> t = m();
+   }
+}