8055963: Inference failure with nested invocation

Summary: Revise heuristics to force eager instantiation of return inference vars
Reviewed-by: vromero

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

@@ -315,11 +315,9 @@ public class Infer {
             for (Type aLowerBound : from.getBounds(InferenceBound.LOWER)) {
                 for (Type anotherLowerBound : from.getBounds(InferenceBound.LOWER)) {
                     if (aLowerBound != anotherLowerBound &&
-                        commonSuperWithDiffParameterization(aLowerBound, anotherLowerBound)) {
-                        /* self comment check if any lower bound may be and undetVar,
-                         * in that case the result of this call may be a false positive.
-                         * Should this be restricted to non free types?
-                         */
+                            !inferenceContext.free(aLowerBound) &&
+                            !inferenceContext.free(anotherLowerBound) &&
+                            commonSuperWithDiffParameterization(aLowerBound, anotherLowerBound)) {
                         return generateReferenceToTargetConstraint(tree, from, to,
                             resultInfo, inferenceContext);
                     }

test/tools/javac/generics/inference/8055963/T8055963.java

+/*
+ * Copyright (c) 2014, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8055963
+ * @summary Inference failure with nested invocation
+ * @compile T8055963.java
+ */
+class T8055963 {
+
+    static class C<T> {}
+
+    <T> T choose(T first, T second) { return null; }
+
+    void test() {
+        C<String> cs = choose(new C<String>(), new C<>());
+    }
+}