8008627: Compiler mishandles three-way return-type-substitutability

Compiler should not enforce an order in how ambiguous methods should be resolved

Reviewed-by: jjg, vromero

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

@@ -1924,24 +1924,11 @@ public class Check {
                 Symbol s3 = e.sym;
                 if (s3 == s1 || s3 == s2 || s3.kind != MTH || (s3.flags() & (BRIDGE|SYNTHETIC)) != 0) continue;
                 Type st3 = types.memberType(site,s3);
-                if (types.overrideEquivalent(st3, st1) && types.overrideEquivalent(st3, st2)) {
-                    if (s3.owner == site.tsym) {
-                        return true;
-                    }
-                    List<Type> tvars1 = st1.getTypeArguments();
-                    List<Type> tvars2 = st2.getTypeArguments();
-                    List<Type> tvars3 = st3.getTypeArguments();
-                    Type rt1 = st1.getReturnType();
-                    Type rt2 = st2.getReturnType();
-                    Type rt13 = types.subst(st3.getReturnType(), tvars3, tvars1);
-                    Type rt23 = types.subst(st3.getReturnType(), tvars3, tvars2);
-                    boolean compat =
-                        !rt13.isPrimitiveOrVoid() &&
-                        !rt23.isPrimitiveOrVoid() &&
-                        (types.covariantReturnType(rt13, rt1, types.noWarnings) &&
-                         types.covariantReturnType(rt23, rt2, types.noWarnings));
-                    if (compat)
-                        return true;
+                if (types.overrideEquivalent(st3, st1) &&
+                        types.overrideEquivalent(st3, st2) &&
+                        types.returnTypeSubstitutable(st3, st1) &&
+                        types.returnTypeSubstitutable(st3, st2)) {
+                    return true;
                 }
             }
         }

langtools/test/tools/javac/generics/rawOverride/T8008627.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2013, 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.
+ *
+ * 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 8008627
+ * @summary Compiler mishandles three-way return-type-substitutability
+ * @compile T8008627.java
+ */
+
+class T8008627 {
+
+    interface I {
+        Object m(Iterable l);
+    }
+
+    interface J<S> {
+        S m(Iterable<String> l);
+    }
+
+    interface K<T> {
+        T m(Iterable<String> l);
+    }
+
+    @FunctionalInterface
+    interface Functional<S,T> extends I, J<S>, K<T> {}
+}

langtools/test/tools/javac/lambda/funcInterfaces/NonSAM2.java

@@ -13,7 +13,7 @@ interface Bar1 { Integer getAge(String s);}
 interface Foo1Bar1 extends Foo1, Bar1 {} //types Bar1 and Foo1 are incompatible; both define getAge(String), but with unrelated return types
 
 interface AC extends A, C {} //name clash: getOldest(List<?>) in C and getOldest(List<Number>) in A have the same erasure, yet neither overrides the other
-interface ABC extends A, B, C {} //name clash: getOldest(List<?>) in C and getOldest(List<Number>) in A have the same erasure, yet neither overrides the other
+interface ABC extends A, B, C {} //ok - raw override
 interface AD extends A, D {} //name clash: getOldest(List<Integer>) in D and getOldest(List<Number>) in A have the same erasure, yet neither overrides the other
 
 interface Foo2<T> { void m(T arg);}

langtools/test/tools/javac/lambda/funcInterfaces/NonSAM2.out

@@ -1,6 +1,5 @@
 NonSAM2.java:13:1: compiler.err.types.incompatible.diff.ret: Bar1, Foo1, getAge(java.lang.String)
 NonSAM2.java:15:1: compiler.err.name.clash.same.erasure.no.override: getOldest(java.util.List<?>), C, getOldest(java.util.List<java.lang.Number>), A
-NonSAM2.java:16:1: compiler.err.name.clash.same.erasure.no.override: getOldest(java.util.List<?>), C, getOldest(java.util.List<java.lang.Number>), A
 NonSAM2.java:17:1: compiler.err.name.clash.same.erasure.no.override: getOldest(java.util.List<java.lang.Integer>), D, getOldest(java.util.List<java.lang.Number>), A
 NonSAM2.java:21:1: compiler.err.name.clash.same.erasure.no.override: m(S), Bar2, m(T), Foo2
-5 errors
+4 errors