8024947: javac should issue the potentially ambiguous overload warning only...

8024947: javac should issue the potentially ambiguous overload warning only where the problem appears
Reviewed-by: jjg

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

@@ -2399,13 +2399,28 @@ public class Check {
          ClashFilter cf = new ClashFilter(site);
         //for each method m1 that is overridden (directly or indirectly)
         //by method 'sym' in 'site'...
+
+        List<MethodSymbol> potentiallyAmbiguousList = List.nil();
+        boolean overridesAny = false;
         for (Symbol m1 : types.membersClosure(site, false).getElementsByName(sym.name, cf)) {
-             if (!sym.overrides(m1, site.tsym, types, false)) {
-                 checkPotentiallyAmbiguousOverloads(pos, site, sym, (MethodSymbol)m1);
-                 continue;
-             }
-             //...check each method m2 that is a member of 'site'
-             for (Symbol m2 : types.membersClosure(site, false).getElementsByName(sym.name, cf)) {
+            if (!sym.overrides(m1, site.tsym, types, false)) {
+                if (m1 == sym) {
+                    continue;
+                }
+
+                if (!overridesAny) {
+                    potentiallyAmbiguousList = potentiallyAmbiguousList.prepend((MethodSymbol)m1);
+                }
+                continue;
+            }
+
+            if (m1 != sym) {
+                overridesAny = true;
+                potentiallyAmbiguousList = List.nil();
+            }
+
+            //...check each method m2 that is a member of 'site'
+            for (Symbol m2 : types.membersClosure(site, false).getElementsByName(sym.name, cf)) {
                 if (m2 == m1) continue;
                 //if (i) the signature of 'sym' is not a subsignature of m1 (seen as
                 //a member of 'site') and (ii) m1 has the same erasure as m2, issue an error
@@ -2424,9 +2439,13 @@ public class Check {
                 }
             }
         }
-    }
-
 
+        if (!overridesAny) {
+            for (MethodSymbol m: potentiallyAmbiguousList) {
+                checkPotentiallyAmbiguousOverloads(pos, site, sym, m);
+            }
+        }
+    }
 
     /** Check that all static methods accessible from 'site' are
      *  mutually compatible (JLS 8.4.8).

test/tools/javac/lambda/T8024947/PotentiallyAmbiguousWarningTest.java

+/*
+ * 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 8024947
+ * @summary javac should issue the potentially ambiguous overload warning only
+ * where the problem appears
+ * @compile/fail/ref=PotentiallyAmbiguousWarningTest.out -XDrawDiagnostics -Werror -Xlint:overloads PotentiallyAmbiguousWarningTest.java
+ * @compile PotentiallyAmbiguousWarningTest.java
+ */
+
+import java.util.function.*;
+
+public interface PotentiallyAmbiguousWarningTest {
+
+    //a warning should be fired
+    interface I1 {
+        void foo(Consumer<Integer> c);
+        void foo(IntConsumer c);
+    }
+
+    //a warning should be fired
+    class C1 {
+        void foo(Consumer<Integer> c) { }
+        void foo(IntConsumer c) { }
+    }
+
+    interface I2 {
+        void foo(Consumer<Integer> c);
+    }
+
+    //a warning should be fired, J1 is provoking the issue
+    interface J1 extends I2 {
+        void foo(IntConsumer c);
+    }
+
+    //no warning here, the issue is introduced in I1
+    interface I3 extends I1 {}
+
+    //no warning here, the issue is introduced in I1. I4 is just overriding an existing method
+    interface I4 extends I1 {
+        void foo(IntConsumer c);
+    }
+
+    class C2 {
+        void foo(Consumer<Integer> c) { }
+    }
+
+    //a warning should be fired, D1 is provoking the issue
+    class D1 extends C2 {
+        void foo(IntConsumer c) { }
+    }
+
+    //a warning should be fired, C3 is provoking the issue
+    class C3 implements I2 {
+        public void foo(Consumer<Integer> c) { }
+        public void foo(IntConsumer c) { }
+    }
+
+    //no warning here, the issue is introduced in C1
+    class C4 extends C1 {}
+
+    //no warning here, the issue is introduced in C1. C5 is just overriding an existing method
+    class C5 extends C1 {
+        void foo(IntConsumer c) {}
+    }
+
+    interface I5<T> {
+        void foo(T c);
+    }
+
+    //a warning should be fired, J2 is provoking the issue
+    interface J2 extends I5<IntConsumer> {
+        void foo(Consumer<Integer> c);
+    }
+}

test/tools/javac/lambda/T8024947/PotentiallyAmbiguousWarningTest.out

+PotentiallyAmbiguousWarningTest.java:39:14: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.I1, foo(java.util.function.IntConsumer), PotentiallyAmbiguousWarningTest.I1
+PotentiallyAmbiguousWarningTest.java:45:14: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.C1, foo(java.util.function.IntConsumer), PotentiallyAmbiguousWarningTest.C1
+PotentiallyAmbiguousWarningTest.java:55:14: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.IntConsumer), PotentiallyAmbiguousWarningTest.J1, foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.I2
+PotentiallyAmbiguousWarningTest.java:72:14: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.IntConsumer), PotentiallyAmbiguousWarningTest.D1, foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.C2
+PotentiallyAmbiguousWarningTest.java:78:21: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.IntConsumer), PotentiallyAmbiguousWarningTest.C3, foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.C3
+PotentiallyAmbiguousWarningTest.java:95:14: compiler.warn.potentially.ambiguous.overload: foo(java.util.function.Consumer<java.lang.Integer>), PotentiallyAmbiguousWarningTest.J2, foo(T), PotentiallyAmbiguousWarningTest.I5
+- compiler.err.warnings.and.werror
+1 error
+6 warnings