6294779: Problem with interface inheritance and covariant return types

Summary: Problematic overriding check when two methods defined in two distinct superinterfaces are overriden by an interface
Reviewed-by: jjg

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

@@ -1367,13 +1367,47 @@ public class Check {
                         types.isSameType(rt1, rt2) ||
                         rt1.tag >= CLASS && rt2.tag >= CLASS &&
                         (types.covariantReturnType(rt1, rt2, Warner.noWarnings) ||
-                         types.covariantReturnType(rt2, rt1, Warner.noWarnings));
+                         types.covariantReturnType(rt2, rt1, Warner.noWarnings)) ||
+                         checkCommonOverriderIn(s1,s2,site);
                     if (!compat) return s2;
                 }
             }
         }
         return null;
     }
+    //WHERE
+    boolean checkCommonOverriderIn(Symbol s1, Symbol s2, Type site) {
+        Map<TypeSymbol,Type> supertypes = new HashMap<TypeSymbol,Type>();
+        Type st1 = types.memberType(site, s1);
+        Type st2 = types.memberType(site, s2);
+        closure(site, supertypes);
+        for (Type t : supertypes.values()) {
+            for (Scope.Entry e = t.tsym.members().lookup(s1.name); e.scope != null; e = e.next()) {
+                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.tag >= CLASS && rt23.tag >= CLASS &&
+                        (types.covariantReturnType(rt13, rt1, Warner.noWarnings) &&
+                         types.covariantReturnType(rt23, rt2, Warner.noWarnings));
+                    if (compat)
+                        return true;
+                }
+            }
+        }
+        return false;
+    }
 
     /** Check that a given method conforms with any method it overrides.
      *  @param tree         The tree from which positions are extracted

test/tools/javac/generics/6294779/T6294779a.java

+/*
+ * Copyright 2008 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     6294779
+ * @summary Problem with interface inheritance and covariant return types
+ * @author  Maurizio Cimadamore
+ * @compile T6294779a.java
+ */
+
+public class T6294779a {
+
+    interface A {
+        A m();
+    }
+
+    interface B extends A {
+        B m();
+    }
+
+    interface C extends A {
+        C m();
+    }
+
+    interface D extends B, C {
+        D m();
+    }
+}

test/tools/javac/generics/6294779/T6294779b.java

+/*
+ * Copyright 2008 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     6294779
+ * @summary Problem with interface inheritance and covariant return types
+ * @author  Maurizio Cimadamore
+ * @compile T6294779b.java
+ */
+
+import java.util.*;
+
+class T6294779b {
+
+    interface I1<E> {
+        List<E> m();
+    }
+
+    interface I2<E> {
+        Queue<E> m();
+    }
+
+    interface I3<E> {
+        LinkedList<E> m();
+    }
+
+    interface I4<E> extends I1<E>, I2<E>, I3<E> {}
+}

test/tools/javac/generics/6294779/T6294779c.java

+/*
+ * Copyright 2008 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     6294779
+ * @summary Problem with interface inheritance and covariant return types
+ * @author  Maurizio Cimadamore
+ * @compile/fail T6294779c.java
+ */
+
+public class T6294779c<X> {
+
+    interface A {}
+
+    interface B {}
+
+    interface C {}
+
+    interface I1 {
+        T6294779c<? extends A> get();
+    }
+
+    interface I2 {
+        T6294779c<? extends B> get();
+    }
+
+    interface I3 {
+        T6294779c<? extends C> get();
+    }
+
+    interface I4 extends I1, I2, I3 {}
+}