GROOVY-7937: CLONE - same linkedlist code different behavior between groovy and java (fix priority of DGM methods vs actual methods on an object) (closes groovy#418)

Author: paulk-asert

src/main/groovy/lang/MetaClassImpl.java

@@ -94,6 +94,7 @@
 
 import static org.codehaus.groovy.ast.tools.GeneralUtils.inSamePackage;
 import static org.codehaus.groovy.ast.tools.GeneralUtils.isDefaultVisibility;
+import static org.codehaus.groovy.reflection.ReflectionCache.isAssignableFrom;
 
 /**
  * Allows methods to be dynamically added to existing classes at runtime
@@ -625,10 +626,26 @@ private void inheritInterfaceNewMetaMethods(Set<CachedClass> interfaces) {
         for (CachedClass cls : interfaces) {
             MetaMethod methods[] = getNewMetaMethods(cls);
             for (MetaMethod method : methods) {
-                if (!newGroovyMethodsSet.contains(method)) {
-                    newGroovyMethodsSet.add(method);
+                boolean skip = false;
+                // skip DGM methods on an interface if the class already has the method
+                // but don't skip for GroovyObject-related methods as it breaks things :-(
+                if (method instanceof GeneratedMetaMethod && !isAssignableFrom(GroovyObject.class, method.getDeclaringClass().getTheClass())) {
+                    for (Method m : theClass.getMethods()) {
+                        if (method.getName().equals(m.getName())
+                                // below not true for DGM#push and also co-variant return scenarios
+                                //&& method.getReturnType().equals(m.getReturnType())
+                                && MetaMethod.equal(method.getParameterTypes(), m.getParameterTypes())) {
+                            skip = true;
+                            break;
+                        }
+                    }
+                }
+                if (!skip) {
+                    if (!newGroovyMethodsSet.contains(method)) {
+                        newGroovyMethodsSet.add(method);
+                    }
+                    addMetaMethodToIndex(method, mainClassMethodHeader);
                 }
-                addMetaMethodToIndex(method, mainClassMethodHeader);
             }
         }
     }

src/test/groovy/bugs/Groovy7937Bug.groovy

@@ -0,0 +1,36 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package groovy.bugs
+
+class Groovy7937Bug extends GroovyTestCase {
+    void testMethodsWithinAnInstanceShouldBeChosenAheadOfDGMMethodsOnAnInterface() {
+        assertScript """
+            class MyList extends LinkedList<String> {
+                MyList(Collection c) { super(c) }
+                String pop() {
+                    'foo'
+                }
+            }
+            MyList stack1 = new MyList(1..3)
+            assert stack1.pop() == 'foo'
+            def stack2 = 1..3 as LinkedList
+            assert stack2.pop() == 1
+        """
+    }
+}