From bdec939be79c133dc4e26837ad9a6b2c7ecd5dda Mon Sep 17 00:00:00 2001
From: paulk <paulk@asert.com.au>
Date: Thu, 9 Jul 2015 17:41:18 +1000
Subject: [PATCH] GROOVY-7495: Diamond inheritance of interfaces makes method
 return type incompatible

---
 .../codehaus/groovy/classgen/Verifier.java    |  6 +--
 .../gls/invocation/CovariantReturnTest.groovy | 46 +++++++++++++++++++
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/src/main/org/codehaus/groovy/classgen/Verifier.java b/src/main/org/codehaus/groovy/classgen/Verifier.java
index 362a19024e9..a107d2442dd 100644
--- a/src/main/org/codehaus/groovy/classgen/Verifier.java
+++ b/src/main/org/codehaus/groovy/classgen/Verifier.java
@@ -1277,7 +1277,7 @@ private void addCovariantMethods(ClassNode classNode, List declaredMethods, Map
 
     }
 
-    private MethodNode getCovariantImplementation(final MethodNode oldMethod, final MethodNode overridingMethod, Map genericsSpec) {
+    private MethodNode getCovariantImplementation(final MethodNode oldMethod, final MethodNode overridingMethod, Map genericsSpec, Map methodsToAdd) {
         // method name
         if (!oldMethod.getName().equals(overridingMethod.getName())) return null;
         if ((overridingMethod.getModifiers() & ACC_BRIDGE) != 0) return null;
@@ -1297,7 +1297,7 @@ private MethodNode getCovariantImplementation(final MethodNode oldMethod, final
         boolean equalReturnType = mr.equals(omr);
 
         ClassNode testmr = correctToGenericsSpec(genericsSpec, omr);
-        if (!isAssignable(mr, testmr)) {
+        if (!isAssignable(mr, testmr) && !methodsToAdd.containsKey(overridingMethod.getTypeDescriptor())) {
             throw new RuntimeParserException(
                     "The return type of " +
                             overridingMethod.getTypeDescriptor() +
@@ -1418,7 +1418,7 @@ private static ClassNode cleanType(ClassNode type) {
     private void storeMissingCovariantMethods(Collection methods, MethodNode method, Map methodsToAdd, Map genericsSpec) {
         for (Object method1 : methods) {
             MethodNode toOverride = (MethodNode) method1;
-            MethodNode bridgeMethod = getCovariantImplementation(toOverride, method, genericsSpec);
+            MethodNode bridgeMethod = getCovariantImplementation(toOverride, method, genericsSpec, methodsToAdd);
             if (bridgeMethod == null) continue;
             methodsToAdd.put(bridgeMethod.getTypeDescriptor(), bridgeMethod);
             return;
diff --git a/src/test/gls/invocation/CovariantReturnTest.groovy b/src/test/gls/invocation/CovariantReturnTest.groovy
index 96786156eab..b7295c0848c 100644
--- a/src/test/gls/invocation/CovariantReturnTest.groovy
+++ b/src/test/gls/invocation/CovariantReturnTest.groovy
@@ -267,6 +267,52 @@ public class CovariantReturnTest extends CompilableTestSupport {
         """
     }
 
+    void testCovariantMethodGenerics_groovy7495() {
+        shouldCompile """
+            interface A {
+               B foo()
+            }
+            interface B {}
+            interface A2 extends A {
+               B2 foo()
+            }
+            interface B2 extends B {}
+
+            class AA implements A {
+               BB foo() { return new BB() }
+            }
+            class AA2 extends AA implements A2 {
+               BB2 foo() { return new BB2() }
+            }
+            class BB implements B {}
+            class BB2 extends BB implements B2 {}
+        """
+        shouldCompile """
+            interface Item {}
+            interface DerivedItem extends Item {}
+
+            interface Base {
+              Item getItem()
+            }
+            class BaseImpl implements Base {
+              Item getItem() { null }
+            }
+
+            interface First extends Base {
+              DerivedItem getItem()
+            }
+
+            class FirstImpl extends BaseImpl implements First {
+              DerivedItem getItem() { null }
+            }
+
+            interface Second extends First {}
+            class SecondImpl extends FirstImpl implements Second {}
+
+            println FirstImpl.name
+        """
+    }
+
     void testCovariantParameter() {
         assertScript """
           interface Interface<SomeType> {