Do not generate toString and other methods if they are inherited.

compiler/backend/src/org/jetbrains/jet/codegen/CodegenUtil.java

@@ -37,6 +37,7 @@ import org.jetbrains.jet.lang.descriptors.impl.TypeParameterDescriptorImpl;
 import org.jetbrains.jet.lang.psi.JetClassOrObject;
 import org.jetbrains.jet.lang.psi.JetObjectDeclaration;
 import org.jetbrains.jet.lang.resolve.DescriptorUtils;
+import org.jetbrains.jet.lang.resolve.calls.CallResolverUtil;
 import org.jetbrains.jet.lang.resolve.name.Name;
 import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.lang.types.TypeUtils;
@@ -163,7 +164,7 @@ public class CodegenUtil {
     ) {
         Collection<FunctionDescriptor> functions = owner.getDefaultType().getMemberScope().getFunctions(name);
         for (FunctionDescriptor function : functions) {
-            if (function.getKind() == CallableMemberDescriptor.Kind.DECLARATION
+            if (!CallResolverUtil.isOrOverridesSynthesized(function)
                 && function.getTypeParameters().isEmpty()
                 && valueParameterClassesMatch(function.getValueParameters(), Arrays.asList(valueParameterClassifiers))
                 && rawTypeMatches(function.getReturnType(), returnedClassifier)) {

compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt

@@ -0,0 +1,10 @@
+trait SuperTrait {
+    public fun toString(): String = "!"
+}
+
+data class A(val x: Int): SuperTrait {
+}
+
+fun box(): String {
+  return if (A(0).toString() == "!") "OK" else "fail"
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxWithStdlibCodegenTestGenerated.java

@@ -343,6 +343,11 @@ public class BlackBoxWithStdlibCodegenTestGenerated extends AbstractBlackBoxCode
                 doTestWithStdlib("compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyDeclaredWrongSignature.kt");
             }
             
+            @TestMetadata("alreadyInherited.kt")
+            public void testAlreadyInherited() throws Exception {
+                doTestWithStdlib("compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/alreadyInherited.kt");
+            }
+            
             @TestMetadata("arrayParams.kt")
             public void testArrayParams() throws Exception {
                 doTestWithStdlib("compiler/testData/codegen/boxWithStdlib/dataClasses/tostring/arrayParams.kt");