Default parameter values are not allowed in overriding functions

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java

@@ -380,6 +380,8 @@ public interface Errors {
     DiagnosticFactory2<PsiElement, JetClassOrObject, CallableMemberDescriptor> MANY_IMPL_MEMBER_NOT_IMPLEMENTED =
             DiagnosticFactory2.create(ERROR);
 
+    SimpleDiagnosticFactory<JetParameter> DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE = SimpleDiagnosticFactory.create(ERROR, PositioningStrategies.PARAMETER_DEFAULT_VALUE);
+
     DiagnosticFactory2<JetDeclaration, CallableMemberDescriptor, String> CONFLICTING_OVERLOADS =
             DiagnosticFactory2.create(ERROR, new PositioningStrategy<JetDeclaration>() {
                 @NotNull

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/PositioningStrategies.java

@@ -28,7 +28,6 @@ import org.jetbrains.jet.lang.psi.*;
 import org.jetbrains.jet.lexer.JetKeywordToken;
 import org.jetbrains.jet.lexer.JetTokens;
 
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -144,4 +143,12 @@ public class PositioningStrategies {
             return markNode(element.getProjectionNode());
         }
     };
+
+    public static PositioningStrategy<JetParameter> PARAMETER_DEFAULT_VALUE = new PositioningStrategy<JetParameter>() {
+        @NotNull
+        @Override
+        public List<TextRange> mark(@NotNull JetParameter element) {
+            return markNode(element.getDefaultValue().getNode());
+        }
+    };
 }

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java

@@ -385,6 +385,8 @@ public class DefaultErrorMessages {
 
         MAP.put(NOT_AN_ANNOTATION_CLASS, "''{0}'' is not an annotation class", TO_STRING);
 
+        MAP.put(DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE, "An overriding function is not allowed to specify default values for its parameters");
+
         MAP.setImmutable();
     }
 

compiler/frontend/src/org/jetbrains/jet/lang/resolve/OverrideResolver.java

@@ -391,6 +391,11 @@ public class OverrideResolver {
                 }
             }
         }
+
+        if (hasOverrideModifier) {
+            checkOverridesForParameters(declared);
+        }
+
         if (hasOverrideModifier && declared.getOverriddenDescriptors().size() == 0) {
             if (!invisibleOverriddenDescriptors.get(declared).isEmpty()) {
                 CallableDescriptor descriptor = invisibleOverriddenDescriptors.values().iterator().next();
@@ -407,6 +412,21 @@ public class OverrideResolver {
         }
     }
 
+    private void checkOverridesForParameters(CallableMemberDescriptor declared) {
+        // Let p1 be a parameter of the overriding function
+        // Let p2 be a parameter of the function being overridden
+        // Then
+        //  a) p1 is not allowed to have a default value declared
+        //  b) p1 must have the same name as p2
+        for (ValueParameterDescriptor parameterFromSubclass : declared.getValueParameters()) {
+            JetParameter parameter =
+                    (JetParameter) BindingContextUtils.descriptorToDeclaration(trace.getBindingContext(), parameterFromSubclass);
+            if (parameterFromSubclass.hasDefaultValue()) {
+                trace.report(DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE.on(parameter));
+            }
+        }
+    }
+
     private boolean checkPropertyKind(CallableMemberDescriptor descriptor, boolean isVar) {
         if (descriptor instanceof PropertyDescriptor) {
             PropertyDescriptor propertyDescriptor = (PropertyDescriptor) descriptor;

compiler/testData/diagnostics/tests/override/DefaultParameterValueInOverride.jet

@@ -0,0 +1,15 @@
+open class A {
+    open fun foo(a : Int) {}
+}
+
+class C : A() {
+    override fun foo(a : Int = <!DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE!>1<!>) {
+        super<A>.foo(a)
+    }
+}
+
+class D : A() {
+    override fun foo(b : Int = <!DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE!>1<!>) {
+        super<A>.foo(b)
+    }
+}