Fix "Cannot infer visibility" for fake overrides

#KT-4785 Fixed

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

@@ -145,24 +145,30 @@ public class PositioningStrategies {
                         property.getTextRange().getStartOffset(), endOfSignatureElement.getTextRange().getEndOffset()));
             }
             else if (element instanceof JetClass) {
-                // primary constructor
-                JetClass klass = (JetClass)element;
-                PsiElement nameAsDeclaration = klass.getNameIdentifier();
+                PsiElement nameAsDeclaration = element.getNameIdentifier();
                 if (nameAsDeclaration == null) {
-                    return markElement(klass);
+                    return markElement(element);
                 }
-                PsiElement primaryConstructorParameterList = klass.getPrimaryConstructorParameterList();
+                PsiElement primaryConstructorParameterList = ((JetClass) element).getPrimaryConstructorParameterList();
                 if (primaryConstructorParameterList == null) {
                     return markRange(nameAsDeclaration.getTextRange());
                 }
                 return markRange(new TextRange(
                         nameAsDeclaration.getTextRange().getStartOffset(), primaryConstructorParameterList.getTextRange().getEndOffset()));
             }
+            else if (element instanceof JetObjectDeclaration) {
+                PsiElement nameAsDeclaration = element.getNameIdentifier();
+                if (nameAsDeclaration == null) {
+                    return markElement(((JetObjectDeclaration) element).getObjectKeyword());
+                }
+                return markRange(nameAsDeclaration.getTextRange());
+            }
             return super.mark(element);
         }
+
         @Override
         public boolean isValid(@NotNull PsiNameIdentifierOwner element) {
-            return element.getNameIdentifier() != null && super.isValid(element);
+            return (element.getNameIdentifier() != null || element instanceof JetObjectDeclaration) && super.isValid(element);
         }
     };
 

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

@@ -174,7 +174,11 @@ public class OverrideResolver {
         OverridingUtil.resolveUnknownVisibilityForMember(descriptor, new OverridingUtil.NotInferredVisibilitySink() {
             @Override
             public void cannotInferVisibility(@NotNull CallableMemberDescriptor descriptor) {
-                PsiElement element = BindingContextUtils.descriptorToDeclaration(trace.getBindingContext(), descriptor);
+                DeclarationDescriptor reportOn = descriptor.getKind() == FAKE_OVERRIDE
+                                                 ? DescriptorUtils.getParentOfType(descriptor, ClassDescriptor.class)
+                                                 : descriptor;
+                //noinspection ConstantConditions
+                PsiElement element = BindingContextUtils.descriptorToDeclaration(trace.getBindingContext(), reportOn);
                 if (element instanceof JetDeclaration) {
                     trace.report(CANNOT_INFER_VISIBILITY.on((JetDeclaration) element));
                 }

compiler/testData/diagnostics/tests/override/kt4785.kt

@@ -0,0 +1,11 @@
+trait T {
+    internal fun foo()
+}
+
+open class C {
+    protected fun foo() {}
+}
+
+class <!CANNOT_INFER_VISIBILITY!>E<!> : C(), T
+
+val z: T = <!CANNOT_INFER_VISIBILITY!>object<!> : C(), T {}

compiler/testData/diagnostics/tests/override/kt4785classObject.kt

@@ -0,0 +1,13 @@
+trait A {
+    internal fun foo()
+}
+
+trait B {
+    protected fun foo() {}
+}
+
+class C {
+    class <!CANNOT_INFER_VISIBILITY!>object<!> : A, B {
+        fun bar() = null
+    }
+}

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -5384,6 +5384,16 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest("compiler/testData/diagnostics/tests/override/kt2052.kt");
             }
             
+            @TestMetadata("kt4785.kt")
+            public void testKt4785() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/override/kt4785.kt");
+            }
+            
+            @TestMetadata("kt4785classObject.kt")
+            public void testKt4785classObject() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/override/kt4785classObject.kt");
+            }
+            
             @TestMetadata("kt880.kt")
             public void testKt880() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/override/kt880.kt");