KT-4960 Redeclaration is not reported for type parameters of interfaces

When resolving a class body for a class without a primary constructor
(e.g., an interface), no checks were performed for redeclarations
in the corresponding class header.
Creating & initializing a lexical scope of an appropriate kind will do it.
Note that since class has no primary constructor, only type parameters
could be redeclared (and that's KT-4960).

compiler/frontend/src/org/jetbrains/kotlin/resolve/BodyResolver.java

@@ -268,6 +268,9 @@ public class BodyResolver {
                 primaryConstructor == null
                 ? null
                 : FunctionDescriptorUtil.getFunctionInnerScope(scopeForConstructorResolution, primaryConstructor, trace, overloadChecker);
+        if (primaryConstructor == null) {
+            checkRedeclarationsInClassHeaderWithoutPrimaryConstructor(descriptor, scopeForConstructorResolution);
+        }
         ExpressionTypingServices typeInferrer = expressionTypingServices; // TODO : flow
 
         Map<KtTypeReference, KotlinType> supertypes = Maps.newLinkedHashMap();
@@ -396,6 +399,25 @@ public class BodyResolver {
         checkSupertypeList(descriptor, supertypes, ktClass);
     }
 
+    private void checkRedeclarationsInClassHeaderWithoutPrimaryConstructor(
+            @NotNull final ClassDescriptor descriptor, @NotNull LexicalScope scopeForConstructorResolution
+    ) {
+        // Initializing a scope will report errors if any.
+        new LexicalScopeImpl(
+                scopeForConstructorResolution, descriptor, true, null, LexicalScopeKind.CLASS_HEADER,
+                new TraceBasedLocalRedeclarationChecker(trace, overloadChecker),
+                new Function1<LexicalScopeImpl.InitializeHandler, Unit>() {
+                    @Override
+                    public Unit invoke(LexicalScopeImpl.InitializeHandler handler) {
+                        // If a class has no primary constructor, it still can have type parameters declared in header.
+                        for (TypeParameterDescriptor typeParameter : descriptor.getDeclaredTypeParameters()) {
+                            handler.addClassifierDescriptor(typeParameter);
+                        }
+                        return Unit.INSTANCE;
+                    }
+                });
+    }
+
     private void resolveConstructorCallForEnumEntryWithoutInitializer(
             @NotNull KtEnumEntry ktEnumEntry,
             @NotNull ClassDescriptor enumEntryDescriptor,

compiler/testData/diagnostics/tests/redeclarations/interfaceTypeParameters.kt

@@ -0,0 +1,6 @@
+interface Test1<<!REDECLARATION!>T<!>, <!REDECLARATION!>T<!>>
+interface Test2<<!REDECLARATION!>X<!>, Y, <!REDECLARATION!>X<!>>
+
+class Outer<T> {
+    interface TestNested<T>
+}

compiler/testData/diagnostics/tests/redeclarations/interfaceTypeParameters.txt

@@ -0,0 +1,26 @@
+package
+
+public final class Outer</*0*/ T> {
+    public constructor Outer</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public interface TestNested</*0*/ T> {
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+public interface Test1</*0*/ T, /*1*/ T> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test2</*0*/ X, /*1*/ Y, /*2*/ X> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -15949,6 +15949,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("interfaceTypeParameters.kt")
+            public void testInterfaceTypeParameters() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/redeclarations/interfaceTypeParameters.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("kt2418.kt")
             public void testKt2418() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/redeclarations/kt2418.kt");

idea/testData/quickfix/supercalls/typeArgumentsRedundantInSuperQualifier.kt

@@ -1,5 +1,5 @@
 // "Remove type arguments" "true"
-interface Foo<T, T> {
+interface Foo<T1, T2> {
     fun f() {}
 }
 

idea/testData/quickfix/supercalls/typeArgumentsRedundantInSuperQualifier.kt.after

@@ -1,5 +1,5 @@
 // "Remove type arguments" "true"
-interface Foo<T, T> {
+interface Foo<T1, T2> {
     fun f() {}
 }