Added special error for incorrect KClass type in signatures.

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -414,6 +414,11 @@ public interface Errors {
     DiagnosticFactory1<KtDeclaration, Collection<KotlinType>> AMBIGUOUS_ANONYMOUS_TYPE_INFERRED =
             DiagnosticFactory1.create(ERROR, DECLARATION_SIGNATURE);
 
+    DiagnosticFactory0<KtNamedDeclaration>
+            KCLASS_WITH_NULLABLE_ARGUMENT_IN_SIGNATURE = DiagnosticFactory0.create(ERROR, PositioningStrategies.DECLARATION_NAME);
+    DiagnosticFactory1<KtNamedDeclaration, TypeParameterDescriptor>
+            KCLASS_WITH_NULLABLE_TYPE_PARAMETER_IN_SIGNATURE = DiagnosticFactory1.create(ERROR, PositioningStrategies.DECLARATION_NAME);
+
     // Property-specific
 
     DiagnosticFactory2<KtNamedDeclaration, PropertyDescriptor, PropertyDescriptor> VAR_OVERRIDDEN_BY_VAL =

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -859,6 +859,9 @@ public class DefaultErrorMessages {
         MAP.put(DATA_CLASS_NOT_PROPERTY_PARAMETER, "Data class primary constructor must have only property (val / var) parameters");
 
         MAP.put(AMBIGUOUS_ANONYMOUS_TYPE_INFERRED, "Right-hand side has anonymous type. Please specify type explicitly", TO_STRING);
+        MAP.put(KCLASS_WITH_NULLABLE_ARGUMENT_IN_SIGNATURE, "Please specify type explicitly");
+        MAP.put(KCLASS_WITH_NULLABLE_TYPE_PARAMETER_IN_SIGNATURE,
+                "Please add upper bound Any for type parameter ''{0}'' or specify return type explicitly", NAME);
 
         MAP.put(EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED,
                 "''{0}'' is a member and an extension at the same time. References to such elements are not allowed", NAME);

compiler/frontend/src/org/jetbrains/kotlin/resolve/TargetPlatform.kt

@@ -74,7 +74,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
         SinceKotlinAnnotationValueChecker,
         ReifiedTypeParameterAnnotationChecker(),
         DynamicReceiverChecker,
-        DelegationChecker()
+        DelegationChecker(),
+        KClassWithIncorrectTypeArgumentChecker
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/KClassWithIncorrectTypeArgumentChecker.kt

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2010-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.resolve.checkers
+
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.diagnostics.DiagnosticSink
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.KtCallableDeclaration
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.types.UnwrappedType
+import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
+import org.jetbrains.kotlin.types.typeUtil.builtIns
+import org.jetbrains.kotlin.types.typeUtil.contains
+
+object KClassWithIncorrectTypeArgumentChecker : SimpleDeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, diagnosticHolder: DiagnosticSink, bindingContext: BindingContext) {
+        if (descriptor !is CallableMemberDescriptor || descriptor.visibility == Visibilities.LOCAL) return
+
+        if (declaration !is KtCallableDeclaration || declaration.typeReference != null) return
+
+        // prevent duplicate reporting
+        if (descriptor is PropertyAccessorDescriptor) return
+
+        val returnType = descriptor.returnType ?: return
+
+        var typeParameterWithoutNotNullableUpperBound: TypeParameterDescriptor? = null
+        val thereIsBadKClassType = returnType.contains {
+            val kClassWithBadArgument = it.isKClassWithBadArgument()
+            if (kClassWithBadArgument) {
+                it.arguments.singleOrNull()?.type?.constructor?.declarationDescriptor?.let {
+                    if (it is TypeParameterDescriptor && it.containingDeclaration == descriptor) {
+                        typeParameterWithoutNotNullableUpperBound = it
+                    }
+                }
+            }
+
+            kClassWithBadArgument
+        }
+
+        if (typeParameterWithoutNotNullableUpperBound != null) {
+            diagnosticHolder.report(Errors.KCLASS_WITH_NULLABLE_TYPE_PARAMETER_IN_SIGNATURE.on(declaration, typeParameterWithoutNotNullableUpperBound!!))
+        }
+        else if (thereIsBadKClassType) {
+            diagnosticHolder.report(Errors.KCLASS_WITH_NULLABLE_ARGUMENT_IN_SIGNATURE.on(declaration))
+        }
+    }
+
+    private fun UnwrappedType.isKClassWithBadArgument(): Boolean {
+        val argumentType = arguments.singleOrNull()?.let { if (it.isStarProjection) null else it.type.unwrap() } ?: return false
+        val klass = (constructor.declarationDescriptor as? ClassDescriptor) ?: return false
+
+        return KotlinBuiltIns.isKClass(klass) && !KotlinTypeChecker.DEFAULT.isSubtypeOf(argumentType, argumentType.builtIns.anyType)
+    }
+}