Error on using extension function type as an upper bound

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

@@ -259,6 +259,7 @@ public interface Errors {
 
     DiagnosticFactory1<KtTypeReference, KotlinType> FINAL_UPPER_BOUND = DiagnosticFactory1.create(WARNING);
     DiagnosticFactory0<KtTypeReference> DYNAMIC_UPPER_BOUND = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<KtTypeReference> UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE = DiagnosticFactory0.create(ERROR);
 
     DiagnosticFactory1<KtNamedDeclaration, TypeParameterDescriptor> CONFLICTING_UPPER_BOUNDS =
             DiagnosticFactory1.create(ERROR, DECLARATION_NAME);

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

@@ -391,6 +391,7 @@ public class DefaultErrorMessages {
 
         MAP.put(UPPER_BOUND_VIOLATED, "Type argument is not within its bounds: should be subtype of ''{0}''", RENDER_TYPE, RENDER_TYPE);
         MAP.put(FINAL_UPPER_BOUND, "''{0}'' is a final type, and thus a value of the type parameter is predetermined", RENDER_TYPE);
+        MAP.put(UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE, "Extension function type can not be used as an upper bound");
         MAP.put(DYNAMIC_UPPER_BOUND, "Dynamic type can not be used as an upper bound");
         MAP.put(USELESS_ELVIS, "Elvis operator (?:) always returns the left operand of non-nullable type {0}", RENDER_TYPE);
         MAP.put(USELESS_ELVIS_ON_FUNCTION_LITERAL, "Left operand of elvis operator (?:) is function literal");

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

@@ -589,6 +589,9 @@ public class DescriptorResolver {
         if (DynamicTypesKt.isDynamic(upperBoundType)) {
             trace.report(DYNAMIC_UPPER_BOUND.on(upperBound));
         }
+        if (KotlinBuiltIns.isExactExtensionFunctionType(upperBoundType)) {
+            trace.report(UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE.on(upperBound));
+        }
     }
 
     @NotNull