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

compiler/testData/diagnostics/tests/generics/nullability/functionalBound.kt

@@ -1,13 +1,13 @@
-fun <E : String?, T : ((CharSequence).() -> Unit)?> foo(x: E, y: T) {
+fun <E : String?, T : ((CharSequence) -> Unit)?> foo(x: E, y: T) {
     if (x != null) {
-        <!DEBUG_INFO_SMARTCAST!>x<!>.<!UNSAFE_CALL, INVOKE_EXTENSION_ON_NOT_EXTENSION_FUNCTION!>y<!>()
+        <!UNSAFE_CALL!>y<!>(<!DEBUG_INFO_SMARTCAST!>x<!>)
     }
 
     if (y != null) {
-        x<!UNSAFE_CALL!>.<!><!INVOKE_EXTENSION_ON_NOT_EXTENSION_FUNCTION, DEBUG_INFO_SMARTCAST!>y<!>()
+        <!DEBUG_INFO_SMARTCAST!>y<!>(<!TYPE_MISMATCH!>x<!>)
     }
 
     if (x != null && y != null) {
-        <!DEBUG_INFO_SMARTCAST!>x<!>.<!INVOKE_EXTENSION_ON_NOT_EXTENSION_FUNCTION, DEBUG_INFO_SMARTCAST!>y<!>()
+        <!DEBUG_INFO_SMARTCAST!>y<!>(<!DEBUG_INFO_SMARTCAST!>x<!>)
     }
 }

compiler/testData/diagnostics/tests/generics/nullability/functionalBound.txt

@@ -1,3 +1,3 @@
 package
 
-public fun </*0*/ E : kotlin.String?, /*1*/ T : (kotlin.CharSequence.() -> kotlin.Unit)?> foo(/*0*/ x: E, /*1*/ y: T): kotlin.Unit
+public fun </*0*/ E : kotlin.String?, /*1*/ T : ((kotlin.CharSequence) -> kotlin.Unit)?> foo(/*0*/ x: E, /*1*/ y: T): kotlin.Unit

compiler/testData/diagnostics/tests/typeParameters/extFunctionTypeAsUpperBound.kt

@@ -0,0 +1,7 @@
+fun <T: <!UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE!>Int.() -> String<!>> foo() {}
+
+val <<!TYPE_PARAMETER_OF_PROPERTY_NOT_USED_IN_RECEIVER!>T: <!UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE!>Int.() -> String<!><!>> bar = fun (x: Int): String { return x.toString() }
+
+class A<T> where T : <!UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE!>Double.(Int) -> Unit<!>
+
+interface B<T, U : <!UPPER_BOUND_IS_EXTENSION_FUNCTION_TYPE!>T.() -> Unit<!>>

compiler/testData/diagnostics/tests/typeParameters/extFunctionTypeAsUpperBound.txt

@@ -0,0 +1,17 @@
+package
+
+public val </*0*/ T : kotlin.Int.() -> kotlin.String> bar: (kotlin.Int) -> kotlin.String
+public fun </*0*/ T : kotlin.Int.() -> kotlin.String> foo(): kotlin.Unit
+
+public final class A</*0*/ T : kotlin.Double.(kotlin.Int) -> kotlin.Unit> {
+    public constructor A</*0*/ T : kotlin.Double.(kotlin.Int) -> kotlin.Unit>()
+    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 B</*0*/ T, /*1*/ U : T.() -> kotlin.Unit> {
+    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/testData/diagnostics/tests/typeParameters/functionTypeAsUpperBound.kt

@@ -0,0 +1,7 @@
+fun <T: (Int) -> String> foo() {}
+
+val <<!TYPE_PARAMETER_OF_PROPERTY_NOT_USED_IN_RECEIVER!>T: (kotlin.Int) -> kotlin.String<!>> bar = fun (x: Int): String { return x.toString() }
+
+class A<T, U, V> where T : () -> Unit, U : (Int) -> Double, V : (T, U) -> U
+
+interface B<T, U : (T) -> Unit>

compiler/testData/diagnostics/tests/typeParameters/functionTypeAsUpperBound.txt

@@ -0,0 +1,17 @@
+package
+
+public val </*0*/ T : (kotlin.Int) -> kotlin.String> bar: (kotlin.Int) -> kotlin.String
+public fun </*0*/ T : (kotlin.Int) -> kotlin.String> foo(): kotlin.Unit
+
+public final class A</*0*/ T : () -> kotlin.Unit, /*1*/ U : (kotlin.Int) -> kotlin.Double, /*2*/ V : (T, U) -> U> {
+    public constructor A</*0*/ T : () -> kotlin.Unit, /*1*/ U : (kotlin.Int) -> kotlin.Double, /*2*/ V : (T, U) -> U>()
+    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 B</*0*/ T, /*1*/ U : (T) -> kotlin.Unit> {
+    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

@@ -16563,6 +16563,18 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("extFunctionTypeAsUpperBound.kt")
+            public void testExtFunctionTypeAsUpperBound() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/typeParameters/extFunctionTypeAsUpperBound.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("functionTypeAsUpperBound.kt")
+            public void testFunctionTypeAsUpperBound() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/typeParameters/functionTypeAsUpperBound.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("misplacedConstraints.kt")
             public void testMisplacedConstraints() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/typeParameters/misplacedConstraints.kt");