Making var arg kParameters default to empty array no argument given

fixes KT-29969

compiler/fir/fir2ir/tests/org/jetbrains/kotlin/codegen/ir/FirBlackBoxCodegenTestGenerated.java

@@ -22728,6 +22728,11 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -23035,6 +23040,11 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByKotlin.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("callJava.kt")
             public void testCallJava() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callJava.kt");

compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt

@@ -0,0 +1,19 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// IGNORE_BACKEND: JS_IR
+// IGNORE_BACKEND: JS, NATIVE
+
+// WITH_REFLECT
+
+import kotlin.test.assertEquals
+
+fun join(vararg strings: String) = strings.toList().joinToString("")
+
+fun sum(vararg bytes: Byte) = bytes.toList().fold(0) { acc, el -> acc + el }
+
+fun box(): String {
+    val j = ::join
+    val s = ::sum
+    assertEquals("", j.callBy(emptyMap()))
+    assertEquals(0, s.callBy(emptyMap()))
+    return "OK"
+}

compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt

@@ -0,0 +1,25 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// IGNORE_BACKEND: JS_IR
+// IGNORE_BACKEND: JS, NATIVE
+
+// WITH_REFLECT
+
+import kotlin.reflect.*
+import kotlin.reflect.full.*
+import kotlin.test.assert
+
+annotation class Foo(vararg val strings: String)
+
+annotation class Bar(vararg val bytes: Byte)
+
+fun box(): String {
+    val fooConstructor = Foo::class.primaryConstructor!!
+    val foo = fooConstructor.callBy(emptyMap())
+    assert(foo.strings.isEmpty())
+
+    val barConstructor = Bar::class.primaryConstructor!!
+    val bar = barConstructor.callBy(emptyMap())
+    assert(bar.bytes.isEmpty())
+
+    return "OK"
+}

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -24289,6 +24289,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -24596,6 +24601,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByKotlin.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("callJava.kt")
             public void testCallJava() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callJava.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -23106,6 +23106,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -23413,6 +23418,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByKotlin.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("callJava.kt")
             public void testCallJava() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callJava.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -22728,6 +22728,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -23035,6 +23040,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByKotlin.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("callJava.kt")
             public void testCallJava() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/callJava.kt");

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KCallableImpl.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.load.java.descriptors.JavaCallableMemberDescriptor
+import java.lang.reflect.Array as ReflectArray
 import java.lang.reflect.ParameterizedType
 import java.lang.reflect.Type
 import java.lang.reflect.WildcardType
@@ -17,6 +18,7 @@ import kotlin.coroutines.Continuation
 import kotlin.reflect.*
 import kotlin.reflect.jvm.internal.calls.Caller
 import kotlin.reflect.jvm.javaType
+import kotlin.reflect.jvm.jvmErasure
 
 internal abstract class KCallableImpl<out R> : KCallable<R> {
     abstract val descriptor: CallableMemberDescriptor
@@ -134,6 +136,9 @@ internal abstract class KCallableImpl<out R> : KCallable<R> {
                     mask = mask or (1 shl (index % Integer.SIZE))
                     anyOptional = true
                 }
+                parameter.isVararg -> {
+                    arguments.add(defaultEmptyArray(parameter.type))
+                }
                 else -> {
                     throw IllegalArgumentException("No argument provided for a required parameter: $parameter")
                 }
@@ -174,6 +179,7 @@ internal abstract class KCallableImpl<out R> : KCallable<R> {
                     args[parameter] ?: throw IllegalArgumentException("Annotation argument value cannot be null ($parameter)")
                 }
                 parameter.isOptional -> null
+                parameter.isVararg -> defaultEmptyArray(parameter.type)
                 else -> throw IllegalArgumentException("No argument provided for a required parameter: $parameter")
             }
         }
@@ -202,6 +208,14 @@ internal abstract class KCallableImpl<out R> : KCallable<R> {
             }
         } else null
 
+    private fun defaultEmptyArray(type: KType): Any =
+        type.jvmErasure.java.run {
+            if (isArray) ReflectArray.newInstance(componentType, 0)
+            else throw KotlinReflectionInternalError(
+                "Cannot instantiate the default empty array of type $simpleName, because it is not an array type"
+            )
+        }
+
     private fun extractContinuationArgument(): Type? {
         if ((descriptor as? FunctionDescriptor)?.isSuspend == true) {
             // kotlin.coroutines.Continuation<? super java.lang.String>

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -19299,6 +19299,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -19496,6 +19501,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/arrayOfKClasses.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("enumKClassAnnotation.kt")
             public void testEnumKClassAnnotation() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/enumKClassAnnotation.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -19359,6 +19359,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
                 runTest("compiler/testData/codegen/box/reflection/callBy/defaultInSuperInterface.kt");
             }
 
+            @TestMetadata("emptyVarArg.kt")
+            public void testEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/callBy/emptyVarArg.kt");
+            }
+
             @TestMetadata("extensionFunction.kt")
             public void testExtensionFunction() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/callBy/extensionFunction.kt");
@@ -19556,6 +19561,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/arrayOfKClasses.kt");
             }
 
+            @TestMetadata("callByWithEmptyVarArg.kt")
+            public void testCallByWithEmptyVarArg() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/createAnnotation/callByWithEmptyVarArg.kt");
+            }
+
             @TestMetadata("enumKClassAnnotation.kt")
             public void testEnumKClassAnnotation() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/createAnnotation/enumKClassAnnotation.kt");