fix(d.ts for Default Argument Value): add question mark to exported funcitons with default parameter.

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/DeclarationOrigins.kt

@@ -15,5 +15,6 @@ object JsLoweredDeclarationOrigin : IrDeclarationOrigin {
     object BRIDGE_WITHOUT_STABLE_NAME : IrDeclarationOriginImpl("BRIDGE_WITHOUT_STABLE_NAME")
     object OBJECT_GET_INSTANCE_FUNCTION : IrDeclarationOriginImpl("OBJECT_GET_INSTANCE_FUNCTION")
     object JS_SHADOWED_EXPORT : IrDeclarationOriginImpl("JS_SHADOWED_EXPORT")
+    object JS_SHADOWED_DEFAULT_PARAMETER : IrDeclarationOriginImpl("JS_SHADOWED_DEFAULT_PARAMETER")
     object ENUM_GET_INSTANCE_FUNCTION : IrDeclarationOriginImpl("ENUM_GET_INSTANCE_FUNCTION")
 }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/export/ExportModel.kt

@@ -80,7 +80,8 @@ data class ExportedClass(
 
 class ExportedParameter(
     val name: String,
-    val type: ExportedType
+    val type: ExportedType,
+    val hasDefaultValue: Boolean = false
 )
 
 sealed class ExportedType {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/export/ExportModelGenerator.kt

@@ -110,7 +110,11 @@ class ExportModelGenerator(
         if (parameterName in allReservedWords)
             parameterName = "_$parameterName"
 
-        return ExportedParameter(parameterName, exportType(parameter.type))
+        return ExportedParameter(
+            parameterName,
+            exportType(parameter.type),
+            parameter.origin == JsLoweredDeclarationOrigin.JS_SHADOWED_DEFAULT_PARAMETER
+        )
     }
 
     private fun exportProperty(property: IrProperty): ExportedDeclaration? {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/export/ExportModelToTsDeclarations.kt

@@ -268,8 +268,12 @@ fun ExportedClass.toReadonlyProperty(): ExportedProperty {
     )
 }
 
-fun ExportedParameter.toTypeScript(indent: String): String =
-    "${sanitizeName(name, withHash = false)}: ${type.toTypeScript(indent)}"
+fun ExportedParameter.toTypeScript(indent: String): String {
+    val name = sanitizeName(name, withHash = false)
+    val type = type.toTypeScript(indent)
+    val questionMark = if (hasDefaultValue) "?" else ""
+    return "$name$questionMark: $type"
+}
 
 fun ExportedType.toTypeScript(indent: String): String = when (this) {
     is ExportedType.Primitive -> typescript

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/ExportedDefaultParameterStub.kt

@@ -112,7 +112,10 @@ class ExportedDefaultParameterStub(val context: JsIrBackendContext) : Declaratio
         exportedDefaultStubFun.parent = declaration.parent
         exportedDefaultStubFun.copyParameterDeclarationsFrom(declaration)
         exportedDefaultStubFun.returnType = declaration.returnType.remapTypeParameters(declaration, exportedDefaultStubFun)
-        exportedDefaultStubFun.valueParameters.forEach { it.defaultValue = null }
+        exportedDefaultStubFun.valueParameters.forEach {
+            it.defaultValue = null
+            it.origin = JsLoweredDeclarationOrigin.JS_SHADOWED_DEFAULT_PARAMETER
+        }
 
         declaration.origin = JsLoweredDeclarationOrigin.JS_SHADOWED_EXPORT