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Please include a sample project that reproduces your issue.

Hello again!

It was very tough but trying to replicate the issue in a sample project (since original project I cannot share it) I finally found the source of the issue and it's related to the length of the names of the objects used when generating code by Navigation component and line wrapping in those files

Please, try to compile project that I've attached and you will see the error. So no problem with inheritance or other possible causes that I commented in first message.

In project example, I've created:

• MyNewDialogWithAVeryLongNameToTriggerAnError that inhertis from DialogFragment

Then I've added it to in nav_graph_test.xmland with arguments that have also long IDs too:

<dialog
    android:id="@+id/very_large_name_for_my_new_dialog_widget_for_trigger_an_error"
    android:name="com.example.navtestapp.MyNewDialogWithAVeryLongNameToTriggerAnError"
    tools:layout="@layout/fragment_my_dialog">

    <argument
        android:name="very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error"
        app:argType="string"
        app:nullable="true"/>

    <argument
        android:name="second_very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error"
        app:argType="string"
        app:nullable="true"/>

    <action
        android:id="@+id/action_dialog"
        app:destination="@id/my_fragment" />

</dialog>

Then, when we try to compile project, we can't. It returns the error comented in first message:

This function must return a value of type MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs

If we look at generated code we can see:

data class MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs(
  val veryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError: String?,
  val secondVeryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError: String?
) : NavArgs {
  fun toBundle(): Bundle {
    val result = Bundle()
    result.putString("very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error",
        this.veryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError)
    result.putString("second_very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error",
        this.secondVeryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError)
    return result
  }

  companion object {
    @JvmStatic
    fun fromBundle(bundle: Bundle): MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs {
      bundle.setClassLoader(MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs::class.java.classLoader)
      val __veryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError : String?
      if
          (bundle.containsKey("very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error")) {
        __veryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError =
            bundle.getString("very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error")
      } else {
        throw IllegalArgumentException("Required argument \"very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error\" is missing and does not have an android:defaultValue")
      }
      val __secondVeryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError : String?
      if
          (bundle.containsKey("second_very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error")) {
        __secondVeryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError =
            bundle.getString("second_very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error")
      } else {
        throw IllegalArgumentException("Required argument \"second_very_large_name_for argument_in_my_new_dialog_widget_for_trigger_an_error\" is missing and does not have an android:defaultValue")
      }
      return
          MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs(__veryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError,
          __secondVeryLargeNameForArgumentInMyNewDialogWidgetForTriggerAnError)
    }
  }
}

Pay attention to return in fromBundle() function that is split into two lines, preventing project to compile since compiler expects an expresion for returning it but it's in the next line. Removing breakline between return and MyNewDialogWithAVeryLongNameToTriggerAnErrorArgs fixes the problem, but since this is generated code, we are not able to do it.

Shouldn't navigation component take into consideration that objects could have long names and ensure that code generated finally is able to compile it?

Thank you!

Thanks, your reproduction project and additional analysis is super helpful.

Safe Args uses a project called KotlinPoet that actually generates the Kotlin code and it is that project that controls line breaks.

We'll look at if this is still reproducible with the latest version of KotlinPoet. If upgrading fixes it, we'll include that upgrade in Navigation 2.3.1.

Otherwise, we'll file an issue against KotlinPoet and have to wait for a release that includes a fix.

This has been fixed internally and will be available in the Navigation 2.3.1 release.