Impossible to use `@ShowkaseColor` or `@ShowkaseTypography` on objects' fields that have a constructor with no parameters

[francescocervone]

I see from the validator that the enclosing class must have exactly one constructor with no parameters here.

Couldn't this be relaxed to have at least one constructor with no parameters?

I mean, could that function be converted to something like this?

fun validateEnclosingClass(enclosingClass: XTypeElement?) {
  if (enclosingClass == null) return

  val hasEmptyConstructor = enclosingClass.getConstructors().any { constructor -> constructor.parameters.isEmpty() }
  if (!hasEmptyConstructor) {
    throw ShowkaseProcessorException(
      "Only classes that have at least one constructor with no parameters can " +
        "hold a @Composable function that's annotated with the " +
        "@${ShowkaseComposable::class.java.simpleName}/@Preview annotation",
      enclosingClass,
    )
  }
}

[vinaygaba]

@francescocervone Yeah I can see this being useful. I worry that it might end up impacting the preview itself but maybe that's acceptable. Can you talk a bit more about your use case. What does the enclosing class look like in your case?

[francescocervone]

Yes, we have a class for the Typography that depends on the colors, but it might have a default value which is overridden when the theme is applied. Basically we have the colors:

interface Colors {
  val content: Color
  val background: Color
}
class LightColors: Colors {
  @ShowkaseColor
  override val content: Color = // something
  @ShowkaseColor
  override val background: Color = // something
}
class DarkColors: Colors {
  @ShowkaseColor
  override val content: Color = // something
  @ShowkaseColor
  override val background: Color = // something
}

Then we have the typography:

interface Typography {
  val title: TextStyle
  val body: TextStyle
}
class DefaultTypography(private val colors: Colors = LightColors): Typography {
  // we'd like to have @ShowkaseTypography here but we can't
  override val title: TextStyle = // something
  // we'd like to have @ShowkaseTypography here but we can't
  override val body: TextStyle = // something
}

Technically, Showkase would be able to instantiate DefaultTypography because it has at least one empty constructor.