Handle date/time conversion in runtime

[drewhamilton]

Closes #230.

This implements the first solution I proposed in #230. I'm not overly attached to this approach, just wanted to prove it out.

This pulls all android.icu imports out of generated code and into the runtime, allowing substitution of non-Android ICU dependencies in JVM unit tests.

Generated code now uses a generic DateTimeConverter interface to format date/time parameters. The default AndroidDateTimeConverter implementation instantiates android.icu.util.Calendars. JVM tests can substitute a JvmDateTimeConverter into their FormattedResources object to instantiate com.ibm.icu.util.Calendars, avoiding the need for Robolectric to format date/time strings.

[drewhamilton]

Since AndroidDateTimeConverter is an object, this ULocale instantiation was happening immediately when FormattedResources was accessed, causing the JVM test to (still) crash. Loading it lazily avoids this.

[JakeWharton]

Definitely not sure how I feel about this. It's basically Dispatchers.setMain which is my mortal enemy.

[JakeWharton]

Painful 🙈

[drewhamilton]

Yep. Nothing better came to mind quickly but I can stew on it a bit longer.

[theisenp]

I just realized I never responded to this, so sorry about that!

I think that in practice this approach probably would work fine (at least for our setup at Cash), even if we're leaking state across tests. Definitely agree that swapping out the static reference is painful though and it would be great to avoid it. We could potentially limit the API surface a bit by hiding the assignment behind a JUnit @Rule, but that doesn't fix the underlying problem.

Another thing we could explore is making the resources themselves injectable. Something like:

val FormattedResources = BaseFormattedResources(dateConverter = AndroidDateConverter)

class BaseFormattedResources(private val dateConverter : DateConverter<*>) {
  fun my_string(date: LocalDate): FormattedResource { ... }
}

People could still reference the default resources statically, but they could also pass in an instance if they need to for testing:

class MyPresenter(private val formattedResources: BaseFormattedResources = FormattedResources) { ... }

class MyPresenterTest {
  private val presenter = MyPresenter(BaseFormattedResources(JvmDateConverter))
}

Lots of options here in terms of naming, the exact configuration, how much we encourage static use vs injecting instances, etc.

[drewhamilton]

Makes sense. I'll give this a try.