fix getLayerAs return optional Layer type.

[ank27]

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• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality. If tests were not written, please explain why.
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Summary of changes

Currently StyleMangerInterface.getLayerAs has return type which is non-nullable.
It should be a nullable type.

User impact (optional)

Breaking change to get layer from style using getLayerAs function.

fun <T : Layer> StyleManagerInterface.getLayerAs(layerId: String): T {
  @Suppress("UNCHECKED_CAST")
  return getLayer(layerId) as T
}

Changed to

inline fun <reified T : Layer> StyleManagerInterface.getLayerAs(layerId: String): T? {
  val layer = getLayer(layerId)
  if (layer !is T) {
    Logger.e("StyleLayerPlugin", "Given layerId = $layerId is not requested type in Layer")
    return null
  }
  return layer
}

[tobrun]

nit: introduce TAG in companion object and use that as first parameter of Logger.e (I do think we had a convention of prefixing with mbgl_ but better to check the codebase).

[tobrun]

Given layerId = $layerId is not requested type in Layer the error statement is a bit confusing.
The layer itself could also just be null

[ank27]

Any suggestion for error message ? :D

[ank27]

nit: introduce TAG in companion object and use that as first parameter of Logger.e (I do think we had a convention of prefixing with mbgl_ but better to check the codebase).

actually, this is not a class, it's an extension function file.

[tobrun]

Could we do something as:

private const val TAG = "mgbl-LayerUtils"

at bottom or top of file?

LayerUtils naming comes from the java name of the LayerExt file.

[tobrun]

could be made private? We might be leaking this tag if not?

[ank27]

getLayerAs is a public inline function, which cannot use Private / internal declarations.
Although I can use @PublishedApi annotation to make TAG internal and let the function use it. but basically, that would be public TAG in a way.

[ank27]

Fixed by annotating TAG with @PublishedApi in order to use it in public inline function getLayerAs.

[kiryldz]

@ank27 how does it all look from Java side?

[ank27]

@ank27 how does it all look from Java side?
we can't use inline functions from java code directly. For that we have getLayer function already. Its the same with SourceExt as well.

[kiryldz]

LGTM

[onXAdamBrown]

Awesome!