Refactor "GeoJSONSource" as a composition "VectorTileSource"

[anandthakker]

See the instructions in this comment for a description of what would currently be required to create a custom variation of VectorTileSource.

On the worker side, it's not bad at all: VectorTileWorkerSource is designed to accept a custom loadVectorTile in its constructor. But on the main thread, the whole VectorTileSource has to be forked in order to add a type: 'my-custom-source-type-name' property to any params sent to the worker (so that messages go to the custom worker source rather than the core VectorTileWorkerSource).

If VectorTileSource just kept a this.type property from its constructor options and sent it along in all its worker requests, this would simplify a custom source author's job significantly.

cc @lucaswoj

[lucaswoj]

Sounds like you're having trouble plumbing a custom Source with its worker. Would this problem go away if we had a WorkerSource per Source (rather than a WorkerSource per Source type)? Would this problem go away if we hit #3034?

[anandthakker]

Would this problem go away if we had a WorkerSource per Source (rather than a WorkerSource per Source type)? Would this problem go away if we hit #3034?

Yep, good point. And, as the custom source interface is still not public, I don't see any reason not to wait and take care of this as part of #3034

[lucaswoj]

I just changed the title of this ticket to preserve the original intent and make the goal more clearly defined 😄