Sharing StyleLayers between WorkerTiles is dangerous

[jfirebaugh]

StyleLayers are shared between WorkerTiles, via the worker StyleLayerIndex. But StyleLayers contain state consisting of the evaluated result of style properties at a certain zoom level, and WorkerTiles may have different zoom levels.

Currently, we avoid any issues that this shared state could cause by carefully calling StyleLayer#recalculate at the entry point to every async callback in WorkerTile. But this is relatively fragile and error prone, and also requires reevaluation of previously-evaluated properties.

A better solution would be to have each WorkerTile call StyleLayer#recalculate once for each necessary layer, and store the logical result state independently of any other WorkerTiles. This would likely require a significant refactor of the internals of style recalculation (refs #2739, #3044).

[DannyDelott]

This is interesting.

I'm noticing a bug where Map#queryRenderedFeatures throws an AssertionError: false === true at lower zoom levels on my custom layer. When I zoom in closer on the map and try again, it is able to get the features from my custom layer no problem. It's hard to reproduce, so I haven't filed a bug for it-- but this might be related?

What areas of the library are affected by this issue?

[jfirebaugh]

I don't believe this is causing any bugs currently -- this is a refactoring issue noting how we could improve the code in the future. An assertion error in queryRenderedFeatures sounds like a separate issue.

[kristfal]

@DannyDelott just encountered the same issue while running V0.23.0. The assertion error should be fixed by #3233.