Nested objects with GeoJSON will not after setFeatureState

[iokill]

Hi!

mapbox-gl-js version: v0.48

browser: Chrome 68.0.3440.106

Steps to Trigger Behavior

Playing around with the hover-styles example (https://www.mapbox.com/mapbox-gl-js/example/hover-styles/), I encountered an issue that nested objects in a features object will not work after setFeatureState is called.

More specifically, doing this will work fine on initial rendering.

"line-color":
    ["case", ["boolean", ["feature-state", "hover"], false],
        ["get", "default-color"],
        ["get", "0", ["get", "colors"]]
],

However, after a mouseover and mouseleave, it will however revert to using the default fallback line color instead of the one retrieved with ["get", "0", ["get", "colors"]].

Additionally, this warning will be logged to the console:
Expected value to be of type object, but found string instead.

Link to Demonstration

https://jsfiddle.net/43bq7mfg/

Expected Behavior

Using get on nested objects in feature properties to work after using setFeatureState()

Actual Behavior

Using get on nested objects in feature properties logs a warning and will revert to the fallback/default value.

I'm not sure, but could this be related to #2434?

[jfirebaugh]

Great find and thanks for the thorough writeup @iokill. You're correct that this is related to #2434. Although I think we should keep this issue open for tracking purposes, the underlying cause is the same:

• GeoJSON features are transferred from a Web Worker that does most of the expression evaluation to the main thread.
• Expression evaluation for expressions that use feature-state is an exception: it's done on the main thread.
• Nested arrays and objects don't currently survive the transfer process, as detailed in Support nested objects and arrays for GeoJSON features in query*Features  #2434.