Text translate is throwing an error

[mcwhittemore]

mapbox-gl-js version: 0.20.0

Steps to Trigger Behavior

1. updating text-translate value throws an error

Expected Behavior

The text should move

Actual Behavior

[samanpwbb]

This is breaking Mapbox Studio in production right now. If user attempts to change text-translate, the map crashes.

[jfirebaugh]

I'm unable to reproduce the issue. I added this test case to the test suite and it passes as expected.

Can you provide more detail about how to reproduce this?

[jfirebaugh]

Never mind, I can reproduce it if I set an explicit starting value for text-translate.

[jfirebaugh]

This seems to be related to #2561, the fix for #2534.

[jfirebaugh]

This is a latent bug in transition calculation that existed prior to #2561. Prior to #2561, a transition between "text-translate": [a, b] and "text-translate": [c, d]:

1. Started with [a, b]
2. Jumped to a value of [0, 0] when the transition began
3. Stayed at [0, 0] for the duration of the transition
4. Jumped to [c, d] at the conclusion of the transition

After #2561, it causes a runtime exception instead. Both behaviors are incorrect; the intended behavior is a smooth transition between the old and new translate values.

The bug arises due to an incorrect condition on when to apply the transition calculations intended for "cross-fading" properties. {background,fill,line}-pattern and line-dasharray are the only properties that are intended to have this type of transition calculation. This condition correctly selects only those properties, but this one incorrectly includes any array-typed property.

(Strict typing would have caught this bug.)

[mcwhittemore]

@jfirebaugh sorry for missing your comment above.