Expressions of Equality throws error

[andest01]

mapbox-gl-js version:
Mapbox Version 0.43.0

Steps to Trigger Behavior

http://jsbin.com/tonekocohu/1/edit?html,output

Create a Mapbox Style with the following paint property:

// Minnesota = 27, BRRRRRR ITS COLD
const VERY_COLD_US_STATE_FIPS_CODE = '27' 

// a string property on your source's GeoJSON
const PROPERTY_NAME = 'fips' 

// lets make a style that will highlight Minnesota's border with a
// thicker border - so you know where it's cold!
const equalityExpression = ['==', ['get', PROPERTY_NAME], VERY_COLD_US_STATE_FIPS_CODE]
const widthExpression = ['case',
  equalityExpression, 2.5,
  0.5,
]

// apply our expression to the `line-width` property
// per the mapbox style spec

// this doesnt work :(
const paintProperty = {
    'line-width': widthExpression,
    'line-color': '#FFFFFF',
  },
}

Expected Behavior

The style for the applied geometry uses the expression correctly.

Actual Behavior

The mapbox engine crashes: Uncaught Error: can't serialize object of type function

== is undocumented, but clearly exists in the code base.
https://github.com/mapbox/mapbox-gl-js/blob/919be588592509f97eeb4a22510b56e7982dbcc6/src/style-spec/expression/definitions/equals.js
https://github.com/mapbox/mapbox-gl-js/blob/master/src/style-spec/expression/definitions/index.js#L37

The == operator did work in a prior mapbox version, specifically 0.42.0.

[andest01]

There's a workaround: Use all with <= and >=.

const greaterThanCondition = ['>=', ['to-string', ['get', PROPERTY_ID]], expectedProperty]
const lessThanCondition = ['<=', ['to-string', ['get', PROPERTY_ID]], expectedProperty]
const unfortunateEquality = ['all', greaterThanCondition, lessThanCondition]
const widthExpression = ['case',
  unfortunateEquality, 2.5,
  0.5,
]

[jfirebaugh]

@andest01, thanks for the report. Could you please provide a self-contained example on jsbin.com or similar that shows the issue?

[andest01]

@jfirebaugh http://jsbin.com/cumotohelu/3/edit?html,output

[jfirebaugh]

That seems to be generating some unrelated style validation errors.

[andest01]

@jfirebaugh How frustrating - I inadvertently pasted an older version. My apologies.

I tested this version in a new tab and it's exhibiting the above behavior.
http://jsbin.com/tonekocohu/1/edit?html,output

[jfirebaugh]

Thanks, I see the issue now! Should be an easy fix.