showTileBoundaries debug option should read from a source whose min/maxzoom include current zoom if available

[DanielCeregatti]

mapbox-gl-js version: 0.38.0

Steps to Trigger Behavior

1. Visit the openmaptiles style page, open the javascript console.
2. Paste maps['osm-liberty'].showTileBoundaries = true; in the console.
3. Note the red tile boundaries appear in osm-liberty map on that page. If you zoom that map beyond zoom 6 the tile boundaries disappear.

Expected Behavior

The boundary tiles should not disappear.

Actual Behavior

The boundary tiles disappear.

While the instructions above reference a page that's using mapbox-gl 0.31.0, I have a private test case that's using 0.38.0 that's exhibiting the same behavior. Unfortunately I can't link to it because it's behind firewalls.

I've opened a ticket on the style maker's github here: maputnik/osm-liberty#13. Here's a relevant excerpt from that ticket:

I found this out because I've copied this style to a map I'm working on as a proof-of-concept for the use of mapbox-gl for my company. I've noticed this problem is tied to the natural_earth layer in style.json. If I completely remove this layer definition and reload the page, setting showTileBoundaries = true does absolutely nothing. If I remove the source declaration for natural_earth_shaded_relief after removing the natural_earth layer, everything works as expected.

[lbud]

Thanks for the report @DanielCeregatti. This is happening because the code for rendering tile boundaries does so based on the first present source, which in the case of OSM Liberty is natural_earth_shaded_relief, with a maxzoom of 6. We should consider hardening this logic on the gl-js side, but on the OSM Liberty side, you could move the most complete source (in this case, openmaptiles) to be the first source listed in sources as a workaround for now.

[DanielCeregatti]

Thanks @lbud! This solution worked. Considering this could technically still be considered a bug, I'm opting to leave this open, unless you object, in which case I'd be happy to close it.