Tiles with raster-fade-duration: 0 inappropriately held for underzooming

[ChrisLoer]

When you zoom out on a raster layer, MapLibre holds on to underzoomed child tiles for the "raster fade duration" so that it can apply a cross fade. In the case where the fade-duration is 0, it shouldn't hold onto them at all once the parent is loaded, but its logic to do that incorrectly always retains when fade-duration is 0:

maplibre-gl-js/src/source/source_cache.ts

Line 560 in c03607b

if (!tile || tile.fadeEndTime && tile.fadeEndTime <= browser.now()) continue;

The tiles will stay in the pyramid potentially indefinitely, although only while in the viewport and within the "max underzooming" range. Here's an example of a satellite layer with higher-zoom (cloudy) tiles persistently drawn where we should have lower zoom tiles:

At Felt, we're working around this by using raster-fade-duration: 1 which isn't visibly different but avoids the logic error.

I believe the correct logic should be:

if (!tile || !tile.fadeEndTime || tile.fadeEndTime <= browser.now()) continue;

a.k.a. "don't hold for fading, if (1) the tile is already out of the pyramid, (2) the tile doesn't have a fade duration set, or (3) the tile has a fade duration set, but it's expired"

cc @ibesora

[HarelM]

Javascript ! operation is tricky as I'm sure you know. 0, null and undefined all return true if you place a ! operation before them, in both proposals this will not work, I think - you'll need to explicitly check for undefined i.e. fadeEndTime === undefined.
In any case, this looks like a bug that would love a PR :-)