When loading the Leaflet library with Resource Loader, the default marker icon does not show properly.
{F31720325}
The issue vanishes when putting resource loader in debug mode or when making this modification (based on MW 1.34): https://github.com/JeroenDeDauw/MediaWiki/commit/1713ccde9de7d59634b1a134c58ee3c84ba01642
The issue has been present for at least 2 years. (Up till MW 1.34 the Maps extension used a hack to avoid the problem: stuffing an Html::linkedStyle() into the header on top of using the Resouce Loader. This no longer works as of 1.34, though is likely not related to the root cause of the problem.)
Using https://github.com/ghybs/leaflet-defaulticon-compatibility does not resolve the issue. (Wider context: https://github.com/Leaflet/Leaflet/issues/4968)
Related:
* Wikitech mail: https://lists.wikimedia.org/pipermail/wikitech-l/2020-March/093257.html
* Wikitech replies: https://lists.wikimedia.org/pipermail/wikitech-l/2020-April/thread.html
* Maps issue: https://github.com/JeroenDeDauw/Maps/issues/607
Some relevant code:
* Resource loader module definition:
https://github.com/JeroenDeDauw/Maps/blob/24359f3236f0e1488127eeef5697a7b288fdc16e/extension.json#L111
* leaflet.css:
https://github.com/JeroenDeDauw/Maps/blob/24359f3236f0e1488127eeef5697a7b288fdc16e/resources/lib/leaflet/leaflet.css