Wikimedia sites are apparently going https only, which means that any code using http:// may break.
The announcement is very light on details.
Both core and compat support using https, however they both have instances where a URL is created manually (not via Family methods), and that URL has a http:// protocol/schema.
I suspect that the servers will still forward http:// URLs to https:// , but that needs to be confirmed.
In any case, we should fix any instances where the code is using the Family methods to create a URL.
Here is one regex to see some examples of the problem
git grep '^[^#@]*http:\/\/.*wiki.*\.org'