//This bug report awaits {T93546} //
https://gerrit.wikimedia.org/r/#/c/223165/ has a top-level template `Skin.mustache` that includes the partial template `sidebar.mustache` using
{{>sidebar}}
I notice on my local wiki if I edit `Skin.mustache` and view a page with the skin, I see the change to it (good!), but if I edit the partial `sidebar.mustache`, I don't see the change to it, even if I use ?action=purge (bug!).
Looking at `includes/TemplateParser.php` in core, it does a simple
// Read the template file
$fileContents = file_get_contents( $filename );
// Generate a quick hash for cache invalidation
$fastHash = md5( $fileContents );
this doesn't notice changes to partials included by $filename.
This is probably hard to fix. A workaround is to make cosmetic changes to all parent templates that include the edited partial template. I documented the bug and workaround in https://www.mediawiki.org/wiki/Manual:HTML_templates#Caching.