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. The bug and workaround is documented in https://www.mediawiki.org/wiki/Manual:HTML_templates#Caching.)
= Developer notes
We'd like to restrict these changes to Vector for the time being to check the performance implications of such a change. We could use a custom template partial validator if necessary or allow the passing of an alternative cache key.
= QA steps
Quick smoke test to check obvious UI elements are still there.
View https://en.wikipedia.beta.wmflabs.org/wiki/Main_Page
[] Verify edit tabs are present
[] Verify side bar contains links to random, interaction, tools, in other projects, languages
[] With correct permissions you should be able to see the more menu with delete/move
[] personal tools (username in top right) is present
[] there is still a footer
[] an article is rendered correctly