locate_template calls file_exists a lot

[spacedmonkey]

The function locate_template calls file_exists three times for every each template name. As locate_template can be called multiple times on a page request for both classic and block themes, this can result in poor performance for this function.

As file_exists can be an expensive function to run, as the file lookup on file system can be slow, some level of caching should be added to this function.

[costdev]

Thanks for opening this ticket @spacedmonkey! Worth looking into for sure.

file_exists results are cached by PHP:

Note: The results of this function are cached. See clearstatcache() for more details.
​Reference

So while this reduces the impact of filesystem calls, having a cache for the results of the foreach() loop may be useful here.

Have you run any tests to see how much of a performance improvement a cache of these results brings?

[spacedmonkey]

Duplicate of #58576.