One of my most commonly used commands with projectile is helm-projectile. This
lets me locate any file in my project by pressing
C-c p h. Using the
narrowing abilities of helm, I can quickly filter the list of options to
exactly the one I want.
Because I work on some projects that are extremely large in size, I have
enabled projectiles caching mechanism. This tells projectile to maintain a
local cache of all the files within a project for faster searching. You can
enable this with
(setq projectile-enable-caching t)
Projectile helps maintain the current state of this cache by adding a hook to
find-file. Whenever a new file is found or created, projectile will
automatically add that new file to the cache. This saves me from having to
manually invalidate the cache with
C-c p i every time a create a new file.
However, if I delete a file, projectile does not automatically remove it from the cache. The next time I search for a similarly named file, the deleted file will still show up in the helm list of candidates. While not a deal breaker, it is certainly a source of annoyance for me. Since emacs is all about tweaking your environment to eliminate those little headaches, I knew I had to fix it.
At first, I thought adding a hook to delete-file would be the easy, straightforward fix. I couldn’t find any documentation for a delete-file-hook. Having tried to check out the source code, I realized that while find-file is implemented in lisp, delete-file is actually implemented in C.
Having been unable to find a hook associated with this function, what was I do to?
This is where defadvice comes in. I won’t go into detail about how defadvice works, but the short version is that defadvice allows you to suggest behavior to emacs before, after, or around an invocation of a particular function. You can read more about defadvice in the manual.
The below snippet adds advice before the delete-file function is called. It checks to see if the file is part of a projectile project; if the file is cached by projectile, it removes it from the cache.
NOTE This defadvice function is no longer necessary. This functionality has now been incorporated into projectile.
(defadvice delete-file (before purge-from-projectile-cache (filename &optional trash)) (if (and (projectile-project-p) projectile-enable-caching) (let* ((project-root (projectile-project-root)) (true-filename (file-truename filename)) (relative-filename (file-relative-name true-filename project-root))) (if (projectile-file-cached-p relative-filename project-root) (projectile-purge-file-from-cache relative-filename))))) (ad-activate 'delete-file)
That’s it. With just a few short lines, projectile will now invalidate the cache as soon as I delete a file, just as I would like. Isn’t emacs great?