Update command cache when editing the .dir-locals.el file

[sfavazza]

Expected behavior

When editing a project .dir-locals.el (e.g. updating projectile-project-[install|test|run|etc..]-cmd) the projectile-*-cmd-map should be updated such that the first prompt on next invocation should be the latest from .dir-locals.el.

Actual behavior

• after modifying a projectile command definition in .dir-locals.el
• invoking the same command shows the last used command (before editing the configuration file)
• since the first time the project is accessed and the .dir-locals.el read for the first time, any change to the dir-locals.el is not read anymore

Steps to reproduce the problem

• create a .dir-locals.el file in your project, defining, say, projectile-project-test-cmd
• open the project in Emacs
• invoke projectile-test-project (the value read from the .dir-locals.el will be proposed)
• open the .dir-locals.el buffer
  • modify the command
  • save the buffer
  • revert the buffer such that the changes are applied
• try to invoke projectile-test-project again ==> the old version of the command is proposed

Environment & Version information

Projectile version information

Projectile 20230713.1023

Emacs version

GNU Emacs 28.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo version 1.16.0) of 2023-03-10

Operating system

Linux 5.19.0-46-generic #47~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC

[sfavazza]

@bbatsov any thoughts?

[bbatsov]

I recall there was some command to force a re-read of dir-locals (e.g. (dir-locals-read-from-dir (dired-current-directory)), so using something like this might be a solution to your problem. Not sure if you have some different solution in mind.

[sfavazza]

This won't solve the issue, because the problem is not with the dir-locals per-se, rather with the projectile cache. See the projectile-test-command case below:

(defun projectile-test-command (compile-dir)
  "Retrieve the test command for COMPILE-DIR.

The command is determined like this:

- first we check `projectile-test-cmd-map' for the last
test command that was invoked on the project

- then we check for `projectile-project-test-cmd' supplied
via .dir-locals.el

- finally we check for the default test command for a
project of that type"
  (or (gethash compile-dir projectile-test-cmd-map)
      projectile-project-test-cmd
      (projectile-default-test-command (projectile-project-type))))

Basically after the cache is initialized the dir-locals is not considered anymore. As a solution I was thinking the following:

• record the modify time-stamp of the dir-locals
• on following invocation of the same command the timestamp is checked to detect changes
• if the actual is newer than the last saved, use it (this will automatically update the cache)
• otherwise use the cache

This would require saving a timestamp (not a fun of this approach).

Otherwise projectile should add a function to the lisp-data-mode-hook (or the after-save-hook), to update projectile cache when a .dir-local.el buffer is saved.

Open to other suggestions as well 😃

I would be more than happy to open a merge-request if we agree on a solution.

[bbatsov]

I guess a third approach would be a command that people can manually trigger to update the cache when needed, that they can optionally use as a hook function as you suggested. PR welcome!