Re: New feature in project.el: Remembering the previously used projects

["Simen Heggestøyl" <simenheg@runbox.com>]

Dmitry Gutov <dgutov@yandex.ru> writes:

> And another thought: maybe we should only add a project to the project
> list if user interaction happened (i.e. going through
> project-prompt-project-dir). Simen, what do you think?
>
> The patch below mostly does that, except it misses the case when a
> directory was selected from project-switch-project. [...]

Hm, I think it misses all cases when project-switch-project is used,
since project-current will find the project using
project--find-in-directory (project-switch-project already did the
prompting part).

Maybe a simple solution could be to only write to the file when the
addition caused the project list to change? I think it's a good change
regardless, but is it enough to fix your issue, Kévin?

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 1f2a4e8471..a2ef84e444 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -751,14 +751,15 @@ project--write-project-list
       (write-region nil nil filename nil 'silent))))

 (defun project--add-to-project-list-front (pr)
-  "Add project PR to the front of the project list and save it.
-Return PR."
+  "Add project PR to the front of the project list.
+Save the result to disk if the project list was changed."
   (project--ensure-read-project-list)
-  (let ((dir (project-root pr)))
+  (let* ((dir (project-root pr))
+         (do-write (not (equal (car project--list) dir))))
     (setq project--list (delete dir project--list))
-    (push dir project--list))
-  (project--write-project-list)
-  pr)
+    (push dir project--list)
+    (when do-write
+      (project--write-project-list))))

 (defun project--remove-from-project-list (pr-dir)
   "Remove directory PR-DIR from the project list.

Dmitry Gutov <dgutov@yandex.ru> writes:

> Alternatively, we could defer writing the file until Emacs is being
> closed (and do that in kill-emacs-hook).

Maybe. I think doing it more eagerly has some advantages though if we
can make it work:

- Launching a new Emacs session while another one is running will use
  the latest project list.

- If there's any problem writing to the file I imagine it's better to be
  notified about it up front rather than at the time Emacs is killed.

-- Simen