bug#70577: [PATCH] New command other-project-prefix

[Dmitry Gutov <dmitry@gutov.dev>]

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On 02/05/2024 09:12, Juri Linkov wrote:
>>> Something is wrong here.  I bound 'other-project-prefix' to 'C-x p P'.
>>> Then typing 'C-x p P C-x d' asked a directory name, then later
>>> after selecting a project asked for the directory name again.
>>
>> Looks like that has to do with the interactive spec. See the attached next
>> revision, it seems to behave better.
> 
> Thanks, this works now (except that it can't be debugged because of the
> Lisp error: (wrong-type-argument listp ignore)).
> 
> Also 'C-h' is not a problem: 'help-form-show' does nothing
> without 'help-form', but with 'help-form' works fine:
> 
>        (define-key map (vector help-char)
>                    (lambda ()
>                      (interactive)
>                      (let ((help-form "You can use any global keybinding."))
>                        (help-form-show))))

We would want 'C-h' to show the regular buffer with key bindings, won't 
we? With similar output to the one that we get after 'C-x p C-h' or 'C-x 
v C-h'. The output might be weirder because of the composed keymap, but 
it could still be useful.

Also, with which-key-mode, C-h would do its thing.

> However, a much bigger problem is that unfortunately many test cases from
> https://debbugs.gnu.org/63648#203 are broken.  For example,
> 'C-x p p C-b' fails the same way as in bug#58784.
> 'C-x p p f M-n' fails because it expects to read arguments
> in a previous project with an old value of default-directory, etc.

Thanks for noticing. Looks like the call to project-prompter can change 
the value of this-command, and that's why the subsequent check went down 
the wrong branch. See the attached v3 with the fix.

> Maybe this could be fixed by running 'interactive' in a previous project
> by using something like:
> 
>    (around-fun
>     (lambda (command &rest _args)
>       (interactive (lambda (spec)
>                      (let ((default-directory prev-dir))
>                        (advice-eval-interactive-spec spec))))

I think the command might rather expect to be called in the "new" 
project. And also while some have interactive specs with significant 
logic inside, others don't; introducing a difference there could cause 
more problems.

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diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 000a05804a8..1ee6e5848a3 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -952,6 +952,48 @@ project-other-tab-command
 (when (bound-and-true-p tab-prefix-map)
   (define-key tab-prefix-map "p" #'project-other-tab-command))
 
+;;;###autoload
+(defun other-project-prefix ()
+  "\"Switch\" to another project before running an Emacs command.
+Makes sure the next command invoked asks for the project to run it in."
+  (interactive)
+  (prefix-command-preserve-state)
+  (letrec ((depth (minibuffer-depth))
+           (echofun (lambda () "[switch-project]"))
+           (around-fun
+            (lambda (command &rest _args)
+              (interactive)
+              (advice-remove this-command around-fun)
+              (unless (or (eq this-command 'other-project-prefix)
+                          (eq last-command-event help-char))
+                (let* ((this-command-saved this-command)
+                       (root (funcall project-prompter)))
+                  (if (or (string-prefix-p "project-"
+                                           (symbol-name this-command-saved))
+                          (get this-command-saved 'project-aware))
+                      (let ((project-current-directory-override root))
+                        (call-interactively command))
+                    (let ((default-directory root))
+                      (call-interactively command)))))))
+           (prefun
+            (lambda ()
+              (unless (> (minibuffer-depth) depth)
+                (remove-hook 'pre-command-hook prefun)
+                (remove-hook 'prefix-command-echo-keystrokes-functions echofun)
+                (when (and this-command (symbolp this-command))
+                  (advice-add this-command :around around-fun))))))
+    (add-hook 'pre-command-hook prefun)
+    (add-hook 'prefix-command-echo-keystrokes-functions echofun)
+    (let ((map (make-sparse-keymap)))
+      (set-keymap-parent map project-prefix-map)
+      ;; Doesn't work ;-(
+      ;; (define-key map (vector help-char)
+      ;;             (lambda () (interactive) (help-form-show)))
+      (set-transient-map map))
+    (message (concat "Type " (project--keymap-prompt) " or any global key"))))
+
+;; (define-key project-prefix-map (kbd "P") #'other-project-prefix)
+
 (declare-function grep-read-files "grep")
 (declare-function xref--find-ignores-arguments "xref")