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

[Dmitry Gutov <dmitry@gutov.dev>]

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On 05/05/2024 19:40, Juri Linkov wrote:
>> 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.
> 
> Then maybe something like
> 
>    (define-key map (vector help-char)
>                (lambda () (interactive) (describe-bindings)))
> 
> or
> 
>    (define-key map (vector help-char)
>                (lambda () (interactive) (describe-keymap (cons 'keymap (current-active-maps)))))
> 
> or
> 
>    (define-key map (vector help-char)
>                (lambda () (interactive) (describe-keymap (cons 'keymap project-prefix-map))))

This actually seems unnecessary. See the attached latest version where 
the binding works automatically without explicit assignment.

>>> 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.
> 
> Wow, everything works now, will test more as a primary 'C-x p p' command.

Thanks, let me know if you find any other problems.

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diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 52fe4df9080..e41a23fe13d 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -967,6 +967,45 @@ 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.
+The next command you invoke will prompt for the project in which to run
+the command."
+  (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)
+              (if (or (eq this-command 'other-project-prefix)
+                          (eq last-command-event help-char))
+                  (call-interactively command)
+                (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)
+    (set-transient-map project-prefix-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")