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

[Juri Linkov <juri@linkov.net>]

>>> +(defvar other-project-prefix-transient-commands '(project-other-window-command
>>> +                                                  project-other-frame-command
>>> +                                                  project-other-tab-command
>>> +                                                  other-window-prefix
>>> +                                                  other-frame-prefix
>>> +                                                  other-tab-prefix)
>>> +  "List of commands that `other-project-prefix' does not apply to.
>> This doesn't yet support such things as 'C-x 5 p p'?
>
> I'm not sure that other-project-prefix can do that.
>
> How does other-frame-prefix work? display-buffer-override-next-command sets
> up hooks in the very familiar fashion, so that the next command (and only
> the next command) is affected by a number of changed variables, which get
> restored after.
>
> I suppose other-project-prefix could learn all the new variables it needs
> to "carry on", look up their values, and set them additionally for the next
> command. But that seems very ad-hoc.
>
> It seems the "proper" way to fix that would be a cross-codebase change
> where all similar "prefix" commands themselves check whether the next
> command is a "prefix" command as well, and if so, keep the variables and
> hooks in place for the command after it. This would also mean moving the
> information from other-project-prefix-transient-commands to symbol
> properties (the alternative I've mentioned previously).

In https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63648#95
I made an unfinished attempt to handle this by:

```
diff --git a/lisp/window.el b/lisp/window.el
index ab7dd5ced12..52ba407d9c8 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -9099,7 +9091,8 @@ display-buffer-override-next-command
 		     (> (minibuffer-depth) minibuffer-depth)
 		     ;; But don't remove immediately after
 		     ;; adding the hook by the same command below.
-		     (eq this-command command))
+		     (eq this-command command)
+		     (memq this-command '(other-project-prefix)))
               (funcall exitfun))))
     ;; Call post-function after the next command finishes (bug#49057).
     (add-hook 'post-command-hook postfun)
```

I'm not sure if this is a proper way, this needs more trial-and-error.