New command vc-working-tree-switch-project (bug#79024)

* lisp/vc/vc.el (vc-working-tree-switch-project): New command.
* lisp/vc/vc-hooks.el (vc-prefix-map): Bind it to C-x v w s.
* doc/emacs/vc1-xtra.texi (Other Working Trees):
* etc/NEWS: Document it.

doc/emacs/vc1-xtra.texi

@@ -285,7 +285,11 @@ tree.
 Add a new working tree.
 
 @item C-x v w w
-Visit this file in another working tree.
+Visit this file or directory in another working tree.
+
+@item C-x v w s
+Invoke @kbd{C-x p p} (@code{project-switch-project}) but limited to
+other working trees.
 
 @item C-x v w x
 Delete a working tree you no longer need.
@@ -313,12 +317,24 @@ new working tree.
 @findex vc-switch-working-tree
 Once your repository has other working trees, you can use the command
 @kbd{C-x v w w} (@code{vc-switch-working-tree}) to switch between them.
-It tries to find the analogue of the current buffer's file
-under another working tree.  Typically the sets of workfiles
-under different working trees differ more in file contents than in which
-files do and do not exist.  In other words, the file the
-current buffer visits probably exists in other working trees too, and
-this command lets you switch to those versions of the file.
+It tries to find the analogue of the current buffer's file or directory
+under another working tree.  Typically the sets of workfiles under
+different working trees differ more in file contents than in which files
+do and do not exist.  In other words, the file or directory the current
+buffer visits probably exists in other working trees too, and this
+command lets you switch to those versions of the file.
+
+@kindex C-x v w s
+@findex vc-working-tree-switch-project
+An alternative way to switch between working trees is @kbd{C-x v w s}
+(@code{vc-working-tree-switch-project}).  This prompts you to select a
+working tree, and then displays a menu of commands to operate on it.
+This is in fact just @kbd{C-x p p} (@code{project-switch-project})
+(@pxref{Switching Projects}) but with the selection of projects limited
+to other working trees.  The main difference between @kbd{C-x v w w} and
+@kbd{C-x v w s} is that the former looks for an analogue of the current
+buffer in the other working tree while the latter considers the other
+working tree as a whole, independent project.
 
 @kindex C-x v w x
 @kindex C-x v w R

etc/NEWS

@@ -1946,6 +1946,7 @@ other working trees:
 
 - 'C-x v w c': Add a new working tree.
 - 'C-x v w w': Visit this file in another working tree.
+- 'C-x v w s': Like 'C-x p p' but limited to other working trees.
 - 'C-x v w x': Delete a working tree you no longer need.
 - 'C-x v w R': Relocate a working tree to another file name.
 

lisp/vc/vc-hooks.el

@@ -968,6 +968,7 @@ In the latter case, VC mode is deactivated for this buffer."
   "!"   #'vc-edit-next-command
   "w c" #'vc-add-working-tree
   "w w" #'vc-switch-working-tree
+  "w s" #'vc-working-tree-switch-project
   "w x" #'vc-delete-working-tree
   "w R" #'vc-move-working-tree)
 (fset 'vc-prefix-map vc-prefix-map)

lisp/vc/vc.el

@@ -4443,6 +4443,20 @@ to the root of this working tree."
   (let ((project-current-directory-override directory))
     (project-find-matching-buffer)))
 
+;;;###autoload
+(defun vc-working-tree-switch-project (dir)
+  "Like \\[project-switch-project] but limited to projects with the same backing repository.
+Must be called from within an existing VC working tree.
+Prompts for the directory file name of the other working tree."
+  ;; There is no point in calling this from Lisp as opposed to calling
+  ;; `project-switch-project' directly because it is a trivial wrapper.
+  (declare (interactive-only project-switch-project))
+  (interactive
+   (list
+    (vc--prompt-other-working-tree (vc-responsible-backend default-directory)
+                                   "Other working tree to switch to")))
+  (project-switch-project dir))
+
 ;;;###autoload
 (defun vc-delete-working-tree (backend directory)
   "Delete working tree DIRECTORY with same backing repository as this tree.