New hook 'vc-retrieve-tag-hook' (Bug#32754)

* etc/NEWS: Mention the new variable.

* lisp/vc/vc.el (vc-retrieve-tag-hook): New hook.
(vc-retrieve-tag): Run the new hook and update its
documentation string.

etc/NEWS

@@ -329,6 +329,8 @@ git-grep when 'vc-git-grep' is used.
 When some files are marked, only those are stashed.
 When no files are marked, all modified files are stashed, as before.
 
+*** The new hook 'vc-retrieve-tag-hook' runs after retrieving a tag.
+
 ** diff-mode
 *** Hunks are now automatically refined by default.
 To disable it, set the new defcustom 'diff-font-lock-refine' to nil.

lisp/vc/vc.el

@@ -834,6 +834,13 @@ See `run-hooks'."
   :type 'hook
   :group 'vc)
 
+;;;###autoload
+(defcustom vc-retrieve-tag-hook nil
+  "Normal hook (list of functions) run after retrieving a tag."
+  :type 'hook
+  :group 'vc
+  :version "27.1")
+
 (defcustom vc-revert-show-diff t
   "If non-nil, `vc-revert' shows a `vc-diff' buffer before querying."
   :type 'boolean
@@ -2153,7 +2160,8 @@ otherwise use the repository root of the current buffer.
 If NAME is empty, it refers to the latest revisions of the current branch.
 If locking is used for the files in DIR, then there must not be any
 locked files at or below DIR (but if NAME is empty, locked files are
-allowed and simply skipped)."
+allowed and simply skipped).
+This function runs the hook `vc-retrieve-tag-hook' when finished."
   (interactive
    (let* ((granularity
            (vc-call-backend (vc-responsible-backend default-directory)
@@ -2180,6 +2188,7 @@ allowed and simply skipped)."
     (vc-call-backend (vc-responsible-backend dir)
 		     'retrieve-tag dir name update)
     (vc-resynch-buffer dir t t t)
+    (run-hooks 'vc-retrieve-tag-hook)
     (message "%s" (concat msg "done"))))