bug#50422: 28.0.50; vc-git-checkout: accept nil as first argument

[Tino Calancha]

X-Debbugs-Cc: 39452@debbugs.gnu.org

Before the fix from bug#39452, the following was a valid call:

(vc-git-checkout nil "master")

Note that `vc-git-command' handles a nil 3rd argument.
(I rely in such a behavior).

Since we call now `vc-git--literal-pathspec' in several commands, then
we could add a check at the beginning of this function:

--8<-----------------------------cut here---------------start------------->8---
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 037fbcbc48..18ec4b6075 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -245,11 +245,12 @@ vc-git-update-on-retrieve-tag
 (defun vc-git--literal-pathspec (file)
   "Prepend :(literal) path magic to FILE."
   ;; Good example of file name that needs this: "test[56].xx".
-  (let ((lname (file-local-name file)))
-    ;; Expand abbreviated file names.
-    (when (file-name-absolute-p lname)
-      (setq lname (expand-file-name lname)))
-    (and file (concat ":(literal)" lname))))
+  (when (stringp file)
+    (let ((lname (file-local-name file)))
+      ;; Expand abbreviated file names.
+      (when (file-name-absolute-p lname)
+        (setq lname (expand-file-name lname)))
+      (and file (concat ":(literal)" lname)))))
 
 (defun vc-git--literal-pathspecs (files)
   "Prepend :(literal) path magic to FILES."
--8<-----------------------------cut here---------------end--------------->8---


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo 
version 1.16.0)
 of 2021-09-05 built on localhost.example.com
Repository revision: c61e2bff44bc494be15ba0a9f0f964389fd45b25
Repository branch: 46374-fix-regression
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: openSUSE Tumbleweed