git: Remove untracked files from cached checkouts.

Cached checkouts could end up with stale untracked files, for example
because the checkout was interrupted.  As a result, when this happens
for the Guix checkout, users would not get substitutes for ‘guix pull’.

* guix/git.scm (delete-untracked-files): New procedure.
(switch-to-ref): Use it.
* tests/git.scm ("update-cached-checkout, untracked files removed"): New
test.

Co-authored-by: Ricardo Wurmus <rekado@elephly.net>
Change-Id: Iccbe644ade396ad27a037db7e0ef1c2a68ef91ce

1 files changed, 21 insertions, 1 deletions

diff --git a/tests/git.scm b/tests/git.scm
index ad43435b674..9ccd04f0cdf 100644
--- a/tests/git.scm
+++ b/tests/git.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2019, 2020, 2022 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2019-2020, 2022, 2024 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz
 ;;;
 ;;; This file is part of GNU Guix.
@@ -259,4 +259,24 @@
          ;; COMMIT should be the ID of the commit object, not that of the tag.
          (string=? commit head))))))
 
+(test-assert "update-cached-checkout, untracked files removed"
+  (call-with-temporary-directory
+   (lambda (cache)
+     (with-temporary-git-repository directory
+         '((add "a.txt" "A")
+           (add ".gitignore" ".~\n")
+           (commit "First commit"))
+       (let ((directory commit relation
+                        (update-cached-checkout directory
+                                                #:ref '()
+                                                #:cache-directory cache)))
+         (close-port
+          (open-output-file (in-vicinity cache "stale-untracked-file")))
+         (let ((directory2 commit2 relation2
+                           (update-cached-checkout directory
+                                                   #:ref '()
+                                                   #:cache-directory cache)))
+           (not (file-exists?
+                 (in-vicinity cache "stale-untracked-file")))))))))
+
 (test-end "git")