From 0419734fd39f8cd67472c0294295ef1508e39d85 Mon Sep 17 00:00:00 2001
From: Phillip Lord <phillip.lord@russet.org.uk>
Date: Wed, 15 Jun 2016 17:36:42 +0100
Subject: [PATCH] Fix error from vc-git when GIT_DIR is set

* lisp/vc/vc-git.el (vc-git-working-revision): Set default-directory to
  repository root to prevent an error when GIT_DIR is relative to it.
* test/automated/vc-git-tests.el: New file.

Addresses Bug#23769
---
 lisp/vc/vc-git.el              |  8 ++++--
 test/automated/vc-git-tests.el | 60 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 test/automated/vc-git-tests.el

diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index f35c84d..ea26a7d 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -260,9 +260,13 @@ vc-git-state
             (vc-git--state-code diff-letter)))
       (if (vc-git--empty-db-p) 'added 'up-to-date))))
 
-(defun vc-git-working-revision (_file)
+(defun vc-git-working-revision (file)
   "Git-specific version of `vc-working-revision'."
-  (let (process-file-side-effects)
+  ;; Call this in the root directory, or Emacs may error when setting
+  ;; the modeline when called from a git pre-commit hook, which sets
+  ;; GIT_DIR. (Bug #23769)
+  (let ((default-directory (vc-git-root file))
+        (process-file-side-effects))
     (vc-git--rev-parse "HEAD")))
 
 (defun vc-git--symbolic-ref (file)
diff --git a/test/automated/vc-git-tests.el b/test/automated/vc-git-tests.el
new file mode 100644
index 0000000..8001bcb
--- /dev/null
+++ b/test/automated/vc-git-tests.el
@@ -0,0 +1,60 @@
+;;; vc-git-tests.el --- tests for vc/vc-git.el
+
+;; Copyright (C) 2016 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'ert)
+(require 'vc-git)
+
+;; This will break when merged from the emacs-25 branch to master,
+;; because of the change of directory structure. The actual file is
+;; not important at all, so long as it is checked into git.
+(defvar vc-git-tests-file
+  (concat
+   (expand-file-name
+    "data/xref/"
+    (file-name-directory (or load-file-name (buffer-file-name))))
+   "file1.txt"))
+
+
+(ert-deftest open-this-file ()
+  "Test for Bug #23769."
+  (should
+   (let ((git-dir (getenv "GIT_DIR")))
+     (unwind-protect
+         (progn
+           (setenv "GIT_DIR" nil)
+           (find-file vc-git-tests-file))
+       (when (get-file-buffer vc-git-tests-file)
+         (setenv "GIT_DIR" git-dir)
+         (kill-buffer (get-file-buffer vc-git-tests-file))))))
+  (should
+   (let ((git-dir (getenv "GIT_DIR")))
+     (unwind-protect
+         (progn
+           (setenv "GIT_DIR" ".git")
+           (find-file vc-git-tests-file))
+       (when (get-file-buffer vc-git-tests-file)
+         (setenv "GIT_DIR" git-dir)
+         (kill-buffer (get-file-buffer vc-git-tests-file)))))))
+
+
+;;; vc-git-tests.el ends here
-- 
2.8.4