Improve handling of non-ASCII characters in Git log messages

* lisp/vc/vc-git.el (vc-git-commits-coding-system): Now a defcustom.
(vc-git-log-output-coding-system): New defcustom.
(vc-git-print-log, vc-git-command, vc-git--call): Use
'vc-git-log-output-coding-system' for reading stuff from Git.
Don't override values of 'coding-system-for-read/write' if they
are bound by caller -- this allows the user to force an encoding
via "C-x RET c".
(vc-git-checkin): On MS-Windows, pass the log message via a
temporary file, to work around the limitations on passing
non-ASCII characters via command-line arguments.  Force using the
'locale-coding-system' for Git command-line arguments.  This fixes
problems with non-ASCII commit log messages on MS-Windows.
(Bug#23076)

* etc/NEWS: Mention the new vc-git related defcustoms.

1 files changed, 11 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 78d725bddf2..f5e5548ad63 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -987,6 +987,17 @@ back-end for the buffer's file, or remove it from version control.
 the color range from 'vc-annotate-color-map' is applied to the
 background or to the foreground.
 
+---
+*** New options for customizing encoding of Git commit log messages.
+The new options `vc-git-commits-coding-system' and
+`vc-git-log-output-coding-system' allow to customize the encoding of
+the log messages sent to Git when committing, and the decoding of the
+log messages read from Git history commands.  Both default to UTF-8;
+if you customize them, make sure they are consistent with the Git
+config variables i18n.commitEncoding and i18n.logOutputEncoding.
+(`vc-git-commits-coding-system' existed previously, but was a
+variable, not a user option.)
+
 +++
 *** 'compare-windows' now compares text with the most recently selected window
 instead of the next window.  If you want the previous behavior of