Extend sample pre-commit hook to check for non ascii filenames

At the moment non-ascii encodings of filenames are not portably
converted between different filesystems by git. This will most likely
change in the future but to allow repositories to be portable among
different file/operating systems this check is enabled by default.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

templates/hooks--pre-commit.sample

@@ -7,6 +7,31 @@
 #
 # To enable this hook, rename this file to "pre-commit".
 
+# If you want to allow non-ascii filenames set this variable to true.
+allownonascii=$(git config hooks.allownonascii)
+
+# Cross platform projects tend to avoid non-ascii filenames; prevent
+# them from being added to the repository. We exploit the fact that the
+# printable range starts at the space character and ends with tilde.
+if [ "$allownonascii" != "true" ] &&
+	test "$(git diff --cached --name-only --diff-filter=A -z |
+	  LC_ALL=C tr -d '[ -~]\0')"
+then
+	echo "Error: Attempt to add a non-ascii filename."
+	echo
+	echo "This can cause problems if you want to work together"
+	echo "with people on other platforms than you."
+	echo
+	echo "To be portable it is adviseable to rename the file ..."
+	echo
+	echo "If you know what you are doing you can disable this"
+	echo "check using:"
+	echo
+	echo "  git config hooks.allownonascii true"
+	echo
+	exit 1
+fi
+
 if git-rev-parse --verify HEAD >/dev/null 2>&1
 then
 	against=HEAD