meta:hooks: Refactor pre-commit + check renaming

Refactor the script to match my coding style more and update the
comments.
When checking the filenames for non-ASCII characters, check also
renaming of files instead of only additions.

meta/git/hooks/pre-commit

@@ -1,49 +1,46 @@
 #!/bin/sh
 #
-# An example hook script to verify what is about to be committed.
-# Called by "git commit" with no arguments.  The hook should
-# exit with non-zero status after issuing an appropriate message if
-# it wants to stop the commit.
+# A hook script to verify what is about to be committed.
+# Called by "git commit" with no arguments. The hook should exit with non-zero
+# status after issuing an appropriate message if it wants to stop the commit.
 #
-# To enable this hook, rename this file to "pre-commit".
+# To enable this hook, save this file in ".git/hooks/pre-commit".
 
-if git rev-parse --verify HEAD >/dev/null 2>&1
-then
+die() {
+	printf "$1" >&2
+	exit ${2:-1}
+}
+
+if git rev-parse --verify HEAD >/dev/null 2>&1; then
 	against=HEAD
 else
 	# Initial commit: diff against an empty tree object
 	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
 fi
 
-# If you want to allow non-ASCII filenames set this variable to true.
-allownonascii=$(git config --bool hooks.allownonascii)
-
 # Redirect output to stderr.
 exec 1>&2
 
-# 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 [ "$allownonascii" != "true" ] &&
+# Check that all filenames include only ASCII characters.
+allownonascii=$(git config --bool hooks.allownonascii)
+if [ "$allownonascii" != "true" ]; then
+	# We exploit the fact that the printable range starts at the space character
+	# and ends with tilde.
 	# Note that the use of brackets around a tr range is ok here, (it's
 	# even required, for portability to Solaris 10's /usr/bin/tr), since
 	# the square bracket bytes happen to fall in the designated range.
-	test $(git diff --cached --name-only --diff-filter=A -z $against |
-	  LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
-then
-	cat <<\EOF
-Error: Attempt to add a non-ASCII file name.
-
-This can cause problems if you want to work with people on other platforms.
-
-To be portable it is advisable to rename the file.
-
-If you know what you are doing you can disable this check using:
-
-  git config hooks.allownonascii true
-EOF
-	exit 1
+	num_nonascii=$(
+		git diff --cached --name-only --diff-filter=AR -z $against \
+		| LC_ALL=C tr -d '[ -~]\0' \
+		| wc -c
+	)
+	if [ $num_nonascii != 0 ]; then
+		printf "Rename files to only include ASCII characters.\n" >&2
+		die "Or set hooks.allownonascii to true.\n"
+	fi
 fi
 
-# If there are whitespace errors, print the offending file names and fail.
-exec git diff-index --check --cached $against --
+# Check for whitespace errors.
+if ! git diff-index --check --cached $against --; then
+	die
+fi