maint: add git hook scripts

We find it worthwhile to use consistent commit summary prefixes.
To that end, the commit-msg script requires that all commits I make
start with "$P: " (where $P is one of ~100 programs in coreutils)
or one of a few other words, like gnulib tests maint doc build.
It allows more than one word, so e.g., "cat tail head: " would also
be accepted.  Pádraig Brady wrote the initial version, with its
72-column and blank-if-present second line checks.
The pre-commit script is the same as the git-supplied sample script,
modulo a bug fix and the "exec 1>&2" redirection.
* scripts/git-hooks/commit-msg: New file.
* scripts/git-hooks/pre-commit: New file.
* scripts/git-hooks/applypatch-msg: New file.  Verbatim from .sample.
* cfg.mk: Exempt two of the new scripts from the no-leading-TABs check,
since they're nearly verbatim from git, and we want to stay in sync.
Exempt the commit-msg script from the no-"fail=0" check.

1 files changed, 50 insertions, 0 deletions

diff --git a/scripts/git-hooks/pre-commit b/scripts/git-hooks/pre-commit
new file mode 100755
index 000000000..1addec552
--- /dev/null
+++ b/scripts/git-hooks/pre-commit
@@ -0,0 +1,50 @@
+#!/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.
+#
+# To enable this hook, rename this file to "pre-commit".
+
+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=$(git config hooks.allownonascii)
+
+# Redirect output to stderr.
+exec 1>&2
+
+# Cross platform projects tend to avoid non-ascii filenames; prevent
+# them from being added to the repository. We exploit the fact that the
+# printable range starts at the space character and ends with tilde.
+if [ "$allownonascii" != "true" ] &&
+	# 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
+	echo "Error: Attempt to add a non-ascii file name."
+	echo
+	echo "This can cause problems if you want to work"
+	echo "with people on other platforms."
+	echo
+	echo "To be portable it is advisable 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 there are whitespace errors, print the offending file names and fail.
+exec git diff-index --check --cached $against --