Add git commit hooks that do some simple checks on commits.

* autogen.sh: Install Git hooks, if using Git.
* build-aux/git-hooks/commit-msg, build-aux/git-hooks/pre-commit:
New files, which are Git hooks that check for portable file names, and
do some simple checks for commit message format.

autogen.sh

@@ -208,6 +208,46 @@ autoreconf -i -I m4 || exit $?
 ## cause 'make' to needlessly run 'autoheader'.
 echo timestamp > src/stamp-h.in || exit
 
+## Install Git hooks, if using Git.
+if test -d .git/hooks; then
+    tailored_hooks=
+    sample_hooks=
+
+    for hook in commit-msg pre-commit; do
+	cmp build-aux/git-hooks/$hook .git/hooks/$hook >/dev/null 2>&1 ||
+	tailored_hooks="$tailored_hooks $hook"
+    done
+    for hook in applypatch-msg pre-applypatch; do
+	cmp .git/hooks/$hook.sample .git/hooks/$hook >/dev/null 2>&1 ||
+	sample_hooks="$sample_hooks $hook"
+    done
+
+    if test -n "$tailored_hooks$sample_hooks"; then
+	echo "Installing git hooks..."
+
+	case `cp --help 2>/dev/null` in
+	  *--backup*--verbose*)
+	    cp_options='--backup=numbered --verbose';;
+	  *)
+	    cp_options='';;
+	esac
+
+	if test -n "$tailored_hooks"; then
+	    for hook in $tailored_hooks; do
+		cp $cp_options build-aux/git-hooks/$hook .git/hooks || exit
+		chmod a-w .git/hooks/$hook || exit
+	    done
+	fi
+
+	if test -n "$sample_hooks"; then
+	    for hook in $sample_hooks; do
+		cp $cp_options .git/hooks/$hook.sample .git/hooks/$hook || exit
+		chmod a-w .git/hooks/$hook || exit
+	    done
+	fi
+    fi
+fi
+
 echo "You can now run \`./configure'."
 
 exit 0

build-aux/git-hooks/commit-msg

@@ -0,0 +1,90 @@
+#!/bin/sh
+# Check the format of GNU Emacs change log entries.
+
+# Copyright 2014 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/>.
+
+# Written by Paul Eggert.
+
+# Use a UTF-8 locale if available, so that the UTF-8 check works.
+# Use U+00A2 CENT SIGN to test whether the locale works.
+cent_sign_utf8_octal='\302\242'
+at_sign=`
+  printf "${cent_sign_utf8_octal}@" |
+  awk '{print substr($0, 2)}' 2>/dev/null
+`
+if test "$at_sign" != @; then
+  at_sign=`
+    printf "${cent_sign_utf8_octal}@" |
+    LC_ALL=en_US.utf8 awk '{print substr($0, 2)}' 2>/dev/null
+  `
+  if test "$at_sign" = @; then
+    LC_ALL=en_US.utf8; export LC_ALL
+  fi
+fi
+
+# Check the log entry.
+exec awk '
+  /^#/ { next }
+
+  !/^.*$/ {
+    print "Invalid character (not UTF-8)"
+    status = 1
+  }
+
+  nlines == 0 && !/[^[:space:]]/ { next }
+
+  { nlines++ }
+
+  nlines == 1 && /^[[:space:]]/ {
+    print "White space at start of first line"
+    status = 1
+  }
+
+  nlines == 2 && /[^[:space:]]/ {
+    print "Nonempty second line"
+    status = 1
+  }
+
+  /[[:cntrl:]]/ {
+    print "Text contains control character; please use spaces instead of tabs"
+    status = 1
+  }
+
+  72 < length && /[[:space:]]/ {
+    print "Line longer than 72 characters"
+    status = 1
+  }
+
+  140 < length {
+    print "Word longer than 140 characters"
+    status = 1
+  }
+
+  /^Signed-off-by: / {
+    print "'Signed-off-by:' present"
+    status = 1
+  }
+
+  END {
+    if (nlines == 0) {
+      print "Empty change log entry"
+      status = 1
+    }
+    exit status
+  }
+' <"$1"

build-aux/git-hooks/pre-commit

@@ -0,0 +1,46 @@
+#!/bin/sh
+# Check file names in git commits for GNU Emacs.
+
+# Copyright 2014 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/>.
+
+LC_ALL=C
+export LC_ALL
+
+exec >&2
+
+. git-sh-setup
+
+git_diff='git diff --cached --name-only --diff-filter=A'
+ok_chars='\0+[=-=]./0-9A-Z_a-z'
+nbadchars=`$git_diff -z HEAD | tr -d "$ok_chars" | wc -c`
+
+if test "$nbadchars" -ne 0; then
+  echo "File name does not consist of -+./_ or ASCII letters or digits."
+  exit 1
+fi
+
+new_names=`$git_diff HEAD` || exit
+case "
+$new_names" in
+  */-* | *'
+'-*)
+    echo "File name component begins with '-'."
+    exit 1;;
+esac
+
+exec git diff-index --check --cached HEAD --