merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/contrib/workdir/git-new-workdir

@@ -0,0 +1,105 @@
+#!/bin/sh
+
+usage () {
+	echo "usage:" $@
+	exit 127
+}
+
+die () {
+	echo $@
+	exit 128
+}
+
+failed () {
+	die "unable to create new workdir '$new_workdir'!"
+}
+
+if test $# -lt 2 || test $# -gt 3
+then
+	usage "$0 <repository> <new_workdir> [<branch>]"
+fi
+
+orig_git=$1
+new_workdir=$2
+branch=$3
+
+# want to make sure that what is pointed to has a .git directory ...
+git_dir=$(cd "$orig_git" 2>/dev/null &&
+  git rev-parse --git-dir 2>/dev/null) ||
+  die "Not a git repository: \"$orig_git\""
+
+case "$git_dir" in
+.git)
+	git_dir="$orig_git/.git"
+	;;
+.)
+	git_dir=$orig_git
+	;;
+esac
+
+# don't link to a configured bare repository
+isbare=$(git --git-dir="$git_dir" config --bool --get core.bare)
+if test ztrue = "z$isbare"
+then
+	die "\"$git_dir\" has core.bare set to true," \
+		" remove from \"$git_dir/config\" to use $0"
+fi
+
+# don't link to a workdir
+if test -h "$git_dir/config"
+then
+	die "\"$orig_git\" is a working directory only, please specify" \
+		"a complete repository."
+fi
+
+# make sure the links in the workdir have full paths to the original repo
+git_dir=$(cd "$git_dir" && pwd) || exit 1
+
+# don't recreate a workdir over an existing directory, unless it's empty
+if test -d "$new_workdir"
+then
+	if test $(ls -a1 "$new_workdir/." | wc -l) -ne 2
+	then
+		die "destination directory '$new_workdir' is not empty."
+	fi
+	cleandir="$new_workdir/.git"
+else
+	cleandir="$new_workdir"
+fi
+
+mkdir -p "$new_workdir/.git" || failed
+cleandir=$(cd "$cleandir" && pwd) || failed
+
+cleanup () {
+	rm -rf "$cleandir"
+}
+siglist="0 1 2 15"
+trap cleanup $siglist
+
+# create the links to the original repo.  explicitly exclude index, HEAD and
+# logs/HEAD from the list since they are purely related to the current working
+# directory, and should not be shared.
+for x in config refs logs/refs objects info hooks packed-refs remotes rr-cache svn
+do
+	# create a containing directory if needed
+	case $x in
+	*/*)
+		mkdir -p "$new_workdir/.git/${x%/*}"
+		;;
+	esac
+
+	ln -s "$git_dir/$x" "$new_workdir/.git/$x" || failed
+done
+
+# commands below this are run in the context of the new workdir
+cd "$new_workdir" || failed
+
+# copy the HEAD from the original repository as a default branch
+cp "$git_dir/HEAD" .git/HEAD || failed
+
+# the workdir is set up.  if the checkout fails, the user can fix it.
+trap - $siglist
+
+# checkout the branch (either the same as HEAD from the original repository,
+# or the one that was asked for)
+git checkout -f $branch