1 files changed, 293 insertions, 0 deletions
diff --git a/git-checkout.sh b/git-checkout.sh
new file mode 100755
index 0000000000..7c5ca3d62f
--- /dev/null
+++ b/git-checkout.sh
@@ -0,0 +1,293 @@
+#!/bin/sh
+
+USAGE='[-q] [-f] [-b <new_branch>] [-m] [<branch>] [<paths>...]'
+SUBDIRECTORY_OK=Sometimes
+. git-sh-setup
+require_work_tree
+
+old_name=HEAD
+old=$(git-rev-parse --verify $old_name 2>/dev/null)
+oldbranch=$(git-symbolic-ref $old_name 2>/dev/null)
+new=
+new_name=
+force=
+branch=
+track=
+newbranch=
+newbranch_log=
+merge=
+quiet=
+v=-v
+LF='
+'
+while [ "$#" != "0" ]; do
+    arg="$1"
+    shift
+    case "$arg" in
+	"-b")
+		newbranch="$1"
+		shift
+		[ -z "$newbranch" ] &&
+			die "git checkout: -b needs a branch name"
+		git-show-ref --verify --quiet -- "refs/heads/$newbranch" &&
+			die "git checkout: branch $newbranch already exists"
+		git-check-ref-format "heads/$newbranch" ||
+			die "git checkout: we do not like '$newbranch' as a branch name."
+		;;
+	"-l")
+		newbranch_log=-l
+		;;
+	"--track"|"--no-track")
+		track="$arg"
+		;;
+	"-f")
+		force=1
+		;;
+	-m)
+		merge=1
+		;;
+	"-q")
+		quiet=1
+		v=
+		;;
+	--)
+		break
+		;;
+	-*)
+		usage
+		;;
+	*)
+		if rev=$(git-rev-parse --verify "$arg^0" 2>/dev/null)
+		then
+			if [ -z "$rev" ]; then
+				echo "unknown flag $arg"
+				exit 1
+			fi
+			new_name="$arg"
+			if git-show-ref --verify --quiet -- "refs/heads/$arg"
+			then
+				rev=$(git-rev-parse --verify "refs/heads/$arg^0")
+				branch="$arg"
+			fi
+			new="$rev"
+		elif rev=$(git-rev-parse --verify "$arg^{tree}" 2>/dev/null)
+		then
+			# checking out selected paths from a tree-ish.
+			new="$rev"
+			new_name="$arg^{tree}"
+			branch=
+		else
+			new=
+			new_name=
+			branch=
+			set x "$arg" "$@"
+			shift
+		fi
+		case "$1" in
+		--)
+			shift ;;
+		esac
+		break
+		;;
+    esac
+done
+
+case "$newbranch,$track" in
+,--*)
+	die "git checkout: --track and --no-track require -b"
+esac
+
+case "$force$merge" in
+11)
+	die "git checkout: -f and -m are incompatible"
+esac
+
+# The behaviour of the command with and without explicit path
+# parameters is quite different.
+#
+# Without paths, we are checking out everything in the work tree,
+# possibly switching branches.  This is the traditional behaviour.
+#
+# With paths, we are _never_ switching branch, but checking out
+# the named paths from either index (when no rev is given),
+# or the named tree-ish (when rev is given).
+
+if test "$#" -ge 1
+then
+	hint=
+	if test "$#" -eq 1
+	then
+		hint="
+Did you intend to checkout '$@' which can not be resolved as commit?"
+	fi
+	if test '' != "$newbranch$force$merge"
+	then
+		die "git checkout: updating paths is incompatible with switching branches/forcing$hint"
+	fi
+	if test '' != "$new"
+	then
+		# from a specific tree-ish; note that this is for
+		# rescuing paths and is never meant to remove what
+		# is not in the named tree-ish.
+		git-ls-tree --full-name -r "$new" "$@" |
+		git-update-index --index-info || exit $?
+	fi
+
+	# Make sure the request is about existing paths.
+	git-ls-files --error-unmatch -- "$@" >/dev/null || exit
+	git-ls-files -- "$@" |
+	git-checkout-index -f -u --stdin
+	exit $?
+else
+	# Make sure we did not fall back on $arg^{tree} codepath
+	# since we are not checking out from an arbitrary tree-ish,
+	# but switching branches.
+	if test '' != "$new"
+	then
+		git-rev-parse --verify "$new^{commit}" >/dev/null 2>&1 ||
+		die "Cannot switch branch to a non-commit."
+	fi
+fi
+
+# We are switching branches and checking out trees, so
+# we *NEED* to be at the toplevel.
+cd_to_toplevel
+
+[ -z "$new" ] && new=$old && new_name="$old_name"
+
+# If we don't have an existing branch that we're switching to,
+# and we don't have a new branch name for the target we
+# are switching to, then we are detaching our HEAD from any
+# branch.  However, if "git checkout HEAD" detaches the HEAD
+# from the current branch, even though that may be logically
+# correct, it feels somewhat funny.  More importantly, we do not
+# want "git checkout" nor "git checkout -f" to detach HEAD.
+
+detached=
+detach_warn=
+
+describe_detached_head () {
+	test -n "$quiet" || {
+		printf >&2 "$1 "
+		GIT_PAGER= git log >&2 -1 --pretty=oneline --abbrev-commit "$2"
+	}
+}
+
+if test -z "$branch$newbranch" && test "$new_name" != "$old_name"
+then
+	detached="$new"
+	if test -n "$oldbranch" && test -z "$quiet"
+	then
+		detach_warn="Note: moving to \"$new_name\" which isn't a local branch
+If you want to create a new branch from this checkout, you may do so
+(now or later) by using -b with the checkout command again. Example:
+  git checkout -b <new_branch_name>"
+	fi
+elif test -z "$oldbranch" && test "$new" != "$old"
+then
+	describe_detached_head 'Previous HEAD position was' "$old"
+fi
+
+if [ "X$old" = X ]
+then
+	if test -z "$quiet"
+	then
+		echo >&2 "warning: You appear to be on a branch yet to be born."
+		echo >&2 "warning: Forcing checkout of $new_name."
+	fi
+	force=1
+fi
+
+if [ "$force" ]
+then
+    git-read-tree $v --reset -u $new
+else
+    git-update-index --refresh >/dev/null
+    merge_error=$(git-read-tree -m -u --exclude-per-directory=.gitignore $old $new 2>&1) || (
+	case "$merge" in
+	'')
+		echo >&2 "$merge_error"
+		exit 1 ;;
+	esac
+
+	# Match the index to the working tree, and do a three-way.
+    	git diff-files --name-only | git update-index --remove --stdin &&
+	work=`git write-tree` &&
+	git read-tree $v --reset -u $new || exit
+
+	eval GITHEAD_$new='${new_name:-${branch:-$new}}' &&
+	eval GITHEAD_$work=local &&
+	export GITHEAD_$new GITHEAD_$work &&
+	git merge-recursive $old -- $new $work
+
+	# Do not register the cleanly merged paths in the index yet.
+	# this is not a real merge before committing, but just carrying
+	# the working tree changes along.
+	unmerged=`git ls-files -u`
+	git read-tree $v --reset $new
+	case "$unmerged" in
+	'')	;;
+	*)
+		(
+			z40=0000000000000000000000000000000000000000
+			echo "$unmerged" |
+			sed -e 's/^[0-7]* [0-9a-f]* /'"0 $z40 /"
+			echo "$unmerged"
+		) | git update-index --index-info
+		;;
+	esac
+	exit 0
+    )
+    saved_err=$?
+    if test "$saved_err" = 0 && test -z "$quiet"
+    then
+	git diff-index --name-status "$new"
+    fi
+    (exit $saved_err)
+fi
+
+# 
+# Switch the HEAD pointer to the new branch if we
+# checked out a branch head, and remove any potential
+# old MERGE_HEAD's (subsequent commits will clearly not
+# be based on them, since we re-set the index)
+#
+if [ "$?" -eq 0 ]; then
+	if [ "$newbranch" ]; then
+		git-branch $track $newbranch_log "$newbranch" "$new_name" || exit
+		branch="$newbranch"
+	fi
+	if test -n "$branch"
+	then
+		GIT_DIR="$GIT_DIR" git-symbolic-ref -m "checkout: moving to $branch" HEAD "refs/heads/$branch"
+		if test -n "$quiet"
+		then
+			true	# nothing
+		elif test "refs/heads/$branch" = "$oldbranch"
+		then
+			echo >&2 "Already on branch \"$branch\""
+		else
+			echo >&2 "Switched to${newbranch:+ a new} branch \"$branch\""
+		fi
+	elif test -n "$detached"
+	then
+		# NEEDSWORK: we would want a command to detach the HEAD
+		# atomically, instead of this handcrafted command sequence.
+		# Perhaps:
+		#	git update-ref --detach HEAD $new
+		# or something like that...
+		#
+		git-rev-parse HEAD >"$GIT_DIR/HEAD.new" &&
+		mv "$GIT_DIR/HEAD.new" "$GIT_DIR/HEAD" &&
+		git-update-ref -m "checkout: moving to $arg" HEAD "$detached" ||
+			die "Cannot detach HEAD"
+		if test -n "$detach_warn"
+		then
+			echo >&2 "$detach_warn"
+		fi
+		describe_detached_head 'HEAD is now at' HEAD
+	fi
+	rm -f "$GIT_DIR/MERGE_HEAD"
+else
+	exit 1
+fi