rebase: factor out reference parsing

Remove the parsing and validation of references (onto, upstream, branch)
from git-rebase--interactive.sh and rely on the information exported from
git-rebase.sh.

By using the parsing of the --onto parameter in git-rebase.sh, this
improves the error message when the parameter is invalid.

Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -682,25 +682,6 @@ rearrange_squash () {
 	rm -f "$1.sq" "$1.rearranged"
 }
 
-LF='
-'
-parse_onto () {
-	case "$1" in
-	*...*)
-		if	left=${1%...*} right=${1#*...} &&
-			onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
-		then
-			case "$onto" in
-			?*"$LF"?* | '')
-				exit 1 ;;
-			esac
-			echo "$onto"
-			exit 0
-		fi
-	esac
-	git rev-parse --verify "$1^0"
-}
-
 case "$action" in
 continue)
 	get_saved_options
@@ -769,47 +750,26 @@ skip)
 	;;
 esac
 
-if test -n "$onto"
-then
-	onto=$(parse_onto "$onto") || die "Does not point to a valid commit: $1"
-fi
-
-test -z "$rebase_root" -a $# -ge 1 -a $# -le 2 ||
-test ! -z "$rebase_root" -a $# -le 1 || usage
-
 git var GIT_COMMITTER_IDENT >/dev/null ||
 	die "You need to set your committer info first"
 
-if test -z "$rebase_root"
-then
-	upstream_arg="$1"
-	upstream=$(git rev-parse --verify "$1") || die "Invalid base"
-	test -z "$onto" && onto=$upstream
-	shift
-else
-	upstream=
-	upstream_arg=--root
-	test -z "$onto" &&
-		die "You must specify --onto when using --root"
-fi
 require_clean_work_tree "rebase" "Please commit or stash them."
 
 run_pre_rebase_hook "$upstream_arg" "$@"
 
 comment_for_reflog start
 
-if test ! -z "$1"
+if test ! -z "$switch_to"
 then
-	output git checkout "$1" -- ||
-		die "Could not checkout $1"
+	output git checkout "$switch_to" -- ||
+		die "Could not checkout $switch_to"
 fi
 
 head=$(git rev-parse --verify HEAD) || die "No HEAD?"
 mkdir "$dotest" || die "Could not create temporary $dotest"
 
 : > "$dotest"/interactive || die "Could not mark as interactive"
-git symbolic-ref HEAD > "$dotest"/head-name 2> /dev/null ||
-	echo "detached HEAD" > "$dotest"/head-name
+echo "$head_name" > "$dotest"/head-name
 
 echo $head > "$dotest"/head
 case "$rebase_root" in

git-rebase.sh

@@ -431,8 +431,6 @@ else
 	state_dir="$apply_dir"
 fi
 
-test "$type" = interactive && run_interactive_rebase "$@"
-
 if test -z "$rebase_root"
 then
 	# The upstream head must be given.  Make sure it is valid.
@@ -443,7 +441,7 @@ then
 	unset root_flag
 	upstream_arg="$upstream_name"
 else
-	test -z "$onto" && die "--root must be used with --onto"
+	test -z "$onto" && die "You must specify --onto when using --root"
 	unset upstream_name
 	unset upstream
 	root_flag="--root"
@@ -470,7 +468,8 @@ case "$onto_name" in
 	fi
 	;;
 *)
-	onto=$(git rev-parse --verify "${onto_name}^0") || exit
+	onto=$(git rev-parse --verify "${onto_name}^0") ||
+	die "Does not point to a valid commit: $1"
 	;;
 esac
 
@@ -512,6 +511,8 @@ case "$#" in
 esac
 orig_head=$branch
 
+test "$type" = interactive && run_interactive_rebase "$@"
+
 require_clean_work_tree "rebase" "Please commit or stash them."
 
 # Now we are rebasing commits $upstream..$branch (or with --root,