[PATCH 2/3] rebase: accept -<number> as another way of saying HEAD~<number>

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

This is "rev-list style", where people can do "git rev-list -3" in
addition to "git rev-list HEAD~3". A lot of commands are driven by the
revision machinery and also accept this form. This addition to rebase
is just for convenience.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-rebase.txt | 3 +++
 git-rebase.sh                | 9 +++++++++
 t/t3400-rebase.sh            | 6 ++++++
 3 files changed, 18 insertions(+)

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 2a93c64..52c3561 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -223,6 +223,9 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+-<number>::
+	Specify <upstream> as "HEAD~<number>".
+
 <upstream>::
 	Upstream branch to compare against.  May be any valid commit,
 	not just an existing branch name. Defaults to the configured
diff --git a/git-rebase.sh b/git-rebase.sh
index 5f6732b..33face1 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -43,6 +43,7 @@ continue!          continue
 abort!             abort and check out the original branch
 skip!              skip current patch and continue
 edit-todo!         edit the todo list during an interactive rebase
+-NUM               equivalent of HEAD~<NUM>
 "
 . git-sh-setup
 . git-sh-i18n
@@ -335,6 +336,9 @@ do
 	--gpg-sign=*)
 		gpg_sign_opt="-S${1#--gpg-sign=}"
 		;;
+	-NUM=*)
+		NUM="${1#-NUM=}"
+		;;
 	--)
 		shift
 		break
@@ -342,6 +346,11 @@ do
 	esac
 	shift
 done
+if [ -n "$NUM" ]
+then
+	test $# -gt 0 && usage
+	set -- "$@" "HEAD~$NUM"
+fi
 test $# -gt 2 && usage
 
 if test -n "$cmd" &&
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 6d94b1f..11db7ea 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -215,4 +215,10 @@ test_expect_success 'rebase commit with an ancient timestamp' '
 	grep "author .* 34567 +0600$" actual
 '
 
+test_expect_success 'rebase -<number>' '
+	git reset --hard &&
+	test_must_fail git rebase -2 HEAD^^ &&
+	git rebase -2
+'
+
 test_done
-- 
1.9.0.40.gaa8c3ea