rebase: fix --onto A...B parsing and add tests

The previous patch didn't parse "rebase --onto A...B" correctly when A
isn't an empty string. It also tried to be careful to notice a case in
which there are more than one merge bases, but forgot to give --all option
to merge-base, making the test pointless.

Fix these problems and add a test script to verify. Improvements to the
script to parse A...B syntax was taken from review comments by Johannes
Schindelin.

Signed-off-by: しらいし ななこ <nanako3@lavabit.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -419,10 +419,10 @@ fi
 
 # Make sure the branch to rebase onto is valid.
 onto_name=${newbase-"$upstream_name"}
-if	left=$(expr "$onto_name" : '\(.*\)\.\.\.') &&
+case "$onto_name" in
-	right=$(expr "$onto_name" : '\.\.\.\(.*\)$') &&
+*...*)
-	: ${left:=HEAD} ${right:=HEAD} &&
+	if	left=${onto_name%...*} right=${onto_name#*...} &&
-	onto=$(git merge-base "$left" "$right")
+		onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
 	then
 		case "$onto" in
 		?*"$LF"?*)
@@ -433,8 +433,13 @@ then
 			;;
 		esac
 	else
-	onto=$(git rev-parse --verify "${onto_name}^0") || exit
+		die "$onto_name: there is no merge base"
 	fi
+	;;
+*)
+	onto=$(git rev-parse --verify "${onto_name}^0") || exit
+	;;
+esac
 
 # If a hook exists, give it a chance to interrupt
 run_pre_rebase_hook "$upstream_arg" "$@"

t/t3415-rebase-onto-threedots.sh

@@ -0,0 +1,75 @@
+#!/bin/sh
+
+test_description='git rebase --onto A...B'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-rebase.sh"
+
+# Rebase only the tip commit of "topic" on merge base between "master"
+# and "topic".  Cannot do this for "side" with "master" because there
+# is no single merge base.
+#
+#
+#	    F---G topic                             G'
+#	   /                                       /
+# A---B---C---D---E master      -->       A---B---C---D---E
+#      \   \ /
+#	\   x
+#	 \ / \
+#	  H---I---J---K side
+
+test_expect_success setup '
+	test_commit A &&
+	test_commit B &&
+	git branch side &&
+	test_commit C &&
+	git branch topic &&
+	git checkout side &&
+	test_commit H &&
+	git checkout master &&
+	test_tick &&
+	git merge H &&
+	git tag D &&
+	test_commit E &&
+	git checkout topic &&
+	test_commit F &&
+	test_commit G &&
+	git checkout side &&
+	test_tick &&
+	git merge C &&
+	git tag I &&
+	test_commit J &&
+	test_commit K
+'
+
+test_expect_success 'rebase --onto master...topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --onto master...topic F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --onto master...' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --onto master... F &&
+	git rev-parse HEAD^1 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --onto master...side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --onto master...side J
+'
+
+test_done