rebase: learn to rebase root commit

Teach git-rebase a new option --root, which instructs it to rebase the
entire history leading up to <branch>.  This option must be used with
--onto <newbase>, and causes commits that already exist in <newbase>
to be skipped.  (Normal operation skips commits that already exist in
<upstream> instead.)

One possible use-case is with git-svn: suppose you start hacking
(perhaps offline) on a new project, but later notice you want to
commit this work to SVN.  You will have to rebase the entire history,
including the root commit, on a (possibly empty) commit coming from
git-svn, to establish a history connection.  This previously had to
be done by cherry-picking the root commit manually.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/t/t3412-rebase-root.sh b/t/t3412-rebase-root.sh
new file mode 100755
index 0000000000..dd919100d6
--- /dev/null
+++ b/t/t3412-rebase-root.sh
@@ -0,0 +1,86 @@
+#!/bin/sh
+
+test_description='git rebase --root
+
+Tests if git rebase --root --onto <newparent> can rebase the root commit.
+'
+. ./test-lib.sh
+
+test_expect_success 'prepare repository' '
+	echo 1 > A &&
+	git add A &&
+	git commit -m 1 &&
+	echo 2 > A &&
+	git add A &&
+	git commit -m 2 &&
+	git symbolic-ref HEAD refs/heads/other &&
+	rm .git/index &&
+	echo 3 > B &&
+	git add B &&
+	git commit -m 3 &&
+	echo 1 > A &&
+	git add A &&
+	git commit -m 1b &&
+	echo 4 > B &&
+	git add B &&
+	git commit -m 4
+'
+
+test_expect_success 'rebase --root expects --onto' '
+	test_must_fail git rebase --root
+'
+
+test_expect_success 'setup pre-rebase hook' '
+	mkdir -p .git/hooks &&
+	cat >.git/hooks/pre-rebase <<EOF &&
+#!$SHELL_PATH
+echo "\$1,\$2" >.git/PRE-REBASE-INPUT
+EOF
+	chmod +x .git/hooks/pre-rebase
+'
+cat > expect <<EOF
+4
+3
+2
+1
+EOF
+
+test_expect_success 'rebase --root --onto <newbase>' '
+	git checkout -b work &&
+	git rebase --root --onto master &&
+	git log --pretty=tformat:"%s" > rebased &&
+	test_cmp expect rebased
+'
+
+test_expect_success 'pre-rebase got correct input (1)' '
+	test "z$(cat .git/PRE-REBASE-INPUT)" = z--root,
+'
+
+test_expect_success 'rebase --root --onto <newbase> <branch>' '
+	git branch work2 other &&
+	git rebase --root --onto master work2 &&
+	git log --pretty=tformat:"%s" > rebased2 &&
+	test_cmp expect rebased2
+'
+
+test_expect_success 'pre-rebase got correct input (2)' '
+	test "z$(cat .git/PRE-REBASE-INPUT)" = z--root,work2
+'
+
+test_expect_success 'setup pre-rebase hook that fails' '
+	mkdir -p .git/hooks &&
+	cat >.git/hooks/pre-rebase <<EOF &&
+#!$SHELL_PATH
+false
+EOF
+	chmod +x .git/hooks/pre-rebase
+'
+
+test_expect_success 'pre-rebase hook stops rebase' '
+	git checkout -b stops1 other &&
+	GIT_EDITOR=: test_must_fail git rebase --root --onto master &&
+	test "z$(git symbolic-ref HEAD)" = zrefs/heads/stops1
+	test 0 = $(git rev-list other...stops1 | wc -l)
+'
+
+test_done