rebase: teach rebase --keep-base

A common scenario is if a user is working on a topic branch and they
wish to make some changes to intermediate commits or autosquash, they
would run something such as

	git rebase -i --onto master... master

in order to preserve the merge base. This is useful when contributing a
patch series to the Git mailing list, one often starts on top of the
current 'master'. While developing the patches, 'master' is also
developed further and it is sometimes not the best idea to keep rebasing
on top of 'master', but to keep the base commit as-is.

In addition to this, a user wishing to test individual commits in a
topic branch without changing anything may run

	git rebase -x ./test.sh master... master

Since rebasing onto the merge base of the branch and the upstream is
such a common case, introduce the --keep-base option as a shortcut.

This allows us to rewrite the above as

	git rebase -i --keep-base master

and

	git rebase -x ./test.sh --keep-base master

respectively.

Add tests to ensure --keep-base works correctly in the normal case and
fails when there are multiple merge bases, both in regular and
interactive mode. Also, test to make sure conflicting options cause
rebase to fail. While we're adding test cases, add a missing
set_fake_editor call to 'rebase -i --onto master...side'.

While we're documenting the --keep-base option, change an instance of
"merge-base" to "merge base", which is the consistent spelling.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 72 insertions, 0 deletions

diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index ddf2f64853..9c2548423b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -99,7 +99,64 @@ test_expect_success 'rebase -i --onto master...side' '
 	git checkout side &&
 	git reset --hard K &&
 
+	set_fake_editor &&
 	test_must_fail git rebase -i --onto master...side J
 '
 
+test_expect_success 'rebase --keep-base --onto incompatible' '
+	test_must_fail git rebase --keep-base --onto master...
+'
+
+test_expect_success 'rebase --keep-base --root incompatible' '
+	test_must_fail git rebase --keep-base --root
+'
+
+test_expect_success 'rebase --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	git rebase --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	test_must_fail git rebase --keep-base master
+'
+
+test_expect_success 'rebase -i --keep-base master from topic' '
+	git reset --hard &&
+	git checkout topic &&
+	git reset --hard G &&
+
+	set_fake_editor &&
+	EXPECT_COUNT=2 git rebase -i --keep-base master &&
+	git rev-parse C >base.expect &&
+	git merge-base master HEAD >base.actual &&
+	test_cmp base.expect base.actual &&
+
+	git rev-parse HEAD~2 >actual &&
+	git rev-parse C^0 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase -i --keep-base master from side' '
+	git reset --hard &&
+	git checkout side &&
+	git reset --hard K &&
+
+	set_fake_editor &&
+	test_must_fail git rebase -i --keep-base master
+'
+
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 2d5c6e641e..78851b9a2a 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -43,11 +43,15 @@ test_rebase () {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
+test_rebase 'G F B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
+test_rebase 'G F C B A' --no-fork-point --keep-base
 test_rebase 'G F E D B A' --fork-point refs/heads/master
 test_rebase 'G F D B A' --fork-point --onto D refs/heads/master
+test_rebase 'G F B A' --fork-point --keep-base refs/heads/master
 test_rebase 'G F C E D B A' refs/heads/master
 test_rebase 'G F C D B A' --onto D refs/heads/master
+test_rebase 'G F C B A' --keep-base refs/heads/master
 
 test_done
diff --git a/t/t3432-rebase-fast-forward.sh b/t/t3432-rebase-fast-forward.sh
index 9ce0750b43..034ffc7e76 100755
--- a/t/t3432-rebase-fast-forward.sh
+++ b/t/t3432-rebase-fast-forward.sh
@@ -75,11 +75,15 @@ test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --keep-base master
+test_rebase_same_head success noop same success noop-force same --keep-base
 test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --keep-base --keep-base master
 
 test_expect_success 'add work same to side' '
 	test_commit E
@@ -91,11 +95,15 @@ test_rebase_same_head success noop same success noop-force same master
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success noop-force same --onto master... master
+test_rebase_same_head success noop same success noop-force same --keep-base master
+test_rebase_same_head success noop same success noop-force same --keep-base
 test_rebase_same_head success noop same success noop-force same --no-fork-point
+test_rebase_same_head success noop same success noop-force same --keep-base --no-fork-point
 test_rebase_same_head success noop same success work same --fork-point master
 test_rebase_same_head success noop same success work diff --fork-point --onto B B
 test_rebase_same_head success noop same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work same --fork-point --onto master... master
+test_rebase_same_head success noop same success work same --fork-point --keep-base master
 
 test_expect_success 'add work same to upstream' '
 	git checkout master &&
@@ -107,8 +115,11 @@ changes='our and their changes'
 test_rebase_same_head success noop same success noop-force diff --onto B B
 test_rebase_same_head success noop same success noop-force diff --onto B... B
 test_rebase_same_head success noop same success work diff --onto master... master
+test_rebase_same_head success noop same success work diff --keep-base master
+test_rebase_same_head success noop same success work diff --keep-base
 test_rebase_same_head failure work same success work diff --fork-point --onto B B
 test_rebase_same_head failure work same success work diff --fork-point --onto B... B
 test_rebase_same_head success noop same success work diff --fork-point --onto master... master
+test_rebase_same_head success noop same success work diff --fork-point --keep-base master
 
 test_done