[RFC] Interactive-rebase doesn't pick all children of "upstream"

[Andrew Wong <andrew.kw.w@gmail.com>]

Consider this graph:

        D---E    (topic, HEAD)
       /   /
  A---B---C      (master)
   \
    F            (topic2)

and the following three commands:
  1. git rebase -i A
  2. git rebase -i --onto F B
  3. git rebase -i B

Currently, (1) and (2) will pick B, D, C, and E onto A and F,
respectively.  However, (3) will only pick D and E onto B.  This
behavior of (3) is inconsistent with (1) and (2).

This also creates a bug if we do:
  4. git rebase -i C

In (4), E is never picked. And since interactive-rebase resets "HEAD" to
"onto", E is lost after the interactive-rebase.

This patch fixes the inconsistency and bug by ensuring that all children
of upstream are always picked.

Two of the tests contain a scenario like (3).  Since the new behavior
added more commits for picking, these tests need to be updated to edit
the "todo" list properly.
---
 git-rebase--interactive.sh               |    7 +++++--
 t/t3404-rebase-interactive.sh            |    2 +-
 t/t3411-rebase-preserve-around-merges.sh |    2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 41ba96a..b6d1e5b 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -711,7 +711,7 @@ then
 	# parents to rewrite and skipping dropped commits would
 	# prematurely end our probe
 	merges_option=
-	first_after_upstream="$(git rev-list --reverse --first-parent $upstream..$orig_head | head -n 1)"
+	commits_after_upstream="$(git rev-list --reverse --parents $upstream..$orig_head | sane_grep " $upstream" | cut -d' ' -s -f1)"
 else
 	merges_option="--no-merges --cherry-pick"
 fi
@@ -744,7 +744,10 @@ do
 			preserve=t
 			for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -s -f2-)
 			do
-				if test -f "$rewritten"/$p -a \( $p != $onto -o $sha1 = $first_after_upstream \)
+				if test -f "$rewritten"/$p && (
+					test $p != $onto ||
+					expr "$commits_after_upstream" ":" ".*$sha1.*"
+					)
 				then
 					preserve=f
 				fi
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 7d8147b..c3cddcd 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -295,7 +295,7 @@ test_expect_success 'preserve merges with -p' '
 '
 
 test_expect_success 'edit ancestor with -p' '
-	FAKE_LINES="1 edit 2 3 4" git rebase -i -p HEAD~3 &&
+	FAKE_LINES="1 2 edit 3 4" git rebase -i -p HEAD~3 &&
 	echo 2 > unrelated-file &&
 	test_tick &&
 	git commit -m L2-modified --amend unrelated-file &&
diff --git a/t/t3411-rebase-preserve-around-merges.sh b/t/t3411-rebase-preserve-around-merges.sh
index 14a23cd..ace8e54 100755
--- a/t/t3411-rebase-preserve-around-merges.sh
+++ b/t/t3411-rebase-preserve-around-merges.sh
@@ -37,7 +37,7 @@ test_expect_success 'setup' '
 #        -- C1 --
 #
 test_expect_success 'squash F1 into D1' '
-	FAKE_LINES="1 squash 3 2" git rebase -i -p B1 &&
+	FAKE_LINES="1 squash 4 2 3" git rebase -i -p B1 &&
 	test "$(git rev-parse HEAD^2)" = "$(git rev-parse C1)" &&
 	test "$(git rev-parse HEAD~2)" = "$(git rev-parse B1)" &&
 	git tag E2
-- 
1.7.5.2.316.gd7d8c.dirty