rebase--interactive: fix parent rewriting for dropped commits

`rebase -i -p` got its rev-list of commits to keep by --left-right and
--cherry-pick. Adding --cherry-pick would drop commits that duplicated changes
already in the rebase target.

The dropped commits were then forgotten about when it came to rewriting the
parents of their descendents, so the descendents would get cherry-picked with
their old, unwritten parents and essentially make the rebase a no-op.

This commit adds a $DOTEST/dropped directory to remember dropped commits and
rewrite their children's parent as the dropped commit's possibly-rewritten
first-parent.

Signed-off-by: Stephen Haberman <stephen@exigencecorp.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

2 files changed, 174 insertions, 2 deletions

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 124cb58..30e4523 100755
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -37,6 +37,7 @@ DONE="$DOTEST"/done
 MSG="$DOTEST"/message
 SQUASH_MSG="$DOTEST"/message-squash
 REWRITTEN="$DOTEST"/rewritten
+DROPPED="$DOTEST"/dropped
 PRESERVE_MERGES=
 STRATEGY=
 ONTO=
@@ -179,8 +180,12 @@ pick_one_preserving_merges () {
 
 	# rewrite parents; if none were rewritten, we can fast-forward.
 	new_parents=
-	for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -f2-)
+	pend=" $(git rev-list --parents -1 $sha1 | cut -d' ' -f2-)"
+	while [ "$pend" != "" ]
 	do
+		p=$(expr "$pend" : ' \([^ ]*\)')
+		pend="${pend# $p}"
+
 		if test -f "$REWRITTEN"/$p
 		then
 			new_p=$(cat "$REWRITTEN"/$p)
@@ -193,7 +198,13 @@ pick_one_preserving_merges () {
 				;;
 			esac
 		else
-			new_parents="$new_parents $p"
+			if test -f "$DROPPED"/$p
+			then
+				fast_forward=f
+				pend=" $(cat "$DROPPED"/$p)$pend"
+			else
+				new_parents="$new_parents $p"
+			fi
 		fi
 	done
 	case $fast_forward in
@@ -599,6 +610,28 @@ first and then run 'git rebase --continue' again."
 #
 EOF
 
+		# Watch for commits that been dropped by --cherry-pick
+		if test t = "$PRESERVE_MERGES"
+		then
+			mkdir "$DROPPED"
+			# drop the --cherry-pick parameter this time
+			git rev-list $MERGES_OPTION --abbrev-commit \
+				--abbrev=7 $UPSTREAM...$HEAD --left-right | \
+				sed -n "s/^>//p" | while read rev
+			do
+				grep --quiet "$rev" "$TODO"
+				if [ $? -ne 0 ]
+				then
+					# Use -f2 because if rev-list is telling this commit is not
+					# worthwhile, we don't want to track its multiple heads,
+					# just the history of its first-parent for others that will
+					# be rebasing on top of us
+					full=$(git rev-parse $rev)
+					git rev-list --parents -1 $rev | cut -d' ' -f2 > "$DROPPED"/$full
+				fi
+			done
+		fi
+
 		has_action "$TODO" ||
 			die_abort "Nothing to do"
 
diff --git a/t/t3410-rebase-preserve-dropped-merges.sh b/t/t3410-rebase-preserve-dropped-merges.sh
new file mode 100755
index 0000000..5816415
--- /dev/null
+++ b/t/t3410-rebase-preserve-dropped-merges.sh
@@ -0,0 +1,139 @@
+#!/bin/sh
+#
+# Copyright (c) 2008 Stephen Haberman
+#
+
+test_description='git rebase preserve merges
+
+This test runs git rebase with preserve merges and ensures commits
+dropped by the --cherry-pick flag have their childrens parents
+rewritten.
+'
+. ./test-lib.sh
+
+# set up two branches like this:
+#
+# A - B - C - D - E
+#   \
+#     F - G - H
+#       \
+#         I
+#
+# where B, D and G touch the same file.
+
+test_expect_success 'setup' '
+	: > file1 &&
+	git add file1 &&
+	test_tick &&
+	git commit -m A &&
+	git tag A &&
+	echo 1 > file1 &&
+	test_tick &&
+	git commit -m B file1 &&
+	: > file2 &&
+	git add file2 &&
+	test_tick &&
+	git commit -m C &&
+	echo 2 > file1 &&
+	test_tick &&
+	git commit -m D file1 &&
+	: > file3 &&
+	git add file3 &&
+	test_tick &&
+	git commit -m E &&
+	git tag E &&
+	git checkout -b branch1 A &&
+	: > file4 &&
+	git add file4 &&
+	test_tick &&
+	git commit -m F &&
+	git tag F &&
+	echo 3 > file1 &&
+	test_tick &&
+	git commit -m G file1 &&
+	git tag G &&
+	: > file5 &&
+	git add file5 &&
+	test_tick &&
+	git commit -m H &&
+	git tag H &&
+	git checkout -b branch2 F &&
+	: > file6 &&
+	git add file6 &&
+	test_tick &&
+	git commit -m I &&
+	git tag I
+'
+
+# A - B - C - D - E
+#   \             \ \
+#     F - G - H -- L \        -->   L
+#       \            |               \
+#         I -- G2 -- J -- K           I -- K
+# G2 = same changes as G
+test_expect_success 'skip same-resolution merges with -p' '
+	git checkout branch1 &&
+	! git merge E &&
+	echo 23 > file1 &&
+	git add file1 &&
+	git commit -m L &&
+	git checkout branch2 &&
+	echo 3 > file1 &&
+	git commit -a -m G2 &&
+	! git merge E &&
+	echo 23 > file1 &&
+	git add file1 &&
+	git commit -m J &&
+	echo file7 > file7 &&
+	git add file7 &&
+	git commit -m K &&
+	GIT_EDITOR=: git rebase -i -p branch1 &&
+	test $(git rev-parse branch2^^) = $(git rev-parse branch1) &&
+	test "23" = "$(cat file1)" &&
+	test "" = "$(cat file6)" &&
+	test "file7" = "$(cat file7)" &&
+
+	git checkout branch1 &&
+	git reset --hard H &&
+	git checkout branch2 &&
+	git reset --hard I
+'
+
+# A - B - C - D - E
+#   \             \ \
+#     F - G - H -- L \        -->   L
+#       \            |               \
+#         I -- G2 -- J -- K           I -- G2 -- K
+# G2 = different changes as G
+test_expect_success 'keep different-resolution merges with -p' '
+	git checkout branch1 &&
+	! git merge E &&
+	echo 23 > file1 &&
+	git add file1 &&
+	git commit -m L &&
+	git checkout branch2 &&
+	echo 4 > file1 &&
+	git commit -a -m G2 &&
+	! git merge E &&
+	echo 24 > file1 &&
+	git add file1 &&
+	git commit -m J &&
+	echo file7 > file7 &&
+	git add file7 &&
+	git commit -m K &&
+	! GIT_EDITOR=: git rebase -i -p branch1 &&
+	echo 234 > file1 &&
+	git add file1 &&
+	GIT_EDITOR=: git rebase --continue &&
+	test $(git rev-parse branch2^^^) = $(git rev-parse branch1) &&
+	test "234" = "$(cat file1)" &&
+	test "" = "$(cat file6)" &&
+	test "file7" = "$(cat file7)" &&
+
+	git checkout branch1 &&
+	git reset --hard H &&
+	git checkout branch2 &&
+	git reset --hard I
+'
+
+test_done