rebase -i -p: fix parent rewriting

The existing parent rewriting did not handle the case where a previous
commit was amended (via edit or squash).  Fix by always putting the
new sha1 of the last commit into the $REWRITTEN map.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>

git-rebase--interactive.sh

@@ -165,14 +165,14 @@ pick_one_preserving_merges () {
 		die "Cannot write current commit's replacement sha1"
 	fi
 
+	echo $sha1 > "$DOTEST"/current-commit
+
 	# rewrite parents; if none were rewritten, we can fast-forward.
-	preserve=t
 	new_parents=
 	for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -f2-)
 	do
 		if test -f "$REWRITTEN"/$p
 		then
-			preserve=f
 			new_p=$(cat "$REWRITTEN"/$p)
 			test $p != $new_p && fast_forward=f
 			case "$new_parents" in
@@ -189,7 +189,6 @@ pick_one_preserving_merges () {
 	case $fast_forward in
 	t)
 		output warn "Fast forward to $sha1"
-		test $preserve = f || echo $sha1 > "$REWRITTEN"/$sha1
 		output git reset --hard $sha1 ||
 			die "Cannot fast forward to $sha1"
 		;;
@@ -201,7 +200,6 @@ pick_one_preserving_merges () {
 		output git checkout $first_parent 2> /dev/null ||
 			die "Cannot move HEAD to $first_parent"
 
-		echo $sha1 > "$DOTEST"/current-commit
 		case "$new_parents" in
 		' '*' '*)
 			# redo merge

t/t3404-rebase-interactive.sh

@@ -250,6 +250,18 @@ test_expect_success 'preserve merges with -p' '
 	test $(git show HEAD:unrelated-file) = 1
 '
 
+test_expect_success 'edit ancestor with -p' '
+	FAKE_LINES="1 edit 2 3 4" git rebase -i -p HEAD~3 &&
+	echo 2 > unrelated-file &&
+	test_tick &&
+	git commit -m L2-modified --amend unrelated-file &&
+	git rebase --continue &&
+	git update-index --refresh &&
+	git diff-files --quiet &&
+	git diff-index --quiet --cached HEAD -- &&
+	test $(git show HEAD:unrelated-file) = 2
+'
+
 test_expect_success '--continue tries to commit' '
 	test_tick &&
 	test_must_fail git rebase -i --onto new-branch1 HEAD^ &&