rebase -i: correctly remember --root flag across --continue

d911d14 (rebase -i: learn to rebase root commit, 2009-01-02) tried to
remember the --root flag across a merge conflict in a broken way.
Introduce a flag file $DOTEST/rebase-root to fix and clarify.

While at it, also make sure $UPSTREAM is always initialized to guard
against existing values in the environment.

[tr: added tests]

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

git-rebase--interactive.sh

@@ -456,7 +456,7 @@ get_saved_options () {
 	test -d "$REWRITTEN" && PRESERVE_MERGES=t
 	test -f "$DOTEST"/strategy && STRATEGY="$(cat "$DOTEST"/strategy)"
 	test -f "$DOTEST"/verbose && VERBOSE=t
-	test ! -s "$DOTEST"/upstream && REBASE_ROOT=t
+	test -f "$DOTEST"/rebase-root && REBASE_ROOT=t
 }
 
 while test $# != 0
@@ -586,6 +586,7 @@ first and then run 'git rebase --continue' again."
 			test -z "$ONTO" && ONTO=$UPSTREAM
 			shift
 		else
+			UPSTREAM=
 			UPSTREAM_ARG=--root
 			test -z "$ONTO" &&
 				die "You must specify --onto when using --root"
@@ -612,7 +613,12 @@ first and then run 'git rebase --continue' again."
 			echo "detached HEAD" > "$DOTEST"/head-name
 
 		echo $HEAD > "$DOTEST"/head
-		echo $UPSTREAM > "$DOTEST"/upstream
+		case "$REBASE_ROOT" in
+		'')
+			rm -f "$DOTEST"/rebase-root ;;
+		*)
+			: >"$DOTEST"/rebase-root ;;
+		esac
 		echo $ONTO > "$DOTEST"/onto
 		test -z "$STRATEGY" || echo "$STRATEGY" > "$DOTEST"/strategy
 		test t = "$VERBOSE" && : > "$DOTEST"/verbose

t/t3412-rebase-root.sh

@@ -184,4 +184,98 @@ test_expect_success 'pre-rebase hook stops rebase -i' '
 	test 0 = $(git rev-list other...stops2 | wc -l)
 '
 
+test_expect_success 'remove pre-rebase hook' '
+	rm -f .git/hooks/pre-rebase
+'
+
+test_expect_success 'set up a conflict' '
+	git checkout master &&
+	echo conflict > B &&
+	git add B &&
+	git commit -m conflict
+'
+
+test_expect_success 'rebase --root with conflict (first part)' '
+	git checkout -b conflict1 other &&
+	test_must_fail git rebase --root --onto master &&
+	git ls-files -u | grep "B$"
+'
+
+test_expect_success 'fix the conflict' '
+	echo 3 > B &&
+	git add B
+'
+
+cat > expect-conflict <<EOF
+6
+5
+4
+3
+conflict
+2
+1
+EOF
+
+test_expect_success 'rebase --root with conflict (second part)' '
+	git rebase --continue &&
+	git log --pretty=tformat:"%s" > conflict1 &&
+	test_cmp expect-conflict conflict1
+'
+
+test_expect_success 'rebase -i --root with conflict (first part)' '
+	git checkout -b conflict2 other &&
+	GIT_EDITOR=: test_must_fail git rebase -i --root --onto master &&
+	git ls-files -u | grep "B$"
+'
+
+test_expect_success 'fix the conflict' '
+	echo 3 > B &&
+	git add B
+'
+
+test_expect_success 'rebase -i --root with conflict (second part)' '
+	git rebase --continue &&
+	git log --pretty=tformat:"%s" > conflict2 &&
+	test_cmp expect-conflict conflict2
+'
+
+cat >expect-conflict-p <<\EOF
+commit conflict3 conflict3~1 conflict3^2
+Merge branch 'third' into other
+commit conflict3^2 conflict3~4
+6
+commit conflict3~1 conflict3~2 conflict3~1^2
+Merge branch 'side' into other
+commit conflict3~1^2 conflict3~3
+5
+commit conflict3~2 conflict3~3
+4
+commit conflict3~3 conflict3~4
+3
+commit conflict3~4 conflict3~5
+conflict
+commit conflict3~5 conflict3~6
+2
+commit conflict3~6
+1
+EOF
+
+test_expect_success 'rebase -i -p --root with conflict (first part)' '
+	git checkout -b conflict3 other &&
+	GIT_EDITOR=: test_must_fail git rebase -i -p --root --onto master &&
+	git ls-files -u | grep "B$"
+'
+
+test_expect_success 'fix the conflict' '
+	echo 3 > B &&
+	git add B
+'
+
+test_expect_success 'rebase -i -p --root with conflict (second part)' '
+	git rebase --continue &&
+	git rev-list --topo-order --parents --pretty="tformat:%s" HEAD |
+	git name-rev --stdin --name-only --refs=refs/heads/conflict3 >out &&
+	test_cmp expect-conflict-p out
+'
+
 test_done