rebase -i: fix parsing of "fixup -C<commit>"

If the user omits the space between "-C" and the commit in a fixup
command then it is parsed as an ordinary fixup and the commit message is
not updated as it should be. Fix this by making the space between "-C"
and "<commit>" optional as it is for the "merge" command.

Note that set_replace_editor() is changed to set $GIT_SEQUENCE_EDITOR
instead of $EDITOR in order to be able to replace the todo list and
reword commits with $FAKE_COMMIT_MESSAGE. This is safe as all the
existing users are using set_replace_editor to replace the todo list.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>

sequencer.c

@@ -2542,12 +2542,10 @@ static int parse_insn_line(struct repository *r, struct todo_item *item,
 	}
 
 	if (item->command == TODO_FIXUP) {
-		if (skip_prefix(bol, "-C", &bol) &&
-		   (*bol == ' ' || *bol == '\t')) {
+		if (skip_prefix(bol, "-C", &bol)) {
 			bol += strspn(bol, " \t");
 			item->flags |= TODO_REPLACE_FIXUP_MSG;
-		} else if (skip_prefix(bol, "-c", &bol) &&
-				  (*bol == ' ' || *bol == '\t')) {
+		} else if (skip_prefix(bol, "-c", &bol)) {
 			bol += strspn(bol, " \t");
 			item->flags |= TODO_EDIT_FIXUP_MSG;
 		}

t/lib-rebase.sh

@@ -211,6 +211,9 @@ check_reworded_commits () {
 # usage: set_replace_editor <file>
 #
 # Replace the todo file with the exact contents of the given file.
+# N.B. sets GIT_SEQUENCE_EDITOR rather than EDITOR so it can be
+# combined with set_fake_editor to reword commits and replace the
+# todo list
 set_replace_editor () {
 	cat >script <<-\EOF &&
 	cat FILENAME >"$1"
@@ -219,6 +222,7 @@ set_replace_editor () {
 	cat "$1"
 	EOF
 
-	sed -e "s/FILENAME/$1/g" <script | write_script fake-editor.sh &&
-	test_set_editor "$(pwd)/fake-editor.sh"
+	sed -e "s/FILENAME/$1/g" script |
+		write_script fake-sequence-editor.sh &&
+	test_set_sequence_editor "$(pwd)/fake-sequence-editor.sh"
 }

t/t3437-rebase-fixup-options.sh

@@ -51,6 +51,7 @@ test_expect_success 'setup' '
 	body
 	EOF
 
+	test_commit initial &&
 	test_commit A A &&
 	test_commit B B &&
 	get_author HEAD >expected-author &&
@@ -209,4 +210,29 @@ test_expect_success 'fixup -C works upon --autosquash with amend!' '
 		actual-squash-message
 '
 
+test_expect_success 'fixup -[Cc]<commit> works' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	cat >todo <<-\EOF &&
+	pick A
+	fixup -CA1
+	pick B
+	fixup -cA2
+	EOF
+	(
+		set_replace_editor todo &&
+		FAKE_COMMIT_MESSAGE="edited and fixed up" \
+			git rebase -i initial initial
+	) &&
+	git log --pretty=format:%B initial.. >actual &&
+	cat >expect <<-EOF &&
+	edited and fixed up
+	$EMPTY
+	new subject
+	$EMPTY
+	new
+	body
+	EOF
+	test_cmp expect actual
+'
+
 test_done

t/test-lib-functions.sh

@@ -32,6 +32,14 @@ test_set_editor () {
 	export EDITOR
 }
 
+# Like test_set_editor but sets GIT_SEQUENCE_EDITOR instead of EDITOR
+test_set_sequence_editor () {
+	FAKE_SEQUENCE_EDITOR="$1"
+	export FAKE_SEQUENCE_EDITOR
+	GIT_SEQUENCE_EDITOR='"$FAKE_SEQUENCE_EDITOR"'
+	export GIT_SEQUENCE_EDITOR
+}
+
 test_decode_color () {
 	awk '
 		function name(n) {