commit: restore --edit when combined with --fixup

Recent changes to --fixup, adding amend suboption, caused the
--edit flag to be ignored as use_editor was always set to zero.

Restore edit_flag having higher priority than fixup_message when
deciding the value of use_editor by only changing the default
if edit_flag is not set.

Signed-off-by: Joel Klinghed <the_jk@spawned.biz>

builtin/commit.c

@@ -1333,7 +1333,8 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		} else {
 			fixup_commit = fixup_message;
 			fixup_prefix = "fixup";
-			use_editor = 0;
+			if (0 > edit_flag)
+				use_editor = 0;
 		}
 	}
 

t/t7500-commit-template-squash-signoff.sh

@@ -281,6 +281,21 @@ test_expect_success 'commit --fixup -m"something" -m"extra"' '
 
 extra"
 '
+test_expect_success 'commit --fixup --edit' '
+	commit_for_rebase_autosquash_setup &&
+	cat >e-append <<-\EOF &&
+	#!/bin/sh
+	sed -e "2a\\
+something\\
+extra" <"$1" >"$1-"
+	mv "$1-" "$1"
+	EOF
+	chmod 755 e-append &&
+	EDITOR="./e-append" git commit --fixup HEAD~1 --edit &&
+	commit_msg_is "fixup! target message subject linesomething
+extra"
+'
+
 get_commit_msg () {
 	rev="$1" &&
 	git log -1 --pretty=format:"%B" "$rev"