[PATCH] rebase -x: sanity check command

[Phillip Wood <phillip.wood@talktalk.net>]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

If the user gives an empty argument to --exec then the rebase starts to
run before erroring out with

  error: missing arguments for exec
  error: invalid line 2: exec
  You can fix this with 'git rebase --edit-todo' and then run 'git rebase --continue'.
  Or you can abort the rebase with 'git rebase --abort'.

Instead check for empty commands before starting the rebase.

Also check that the command does not contain any newlines as the
todo-list format is unable to cope with multiline commands. Note that
this changes the behavior, before this change one could do

git rebase --exec='echo one
exec echo two'

and it would insert two exec lines in the todo list, now it will error
out.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/rebase.c              | 22 ++++++++++++++++++++++
 t/t3404-rebase-interactive.sh | 19 +++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 00de70365e..b6c54b03c1 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -793,6 +793,24 @@ static void set_reflog_action(struct rebase_options *options)
 	strbuf_release(&buf);
 }
 
+static int check_exec_cmd(const char *cmd)
+{
+	int non_blank = 0;
+
+	while (*cmd) {
+		if (*cmd == '\n')
+			return error(_("exec commands cannot contain newlines"));
+		if (!isspace(*cmd))
+			non_blank = 1;
+		cmd++;
+	}
+
+	if (non_blank)
+		return 0;
+
+	return error(_("empty exec command"));
+}
+
 int cmd_rebase(int argc, const char **argv, const char *prefix)
 {
 	struct rebase_options options = {
@@ -1130,6 +1148,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	for (i = 0; i < exec.nr; i++)
+		if (check_exec_cmd(exec.items[i].string))
+			exit(1);
+
 	if (!(options.flags & REBASE_NO_QUIET))
 		argv_array_push(&options.git_am_opts, "-q");
 
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 7a440e08d8..c98f64eb2d 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -147,6 +147,25 @@ test_expect_success 'rebase -i with the exec command checks tree cleanness' '
 	git rebase --continue
 '
 
+test_expect_success 'rebase -x with empty command fails' '
+	test_when_finished "git rebase --abort ||:" &&
+	test_must_fail git rebase -x "" @ 2>actual &&
+	test_write_lines "error: empty exec command" >expected &&
+	test_i18ncmp expected actual &&
+	test_must_fail git rebase -x " " @ 2>actual &&
+	test_i18ncmp expected actual
+'
+
+LF='
+'
+test_expect_success 'rebase -x with newline in command fails' '
+	test_when_finished "git rebase --abort ||:" &&
+	test_must_fail git rebase -x "a${LF}b" @ 2>actual &&
+	test_write_lines "error: exec commands cannot contain newlines" \
+			 >expected &&
+	test_i18ncmp expected actual
+'
+
 test_expect_success 'rebase -i with exec of inexistent command' '
 	git checkout master &&
 	test_when_finished "git rebase --abort" &&
-- 
2.20.1