write_since(): Include TODO lines from untracked files

Previously, untracked files were not included in the diff, so TODO lines
in those files would not be printed by the program.

Add the untracked `DiffOptions` to include the content of these files
when searching for TODOs.

2 files changed, 60 insertions, 2 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 0fe8f3f..910b488 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,7 +18,7 @@
 
 use std::io::Write;
 
-use git2::{Repository, Tree};
+use git2::{DiffOptions, Repository, Tree};
 use thiserror::Error;
 
 
@@ -46,7 +46,15 @@ impl Todos<'_> {
         tree: Tree<'_>,
         write_to: &mut W,
     ) -> Result<(), Error> {
-        let diff = self.repo.diff_tree_to_workdir(Some(&tree), None)?;
+        let mut diff_options = DiffOptions::new();
+        diff_options
+            .show_untracked_content(true)
+            .recurse_untracked_dirs(true);
+
+        let diff = self.repo.diff_tree_to_workdir_with_index(
+            Some(&tree),
+            Some(&mut diff_options),
+        )?;
 
         diff.foreach(
             &mut |_file, _progress| {
diff --git a/t/105-works-on-untracked-files.t b/t/105-works-on-untracked-files.t
new file mode 100644
index 0000000..9c7683f
--- /dev/null
+++ b/t/105-works-on-untracked-files.t
@@ -0,0 +1,50 @@
+#!/usr/bin/env perl -w
+
+# Copyright (c) 2020  Teddy Wing
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+
+use strict;
+
+use File::Copy;
+use Test::More;
+
+use Bin qw($BIN);
+
+my $file = 'untracked.rs';
+
+chdir 't-git-repo' or die $!;
+
+system('git checkout -b fork-point');
+ok !$?;
+
+open(my $output, '>', $file) or die $!;
+
+print $output "    // TODO: untracked to-do\n";
+
+close $output;
+
+my $todos = qx($BIN);
+is $todos, 'untracked.rs:1:    // TODO: untracked to-do
+';
+
+
+# Teardown
+unlink $file;
+system('git checkout master');
+system('git branch -D fork-point');
+
+
+done_testing;