triggers modified_files on file deletion

lib/Mojo/Server/Morbo/Backend/Poll.pm

@@ -6,16 +6,26 @@ use Mojo::File qw(path);
 sub modified_files {
   my $self = shift;
 
-  my $cache = $self->{cache} //= {};
+  my $cache       = $self->{cache} //= {};
+  my $known_files = {map { $_ => 1 } keys %$cache};
   my @files;
   for my $file (map { -f $_ && -r _ ? $_ : _list($_) } @{$self->watch}) {
+    delete $known_files->{$file};
     my ($size, $mtime) = (stat $file)[7, 9];
     next unless defined $size and defined $mtime;
     my $stats = $cache->{$file} ||= [$^T, $size];
     next if $mtime <= $stats->[0] && $size == $stats->[1];
     @$stats = ($mtime, $size);
     push @files, $file;
   }
+
+  for my $file (keys %$known_files) {
+
+    # any leftover file means they were deleted
+    push @files, $file;
+    delete $cache->{$file};
+  }
+
   sleep $self->watch_timeout unless @files;
 
   return \@files;

t/mojo/morbo.t

@@ -131,6 +131,19 @@ EOF
   is $tx->res->body, 'Hello!', 'right content';
 };
 
+subtest 'Watch for deleted files' => sub {
+  my $morbo = Mojo::Server::Morbo->new;
+  $morbo->backend->watch([$dir]);
+  $morbo->backend->modified_files;
+  my $tmp_file = $dir->child('tmp_file.txt');
+  $tmp_file->spew("some data");
+  is_deeply $morbo->backend->modified_files, [$tmp_file], 'file was created';
+  is_deeply $morbo->backend->modified_files, [], 'no files changed';
+  unlink $tmp_file;
+  is_deeply $morbo->backend->modified_files, [$tmp_file], 'file was deleted';
+  is_deeply $morbo->backend->modified_files, [], 'no files changed';
+};
+
 subtest 'New file(s)' => sub {
   is_deeply $morbo->backend->modified_files, [], 'directory has not changed';
   my @new = map { $subdir->child("$_.txt") } qw/test testing/;