[PATCH] checkpatch: Allow not using -f with files that are in git

[Joe Perches <joe@perches.com>]

If a file exists in git and checkpatch is used without the -f
flag for scanning a file, then checkpatch will scan the file
assuming it's a patch and emit:

ERROR: Does not appear to be a unified-diff format patch

Change the behavior to assume the -f flag if the file exists
in git.

Signed-off-by: Joe Perches <joe@perches.com>
---
 scripts/checkpatch.pl | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 79fc357b18cd..cdee7cfadc11 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -976,6 +976,16 @@ sub seed_camelcase_includes {
 	}
 }
 
+sub git_is_single_file {
+	my ($filename) = @_;
+
+	return 0 if ((which("git") eq "") || !(-e "$gitroot"));
+
+	my $output = `${git_command} ls-files -- $filename`;
+	my $count = $output =~ tr/\n//;
+	return $count eq 1 && $output =~ m{^${filename}$};
+}
+
 sub git_commit_info {
 	my ($commit, $id, $desc) = @_;
 
@@ -1049,6 +1059,9 @@ my $vname;
 $allow_c99_comments = !defined $ignore_type{"C99_COMMENT_TOLERANCE"};
 for my $filename (@ARGV) {
 	my $FILE;
+	my $is_git_file = git_is_single_file($filename);
+	my $oldfile = $file;
+	$file = 1 if ($is_git_file);
 	if ($git) {
 		open($FILE, '-|', "git format-patch -M --stdout -1 $filename") ||
 			die "$P: $filename: git format-patch failed - $!\n";
@@ -1093,6 +1106,7 @@ for my $filename (@ARGV) {
 	@modifierListFile = ();
 	@typeListFile = ();
 	build_types();
+	$file = $oldfile if ($is_git_file);
 }
 
 if (!$quiet) {