[PATCH] checkpatch: do not allow using -f/--file option without a filename

[Dwaipayan Ray]

When checkpatch is run without a filename, it reads from stdin.
But if --file option is used along with that, it may generate
false positives.

Consider the following test file:
$cat test.c
int x = a - b;

$cat test.c | ./scripts/checkpatch.pl -f
WARNING: It's generally not useful to have the filename in the file
+int x = a - b;

This is a false positive and occurs because $realfile is set to "-".
Also since checkpatch relies on the file's extension to run specific
checks for c files, assembly files, etc, most of the checks are
not run as well.

So it is better to disable -f/--file option when checkpatch is
run without a filename.

Link: https://lore.kernel.org/lkml/294bb4a2c3f5f8cf4a744cf59bfd37562653afb9.camel@xxxxxxxxxxx/T/#t
Suggested-by: Joe Perches <joe@xxxxxxxxxxx>
Signed-off-by: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx>
---
 scripts/checkpatch.pl | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 3e1795311c87..7dff9206f9f0 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -331,6 +331,7 @@ help(0) if ($help);
 
 die "$P: --git cannot be used with --file or --fix\n" if ($git && ($file || $fix));
 die "$P: --verbose cannot be used with --terse\n" if ($verbose && $terse);
+die "$P: -f/--file requires at least one filename\n" if ($file && $#ARGV < 0);
 
 if ($color =~ /^[01]$/) {
 	$color = !$color;
-- 
2.28.0