checkpatch: fix the usage of capture group ( ... )

The usage of "capture group (...)" in the immediate condition after `&&`
results in `$1` being uninitialized.  This issues a warning "Use of
uninitialized value $1 in regexp compilation at ./scripts/checkpatch.pl
line 2638".

I noticed this bug while running checkpatch on the set of commits from
v5.7 to v5.8-rc1 of the kernel on the commits with a diff content in
their commit message.

This bug was introduced in the script by commit a57c91c59d73
("checkpatch: emit an error when there's a diff in a changelog").  It
has been in the script since then.

The author intended to store the match made by capture group in variable
`$1`.  This should have contained the name of the file as `[\w/]+`
matched.  However, this couldn't be accomplished due to usage of capture
group and `$1` in the same regular expression.

Fix this by placing the capture group in the condition before `&&`.
Thus, `$1` can be initialized to the text that capture group matches
thereby setting it to the desired and required value.

Fixes: a57c91c59d73 ("checkpatch: emit an error when there's a diff in a changelog")
Signed-off-by: Mrinal Pandey <mrinalmni@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Joe Perches <joe@perches.com>
Link: https://lkml.kernel.org/r/20200714032352.f476hanaj2dlmiot@mrinalpandey
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 60d4a79674b6efd5f82d5f5ac052e9c3bdba8796..504d2e431c60412dd3720ddfe4df9a0c6ae2e338 100755 (executable)
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2639,8 +2639,8 @@ sub process {
 
 # Check if the commit log has what seems like a diff which can confuse patch
                if ($in_commit_log && !$commit_log_has_diff &&
-                   (($line =~ m@^\s+diff\b.*a/[\w/]+@ &&
-                     $line =~ m@^\s+diff\b.*a/([\w/]+)\s+b/$1\b@) ||
+                   (($line =~ m@^\s+diff\b.*a/([\w/]+)@ &&
+                     $line =~ m@^\s+diff\b.*a/[\w/]+\s+b/$1\b@) ||
                     $line =~ m@^\s*(?:\-\-\-\s+a/|\+\+\+\s+b/)@ ||
                     $line =~ m/^\s*\@\@ \-\d+,\d+ \+\d+,\d+ \@\@/)) {
                        ERROR("DIFF_IN_COMMIT_MSG",