Re: [PATCH v2] checkpatch: use patch subject when reading from stdin

[Joe Perches]

On Tue, 2020-05-05 at 15:26 +0200, Geert Uytterhoeven wrote:
> While "git am" can apply an mbox file containing multiple patches (e.g.
> as created by b4[1], or a patch bundle downloaded from patchwork),
> checkpatch does not have proper support for that.  When operating on an
> mbox, checkpatch will merge all detected tags, and complain falsely
> about duplicates:
> 
>     WARNING: Duplicate signature
> 
> As modifying checkpatch to reset state in between each patch is a lot of
> work, a simple solution is splitting the mbox into individual patches,
> and invoking checkpatch for each of them.  Fortunately checkpatch can read
> a patch from stdin, so the classic "formail" tool can be used to split
> the mbox, and pipe all individual patches to checkpatch:
> 
>     formail -s scripts/checkpatch.pl < my-mbox
> 
> However, when reading a patch file from standard input, checkpatch calls
> it "Your patch", and reports its state as:
> 
>     Your patch has style problems, please review.
> 
> or:
> 
>     Your patch has no obvious style problems and is ready for submission.
> 
> Hence it can be difficult to identify which patches need to be reviewed
> and improved.
> 
> Fix this by replacing "Your patch" by (the first line of) the email
> subject, if present.
> 
> Note that "git mailsplit" can also be used to split an mbox, but it will
> create individual files for each patch, thus requiring cleanup
> afterwards.  Formail does not have this disadvantage.
> 
> [1] https://git.kernel.org/pub/scm/utils/b4/b4.git
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> v2:
>   - Add more rationale,
>   - Refer to the new b4 tool.
> ---
>  scripts/checkpatch.pl | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index eac40f0abd56a9f4..3355358697d9e790 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -1057,6 +1057,10 @@ for my $filename (@ARGV) {
>  	}
>  	while (<$FILE>) {
>  		chomp;
> +		if ($vname eq 'Your patch') {
> +			my ($subject) = $_ =~ /^Subject:\s*(.*)/;
> +			$vname = '"' . $subject . '"' if $subject;
> +		}
>  		push(@rawlines, $_);
>  	}
>  	close($FILE);

There's a less cpu intensive way to do this,
for small patches, on my little laptop it's a
few dozen milliseconds faster, and for very
large patches multiple seconds faster to use
the following patch:

Substitute Geert's patch with the below but:

Acked-by: Joe Perches <joe@xxxxxxxxxxx>

---

 scripts/checkpatch.pl | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index f0092104ff7b..29786a097862 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1062,6 +1062,7 @@ for my $filename (@ARGV) {
 	while (<$FILE>) {
 		chomp;
 		push(@rawlines, $_);
+		$vname = "\"$1\"" if ($filename eq '-' && $_ =~ /^Subject:\s*(.*)/);
 	}
 	close($FILE);