[PATCH 2/3] checkpatch: warn when Reported-by: is not followed by Link:

[Kai Wasserbäch]

Encourage patch authors to link to reports by issuing a warning, if
a Reported-by: is not accompanied by a link to the report. Those links
are often extremely useful for any code archaeologist that wants to know
more about the backstory of a change than the commit message provides.
That includes maintainers higher up in the patch-flow hierarchy, which
is why Linus asks developers to add such links [1, 2, 3]. To quote [1]:

> Again, the commit has a link to the patch *submission*, which is
> almost entirely useless. There's no link to the actual problem the
> patch fixes.
>
> [...]
>
> Put another way: I can see that
>
> Reported-by: Zhangfei Gao <zhangfei.gao@xxxxxxxxxxx>
>
> in the commit, but I don't have a clue what the actual report was, and
> there really isn't enough information in the commit itself, except for
> a fairly handwavy "Device drivers might, for instance, still need to
> flush operations.."
>
> I don't want to know what device drivers _might_ do. I would want to
> have an actual pointer to what they do and where.

Another reason why these links are wanted: the ongoing regression
tracking efforts can only scale with them, as they allow the regression
tracking bot 'regzbot' to automatically connect tracked reports with
patches that are posted or committed to fix tracked regressions.

Link: https://lore.kernel.org/all/CAHk-=wjMmSZzMJ3Xnskdg4+GGz=5p5p+GSYyFBTh0f-DgvdBWg@xxxxxxxxxxxxxx/ [1]
Link: https://lore.kernel.org/all/CAHk-=wgs38ZrfPvy=nOwVkVzjpM3VFU1zobP37Fwd_h9iAD5JQ@xxxxxxxxxxxxxx/ [2]
Link: https://lore.kernel.org/all/CAHk-=wjxzafG-=J8oT30s7upn4RhBs6TX-uVFZ5rME+L5_DoJA@xxxxxxxxxxxxxx/ [3]
Co-developed-by: Thorsten Leemhuis <linux@xxxxxxxxxxxxx>
Signed-off-by: Thorsten Leemhuis <linux@xxxxxxxxxxxxx>
Signed-off-by: Kai Wasserbäch <kai@xxxxxxxxxxxxxxxxxxxxxx>
---
 scripts/checkpatch.pl | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index d739ce0909..9434f94d2d 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3155,6 +3155,20 @@ sub process {
 					     "Co-developed-by and Signed-off-by: name/email do not match \n" . "$here\n" . $rawline . "\n" .$rawlines[$linenr]);
 				}
 			}
+
+			# check if Reported-by: is followed by a Link:
+			if ($sign_off =~ /^reported-by:$/i) {
+				if (!defined $lines[$linenr]) {
+					WARN("BAD_REPORTED_BY_LINK",
+					     "Reported-by: should be immediately followed by Link: to the report\n" . $herecurr . $rawlines[$linenr] . "\n");
+				} elsif ($rawlines[$linenr] !~ /^\s*link:\s*(.*)/i) {
+					WARN("BAD_REPORTED_BY_LINK",
+					     "Reported-by: should be immediately followed by Link: to the report\n" . $herecurr . $rawlines[$linenr] . "\n");
+				} elsif ($lines[$linenr] !~ /https?:\/\//i) {
+					WARN("BAD_REPORTED_BY_LINK",
+					     "Link: following Reported-by: should contain a URL\n" . $herecurr . $rawlines[$linenr] . "\n");
+				}
+			}
 		}
 
 # Check Fixes: styles is correct
-- 
2.35.1