[PATCH v6] checkpatch: add fix for non-standard signature - co-authored-by

[Aditya Srivastava <yashsri421@gmail.com>]

Currently, checkpatch.pl warns us for BAD_SIGN_OFF on the usage of
non-standard signatures.

An evaluation on v4.13..v5.8 showed that out of 539 warnings due to
non-standard signatures, 43 are due to the use of 'Co-authored-by'
tag, which may seem correct, but is not standard.

The standard signature equivalent for 'Co-authored-by' is
'Co-developed-by'.

Provide a fix by suggesting users with this signature alternative and
replacing.

Signed-off-by: Aditya Srivastava <yashsri421@gmail.com>
---
applies perfectly on the latest next-20201204 branch

changes in v2: replace commit specific example with brief evaluation

changes in v3: provide rationale to users for every signature tag suggestion;
modify commit message describing arrival to conclusion in a structured way

changes in v4: modify rationale for certain suggestions

changes in v5: remove the tag deletion suggestions, ie "Generated-by" and "Celebrated-by"; rebase on last accepted changes; modify commit message

changes in v6: reduce tag suggestions to only "Co-authored-by"; modify commit message accordingly; include complete version changelog

 scripts/checkpatch.pl | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 4a026926139f..fc036d545d2d 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2832,6 +2832,9 @@ sub process {
 
 			if ($sign_off !~ /$signature_tags/) {
 				my $suggested_signature = find_standard_signature($sign_off);
+				if ($sign_off =~ /co-authored-by:/i) {
+					$suggested_signature = "Co-developed-by:";
+				}
 				if ($suggested_signature eq "") {
 					WARN("BAD_SIGN_OFF",
 					     "Non-standard signature: $sign_off\n" . $herecurr);
-- 
2.17.1