scripts/checkpatch.pl: check for non-permalinks to Zulip

Zulip links to https://rust-for-linux.zulipchat.com can break in
case of renaming the topic or channel if they are not message
links (which are permanent links).

If a non-permanent Zulip link is referenced then emit a warning
and direct the user to the Zulip documentation.

Permanent links are of the format:
https://.../#narrow/stream/x/topic/x/near/<numerical_id>

Suggested-by: Miguel Ojeda <[email protected]>
Link: Rust-for-Linux#1104
Signed-off-by: Siddharth Menon <[email protected]>

Author: BiscuitBobby

scripts/checkpatch.pl

@@ -735,6 +735,10 @@ sub find_standard_signature {
 	\Qspinics.net\E
 )};
 
+our $zulip_forums = qr{(?xi:
+	\Qrust-for-linux.zulipchat.com\E
+)};
+
 our @typeListMisordered = (
 	qr{char\s+(?:un)?signed},
 	qr{int\s+(?:(?:un)?signed\s+)?short\s},
@@ -3415,6 +3419,12 @@ sub process {
 			     "Use lore.kernel.org archive links when possible - see https://lore.kernel.org/lists.html\n" . $herecurr);
 		}
 
+# Check for permanent Zulip URL
+		if ($rawline =~ m{http.*\b$zulip_forums(?!(?:/#narrow/stream/.+/topic/.+/(?:near|with)/\d+)?($|\s+.*))}) {
+			WARN("PREFER_PERMANENT_URL",
+			     "Use permanent Zulip links when possible - see https://zulip.com/help/link-to-a-message-or-conversation#get-a-link-to-a-specific-message\n" . $herecurr);
+		}
+
 # Check for added, moved or deleted files
 		if (!$reported_maintainer_file && !$in_commit_log &&
 		    ($line =~ /^(?:new|deleted) file mode\s*\d+\s*$/ ||