checkpatches: verify in-reply-to header when possible

When using checkpatches.sh locally, verify that there is an In-Reply-To
header when the patch is a respin (i.e. v2, v3, etc.). This is currently
only enforced by the upstream CI but cannot be verified locally.

This cannot be verified when checking commit ids since --in-reply-to is
a git-format-patch option which is not specified by checkpatches.sh when
generating temporary files.

Here is an example:

 $ git format-patch -v6 -1 --stdout | devtools/checkpatches.sh
 warning: [PATCH v6] graph: expose node context as pointers
 warning: respins must be --in-reply-to=<v1.patch@message.id>.
 0/1 valid patch

 $ git format-patch -v6 -1 --stdout --in-reply-to=foo | \
                     devtools/checkpatches.sh
 1/1 valid patch

Link: https://git.dpdk.org/tools/dpdk-ci/commit/?id=070b31649e48460b3
Signed-off-by: Robin Jarry <rjarry@redhat.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>

devtools/checkpatches.sh

@@ -399,11 +399,13 @@ status=0
 check () { # <patch-file> <commit>
 	local ret=0
 	local subject=''
+	local check_in_reply_to=false
 	headline_printed=false
 
 	total=$(($total + 1))
 	if [ -n "$1" ] ; then
 		tmpinput=$1
+		check_in_reply_to=true
 	else
 		tmpinput=$(mktemp -t dpdk.checkpatches.XXXXXX)
 		trap "rm -f '$tmpinput'" INT
@@ -413,13 +415,24 @@ check () { # <patch-file> <commit>
 			--no-stat --stdout -1 $commit > "$tmpinput"
 		else
 			cat > "$tmpinput"
+			check_in_reply_to=true
 		fi
 	fi
 
 	# Subject can be on 2 lines
 	subject=$(sed '/^Subject: */!d;s///;N;s,\n[[:space:]]\+, ,;s,\n.*,,;q' "$tmpinput")
 	! $verbose || print_headline "$subject"
 
+	# check In-Reply-To for version > 1
+	if [ "$check_in_reply_to" = true ] \
+		&& echo "$subject" | grep -qi 'v[2-9].*\]' \
+		&& ! grep -qi '^In-Reply-To: ' "$tmpinput"
+	then
+		echo "warning: $subject"
+		echo "warning: respins must be --in-reply-to=<v1.patch@message.id>."
+		ret=1
+	fi
+
 	! $verbose || printf 'Running checkpatch.pl:\n'
 	report=$($DPDK_CHECKPATCH_PATH $options "$tmpinput" 2>/dev/null)
 	if [ $? -ne 0 ] ; then