Check for errors in html files

xmllint doesn't know about the HTML 5 <section> tag so filter
those out.

.gitlab-ci.yml

@@ -420,6 +420,7 @@ misc:
     - sh util/check-categories.sh
     - if git grep SYSTEMTESTTOP -- ':!.gitlab-ci.yml'; then echo 'Please use relative paths instead of $SYSTEMTESTTOP.'; exit 1; fi
     - bash util/unused-headers.sh
+    - bash util/xmllint-html.sh
   needs: []
   artifacts:
     paths:

util/copyrights

@@ -1993,3 +1993,4 @@
 ./util/tabify-changes				SH	2004,2007,2012,2016,2018,2019,2020,2021
 ./util/unused-headers.sh			SH	2020,2021
 ./util/update_copyrights			PERL	1998,1999,2000,2001,2004,2005,2006,2007,2008,2009,2010,2012,2013,2014,2015,2016,2017,2018,2019,2020,2021
+./util/xmllint-html.sh				SH	2021

util/xmllint-html.sh

@@ -0,0 +1,21 @@
+#!/bin/sh -f
+#
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+files=`git ls-files '*.html'`
+if test -n "$files"
+then
+	xmllint --noout --nonet --html $files 2>&1 |
+	awk 'BEGIN { status = 0; }
+	     # suppress HTML 5 <section> tag errors
+	     /HTML parser error : Tag section invalid/ { getline; getline; next; }
+	     { print; status = 1; }
+	     END { exit status }'
+fi