lint_config: ensure NPROC is set to something usable

We use NPROC for managing the number of parallel jobs to run, so it is
essentially that this is a valid number.  Add a lint pass, and move the
setting of the default value to this location.

Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/libmakepkg/lint_config/meson.build

@@ -2,6 +2,7 @@ libmakepkg_module = 'lint_config'
 
 sources = [
   'ext.sh.in',
+  'nproc.sh.in',
   'paths.sh.in',
   'source_date_epoch.sh.in',
   'variable.sh.in',

scripts/libmakepkg/lint_config/nproc.sh.in

@@ -0,0 +1,40 @@
+#!/bin/bash
+#
+#   nproc.sh - Check that NPROC setting is valid
+#
+#   Copyright (c) 2025 Pacman Development Team <pacman-dev@lists.archlinux.org>
+#
+#   This program is free software; you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation; either version 2 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+[[ -n $LIBMAKEPKG_LINT_CONFIG_NPROC_SH ]] && return
+LIBMAKEPKG_LINT_CONFIG_NPROC_SH=1
+
+MAKEPKG_LIBRARY=${MAKEPKG_LIBRARY:-'@libmakepkgdir@'}
+
+source "$MAKEPKG_LIBRARY/util/message.sh"
+
+lint_config_functions+=('lint_nproc')
+
+
+lint_nproc() {
+	# provide default value if NPROC is not set
+	[[ -z $NPROC ]] && NPROC=1
+
+	if [[ $NPROC = *[^[:digit:]]* ]]; then
+		error "$(gettext "%s contains invalid characters: %s")" \
+			"\$NPROC" "${NPROC//[[:digit:]]}"
+		return 1
+	fi
+}

scripts/libmakepkg/lint_config/variable.sh.in

@@ -66,8 +66,5 @@ lint_config_variables() {
 		warning "$(gettext "PACKAGER should have the format 'Example Name <email@address.invalid>'")"
 	fi
 
-	# provide default value if NPROC is not set
-	[[ -z $NPROC ]] && NPROC=1
-
 	return $ret
 }