tools: add a luacheckrc generator

tools/make-luacheck-files.sh will generate a .luacheckrc with the
following rules:
 - any rules set in the project header (.luacheck.head)
 - each mod is allowed to use a single global sharing its mod name
 - mod dependency information is parsed, and those mods' globals are
   permitted for read access

.luacheck.head

@@ -0,0 +1,17 @@
+std = "min"
+
+read_globals = {
+	"ItemStack",
+	"dump", "dump2",
+	"vector",
+	"VoxelArea",
+	"minetest",
+	"PseudoRandom",
+	"PerlinNoise",
+	"PcgRandom",
+
+	string = {fields = {"split", "trim"}},
+	table  = {fields = {"copy", "getn", "indexof", "insert_all"}},
+	math   = {fields = {"hypot", "round"}},
+}
+

tools/make-luacheck-files.sh

@@ -0,0 +1,95 @@
+#!/bin/sh
+#
+# make-luacheck-files.sh
+# v1 - E - Initial version
+
+set -ue
+
+if [ ! -d "mods" ] || [ ! -r ".luacheck.head" ]; then
+	printf "error: this script needs to be run from the mineclonia project root\n" 1>&2
+	exit 1
+fi
+
+# We need these to be explicitly NOT expanded.
+# shellcheck disable=2016
+{
+	# This creates a luacheckrc-compatible line from a mod (supplied on
+	# the command line with -v MOD="mod_name"), a directory (-v DIR="..."),
+	# and a list of dependencies (via STDIN). The `read_globals` section is
+	# skipped if there are no dependencies (-v EMPTY=1).
+	AWK_DEPS2LCHECK='
+	BEGIN {
+		printf("files[\"" DIR "\"] = { globals = { \"" MOD "\" }");
+		if (!EMPTY) {
+			printf(", read_globals = { ");
+		}
+	};
+
+	# Without a pattern, this will match on empty lines
+	# and mess up the entry. We clean up the extra commas
+	# later in the script.
+	/.+/{
+		sub("?$", "");
+		sub("\xd", "");
+		printf("\"" $1 "\", ");
+	};
+
+	END {
+		if (!EMPTY) {
+			printf("}");
+		}
+		printf(" }\n");
+	};'
+
+	# This takes any line that contains 'depends' and an equal sign
+	# and spits out each (comma-separated) entry on its own line.
+	SED_MODCONF2DEPS='
+	/depends *=/{
+		s/.*depends *=//;
+		s/, ?/\n/g;
+		p;
+	}'
+
+	HEADER='
+-------------------------------------------------------------------
+-- THIS FILE WAS AUTOGENERATED BY tools/make-luacheck-files.sh ! --
+--    DO NOT EDIT BY HAND. YOUR CHANGES WILL BE LOST NEXT RUN!   --
+-------------------------------------------------------------------
+
+'
+}
+
+find mods -type d -print | while read -r DIR; do
+	if [ -r "$DIR/depends.txt" ]; then
+		printf "found: %s (%s)\n" "$DIR" "depends.txt" 1>&2
+		# depends.txt is a simple newline-delimited file,
+		# so we can just read it in.
+		DEPS="$(cat "$DIR/depends.txt")"
+	elif [ -r "$DIR/mod.conf" ]; then
+		printf "found: %s (%s)\n" "$DIR" "mod.conf" 1>&2
+		# mod.conf needs some more help to get usable
+		# data out of it.
+		DEPS="$(sed -n -r -e "$SED_MODCONF2DEPS" "$DIR/mod.conf")"
+	else
+		# Empty dir, or not a mod dir.
+		continue
+	fi
+
+	EMPTY=0
+	if [ -z "$DEPS" ]; then
+		EMPTY=1
+	fi
+
+	# Get only the last chunk of the directory
+	# for the mod name.
+	MOD="${DIR##*/}"
+
+	# Now we run through it through the formatter,
+	# and remove any rogue trailing commas.
+	{ awk -v DIR="$DIR" -v EMPTY="$EMPTY" -v MOD="$MOD" -- "$AWK_DEPS2LCHECK" | sed -e "s/, }/ }/"; } <<-EOF
+		$DEPS
+	EOF
+done > .luacheck.files
+
+# Put the final thing together with the warning header
+{ printf "%s" "$HEADER"; cat .luacheck.head .luacheck.files; } > .luacheckrc