util.array: Fix equality metamethod in Lua 5.3 Lua 5.2 only used the __eq metamethod if both operands have the same __eq, but Lua 5.3 will pick one from either operands that has one as long as both are tables. This results in array() == {} and all sorts of odd behavior, including array() == util.json.null. <MattJ> I think [array() == {}] should have the same semantics as {} == {}

author: Kim Alvefur <zash@zash.se>
date: Wed, 15 Jan 2020 21:08:01 +0100
parent: 9529:6a1e7723208b
child: 10895:5777968301e8
--- a/util/array.lua	Wed Jan 15 21:14:06 2020 +0100
+++ b/util/array.lua	Wed Jan 15 21:08:01 2020 +0100
@@ -10,6 +10,7 @@
     = table.insert, table.sort, table.remove, table.concat;
 
 local setmetatable = setmetatable;
+local getmetatable = getmetatable;
 local math_random = math.random;
 local math_floor = math.floor;
 local pairs, ipairs = pairs, ipairs;
@@ -40,6 +41,10 @@
 end
 
 function array_mt.__eq(a, b)
+	if getmetatable(a) ~= array_mt or getmetatable(b) ~= array_mt then
+		-- Lua 5.3+ calls this if both operands are tables, even if metatables differ
+		return false;
+	end
 	if #a == #b then
 		for i = 1, #a do
 			if a[i] ~= b[i] then