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 {} == {}

1 files changed, 5 insertions, 0 deletions

diff --git a/util/array.lua b/util/array.lua
index 0b60a4fd..32d2d6a5 100644
--- a/util/array.lua
+++ b/util/array.lua
@@ -10,6 +10,7 @@ local t_insert, t_sort, t_remove, t_concat
     = 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 @@ function array_mt.__add(a1, a2)
 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