[Enhancement] Infer @operator from implementations of metamethods #2941

---@class Rule
---@field def fun(source: string, index: number): number, ...
T.Rule = {__metatable = false}
-- Prevent infinite recursion by not taking the shortcut of __index: table 
setmetatable(T.Rule, {
    __call = function(t, source, index) return t:parse(source, index) end,
    __index = function(t, k) if t ~= T.Rule then return T.Rule[k] end end,
    __newindex = function() error("cannot create fields on a value of type Rule") end,
    __metatable = false
})

---@param def fun(source: string, index: number): number, ...
---@return Rule
---@nodiscard
function T.Rule.new(def)
    local o = {def = def}
    setmetatable(o, T.Rule)
    return o
end

---@param other Rule
---@return Rule
---@nodiscard
function T.Rule:__add(other)
    return T.Rule.new(function(source, index)
        local succ, i = pcall(self.def, source, index)
        if not succ then error(i, 2) end

        return other.def(source, i)
    end)
end