macroexp methods on union types are miscompiled

[purplesyringa]

local record I1
    where true -- imagine a real condition here
    method: function(self) = macroexp(self: I1): boolean
        return false
    end
end
local record I2
    where true
    method: function(self) = macroexp(self: I1): boolean
        return true
    end
end

local function f(x: I1 | I2): boolean
    return x:method()
end

...compiles to:

local function f(x)
   return false
end

I believe calling macroexp methods on union types should be forbidden.

[lenscas]

considering they by definition work with is, the compiler could also emit the right code so it can call the correct macro instead of forbidding it.

But, I do agree that making this an error is probably better.

[purplesyringa]

I assumed that macro expressions are supposed to be zero-cost, and checking the type for unions would be counter to that, hence my suggestion to error.

[hishamhm]

But, I do agree that making this an error is probably better.

Agreed. A PR is welcome!