New type solver throws unclear type error when returning table with an optional Roblox data type

[melindatrace]

This issue only seems to occur for Vector3, Vector2, CFrame, and other Roblox data types, but not for Luau primitive data types.

local function FuncA(): { Value: Vector3? }
	return {
		Value = Vector3.zero -- TypeError: Type pack '{ Value: Vector3 }' could not be converted into '{ Value: Vector3? }'; type { Value: Vector3 }[0][read "Value"] (Vector3) is not exactly { Value: Vector3? }[0][read "Value"][1] (nil) Luau(1035)
	}
end

FuncA()

local function FuncB(): { Value: number? }
	return {
		Value = 1 -- OK
	}
end

FuncB()

[aatxe]

This probably has absolutely nothing to do with Roblox data types. My immediate best guess is that this is a problem with some of the expected type code, but we'll investigate it when we can.

[hgoldstein]

Hello! Sorry to report so late, but this should be fixed as of a couple Luau releases ago. If I remember correctly, the root cause was that the aforementioned expected type code did the incorrect thing for non-literal expressions. This happened for any type, for example:

local Numbers = { zero = 0 }
local function FuncA(): { Value: number? }
    return { Value = 0 } -- As noted, worked fine for literals
end
local function FuncB(): { Value: number ? }
  return { Value = Numbers.zero } -- Used to error, claiming `number?` is incompatible with `number`
end

Feel free to re-open this issue if the problem is still occuring!