Luau Recap: April 2022

[fun_enthusiast]

Luau is our new language that you can read more about at https://luau-lang.org.

It’s been a bit of a quiet month. We mostly have small optimizations and bug fixes for you.

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You can now define functions on sealed tables that have string indexers. These functions will be type-checked against the indexer type. For example, the following is now valid:

local a : {[string]: () -> number} = {}

function a.y() return 4 end -- OK

Autocomplete will now provide string literal suggestions for singleton types, for example:

local function f(x: "a" | "b") end

f("_") -- suggest "a" and "b"

Improve error recovery in the case where we encounter a type pack variable in a place where one is not allowed, for example: type Foo<A...> = { value: A... }

Error feedback has been improved when code does not pass enough arguments to a variadic function.

For example, the following script now produces a much nicer error message:

type A = { [number]: number }

type B = { [number]: string }

local a: A = { 1, 2, 3 }

-- ERROR: Type 'A' could not be converted into 'B'

-- caused by:

-- Property '[indexer value]' is not compatible. Type 'number' could not be converted into 'string'

local b: B = a

If the following code were to error because Hello was undefined, we would erroneously include the comment in the span of the error. This is now fixed.

type Foo = Hello -- some comment over here

Fixed a crash that could occur when strict scripts have cyclic require() dependencies.

Added an option to autocomplete to cause it to abort processing after a certain amount of time has elapsed.

[chainreactionist]

Really love the improvements to Luau, Every update pushes us further and further toward the true type of safety. Any plans to add type checking to remote events ?

[C_Corpze (Cartoon_Corpze)]

Oh sweet, can’t wait to see what Luau is going to look like and how it will perform in the far future.
The language really seems to develop pretty well.

[Sharksie]

Looks like a regression with metatable handling. table library functions no longer accept arrays with metatables.

[HugeCoolboy2007 (omega)]

This is a recap of everything that was added over the course of April for Luau, this has nothing to do with the servers.

[TrulyChxse (Truly)]

Great improvements, hope to see more features that improve workflow in the future!

[seanieplays (syl)]

I <3 the team that works on luau
thank you for all the updates!

[Qinrir (Quin)]

Enable highlights : ). And great! knowing i didnt understand anything but eh still pretty good.

[Qualadore]

This will incorrectly warn with “Expected type table, got ‘Instance’ instead”.

local function execute(object: Instance, name: string)
	print(object[name])
end

This won’t occur if the object is explicitly specified, so this will correctly not warn.

local function execute(name: string)
	print(workspace[name])
end

[Qualadore]

This will incorrectly warn and I have filed an issue.

--!strict
type value = {true}?
local value: value = {true}
value = value

[zeuxcg]

Can you elaborate on this? I’m not sure if you’re talking about runtime behavior or type checking. In terms of runtime behavior table. functions in Luau never used metamethods like __index and we currently have no plans to change it.

[Sharksie]

Referring to type checking. Today if I write

--!strict
local t = setmetatable({} :: {Instance}, {__mode='v'})
table.insert(t, workspace)

I get Type 't' could not be converted into '{a}'
This happens for all table library functions as far as I can tell. I didn’t see it before this update.

[Eac12a (asimo3080)]

I think about that maybe we should fix today show me a script and I will fix it today

[Huonzales (Meowtsun)]

literal suggestions is really nice ,However the autocomplete
can get really messy with all the suggestions.

Problem :

I think you could just hide it or give us some way to do so.
while still keeping the suggestions ,of course.

Hidden :