Type mis-match in destructuring of @optional field

[mununki]

This is related #5423 #5452

type t0 = {@optional x: int}
let f0: t0 = {x: 1} // x: option<int>
let {x} = f0 // x: int instead option<int>

I think there's a type mis-match after destructuring. Isn't it correct that type of x is option<int>?

[cristianoc]

Not sure what's in the comments is accurate: in the f0 case it's still true x:int. You can check that {x:x} works i.e. {x} works, when x has type int.
But there's an implicit mismatch in that f0.x has type option<int>. That is unavoidable I'm afraid.

[mununki]

// definition
type props<'name> = { @optional name: 'name } // 1
let make = ({ name }: props<_>) => name->Belt.Option.getWithDefault("")->React.string // 2

// application
React.createElement(Foo.make, {name: "Foo"}) // Error, wanted: option<string>

I encountered this issue when I write the jsx ppx v4. The name is inferred to option<string> at 2. That is correct. The props is inferred to type props<'name> = { name: option<'name> } at 1. In this case, I guess that the type of props.name is inferred to option<option<name> finally. So, the name should be Some("Foo") in the application site.

// correct
<Foo name="Foo">

// wrong
<Foo name=Some("Foo") />

[cristianoc]

What's the original component definitions? Looks like this is what was intended:

module Foo = {
  // definition
  type props<'name> = {@optional name: 'name} // 1
  let make = ({name: @optional name}: props<_>) => name->Belt.Option.getWithDefault("")->React.string // 2
}

[mununki]

The original definition is below.

@react.component
  let make = (~name=?) => {
    <div> {name->Belt.Option.getWithDefault("")->React.string} </div>
  }

[mununki]

{name: @optional name}: props<_>

This would work, unless the refmt removes the type annotation. I'll fix the ppx v4 accordingly.

[mununki]

Back to the first example, can user add the type annotation in this case? At least, when they want.

type t0 = {@optional x: int}
let f0: t0 = {x: 1}
let {x: @optional x} = f0 // add type annotation

[cristianoc]

```rescript
{name: @optional name}: props<_>

This would work, unless the refmt removes the type annotation. I'll fix the ppx v4 accordingly.

Yes I've noticed the issue with formatting, will bring it to the syntax repo. And then to the editor repo which vendors it.

[cristianoc]

Back to the first example, can user add the type annotation in this case? At least, when they want.

type t0 = {@optional x: int}
let f0: t0 = {x: 1}
let {x: @optional x} = f0 // add type annotation

Yes they can write type annotations.

[mununki]

Checked! rescript-lang/syntax#582
Thanks!

[cristianoc]

The issue about formatting: rescript-lang/syntax#583