satisfies changes typechecking behavior

[sliminality]

🔎 Search Terms

satisfies upcast, satisfies changes typechecking behavior

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about satisfies

⏯ Playground Link

Playground link

💻 Code

type Table = "block" | "collection" | "space"

type RecordPointer<T extends Table> = {
	[T_ in T]: {
		id: string,
		table: T_
	}
}[T]

function g<T extends Table>(t: T): RecordPointer<Table> {
	// Uncommenting `satisfies RecordPointer<Table>` affects whether this program typechecks.
	const x = { table: t, id: "foo" } as const // satisfies RecordPointer<Table>
	return x
}

🙁 Actual behavior

This program fails to typecheck as written:

Type '{ readonly table: T; readonly id: "foo"; }' is not assignable to type 'RecordPointer<Table>'.
  Type '{ readonly table: T; readonly id: "foo"; }' is not assignable to type '{ id: string; table: "space"; }'.
    Types of property 'table' are incompatible.
      Type 'T' is not assignable to type '"space"'.
        Type 'Table' is not assignable to type '"space"'.
          Type '"block"' is not assignable to type '"space"'.(2322)

However, if we uncomment the satisfies expression on the second-to-last line, the type error goes away:

  function g<T extends Table>(t: T): RecordPointer<Table> {
- 	const x = { table: t, id: "foo" } as const
+ 	const x = { table: t, id: "foo" } as const satisfies RecordPointer<Table>
  	return x
  }

🙂 Expected behavior

My understanding from reading #47920 is that:

• satisfies does not perform safe upcast
• e satisfies T should have the inferred type typeof e, rather than T or T & typeof e

Assuming both of these are correct, I would not expect satisfies to affect whether this function typechecks.

Additional information about the issue

No response

[MartinJohns]

This sounds like a duplicate of #52394.

[sliminality]

You're totally right, I missed that. Thanks!