Surprising excess property check with recursive generic constraint

🔎 Search Terms

excess property check recursive generic contraint type variable inference

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20230906#code/C4TwDgpgBAysCGwIwMYAsIFt5QLxQG8AoKKAZwSTIH4AuKAJQhQHsAnAEwB4K2BLAHYBzADSxKydFngA+ANxEAvgqIdmAG3htoAMwCuAlMD4sBUFNsQQAsvHSCIXACoBhUzr5CoEAB5IBHGTiVqgY2DIAFCTm7p70rrGiRACU8W4CHkIqFhBWtvYCEBHEpBACwGwg9ADaBFCgkPQARDosLE1QigC6ItEUVmT0JaRQ8EPRI97llTV1DRDNAEZaHd29k4rrnb2KyQpAA

💻 Code

type StateSchema = {
  states?: Record<string, StateSchema>;
};

declare function createMachine<TConfig extends StateSchema>(
  config: TConfig,
): TConfig;

createMachine({
  entry: [{ type: "foo" }],
  states: {
    a: {
      entry: [{ type: "bar" }],
    },
  },
});

🙁 Actual behavior

At the nested entry property the error is raised:

Object literal may only specify known properties, and 'entry' does not exist in type 'StateSchema'.(2353)

but it isn't raised at the entry property at the root of this object.

🙂 Expected behavior

I'd expect no excess property error to be raised with a recursive constraint like this.

Additional information about the issue

This particular case is somewhat easily fixable by adding [k: string]: unknown to StateSchema. I still find the reported behavior to be a problem though.

Start by opening the linked TypeScript Playground reproduction and tracing the excess-property check for the root and nested entry properties under the recursive StateSchema constraint. Done means the nested case no longer reports diagnostic 2353, consistently with the stated expected behavior; the issue names no repository file or test.