Low priority inference trumps a much better inference that can be made from a generic signature

🔎 Search Terms

inference generic signature type parameters low priority

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.0-dev.20240102#code/CYUwxgNghgTiAEAzArgOzAFwJYHtX1ES1RAGEcBbABzxFQwB4AFGHKgZ3hAA8M7hOAJXA4YwBuwwxiAcwA08KKgCeAPlUAKAFDx47EBmRUAXPA1VWHUyzbsAlPAC8q+ADccWYHJ3w22POwA-KYA3j66FrbBZgDWIMo4iPA2HHYA2gC6ANw+AL7edqbmluzWJQ7O8GgxqDgA7qg5WmABGPBw7ACMTgQgRCTk1LT02roMACpcvPycktKoMpoA+pFW8CHwFOwyppO5FS5hurpwhjD4GgfruTm6uVp2TR2dWgD0r-AAeoFaza3tIHYACYeoRiGRKDQSCMfBMpnxUAI9FJZMtVqV1pttrt4PsnIdwgCzhcriEbnlvLojsd0aY0gAiLYyekZSm4gpPQFAt4fb5aIA

💻 Code

declare function defineComponent<Props extends Record<string, any>>(
  setup: (props: Props) => void,
  options?: {
    props?: (keyof Props)[];
  },
): (props: Props) => unknown;

const res1 = defineComponent(
  <T extends string>(_props: { msg: T }) => {
    return () => {};
  }
);

res1
// ^? const res1: <T extends string>(props: { msg: T; }) => unknown

const res2 = defineComponent(
  <T extends string>(_props: { msg: T }) => {
    return () => {};
  },
  {
    props: ["msg"],
  },
);

res2
// ^? const res2: (props: { msg: any; }) => unknown

🙁 Actual behavior

A low-priority inference made from keyof Props prevents inference from the generic signature

🙂 Expected behavior

I'd expect both of those to infer the same result: <T extends string>(props: { msg: T; }) => unknown

Additional information about the issue

There is an existential question to be asked here... what is a low-priority inference in the first place? :P Where is the line? Should every inference priority other than InferencePriority.None be treated as low-priority here?

Reproduce the inference difference in the linked TypeScript Playground, starting with the generic signature and the keyof Props inference path described in the issue. Trace how low-priority inference is handled, then verify that res2 infers the same generic signature as res1 without regressing related inference cases.