as const breaks intra expression inference #62220

🔎 Search Terms

const context expression assertion inference type parameter

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250806#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXwxAGcMAeAFQBp4ARAPgApYBzALngG8AoeeLVAA7IM7GgG4e8ATBzBkYEOyYw2tAJTwAvHXjkJvMHiLIAtovjLV5DdvipTAIxAwJAXzWiJXQ6hLwHMgDWIPiaBMQYDNy8-EIi8ACMAAxJlJLSsvLmljY6LAB0GDgAyhgw-MwMamkGRqbZLLnwBRAhzBgAFmmuzUTwPiRqXgMY8ADuODCBFVrhJFGSscLsyanpMnIKSo1aeSqFJWUVVTX9dWbbKk0tbZ3dQ1xAA

💻 Code

declare function test<T, D>(arg: {
  input: D;
  produce: (arg: D) => T;
  consume: (arg: T) => number;
}): D;

const broken = test({
  input: 100,
  produce: (arg) => arg.toString(), // 'arg' is of type 'unknown'.(18046)
  consume: (arg) => arg.length,
} as const);

const working = test({
  input: 100,
  produce: (arg) => arg.toString(), // `arg` inferred as `number`
  consume: (arg) => arg.length,
});

🙁 Actual behavior

as const is the only difference between those two and its presence breaks assigned parameter type in produce

🙂 Expected behavior

I think as const should not impact inference this way and both should be inferred just OK. It's just that the broken case should infer 100 instead of number for the D type parameter

Additional information about the issue

No response