Generic function type gets inferred to any without explicit typing

[KSchala]

Bug Report

Type has to be explicit defined while being resolved correctly?!

🕗 Version & Regression Information

• This is the behavior in every version I tried

🔎 Search Terms

Type inference, Union, Pattern

⏯ Playground Link

Playground link with relevant code

💻 Code

type Union<T extends object> = {
  [P in keyof T]: ({ [Q in "kind"]: P } & T[P]) extends infer U ? { [Q in keyof U]: U[Q] } : never
}[keyof T]
type UnionMap<U extends { kind: string }> = { [K in U["kind"]]: U extends { kind: K } ? U : never }
type ExhaustivePattern<T extends { kind: string }, R> = { [K in T["kind"]]: (union: UnionMap<T>[K]) => R };
type NonExhaustivePattern<T extends { kind: string }, R> = { [K in T["kind"]]?: (union: UnionMap<T>[K]) => R } & {_: (union: T) => R};
type Pattern<T extends { kind: string }, R> = ExhaustivePattern<T, R> | NonExhaustivePattern<T, R>;


function match<U extends { kind: string }, T>(union: U, pattern: Pattern<U, T>): T {
  if((pattern as any)[union.kind]) {
    return (pattern as any)[union.kind](union as U) as T
  }
  return (pattern as any)["_"](union as U) as T
}

type ValueType = Union<{
  String: {value: string},
  Number: {value: number},
  Boolean: {value: boolean},
  Date: {value: Date}
}>

let value: ValueType = {kind: "String", value: "Hello"};

function main(value: ValueType) {
  let test1 = match(value, {
    String: ({value}) => value,
    Number: ({value}) => value.toString(),
    _: (token) => "Unknown"
  });
  console.log(test1);

  let test2 = match<ValueType, string>(value, {
    String: ({value}) => value,
    Number: ({value}) => value.toString(),
    _: ({kind}) => kind
  });
  console.log(test2);
}

🙁 Actual behavior

Typescript throws an type error

🙂 Expected behavior

Type should be correctly inferred without explicitly defining the type

[RyanCavanaugh]

See #47599

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.