['a' | 'b'] expect to receive ['a']

[crazyair]

Bug Report

DeepNamePath<T> result is equal to ['a'] | ['b'], but result different

🔎 Search Terms

🕗 Version & Regression Information

• This is a crash
• This changed between versions ______ and _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
• I was unable to test this on prior versions because _______

⏯ Playground Link

Playground link with relevant code

💻 Code

export type DeepNamePath<T = any> = T extends Record<string, any>
  ? {
    [P in keyof T]: [P] | DeepNamePath<T[P]>;
  }[keyof T]
  : never;

type ddd<T = any> = ['a'] | ['b']  // result is ['a']
// type ddd<T = any> = DeepNamePath<T>;  // result is ['a'] | ['b']


function func<T = any, T1 extends ddd<T> = ddd<T>>(data: T, params: T1) {
  console.log('data', data);
  return params;
}

export const d = func({ a: '', b: '' }, ['a']);
type result = typeof d
//  ^?

🙁 Actual behavior

['a']

🙂 Expected behavior

['a' , 'b']

[MartinJohns]

🙂 Expected behavior

['a' , 'b']

Why do you expect this behaviour? What's your reasoning and thought process?

The return argument of your function is just params, and params is just typed T1. This type argument is inferred from the provided parameter, and you provide ["a"] as the value. This looks just fine.

[crazyair]

🙂 Expected behavior

['a' , 'b']

Why do you expect this behaviour? What's your reasoning and thought process?

The return argument of your function is just params, and params is just typed T1. This type argument is inferred from the provided parameter, and you provide ["a"] as the value. This looks just fine.

I want result is ['a'], will be used to obtain the value of data

[crazyair]

func({ a: { a1: string }, b: number }, ['a']);

input ['a', 'a1'] result string
input b result number

[crazyair]

 export type DeepNamePath<T = any> = T extends Record<string, any>
   ? {
-      [P in keyof T]: [P] | DeepNamePath<T[P]>;
+      [P in keyof T]: [P] | [...DeepNamePath<T[P]>];
     }[keyof T]
   : never;

If I write this way, I can get ['a'], but it requires DeepNamePath to return an array

[Andarist]

Your second argument gets widened to string[] in the first inference pass. That's gathered as the inference candidate, it fails the constraint check so the constraint gets selected as the inference result.

TS doesn't recognize that your T1 has a tuple-like constraint (getBaseConstraintOfType just returns unknown). I suspect that's because it's a recursive type without a direct hint that it returns a tuple type. When u wrapped the second union member with [...T] you essentially gave it that hint and that's why it works.

For similar reasons this one work:

export type DeepNamePath<T = any> = T extends Record<string, any>
  ? {
    [P in keyof T]: readonly [P] | DeepNamePath<T[P]>;
  }[keyof T]
  : never;

type ddd<T = any> = DeepNamePath<T>;

function func<T = any, const T1 extends ddd<T> = ddd<T>>(data: T, params: T1) {
  console.log('data', data);
  return params;
}

export const d = func({ a: '', b: '' }, ['a']);

This one doesn't really recognize the tuple-like base constraint but it introduces a const context and has a similar effect on the overall thing.

[crazyair]

Your second argument gets widened to string[] in the first inference pass. That's gathered as the inference candidate, it fails the constraint check so the constraint gets selected as the inference result.

TS doesn't recognize that your T1 has a tuple-like constraint (getBaseConstraintOfType just returns unknown). I suspect that's because it's a recursive type without a direct hint that it returns a tuple type. When u wrapped the second union member with [...T] you essentially gave it that hint and that's why it works.

For similar reasons this one work:

export type DeepNamePath<T = any> = T extends Record<string, any>
  ? {
    [P in keyof T]: readonly [P] | DeepNamePath<T[P]>;
  }[keyof T]
  : never;

type ddd<T = any> = DeepNamePath<T>;

function func<T = any, const T1 extends ddd<T> = ddd<T>>(data: T, params: T1) {
  console.log('data', data);
  return params;
}

export const d = func({ a: '', b: '' }, ['a']);

This one doesn't really recognize the tuple-like base constraint but it introduces a const context and has a similar effect on the overall thing.

I thought of const, but I couldn't write it at the time. const T1 extends ddd<T> = ddd<T>

[jcalz]

Since this hasn't been said explicitly yet: this isn't a bug in TypeScript so this isn't really the right place for this discussion. Stack Overflow or the TS Discord would be more appropriate venues. @crazyair, could you please close the issue to free up the TS team's time? Once it's closed I imagine anyone who's still interested could continue discussing here.

edit: Thanks! 🙏

[crazyair]

@Andarist

export type DeepNamePath<T = any> = T extends Record<string, any>
  ? {
      [P in keyof T]: readonly [P] | DeepNamePath<T[P]>;
    }[keyof T]
  : never;

type ddd<T = any> = DeepNamePath<T>;

function func<T = any, const T1 extends ddd<T> = ddd<T>>(data: T, params: T1) {
  console.log('data', data);
  return params;
}

// export const d = func({ a: '', b: '' }, ['a']);

export interface ColumnType<
  RecordType = any,
  T1 extends DeepNamePath<RecordType> = DeepNamePath<RecordType>,
> {
  dataIndex?: T1;
  render?: (value: T1) => any;
}

export interface DemoProps<T = any> {
  data: readonly T[];
  columns: ColumnType<T, DeepNamePath<T>>[];
}

export const result: DemoProps<{ a: number; b: string }> = {
  data: [{ a: 1, b: '' }],
  columns: [{ dataIndex: ['a'], render: value => value }],
};

value type is readonly ["a"] | readonly ["b"], i want readonly ["a"]

[crazyair]

-export interface ColumnType<RecordType = any, T1 extends DeepNamePath<RecordType> = any> {
+export interface ColumnType<RecordType = any, const T1 extends DeepNamePath<RecordType> = any> {
   dataIndex?: T1;
   render?: (value: T1) => any;
 }

'const' modifier can only appear on a type parameter of a function, method or classts(1277)

[Andarist]

To make it work you need to be in some inference context and that means that you need a function call to make it work (and annotate its type params as const). This kinda should work:

export type DeepNamePath<T = any> = T extends Record<string, any>
  ? {
      [P in keyof T]: readonly [P] | readonly [...DeepNamePath<T[P]>];
    }[keyof T]
  : never;

declare function make<T, const T2 extends readonly DeepNamePath<T>[]>(arg: {
  data: T[];
  columns: {
    [K in keyof T2]: {
      dataIndex: T2[K];
      render: (value: T2[K]) => void;
    };
  };
}): void;

export const result = make({
  data: [{ a: 1, b: "" }],
  columns: [{ dataIndex: ["a"], render: (value) => value }],
});

but it doesn't because TS doesn't currently handle context-sensitive functions in reverse-mapped types that well. It's something I want to improve in #54029

[crazyair]

I need

const demo: DemoProps<xx> = xxx

[crazyair]

If list there are 2 pieces of data (parameter) value: "a" | "b"
If list there are 1 pieces of data (parameter) value: "a"

declare function func<TData = any, const T1 extends keyof TData = any>(data: {
  data: TData[];
  list: {
    key?: T1;
    render?: (value: T1) => any;
  }[];
}): any;

func({
  data: [{ a: 1, b: '2' }],
  list: [
    { key: 'a', render: value => value },
    { key: 'b', render: value => value },
  ],
});