TypeScript generic functions causing incorrect typing issues with nested correlated unions

I am currently working on incorporating a predefined TypeScript configuration that can be dynamically loaded into my application. The configuration is structured as shown below:

// Base object types
type Config<D> = {
  fn: ({ option }: { option: D }) => any;
  option: D;
};

type ConfigRecord<T extends Record<keyof T, any>> = {
  [K in keyof T]: Config<T[K]> & { type: K };
};

// Helper function to type function argument
const typeConfigRecord = <T extends Record<keyof T, any>>(
  map: ConfigRecord<T>
) => map;

// Actual implementation of type
const tableConfig = typeConfigRecord({
  test: {
    type: "test",
    fn: ({ option }) => {
      return option;
    },
    option: "test",
  },
  test2: {
    type: "test2",
    fn: ({ option }) => {
      return option;
    },
    option: 2,
  },
});

const defaultConfig = typeConfigRecord({
  tester: {
    type: "tester",
    fn: ({ option }) => {
      return option;
    },
    option: "test3",
  },
  test2: {
    type: "test2",
    fn: ({ option }) => {
      return option;
    },
     option: "A"',
  },
});

const configRecordMap = {
    table: tableConfig,
    default: defaultConfig
}

My goal is to interact with this logic using nested generic functions setup:

const dynamicLogic = <S extends keyof typeof configRecordMap>(variant: S) => {
    const selectedRecord = configRecordMap[variant];

    const dynamicExecute = <K extends keyof typeof selectedRecord>(type: K) => {
        const config = selectedRecord[type];

        return config.fn({ option: config.option }); // Issue
    }
}

In addition, I have included the following typing for the configRecordMap:

type ConfigRecordMap<T extends Record<keyof T, any>> = {
  [K in keyof T]: ConfigRecord<T[K]>;
};
const typeConfigRecordMap = <T extends Record<keyof T, any>>(
  map: ConfigRecordMap<T>
) => map;

const configRecordMap = typeConfigRecordMap({
    table: tableConfig,
    default: defaultConfig
});

However, this results in errors where the property option represents an intersection of all potential parameter types. How can I relate this to the config.option object?

TS Playground

Answer №1

There appears to be a striking resemblance in the reasoning behind this recently implemented PR for tsc. It's possible that the error you're encountering is due to an additional layer of complexity that the compiler struggles to handle.

My suggestion would be to simplify your data structure, or eliminate the use of generics altogether. If you have a clear understanding of the valid types involved, consider defining (or generating) the type declarations statically. Alternatively, if you are handling various types generically, simply utilize their JavaScript equivalent.

Moreover, if there's a certain rule you wish the type system to enforce beyond standard interface adherence, requiring a type guard or specialized processing, consider implementing type branding and restricting data casting within your type guard or factory function.

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