Inference not work in object getter when use ThisType with additional fields

[guyskk]

Bug Report

🔎 Search Terms

Inference, ThisType, this, getter

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about keyword "this"

⏯ Playground Link

Playground link with relevant code

💻 Code

function myfunc<T>(
  options: T & ThisType<T & { name: string }>
): T & { name: string } {
  return options as any;
}

const A = myfunc({
  get nickname() {
    const name = this.name;
    return name;
  },
  getNickname() {
    const name = this.name;
    return name;
  },
});

🙁 Actual behavior

this.name is string:

but const name is any:

🙂 Expected behavior

expect const name infer to string type, the same as this.name.

[vincent-yao27]

Similar issue with ThisType and generic constraints:

Sometimes it's

and sometimes it's

If Record<string, PropertyDefinition> constraint of generic param T of function model is removed, it works as expected

Code

type TypeMap<T> = StringConstructor extends T
  ? string
  : NumberConstructor extends T
  ? number
  : T;

type PropertyDefinition = {
  type?: StringConstructor | NumberConstructor;
  required?: true;
  computed?(): unknown;
};

type Expanded<T> = T extends infer U ? { [P in keyof U]: U[P] } : never;

type DeriveType<T> = T extends { type: infer U }
  ? TypeMap<U> | (T extends { required: true } ? never : undefined)
  : T extends { computed: () => infer U }
  ? U
  : never;

type Entity<T> = Expanded<{
  [K in keyof T]: DeriveType<T[K]>;
}>;

function model<T extends Record<string, PropertyDefinition>>(
  definition: T & ThisType<Entity<T>>
): T {
  return definition;
}

const BillItem = model({
  price: { type: Number, required: true },
  amount: { type: Number, required: true },
  description: { type: String },
  total: {
    computed() {
      return this.amount * this.price;
    },
  },
});