DeepPartial typing does not play nicely with branded types

[flakey-bit]

Prior Issues

• TypeScript: DeepPartial breaks when using unknown #3368

What is the current behavior?

Assume some simple branded type, for example

type Money = string & { __brand: "Money" };

Assume some type, e.g. Transaction that makes use of the branded type in a property, for example

export interface Transaction {
  amount: Money;
  postedDateTime: string;
}

For a given type T, and an instance variable declared as of type DeepPartial<T>, an instance of T should be assignable to the instance variable of type DeepPartial<T>, but with the current implementation this is violated.

The problem is an overly simplisitic DeepPartial definition, there are better implementations out there. NB: I believe the implementation prior to #3369 did not have this problem (but obviously that PR addressed other issues).

Steps to Reproduce

// Money is a "branded" string
type Money = string & { __brand: "Money" };

export interface Transaction {
  amount: Money;
  postedDateTime: string;
}

let foo: DeepPartial<Transaction> = {
  postedDateTime: "2019-11-01"
};

const bar: Transaction = {
  amount: "300.50" as Money,
  postedDateTime: "2019-11-02"
};

foo = bar; // barfs with compile error

The error:

Error:(29, 1) TS2322: Type 'Transaction' is not assignable to type 'DeepPartial<Transaction>'.
  Types of property 'amount' are incompatible.
    Type 'Money' is not assignable to type 'undefined'.

What is the expected behavior?

An instance of T is assignable to a variable of type DeepPartial<T>, even if T includes properties that are branded strings / branded numbers.

Environment Details

Redux 4.1.2
TypeScript 4.5.2

Unsure as to whether it worked with previous versions of Redux.

[timdorr]

This is actually already fixed and tested against in 5.0. I suggest giving the alpha a try.

[flakey-bit]

Thanks ❤️ and sorry for not checking the alpha first 🤦‍♂️