Proposed Changes

DeepPartial and DeepPartialSkipArrayKey incorrectly expanded branded types into object structures instead of treating them as atomic values.

The Problem

type BrandedType<T, Brand extends symbol | string> = T & {
  [K in Brand]: unknown;
};

type FormValues = {
  firstName: BrandedType<string, "FirstName">;
};

Before:
DeepPartial expanded branded strings into all string methods

{
  firstName?: {
    toString?: {} | undefined;
    charAt?: {} | undefined;
    concat?: {} | undefined;
    // ... 35+ more methods ...
    FirstName?: unknown;
  } | undefined
}

After:
Correctly preserves the branded type

{
  firstName?: BrandedType<string, "FirstName">;
}

Solution

Added IsPrimitiveLike<T> helper to detect primitive types (including branded primitives) and prevent DeepPartial/DeepPartialSkipArrayKey from recursively expanding them.

Fixes #13221

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes