Exact: Fix support for Date in union (#902)

source/exact.d.ts

@@ -1,7 +1,7 @@
 import type {ArrayElement, ObjectValue} from './internal';
-import type {Opaque, TagContainer} from './opaque';
 import type {IsEqual} from './is-equal';
 import type {KeysOfUnion} from './keys-of-union';
+import type {JsonObject} from './basic';
 
 /**
 Create a type from `ParameterType` and `InputType` and change keys exclusive to `InputType` to `never`.
@@ -57,7 +57,6 @@ export type Exact<ParameterType, InputType> =
  : ParameterType extends unknown[] ? Array<Exact<ArrayElement<ParameterType>, ArrayElement<InputType>>>
  // In TypeScript, Array is a subtype of ReadonlyArray, so always test Array before ReadonlyArray.
  : ParameterType extends readonly unknown[] ? ReadonlyArray<Exact<ArrayElement<ParameterType>, ArrayElement<InputType>>>
- // Leave tagged types as-is. We could try to make the untagged part Exact, and just leave the tag as-is, but that seems to create instanitation excessively deep errors.
- : ParameterType extends TagContainer<unknown> ? ParameterType
- : ParameterType extends object ? ExactObject<ParameterType, InputType>
- : ParameterType;
+ // Only apply Exact for pure object types. For types from a class, leave it unchanged to TypeScript to handle.
+ : ParameterType extends JsonObject ? ExactObject<ParameterType, InputType>
+ : ParameterType;

test-d/exact.ts

@@ -450,3 +450,20 @@ import type {Exact, Opaque} from '../index';
  },
  });
 }
+
+// Spec - special test case for Date type + union
+// @see https:/sindresorhus/type-fest/issues/896
+{
+ type A = {
+ a: string;
+ b?: Date | null;
+ };
+
+ const function_ = <T extends Exact<A, T>>(arguments_: T) => arguments_;
+
+ function_({a: 'a'});
+ function_({a: 'a', b: new Date()});
+ function_({a: 'a', b: new Date() as Date | null});
+ // @ts-expect-error
+ function_({a: 'a', b: 1});
+}