fix: partial fix for type inference when accepting specialized valida…

…tor in function (#43)

* fix: partial fix for type inference when accepting specialized validator in function

* cleaner markdown

etc/types.api.md

@@ -24,7 +24,7 @@ export class ArrayType<ElementType extends BaseTypeImpl<Element>, Element, Resul
 
 // @public
 export abstract class BaseObjectLikeTypeImpl<ResultType> extends BaseTypeImpl<ResultType> {
-    and<Other extends BaseObjectLikeTypeImpl<any>>(_other: Other): TypeImpl<BaseObjectLikeTypeImpl<MergeIntersection<ResultType & Other[typeof designType]>>> & TypedPropertyInformation<this['props'] & Other['props']>;
+    and<Other extends BaseObjectLikeTypeImpl<any>>(_other: Other): ObjectType<MergeIntersection<ResultType & Other[typeof designType]>> & TypedPropertyInformation<this['props'] & Other['props']>;
     // (undocumented)
     abstract readonly isDefaultName: boolean;
     // (undocumented)
@@ -58,12 +58,12 @@ export abstract class BaseTypeImpl<ResultType> implements TypeLink<ResultType> {
     is(input: unknown): input is ResultType;
     literal(input: DeepUnbranded<ResultType>): ResultType;
     abstract readonly name: string;
-    or<Other>(_other: BaseTypeImpl<Other>): TypeImpl<BaseTypeImpl<ResultType | Other>>;
+    or<Other>(_other: BaseTypeImpl<Other>): Type<ResultType | Other>;
     protected typeParser?(input: unknown, options: ValidationOptions): Result<unknown>;
     protected abstract typeValidator(input: unknown, options: ValidationOptions): Result<ResultType>;
     validate(input: unknown, options?: ValidationOptions): Result<ResultType>;
-    withBrand<BrandName extends string>(name: BrandName): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>>;
-    withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<ResultType>): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>>;
+    withBrand<BrandName extends string>(name: BrandName): Type<Branded<ResultType, BrandName>>;
+    withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<ResultType>): Type<Branded<ResultType, BrandName>>;
     withName(name: string): this;
     withParser(...args: [name: string, newConstructor: (i: unknown) => unknown] | [newConstructor: (i: unknown) => unknown]): this;
     withValidation(validation: Validator<ResultType>): this;

markdown/types.baseobjectliketypeimpl.and.md

@@ -9,7 +9,7 @@ Intersect this Type with another Type.
 <b>Signature:</b>
 
 ```typescript
-and<Other extends BaseObjectLikeTypeImpl<any>>(_other: Other): TypeImpl<BaseObjectLikeTypeImpl<MergeIntersection<ResultType & Other[typeof designType]>>> & TypedPropertyInformation<this['props'] & Other['props']>;
+and<Other extends BaseObjectLikeTypeImpl<any>>(_other: Other): ObjectType<MergeIntersection<ResultType & Other[typeof designType]>> & TypedPropertyInformation<this['props'] & Other['props']>;
 ```
 
 ## Parameters
@@ -20,7 +20,7 @@ and<Other extends BaseObjectLikeTypeImpl<any>>(_other: Other): TypeImpl<BaseObje
 
 <b>Returns:</b>
 
-[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[BaseObjectLikeTypeImpl](./types.baseobjectliketypeimpl.md)<!-- -->&lt;[MergeIntersection](./types.mergeintersection.md)<!-- -->&lt;ResultType &amp; Other\[typeof designType\]&gt;&gt;&gt; &amp; [TypedPropertyInformation](./types.typedpropertyinformation.md)<!-- -->&lt;this\['props'\] &amp; Other\['props'\]&gt;
+[ObjectType](./types.objecttype.md)<!-- -->&lt;[MergeIntersection](./types.mergeintersection.md)<!-- -->&lt;ResultType &amp; Other\[typeof designType\]&gt;&gt; &amp; [TypedPropertyInformation](./types.typedpropertyinformation.md)<!-- -->&lt;this\['props'\] &amp; Other\['props'\]&gt;
 
 ## Remarks
 

markdown/types.basetypeimpl.or.md

@@ -9,7 +9,7 @@ Union this Type with another Type.
 <b>Signature:</b>
 
 ```typescript
-or<Other>(_other: BaseTypeImpl<Other>): TypeImpl<BaseTypeImpl<ResultType | Other>>;
+or<Other>(_other: BaseTypeImpl<Other>): Type<ResultType | Other>;
 ```
 
 ## Parameters
@@ -20,7 +20,7 @@ or<Other>(_other: BaseTypeImpl<Other>): TypeImpl<BaseTypeImpl<ResultType | Other
 
 <b>Returns:</b>
 
-[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;ResultType \| Other&gt;&gt;
+[Type](./types.type.md)<!-- -->&lt;ResultType \| Other&gt;
 
 ## Remarks
 

markdown/types.basetypeimpl.withbrand.md

@@ -9,7 +9,7 @@ Create a new instance of this Type with the given name.
 <b>Signature:</b>
 
 ```typescript
-withBrand<BrandName extends string>(name: BrandName): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>>;
+withBrand<BrandName extends string>(name: BrandName): Type<Branded<ResultType, BrandName>>;
 ```
 
 ## Parameters
@@ -20,7 +20,7 @@ withBrand<BrandName extends string>(name: BrandName): TypeImpl<BaseTypeImpl<Bran
 
 <b>Returns:</b>
 
-[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;[Branded](./types.branded.md)<!-- -->&lt;ResultType, BrandName&gt;&gt;&gt;
+[Type](./types.type.md)<!-- -->&lt;[Branded](./types.branded.md)<!-- -->&lt;ResultType, BrandName&gt;&gt;
 
 ## Remarks
 

markdown/types.basetypeimpl.withconstraint.md

@@ -9,7 +9,7 @@ Create a new type use the given constraint function to restrict the current type
 <b>Signature:</b>
 
 ```typescript
-withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<ResultType>): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>>;
+withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<ResultType>): Type<Branded<ResultType, BrandName>>;
 ```
 
 ## Parameters
@@ -21,7 +21,7 @@ withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<
 
 <b>Returns:</b>
 
-[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;[Branded](./types.branded.md)<!-- -->&lt;ResultType, BrandName&gt;&gt;&gt;
+[Type](./types.type.md)<!-- -->&lt;[Branded](./types.branded.md)<!-- -->&lt;ResultType, BrandName&gt;&gt;
 
 ## Remarks
 

src/base-type.ts

@@ -4,9 +4,11 @@ import type {
     DeepUnbranded,
     LiteralValue,
     MergeIntersection,
+    ObjectType,
     Properties,
     PropertiesInfo,
     Result,
+    Type,
     TypeImpl,
     TypeLink,
     ValidationOptions,
@@ -273,7 +275,7 @@ export abstract class BaseTypeImpl<ResultType> implements TypeLink<ResultType> {
      *
      * @param name - the new name to use in error messages
      */
-    withBrand<BrandName extends string>(name: BrandName): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>> {
+    withBrand<BrandName extends string>(name: BrandName): Type<Branded<ResultType, BrandName>> {
         return createType(branded<ResultType, BrandName>(this), { name: { configurable: true, value: name } });
     }
 
@@ -353,12 +355,9 @@ export abstract class BaseTypeImpl<ResultType> implements TypeLink<ResultType> {
      * @param name - the new name to use in error messages
      * @param constraint - the additional validation to restrict the current type
      */
-    withConstraint<BrandName extends string>(
-        name: BrandName,
-        constraint: Validator<ResultType>,
-    ): TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>> {
+    withConstraint<BrandName extends string>(name: BrandName, constraint: Validator<ResultType>): Type<Branded<ResultType, BrandName>> {
         // Ignoring Brand here, because that is a typings-only feature.
-        const fn: TypeImpl<BaseTypeImpl<Branded<ResultType, BrandName>>>['typeValidator'] = (input, options) => {
+        const fn: BaseTypeImpl<Branded<ResultType, BrandName>>['typeValidator'] = (input, options) => {
             const baseResult = this.typeValidator(input, options);
             if (!baseResult.ok) {
                 return newType.createResult(input, undefined, prependContextToDetails(baseResult, 'base type'));
@@ -400,7 +399,7 @@ export abstract class BaseTypeImpl<ResultType> implements TypeLink<ResultType> {
      * See {@link UnionType} for more information about unions.
      */
     // istanbul ignore next: using ordinary stub instead of module augmentation to lighten the load on the TypeScript compiler
-    or<Other>(_other: BaseTypeImpl<Other>): TypeImpl<BaseTypeImpl<ResultType | Other>> {
+    or<Other>(_other: BaseTypeImpl<Other>): Type<ResultType | Other> {
         throw new Error('stub');
     }
 
@@ -455,8 +454,7 @@ export abstract class BaseObjectLikeTypeImpl<ResultType> extends BaseTypeImpl<Re
     // istanbul ignore next: using ordinary stub instead of module augmentation to lighten the load on the TypeScript compiler
     and<Other extends BaseObjectLikeTypeImpl<any>>(
         _other: Other,
-    ): TypeImpl<BaseObjectLikeTypeImpl<MergeIntersection<ResultType & Other[typeof designType]>>> &
-        TypedPropertyInformation<this['props'] & Other['props']> {
+    ): ObjectType<MergeIntersection<ResultType & Other[typeof designType]>> & TypedPropertyInformation<this['props'] & Other['props']> {
         throw new Error('stub');
     }
 }

src/types.test.ts

@@ -223,6 +223,7 @@ testTypeImpl({
 });
 
 /** RestrictedUser is the User type with additional validation logic. */
+type RestrictedUser = The<typeof RestrictedUser>;
 const RestrictedUser = User.withConstraint('RestrictedUser', user => {
     const errors: MessageDetails[] = [];
     if (user.name.first === 'Bobby' && user.name.last === 'Tables') {
@@ -297,6 +298,7 @@ const NumberFromString = number.withParser(
         return +n;
     }),
 );
+type NestedFromString = The<typeof NestedFromString>;
 const NestedFromString = object('NestedFromString', { a: NumberFromString, b: NumberFromString });
 
 testTypeImpl({
@@ -356,6 +358,7 @@ testTypeImpl({
     ],
 });
 
+type ComplexNesting = The<typeof ComplexNesting>;
 const ComplexNesting = object('ComplexNesting', {
     pos: NumberFromString.withValidation(n => n > 0 || 'should be positive'),
     neg: NumberFromString.withValidation(n => n < 0 || 'should be negative'),
@@ -679,3 +682,22 @@ testTypes('usability of assert', () => {
     // Does work:
     MyExplicitType.assert(value);
 });
+
+testTypes('type inference', () => {
+    function elementOfType<T>(_type: Type<T>): T {
+        return 0 as any;
+    }
+
+    assignableTo<number>(elementOfType(number));
+    assignableTo<ConfirmedAge>(elementOfType(ConfirmedAge));
+    assignableTo<User>(elementOfType(User));
+    assignableTo<RestrictedUser>(elementOfType(RestrictedUser));
+    assignableTo<NestedFromString>(elementOfType(NestedFromString));
+    assignableTo<ComplexNesting>(elementOfType(ComplexNesting));
+    assignableTo<IntersectionTest>(elementOfType(IntersectionTest));
+    assignableTo<MyGenericWrapper<User>>(elementOfType(MyGenericWrapper(User)));
+    assignableTo<GenericAugmentation<User>>(elementOfType(GenericAugmentation(User)));
+
+    // @ts-expect-error I still don't know how to fix this for `extendWith`:
+    assignableTo<Age>(elementOfType(Age));
+});