fix: correct inference of arrays of branded literal types (#85)

BREAKING CHANGE: This changes the meaning of the type parameter of the `array` function.
skunkteam · Oct 26, 2023 · e6521cf · e6521cf
1 parent 56184f3
commit e6521cf
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Showing 4 changed files with 28 additions and 14 deletions.
diff --git a/etc/types.api.md b/etc/types.api.md
@@ -5,7 +5,7 @@
 ```ts
 
 // @public
-export function array<Element>(...args: [name: string, elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig] | [elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig]): TypeImpl<ArrayType<BaseTypeImpl<Element>, Element, Element[]>>;
+export function array<ElementType extends BaseTypeImpl<any>>(...args: [name: string, elementType: ElementType, typeConfig?: ArrayTypeConfig] | [elementType: ElementType, typeConfig?: ArrayTypeConfig]): TypeImpl<ArrayType<ElementType, TypeOf<ElementType>, Array<TypeOf<ElementType>>>>;
 
 // @public
 export class ArrayType<ElementType extends BaseTypeImpl<Element>, Element, ResultType extends Element[]> extends BaseTypeImpl<ResultType, ArrayTypeConfig> {

diff --git a/markdown/types.array.md b/markdown/types.array.md
@@ -9,19 +9,19 @@ Create a type that checks whether the input is an array and all elements conform
 **Signature:**
 
 ```typescript
-declare function array<Element>(
+declare function array<ElementType extends BaseTypeImpl<any>>(
     ...args:
-        | [name: string, elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig]
-        | [elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig]
-): TypeImpl<ArrayType<BaseTypeImpl<Element>, Element, Element[]>>;
+        | [name: string, elementType: ElementType, typeConfig?: ArrayTypeConfig]
+        | [elementType: ElementType, typeConfig?: ArrayTypeConfig]
+): TypeImpl<ArrayType<ElementType, TypeOf<ElementType>, Array<TypeOf<ElementType>>>>;
 ```
 
 ## Parameters
 
-| Parameter | Type                                                                                                                                                                                                                                                                                                                     | Description                    |
-| --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------ |
-| args      | \[name: string, elementType: [BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;Element&gt;, typeConfig?: [ArrayTypeConfig](./types.arraytypeconfig.md)<!-- -->\] \| \[elementType: [BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;Element&gt;, typeConfig?: [ArrayTypeConfig](./types.arraytypeconfig.md)<!-- -->\] | optional name and element-type |
+| Parameter | Type                                                                                                                                                                                                               | Description                    |
+| --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------ |
+| args      | \[name: string, elementType: ElementType, typeConfig?: [ArrayTypeConfig](./types.arraytypeconfig.md)<!-- -->\] \| \[elementType: ElementType, typeConfig?: [ArrayTypeConfig](./types.arraytypeconfig.md)<!-- -->\] | optional name and element-type |
 
 **Returns:**
 
-[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[ArrayType](./types.arraytype.md)<!-- -->&lt;[BaseTypeImpl](./types.basetypeimpl.md)<!-- -->&lt;Element&gt;, Element, Element\[\]&gt;&gt;
+[TypeImpl](./types.typeimpl.md)<!-- -->&lt;[ArrayType](./types.arraytype.md)<!-- -->&lt;ElementType, [TypeOf](./types.typeof.md)<!-- -->&lt;ElementType&gt;, Array&lt;[TypeOf](./types.typeof.md)<!-- -->&lt;ElementType&gt;&gt;&gt;&gt;
diff --git a/src/types/array.test.ts b/src/types/array.test.ts
@@ -146,3 +146,17 @@ testTypes(() => {
     // @ts-expect-error wrong element type
     assignableTo<MyArray>([1]);
 });
+
+testTypes('correct inference of arrays of branded types', () => {
+    type MyBrandedType = The<typeof MyBrandedType>;
+    const MyBrandedType = string.withConfig('MyBrandedType', { minLength: 2, maxLength: 2 });
+    type MyBrandedTypeArray = The<typeof MyBrandedTypeArray>;
+    const MyBrandedTypeArray = array(MyBrandedType);
+
+    const brandedArray = MyBrandedTypeArray.literal(['ab']);
+
+    assignableTo<MyBrandedType[]>(brandedArray);
+    assignableTo<MyBrandedTypeArray>([MyBrandedType.literal('ab')]);
+    // @ts-expect-error not a branded string
+    assignableTo<MyBrandedTypeArray>(['ab']);
+});
diff --git a/src/types/array.ts b/src/types/array.ts
@@ -1,5 +1,5 @@
 import { BaseTypeImpl, createType } from '../base-type';
-import type { ArrayTypeConfig, Result, TypeImpl, ValidationOptions, Visitor } from '../interfaces';
+import type { ArrayTypeConfig, Result, TypeImpl, TypeOf, ValidationOptions, Visitor } from '../interfaces';
 import {
     castArray,
     decodeOptionalName,
@@ -98,11 +98,11 @@ define(ArrayType, 'createAutoCastAllType', function (this: ArrayType<BaseTypeImp
  *
  * @param args - optional name and element-type
  */
-export function array<Element>(
+export function array<ElementType extends BaseTypeImpl<any>>(
     ...args:
-        | [name: string, elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig]
-        | [elementType: BaseTypeImpl<Element>, typeConfig?: ArrayTypeConfig]
-): TypeImpl<ArrayType<BaseTypeImpl<Element>, Element, Element[]>> {
+        | [name: string, elementType: ElementType, typeConfig?: ArrayTypeConfig]
+        | [elementType: ElementType, typeConfig?: ArrayTypeConfig]
+): TypeImpl<ArrayType<ElementType, TypeOf<ElementType>, Array<TypeOf<ElementType>>>> {
     const [name, elementType, typeConfig] = decodeOptionalName(args);
     return createType(new ArrayType(elementType, typeConfig ?? {}, name));
 }