feat(core): add strongly-typed decorators factory (reflector)

packages/core/services/reflector.service.ts

@@ -1,5 +1,30 @@
-import { Type } from '@nestjs/common';
+import { CustomDecorator, SetMetadata, Type } from '@nestjs/common';
 import { isEmpty, isObject } from '@nestjs/common/utils/shared.utils';
+import { uid } from 'uid';
+
+/**
+ * @publicApi
+ */
+export interface CreateDecoratorOptions<T = any> {
+  /**
+   * The key for the metadata.
+   * @default uid(21)
+   */
+  key?: string;
+
+  /**
+   * The transform function to apply to the metadata value.
+   * @default value => value
+   */
+  transform?: (value: T) => T;
+}
+
+/**
+ * @publicApi
+ */
+export type ReflectableDecorator<T> = ((opts?: T) => CustomDecorator) & {
+  KEY: string;
+};
 
 /**
  * Helper class providing Nest reflection capabilities.
@@ -9,6 +34,43 @@ import { isEmpty, isObject } from '@nestjs/common/utils/shared.utils';
  * @publicApi
  */
 export class Reflector {
+  /**
+   * Creates a decorator that can be used to decorate classes and methods with metadata.
+   * Can be used as a strongly-typed alternative to `@SetMetadata`.
+   * @param options Decorator options.
+   * @returns A decorator function.
+   */
+  static createDecorator<T>(
+    options: CreateDecoratorOptions = {},
+  ): ReflectableDecorator<T> {
+    const metadataKey = options.key ?? uid(21);
+    const decoratorFn =
+      (metadataValue: T) =>
+      (target: object | Function, key?: string | symbol, descriptor?: any) => {
+        const value = options.transform
+          ? options.transform(metadataValue)
+          : metadataValue;
+        SetMetadata(metadataKey, value ?? {})(target, key, descriptor);
+      };
+
+    decoratorFn.KEY = metadataKey;
+    return decoratorFn as ReflectableDecorator<T>;
+  }
+
+  /**
+   * Retrieve metadata for a reflectable decorator for a specified target.
+   *
+   * @example
+   * `const roles = this.reflector.get(Roles, context.getHandler());`
+   *
+   * @param decorator reflectable decorator created through `Reflector.createDecorator`
+   * @param target context (decorated object) to retrieve metadata from
+   *
+   */
+  public get<T extends ReflectableDecorator<any>>(
+    decorator: T,
+    target: Type<any> | Function,
+  ): T extends ReflectableDecorator<infer R> ? R : unknown;
   /**
    * Retrieve metadata for a specified key for a specified target.
    *
@@ -22,10 +84,43 @@ export class Reflector {
   public get<TResult = any, TKey = any>(
     metadataKey: TKey,
     target: Type<any> | Function,
+  ): TResult;
+  /**
+   * Retrieve metadata for a specified key or decorator for a specified target.
+   *
+   * @example
+   * `const roles = this.reflector.get<string[]>('roles', context.getHandler());`
+   *
+   * @param metadataKey lookup key or decorator for metadata to retrieve
+   * @param target context (decorated object) to retrieve metadata from
+   *
+   */
+  public get<TResult = any, TKey = any>(
+    metadataKeyOrDecorator: TKey,
+    target: Type<any> | Function,
   ): TResult {
+    const metadataKey =
+      (metadataKeyOrDecorator as ReflectableDecorator<unknown>).KEY ??
+      metadataKeyOrDecorator;
+
     return Reflect.getMetadata(metadataKey, target);
   }
 
+  /**
+   * Retrieve metadata for a specified decorator for a specified set of targets.
+   *
+   * @param decorator lookup decorator for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAll<T extends ReflectableDecorator<any>>(
+    decorator: T,
+    targets: (Type<any> | Function)[],
+  ): T extends ReflectableDecorator<infer R>
+    ? R extends Array<any>
+      ? R[]
+      : R
+    : unknown;
   /**
    * Retrieve metadata for a specified key for a specified set of targets.
    *
@@ -36,25 +131,58 @@ export class Reflector {
   public getAll<TResult extends any[] = any[], TKey = any>(
     metadataKey: TKey,
     targets: (Type<any> | Function)[],
+  ): TResult;
+  /**
+   * Retrieve metadata for a specified key or decorator for a specified set of targets.
+   *
+   * @param metadataKeyOrDecorator lookup key or decorator for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAll<TResult extends any[] = any[], TKey = any>(
+    metadataKeyOrDecorator: TKey,
+    targets: (Type<any> | Function)[],
   ): TResult {
     return (targets || []).map(target =>
-      this.get(metadataKey, target),
+      this.get(metadataKeyOrDecorator, target),
     ) as TResult;
   }
 
+  /**
+   * Retrieve metadata for a specified decorator for a specified set of targets and merge results.
+   *
+   * @param decorator lookup decorator for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAllAndMerge<T extends ReflectableDecorator<any>>(
+    decorator: T,
+    targets: (Type<any> | Function)[],
+  ): T extends ReflectableDecorator<infer R> ? R : unknown;
   /**
    * Retrieve metadata for a specified key for a specified set of targets and merge results.
    *
    * @param metadataKey lookup key for metadata to retrieve
    * @param targets context (decorated objects) to retrieve metadata from
    *
    */
-  public getAllAndMerge<TResult extends any[] = any[], TKey = any>(
+  public getAllAndMerge<TResult extends any[] | object = any[], TKey = any>(
     metadataKey: TKey,
     targets: (Type<any> | Function)[],
+  ): TResult;
+  /**
+   * Retrieve metadata for a specified key or decorator for a specified set of targets and merge results.
+   *
+   * @param metadataKeyOrDecorator lookup key for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAllAndMerge<TResult extends any[] | object = any[], TKey = any>(
+    metadataKeyOrDecorator: TKey,
+    targets: (Type<any> | Function)[],
   ): TResult {
-    const metadataCollection = this.getAll<TResult, TKey>(
-      metadataKey,
+    const metadataCollection = this.getAll<any[], TKey>(
+      metadataKeyOrDecorator,
       targets,
     ).filter(item => item !== undefined);
 
@@ -75,6 +203,17 @@ export class Reflector {
     });
   }
 
+  /**
+   * Retrieve metadata for a specified decorator for a specified set of targets and return a first not undefined value.
+   *
+   * @param decorator lookup decorator for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAllAndOverride<T extends ReflectableDecorator<any>>(
+    decorator: T,
+    targets: (Type<any> | Function)[],
+  ): T extends ReflectableDecorator<infer R> ? R : unknown;
   /**
    * Retrieve metadata for a specified key for a specified set of targets and return a first not undefined value.
    *
@@ -85,9 +224,20 @@ export class Reflector {
   public getAllAndOverride<TResult = any, TKey = any>(
     metadataKey: TKey,
     targets: (Type<any> | Function)[],
+  ): TResult;
+  /**
+   * Retrieve metadata for a specified key or decorator for a specified set of targets and return a first not undefined value.
+   *
+   * @param metadataKeyOrDecorator lookup key or metadata for metadata to retrieve
+   * @param targets context (decorated objects) to retrieve metadata from
+   *
+   */
+  public getAllAndOverride<TResult = any, TKey = any>(
+    metadataKeyOrDecorator: TKey,
+    targets: (Type<any> | Function)[],
   ): TResult {
     for (const target of targets) {
-      const result = this.get(metadataKey, target);
+      const result = this.get(metadataKeyOrDecorator, target);
       if (result !== undefined) {
         return result;
       }

packages/core/test/services/reflector.service.spec.ts

@@ -8,12 +8,35 @@ describe('Reflector', () => {
     reflector = new Reflector();
   });
   describe('get', () => {
-    it('should reflect metadata', () => {
+    it('should reflect metadata by key', () => {
       const key = 'key';
       const value = 'value';
       Reflect.defineMetadata(key, value, Test);
       expect(reflector.get(key, Test)).to.eql(value);
     });
+    it('should reflect metadata by decorator', () => {
+      const decorator = Reflector.createDecorator<string>();
+      const value = 'value';
+      Reflect.defineMetadata(decorator.KEY, value, Test);
+
+      let reflectedValue = reflector.get(decorator, Test);
+      expect(reflectedValue).to.eql(value);
+
+      // @ts-expect-error 'value' is not assignable to parameter of type 'string'
+      reflectedValue = true;
+    });
+
+    it('should reflect metadata by decorator (custom key)', () => {
+      const decorator = Reflector.createDecorator<string[]>({ key: 'custom' });
+      const value = ['value'];
+      Reflect.defineMetadata('custom', value, Test);
+
+      let reflectedValue = reflector.get(decorator, Test);
+      expect(reflectedValue).to.eql(value);
+
+      // @ts-expect-error 'value' is not assignable to parameter of type 'string[]'
+      reflectedValue = true;
+    });
   });
 
   describe('getAll', () => {

sample/01-cats-app/src/cats/cats.controller.ts

@@ -12,7 +12,7 @@ export class CatsController {
   constructor(private readonly catsService: CatsService) {}
 
   @Post()
-  @Roles('admin')
+  @Roles(['admin'])
   async create(@Body() createCatDto: CreateCatDto) {
     this.catsService.create(createCatDto);
   }

sample/01-cats-app/src/common/decorators/roles.decorator.ts

@@ -1,3 +1,3 @@
-import { SetMetadata } from '@nestjs/common';
+import { Reflector } from '@nestjs/core';
 
-export const Roles = (...roles: string[]) => SetMetadata('roles', roles);
+export const Roles = Reflector.createDecorator<string[]>();

sample/01-cats-app/src/common/guards/roles.guard.ts

@@ -1,12 +1,13 @@
 import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
 import { Reflector } from '@nestjs/core';
+import { Roles } from '../decorators/roles.decorator';
 
 @Injectable()
 export class RolesGuard implements CanActivate {
   constructor(private readonly reflector: Reflector) {}
 
   canActivate(context: ExecutionContext): boolean {
-    const roles = this.reflector.get<string[]>('roles', context.getHandler());
+    const roles = this.reflector.get(Roles, context.getHandler());
     if (!roles) {
       return true;
     }