fix(core/common): allow to use symbol token in the module exports

Symbol token can be used in the exports section as well as the string token.

Closes nestjs#1246

packages/common/utils/shared.utils.ts

@@ -8,4 +8,4 @@ export const validatePath = (path): string =>
   path.charAt(0) !== '/' ? '/' + path : path;
 export const isNil = (obj): boolean => isUndefined(obj) || obj === null;
 export const isEmpty = (array): boolean => !(array && array.length > 0);
-export const isSymbol = (fn): boolean => typeof fn === 'symbol';
+export const isSymbol = (fn): fn is symbol => typeof fn === 'symbol';

packages/core/injector/module.ts

@@ -47,7 +47,7 @@ export class Module {
   private readonly _components = new Map<any, InstanceWrapper<Injectable>>();
   private readonly _injectables = new Map<any, InstanceWrapper<Injectable>>();
   private readonly _routes = new Map<string, InstanceWrapper<Controller>>();
-  private readonly _exports = new Set<string>();
+  private readonly _exports = new Set<string | symbol>();
 
   constructor(
     private readonly _metatype: Type<any>,
@@ -82,7 +82,7 @@ export class Module {
     return this._routes;
   }
 
-  get exports(): Set<string> {
+  get exports(): Set<string | symbol> {
     return this._exports;
   }
 
@@ -279,14 +279,14 @@ export class Module {
   }
 
   public addExportedComponent(
-    exportedComponent: ComponentMetatype | string | DynamicModule,
+    exportedComponent: ComponentMetatype | string | symbol | DynamicModule,
   ) {
-    const addExportedUnit = (token: string) =>
+    const addExportedUnit = (token: string | symbol) =>
       this._exports.add(this.validateExportedProvider(token));
 
     if (this.isCustomProvider(exportedComponent as any)) {
       return this.addCustomExportedComponent(exportedComponent as any);
-    } else if (isString(exportedComponent)) {
+    } else if (isString(exportedComponent) || isSymbol(exportedComponent)) {
       return addExportedUnit(exportedComponent);
     } else if (this.isDynamicModule(exportedComponent)) {
       const { module } = exportedComponent;
@@ -305,7 +305,7 @@ export class Module {
     this._exports.add(this.validateExportedProvider(provide.name));
   }
 
-  public validateExportedProvider(token: string) {
+  public validateExportedProvider(token: string | symbol) {
     if (this._components.has(token)) {
       return token;
     }
@@ -316,7 +316,7 @@ export class Module {
       .filter(metatype => metatype)
       .map(({ name }) => name);
 
-    if (!importedRefNames.includes(token)) {
+    if (!importedRefNames.includes(token as any)) {
       const { name } = this.metatype;
       throw new UnknownExportException(name);
     }