feature(core): Add multi option for custom useValue-providers

packages/common/interfaces/modules/provider.interface.ts

@@ -16,6 +16,11 @@ export interface ClassProvider {
 export interface ValueProvider {
   provide: any;
   useValue: any;
+  /**
+   * If true, then injector returns an array of instances. This is useful to allow multiple
+   * providers spread across many files to provide configuration information to a common token.
+   */
+  multi?: boolean | undefined;
 }
 
 export interface FactoryProvider {

packages/core/injector/instance-wrapper.ts

@@ -34,6 +34,7 @@ export class InstanceWrapper<T = any> {
   public readonly inject?: (string | symbol | Function | Type<any>)[];
   public readonly async?: boolean;
   public readonly host?: Module;
+  public readonly multi?: boolean | undefined;
   public readonly scope?: Scope = Scope.DEFAULT;
   public forwardRef?: boolean;
 

packages/core/injector/module.ts

@@ -25,6 +25,11 @@ import { ModuleRef } from './module-ref';
 export interface CustomProvider {
   provide: any;
   name: string;
+  /**
+   * If true, then injector returns an array of instances. This is useful to allow multiple
+   * providers spread across many files to provide configuration information to a common token.
+   */
+  multi?: boolean;
 }
 export type OpaqueToken = string | symbol | Type<any>;
 export type CustomClass = CustomProvider & {
@@ -262,7 +267,28 @@ export class Module {
     provider: CustomValue,
     collection: Map<string, InstanceWrapper>,
   ) {
-    const { name, useValue: value } = provider;
+    const { name, multi } = provider;
+    let value = provider.useValue;
+
+    if (multi === true) {
+      // If the provider indicates that it's a multi-provider, process it specially.
+      // First check whether it's been defined already.
+      const multiItem = collection.get(name);
+      if (multiItem) {
+        // It has. Throw a nice error if
+        if (multiItem.multi === undefined) {
+          throw new Error(`Mixed multi-provider for ${name}.`);
+        } else {
+          // A provider already exists. Append new value
+          value = [...multiItem.instance, value];
+        }
+      } else {
+        // First multi provider
+        value = [value];
+      }
+
+    }
+
     collection.set(
       name,
       new InstanceWrapper({
@@ -272,6 +298,7 @@ export class Module {
         isResolved: true,
         async: value instanceof Promise,
         host: this,
+        multi,
       }),
     );
   }