put in fork using

src/register.ts

@@ -92,7 +92,11 @@ export function DefinePlugin<T>(
       }
 
       static get using() {
-        const list = reflector.getArray(KoishiAddUsingList, newClass);
+        let list = reflector.getArray(KoishiAddUsingList, newClass);
+        const fork = reflector.get('KoishiFork', newClass);
+        if (fork) {
+          list = [...list, ...reflector.getArray(KoishiAddUsingList, fork)];
+        }
         return _.uniq(list);
       }
 

tests/inject-using.spec.ts

-import { RegisterSchema, SchemaProperty, StarterPlugin } from '..';
+import { Fork, RegisterSchema, SchemaProperty, StarterPlugin } from '..';
 import { Assets, Bot, Cache } from 'koishi';
 import { Inject, PluginName, UsingService } from '../src/decorators';
 import { DefinePlugin } from '../src/register';
@@ -11,10 +11,15 @@ class Config {
 }
 
 describe('InjectUsing', () => {
+  @DefinePlugin()
+  @UsingService('foo')
+  class MyFork extends StarterPlugin(Config) {}
+
   @PluginName('foo-plugin')
   @UsingService('router')
   @DefinePlugin({ using: ['database'], schema: Config })
   @UsingService('http')
+  @Fork(MyFork)
   class MyPlugin extends StarterPlugin(Config) {
     @Inject(true)
     cache: Cache;
@@ -31,12 +36,13 @@ describe('InjectUsing', () => {
     expect(MyPlugin['Config']).toEqual(Config);
     const usingList = (MyPlugin as any).using as ServiceName[];
     expect(usingList).toBeInstanceOf(Array);
-    expect(usingList.length).toEqual(5);
+    expect(usingList.length).toEqual(6);
     expect(usingList.includes('database')).toEqual(true);
     expect(usingList.includes('assets')).toEqual(true);
     expect(usingList.includes('cache')).toEqual(true);
     expect(usingList.includes('router')).toEqual(true);
     expect(usingList.includes('bots')).toEqual(false);
     expect(usingList.includes('http')).toEqual(true);
+    expect(usingList.includes('foo')).toEqual(true);
   });
 });