feat(expand): add dotenv-expand options support

lib/config.module.ts

@@ -2,7 +2,7 @@ import { DynamicModule, Module } from '@nestjs/common';
 import { FactoryProvider } from '@nestjs/common/interfaces';
 import { isObject } from '@nestjs/common/utils/shared.utils';
 import * as dotenv from 'dotenv';
-import { expand } from 'dotenv-expand';
+import { DotenvExpandOptions, expand } from 'dotenv-expand';
 import * as fs from 'fs';
 import { resolve } from 'path';
 import { ConfigHostModule } from './config-host.module';
@@ -184,7 +184,8 @@ export class ConfigModule {
           config,
         );
         if (options.expandVariables) {
-          config = expand({ parsed: config }).parsed || config;
+          const expandOptions: DotenvExpandOptions = typeof options.expandVariables === 'object' ? options.expandVariables : {};
+          config = expand({ ...expandOptions, parsed: config }).parsed || config;
         }
       }
     }

lib/interfaces/config-module-options.interface.ts

@@ -1,4 +1,5 @@
 import { ConfigFactory } from './config-factory.interface';
+import { DotenvExpandOptions } from 'dotenv-expand'
 
 export interface ConfigModuleOptions {
   /**
@@ -61,9 +62,10 @@ export interface ConfigModuleOptions {
   load?: Array<ConfigFactory>;
 
   /**
-   * A boolean value indicating the use of expanded variables.
+   * A boolean value indicating the use of expanded variables, or object
+   * containing options to pass to dotenv-expand.
    * If .env contains expanded variables, they'll only be parsed if
    * this property is set to true.
    */
-  expandVariables?: boolean;
+  expandVariables?: boolean | DotenvExpandOptions;
 }

tests/e2e/load-env-expanded-ignore-process-env.spec.ts

@@ -0,0 +1,28 @@
+import { INestApplication } from '@nestjs/common';
+import { Test } from '@nestjs/testing';
+import { AppModule } from '../src/app.module';
+
+describe('Environment variables', () => {
+  let app: INestApplication;
+
+  beforeEach(async () => {
+    process.env.URL = 'process-app.test';
+
+    const module = await Test.createTestingModule({
+      imports: [AppModule.withExpandedEnvVarsIgnoreProcessEnv()],
+    }).compile();
+
+    app = module.createNestApplication();
+    await app.init();
+  });
+
+  it(`should ignore process environment variable`, () => {
+    const envVars = app.get(AppModule).getEnvVariables();
+    expect(envVars.EMAIL).toEqual('support@myapp.test');
+  });
+
+  afterEach(async () => {
+    process.env.URL = undefined
+    await app.close();
+  });
+});

tests/src/app.module.ts

@@ -92,6 +92,18 @@ export class AppModule {
     };
   }
 
+  static withExpandedEnvVarsIgnoreProcessEnv(): DynamicModule {
+    return {
+      module: AppModule,
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(__dirname, '.env.expanded'),
+          expandVariables: { ignoreProcessEnv: true }
+        }),
+      ],
+    };
+  }
+
   static withMultipleEnvFiles(): DynamicModule {
     return {
       module: AppModule,