feat: create a conditional module

With the new `ConditionalModule` devs can now register
modules based on keys in the `process.env` or have them
registered as blanks modules under the guise of a dyanmic module.
This works for nested modules, multiple imports, and dynamic modules.

Signed-off-by: Jay McDoniel <jmcdo29@gmail.com>

lib/conditional.module.ts

@@ -0,0 +1,24 @@
+import { ModuleMetadata } from '@nestjs/common';
+import { ConfigModule } from './config.module';
+
+export class ConditionalModule {
+  static async registerWhen(
+    module: Required<ModuleMetadata>['imports'][number],
+    condition: string | ((env: NodeJS.ProcessEnv) => boolean),
+  ) {
+    if (typeof condition === 'string') {
+      const key = condition;
+      condition = env => {
+        return env[key]?.toLowerCase() !== 'false';
+      };
+    }
+    await ConfigModule.envVariablesLoaded;
+    return condition(process.env)
+      ? {
+          module: ConditionalModule,
+          imports: [module],
+          exports: [module],
+        }
+      : { module: ConditionalModule, imports: [] };
+  }
+}

lib/index.ts

@@ -1,3 +1,4 @@
+export * from './conditional.module';
 export * from './config.module';
 export * from './config.service';
 export * from './types';

tests/e2e/.env.conditional

@@ -0,0 +1,7 @@
+FOO="use it"
+FOO_FALSE="false"
+FOO_DYNAMIC="yes"
+FOO_CUSTOM="yeah!"
+BAR="yay"
+FOOBAR="do it"
+QUU="nested!"

tests/e2e/conditional.module.spec.ts

@@ -0,0 +1,128 @@
+import { Injectable, Module } from '@nestjs/common';
+import { Test } from '@nestjs/testing';
+import { ConfigModule, ConditionalModule } from '../../lib';
+import { join } from 'path';
+
+@Injectable()
+class FooService {}
+
+@Injectable()
+class FooDynamicService {}
+
+@Module({
+  providers: [FooService],
+  exports: [FooService],
+})
+class FooModule {
+  static forRoot() {
+    return {
+      module: FooModule,
+      providers: [FooDynamicService],
+      exports: [FooDynamicService],
+    };
+  }
+}
+
+@Injectable()
+class BarService {}
+
+@Module({
+  providers: [BarService],
+  exports: [BarService],
+})
+class BarModule {}
+
+@Module({
+  providers: [
+    {
+      provide: 'quu',
+      useValue: 42,
+    },
+  ],
+  exports: ['quu'],
+})
+class QuuModule {}
+
+@Module({
+  imports: [ConditionalModule.registerWhen(QuuModule, 'QUU')],
+  exports: [ConditionalModule],
+})
+class FooBarModule {}
+
+describe('ConditionalModule', () => {
+  it('it should work for a regular module', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooModule, 'FOO'),
+      ],
+    }).compile();
+    expect(modRef.get(FooService, { strict: false })).toBeDefined();
+    await modRef.close();
+  });
+  it('should work for a dynamic module', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooModule.forRoot(), 'FOO_DYNAMIC'),
+      ],
+    }).compile();
+    expect(modRef.get(FooDynamicService, { strict: false })).toBeDefined();
+    await modRef.close();
+  });
+  it('should not register when the value is false', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooModule, 'FOO_FALSE'),
+      ],
+    }).compile();
+    expect(() => modRef.get(FooService, { strict: false })).toThrow();
+    await modRef.close();
+  });
+  it('should work for a custom condition', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooModule, env => {
+          return env.FOO_CUSTOM === 'yeah!';
+        }),
+      ],
+    }).compile();
+    expect(modRef.get(FooService, { strict: false })).toBeDefined();
+    await modRef.close();
+  });
+  it('should handle two conditional modules', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooModule, 'FOO'),
+        ConditionalModule.registerWhen(BarModule, 'BAR'),
+      ],
+    }).compile();
+    expect(modRef.get(FooService, { strict: false })).toBeDefined();
+    expect(modRef.get(BarService, { strict: false })).toBeDefined();
+    await modRef.close();
+  });
+  it('should handle nested conditional module', async () => {
+    const modRef = await Test.createTestingModule({
+      imports: [
+        ConfigModule.forRoot({
+          envFilePath: join(process.cwd(), 'tests', 'e2e', '.env.conditional'),
+        }),
+        ConditionalModule.registerWhen(FooBarModule, 'FOOBAR'),
+      ],
+    }).compile();
+    expect(modRef.get('quu', { strict: false })).toBeDefined();
+  });
+});