feat: support {env}.js when load extend

it's useful when want to export some unittest api
that can't be used in production

lib/loader/mixin/extend.js

@@ -73,6 +73,12 @@ module.exports = {
   loadExtend(name, proto) {
     // 获取需要加载的文件
     const filepaths = this.getLoadUnits().map(unit => path.join(unit.path, 'app/extend', name));
+    for (let i = 0, l = filepaths.length; i < l; i++) {
+      const filepath = filepaths[i];
+      filepaths.push(filepath + `.${this.serverEnv}`);
+    }
+
+
     const mergeRecord = new Map();
     for (const filepath of filepaths) {
       if (!utils.existsModule(filepath)) {

test/fixtures/extend-env/app/extend/application.custom.js

@@ -0,0 +1,5 @@
+'use strict';
+
+exports.a = 'a1';
+
+exports.custom = true;

test/fixtures/extend-env/app/extend/application.js

@@ -0,0 +1,4 @@
+'use strict';
+
+exports.a = 'a';
+exports.b = 'b';

test/fixtures/extend-env/config/plugin.js

@@ -0,0 +1,8 @@
+'use strict';
+
+const path = require('path');
+
+exports.a = {
+  enable: true,
+  path: path.join(__dirname, '../plugins/a'),
+};

test/fixtures/extend-env/package.json

@@ -0,0 +1,3 @@
+{
+  "name": "extend-env"
+}

test/fixtures/extend-env/plugins/a/app/extend/application.custom.js

@@ -0,0 +1,3 @@
+'use strict';
+
+exports.b = 'b1';

test/fixtures/extend-env/plugins/a/package.json

@@ -0,0 +1,5 @@
+{
+  "eggPlugin": {
+    "name": "a"
+  }
+}

test/loader/mixin/load_extend.test.js

@@ -2,6 +2,7 @@
 
 require('should');
 const request = require('supertest');
+const mm = require('mm');
 const utils = require('../../utils');
 
 describe('test/loader/mixin/load_extend.test.js', function() {
@@ -95,4 +96,17 @@ describe('test/loader/mixin/load_extend.test.js', function() {
     app.loader.loadApplicationExtend();
     app[utils.symbol.view].should.equal('view');
   });
+
+  it('should load application by custom env', function() {
+    mm(process.env, 'EGG_SERVER_ENV', 'custom');
+    const app = utils.createApp('extend-env');
+    app.loader.loadPlugin();
+    app.loader.loadApplicationExtend();
+    app.custom.should.be.true();
+    // application.custom.js override application.js
+    app.a.should.eql('a1');
+    // application.custom.js in plugin also can override application.js in app
+    app.b.should.eql('b1');
+  });
+
 });