Support returning promises from serverless.js

lib/classes/Service.js

@@ -69,8 +69,10 @@ class Service {
       return BbPromise.try(() => {
         // use require to load serverless.js file
         // eslint-disable-next-line global-require
-        const config = require(serviceFilePath);
-
+        const configExport = require(serviceFilePath);
+        // In case of a promise result, first resolve it.
+        return configExport;
+      }).then(config => {
         if (!_.isPlainObject(config)) {
           throw new Error('serverless.js must export plain object');
         }

lib/classes/Service.test.js

@@ -342,6 +342,61 @@ describe('Service', () => {
       });
     });
 
+    it('should load serverless.js from filesystem', () => {
+      const SUtils = new Utils();
+      const serverlessJSON = {
+        service: 'new-service',
+        provider: {
+          name: 'aws',
+          stage: 'dev',
+          region: 'us-east-1',
+          variableSyntax: '\\${{([ ~:a-zA-Z0-9._\'",\\-\\/\\(\\)]+?)}}',
+        },
+        plugins: ['testPlugin'],
+        functions: {
+          functionA: {},
+        },
+        resources: {
+          aws: {
+            resourcesProp: 'value',
+          },
+          azure: {},
+          google: {},
+        },
+        package: {
+          exclude: ['exclude-me'],
+          include: ['include-me'],
+          artifact: 'some/path/foo.zip',
+        },
+      };
+
+      SUtils.writeFileSync(path.join(tmpDirPath, 'serverless.js'),
+        `module.exports = new Promise(resolve => { resolve(${JSON.stringify(serverlessJSON)}) });`);
+
+      const serverless = new Serverless();
+      serverless.config.update({ servicePath: tmpDirPath });
+      serviceInstance = new Service(serverless);
+
+      return expect(serviceInstance.load()).to.eventually.be.fulfilled
+      .then(() => {
+        expect(serviceInstance.service).to.be.equal('new-service');
+        expect(serviceInstance.provider.name).to.deep.equal('aws');
+        expect(serviceInstance.provider.variableSyntax).to.equal(
+          '\\${{([ ~:a-zA-Z0-9._\'",\\-\\/\\(\\)]+?)}}'
+        );
+        expect(serviceInstance.plugins).to.deep.equal(['testPlugin']);
+        expect(serviceInstance.resources.aws).to.deep.equal({ resourcesProp: 'value' });
+        expect(serviceInstance.resources.azure).to.deep.equal({});
+        expect(serviceInstance.resources.google).to.deep.equal({});
+        expect(serviceInstance.package.exclude.length).to.equal(1);
+        expect(serviceInstance.package.exclude[0]).to.equal('exclude-me');
+        expect(serviceInstance.package.include.length).to.equal(1);
+        expect(serviceInstance.package.include[0]).to.equal('include-me');
+        expect(serviceInstance.package.artifact).to.equal('some/path/foo.zip');
+        expect(serviceInstance.package.excludeDevDependencies).to.equal(undefined);
+      });
+    });
+
     it('should throw error if serverless.js exports invalid config', () => {
       const SUtils = new Utils();
 

lib/utils/getServerlessConfigFile.js

@@ -28,8 +28,10 @@ const getServerlessConfigFile = _.memoize((servicePath) => {
       return BbPromise.try(() => {
         // use require to load serverless.js
         // eslint-disable-next-line global-require
-        const config = require(jsPath);
-
+        const configExport = require(jsPath);
+        // In case of a promise result, first resolve it.
+        return configExport;
+      }).then(config => {
         if (_.isPlainObject(config)) {
           return config;
         }

lib/utils/getServerlessConfigFile.test.js

@@ -63,6 +63,20 @@ describe('#getServerlessConfigFile()', () => {
     );
   });
 
+  it('should return the resolved value if a promise-using serverless.js file found', () => {
+    const serverlessFilePath = path.join(tmpDirPath, 'serverless.js');
+    writeFileSync(
+      serverlessFilePath,
+      'module.exports = new Promise(resolve => { resolve({"service": "my-json-service"}); });'
+    );
+
+    return expect(getServerlessConfigFile(tmpDirPath)).to.be.fulfilled.then(
+      (result) => {
+        expect(result).to.deep.equal({ service: 'my-json-service' });
+      }
+    );
+  });
+
   it('should throw an error, if serverless.js export not a plain object', () => {
     const serverlessFilePath = path.join(tmpDirPath, 'serverless.js');
     writeFileSync(