feat(babel-transpiler): support object-style babel.config.js (#1762)

The babel transpiler will now also work with babel.config.js files that export object instead of function.

packages/babel-transpiler/src/BabelConfigReader.ts

@@ -50,8 +50,13 @@ export class BabelConfigReader {
             return require(babelrcPath) as babel.TransformOptions;
           }
           if (path.basename(babelrcPath) === 'babel.config.js') {
-            const config: babel.ConfigFunction = require(babelrcPath);
-            return config(optionsApi as babel.ConfigAPI);
+            const config = require(babelrcPath);
+            if (typeof config === 'function') {
+              const configFunction = config as babel.ConfigFunction;
+              return configFunction(optionsApi as babel.ConfigAPI);
+            } else {
+              return config as babel.TransformOptions;
+            }
           }
           return JSON.parse(fs.readFileSync(babelrcPath, 'utf8')) as babel.TransformOptions;
         } catch (error) {

packages/babel-transpiler/test/integration/BabelProjects.it.spec.ts

@@ -63,14 +63,20 @@ describe('Project with binary files', () => {
 describe('Different extensions', () => {
   describeIntegrationTest('differentExtensions');
 });
-describe('A Babel project with babel.config.js config file', () => {
+describe('A Babel project with babel.config.js config file that exports function', () => {
   const noop = () => {};
   describeIntegrationTest('babelProjectWithBabelConfigJs', {
     extensions: ['.ts'],
     optionsApi: { cache: { forever: noop } } as ConfigAPI,
     optionsFile: 'babel.config.js'
   });
 });
+describe('A Babel project with babel.config.js config file that exports object', () => {
+  describeIntegrationTest('babelProjectWithBabelConfigJsObject', {
+    extensions: ['.ts'],
+    optionsFile: 'babel.config.js'
+  });
+});
 describe('A Babel project with .babelrc.js config file', () => {
   describeIntegrationTest('babelProjectWithBabelRcJs', {
     extensions: ['.ts'],

packages/babel-transpiler/testResources/babelProjectWithBabelConfigJsObject/babel.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  presets: ["@babel/preset-typescript"]
+}

packages/babel-transpiler/testResources/babelProjectWithBabelConfigJsObject/expectedResult/foo.js

@@ -0,0 +1 @@
+export const foo = 4;

packages/babel-transpiler/testResources/babelProjectWithBabelConfigJsObject/expectedResult/main.js

@@ -0,0 +1 @@
+const x = 0;

packages/babel-transpiler/testResources/babelProjectWithBabelConfigJsObject/source/foo.ts

@@ -0,0 +1 @@
+export const foo: number = 4;

packages/babel-transpiler/testResources/babelProjectWithBabelConfigJsObject/source/main.ts

@@ -0,0 +1 @@
+const x: number = 0;