refactor: logic to find babel config file

Use find-up matcher function to automatically stop looking for babel config file
once cwd is reached, thus increasing performance.

Author: Robin-Hoodie

lib/build.js

@@ -25,6 +25,11 @@ const BABEL_RELATIVE_CONFIG_FILENAMES = [
   '.babelrc.json',
 ];
 
+const BABEL_CONFIG_FILENAMES = [
+  ...BABEL_ROOT_CONFIG_FILENAMES,
+  ...BABEL_RELATIVE_CONFIG_FILENAMES,
+];
+
 const testFilePattern = '\\.(test|spec)\\.?';
 
 // custom babel target for each node version
@@ -38,9 +43,23 @@ function getBabelTarget(envConfig) {
 
 function existsBabelConfig(functionsDir) {
   const babelConfigFile = findUp.sync(
-    [...BABEL_ROOT_CONFIG_FILENAMES, ...BABEL_RELATIVE_CONFIG_FILENAMES],
+    (dir) => {
+      console.log('Dir ', dir);
+      const babelConfigFile = BABEL_CONFIG_FILENAMES.find(
+        (babelConfigFilename) =>
+          findUp.sync.exists(path.join(dir, babelConfigFilename)),
+      );
+      if (babelConfigFile) {
+        return path.join(dir, babelConfigFile);
+      }
+      // Don't search higher than wherever 'netlify-lambda build' was invoked from
+      if (dir === process.cwd()) {
+        return findUp.stop;
+      }
+      return undefined;
+    },
     {
-      cwd: path.join(process.cwd(), functionsDir),
+      cwd: functionsDir,
     },
   );
   if (babelConfigFile) {

lib/build.spec.js

@@ -90,43 +90,50 @@ describe('build', () => {
       ]);
     });
 
-    describe("babel config file resolution", () => {
-      const findBabelLoaderRule = rules => rules.find(rule => rule.use.loader.includes("babel-loader"));
+    describe('babel config file resolution', () => {
+      const findBabelLoaderRule = (rules) =>
+        rules.find((rule) => rule.use.loader.includes('babel-loader'));
 
-      it("should alter the default babelOpts when no valid babel config file is found", async () => {
-        setupFunction("", "not-babel.config.js");
+      it('should alter the default babelOpts when no valid babel config file is found', async () => {
+        setupFunction('', 'not-babel.config.js');
 
         const stats = await build.run(functions);
-        const babelLoaderRuleOptions = findBabelLoaderRule(stats.compilation.options.module.rules).use.options;
+        const babelLoaderRuleOptions = findBabelLoaderRule(
+          stats.compilation.options.module.rules,
+        ).use.options;
 
         expect(babelLoaderRuleOptions.presets).toBeDefined();
         expect(babelLoaderRuleOptions.plugins).toBeDefined();
       });
 
-      it("should not alter the default babelOpts when a valid babel config file is found in same directory as the functions directory", async () => {
-        setupFunction("", "babel.config.js");
+      it('should not alter the default babelOpts when a valid babel config file is found in same directory as the functions directory', async () => {
+        setupFunction('', 'babel.config.js');
 
         const stats = await build.run(functions);
-        const babelLoaderRuleOptions = findBabelLoaderRule(stats.compilation.options.module.rules).use.options;
+        const babelLoaderRuleOptions = findBabelLoaderRule(
+          stats.compilation.options.module.rules,
+        ).use.options;
 
         expect(babelLoaderRuleOptions.presets).toBeUndefined();
         expect(babelLoaderRuleOptions.plugins).toBeUndefined();
       });
 
-      it("should not alter the default babelOpts when a valid babel config is found in directory above the functions directory", async () => {
-        setupFunction("", "babel.config.js");
+      it('should not alter the default babelOpts when a valid babel config is found in directory above the functions directory', async () => {
+        setupFunction('', 'babel.config.js');
 
-        const functionsSubDir = path.join(functions, "subdir");
+        const functionsSubDir = path.join(functions, 'subdir');
 
         fs.mkdirSync(functionsSubDir);
-        fs.writeFileSync(path.join(functionsSubDir, "index.js"), "");
+        fs.writeFileSync(path.join(functionsSubDir, 'index.js'), '');
 
         const stats = await build.run(functionsSubDir);
-        const babelLoaderRuleOptions = findBabelLoaderRule(stats.compilation.options.module.rules).use.options;
+        const babelLoaderRuleOptions = findBabelLoaderRule(
+          stats.compilation.options.module.rules,
+        ).use.options;
 
         expect(babelLoaderRuleOptions.presets).toBeUndefined();
         expect(babelLoaderRuleOptions.plugins).toBeUndefined();
       });
-    })
+    });
   });
 });