When using the "clean" option, empty the dir, but don't remove it entirely

lib/config-generator.js

@@ -344,17 +344,9 @@ class ConfigGenerator {
 
         if (this.webpackConfig.cleanupOutput) {
             plugins.push(
-                new CleanWebpackPlugin([this.webpackConfig.outputPath], {
+                new CleanWebpackPlugin(['**/*'], {
+                    root: this.webpackConfig.outputPath,
                     verbose: false,
-                    /*
-                     * Instead of passing the "root" option and then making
-                     * the first argument (this.webpackConfig.outputPath) relative
-                     * to that (e.g. "builds"), we pass the absolute path as
-                     * the first argument. To the plugin, this looks like a
-                     * path that is "outside of the project root". This flag
-                     * says to ignore that.
-                     */
-                    allowExternal: true
                 })
             );
         }

lib/test/setup.js

@@ -94,6 +94,8 @@ function emptyTmpDir() {
 
 function touchFileInOutputDir(filename, webpackConfig) {
     const fullPath = path.join(webpackConfig.outputPath, filename);
+    fs.ensureDirSync(path.dirname(fullPath));
+
     fs.writeFileSync(
         fullPath,
         ''

test/functional.js

@@ -554,12 +554,16 @@ module.exports = {
             config.addEntry('main', './js/no_require');
             config.cleanupOutputBeforeBuild();
             testSetup.touchFileInOutputDir('file.txt', config);
+            testSetup.touchFileInOutputDir('deeper/other.txt', config);
 
             testSetup.runWebpack(config, (webpackAssert) => {
                 // make sure the file was cleaned up!
                 webpackAssert.assertOutputFileDoesNotExist(
                     'file.txt'
                 );
+                webpackAssert.assertOutputFileDoesNotExist(
+                    'deeper/other.txt'
+                );
 
                 done();
             });