Fix custom webpack config warnings

lib/core/src/server/config/interpret-files.js

@@ -19,3 +19,12 @@ export function getInterpretedFile(pathToFile) {
     .map(ext => `${pathToFile}${ext}`)
     .find(candidate => fs.existsSync(candidate));
 }
+
+export function getInterpretedFileWithExt(pathToFile) {
+  return possibleExtensions
+    .map(ext => ({
+      path: `${pathToFile}${ext}`,
+      ext,
+    }))
+    .find(candidate => fs.existsSync(candidate.path));
+}

lib/core/src/server/loadCustomWebpackConfig.js

@@ -1,87 +1,7 @@
-/* eslint-disable global-require, import/no-dynamic-require */
-import fs from 'fs';
 import path from 'path';
-import interpret from 'interpret';
-import { logger } from '@storybook/node-logger';
+import serverRequire from './serverRequire';
 
-// Copied and modified from
-// https://github.com/webpack/webpack-cli/blob/ca504de8c7c0ea66278021b72fa6a953e3ffa43c/bin/convert-argv.js#L102-L119
-function registerCompiler(moduleDescriptor) {
-  if (!moduleDescriptor) {
-    return 0;
-  }
+const webpackConfigs = ['webpack.config', 'webpackfile'];
 
-  if (typeof moduleDescriptor === 'string') {
-    require(moduleDescriptor);
-    return 1;
-  }
-
-  if (!Array.isArray(moduleDescriptor)) {
-    moduleDescriptor.register(require(moduleDescriptor.module));
-    return 1;
-  }
-
-  let registered = 0;
-
-  for (let i = 0; i < moduleDescriptor.length; i += 1) {
-    try {
-      registered += registerCompiler(moduleDescriptor[i]);
-      break;
-    } catch (e) {
-      // do nothing
-    }
-  }
-
-  return registered;
-}
-
-// Copied and modified from
-// https://github.com/webpack/webpack-cli/blob/ca504de8c7c0ea66278021b72fa6a953e3ffa43c/bin/convert-argv.js#L121-L137
-function requireConfig(configPath) {
-  const config = require(configPath);
-
-  const isES6DefaultExported =
-    typeof config === 'object' && config !== null && typeof config.default !== 'undefined';
-
-  return isES6DefaultExported ? config.default : config;
-}
-
-// Copied and modified from
-// https://github.com/webpack/webpack-cli/blob/ca504de8c7c0ea66278021b72fa6a953e3ffa43c/bin/convert-argv.js#L45-L143
-export default configDir => {
-  const extensions = Object.keys(interpret.extensions).sort((a, b) => {
-    if (a === '.js') {
-      return -1;
-    }
-    if (b === '.js') {
-      return 1;
-    }
-    return a.length - b.length;
-  });
-
-  const customConfigCandidates = ['webpack.config', 'webpackfile']
-    .map(filename =>
-      extensions.map(ext => ({
-        path: path.resolve(configDir, filename + ext),
-        ext,
-      }))
-    )
-    .reduce((a, i) => a.concat(i), []);
-
-  for (let i = 0; i < customConfigCandidates.length; i += 1) {
-    const customConfigPath = customConfigCandidates[i].path;
-    if (fs.existsSync(customConfigPath)) {
-      if (registerCompiler(interpret.extensions[customConfigCandidates[i].ext]) === 0) {
-        logger.warn(`=> Custom configuration file ${customConfigPath} is detected`);
-        logger.warn(`   but impossible to import loader for ${customConfigCandidates[i].ext}`);
-      }
-      try {
-        return requireConfig(customConfigPath);
-      } catch (e) {
-        // do nothing
-      }
-    }
-  }
-
-  return null;
-};
+export default configDir =>
+  serverRequire(webpackConfigs.map(configName => path.resolve(configDir, configName)));

lib/core/src/server/serverRequire.js

@@ -0,0 +1,95 @@
+import interpret from 'interpret';
+import { logger } from '@storybook/node-logger';
+import { getInterpretedFileWithExt } from './config/interpret-files';
+
+// The code based on https://github.com/webpack/webpack-cli/blob/ca504de8c7c0ea66278021b72fa6a953e3ffa43c/bin/convert-argv
+
+const compilersState = new Map();
+
+function registerCompiler(moduleDescriptor) {
+  if (!moduleDescriptor) {
+    return 0;
+  }
+
+  const state = compilersState.get(moduleDescriptor);
+
+  if (state !== undefined) {
+    return state;
+  }
+
+  if (typeof moduleDescriptor === 'string') {
+    // eslint-disable-next-line import/no-dynamic-require,global-require
+    require(moduleDescriptor);
+    compilersState.set(moduleDescriptor, 1);
+    return 1;
+  }
+
+  if (!Array.isArray(moduleDescriptor)) {
+    // eslint-disable-next-line import/no-dynamic-require,global-require
+    moduleDescriptor.register(require(moduleDescriptor.module));
+    compilersState.set(moduleDescriptor, 1);
+    return 1;
+  }
+
+  let registered = 0;
+
+  for (let i = 0; i < moduleDescriptor.length; i += 1) {
+    try {
+      registered += registerCompiler(moduleDescriptor[i]);
+      break;
+    } catch (e) {
+      // do nothing
+    }
+  }
+
+  compilersState.set(moduleDescriptor, registered);
+  return registered;
+}
+
+function interopRequireDefault(filePath) {
+  // eslint-disable-next-line import/no-dynamic-require,global-require
+  const result = require(filePath);
+
+  const isES6DefaultExported =
+    typeof result === 'object' && result !== null && typeof result.default !== 'undefined';
+
+  return isES6DefaultExported ? result.default : result;
+}
+
+function getCandidate(paths) {
+  for (let i = 0; i < paths.length - 1; i += 1) {
+    const candidate = getInterpretedFileWithExt(paths[i]);
+
+    if (candidate) {
+      return candidate;
+    }
+  }
+
+  return undefined;
+}
+
+export default function serverRequire(filePath) {
+  const paths = Array.isArray(filePath) ? filePath : [filePath];
+  const existingCandidate = getCandidate(paths);
+
+  if (!existingCandidate) {
+    return null;
+  }
+
+  const { path: candidatePath, ext: candidateExt } = existingCandidate;
+
+  if (candidateExt === '.js') {
+    return interopRequireDefault(candidatePath);
+  }
+
+  const moduleDescriptor = interpret.extensions[candidateExt];
+
+  if (registerCompiler(moduleDescriptor) === 0) {
+    logger.warn(`=> File ${candidatePath} is detected`);
+    logger.warn(`   but impossible to import loader for ${candidateExt}`);
+
+    return null;
+  }
+
+  return interopRequireDefault(candidatePath);
+}