Fix commonjs handling.

lib/node-loader-babel.js

@@ -1,57 +1,102 @@
-import babel from "@babel/core";
-import path from "path";
-import urlModule from "url";
-
-const { loadOptionsAsync, transformAsync } = babel;
-
-function isBabelConfigFile(filename) {
-  const basename = path.basename(filename);
-  return (
-    basename === ".babelrc.js" ||
-    basename === ".babelrc.mjs" ||
-    basename === "babel.config.js" ||
-    basename === "babel.config.mjs" ||
-    basename === ".babelrc" ||
-    basename === ".babelrc.cjs" ||
-    basename === "babel.config.cjs"
-  );
-}
-
-export async function load(url, context, defaultLoad) {
-  if (useLoader(url)) {
-    const { source } = await defaultLoad(url, context, defaultLoad);
-
-    const filename = urlModule.fileURLToPath(url);
-    // Babel config files can themselves be ES modules,
-    // but we cannot transform those since doing so would cause an infinite loop.
-    if (isBabelConfigFile(filename)) {
-      return {
-        source,
-        format: /\.(c|m)?js$/.test(filename) ? "module" : "json",
-      };
-    }
-
-    const options = await loadOptionsAsync({
-      sourceType: "module",
-      root: process.cwd(),
-      rootMode: "root",
-      filename: filename,
-      configFile: true,
-    });
-
-    const transformed = await transformAsync(source, options);
-
-    return {
-      source: transformed.code,
-      // Maybe a shaky assumption
-      // TODO: look at babel config to see whether it will output ESM/CJS or other formats
-      format: "module",
-    };
-  } else {
-    return defaultLoad(url, context, defaultLoad);
-  }
-}
-
-function useLoader(url) {
-  return !/node_modules/.test(url) && !/node:/.test(url);
-}
+import process from 'process';
+import path from 'path';
+import {fileURLToPath} from 'url';
+import {loadOptionsAsync, transformAsync} from '@babel/core';
+
+const BABEL_FORMATS_TRANSFORMED = new Set(['module']);
+
+const BABEL_CONFIG_FILES = new Set([
+	'.babelrc.js',
+	'.babelrc.mjs',
+	'babel.config.js',
+	'babel.config.mjs',
+	'.babelrc',
+	'.babelrc.cjs',
+	'babel.config.cjs',
+]);
+
+const anyURLToPathOrUndefined = (url) => {
+	try {
+		return fileURLToPath(url);
+	} catch (error) {
+		if (error instanceof TypeError && error.code === 'ERR_INVALID_URL_SCHEME') {
+			return undefined;
+		}
+
+		throw error;
+	}
+};
+
+const isBabelConfigFile = (filename) => {
+	const basename = path.basename(filename);
+	return BABEL_CONFIG_FILES.has(basename);
+};
+
+const getSourceType = (format) => {
+	switch (format) {
+		case 'module':
+			return 'module';
+		case 'commonjs':
+			return 'script';
+		default:
+			return 'unambiguous';
+	}
+};
+
+const prepare = async (url, context, defaultLoad) => {
+	const original = await defaultLoad(url, context, defaultLoad);
+
+	const noop = () => ({
+		transform: false,
+		original,
+	});
+
+	if (
+		/node_modules/.test(url) ||
+		/node:/.test(url) ||
+		!BABEL_FORMATS_TRANSFORMED.has(original.format)
+	) {
+		return noop();
+	}
+
+	const filename = anyURLToPathOrUndefined(url);
+
+	// Babel config files can themselves be ES modules,
+	// but transforming those could require more than one pass.
+	if (isBabelConfigFile(filename)) return noop();
+
+	return {
+		transform: true,
+		original,
+		options: {
+			filename,
+		},
+	};
+};
+
+const transformed = async ({format, source}, {filename}) => {
+	const options = await loadOptionsAsync({
+		sourceType: getSourceType(format),
+		root: process.cwd(),
+		rootMode: 'root',
+		filename,
+		configFile: true,
+	});
+
+	const result = await transformAsync(source, options);
+
+	return {
+		source: result.code,
+		// TODO: look at babel config to see whether it will output ESM/CJS or other formats
+		format,
+	};
+};
+
+export const load = async (url, context, defaultLoad) => {
+	const {transform, original, options} = await prepare(
+		url,
+		context,
+		defaultLoad,
+	);
+	return transform ? transformed(original, options) : original;
+};