refactor(cjs): implement custom resolver (#36)

src/cjs/api/module-extensions.ts

@@ -87,42 +87,38 @@ const transformer = (
 	module._compile(code, cleanFilePath);
 };
 
-[
-	/**
-	 * Handles .cjs, .cts, .mts & any explicitly specified extension that doesn't match any loaders
-	 *
-	 * Any file requested with an explicit extension will be loaded using the .js loader:
-	 * https://github.com/nodejs/node/blob/e339e9c5d71b72fd09e6abd38b10678e0c592ae7/lib/internal/modules/cjs/loader.js#L430
-	 */
-	'.js',
+/**
+ * Handles .cjs, .cts, .mts & any explicitly specified extension that doesn't match any loaders
+ *
+ * Any file requested with an explicit extension will be loaded using the .js loader:
+ * https://github.com/nodejs/node/blob/e339e9c5d71b72fd09e6abd38b10678e0c592ae7/lib/internal/modules/cjs/loader.js#L430
+ */
+extensions['.js'] = transformer;
 
-	/**
-	 * Loaders for implicitly resolvable extensions
-	 * https://github.com/nodejs/node/blob/v12.16.0/lib/internal/modules/cjs/loader.js#L1166
-	 */
+[
 	'.ts',
 	'.tsx',
 	'.jsx',
-].forEach((extension) => {
-	extensions[extension] = transformer;
-});
-
-/**
- * Loaders for explicitly resolvable extensions
- * (basically just .mjs because CJS loader has a special handler for it)
- *
- * Loaders for extensions .cjs, .cts, & .mts don't need to be
- * registered because they're explicitly specified and unknown
- * extensions (incl .cjs) fallsback to using the '.js' loader:
- * https://github.com/nodejs/node/blob/v18.4.0/lib/internal/modules/cjs/loader.js#L430
- *
- * That said, it's actually ".js" and ".mjs" that get special treatment
- * rather than ".cjs" (it might as well be ".random-ext")
- */
-Object.defineProperty(extensions, '.mjs', {
-	value: transformer,
 
-	// Prevent Object.keys from detecting these extensions
-	// when CJS loader iterates over the possible extensions
-	enumerable: false,
+	/**
+	 * Loaders for extensions .cjs, .cts, & .mts don't need to be
+	 * registered because they're explicitly specified. And unknown
+	 * extensions (incl .cjs) fallsback to using the '.js' loader:
+	 * https://github.com/nodejs/node/blob/v18.4.0/lib/internal/modules/cjs/loader.js#L430
+	 *
+	 * That said, it's actually ".js" and ".mjs" that get special treatment
+	 * rather than ".cjs" (it might as well be ".random-ext")
+	 */
+	'.mjs',
+].forEach((extension) => {
+	Object.defineProperty(extensions, extension, {
+		value: transformer,
+
+		/**
+		 * Prevent Object.keys from detecting these extensions
+		 * when CJS loader iterates over the possible extensions
+		 * https://github.com/nodejs/node/blob/v22.2.0/lib/internal/modules/cjs/loader.js#L609
+		 */
+		enumerable: false,
+	});
 });

src/cjs/api/module-resolve-filename.ts

@@ -8,6 +8,8 @@ import { tsconfigPathsMatcher, allowJs } from '../../utils/tsconfig.js';
 
 type ResolveFilename = typeof Module._resolveFilename;
 
+type SimpleResolve = (request: string) => string;
+
 const nodeModulesPath = `${path.sep}node_modules${path.sep}`;
 
 export const interopCjsExports = (
@@ -39,11 +41,9 @@ export const interopCjsExports = (
  * Typescript gives .ts, .cts, or .mts priority over actual .js, .cjs, or .mjs extensions
  */
 const resolveTsFilename = (
-	nextResolve: ResolveFilename,
+	resolve: SimpleResolve,
 	request: string,
 	parent: Module.Parent,
-	isMain: boolean,
-	options?: Record<PropertyKey, unknown>,
 ) => {
 	if (
 		!(parent?.filename && tsExtensionsPattern.test(parent.filename))
@@ -59,12 +59,7 @@ const resolveTsFilename = (
 
 	for (const tryTsPath of tsPath) {
 		try {
-			return nextResolve(
-				tryTsPath,
-				parent,
-				isMain,
-				options,
-			);
+			return resolve(tryTsPath);
 		} catch (error) {
 			const { code } = error as NodeError;
 			if (
@@ -77,6 +72,19 @@ const resolveTsFilename = (
 	}
 };
 
+const extensions = ['.ts', '.tsx', '.jsx'] as const;
+
+const tryExtensions = (
+	resolve: SimpleResolve,
+	request: string,
+) => {
+	for (const extension of extensions) {
+		try {
+			return resolve(request + extension);
+		} catch {}
+	}
+};
+
 export const createResolveFilename = (
 	nextResolve: ResolveFilename,
 ): ResolveFilename => (
@@ -99,39 +107,66 @@ export const createResolveFilename = (
 		request = fileURLToPath(request);
 	}
 
+	const resolve: SimpleResolve = request_ => nextResolve(
+		request_,
+		parent,
+		isMain,
+		options,
+	);
+
 	// Resolve TS path alias
 	if (
 		tsconfigPathsMatcher
 
-			// bare specifier
-			&& !isRelativePath(request)
+		// bare specifier
+		&& !isRelativePath(request)
 
-			// Dependency paths should not be resolved using tsconfig.json
-			&& !parent?.filename?.includes(nodeModulesPath)
+		// Dependency paths should not be resolved using tsconfig.json
+		&& !parent?.filename?.includes(nodeModulesPath)
 	) {
 		const possiblePaths = tsconfigPathsMatcher(request);
 
 		for (const possiblePath of possiblePaths) {
-			const tsFilename = resolveTsFilename(nextResolve, possiblePath, parent, isMain, options);
+			const tsFilename = resolveTsFilename(resolve, possiblePath, parent);
 			if (tsFilename) {
 				return tsFilename + query;
 			}
 
 			try {
-				return nextResolve(
-					possiblePath,
-					parent,
-					isMain,
-					options,
-				) + query;
-			} catch {}
+				return resolve(possiblePath) + query;
+			} catch {
+				/**
+				 * Try order:
+				 * https://github.com/nodejs/node/blob/v22.2.0/lib/internal/modules/cjs/loader.js#L410-L413
+				 */
+				const resolved = (
+					tryExtensions(resolve, possiblePath)
+					|| tryExtensions(resolve, path.resolve(possiblePath, 'index'))
+				);
+				if (resolved) {
+					return resolved + query;
+				}
+			}
 		}
 	}
 
-	const tsFilename = resolveTsFilename(nextResolve, request, parent, isMain, options);
+	// If extension exists
+	const tsFilename = resolveTsFilename(resolve, request, parent);
 	if (tsFilename) {
 		return tsFilename + query;
 	}
 
-	return nextResolve(request, parent, isMain, options) + query;
+	try {
+		return resolve(request) + query;
+	} catch (error) {
+		const resolved = (
+			tryExtensions(resolve, request)
+			|| tryExtensions(resolve, path.resolve(request, 'index'))
+		);
+		if (resolved) {
+			return resolved + query;
+		}
+
+		throw error;
+	}
 };