perf: strip source map when unused (#374)

src/cjs/index.ts

@@ -8,7 +8,7 @@ import {
 	createFilesMatcher,
 } from 'get-tsconfig';
 import type { TransformOptions } from 'esbuild';
-import { installSourceMapSupport } from '../source-map';
+import { installSourceMapSupport, shouldStripSourceMap, stripSourceMap } from '../source-map';
 import { transformSync, transformDynamicImport } from '../utils/transform';
 import { resolveTsPath } from '../utils/resolve-ts-path';
 import { isESM } from '../utils/esm-pattern';
@@ -67,6 +67,12 @@ const transformer = (
 	}
 
 	let code = fs.readFileSync(filePath, 'utf8');
+
+	// Strip source maps if originally disabled
+	if (shouldStripSourceMap) {
+		code = stripSourceMap(code);
+	}
+
 	if (filePath.endsWith('.cjs')) {
 		// Contains native ESM check
 		const transformed = transformDynamicImport(filePath, code);

src/esm/loaders.ts

@@ -7,8 +7,8 @@ import type {
 import type { TransformOptions } from 'esbuild';
 import { transform, transformDynamicImport } from '../utils/transform';
 import { resolveTsPath } from '../utils/resolve-ts-path';
+import { installSourceMapSupport, shouldStripSourceMap, stripSourceMap } from '../source-map';
 import {
-	applySourceMap,
 	tsconfigPathsMatcher,
 	fileMatcher,
 	tsExtensionsPattern,
@@ -19,6 +19,8 @@ import {
 	type NodeError,
 } from './utils.js';
 
+const applySourceMap = installSourceMapSupport();
+
 const isDirectoryPattern = /\/(?:$|\?)/;
 
 type NextResolve = (
@@ -274,7 +276,12 @@ export const load: LoadHook = async function (
 	}
 
 	const filePath = url.startsWith('file://') ? fileURLToPath(url) : url;
-	const code = loaded.source.toString();
+	let code = loaded.source.toString();
+
+	// Strip source maps if originally disabled
+	if (shouldStripSourceMap) {
+		code = stripSourceMap(code);
+	}
 
 	if (
 		// Support named imports in JSON modules

src/esm/utils.ts

@@ -6,11 +6,8 @@ import {
 	createPathsMatcher,
 	createFilesMatcher,
 } from 'get-tsconfig';
-import { installSourceMapSupport } from '../source-map';
 import { getPackageType } from './package-json.js';
 
-export const applySourceMap = installSourceMapSupport();
-
 const tsconfig = (
 	process.env.TSX_TSCONFIG_PATH
 		? {

src/source-map.ts

@@ -10,15 +10,31 @@ type PortMessage = {
 	map: RawSourceMap;
 };
 
-const inlineSourceMapPrefix = '\n//# sourceMappingURL=data:application/json;base64,';
+// If Node.js has source map disabled, we should strip source maps to speed up processing
+export const shouldStripSourceMap = (
+	('sourceMapsEnabled' in process)
+	&& process.sourceMapsEnabled === false
+);
 
-export function installSourceMapSupport(
+const sourceMapPrefix = '\n//# sourceMappingURL=';
+
+export const stripSourceMap = (code: string) => {
+	const sourceMapIndex = code.indexOf(sourceMapPrefix);
+	if (sourceMapIndex !== -1) {
+		return code.slice(0, sourceMapIndex);
+	}
+	return code;
+};
+
+const inlineSourceMapPrefix = `${sourceMapPrefix}data:application/json;base64,`;
+
+export const installSourceMapSupport = (
 	/**
 	 * To support Node v20 where loaders are executed in its own thread
 	 * https://nodejs.org/docs/latest-v20.x/api/esm.html#globalpreload
 	 */
 	loaderPort?: MessagePort,
-) {
+) => {
 	const hasNativeSourceMapSupport = (
 		/**
 		 * Check if native source maps are supported by seeing if the API is available
@@ -77,4 +93,4 @@ export function installSourceMapSupport(
 		}
 		return code;
 	};
-}
+};

src/utils/debug.ts

@@ -1,36 +1,37 @@
-export const time = <Argument>(
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const time = <T extends (...args: any[]) => unknown>(
 	name: string,
-	_function: (...args: Argument[]) => unknown,
-) => function (
-		this: unknown,
-		...args: Argument[]
-	) {
-		const timeStart = Date.now();
-		const logTimeElapsed = () => {
-			const elapsed = Date.now() - timeStart;
+	_function: T,
+	threshold = 100,
+): T => function (
+	this: unknown,
+	...args: Parameters<T>
+) {
+	const timeStart = Date.now();
+	const logTimeElapsed = () => {
+		const elapsed = Date.now() - timeStart;
 
-			if (elapsed > 10) {
-			// console.log({
-			// 	name,
-			// 	args,
-			// 	elapsed,
-			// });
-			}
-		};
+		if (elapsed > threshold) {
+			console.log(name, {
+				args,
+				elapsed,
+			});
+		}
+	};
 
-		const result = Reflect.apply(_function, this, args);
-		if (
-			result
+	const result = Reflect.apply(_function, this, args);
+	if (
+		result
 		&& typeof result === 'object'
 		&& 'then' in result
-		) {
-			(result as Promise<unknown>).then(
-				logTimeElapsed,
-				// Ignore error in this chain
-				() => {},
-			);
-		} else {
-			logTimeElapsed();
-		}
-		return result;
-	};
+	) {
+		(result as Promise<unknown>).then(
+			logTimeElapsed,
+			// Ignore error in this chain
+			() => {},
+		);
+	} else {
+		logTimeElapsed();
+	}
+	return result;
+} as T;

src/utils/esm-pattern.ts

@@ -1,6 +1,10 @@
 import { parseEsm } from './es-module-lexer';
+
 /*
-TODO: Add tests
+Previously, this regex was used as a naive ESM catch,
+but turns out regex is slower than the lexer so removing
+it made the check faster.
+
 Catches:
 import a from 'b'
 import 'b';
@@ -12,11 +16,12 @@ Doesn't catch:
 EXPORT{a}
 exports.a = 1
 module.exports = 1
- */
+
 const esmPattern = /\b(?:import|export)\b/;
+*/
 
 export const isESM = (code: string) => {
-	if (esmPattern.test(code)) {
+	if (code.includes('import') || code.includes('export')) {
 		const [imports, exports] = parseEsm(code);
 		return imports.length > 0 || exports.length > 0;
 	}