feat: add source map support for production stack trace rewriting #284

aheissenberger · 2025-11-14T09:18:13Z

Source Map Support for Production Error Stack Traces

Overview

This implementation adds support for converting production error stack traces back to their original source locations using source maps. When you build with the --sourcemap flag, error messages in production will show the original file locations and line numbers instead of the compiled/bundled locations.

How It Works

1. Source Map Detection

When the server starts in production mode, it checks if source map files (.map) exist alongside the built files in the output directory (default: .react-server/server/). If found, the SOURCEMAP_ENABLED flag is set in the runtime context.

File: lib/start/ssr-handler.mjs

Checks for .map files during initialization
Sets the SOURCEMAP_ENABLED runtime flag

2. Stack Trace Conversion

The source-map-support package is dynamically imported and installed at server startup when source maps are detected. It automatically hooks into Node.js's Error.prepareStackTrace to convert stack traces:

Package: source-map-support (dynamically loaded)

Only imported when .map files are detected
Automatically loads .map files from the file system
Caches parsed source maps for performance
Hooks into Node.js error handling
Transparently converts all stack traces system-wide

3. Error Logging Integration

Once source-map-support is installed, all errors throughout the application automatically have their stack traces converted. No manual conversion is needed at individual error points.

Files Modified:

lib/start/ssr-handler.mjs - Installs source-map-support at startup

Usage

Building with Source Maps

# Build with separate source map files
npx react-server build --sourcemap

# Build with inline source maps
npx react-server build --sourcemap inline

# Build with hidden source maps (not referenced in code)
npx react-server build --sourcemap hidden

Starting the Production Server

npx react-server start

The server will automatically detect if source maps are available and use them for error reporting.

Example

Without Source Maps

Error: Something went wrong
    at /app/.react-server/server/index.mjs:1234:56
    at /app/.react-server/server/render.mjs:789:12

With Source Maps

Error: Something went wrong
    at /app/src/components/MyComponent.jsx:45:23
    at /app/src/pages/index.jsx:12:8

Implementation Details

Modified Files

server/symbols.mjs
- Added SOURCEMAP_ENABLED symbol for runtime flag
lib/start/ssr-handler.mjs
- Detects source map availability on startup (checks for .map files)
- Dynamically imports source-map-support only when source maps are detected
- Sets SOURCEMAP_ENABLED runtime flag
- Installs source-map-support when source maps are available

Dependencies Added

source-map-support - Automatically converts stack traces using source maps (dynamically loaded only when needed)

Performance Considerations

Dynamic Loading: source-map-support is only imported when source maps are detected, reducing memory footprint in development and when source maps aren't available
One-time Check: Source map detection happens once at server startup, not on every request
Efficient Caching: source-map-support caches parsed source maps in memory after first load
Minimal Overhead: Hooks are installed once at startup with negligible performance impact
Graceful Fallback: Falls back to original stack trace if source map lookup fails

Conditional Execution

The source map conversion only happens when:

The build was created with --sourcemap flag
The .map files exist in the output directory
Running in production mode (not dev mode)
An error occurs

Notes

Dev mode already has source map support through Vite's module graph
This implementation is specifically for production builds
Source maps should be kept secure and not deployed to public-facing servers if they contain sensitive information
The --sourcemap hidden option generates source maps but doesn't reference them in the code (useful for error tracking without exposing sources)

Copilot

Pull Request Overview

This pull request adds source map support for production error stack traces by dynamically loading and installing the source-map-support package when .map files are detected at server startup. This allows production errors to display original source locations instead of compiled bundle locations.

Key Changes

Added SOURCEMAP_ENABLED runtime flag to track source map availability
Implemented source map detection by checking for .map files in the build output directory
Dynamically imports and installs source-map-support only when source maps are present

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pnpm-lock.yaml	Added `[email protected]` dependency and updated peer dependency resolution for various packages
packages/react-server/server/symbols.mjs	Added new `SOURCEMAP_ENABLED` symbol for runtime flag tracking
packages/react-server/package.json	Added `source-map-support` dependency specification
packages/react-server/lib/start/ssr-handler.mjs	Implemented source map detection logic and dynamic loading of source-map-support at server startup
packages/react-server/lib/start/action.mjs	Added default initialization of `SOURCEMAP_ENABLED` flag in worker function

Files not reviewed (1)

pnpm-lock.yaml: Language not supported

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packages/react-server/lib/start/ssr-handler.mjs

packages/react-server/lib/start/action.mjs

lazarv · 2025-11-15T21:17:46Z

Hi @aheissenberger!

This is so nice to have finally, and sourcemap handling has been a missing feature for more than 2 years now! I totally forgot to add this to the production server.

I made some suggested changes in review/sourcemap-error.

The most prominent change I would suggest is to use the entry module code and check for the sourceMappingURL line to support inline sourcemaps, and not load the source-map-support module for hidden sourcemaps.

Also, I would rename SOURCEMAP_ENABLED to SOURCEMAP_SUPPORT as this is the name of the feature, and enabled/disabled is its value.

aheissenberger · 2025-11-17T17:41:40Z

When switching to source map detection by checking for the url, the hidden source maps will break.

Have a look at my latest changes which require less code changes and no runtime detection:

create a build meta file which allows to access build settings like source map options at runtime
packages/react-server/server/render-rsc.jsx - fix missing stack trace in server log from react server components in production. Without this fix the server log logs the same anonymous message as shown on the client An error occurred in the Server Components render. The specific message is omitted in production ...

I tested the rsc component by adding a throw error to function allTodos(), it worked very well in production including mapping to the right source position. But the already existing stack trace in dev mode does not provide the correct line number - see #285

aheissenberger · 2025-11-17T19:22:14Z

maybe using the cli option --enable-source-maps and adding some infos to the docs is the best way to go since this option exists since node 12.12.0

NODE_OPTIONS='--enable-source-maps' react-server start

lazarv · 2025-11-19T07:23:19Z

packages/react-server/server/render-rsc.jsx

 import { ServerFunctionNotFoundError } from "./action-state.mjs";
 import { cwd } from "../lib/sys.mjs";

+/**


This wrapper could be moved to https://github.com/lazarv/react-server/blob/main/packages/react-server/lib/start/create-logger.mjs, so that the logger would use this everywhere by default. Also, the wrapper should only be enabled when using source maps.

lazarv · 2025-11-19T07:28:30Z

packages/react-server/lib/build/server.mjs

+
+  // Write build metadata with sourcemap option
+  await writeFile(
+    join(cwd, options.outDir, "server/build-meta.json"),


As all other manifests have the server/<type>-manifest.json name, I would suggest to have this also named server/build-manifest.json.

lazarv · 2025-11-19T07:29:57Z

packages/react-server/lib/start/ssr-handler.mjs

  const moduleCacheStorage = new ContextManager();
  await module_loader_init$(moduleLoader, moduleCacheStorage);

+  if (buildMetadata.sourcemap && buildMetadata.sourcemap !== false) {


As this is now related to manifests, I would move this into https://github.com/lazarv/react-server/blob/main/packages/react-server/lib/start/manifest.mjs#L52-L56 and also store it in the context.

feat: add source map support for production stack trace rewriting

71e5d9f

Copilot AI review requested due to automatic review settings November 14, 2025 09:18

aheissenberger requested a review from lazarv as a code owner November 14, 2025 09:18

Copilot started reviewing on behalf of aheissenberger November 14, 2025 09:18 View session

Copilot finished reviewing on behalf of aheissenberger November 14, 2025 09:22

Copilot AI reviewed Nov 14, 2025

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packages/react-server/lib/start/ssr-handler.mjs Outdated Show resolved Hide resolved

packages/react-server/lib/start/action.mjs Outdated Show resolved Hide resolved

aheissenberger added 2 commits November 14, 2025 10:33

fix: improve source map logging in SSR handler

6a944a6

fix: use info logger and fix text

8bacc49

aheissenberger added 4 commits November 17, 2025 12:21

feat: switch flag to SOURCEMAP_SUPPORT

bbb4b62

fix: replace runtime sourcemap detection with build meta data

275a497

feat: stack trace for react server components in production

45b9569

fix: remove not required file

0de6b4a

lazarv reviewed Nov 19, 2025

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aheissenberger commented Nov 14, 2025

Source Map Support for Production Error Stack Traces

Overview

How It Works

1. Source Map Detection

2. Stack Trace Conversion

3. Error Logging Integration

Usage

Building with Source Maps

Starting the Production Server

Example

Without Source Maps

With Source Maps

Implementation Details

Modified Files

Dependencies Added

Performance Considerations

Conditional Execution

Notes

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Pull Request Overview

Key Changes

Reviewed Changes

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