[Flight] Add findSourceMapURL option to get a URL to load Server source maps from

fixtures/flight/config/webpack.config.js

@@ -199,7 +199,7 @@ module.exports = function (webpackEnv) {
       ? shouldUseSourceMap
         ? 'source-map'
         : false
-      : isEnvDevelopment && 'cheap-module-source-map',
+      : isEnvDevelopment && 'source-map',
     // These are the "entry points" to our application.
     // This means they will be the "root" imports that are included in JS bundle.
     entry: isEnvProduction

fixtures/flight/loader/region.js

@@ -16,6 +16,7 @@ const babelOptions = {
     '@babel/plugin-syntax-import-meta',
     '@babel/plugin-transform-react-jsx',
   ],
+  sourceMaps: process.env.NODE_ENV === 'development' ? 'inline' : false,
 };
 
 async function babelLoad(url, context, defaultLoad) {

fixtures/flight/package.json

@@ -71,7 +71,7 @@
     "prebuild": "cp -r ../../build/oss-experimental/* ./node_modules/",
     "dev": "concurrently \"npm run dev:region\" \"npm run dev:global\"",
     "dev:global": "NODE_ENV=development BUILD_PATH=dist node --experimental-loader ./loader/global.js server/global",
-    "dev:region": "NODE_ENV=development BUILD_PATH=dist nodemon --watch src --watch dist -- --experimental-loader ./loader/region.js --conditions=react-server server/region",
+    "dev:region": "NODE_ENV=development BUILD_PATH=dist nodemon --watch src --watch dist -- --enable-source-maps --experimental-loader ./loader/region.js --conditions=react-server server/region",
     "start": "node scripts/build.js && concurrently \"npm run start:region\" \"npm run start:global\"",
     "start:global": "NODE_ENV=production node --experimental-loader ./loader/global.js server/global",
     "start:region": "NODE_ENV=production node --experimental-loader ./loader/region.js --conditions=react-server server/region",

fixtures/flight/server/global.js

@@ -214,6 +214,43 @@ app.all('/', async function (req, res, next) {
 
 if (process.env.NODE_ENV === 'development') {
   app.use(express.static('public'));
+
+  app.get('/source-maps', async function (req, res, next) {
+    // Proxy the request to the regional server.
+    const proxiedHeaders = {
+      'X-Forwarded-Host': req.hostname,
+      'X-Forwarded-For': req.ips,
+      'X-Forwarded-Port': 3000,
+      'X-Forwarded-Proto': req.protocol,
+    };
+
+    const promiseForData = request(
+      {
+        host: '127.0.0.1',
+        port: 3001,
+        method: req.method,
+        path: req.originalUrl,
+        headers: proxiedHeaders,
+      },
+      req
+    );
+
+    try {
+      const rscResponse = await promiseForData;
+      res.set('Content-type', 'application/json');
+      rscResponse.on('data', data => {
+        res.write(data);
+        res.flush();
+      });
+      rscResponse.on('end', data => {
+        res.end();
+      });
+    } catch (e) {
+      console.error(`Failed to proxy request: ${e.stack}`);
+      res.statusCode = 500;
+      res.end();
+    }
+  });
 } else {
   // In production we host the static build output.
   app.use(express.static('build'));

fixtures/flight/server/region.js

@@ -24,6 +24,7 @@ babelRegister({
   ],
   presets: ['@babel/preset-react'],
   plugins: ['@babel/transform-modules-commonjs'],
+  sourceMaps: process.env.NODE_ENV === 'development' ? 'inline' : false,
 });
 
 if (typeof fetch === 'undefined') {
@@ -38,6 +39,8 @@ const app = express();
 const compress = require('compression');
 const {Readable} = require('node:stream');
 
+const nodeModule = require('node:module');
+
 app.use(compress());
 
 // Application
@@ -176,6 +179,69 @@ app.get('/todos', function (req, res) {
   ]);
 });
 
+if (process.env.NODE_ENV === 'development') {
+  const rootDir = path.resolve(__dirname, '../');
+
+  app.get('/source-maps', async function (req, res, next) {
+    try {
+      res.set('Content-type', 'application/json');
+      let requestedFilePath = req.query.name;
+
+      if (requestedFilePath.startsWith('file://')) {
+        requestedFilePath = requestedFilePath.slice(7);
+      }
+
+      const relativePath = path.relative(rootDir, requestedFilePath);
+      if (relativePath.startsWith('..') || path.isAbsolute(relativePath)) {
+        // This is outside the root directory of the app. Forbid it to be served.
+        res.status = 403;
+        res.write('{}');
+        res.end();
+        return;
+      }
+
+      const sourceMap = nodeModule.findSourceMap(requestedFilePath);
+      let map;
+      // There are two ways to return a source map depending on what we observe in error.stack.
+      // A real app will have a similar choice to make for which strategy to pick.
+      if (!sourceMap || Error.prepareStackTrace === undefined) {
+        // When --enable-source-maps is enabled, the error.stack that we use to track
+        // stacks will have had the source map already applied so it's pointing to the
+        // original source. We return a blank source map that just maps everything to
+        // the original source in this case.
+        const sourceContent = await readFile(requestedFilePath, 'utf8');
+        const lines = sourceContent.split('\n').length;
+        map = {
+          version: 3,
+          sources: [requestedFilePath],
+          sourcesContent: [sourceContent],
+          // Note: This approach to mapping each line only lets you jump to each line
+          // not jump to a column within a line. To do that, you need a proper source map
+          // generated for each parsed segment or add a segment for each column.
+          mappings: 'AAAA' + ';AACA'.repeat(lines - 1),
+          sourceRoot: '',
+        };
+      } else {
+        // If something has overridden prepareStackTrace it is likely not getting the
+        // natively applied source mapping to error.stack and so the line will point to
+        // the compiled output similar to how a browser works.
+        // E.g. ironically this can happen with the source-map-support library that is
+        // auto-invoked by @babel/register if external source maps are generated.
+        // In this case we just use the source map that the native source mapping would
+        // have used.
+        map = sourceMap.payload;
+      }
+      res.write(JSON.stringify(map));
+      res.end();
+    } catch (x) {
+      res.status = 500;
+      res.write('{}');
+      res.end();
+      console.error(x);
+    }
+  });
+}
+
 app.listen(3001, () => {
   console.log('Regional Flight Server listening on port 3001...');
 });

fixtures/flight/src/index.js

@@ -39,6 +39,9 @@ async function hydrateApp() {
     }),
     {
       callServer,
+      findSourceMapURL(fileName) {
+        return '/source-maps?name=' + encodeURIComponent(fileName);
+      },
     }
   );
 

packages/react-client/src/ReactFlightClient.js

@@ -239,6 +239,8 @@ Chunk.prototype.then = function <T>(
   }
 };
 
+export type FindSourceMapURLCallback = (fileName: string) => null | string;
+
 export type Response = {
   _bundlerConfig: SSRModuleMap,
   _moduleLoading: ModuleLoading,
@@ -255,6 +257,7 @@ export type Response = {
   _buffer: Array<Uint8Array>, // chunks received so far as part of this row
   _tempRefs: void | TemporaryReferenceSet, // the set temporary references can be resolved from
   _debugRootTask?: null | ConsoleTask, // DEV-only
+  _debugFindSourceMapURL?: void | FindSourceMapURLCallback, // DEV-only
 };
 
 function readChunk<T>(chunk: SomeChunk<T>): T {
@@ -696,7 +699,7 @@ function createElement(
           console,
           getTaskName(type),
         );
-        const callStack = buildFakeCallStack(stack, createTaskFn);
+        const callStack = buildFakeCallStack(response, stack, createTaskFn);
         // This owner should ideally have already been initialized to avoid getting
         // user stack frames on the stack.
         const ownerTask =
@@ -1140,6 +1143,7 @@ export function createResponse(
   encodeFormAction: void | EncodeFormActionCallback,
   nonce: void | string,
   temporaryReferences: void | TemporaryReferenceSet,
+  findSourceMapURL: void | FindSourceMapURLCallback,
 ): Response {
   const chunks: Map<number, SomeChunk<any>> = new Map();
   const response: Response = {
@@ -1166,6 +1170,9 @@ export function createResponse(
     // TODO: Make this string configurable.
     response._debugRootTask = (console: any).createTask('"use server"');
   }
+  if (__DEV__) {
+    response._debugFindSourceMapURL = findSourceMapURL;
+  }
   // Don't inline this call because it causes closure to outline the call above.
   response._fromJSON = createFromJSONCallback(response);
   return response;
@@ -1673,6 +1680,7 @@ const fakeFunctionCache: Map<string, FakeFunction<any>> = __DEV__
 function createFakeFunction<T>(
   name: string,
   filename: string,
+  sourceMap: null | string,
   line: number,
   col: number,
 ): FakeFunction<T> {
@@ -1697,7 +1705,9 @@ function createFakeFunction<T>(
       '_()\n';
   }
 
-  if (filename) {
+  if (sourceMap) {
+    code += '//# sourceMappingURL=' + sourceMap;
+  } else if (filename) {
     code += '//# sourceURL=' + filename;
   }
 
@@ -1720,10 +1730,18 @@ function createFakeFunction<T>(
   return fn;
 }
 
+// This matches either of these V8 formats.
+//     at name (filename:0:0)
+//     at filename:0:0
+//     at async filename:0:0
 const frameRegExp =
-  /^ {3} at (?:(.+) \(([^\)]+):(\d+):(\d+)\)|([^\)]+):(\d+):(\d+))$/;
+  /^ {3} at (?:(.+) \(([^\)]+):(\d+):(\d+)\)|(?:async )?([^\)]+):(\d+):(\d+))$/;
 
-function buildFakeCallStack<T>(stack: string, innerCall: () => T): () => T {
+function buildFakeCallStack<T>(
+  response: Response,
+  stack: string,
+  innerCall: () => T,
+): () => T {
   const frames = stack.split('\n');
   let callStack = innerCall;
   for (let i = 0; i < frames.length; i++) {
@@ -1739,7 +1757,13 @@ function buildFakeCallStack<T>(stack: string, innerCall: () => T): () => T {
       const filename = parsed[2] || parsed[5] || '';
       const line = +(parsed[3] || parsed[6]);
       const col = +(parsed[4] || parsed[7]);
-      fn = createFakeFunction(name, filename, line, col);
+      const sourceMap = response._debugFindSourceMapURL
+        ? response._debugFindSourceMapURL(filename)
+        : null;
+      fn = createFakeFunction(name, filename, sourceMap, line, col);
+      // TODO: This cache should technically live on the response since the _debugFindSourceMapURL
+      // function is an input and can vary by response.
+      fakeFunctionCache.set(frame, fn);
     }
     callStack = fn.bind(null, callStack);
   }
@@ -1770,7 +1794,7 @@ function initializeFakeTask(
     console,
     getServerComponentTaskName(componentInfo),
   );
-  const callStack = buildFakeCallStack(stack, createTaskFn);
+  const callStack = buildFakeCallStack(response, stack, createTaskFn);
 
   if (ownerTask === null) {
     const rootTask = response._debugRootTask;
@@ -1832,6 +1856,7 @@ function resolveConsoleEntry(
     return;
   }
   const callStack = buildFakeCallStack(
+    response,
     stackTrace,
     printToConsole.bind(null, methodName, args, env),
   );

packages/react-server-dom-esm/src/ReactFlightDOMClientBrowser.js

@@ -9,7 +9,10 @@
 
 import type {Thenable} from 'shared/ReactTypes.js';
 
-import type {Response as FlightResponse} from 'react-client/src/ReactFlightClient';
+import type {
+  Response as FlightResponse,
+  FindSourceMapURLCallback,
+} from 'react-client/src/ReactFlightClient';
 
 import type {ReactServerValue} from 'react-client/src/ReactFlightReplyClient';
 
@@ -38,6 +41,7 @@ export type Options = {
   moduleBaseURL?: string,
   callServer?: CallServerCallback,
   temporaryReferences?: TemporaryReferenceSet,
+  findSourceMapURL?: FindSourceMapURLCallback,
 };
 
 function createResponseFromOptions(options: void | Options) {
@@ -50,6 +54,9 @@ function createResponseFromOptions(options: void | Options) {
     options && options.temporaryReferences
       ? options.temporaryReferences
       : undefined,
+    __DEV__ && options && options.findSourceMapURL
+      ? options.findSourceMapURL
+      : undefined,
   );
 }
 

packages/react-server-dom-esm/src/ReactFlightDOMClientNode.js

@@ -9,7 +9,10 @@
 
 import type {Thenable, ReactCustomFormAction} from 'shared/ReactTypes.js';
 
-import type {Response} from 'react-client/src/ReactFlightClient';
+import type {
+  Response,
+  FindSourceMapURLCallback,
+} from 'react-client/src/ReactFlightClient';
 
 import type {Readable} from 'stream';
 
@@ -46,6 +49,7 @@ type EncodeFormActionCallback = <A>(
 export type Options = {
   nonce?: string,
   encodeFormAction?: EncodeFormActionCallback,
+  findSourceMapURL?: FindSourceMapURLCallback,
 };
 
 function createFromNodeStream<T>(
@@ -61,6 +65,9 @@ function createFromNodeStream<T>(
     options ? options.encodeFormAction : undefined,
     options && typeof options.nonce === 'string' ? options.nonce : undefined,
     undefined, // TODO: If encodeReply is supported, this should support temporaryReferences
+    __DEV__ && options && options.findSourceMapURL
+      ? options.findSourceMapURL
+      : undefined,
   );
   stream.on('data', chunk => {
     processBinaryChunk(response, chunk);

packages/react-server-dom-turbopack/src/ReactFlightDOMClientBrowser.js

@@ -9,7 +9,10 @@
 
 import type {Thenable} from 'shared/ReactTypes.js';
 
-import type {Response as FlightResponse} from 'react-client/src/ReactFlightClient';
+import type {
+  Response as FlightResponse,
+  FindSourceMapURLCallback,
+} from 'react-client/src/ReactFlightClient';
 
 import type {ReactServerValue} from 'react-client/src/ReactFlightReplyClient';
 
@@ -37,6 +40,7 @@ type CallServerCallback = <A, T>(string, args: A) => Promise<T>;
 export type Options = {
   callServer?: CallServerCallback,
   temporaryReferences?: TemporaryReferenceSet,
+  findSourceMapURL?: FindSourceMapURLCallback,
 };
 
 function createResponseFromOptions(options: void | Options) {
@@ -49,6 +53,9 @@ function createResponseFromOptions(options: void | Options) {
     options && options.temporaryReferences
       ? options.temporaryReferences
       : undefined,
+    __DEV__ && options && options.findSourceMapURL
+      ? options.findSourceMapURL
+      : undefined,
   );
 }