fix: resolve absolute stack frame paths in the webpack compiler

.changeset/webpack-symbolicate-absolute-paths.md

@@ -0,0 +1,5 @@
+---
+"@callstack/repack": patch
+---
+
+Fix missing source code frames on the React Native redbox when using webpack. The dev server resolves symbolicated stack frames to absolute paths, but the webpack compiler joined them onto the project root a second time, so the file was never found and every frame was rendered without its source.

packages/repack/src/commands/webpack/Compiler.ts

@@ -276,7 +276,9 @@ export class Compiler implements CompilerInterface {
     }
 
     try {
-      const filePath = path.join(this.rootDir, filename);
+      const filePath = path.isAbsolute(filename)
+        ? filename
+        : path.join(this.rootDir, filename);
       const source = await fs.promises.readFile(filePath, 'utf8');
       return source;
     } catch {

packages/repack/src/commands/webpack/__tests__/Compiler.test.ts

@@ -1,8 +1,11 @@
 import type { EventEmitter } from 'node:events';
 import { Worker } from 'node:worker_threads';
+import { fs, vol } from 'memfs';
 import type { Reporter } from '../../../logging/types.js';
 import { Compiler } from '../Compiler.js';
 
+jest.mock('node:fs', () => jest.requireActual('memfs').fs);
+
 jest.mock('node:worker_threads', () => {
   const { EventEmitter } =
     jest.requireActual<typeof import('node:events')>('node:events');
@@ -70,3 +73,42 @@ test('terminates active workers when closed', async () => {
 
   expect(worker.terminate).toHaveBeenCalledTimes(1);
 });
+
+describe('getSource', () => {
+  const reporter: Reporter = {
+    process: jest.fn(),
+    flush: jest.fn(),
+    stop: jest.fn(),
+  };
+
+  const createCompiler = () =>
+    new Compiler(['ios'], { host: '' }, reporter, '/project', '/react-native');
+
+  beforeEach(() => {
+    vol.reset();
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  test('reads an absolute filename as-is', async () => {
+    vol.fromJSON({ '/outside/project/file.js': 'absolute source' });
+    const readFile = jest.spyOn(fs.promises, 'readFile');
+
+    await expect(
+      createCompiler().getSource('/outside/project/file.js', 'ios')
+    ).resolves.toBe('absolute source');
+    expect(readFile).toHaveBeenCalledWith('/outside/project/file.js', 'utf8');
+  });
+
+  test('resolves a relative filename against the project root', async () => {
+    vol.fromJSON({ '/project/src/index.js': 'source under the project root' });
+    const readFile = jest.spyOn(fs.promises, 'readFile');
+
+    await expect(
+      createCompiler().getSource('src/index.js', 'ios')
+    ).resolves.toBe('source under the project root');
+    expect(readFile).toHaveBeenCalledWith('/project/src/index.js', 'utf8');
+  });
+});