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Rust React Compiler Produces Inaccurate Source Maps For Expressions Hoisted From Component Callbacks

When `turbopackRustReactCompiler` is enabled in Next.js 16.3.1, expressions hoisted or memoized from client component callbacks (e.g., inside `setTimeout`, `Promise.reject`, `console.error`) are mapped to unrelated lines/columns in production source maps, causing incorrect stack traces. Disabling the Rust compiler restores correct mappings.

highConfidence 88%Next.js Affected V16.3.1 Affected V16.3.1-Canary.18

Origin Analysis

The Rust React Compiler's code generation or transformation step does not preserve original source span information when it hoists or memoizes expressions from component callbacks. This leads to incorrect source map offsets during emission, resulting in generated positions resolving to wrong locations within the source file.

1. Clone https://github.com/istarkov/next-rust-react-compiler-sourcemap-repro and run `pnpm install`. 2. Run `pnpm repro` to build and decode the source map. 3. Observe that errors thrown in `setTimeout`, `Promise.reject`, and `console.error` inside component callbacks map to incorrect lines. 4. Alternatively, run `pnpm build && pnpm next start`, open the browser, click buttons, and inspect console stack traces. 5. Set `turbopackRustReactCompiler: false` in `next.config.js`, rebuild, and observe correct mappings.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This workaround disables the Rust compiler, which may significantly increase build times and reduce performance benefits. It should be treated as a temporary mitigation and reverted as soon as an official fix is released. Users relying on the Rust compiler for large builds should monitor upstream Next.js releases and apply the appropriate patch. No data is corrupted, but stack traces remain inaccurate until fixed.