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WASM CodeFrameColumns Rejects Boolean Color And Undefined MaxWidth, Hiding Real Errors

On the WASM SWC bindings, codeFrameColumns deserializes options directly into a strict CodeFrameOptions struct that cannot accept boolean color or undefined maxWidth, unlike the native N-API binding. This causes 100% of code frames to fail on the WASM fallback, replacing the actual error with a serialization error in the dev overlay, server console, and build diagnostics.

highConfidence 85%Next.js Affected V16.3.5 Affected V16.4.0-Canary.51

Origin Analysis

The WASM binding in crates/wasm/src/lib.rs uses serde_wasm_bindgen::from_value to deserialize JS options straight into CodeFrameOptions, whose fields are typed as CodeFrameColorMode and usize. serde(default) only applies to missing fields, not explicit boolean/undefined values. The N-API binding uses a tolerant option struct with Either<enum, bool> and Option<usize>, but the WASM path lacks this normalization.

1. Create a Next.js app with next@canary and force WASM bindings (NEXT_TEST_WASM=1, NEXT_TEST_WASM_DIR=node_modules/@next/swc-wasm-nodejs). 2. Run npm run repro to call codeFrameColumns with the four option shapes Next.js itself passes; three throw. 3. Run npm run dev -- --webpack, open http://localhost:3000/trigger-error, observe the dev overlay missing the code frame and server console showing only the binding error. 4. Open the API route equivalent to see the real error never reaching the console. 5. Compare with native bindings where code frames render correctly.

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 change only affects the WASM path. If CodeFrameOptions gains new fields in future versions, WasmCodeFrameOptions must be updated accordingly. Rolling back is safe: revert the commit to restore the original deserialization. Ensure the default values for lines_above, lines_below, and max_width match the native binding's defaults to avoid behavioral differences across bindings. Test on OpenBSD/other platforms where native binaries are unavailable.