expo export: "Chunk containing module not found" for react-native-css components (dual import/require .cjs variants)

[danstepanov]

Summary

npx expo export (production bundling) fails in Expo's async-chunk serializer with:

AssertionError [ERR_ASSERTION]: Chunk containing module not found:
  node_modules/react-native-css/dist/commonjs/components/index.cjs
    at .../@expo/metro-config/build/serializer/serializeChunks.js:211:42
    at Chunk.getComputedPathsForAsyncDependencies (.../serializeChunks.js:207:19)
    at Chunk.serializeToCode (.../serializeChunks.js:266:44)
    at Chunk.serializeToAssetsAsync (.../serializeChunks.js:290:29)
    ...
    at exportAppAsync (.../@expo/cli/build/src/export/exportApp.js:193:13)

The Metro dev server (expo start) bundles fine. Only expo export (and therefore production / EAS builds) fails.

Repro

It reproduces with a minimal config, so it is not caused by a custom resolver/transformer:

// metro.config.js
const { getDefaultConfig } = require("expo/metro-config");
const { withNativewind } = require("nativewind/metro");
module.exports = withNativewind(getDefaultConfig(__dirname));

npx expo export --platform android

Full repo (it also covers a separate nativewind issue, but the export failure repros directly):
https://github.com/danstepanov/nw-1824-repro → cd apps/mobile && npx expo export -p android

Likely cause

The ./components subpath exports map points the import and require conditions at two different files that share the same basename:

"./components": {
  "source":  "./src/components/index.cts",
  "import":  { "default": "./dist/module/components/index.cjs",   ... },
  "require": { "default": "./dist/commonjs/components/index.cjs", ... }
}

So the same logical module resolves to two distinct absolute paths depending on the active condition (dist/module/components/index.cjs vs dist/commonjs/components/index.cjs). Expo's getComputedPathsForAsyncDependencies looks up the chunk for the commonjs variant but the chunk was built around the module variant, so the assertion fires. (components/index.cjs itself is a set of lazy require() getters; the only importer in the graph is nativewind/dist/.../test-utils.)

A couple of things worth checking:

• why the ESM (import) condition points to a .cjs file under dist/module/, and whether collapsing both conditions to a single canonical path resolves the chunk lookup;
• whether test-utils should be reachable from a production graph at all.

Environment

• expo 56.0.12, react-native 0.85.3, react 19.2.3
• nativewind 5.0.0-preview.4, react-native-css 3.0.7 (latest stable)
• @expo/metro-config 56.0.14
• pnpm 10.8.1 monorepo, nodeLinker: hoisted (also note: minimal config, so not resolver-specific)

[github-actions]

🤖 Auto-triage

Status: NEEDS_TIER_2
Type: bug
Version: v5 (react-native-css 3.0.7)

Findings

The reporter's analysis of the package.json exports map looks consistent with the symptom. The ./components subpath at package.json:39-49 resolves to two distinct absolute paths (dist/module/components/index.cjs vs dist/commonjs/components/index.cjs) that share the same basename, which can trip up Expo's serializeChunks chunk lookup. Notably, the ESM import condition points at a .cjs file, which is unusual and worth investigating. This is a Metro/Expo bundling-time bug, not a CSS compilation or runtime issue, and is not reproducible via the Jest unit test harness — it needs a real expo export run against a project that pulls in nativewind/.../test-utils (the only importer of react-native-css/components in the graph per the reporter).

What I tested

• Fetched issue expo export: "Chunk containing module not found" for react-native-css components (dual import/require .cjs variants) #364 and read the reporter's full repro steps and exports-map analysis.
• Verified package.json exports map for ./components — confirmed both import.default and require.default point at index.cjs files in sibling dist/module and dist/commonjs directories.
• Inspected src/components/index.cts — confirmed it is a CommonJS module of lazy require() getters, which matches the reporter's description of why a chunk-graph lookup might fail.
• Did not run the linked nw-1824-repro repo (out of scope for unit-test triage; requires full expo export pipeline).

Next steps

For the maintainer:

1. Decide whether the ./components import condition should point at a true ESM artifact (e.g. dist/module/components/index.js / .mjs) instead of dist/module/components/index.cjs. The .cts source -> .cjs output via react-native-builder-bob esm: true config in package.json:255-273 is likely the root cause of the dual-.cjs shape.
2. Alternatively, collapse both conditions to a single canonical path for ./components so Expo's chunk lookup is unambiguous.
3. Verify whether nativewind's test-utils should be reachable from a production bundle graph at all — that may be a separate fix on the nativewind side.
4. Repro requires running npx expo export -p android against the linked repo; cannot be expressed as a Jest test.

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_{This is an automated triage. See auto-triage.yml.}