[Bug]: Workflow E2E Webpack fails with "TypeError: Cannot read properties of undefined"

[MikeMcC399]

Self-service

• I'd be willing to implement a fix

Describe the bug

The workflow .github/workflows/e2e-webpack-workflow.yml fails in the job ts-loader with

./src/index.ts 39 bytes [built] [code generated] [1 error]

ERROR in ./src/index.ts
Module build failed (from ./.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/index.js):
TypeError: Cannot read properties of undefined (reading 'fileExists')
    at findConfigFile (/tmp/tmp.TxTCW6s5ZX/.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/dist/config.js:105:30)
    at getConfigFile (/tmp/tmp.TxTCW6s5ZX/.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/dist/config.js:43:28)
    at successfulTypeScriptInstance (/tmp/tmp.TxTCW6s5ZX/.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/dist/instances.js:117:58)
    at getTypeScriptInstance (/tmp/tmp.TxTCW6s5ZX/.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/dist/instances.js:86:12)
    at Object.loader (/tmp/tmp.TxTCW6s5ZX/.yarn/__virtual__/ts-loader-virtual-bf010dface/3/home/runner/.yarn/berry/cache/ts-loader-npm-9.6.2-fb95e8881d-10c0.zip/node_modules/ts-loader/dist/index.js:59:67)

webpack 5.109.0 compiled with 1 error in 101 ms

It was last successful on Jul 9, 2026.

To reproduce

View https://github.com/yarnpkg/berry/actions/workflows/e2e-webpack-workflow.yml

The workflow runs in a cron job every 4 hours.

Environment

GitHub Actions `ubuntu-latest`, currently equivalent to `ubuntu-24.04`

Additional context

TypeScript 7.0 was announced on Jul 8, 2026.

typescript@7.0.2 was also published on Jul 8, 2026.

The workflow installs the latest version of typescript:

berry/.github/workflows/e2e-webpack-workflow.yml

Line 62 in 7744e66

yarn add -D webpack webpack-cli ts-loader typescript @types/lodash lodash

It may need typescript pinning to v6 in the workflow until TypeScript releases a v7 version with an API (see Running Side-by-Side with TypeScript 6.0).

---

Although it does not affect the outcome, CI tests are currently running by default under Node.js 25.6, which reached end-of-life at the beginning of June 2026, and they are using deprecated GitHub Actions actions/checkout@v4, actions/setup-node@v4 that run on node20 (also end-of-life). Those should be updated to supported versions.