CommonJS self-reference crashes usedExports code generation #21619

Have you used AI?

Yes

Bug Description

Webpack crashes during bundle generation when an unused CommonJS namespace contains a function that reads one of its own exports. The reduced reproduction uses three small source files and has no runtime dependencies.

The error occurs with production usedExports optimization and a side-effect-free package:

Self-reference dependency has unused export name: This should not happen

Link to Minimal Reproduction and step to reproduce

https://stackblitz.com/edit/webpack-self-reference-repro?file=README.md&view=editor

Steps:

1. Run pnpm install.
2. Run pnpm run build.
3. See the error from src/utility.cjs.

Optionally, run pnpm run build:without-tree-shaking and see how it succeeds.

Expected Behavior

Webpack should tree-shake or retain the unused CommonJS namespace and complete the build.

Actual Behavior

Webpack aborts during bundle generation:

ERROR in ./src/utility.cjs
Self-reference dependency has unused export name: This should not happen

Running pnpm run build:without-tree-shaking succeeds.

Environment

System:
  OS: macOS 26.5.1
  CPU: (16) arm64 Apple M4 Max
  Memory: 586.81 MB / 48.00 GB
Binaries:
  Node: 24.16.0 - ~/.local/state/fnm_multishells/55743_1785937995479/bin/node
  Yarn: 1.22.22 - /opt/homebrew/bin/yarn
  npm: 11.16.0 - /opt/homebrew/bin/npm
  pnpm: 11.1.2 - ~/Library/pnpm/bin/pnpm
Browsers:
  Chrome: 151.0.7922.76
  Safari: 26.5
Packages:
  webpack: 5.109.2 => 5.109.2
  webpack-cli: 6.0.1 => 6.0.1

Is this a regression?

No

Last Working Version

N/A

Additional Context

The reproduction also fails with webpack 5.26.3, 5.40.0, 5.50.0, 5.60.0, 5.70.0, 5.75.0, and 5.107.2. Disabling optimization.usedExports makes it succeed.

This may be related to #13983 and #18315, but this case does not use workers or usedExports: "global".

The issue was reduced from an OpenTelemetry package graph, but the final reproduction contains no OpenTelemetry dependency.

AI assistance was used to organize this report. I reviewed the reproduction, commands, and technical details.