Bug - react-icons - Tree-shaking broken due to missing sideEffects in dist/esm/package.json

[logonoff]

Describe the problem

Starting in the prerelease builds, @patternfly/react-icons ships a dist/esm/package.json file containing {"type": "module"}. This file does not include the "sideEffects": false declaration that exists in the root package.json. Because webpack resolves the nearest package.json for each module, all icons under dist/esm/ are treated as having side effects, completely breaking tree-shaking.

This causes the entire icon library (all 2846 icons, ~7MB minified) to be bundled even when only a handful are used.

How do you reproduce the problem?

1. Install @patternfly/react-icons@6.5.0-prerelease.19 (or any recent prerelease)
2. Import a single icon: import { CheckCircleIcon } from '@patternfly/react-icons'
3. Run a webpack 5 production build
4. Observe that ALL icons are included in the bundle

Root cause: dist/esm/package.json contains {"type": "module"} but is missing "sideEffects": false. The root package.json has "sideEffects": false, but webpack uses the closest package.json to each module file, so the dist/esm/package.json takes precedence and the sideEffects flag is never seen.

Expected behavior

Only the imported icons should be included in the bundle. The dist/esm/package.json should include "sideEffects": false to match the root package.json:

{
  "type": "module",
  "sideEffects": false
}

The stable 6.4.x release does not have a dist/esm/package.json at all, so tree-shaking works correctly there.

Is this issue blocking you?

This adds ~5MB of unused icon SVG data to the production bundle. Workaround: add a webpack module rule to explicitly mark @patternfly/react-icons as side-effect-free:

{
  test: /node_modules\/@patternfly\/react-icons\//,
  sideEffects: false,
}

What is your environment?

• webpack 5.104.1

• @patternfly/react-icons 6.5.0-prerelease.19

• Node.js 22

What is your product and what release date are you targeting?

Console 4.23

Any other information?

This likely affects all packages in the prerelease that added dist/esm/package.json for ESM "type": "module" support. Any package that relies on "sideEffects": false in its root package.json for tree-shaking will be broken if the nested dist/esm/package.json doesn't also include that field.

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Jira Issue: PF-3895

[coderabbitai]

🔗 Related PRs

#12140 - feat(TreeView): add support for disabled TreeViewListItems [merged]
#12222 - feat(react-icons): add newest rh brand icons [merged]
#12245 - feat(icons): add swap support for mapped rh-ui icons [merged]
#12265 - fix(icons): update internal import specifier [merged]
#12282 - fix: bump pf-core version 6.5.0-prerelease.55 [merged]

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