Typescript: Exclude all dunderscore prefixed folders from production compilation

[mrginglymus]

Closes #35663

What I did

Production builds first transpile code to plain .d.ts files. There is an exclusion filter on this process to exclude test files, but it did not capture the file contianing this line:

storybook/code/core/src/core-server/__for-testing__/main.ts

Line 4 in 271a436

import type { StorybookConfig } from '@storybook/react-webpack5';

This transiently imports @storybook/react which reexports Args from storybook/internal/types. If this was found first(?) typescript would deem it the canonical import source and reference it in all usages.

I updated the exclusion glob to exclude any dunderscore prefixed directory.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

1. Run a canary
2. check storybook code contains no type references to @storybook/react.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary Release - 🚢 Released 8dbf69e

This pull request has been released as canary packages. Try it out in a new project or update an existing project with the commands below.

# For a new project
npx --yes --allow-remote=all https://pkg.pr.new/create-storybook@8dbf69e

# or for an existing project
npx --yes --allow-remote=all https://pkg.pr.new/storybook@8dbf69e upgrade

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	Fails
🚫	PR is not labeled with one of: ["qa:needed","qa:skip","qa:success"]

Generated by 🚫 dangerJS against 8dbf69e

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: b7fc67ec-562f-4a9c-a97b-952bafd7d07f

📥 Commits

Reviewing files that changed from the base of the PR and between 16f00d6 and 8dbf69e.

📒 Files selected for processing: 1

• scripts/build/utils/generate-types-rolldown.ts

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review.

Walkthrough

The declaration generator now uses the __*/ pattern to exclude directories whose names begin with double underscores.

Changes

Declaration type exclusions

Layer / File(s)	Summary
Broaden directory exclusions scripts/build/utils/generate-types-rolldown.ts	DTS_EXCLUDES replaces separate exclusions for __tests__, __mocks__, and __testfixtures__ with the __*/ pattern.

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to 8dbf6

The broadened exclusion covers nested double-underscore directories in production declaration generation. No merge-blocking issue was identified.

✨ Finishing Touches: 💡 1

🛠️ Fix failing CI checks: 💡

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• Create a new PR

📝 Generate docstrings

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[mrginglymus]

It works!

If there's a chance this could be backported to 10 that would be phenomenal.

[storybook-contribution-review]

🤖 I am the Storybook contribution review bot; a human maintainer approved this message before it was posted.
Review phase: Runtime verification (stage 3 of 3)

We are trying a three-stage automated review: architecture, code quality, and runtime verification. This message states which stages ran and which were skipped. A human maintainer approves each public message and makes the final decision. Please tell us whether the feedback and evidence are useful.

Hi @mrginglymus, thanks for tracing this leak back to the __for-testing__ fixture. That was a tricky one to find! All three review stages passed on commit 16f00d6: architecture, code quality and runtime verification. No stage was skipped.

Runtime verification. We ran a local production build of the storybook package (scripts/build/build-package.ts --prod, default rolldown-tsgo dts path) at the base commit 271a436 and at this PR's head:

• Base: dist/**/*.d.ts contains 165 import("@storybook/react") type references (162 × Args, 3 × Parameters), for example in the enhanceArgTypes signature. This is the leak from #35663, and a second clean build gave the same count.
• Head: the same build emits 0 of them. Those types now resolve through storybook/internal/types and storybook/internal/csf.
• No production types dropped: the d.ts file list (61 files), the set of emitted source modules (717) and the exported names of every entry file are identical at base and head. Every other changed line is one of these type-reference rewrites.

Architecture and code quality. Every __* directory under code/ holds only tests, mocks or fixtures, and a tsconfig exclude only drops files that no production module imports. So **/__*/** follows the repo convention and cannot remove a type that is in use. It is also simpler than keeping a list of directory names up to date.

One optional suggestion: a short comment on that line, for example // __tests__, __mocks__, __testfixtures__, …: test-only by convention, would record the convention the exclude now depends on. This is not required.

Scope of this check: we verified only the storybook package, which is the one named in #35663. We did not type-check the emitted d.ts in a consumer project. A maintainer makes the final decision on merging this PR and on your request for a 10.x backport.

[storybook-app-bot]

Package Benchmarks

^{Commit: 8dbf69e, ran on 15 October 2026 at 13:19:45 UTC}

No significant changes detected, all good. 👏