Maintenance: Centralize supported file extension lists

[valentinpalkovic]

What I did

Follow-up to #34692. Addresses @Sidnioulz's review feedback that the codebase had several inline extension lists with subtle drift between similar tasks.

Introduces code/core/src/shared/constants/extensions.ts with four task-named constants:

Constant	Purpose	Extensions
jsModuleExtensions	JS-only module loading	.mjs .js .cjs
jsTsSourceExtensions	JS/TS source files for parsers/bundlers	.ts .tsx .js .jsx .mjs .cjs
storybookConfigExtensions	Storybook config files (main, preview, manager)	.js .ts .jsx .tsx .mjs .mts .mtsx .cjs .cts .ctsx
userModuleExtensions	User code for sb.mock() (incl. JSON, SFC)	.js .mjs .cjs .ts .tsx .jsx .json .vue .svelte

Migrates five consumers to import from the central module:

• common/utils/interpret-files.ts → storybookConfigExtensions (keeps the public supportedExtensions re-export used by the React renderer's component manifest)
• mocking-utils/resolve.ts → userModuleExtensions
• common/utils/validate-config.ts → jsModuleExtensions
• shared/utils/module.ts → jsModuleExtensions
• core-server/change-detection/parser-registry/builtins.ts → jsTsSourceExtensions

Three lists were intentionally left inline because they serve different tasks with subtle behavioral coupling:

• bin/loader.ts — runtime ESM/CJS hook loader uses a narrower set (no .mtsx/.ctsx)
• builder-manager/index.ts — esbuild bundler config, changing it would alter what esbuild resolves in the manager bundle
• telemetry/get-application-file-count.ts — git ls-files glob using a no-dot format

No behavioral changes; pure deduplication.

Why now

Reviewer-requested follow-up to #34692 (resolve → oxc-resolver migration). Doing it as a separate PR keeps the dependency migration focused and the refactor reviewable on its own.

Stacking

This PR is stacked on top of #34692. Once #34692 merges, this auto-rebases against next.

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

Existing tests cover all five migrated consumers. The refactor is a pure substitution (each new constant equals the inline list it replaces, byte-for-byte).

Manual testing

yarn nx check core and yarn nx check react both pass. Lint clean on all touched files.

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
• Make sure this PR contains one of the labels below: cleanup or maintenance.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor
  • Centralized file-extension handling across tooling and config resolution for more consistent behavior.
  • Broader file-type support (including .astro) for module, mock and config resolution.
  • Expect fewer resolution/validation errors and more reliable loading of frameworks, imports, and mocks.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 62fff131-9c53-4557-9dcb-a117530a3038

📥 Commits

Reviewing files that changed from the base of the PR and between f692fe6 and 4514507.

📒 Files selected for processing (1)

• code/core/src/shared/constants/extensions.ts

✅ Files skipped from review due to trivial changes (1)

• code/core/src/shared/constants/extensions.ts

---

📝 Walkthrough

Walkthrough

Centralizes multiple hardcoded file-extension lists into a new shared constants module and updates module resolution, Storybook config detection, import parsing, and mock resolution to use those shared extension arrays.

Changes

Extension Consolidation

Layer / File(s)	Summary
Shared extension constants foundation code/core/src/shared/constants/extensions.ts	New module exports four as const extension lists: jsModuleExtensions, jsTsSourceExtensions, storybookConfigExtensions, and userModuleExtensions.
Module resolution with shared constants code/core/src/shared/utils/module.ts, code/core/src/common/utils/validate-config.ts	safeResolveModule and framework preset resolution now default to jsModuleExtensions instead of local hardcoded arrays.
Storybook config file interpretation code/core/src/common/utils/interpret-files.ts	supportedExtensions now references storybookConfigExtensions rather than a file-local hardcoded list.
Import parser extension configuration code/core/src/core-server/change-detection/parser-registry/builtins.ts	oxcImportParser.extensions switches to jsTsSourceExtensions for JS/TS source detection during import analysis.
Mock path resolution with user extensions code/core/src/mocking-utils/resolve.ts	externalResolver and resolveWithExtensions iterate over userModuleExtensions to include JSON and component file types when resolving mocks.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• storybookjs/storybook#32905: Also touches interpret-files.ts and extension-based resolution, overlapping with changes to where supported extensions are defined.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[Sidnioulz]

Thanks so much for that!

WDYT about my suggestion on the other PR to also add e.g. Solid or Astro? Like Vue and Svelte, these are supported when the relevant framework is used.

[valentinpalkovic]

Has Solid its own file extension and DSL? I'm okay with adding astro for sure!

[storybook-app-bot]

Package Benchmarks

^{Commit: 4514507, ran on 22 May 2026 at 11:03:49 UTC}

The following packages have significant changes to their size or dependencies:

@storybook/builder-webpack5

	Before	After	Difference
Dependency count	184	184	0
Self size	79 KB	79 KB	0 B
Dependency size	33.35 MB	33.36 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/angular

	Before	After	Difference
Dependency count	185	185	0
Self size	160 KB	160 KB	🎉 -54 B 🎉
Dependency size	30.73 MB	30.75 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/ember

	Before	After	Difference
Dependency count	188	188	0
Self size	15 KB	15 KB	🚨 +18 B 🚨
Dependency size	30.07 MB	30.08 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/nextjs

	Before	After	Difference
Dependency count	534	534	0
Self size	662 KB	662 KB	🎉 -120 B 🎉
Dependency size	61.51 MB	61.52 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/react-webpack5

	Before	After	Difference
Dependency count	271	271	0
Self size	23 KB	23 KB	🎉 -12 B 🎉
Dependency size	46.05 MB	46.06 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/server-webpack5

	Before	After	Difference
Dependency count	196	196	0
Self size	16 KB	16 KB	0 B
Dependency size	34.61 MB	34.63 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/preset-react-webpack

	Before	After	Difference
Dependency count	164	164	0
Self size	18 KB	18 KB	0 B
Dependency size	32.35 MB	32.37 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link