Angular: Declare style preprocessors as optional peers and name the missing one by valentinpalkovic · Pull Request #36098 · storybookjs/storybook

valentinpalkovic · 2026-08-31T10:39:06Z

What I did

An Angular project that compiles .scss gets its sass implementation from the Angular builder, and @storybook/angular-vite declared nothing at all.
Vite does not bundle a preprocessor either - it resolves one from the Vite root upwards - so whether Storybook could compile SCSS came down to whether the package manager happened to hoist the copy @angular/build installs for itself.
When it did not, the user got Vite's own diagnostic pointing at sass-embedded, which is not the package they are missing.

This declares sass, sass-embedded and less as optional peers, and adds a pre-flight check that names the package the user actually has to install.

Why a peer and not a dependency

This is the one part that is easy to get backwards, so it is worth spelling out:

dependency of @storybook/angular-vite  ->  lands in @storybook/angular-vite/node_modules  ->  Vite never looks there
optional peer                          ->  lands at the consumer root                     ->  exactly where loadPreprocessorPath resolves from

Hence the weaker-looking mechanism is the one that works.
Optional, so nobody writing plain CSS is asked to install a compiler.

Where the check sits

   .scss import
        |
        v
   storybook-angular-vite-style-preprocessor-check     enforce: 'pre'
        |   looks for `sass` in `node_modules` from config.root upwards,
        |   then from Vite's own directory - the same two places, same order
        |
        +-- present ---------> pass through, vite:css compiles as before
        |
        +-- absent ----------> throw AngularMissingStylePreprocessorError
        v
   vite:css        (its own `sass-embedded` message is now unreachable)

It asks whether the package is present, not whether require.resolve succeeds on it.
Vite loads preprocessors with its own conditions, so a package whose exports map declares no require condition resolves for Vite and throws for createRequire.
Reading that as missing would abort a build that in fact works, and this check aborts the build, so it has to be at least as permissive as Vite is.

The createRequire arm survives only for Yarn PnP, which has no node_modules directories to walk. There the same distinction has to be made from the error code, because a refused entry point means the package is installed:

} catch (error) {
  // Node found the package and refused only its entry point, because the `exports` map has no
  // `require` condition. Vite resolves with its own conditions, so that is present, not missing.
  return (error as NodeJS.ErrnoException)?.code === 'ERR_PACKAGE_PATH_NOT_EXPORTED';
}

enforce: 'pre' is load-bearing rather than decorative.
Without it vite:css transforms first and the user reads the old message again, while every unit test on the plugin still passes.
Hence one test asserts the ordering and another asserts that viteFinal registers the plugin at all:

it('runs ahead of `vite:css`, whose message it exists to replace', () => {
  expect(stylePreprocessorCheckPlugin().enforce).toBe('pre');
});

Before

Vite's diagnostic on a project whose root cannot reach sass, from the reproduction repository in #36012:

[vite:css] Preprocessor dependency "sass-embedded" not found. Did you install it? Try `npm install -D sass-embedded`.
file: .../nosass/src/style.scss

sass-embedded is a misdirection: loadSassPackage tries it first and rethrows its error when both are missing, so the user installs a package that was never the problem.

After

Captured from the error class at this head:

Cannot compile '/app/src/styles.scss': the 'sass' package is not installed where Vite can load it.

Add it to your project:

  npm install --save-dev sass

Vite resolves a CSS preprocessor from your project directory upwards, so a copy installed deeper in the tree - such as the one Angular's builders bring in for themselves - is invisible to it. That is why a project which compiles with 'ng build' can still fail here.

'sass-embedded' works as well, if you would rather use that.

More info: https://storybook.js.org/docs/get-started/frameworks/angular-vite?ref=error

.less gets the same shape with less and no alternative.

What this does not fix

Gap 2 of #36012, the sass resolution importer that @angular-devkit/build-angular installs and this preset does not, is untouched.
A workspace-root-relative @use therefore still fails.
It is independent of everything here and I would rather keep it in its own PR, so this one is Refs and not Closes.

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

Caution

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Reproducing this needs a node_modules layout where sass is not hoisted, which a generated sandbox will not give you, so this uses the repository from the issue.

git clone https://github.com/PhilippMDoerner/NimStoryFont && cd NimStoryFont/frontend
npm ci, then npm ls sass. Its committed lockfile declares @angular/build: ^22.1.3 and no top-level sass, so the only copy sits under node_modules/@angular/build/node_modules.
Migrate the project onto angular-vite with npx storybook automigrate angular-to-angular-vite, against a canary of this PR.
Start Storybook and open any SCSS-styled component.
Expected: the build fails naming sass, with the npm install --save-dev sass line from the message above. On next today it names sass-embedded instead.
npm install --save-dev sass, restart Storybook, open the same component.
Expected: it renders.
Shorter variant if cloning is inconvenient: in any Angular app already on angular-vite, rm -rf node_modules/sass node_modules/sass-embedded and repeat steps 4 and 5.

Documentation

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

No docs change here.
The three peers are optional and the error links to the angular-vite docs page, so nothing in the docs is currently wrong.
Happy to add a short "styling" note to that page if you would rather have it in this PR - WDYT?

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

This pull request has been released as version 0.0.0-pr-36098-sha-e4b924c1. Try it out in a new sandbox by running npx storybook@0.0.0-pr-36098-sha-e4b924c1 sandbox or in an existing project with npx storybook@0.0.0-pr-36098-sha-e4b924c1 upgrade.

More information


Published version	`0.0.0-pr-36098-sha-e4b924c1`
Triggered by	@huang-julien
Repository	storybookjs/storybook
Branch	`agent/sto-78-angular-vite-sass`
Commit	`e4b924c1`
Datetime	Tue Sep 1 12:23:35 UTC 2026 (`1788265415`)
Workflow run	33507407142

To request a new release of this pull request, mention the @storybookjs/core team.

core team members can create a new canary release here or locally with gh workflow run --repo storybookjs/storybook publish.yml --field pr=36098

An Angular project gets `sass` as a dependency of `@angular/build`, and npm is free to leave that copy under `node_modules/@angular/build/node_modules`. Vite's `loadPreprocessorPath` only searches from the Vite root upwards, so it never sees it, and every SCSS-styled component 500s. The message the user got was wrong on top of that: `loadSassPackage` tries `sass-embedded` first and rethrows *its* error, so a project that needs `sass` was told to install `sass-embedded`. A pre-enforced plugin now asks the same question from the same directory Vite does, before `vite:css` runs, and fails with the package to install. `sass` and `less` are declared as optional peers so the contract is visible in the manifest.

The eight tests for the check all built the plugin directly, so deleting `enforce: 'pre'` or dropping the plugin from `viteFinal` left the suite green while the user saw Vite's original `sass-embedded` message again. Ordering and registration are the whole feature; two tests now hold them. Also declare `sass-embedded` as an optional peer, since the check accepts it and the error message offers it, and drop a `return;` the guard above already covers.

Yarn Berry stores a workspace package's peerDependencies and peerDependenciesMeta in yarn.lock, so declaring the sass, sass-embedded and less peers made 'yarn install --immutable' fail with YN0028.

…copy lives 'less' is an optional peer of '@angular/build', not a dependency of it, so the message claimed something untrue for every '.less' project. The generic wording holds for both packages.

The check aborted the build whenever `createRequire().resolve()` failed from the Vite root, but that is a stricter question than the one Vite answers. Vite's `loadPreprocessorPath` resolves with Vite's own conditions, and falls back to Vite's install directory when the root cannot see the package, so two layouts Vite compiles were reported as a missing install: exports map with no `require` condition -> ERR_PACKAGE_PATH_NOT_EXPORTED copy reachable only from Vite's own dir -> MODULE_NOT_FOUND Both are false aborts, which is the one failure mode this check must not have. It now asks whether the package is present, from the Vite root and from Vite's directory, and keeps the resolver call as the Yarn PnP arm where there are no `node_modules` directories to walk.

Under Yarn PnP there are no `node_modules` directories to walk, so the resolver is the only witness the check has. It treated every resolver failure as a missing install, but Node reports two different things: MODULE_NOT_FOUND no such package ERR_PACKAGE_PATH_NOT_EXPORTED the package is installed, and its `exports` map has no `require` condition Vite resolves preprocessors with its own conditions, so the second one is a package Vite loads and this check aborted the build over. `sass@1.85.0` still ships a `require` condition, so this closes a trap rather than a live failure. The test fixture could not express the difference before: its resolver mock threw one undifferentiated error, which is the shape of the implementation rather than the shape of Node.

`enforce: 'pre'` puts this hook ahead of every module in the graph, so an unfiltered `transform` was called once per module to answer a question that only stylesheets can raise. Declaring `transform.filter` moves the same predicate in front of the JS boundary, where Rolldown evaluates it natively. The filter is the regex the handler already gated on, so nothing that was checked before stops being checked. The handler keeps its own copy, because a filter is an optimization Vite may skip, never the guard the error depends on.

coderabbitai · 2026-09-01T10:39:48Z

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Walkthrough

Changes

The Angular Vite preset now validates Sass, Sass Embedded, and Less before stylesheet processing. It resolves packages, caches availability checks, excludes Vite special-query requests, and reports missing packages with installation guidance.

Sequence Diagram(s)

sequenceDiagram
  participant AngularVitePreset
  participant StylePreprocessorCheckPlugin
  participant PackageResolution
  participant AngularMissingStylePreprocessorError
  AngularVitePreset->>StylePreprocessorCheckPlugin: register validation plugin
  StylePreprocessorCheckPlugin->>PackageResolution: resolve required preprocessor
  PackageResolution-->>StylePreprocessorCheckPlugin: return package availability
  StylePreprocessorCheckPlugin->>AngularMissingStylePreprocessorError: create diagnostic when missing
  AngularMissingStylePreprocessorError-->>StylePreprocessorCheckPlugin: throw framework error

Merge Risk: 🔵 Low · up to e4b92

This PR adds optional Sass/Less peer dependencies and clearer preflight diagnostics, but its peer ranges may allow Sass versions incompatible with Vite 8, which could cause SCSS builds to fail for affected consumers. It is mergeable with explicit owner awareness or a follow-up to constrain supported versions.

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Actionable comments posted: 2

🧹 Nitpick comments (1)

code/frameworks/angular-vite/src/preset.test.ts (1)
184-208: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Move mock implementations into beforeEach.

transformStyle() configures existsSync and createRequire mocks when each test invokes it. Move these implementations to beforeEach. Keep only test-specific mock state in transformStyle().

As per coding guidelines: “Implement mock behaviors in beforeEach blocks in Vitest tests” and “Avoid mock implementations outside of beforeEach blocks in Vitest tests.”
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In `@code/frameworks/angular-vite/src/preset.test.ts` around lines 184 - 208, Move
the existsSync and createRequire mockImplementation setup from transformStyle()
into the test suite’s beforeEach block, preserving their existing behavior and
access to the shared mock state. Keep transformStyle() limited to configuring
test-specific state and inputs.
Source: Coding guidelines

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Inline comments:
In `@code/frameworks/angular-vite/package.json`:
- Around line 109-110: Update the sass and sass-embedded peer dependency ranges
in package.json from ^1.0.0 to ^1.70.0, keeping both packages aligned with the
required Sass API compatibility.

In `@code/frameworks/angular-vite/src/preset.ts`:
- Line 344: Update STYLE_PREPROCESSOR_ID to exclude Vite’s ?raw, ?url, ?worker,
and ?sharedworker stylesheet requests while preserving normal preprocessor
matching, and add a regression test covering button.scss?raw.

---

Nitpick comments:
In `@code/frameworks/angular-vite/src/preset.test.ts`:
- Around line 184-208: Move the existsSync and createRequire mockImplementation
setup from transformStyle() into the test suite’s beforeEach block, preserving
their existing behavior and access to the shared mock state. Keep
transformStyle() limited to configuring test-specific state and inputs.

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A `.scss?raw` import is read as an asset and never handed to a preprocessor, so aborting the build for a missing one refused a project that compiles.

storybook-app-bot · 2026-09-01T11:36:55Z

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^{Commit: e4b924c, ran on 1 September 2026 at 11:36:51 UTC}

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

`storybook`

	Before	After	Difference
Dependency count	73	73	0
Self size	22.16 MB	22.05 MB	🎉 -114 KB 🎉
Dependency size	31.21 MB	31.21 MB	0 B
Bundle Size Analyzer	Link	Link

`@storybook/cli`

	Before	After	Difference
Dependency count	205	205	0
Self size	869 KB	869 KB	🚨 +84 B 🚨
Dependency size	87.74 MB	87.63 MB	🎉 -114 KB 🎉
Bundle Size Analyzer	Link	Link

`@storybook/codemod`

	Before	After	Difference
Dependency count	198	198	0
Self size	44 KB	44 KB	0 B
Dependency size	86.21 MB	86.10 MB	🎉 -114 KB 🎉
Bundle Size Analyzer	Link	Link

`create-storybook`

	Before	After	Difference
Dependency count	74	74	0
Self size	1.09 MB	1.09 MB	0 B
Dependency size	53.38 MB	53.26 MB	🎉 -114 KB 🎉
Bundle Size Analyzer	node	node

valentinpalkovic and others added 4 commits August 31, 2026 11:48

Angular: Record the new optional peers in the lockfile

4d3ccbe

Yarn Berry stores a workspace package's peerDependencies and peerDependenciesMeta in yarn.lock, so declaring the sass, sass-embedded and less peers made 'yarn install --immutable' fail with YN0028.

Angular: Correct where the missing preprocessor explanation says the …

9ea8b58

…copy lives 'less' is an optional peer of '@angular/build', not a dependency of it, so the message claimed something untrue for every '.less' project. The generic wording holds for both packages.

valentinpalkovic commented Aug 31, 2026

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Angular: Filter the options plugin transform to the preview file #36106

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Angular: Skip the preprocessor check for Vite's asset queries

e4b924c

A `.scss?raw` import is read as an asset and never handed to a preprocessor, so aborting the build for a missing one refused a project that compiles.

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Release: Prerelease 10.6.0-beta.2 #36113

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Angular: Declare style preprocessors as optional peers and name the missing one - #36098

Angular: Declare style preprocessors as optional peers and name the missing one#36098
valentinpalkovic merged 11 commits into
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What I did

Why a peer and not a dependency

Where the check sits

Before

After

What this does not fix

Checklist for Contributors

Testing

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

Manual testing

Documentation

Checklist for Maintainers

🦋 Canary release

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Walkthrough

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Sequence Diagram(s)

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Package Benchmarks

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@storybook/codemod

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