Angular: Skip the runtime source decorator when the docgen server produces snippets

[valentinpalkovic]

Follow-up to #35807.

What I did

With experimentalDocgenServer on, Angular produces two different code snippets for the same story: the story-docs snippet the server builds (a TypeScript host component) and the HTML template the runtime sourceDecorator computes in a post-render effect.
Both are pushed to the manager over the same SNIPPET_RENDERED channel event.
The Source block is safe because it reads the story-docs service directly and prefers it, but the Code panel keeps whichever event arrives last, so what it shows depends on which emit wins the race - while the panel is labelled ts either way.

This gates the decorator on the feature flag, the way @storybook/react already gates jsxDecorator, so exactly one producer is registered.

Before

experimentalDocgenServer: true

core/story-docs (server)          ┌────────────▶ Source block ─── serviceSnippet || snippet ──▶ TS host component
  TS host component ── beforeEach ┤
                  emitTransformCode└──┐
                                      ├── last SNIPPET_RENDERED wins ──▶ Code panel ──▶ whichever landed second
sourceDecorator ─────── useEffect ────┘
  <my-cmp [label]="…">
                  emitTransformCode

After

experimentalDocgenServer: true            experimentalDocgenServer: false

core/story-docs (server)                  sourceDecorator
  TS host component, or                     <my-cmp [label]="…">
  parameters.docs.source.originalSource
        │ beforeEach                              │ useEffect
        │ emitTransformCode                       │ emitTransformCode
        ├──▶ Source block                         ├──▶ Source block
        └──▶ Code panel                           └──▶ Code panel

The decision, in code/frameworks/angular-vite/src/client/docs/config.ts:

-const language = globalThis.FEATURES?.experimentalDocgenServer ? 'ts' : 'html';
+const useStaticServiceSnippets = globalThis.FEATURES?.experimentalDocgenServer === true;

 export const parameters: Parameters = {
   docs: {
     source: {
       type: SourceType.DYNAMIC,
-      language,
+      language: useStaticServiceSnippets ? 'ts' : 'html',
     },
   },
 };

-export const decorators: DecoratorFunction[] = [sourceDecorator];
+export const decorators: DecoratorFunction[] = useStaticServiceSnippets ? [] : [sourceDecorator];

What no longer holds

With the docgen server on, the runtime template no longer reaches the Source block or the Code panel at all, under any timing.
For a story the analyzer produces no snippet for, both surfaces now fall back to raw CSF (parameters.docs.source.originalSource, emitted by the same beforeEach hook) instead of the runtime template.
That is the same trade-off @storybook/react already makes under this flag.

With the flag off, nothing changes.

What a bad run looks like

Reverting the decorator gate while keeping the tests:

 FAIL  src/client/docs/config.test.ts > docs decorators > drops the runtime source decorator when the docgen server produces snippets
AssertionError: expected [ [Function sourceDecorator] ] to deeply equal []

- Expected
+ Received

- []
+ [
+   [Function sourceDecorator],
+ ]

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 the docgen-server sandbox: yarn task --task sandbox --start-from auto --template angular-vite/docgen-server-ts
2. The Code panel is opt-in, so add it to the sandbox's .storybook/preview.ts:

   export const parameters = { docs: { codePanel: true } };

3. Open Example / Button → Primary and select the Code panel.
4. The panel shows the TypeScript host component (a @Component class binding the story's args), highlighted as TypeScript. It must never show the <storybook-button …> HTML template, and it must not flip between the two across reloads or navigation between stories.
5. Open the Docs tab for the same component and expand Show code under the story. It shows the same TypeScript host component.
6. Run the stock sandbox: yarn task --task sandbox --start-from auto --template angular-vite/default-ts
7. Repeat steps 2-5. Both surfaces now show the <storybook-button …> HTML template, highlighted as HTML, exactly as before this PR.

Documentation

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

No documentation change: this is internal wiring behind the experimental experimentalDocgenServer flag, and the user-facing behaviour it describes (server snippets replace the runtime template) is what was already documented.

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📥 Commits

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📒 Files selected for processing (2)

• code/frameworks/angular-vite/src/client/docs/config.test.ts
• code/frameworks/angular-vite/src/client/docs/config.ts

---

Walkthrough

The Angular docs configuration now selects static TypeScript snippets when the experimental docgen server feature is exactly true. It removes the runtime source decorator in that mode and retains HTML snippets and the decorator otherwise. Tests cover enabled, disabled, and unset states.

Changes

Angular documentation snippet configuration

Layer / File(s)	Summary
Static snippet configuration and coverage code/frameworks/angular-vite/src/client/docs/config.ts, code/frameworks/angular-vite/src/client/docs/config.test.ts	The configuration selects ts and no decorators when FEATURES.experimentalDocgenServer is exactly true. Other states select html and retain sourceDecorator. Tests cover each state.

Merge Risk: ⚪ Minimal · up to 6e29d

This narrowly gates the runtime source decorator behind the experimental docgen-server flag, preserving existing behavior when the flag is off and preventing competing snippet producers when it is on; no actionable merge-blocking risk remains beyond normal checks and review.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

---

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Package Benchmarks

^{Commit: 6e29dc5, ran on 17 August 2026 at 07:00:46 UTC}

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

@storybook/cli

	Before	After	Difference
Dependency count	205	205	0
Self size	843 KB	843 KB	0 B
Dependency size	86.39 MB	86.53 MB	🚨 +141 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	84.86 MB	85.00 MB	🚨 +141 KB 🚨
Bundle Size Analyzer	Link	Link