Angular: Declare story args the snippet markup binds by name

[valentinpalkovic]

Closes #

What I did

An Angular story-docs snippet is a complete host component, so a reader can paste it into an app and run it. That promise broke for any story that writes its own template by hand. Story markup runs against the story's props: args, so [label]="label" reads an arg - but the host the snippet ships had an empty class body, and the binding resolved to nothing.

The args a template names are now declared on that host, which restores the scope the story had without touching a character of the author's markup.

 @Component({
   selector: 'app-demo',
   imports: [ButtonComponent],
   template: `<sb-button [label]="label" [count]="count"></sb-button>`,
 })
-export class DemoComponent {}
+export class DemoComponent {
+  label = 'Save';
+  count = 3;
+}

An arg only earns a member when the markup can actually be referring to it:

                              ┌─ already inlined by argsToTemplate ──► skip
  merged args ──► named in ───┼─ shares a name with a bound output ──► skip, handler wins
                  the markup  ├─ value needs the story to run ───────► skip, warn instead
                              └─ otherwise ─────────────────────────► declare `name = value;`

The mixed shape is the one worth looking at, because exclude exists precisely so an author can hand-write one binding and expand the rest. count comes from the expansion and is inlined; label was written by hand and becomes a member:

export const PartlyHandWritten = {
  args: { count: 7 },
  render: (args) => ({
    props: args,
    template: `<sb-button ${argsToTemplate(args, { exclude: ['label'] })} [label]="label.toUpperCase()"></sb-button>`,
  }),
};

import { Component } from '@angular/core';
import { ButtonComponent } from './button.component';

@Component({
  selector: 'app-demo',
  imports: [ButtonComponent],
  template: `
    <sb-button
        [count]="7"
        (clicked)="clicked($event)"
        [label]="label.toUpperCase()">
    </sb-button>`,
})
export class DemoComponent {
  label = 'Save';
  clicked(event: unknown) {}
}

An arg whose value is a name only the story file knows cannot be moved to the host either, since nothing there imports it. Those keep the snippet they had and say what is missing, through the warning channel that already exists for unreadable source text:

[warning] Incomplete snippet: `LOCAL_LABEL` could not be resolved statically.

Two supporting changes came with it. evaluateArgLiteral is split out of evaluateArgExpression so a caller that has to emit code rather than an attribute can tell a real value from source text it merely printed. And a string value carrying a newline is now escaped rather than emitted raw, which was already wrong in the attribute position and would be a syntax error in a class member.

Whether an arg is named is decided by a bare word match on the markup. It over-declares in the rare case where an arg is named after an attribute the markup sets statically, which costs one unused member; missing one costs a snippet that does not compile.

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

Five cases in story-docs-build.test.ts cover declaring the args, skipping expanded ones, the output-name collision, declaring nothing when the markup names no args, and the warning. Two docgen-harness payload baselines move, and their diff is the fix.

Manual testing

Caution

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

1. Generate a sandbox: yarn task sandbox --template angular-vite/default-ts --start-from auto

2. In the sandbox, add a story that writes its own template and binds an arg by name:

   export const HandWritten = {
     args: { label: 'Save' },
     render: (args) => ({
       props: args,
       template: '<storybook-button [label]="label"></storybook-button>',
     }),
   };

3. Open that story's Docs page and expand the Code panel.

4. The snippet's DemoComponent should carry label = 'Save';. Copy the whole snippet into an Angular app and confirm it compiles and renders the label; before this change the button rendered with no label.

5. Change the story's template to use ${argsToTemplate(args)} instead, and confirm the snippet inlines the values into the bindings and declares no member for them.

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.

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• code/frameworks/angular-vite/src/docgen/story-docs-args.ts
• code/frameworks/angular-vite/src/docgen/story-docs-build.test.ts
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• code/frameworks/angular-vite/src/docgen/story-docs-markup.ts

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• code/frameworks/angular-vite/src/docgen/story-docs-markup.ts

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• code/frameworks/angular-vite/src/docgen/story-docs-args.ts
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• code/frameworks/angular-vite/src/docgen/story-docs-build.ts

---

Walkthrough

Angular story documentation now tracks expanded bindings, evaluates literal argument values, and declares referenced values on generated host components. Unresolved expressions produce warnings. Tests and snapshots cover the generated fields and binding cases.

Changes

Angular story argument handling

Layer / File(s)	Summary
Literal argument evaluation code/frameworks/angular-vite/src/docgen/story-docs-args.ts	evaluateArgLiteral evaluates standalone literal expressions. String output now escapes newline and carriage-return characters.
Markup expansion tracking code/frameworks/angular-vite/src/docgen/story-docs-markup.ts	Markup generation records argument names expanded by argsToTemplate and returns them through TemplateResult.expandedArgs.
Host field generation and validation code/frameworks/angular-vite/src/docgen/story-docs-build.ts, code/frameworks/angular-vite/src/docgen/story-docs-snippet.ts, code/frameworks/angular-vite/src/docgen/story-docs-build.test.ts, code/lib/docgen-harness/src/angular/story-docs/__testfixtures__/*	Referenced literal arguments generate host-component fields. Expanded arguments, output handlers, invalid identifiers, and unreferenced values are excluded. Unresolved values produce warnings. Tests and snapshots cover the generated output.

Sequence Diagram(s)

sequenceDiagram
  participant StoryDocsMarkup
  participant StoryDocsBuild
  participant EvaluateArgLiteral
  participant HostComponentSnippet
  StoryDocsMarkup->>StoryDocsBuild: return markup and expandedArgs
  StoryDocsBuild->>EvaluateArgLiteral: evaluate referenced argument nodes
  EvaluateArgLiteral-->>StoryDocsBuild: literal value or undefined
  StoryDocsBuild->>HostComponentSnippet: provide fields and output handlers
  HostComponentSnippet-->>StoryDocsBuild: generate host component snippet

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Possibly related PRs

• storybookjs/storybook#35796: Introduces the Angular static snippet generation flow extended by this change.
• storybookjs/storybook#35799: Adds the host-component snippet generation extended with template-referenced fields here.
• storybookjs/storybook#35888: Introduces argument evaluation logic extended by the literal evaluation changes here.

Merge Risk: 🟡 Moderate · up to c7cbb

Generated Angular documentation snippets can still omit required host handlers or fields for valid bindings and argument names, leaving copied examples uncompilable. Merge should wait for these cases to be fixed or explicitly accepted.

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---

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Inline comments:
In `@code/frameworks/angular-vite/src/docgen/story-docs-build.ts`:
- Around line 244-246: Update the output-binding detection around
snippetMeta.outputs and userMarkup.markup to recognize optional whitespace
between the binding name and “=”, while preserving existing matches without
whitespace. Add a regression test covering markup such as “(clicked) = ...” and
verify the generated host includes the clicked handler.
- Around line 279-291: Update the markup matching logic in the shape-argument
processing loop to escape each name before constructing the regular expression
and use identifier boundaries that treat $ and _ as part of identifiers.
Preserve matching for ordinary names and add regression coverage for bindings
named $label and label$.

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📒 Files selected for processing (7)

• code/frameworks/angular-vite/src/docgen/story-docs-args.ts
• code/frameworks/angular-vite/src/docgen/story-docs-build.test.ts
• code/frameworks/angular-vite/src/docgen/story-docs-build.ts
• code/frameworks/angular-vite/src/docgen/story-docs-markup.ts
• code/frameworks/angular-vite/src/docgen/story-docs-snippet.ts
• code/lib/docgen-harness/src/angular/story-docs/__testfixtures__/meta-render/story-docs.payload.snapshot
• code/lib/docgen-harness/src/angular/story-docs/__testfixtures__/render-function/story-docs.payload.snapshot

[huang-julien]

LGTM