feat(plop): add test and vrt retrofit generators

Add standalone `test` and `vrt` plop generators that retrofit an existing
2nd-gen component with unit + a11y test files and a Chromatic VRT story.
Component-side actions are unchanged from the base scaffolder.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: aramos-adobe

2nd-gen/scaffolding/README.md

@@ -1,117 +1,144 @@
 # 2nd-gen scaffolding
 
-A [plop](https://plopjs.com/) generator that produces the deterministic file
-skeleton for a 2nd-gen component: the `core` base layer, the `swc` concrete
-layer, and the stories, docs, and test files that go with them.
+A [plop](https://plopjs.com/) scaffolder that produces the deterministic file
+skeletons for 2nd-gen components: the component itself, and the **test** and
+**VRT** files that go with it.
 
-The generator exists to take the mechanical, every-time-identical part of
-Phase 2 (`migration-setup`) off the critical path. It writes the boilerplate so
-a human or an agent only has to apply the decisions that actually differ between
-components: the base-vs-concrete property split, the real Spectrum 2 tokens, the
-variant and state API, and the prose in the docs page.
+The generators exist to take the mechanical, every-time-identical part of
+authoring off the critical path. They write the boilerplate so a human or an
+agent only has to apply the decisions that actually differ between components:
+the base-vs-concrete property split, the real Spectrum 2 tokens, the
+variant/state API, the assertions, and the docs prose.
+
+## Generators
+
+| Generator   | Scaffolds                                               | Target                            |
+| ----------- | ------------------------------------------------------- | --------------------------------- |
+| `component` | Core base + SWC concrete + stories, docs, tests         | new component (`core` + `swc`)    |
+| `test`      | Unit (`*.test.ts`) + a11y (`*.a11y.spec.ts`) test files | **existing** component (retrofit) |
+| `vrt`       | A Chromatic VRT story (`test/vrt/<name>.vrt.ts`)        | **existing** component (retrofit) |
+
+`component` always emits a baseline `test` + `a11y` file. Use the standalone
+`test` and `vrt` generators to add coverage to a component that already exists
+(for example, one migrated before these generators landed) — `vrt` in particular
+fills a gap, since the `component` skeleton ships no `.vrt.ts`.
 
 ## Usage
 
 ### Interactive (humans)
 
 ```bash
 yarn plop component
+yarn plop test
+yarn plop vrt
 ```
 
-You will be prompted for a component name. Enter it in any form: `action-button`,
-`actionButton`, `Action Button`, or even `sp-action-button` (the `sp-`/`swc-`
-prefix is stripped). The name is normalized by the built-in case helpers, so the
-output is identical regardless of how you type it.
+You are prompted for a name (enter it in any form: `action-button`,
+`actionButton`, `Action Button`, or `sp-action-button` — the `sp-`/`swc-`
+prefix is stripped and the case helpers normalize the rest).
 
 ### Headless (agents, scripts, CI)
 
-Pass the name as a bypass argument and `--force` to skip the interactive
-confirmation:
+Pass the name as a positional bypass argument, plus `--force`:
 
 ```bash
 yarn plop component "action-button" --force
+yarn plop test "action-button" --force
+yarn plop vrt "action-button" --force
 ```
 
-## What it generates
+Each generator emits a single fixed scaffold (a permutation-grid + forced-colors
+story for `vrt`, and a play-function + a11y-snapshot pair for `test`). The output
+is lint-clean and formatted; `TODO`s mark where the author fills in the
+component-specific detail.
 
-For a component named `action-button`:
+## Retrofit contract (`test`, `vrt`)
 
-```
-2nd-gen/packages/core/components/action-button/
-  ActionButton.types.ts     VALID_SIZES + Size type
-  ActionButton.base.ts       abstract base class (SizedMixin + SpectrumElement)
-  index.ts                   re-exports base + types
-
-2nd-gen/packages/swc/components/action-button/
-  ActionButton.ts            concrete class, render(), styles getter
-  index.ts                   re-exports the concrete class
-  swc-action-button.ts       defineElement registration + tag-name map
-  action-button.css          :host + .swc-ActionButton block, token() scaffolding
-  action-button.mdx          per-unit docs page (DocsHeader/Canvas/DocsFooter)
-  stories/action-button.stories.ts   Playground/Overview/Anatomy/Sizes/States/Accessibility
-  test/action-button.test.ts          Vitest play function reusing the Overview story
-  test/action-button.a11y.spec.ts      Playwright ARIA-snapshot accessibility test
-```
+`test` and `vrt` add files to a component that **already exists**. They:
+
+- **Guard first.** If `2nd-gen/packages/swc/components/<name>/` is missing, the
+  generator aborts with a clear message before writing anything (a typo cannot
+  silently scaffold tests for a non-existent component).
+- **Never clobber by default.** The `add` actions use `skipIfExists`, so an
+  existing test/VRT file is left untouched. Pass `--force` to overwrite, or
+  delete the file first to regenerate it.
+- **Stay scoped.** They format only the `test/` (or `test/vrt/`) subtree they
+  wrote, leaving the surrounding component files untouched.
 
-It also wires the core package's `exports` map: the `swc` package uses wildcard
-exports and needs no edit, but `@spectrum-web-components/core` uses explicit
-per-component entries, so the generator adds `./components/action-button` and
-`./components/action-button/index.js` and re-sorts the `exports` keys
-alphabetically (a minimal, deterministic diff). Finally it runs Prettier on the
-two new directories so the output lands pre-formatted.
+## What gets wired automatically
 
-## What it intentionally does NOT do
+- **Core `exports` + `typesVersions`.** The SWC package (`@adobe/spectrum-wc`)
+  uses wildcard `exports`, so a new component needs no package.json edit there.
+  The core package (`@spectrum-web-components/core`) uses explicit per-component
+  entries, so the `component` generator adds both the `exports` and the matching
+  `typesVersions` entry for the new component and re-sorts the keys (a minimal,
+  deterministic diff). The `test`/`vrt` generators touch no package.json.
+- **Formatting.** Each generator runs Prettier on the directories it wrote.
 
-The skeleton is a starting point, not a finished component. After generating,
-follow `migration-setup` and the later migration phases to:
+## Custom-element registration
 
-- Move properties, methods, and types from 1st-gen into the base and concrete
-  classes (Phase 3, `migration-api`).
-- Implement semantics, ARIA, and keyboard support (Phase 4, `migration-a11y`).
-- Replace the placeholder CSS with migrated Spectrum 2 tokens (Phase 5,
-  `migration-styling`).
-- Flesh out the tests and stories (Phase 6, `migration-testing`).
-- Write the docs prose and any `migration-guide.mdx` (Phase 7,
-  `migration-documentation`; the consumer guide is owned by the
-  `consumer-migration-guide` skill, so it is not scaffolded here).
+Components are custom elements; the split matters:
 
-Every generated file contains `TODO`/placeholder markers showing where this work
-goes.
+- `index.ts` re-exports the class only (no registration).
+- `swc-<tag>.ts` is the side-effectful entry: it calls
+  `defineElement('swc-<tag>', Class)` (from `@adobe/spectrum-wc-core/element`)
+  and augments `HTMLElementTagNameMap`.
+
+## What the generators intentionally do NOT do
+
+The skeletons are starting points, not finished components. After generating,
+follow `migration-setup` and the later migration phases (or the `vrt-authoring`
+skill for VRT) to move properties/types into the classes, implement semantics and
+ARIA, migrate CSS to Spectrum 2 tokens, and flesh out the tests, VRT grids, and
+docs prose. Every generated file contains `TODO`/placeholder markers.
 
 ## Conventions the templates encode
 
-These mirror the `badge` reference component and the project rules in `.ai/`:
+These mirror the `badge` and `button` reference components and the project rules
+in `.ai/`:
 
 - **Two-layer architecture.** Shared, non-visual API lives on the core base
   class; visual and version-specific API lives on the concrete `swc` class.
-- **Sizing via host attribute.** `SizedMixin` reflects `size` to the host, so
-  size is styled with `:host([size="..."])` selectors, never a modifier class.
-- **Public styling API.** Custom properties are exposed as `--swc-<name>-*` with
-  a `token()` fallback.
+- **Sizing via host attribute.** `SizedMixin` reflects `size` to the host, styled
+  with `:host([size="..."])` selectors, never a modifier class.
+- **Public styling API.** Custom properties exposed as `--swc-<name>-*` with a
+  `token()` fallback.
 - **BEM-ish class block.** The render root carries `swc-<PascalCase>`.
-- **Stories + per-unit MDX.** The Playground is tagged `['dev']` (not
-  `['autodocs', 'dev']`) because the generated `.mdx` is the docs page; each
+- **Stories + per-unit MDX.** The Playground is tagged `['dev']`; each
   section-tagged story is referenced from the MDX via `<Canvas of={...} />`.
+- **Sentence-case titles.** Storybook titles are sentence case (`Action button`),
+  matching the project's title rule.
 
 ## Editing the templates
 
-Templates live in `templates/component/` as Handlebars (`.hbs`) files. Name
-derivations use plop's built-in case helpers plus two custom helpers defined in
+Templates live under `templates/` as Handlebars (`.hbs`) files, grouped by
+generator:
+
+```
+templates/
+  component/{core,swc}/*.hbs   the component skeleton
+  test/*.hbs                   the standalone test + a11y files
+  vrt/vrt.ts.hbs               the VRT story
+```
+
+Name derivations use plop's built-in case helpers plus custom helpers defined in
 `plopfile.js`:
 
 | Helper                  | `action-button` renders as |
 | ----------------------- | -------------------------- |
 | `{{dashCase name}}`     | `action-button`            |
 | `{{pascalCase name}}`   | `ActionButton`             |
 | `{{constantCase name}}` | `ACTION_BUTTON`            |
-| `{{titleName name}}`    | `Action Button` (custom)   |
+| `{{titleName name}}`    | `Action button` (custom)   |
 | `{{lb}}` / `{{rb}}`     | `{` / `}` (custom)         |
 
-`titleName` produces the space-separated proper-noun title used for Storybook
+`titleName` produces the space-separated sentence-case title used for Storybook
 titles; plop's built-in `titleCase` keeps the dash (`Action-Button`) and must not
 be used for titles. `lb`/`rb` emit literal braces in `.mdx` templates, where a
-bare `{` next to a `{{helper}}` would otherwise be parsed as Handlebars.
+`{` next to a `{{helper}}` would otherwise be parsed as Handlebars.
 
 When you change the file layout, naming, or wiring, update both the templates and
-the `add` actions in `plopfile.js`, then regenerate a throwaway component and run
-`yarn lint` / `yarn lint:css` on it to confirm the output still passes.
+the actions in `plopfile.js`, then regenerate a throwaway component and run
+`yarn lint`, `yarn lint:css`, and `yarn lint:docs-pages` on it to confirm the
+output still passes. Delete the throwaway component and revert
+`2nd-gen/packages/core/package.json` afterward.

2nd-gen/scaffolding/plopfile.js

@@ -22,20 +22,26 @@ const CORE_COMPONENTS = '2nd-gen/packages/core/components';
 const SWC_COMPONENTS = '2nd-gen/packages/swc/components';
 
 /**
- * 2nd-gen component scaffolder.
+ * 2nd-gen scaffolder.
  *
  * Mirrors the file layout and conventions described by the migration skills
- * (`migration-setup`, `stories-format`, `stories-documentation`) and the `badge`
- * reference component. It produces the deterministic Phase 2 skeleton so the
- * migration-setup skill only has to apply plan-specific architecture decisions
- * (the base-vs-concrete split) rather than author every file by hand.
+ * (`migration-setup`, `stories-format`, `stories-documentation`, `vrt-authoring`)
+ * and the `badge` / `button` reference units. It produces the deterministic
+ * skeleton so a human or an agent only has to apply the decisions that actually
+ * differ between units (the base-vs-concrete split, the real API, the
+ * assertions) rather than author every file by hand.
+ *
+ * Generators:
+ *   component — a custom-element component (core base + swc concrete + docs/tests)
+ *   test      — retrofit an existing component with unit + a11y test files
+ *   vrt       — retrofit an existing component with a Chromatic VRT story
  *
  * Built-in plop case helpers do most name derivation, plus the custom
- * `titleName` helper for the space-separated proper-noun title:
+ * `titleName` helper for the space-separated sentence-case title:
  *   {{dashCase name}}     -> action-button   (kebab tag, dir, css, file names)
  *   {{pascalCase name}}   -> ActionButton    (class names, CSS BEM block)
  *   {{constantCase name}} -> ACTION_BUTTON   (exported constant prefixes)
- *   {{titleName name}}    -> Action Button   (Storybook title, proper noun)
+ *   {{titleName name}}    -> Action button    (Storybook title, sentence case)
  *
  * @param {import('plop').NodePlopAPI} plop
  */
@@ -54,19 +60,37 @@ export default function (plop) {
   plop.setHelper('lb', () => '{');
   plop.setHelper('rb', () => '}');
 
-  // Space-separated Title Case for human-facing labels (Storybook titles,
-  // describe blocks, prose). plop's built-in `titleCase` keeps the dash
-  // ("action-button" -> "Action-Button"), but Spectrum treats component names
-  // as proper nouns rendered with spaces ("Action Button").
-  plop.setHelper('titleName', (text) =>
-    String(text)
+  // Space-separated sentence-case label for human-facing text (Storybook
+  // titles, describe blocks, prose). Spectrum titles are sentence case:
+  // capitalize only the first word ("action-button" -> "Action button").
+  // Authors re-capitalize any acronyms or proper nouns the scaffold can't know.
+  // plop's built-in `titleCase` can't do this (it keeps the dash and caps every
+  // word).
+  plop.setHelper('titleName', (text) => {
+    const words = String(text)
       .replace(/^(sp|swc)-/i, '')
       .replace(/([a-z0-9])([A-Z])/g, '$1 $2') // split camelCase
       .split(/[-_\s]+/)
       .filter(Boolean)
-      .map((word) => word.charAt(0).toUpperCase() + word.slice(1))
-      .join(' ')
-  );
+      .map((word) => word.toLowerCase());
+    if (words.length === 0) {
+      return '';
+    }
+    words[0] = words[0].charAt(0).toUpperCase() + words[0].slice(1);
+    return words.join(' ');
+  });
+
+  // Shared prompt for the retrofit generators. A component name is entered in
+  // any form (`action-button`, `actionButton`, `Action Button`,
+  // `sp-action-button`); the case helpers normalize it.
+  const namePrompt = (message) => ({
+    type: 'input',
+    name: 'name',
+    message,
+    filter: (input) => input.trim().replace(/^(sp|swc)-/i, ''),
+    validate: (input) =>
+      input.trim().length > 0 || 'A name is required. You can rename it later.',
+  });
 
   // ──────────────────────
   //     CUSTOM ACTIONS
@@ -142,8 +166,42 @@ export default function (plop) {
     }
   });
 
+  // Retrofit generators (`test`, `vrt`) only make sense for a component that
+  // already exists. Fail loudly and early — before any file is written — when
+  // the target directory is missing, so a typo does not silently scaffold tests
+  // for a non-existent component.
+  plop.setActionType('assert-component-exists', (answers) => {
+    const name = render('{{dashCase name}}', answers);
+    const dir = path.join(repoRoot, SWC_COMPONENTS, name);
+    if (!fs.existsSync(dir)) {
+      throw new Error(
+        `Component "${name}" does not exist at ${SWC_COMPONENTS}/${name}. ` +
+          `Scaffold it first with: yarn plop component "${name}"`
+      );
+    }
+    return `found component ${name}`;
+  });
+
+  // Format the directories a retrofit generator wrote (a `test/` or `test/vrt/`
+  // subtree), scoped so the surrounding component files are left untouched.
+  // Config: { paths: string[] } — handlebars-templated repo-relative dirs.
+  plop.setActionType('format-dir', (answers, config) => {
+    const targets = (config.paths ?? [])
+      .map((p) => render(p, answers))
+      .join(' ');
+    try {
+      execSync(`yarn prettier --write ${targets}`, {
+        cwd: repoRoot,
+        stdio: 'ignore',
+      });
+      return `formatted ${targets}`;
+    } catch {
+      return `skipped formatting (run "yarn lint" manually)`;
+    }
+  });
+
   // ──────────────────
-  //     GENERATOR
+  //     GENERATORS
   // ──────────────────
 
   plop.setGenerator('component', {
@@ -232,4 +290,50 @@ export default function (plop) {
       ];
     },
   });
+
+  plop.setGenerator('test', {
+    description: 'Retrofit an existing component with unit + a11y test files',
+    prompts: [namePrompt('Component to add tests for (e.g. action-button):')],
+    actions: () => {
+      const swcDir = `${SWC_COMPONENTS}/{{dashCase name}}`;
+
+      return [
+        { type: 'assert-component-exists' },
+        {
+          type: 'add',
+          path: `${swcDir}/test/{{dashCase name}}.test.ts`,
+          templateFile: path.join(here, 'templates/test/test.ts.hbs'),
+          skipIfExists: true,
+        },
+        {
+          type: 'add',
+          path: `${swcDir}/test/{{dashCase name}}.a11y.spec.ts`,
+          templateFile: path.join(here, 'templates/test/a11y.spec.ts.hbs'),
+          skipIfExists: true,
+        },
+        { type: 'format-dir', paths: [`${swcDir}/test`] },
+      ];
+    },
+  });
+
+  plop.setGenerator('vrt', {
+    description: 'Retrofit an existing component with a Chromatic VRT story',
+    prompts: [
+      namePrompt('Component to add a VRT story for (e.g. action-button):'),
+    ],
+    actions: () => {
+      const swcDir = `${SWC_COMPONENTS}/{{dashCase name}}`;
+
+      return [
+        { type: 'assert-component-exists' },
+        {
+          type: 'add',
+          path: `${swcDir}/test/vrt/{{dashCase name}}.vrt.ts`,
+          templateFile: path.join(here, 'templates/vrt/vrt.ts.hbs'),
+          skipIfExists: true,
+        },
+        { type: 'format-dir', paths: [`${swcDir}/test/vrt`] },
+      ];
+    },
+  });
 }