[Niznikr]

Additional description

Breaking change (types only, before GA). Several prop and data types let invalid combinations through, mostly because a | string or an index signature widened them. This PR tightens them into discriminated unions and declared fields. Runtime behaviour is unchanged except for the comboboxFilter fix below. Where old input still works at runtime, a development-only warning now points to the new form.

Component	Root cause	Change	Runtime shim
textarea	maxLength: string, parsed with parseInt	maxLength: number	Strings still parsed, with a dev warning (check-props was never called; it is now)
vertical-navigation	NavigationItem index signature; icon / notificationBadge undeclared and cast	Declared as ReactElement<IconProps> / ReactElement<BadgeProps>; casts removed	—
tree	type: 'branch' | 'item' | string widened to string; nodes allowed on any node	TreeNode = TreeBranchNode | TreeItemNode	—
split-view	Index signatures on SplitViewHeaderProps and SplitViewListboxItem dropped the PageHeader and item types	Header extends PageHeaderProps; SplitViewListbox<T> carries the item type through options, selection, unread, events and listItem	—
color-picker	swatchColors / defaultSelectedTab accepted with any variant and silently ignored	ColorPickerVariantProps union	—
welcome-mat	Any prop accepted with any variant	WelcomeMatVariantProps union: tiles vs. actions; infoBadge only on trailhead-connected	—
menu-dropdown	Every field allowed on every option type; leftIcon.category: string	Item / header / divider option union; IconCategory	—
combobox (options)	type: ... | string widened to string. Items reused type as the comboboxAddSubheadings grouping key, so structural rows couldn't be told apart and labels were cast to string	Union keyed on type: item (new category field, string label), separator, header/footer, deselect	addSubheadings reads category ?? type; dev warning when an item has a non-structural type
combobox (variant)	"options required unless popover" and "popover needs assistiveText.popoverLabel" were runtime warnings only	ComboboxVariantProps: listbox variants require options; popover requires popover + popoverLabel and rejects options	Existing runtime warnings kept

Also in this PR

• comboboxFilter threw on a separator whose label is a render function. It now matches only string labels (regression test added).
• onRenderMenuItem / menuItem receive ComboboxItemOption | ComboboxDeselectOption. That's the only data the menu ever passes them.
• Combobox examples, stories and tests (plus two portal-settings examples) move from type: 'account' to category: 'account'. Rendered markup is identical, so there are no snapshot changes.
• The combobox stories (53 errors) and the tree hashmap story data (37 errors) didn't type-check on master. Both now do.
• New type-level regression tests in components/*/__tests__/*.type-test.tsx, using @ts-expect-error assertions. They get their own tsconfig.type-tests.json because the build config excludes __tests__, and npm run typecheck now runs both projects. I checked that each assertion fails for its intended reason.

Migration

• Combobox items: rename type: '<group>' to category: '<group>'. type is now only 'separator' | 'header' | 'footer' | 'deselect'.
• Textarea: pass maxLength={100}, not maxLength="100".
• Tree nodes: set type: 'branch' or type: 'item'. Only branches take nodes / expanded / loading.
• ColorPickerProps, ComboboxProps and WelcomeMatProps are now type aliases, so interface X extends ComboboxProps no longer compiles. Use type X = ComboboxProps & {...}. Nothing in this repo extends them. MenuDropdownProps stays an interface because builder-header and trial-bar extend it.
• New exported types: TreeBranchNode, TreeItemNode, ColorPickerVariantProps, WelcomeMatVariantProps, MenuDropdownItemOption / HeaderOption / DividerOption, ComboboxItemOption / SeparatorOption / ActionOption / DeselectOption, ComboboxVariantProps.

Not in scope: the other parts of these ROADMAP checklist items (renames, controlled state, child contracts), so no checkboxes are ticked. Runtime warnings for tree, color-picker and welcome-mat were skipped because the runtime already ignores the invalid props.

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CONTRIBUTOR checklist (do not remove)

Please complete for every pull request.

Green gate — all of these must pass locally (CI runs the same):

• npm run lint passes with 0 errors (npm run lint:fix to auto-fix). Warnings are the tracked gradual-migration backlog; do not add new errors. (223 warnings, same as master)
• npm run typecheck is clean (tsc --noEmit). Now also runs the type-test project.
• npm test -- --run passes — this runs both Vitest projects (jsdom unit + real-browser browser) and the story HTML snapshots. If you changed rendered markup on purpose, update snapshots with npm test -- --run -u and review the diff. (1035/1035 with --update=none; no snapshot changes)
• npm run build succeeds (type-check + Vite library build + .d.ts + entry shims).

Behavior & docs:

• First-time contributors: sign the CLA (a bot will comment with instructions). (N/A)
• Added/updated Vitest + React Testing Library tests for the change (template: components/button/__tests__). New props and bug fixes should get a regression test. Tests that genuinely need a real browser (focus traversal, layout/measurement, canvas) go in a *.browser.test.jsx file (the browser project); everything else is jsdom.
• Reviewed the component's Storybook stories: npm run storybook → http://localhost:6007/. Confirm the story actually renders and behaves (deprecated Storyshots/Karma are gone; there is no separate browser-tests server). (Not yet done; snapshots are unchanged)
• Story/example code uses the component's real prop API (e.g. render-props like onRenderContent / onRenderVisualPicker, icon props, events), not assumptions — a common source of "component looks broken" reports has been stories authored against the wrong API. Cross-check against components/<name>/__examples__. (The combobox, color-picker, menu-dropdown and tree stories now type-check against the new types)
• Storybook Accessibility (a11y) panel shows no new violations for the affected stories. (Not yet checked; no markup changes)
• If you added or changed a type, remember runtime PropTypes were removed in the TS migration — types are the contract. Ship accurate .d.ts (they're generated by the build); JS consumers rely on them via editor type-acquisition.

REVIEWER checklist (do not remove)

• CI is green (GitHub Actions CI workflow: lint, typecheck, test, build). Chromatic visual review, if configured, has been checked.
• Change has adequate test coverage; bug fixes include a regression test.
• Reviewed the affected Storybook stories and their a11y panels.
• Rendered markup still conforms to SLDS — check the story HTML snapshot diff (components/__tests__/__snapshots__/story-snapshots.test.jsx.snap).
• Public API / package surface: if exports changed, the deep-import contract still holds (@salesforce/design-system-react/components/<name> and nested paths resolve for ESM, CJS, and types). Removing/renaming a public component or export is a breaking change → feat!:/BREAKING CHANGE: and a major version bump.