[2.0 rc.15 / next] Types: data-* attributes are rejected in props objects typed with ComponentProps / JSX.HTMLAttributes #4082

Summary

In JSX, data-* attributes are accepted on intrinsic elements. In an object typed with the same element's props (ComponentProps<"div">, JSX.HTMLAttributes<T>), they are rejected. That type is the natural one for a function that returns props to spread onto an element. This request is to declare data-* keys in the DOM attribute types with a template-literal index signature.

Reproduction

import type { ComponentProps, JSX } from "@solidjs/web";

// In JSX, data-* attributes are accepted on intrinsic elements:
export const ok = <div data-state="open" />;

// ...but not in an object typed with the same element's props:
export const a: JSX.HTMLAttributes<HTMLDivElement> = { "data-state": "open" };
export const b: ComponentProps<"div"> = { role: "button", "data-state": "open" };

// ...nor when a function returning those props is spread back onto the element:
function disclosure(): ComponentProps<"button"> {
  return { "aria-expanded": "false", "data-state": "closed" };
}
export const c = <button {...disclosure()} />;

tsc -p . (TypeScript 5.9.3 and 7.0.2 give the same errors) with "jsx": "preserve", "jsxImportSource": "@solidjs/web", "strict": true:

data-attrs.tsx(7,56): error TS2353: Object literal may only specify known properties, and '"data-state"' does not exist in type 'HTMLAttributes<HTMLDivElement>'.
data-attrs.tsx(8,59): error TS2353: Object literal may only specify known properties, and '"data-state"' does not exist in type 'HTMLAttributes<HTMLDivElement> & Properties<HTMLDivElement>'.
data-attrs.tsx(12,38): error TS2353: Object literal may only specify known properties, and '"data-state"' does not exist in type 'ButtonHTMLAttributes<HTMLButtonElement> & Properties<HTMLButtonElement>'.

TypeScript exempts hyphenated names from attribute checks only in JSX syntax, so the object forms fail.

Proposal

Add a template-literal index signature to the base attribute interface in @solidjs/web's JSX types. I tested this module augmentation against rc.15:

import "@solidjs/web";
declare module "@solidjs/web" {
  namespace JSX {
    interface ElementAttributes<T> {
      [attr: `data-${string}`]: string | number | boolean | undefined;
    }
  }
}

With it, the three errors above go away, and these still hold:

type P = Omit<ComponentProps<"div">, "ref">;
export const p: P = { "data-x": "1", class: "a" };
// @ts-expect-error unknown non-data keys are still rejected
export const q: P = { foo: 1 };
// @ts-expect-error data values stay primitive
export const r: P = { "data-x": {} };
export const s = <div data-n={1} data-b={true} />;

React's DOM types have the same gap, so this is not a regression. Solid 2 is already rewriting the attribute types (lowercase names, RemoveAttribute), so this seems a good point to close it.

Why it matters

Headless component libraries expose state as data-* attributes (data-state, data-disabled, data-highlighted) and compose behaviour as functions that return props objects, which are merged and spread onto parts. Without the index signature, each such function has to widen its return type or cast. Until this lands, the augmentation above is the workaround.

Versions

• @solidjs/web / solid-js 2.0.0-rc.15. On next at eb4e019, packages/web declares no data-* key.
• TypeScript 5.9.3 and 7.0.2

Runnable repro: https://gist.github.com/cevr/e421f9dbfe6c0da2e92818647dd408f0 (bun install && bun run repro)

Filed with Claude Code on behalf of @cevr.