[svelte-check] Issue with attributes added to HTMLElement with action

[stefanhoelzl]

Describe the bug

svelte-check expects an alt attribute for img Elements.
But when adding the alt attribute with an action svelte-check still complains, that the alt attribute is needed.
The action has an ActionReturn<undefined, { alt: string }> type telling svelte-check that the alt attribute is added when this action is used.

Am I using the ActionReturn type wrongly? Since I am also getting another TypeScript error

Reproduction

<script lang="ts">
  import { type ActionReturn } from "svelte/action";

  function action(
    node: HTMLImageElement,
  ): ActionReturn<undefined, { alt: string; src: string }> {
    node.src = "file://image";
    node.alt = "local file";
    return {};
  }
</script>

<img use:action />

Logs

debug.svelte:13:1
Warn: A11y: <img> element should have an alt attribute (svelte)

<img use:action />


debug.svelte:13:4
Error: Argument of type '{}' is not assignable to parameter of type 'Omit<HTMLImgAttributes, never> & HTMLAttributes<any> & { alt: string; src: string; }'.
  Type '{}' is missing the following properties from type '{ alt: string; src: string; }': alt, src (ts)

<img use:action />

System Info

System:
    OS: Linux 6.5 Fedora Linux 39 (Container Image)
    CPU: (16) x64 AMD Ryzen 7 7840U w/ Radeon  780M Graphics
    Memory: 17.35 GB / 30.53 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 20.10.0 - /usr/bin/node
    npm: 10.2.3 - /usr/bin/npm
  npmPackages:
    svelte: * => 4.2.8

Severity

annoyance

[dummdidumm]

ActionReturn is meant to enhance the typings for that specific element. In your case, you're telling the type checker that alt is now a required attribute.
There's currently no other way besides adding a <!-- svelte-ignore a11y-missing-attribute --> above the img tag.
Keeping this open for further consideration if we should not show a11y warnings of this kind in case an action is used on the element.

[stefanhoelzl]

Thanks for the clarification!

I actually find these warnings helpful. Maybe ActionReturn can be extended, so that it holds the information which attributes are set by the action? Instead of disabling the warning.

[dummdidumm]

This isn't possible because the a11y warning is coming from the Svelte compiler, while the the ActionReturn is a TypeScript thing which only can be handled by intellisense.