Error: Expected 2 arguments, but got 1. (ts) for <div transition:fade >

[bfanger]

Since svelte-check 1.1.29 the transition shorthand <div transition:fade> incorrectly reports the
Error: Expected 2 arguments, but got 1. error.

When using the shorthand notation, svelte calls the fade (or any other function) with 2 arguments, the element and an empty object. REPL

To Reproduce

<script lang="ts">
  import { fade } from "svelte/transition";

  let visible = true;

  function toggle() {
    visible = !visible;
  }
</script>

<button on:click={toggle}>Toggle</button>
{#if visible}
  <div transition:fade>Fades in and out</div>
{/if}

Demo: https://github.com/bfanger/svelte-check-transition-bug

The failed run: https://github.com/bfanger/svelte-check-transition-bug/runs/1783108223?check_suite_focus=true

[dummdidumm]

This is a result of #767 , transitions/animations/use directives are now transpiled differently. Looking at Svelte's source code, the error is actually correct, so Svelte's typings need to be adjusted. Right now they don't mark the second parameter as optional.

[jackwestmoretab]

I have also experienced this issue -- thanks @dummdidumm for looking into it!

[bfanger]

I think the svelte patch fixes the error when using fade (and the other build ins) but svelte-check is still incorrect

Using the transition:fade shorthand behaves as if you'd written transition:fade={ {} } and fade is passed 2 params, not 1.

[dummdidumm]

What do you mean by that?
transition:fade currently is translated (by svelte2tsx) to __sveltets_ensureTransition(fade(__sveltets_ElementNode)) for intellisense purposes. transition:fade={ {} } would be __sveltets_ensureTransition(fade(__sveltets_ElementNode, {})) which is correct.

[bfanger]

Both should be translated to __sveltets_ensureTransition(fade(__sveltets_ElementNode, {}))

Check the repl https://svelte.dev/repl/3dfed2eaa77a4ae9b5be415a22420d48?version=3.32.0

[dummdidumm]

Yes it needs to be translated to that for the current Svelte version, but no longer once the second parameter becomes optional. For compatibility with earlier versions I created a PR which does what you suggest for the built-in transitions/animations.
Or do you mean that the Svelte compiler will always add {} if there are no explicit params given?

[bfanger]

I can't predict what svelte compiler will do in the future, but right now it adds the {} iwhen there are no explicit parameters.
Im not sure if that behavior is the same for all shorthands notations.