@const declaration inside components ignored

[maciej-irl]

Describe the bug

The docs state that

{@const} is only allowed as direct child of {#each}, {:then}, {:catch}, <Component /> or <svelte:fragment />.

but currently if you use it inside a component slot the compiler fails to emit the assignment and the code throws at runtime.

<script>
	import Heading from './Heading.svelte';
</script>
<Heading>
	{@const heading = "Hello world"}
	{heading}
</Heading>

If this is not the intended usage of @const (I hope it is though) the compiler should produce an error, otherwise it should emit the assignment.

Reproduction

https://svelte.dev/repl/d01b574992e04be294ba081cddbf6859?version=3.46.2

Logs

No response

System Info

System:
    OS: macOS 12.1
    CPU: (8) arm64 Apple M1
    Memory: 108.55 MB / 8.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 17.3.0 - /opt/homebrew/bin/node
    npm: 8.3.0 - /opt/homebrew/bin/npm
  Browsers:
    Chrome: 97.0.4692.99
    Safari: 15.2
    Safari Technology Preview: 15.4
  npmPackages:
    rollup: ^2.3.4 => 2.66.1
    svelte: ^3.0.0 => 3.46.2

Severity

annoyance

[Conduitry]

Looking at the tests for this aspect of this feature, I suspect it was intended only to work with let: variables from the component. If that's so, the docs should be made a bit clearer and the compiler should throw an exception rather than ignoring the {@const}.

[Conduitry]

This should be fixed in 3.48.0 - https://svelte.dev/repl/d01b574992e04be294ba081cddbf6859?version=3.48.0