Ability to conditionally use slots

[kevmodrome]

I recently ran into this issue where I want to conditionally check if there's a default slot applied to the component. This currently can't be done without working around the current implementation.

It's a bit hard to explain but here's a REPL for clarity: https://svelte.dev/repl/6d51332a90e54c658647e7c1aaff9359?version=3.37.0

On the second instance of Item I expect it to use the fallback value This should show up!.

Describe alternatives you've considered
One workaround is to do the conditional outside of the slot, like so:

{#if showContent}
    <Item />
{/if}

This works but gets pretty wild once you start adding props to the equation.

How important is this feature to you?
It's a nice-to-have since it can be worked around. It's not something I run into every day.

[j3rem1e]

Personally I like the way it is now, and implementing that will be a big breaking change.

[kevmodrome]

Personally I like the way it is now, and implementing that will be a big breaking change.

Why?

[j3rem1e]

For example, using the VirtualList component in the svelte organization https://github.com/sveltejs/svelte-virtual-list/blob/master/VirtualList.svelte#L166

VirtualList (largely simplified) :

{#each getVirtualItems() as item}
  <slot {item}>Template not set</slot>
{/each}

MyComponent

<VirtualList let:item>
  {#if isVisible(item)}
    {item.name}
  {/if}
</VirtualList>

I don't want the default slot to be rendered here.

It's just an example of code which will break with this issue.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been closed as it was previously marked as stale and saw no subsequent activity.