If condition in default slot or try mount to empty fragment

[stalkerg]

First - example:
https://svelte.technology/repl?version=1.37.0&gist=77279f780755dcecd28eb8899a08e22d
and working one:
https://svelte.technology/repl?version=1.31.0&gist=77279f780755dcecd28eb8899a08e22d

it's happening because Svelte generates next code:

if_block = create_if_block( state, component );
if_block.create();
if_block.mount( modal._slotted.default, null );

but modal._slotted.default it's just empty fragment because in the _fragment you did:

if (slot_content_default) {
  appendNode(slot_content_default, div_1);
}

then slot_content_default it is our modal._slotted.default .

Anyway, we can't mount to slot we should find existent dom element for that.
Example with cycle "each" don't work at all:
https://svelte.technology/repl?version=1.37.0&gist=70649b67d9f75bc91f3cc5c883b2c9e5

[stalkerg]

Wraparound - add root div element around all "slot" content.
It will be like:

if_block.mount( div, null );

[Rich-Harris]

This is fixed in 1.39.1 — thanks