Svelte: site is borked

[Rich-Harris]

1. go to https://svelte.dev/
2. navigate to examples
3. click the logo in the top left to go back to the homepage
4. yikes

[s0kil]

Cannot reproduce this issue

[paulocoghi]

That does not happen to me. The site is working perfectly on Firefox 67 - Ubuntu 18.04 64bits

[zb0t]

Reproducible on Chrome 74.0.3729.169 MacOS on second loop of steps 1-4.

[paulocoghi]

Reproducible on Firefox 67 - Ubuntu 18.04 64bits

Thanks, @zb0t . In fact, it is happening every time now, after I repeated the steps.

[Conduitry]

I updated the version of Svelte the site uses this morning, which is probably what caused this. Running the site locally, it looks like this weirdness appears between Svelte 3.4.4 and 3.5.0.

edit: I don't always see this when following the steps in the OP, clicking quickly back and forth between nav links generally triggers it.

[Conduitry]

I've locally rolled the version of Svelte the site uses back to 3.4.4 and have redeployed.

[zb0t]

Behaving normally for me now

[paulocoghi]

Those images on each item on the left-menu are on purpose?

[Conduitry]

If I revert #2690, this issue with the site seems to go away locally. This is really mysterious, as that _looked_ like a really obvious and correct fix.

[Conduitry]

In particular, if I change this line back to the Clearly Definitely Wrong if (outro_block) {, rebuild Svelte, and link it into the site folder, this borkedness goes away.

[Conduitry]

Something _else_ that seems to make this go away (without reverting the above change) is removing the delay on the slide-in transition in https://github.com/sveltejs/svelte-repl/blob/master/src/Message.svelte - I wonder whether there's a corresponding bug to #2871 except with transitions.

[Conduitry]

I have pretty much no idea about the inner workings of Svelte's transitions, but: https://github.com/sveltejs/svelte/blob/master/src/runtime/internal/transitions.ts Look at create_in_transition - shouldn't there be a started = true; somewhere in there? If I put one right after the if (started) return; this seems to fix the issue.

edit: That may not in fact be the whole solution, but there's definitely _something_ awry in create_in_transition.

edit again: Merely linking the svelte-repl dependency in here is seemingly causing the issue to go away, without changing its transition in Message. So I think I'm actually being affected by https://github.com/rollup/rollup-plugin-svelte/issues/58 except in this case, this is a bug that is being masked by having two copies of Svelte's runtime.

edit: If I edit node_modules/@sveltejs/svelte-repl/src/Message.svelte in place to avoid the linking/duplication complication, then removing the delay from the in transition does _not_ actually seem to help. Removing the out transition entirely _does_ seem to help.

[Rich-Harris]

ok i think i've made a minimal repro of the underlying bug: https://svelte.dev/repl/52955234b8a44873a37b104954854432?version=3.5.1

[Rich-Harris]

possibly related: #2402

[Rich-Harris]

looks like this is fixed in 3.5.2