Support for RxJS Observables and #await blocks, await and error blocks never render, only the then block

[AlexAegis]

When using RxJS observables with the await block the first block and the error block never renders.
It renders: undefined -> 0 -> 1 -> 2

Using svelte-observable it works as expected
and renders: Loading... -> 0 -> 1 -> 2 -> Error

app.svelte

<script>
	import { interval, Subject } from 'rxjs';
	import { tap } from 'rxjs/operators';
	import { onMount } from 'svelte';
	import { observe } from 'svelte-observable';

	const subject = new Subject();
	const o1$ = subject.pipe(
		tap((i) => {
			if (i > 2) {
				throw new Error('O Error');
			}
		})
	);
	const o2$ = observe(o1$);

	const p1 = new Promise((res) => {
		setTimeout(() => {
			res('Promise 1');
		}, 500);
	});

	const p2 = new Promise((res, rej) => {
		setTimeout(() => {
			rej('Promise 2 error');
		}, 700);
	});

	onMount(() => {
		interval(500).subscribe((i) => {
			subject.next(i);
		})
	});
</script>

<h3>Observable, should emit thrice then error</h3>
{#await $o1$}
	O1 Loading...
{:then v}
	O1 Value: {v}
{:catch e}
	O1 Error: {e}
{/await}

<h3>Observable using svelte-observable, will emit thrice then error</h3>
{#await $o2$}
	O2 Loading...
{:then v}
	O2 Value: {v}
{:catch e}
	O2 Error: {e}
{/await}

<h3>Promise 1, will emit</h3>

{#await p1}
	P1 Loading...
{:then v}
	P1 Value: {v}
{:catch e}
	P1 Error: {e}
{/await}

<h3>Promise 2, will error out</h3>
{#await p2}
	P2 Loading...
{:then v}
	P2 Value: {v}
{:catch e}
	P2 Error: {e}
{/await}

Node 14
Chrome 84

	"dependencies": {
		"rxjs": "6.6.0",
		"svelte": "3.24.0",
		"svelte-observable": "0.4.0"
	},
	"devDependencies": {
		"rollup": "2.23.0",
	},

[dummdidumm]

That you never see the catch block is "works as designed" I think. Technically you can await anything but only if it's a promise, you will get the catch behavior. Showing "loading" while undefined and then should work though.

[Conduitry]

I believe {#await} wraps its argument in Promise.resolve() so that it also works with regular values, but yeah by design it doesn't work with whatever interface RxJS exposes. Only store autosubscription interfaces with that, and in a limited way. If there's something svelte-observable ought to be doing differently, you can open an issue in the project, as it's not an official library.