onMount Disappearing

[jessiejs]

Describe the bug

onMount calls in Rollup just flat out disappear, and unfortunately I can't do the $$self.$$.on_mount.push workaround as you're not allowed to use $$self.

Reproduction

Unfortunately, I can't reproduce this in the REPL (my exact same component code works!)

rollup.config.mjs

import nodeResolve from '@rollup/plugin-node-resolve';
import typescript from '@rollup/plugin-typescript';
import { defineConfig } from 'rollup';
import svelte from 'rollup-plugin-svelte';
import preprocess from 'svelte-preprocess';

export default defineConfig({
	input: 'src/main.ts',
	output: {
		file: 'dist/wincfg'
	},
	plugins: [
		nodeResolve(),
		svelte({
			preprocess: preprocess(),
			emitCss: false
		}),
		typescript({
			target: "ES2020"
		}),
	]
})

Component Code

<script lang="ts">
	import { onMount } from "svelte";

	console.log('onmount');
	
	onMount(() => {
		console.log('mounted');
	})
</script>

Output

function instance$2($$self) {
	console.log('onmount');

	return [];
}

Logs

Not seeing any log messages.

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (16) x64 11th Gen Intel(R) Core(TM) i7-11700K @ 3.60GHz
    Memory: 17.70 GB / 31.80 GB
  Binaries:
    Node: 20.4.0 - ~\scoop\apps\nodejs\current\node.EXE
    Yarn: 1.21.1 - ~\AppData\Local\pnpm\yarn.CMD
    npm: 9.8.1 - ~\scoop\apps\nodejs\current\npm.CMD
    pnpm: 8.6.0 - ~\node_modules\.bin\pnpm.CMD
  Browsers:
    Chrome: 118.0.5993.118
    Edge: Spartan (44.19041.3570.0), Chromium (118.0.2088.69)
    Internet Explorer: 11.0.19041.3570
  npmPackages:
    rollup: ^4.0.2 => 4.0.2
    svelte: ^4.2.2 => 4.2.2

Severity

blocking all usage of svelte

[Conduitry]

Presumably, however you're bundling this, you're getting the server-side rendering versions of the svelte exports, where onMount is a no-op and gets tree shaken out, instead of the browser versions. We'd need to seem a minimal reproduction, including your build process.

[jessiejs]

I'm not using SSR.
I made an even simpler reproduction https://github.com/jessiejs/sveltebug (npm build)

[Conduitry]

You need to pass browser: true to the node-resolve plugin, or it will try to use the server-side versions of any imports. See the example config in the readme of the Svelte Rollup plugin that you're using - https://github.com/sveltejs/rollup-plugin-svelte