bind:this produces unwanted read of $props during unmount

[x0k]

Describe the bug

reproduction: click on Del button to get an error in console
expected: no error

Current behavior is understandable from reactive system point of view, but I was very surprised as a consumer of a library that uses code like in the Input.svelte component.

Reproduction

REPL

Logs

No response

System Info

System:
    OS: Linux 6.6 cpe:/o:nixos:nixos:24.11 24.11 (Vicuna)
    CPU: (12) x64 Intel(R) Core(TM) i5-10400F CPU @ 2.90GHz
    Memory: 8.79 GB / 15.56 GB
    Container: Yes
    Shell: 5.9 - /run/current-system/sw/bin/zsh
  Binaries:
    Node: 22.10.0 - /nix/store/hnkyz55vndmvwhg6nzpliv86gh6sxg7h-nodejs-22.10.0/bin/node
    npm: 10.9.0 - /nix/store/hnkyz55vndmvwhg6nzpliv86gh6sxg7h-nodejs-22.10.0/bin/npm
    pnpm: 9.15.3 - /nix/store/by7hqplbckljzzsq6jpmcjp1w4jzvxpg-pnpm-9.15.3/bin/pnpm
  Browsers:
    Brave Browser: 131.1.73.104

Severity

annoyance

[Leonidaz]

It looks like it happens with a props spread.

Without the spread, everything works as expected. Optional chaining in the derived also solves this.

example without attribute spread

with spread compiles to:

	Input($$anchor, $.spread_props(() => $.get(attributes), {
		get value() {
			return value().value;
		},
		set value($$value) {
			value(value().value = $$value, true);
		}
	}));

without spread:

	Input($$anchor, {
		get title() {
			return $.get(attributes).title;
		},
		get value() {
			return value().value;
		},
		set value($$value) {
			value(value().value = $$value, true);
		}
	});

[x0k]

Thanks for the reply.
Unfortunately, this workaround is not suitable for my case:

• I can't avoid the spread operation (I get an object with attributes from the user and mix them with the default attributes).
• Optional chaining cannot be used in this case bind:value={object[property]}

[Leonidaz]

@trueadm it seems that it's inconsistent behavior where a component that is being unmounted behaves differently causing an error if a spread is used vs no spread when props become undefined. wonder if this can be fixed? The issue happens inside the Item.svelte when spreading {...attributes} vs explicitly specifying when App.svelte sets signal state to undefined (used both for {#if} and props).