Compiler throw error when IIFE used as key in each clause

[davidaq]

Describe the bug
Compiler throw an error when using a IIFE as the key in {#each}.

Svelte version: 3.7.1

Logs

TypeError: Cannot set property 'maintain_context' of undefined
    at Expression.render (/orbit/node_modules/svelte/compiler.js:21143:37)
    at EachBlockWrapper.render_keyed (/orbit/node_modules/svelte/compiler.js:14591:23)
    at EachBlockWrapper.render (/orbit/node_modules/svelte/compiler.js:14510:19)
    at fragment.nodes.forEach (/orbit/node_modules/svelte/compiler.js:15757:24)
    at Array.forEach (<anonymous>)
    at ElementWrapper.render (/orbit/node_modules/svelte/compiler.js:15756:34)
    at FragmentWrapper.render (/orbit/node_modules/svelte/compiler.js:17432:28)
    at new Renderer (/orbit/node_modules/svelte/compiler.js:17463:24)
    at dom (/orbit/node_modules/svelte/compiler.js:17662:23)
    at compile (/orbit/node_modules/svelte/compiler.js:23840:16)

To Reproduce

Reproducible in REPL:

<script>
const arr = [1, 2, 3]
</script>

<div>
	{#each arr as item ((() => item)())}
		{item}
	{/each}
</div>

This error can be worked around by passing arguments into the IFFE:

<script>
const arr = [1, 2, 3]
</script>

<div>
	{#each arr as item (((item) => item)(item))}
		{item}
	{/each}
</div>

Expected behavior
Compile as is or just disable IIFE usage as key.

Severity
Minor, not a case usual developers would encounter.

[davidaq]

Looking in to the code I believe block is missing here:

		block.builders.init.add_block(deindent`
			const ${get_key} = ctx => ${
			// @ts-ignore todo: probably error
			this.node.key.render()};   // <--------- .render(block) ?
			for (var #i = 0; #i < ${this.vars.each_block_value}.${length}; #i += 1) {

Inside file src/compiler/compile/render_dom/wrappers/EachBlock.ts:336. The compile outcome seems valid to me after doing this fix.

I haven't read the whole code, so I'm not sure what block is for, and thus not confident enough to make a patch myself.

[Conduitry]

It looks like this will be fixed by #3539.