invalid-binding error in odd places

[brunnerh]

Describe the bug

I tried to fix a typing issue here by extracting the index access to a @const but this raised an invalid-binding in a place where I would not expect it and also did not raise it where I would have expected it.

Reproduction

<script lang="ts">
    import Attribute from './attribute.svelte';

    type Field = string | number | boolean;
    type FieldArray = Array<Field>;

    function isFieldArray(value: Field | FieldArray): value is FieldArray {
        return Array.isArray(value);
    }

    type ExampleObject = {
        document: Record<string, Field | FieldArray>;
    };

    const obj: ExampleObject = {
        document: {
            name: 'John',
            age: 30,
            isMarried: true,
            hobbies: ['coding', 'reading', 'gaming']
        }
    };
</script>

{#each Object.keys(obj.document) as k}
    {@const value = obj.document[k]}
    {#if isFieldArray(value)}
        {#each value as _, index}
            <!-- Cannot bind to a variable declared with {@const ...} -->
            <input bind:value={value[index]} />
        {/each}
    {:else}
        <!-- No error here -->
        <Attribute bind:value={value} />
    {/if}
{/each}

<!-- attribute.svelte -->
<script lang="ts">
	export let value: string | number | boolean;
</script>
{value}

The first binding accesses value[index] and thus does not try to re-assign value itself, yet there is an error.
The second binding should try to re-assign value, yet there is no error.

Logs

No response

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (12) x64 Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
    Memory: 18.14 GB / 31.92 GB
  Binaries:
    Node: 16.16.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.17 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 6.14.13 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 108.0.5359.99
    Edge: Spartan (44.19041.1266.0), Chromium (108.0.1462.46)
    Internet Explorer: 11.0.19041.1566
  npmPackages:
    svelte: ^3.54.0 => 3.54.

Severity

annoyance