[no-let] Add option to ignore lines based on search string

[realmikkifriend]

Thanks very much to the devs for this library, which has helped me understand functional programming more than any tutorial.

Background

Svelte passes props between components using a different method depending on which major version is used:

• export let variable (Svelte 4, what I'm using)
• let { variable } = $props(); (Svelte 5, based on documentation, see discussion)

In addition to this plugin, I enabled ESLint to scan Svelte components in my codebase by installing eslint-plugin-svelte and enabling the recommended configs per documentation.

Issue

Either valid usage of let in Svelte components triggers the no-let rule. I can't find a way to prevent this using this library's existing options, eslint-plugin-svelte, or ESLint configuration.

export let variable; // valid Svelte 4 syntax, incorrectly shows no-let error

let { variable } = $props(); // valid Svelte 5 syntax, incorrectly shows no-let error

let variable; // correctly shows no-let error

For reference, while I don't want to lose the benefit of no-let linting, it's possible to disable this rule in Svelte files in eslint.config.mjs:

{
    files: ["**/*.svelte"],
    rules: {
        "functional/no-let": "off",
    },
},

Suggestion

In addition to the ignoreIdentifierPattern option, it would be great if the no-let rule had an ignoreLinePattern (or ignoreCodePattern for consistency with rules like no-classes) option that skips matching lines. It would accept either search strings or arrays of search strings (e.g. ^export and \$props\(\)).

I barely understand ESLint but have searched and prompted for a way to configure it like this. As far as I can tell, ESLint configuration blocks (like above) can't disable linting by search string. I would love for this to be incorrect, because it would bypass the need to add new features.

[RebeccaStevens]

Svelte is one of those things I've been meaning to look into for ages but still haven't gotten around to it.

I assume there is a reason you can't simply use const instead of let, but I'm not aware of it. Could you enlighten me?

export const variable;
const { variable } = $props();

[realmikkifriend]

EDIT: I modified the last paragraph of my original post and renamed this issue.

Great question...

Svelte 4

Changing export let variable to export const variable breaks my app in ways that I couldn't immediately chase down/refactor. There also isn't documentation or much discussion of this use. Svelte 4 assumes you will use export let variable in a component receiving variable as a prop.

Svelte 5

I can't test this myself in my current project/workspace, but per this discussion, const { value } = $props() is also valid.

However, almost all Svelte 5 documentation uses let in this case, I think to acknowledge that the value is reactive and will therefore probably change. I personally think of reactivity as separate from functional patterns (which I'm still learning), so I would use const for it. But I wonder if other Svelte devs will be confused over this (if so, I hope they find this issue).