Add svelte/no-constant-condition rule

[AlexRMU]

Description

You need to take all the rules from eslint and try to adapt them to the markup.

if (2) { // no-constant-condition
    "foo";
} else if (3) { // no-constant-condition
    "bar";
} else if (3) { // no-constant-condition no-dupe-else-if
    "baz";
}

{#if 2}
    <div>foo</div>
{:else if 3}
    <div>bar</div>
{:else if 3} <!-- svelte/no-dupe-else-if-blocks -->
    <div>baz</div>
{/if}

Perhaps you need to try to convert the markup to (pseudo) regular js and, in addition to the rules of the svelte, apply the rules for js to it (including other plugins and future ts support in the markup).

[ota-meshi]

Thank you for posting this issue.
Since template logic blocks are different from JavaScript, I think we need to create rules like svelte/no-constant-condition separately.
If you think there is a rule we need, please post rule proposal in an new issue.

[ota-meshi]

Perhaps you need to try to convert the markup to (pseudo) regular js and, in addition to the rules of the svelte, apply the rules for js to it (including other plugins and future ts support in the markup).

If you want to try out the idea of linting from pseudo JavaScript code, please create your own new plugin and try it out, as the mechanism is different from eslint-plugin-svelte.