Some way to get advance warning of incorrect asset paths

[Rich-Harris]

Scenario: you have a file, like static/images/potato.jpg, referenced like so:

<img alt="potato" src="/images/potato.jpg">

But you also have a paths config:

// svelte.config.js
module.exports = {
  kit: {
    paths: {
      assets: 'https://cdn.example.com/my/bucket'
    }
  }
};

When the app is deployed, the image will be broken, because it should have been written like so:

<script>
  import { assets } from '$app/paths';
</script>

<img alt="potato" src="${assets}/images/potato.jpg">

But because assets === '/.' during development, the wrong version is indistinguishable from the right version.

Not totally sure what the right solution is. We don't want to force people to always use ${assets} in the case where they don't use the paths config, but it causes confusing problems if it's absent when there is a paths config. Maybe if there's a paths config, assets should be set during development to something like /_static_assets to force you to use the prefix, but otherwise it should behave as it currently does?

[Rich-Harris]

Relatedly, it appears that prerendered pages have the wrong assets path (i.e. the empty string) reflected in the HTML — the correct path doesn't come in until JS runs

[Rich-Harris]

This can be closed — in dev, assets is replaced with _svelte_kit_assets