CSS asset preload error

[fracsi]

Describe the bug
<link rel="preload"> only instruct the browser to preload the asset, but it does not instruct it to apply it.
See: MDN example
There should be 2 HTML link tags if you want to use HTML for preload.
Using symfony/web-link and preload twig function the Link header is added to the response HTTP headers.

To Reproduce
Add CSS assets with preload.

#[Override]
public function configureAssets(): Assets
{
    return parent::configureAssets()
        ->addCssFile(Asset::new('custom.css')->preload());
}

(OPTIONAL) Additional context
Generated HTML:

<link rel="preload" href="/custom.css">

Response header contains preload link as well (if the preload twig function is callable).

Link: </custom.css>; rel="preload"; as="style"

Possible solution
If preload twig function is available:

<link rel="stylesheet" href="{{ preload(asset(css_asset.value, css_asset.packageName), {as: 'style', nopush: css_asset.nopush}) }}" {% for attr, value in css_asset.htmlAttributes %}{{ attr }}="{{ value|e('html_attr') }}" {% endfor %}>

If preload is not available we need 2 link tags:

<link rel="preload" href="{{ asset(css_asset.value, css_asset.packageName) }}" as="style">
<link rel="stylesheet" href="{{ asset(css_asset.value, css_asset.packageName) }}" {% for attr, value in css_asset.htmlAttributes %}{{ attr }}="{{ value|e('html_attr') }}" {% endfor %}>

[javiereguiluz]

Yes, this looks like a bug. Can you please send a pull request to fix this? Thanks!

[javiereguiluz]

Fixed by #6697. Thanks!