Description

There is a warning in the iframed Full Site Editor when enqueueing a stylesheet that isn't associated with a block.

I build a lot of plugins that use block filters only to enhance core blocks, which don't require creating custom blocks.

For plugins, the warning suggests using the block API's style or editorStyle:

I'm creating this issue b/c I'm concerned that there may not be a way to properly enqueue stylesheets in the iframed editor without being associated with a block.

Step-by-step reproduction instructions

1. Enqueue stylesheet for a plugin in the Full Site Editor:

function enqueue_editor_styles() {
  // Enqueue editor only styles.
  wp_enqueue_style(
    'my-plugin-block-editor',
    plugin_dir_url( __FILE__ ) . 'build/index.css',
    array(),
    '1.0.0'
  );
}
add_action(  'enqueue_block_editor_assets', 'enqueue_editor_styles'  );

2. Go to Site Editor
3. Open browser console to see warning

WordPress information

• WordPress version: 5.7.2
• Gutenberg version: 10.9.1
• Are all plugins except Gutenberg deactivated? No
• Are you using a default theme (e.g. Twenty Twenty-One)? No

Device information

• Device: Desktop
• Operating system: macOS Catalina
• Browser: Chrome 91.0.4472.114