No favicon, if sub-theme does not have a copy of the base theme favicons

[donquixote]

In

• EWPP-3652: Add favicon in ico, svg and png formats based on component library. #1326
  a mechanism was added to set the favicon based on the chosen component library.

The path of the favicon is in the respective sub-theme, e.g.

function oe_theme_page_attachments_alter(array &$attachments) {
  [..]
  $active_theme = \Drupal::theme()->getActiveTheme();
      [..]
      $link[0]['href'] = base_path() . $active_theme->getPath() . "/images/favicons/$component_library/favicon.ico";

This means that:

• Every sub-theme now needs a copy of these favicons. Otherwise the favicon won't work.
• Any custom favicon in the sub-theme is overridden, unless the sub-theme also implements hook_page_attachments_alter().

[donquixote]

Thoughts for the solution:

• By default use the icons in oe_theme, so that sub-themes don't have to copy them.
• Provide a mechanism for sub-themes to override the favicon - unless you want to completely forbid this. Maybe detect if the directory in the sub-theme exists?

But before introducing a change like this, you should have a look at existing sub-themes.
I currently have no idea how many of them exist, and how many of them were updated to provide a copy of the favicons.

[nagyad]

We are looking to address the issue in the #1492 PR.