Enable anchors to (other) internal pages

[BrandSven]

Hi, thanks for this very useful plugin. :-)

Here's an idea for a new feature:
Right now, one can either link to another internal page, OR to an anchor on the current page.

Many times we need to do both - link to an anchor on ANOTHER internal page. This could backend-wise easily be implemented by showing the link-internal field next to the link-anchor field:

src/Forms/LinkItemField.php, Line 157+:

TreeDropdownField::create('InternalLinkID', 'Internal Link', SiteTree::class)
  ->addExtraClass('link-hidden link-internal link-anchor'),
                                             ^^^^^^^^^^^

The final link could be something like:
/about-us/#map

src/Model/LinkItem.php, Line 178-180:

switch($this->LinkType) {
  case 'anchor':
      $link = ($this->InternalLink()->Link() ? : '') . '#'.$this->Anchor;

If you like, I can create a merge request. Not sure though if LinkItem->getCMSFields() needs to be adjusted, too. I'm fairly new to Silverstripe.

[davejtoews]

We've solved this same thing by adding this in a DataExtension.

    public function updateCMSFields(FieldList $fields)
    {
        $fields->replaceField(
            'Anchor',
            TextField::create('Anchor', 'Anchor Link (without #)')
                ->displayIf('LinkType')->isEqualTo('anchor')->orIf('LinkType')->isEqualTo('internal')->end(),
        );
    }

    public function updateLink(&$link)
    {
        if ($this->owner->LinkType == 'internal') {
            // Use absolute URL in case the reference is on another subsite
            $link = $this->owner->InternalLink()->AbsoluteLink();
            // Add Anchor tag if added in custom field
            $link .= $this->owner->Anchor ? '#' . $this->owner->Anchor : '';
        }
    }

Would be great to have this integrated in the module.