Add link dialog tab - configuration

Provide a configuration to configure the tabs in the link dialog. It is now possible to add new tabs without overwriting or defacing the Admin UI.

app/views/alchemy/admin/pages/link.html.erb

@@ -1,6 +1,5 @@
 <sl-tab-group id="overlay_tabs">
-  <% tabs = [Alchemy::Admin::LinkDialog::InternalTab, Alchemy::Admin::LinkDialog::AnchorTab, Alchemy::Admin::LinkDialog::ExternalTab, Alchemy::Admin::LinkDialog::FileTab] %>
-  <% tabs.each do |tab| %>
+  <% Alchemy.link_dialog_tabs.each do |tab| %>
     <%= render tab.new %>
   <% end %>
 </sl-tab-group>

lib/alchemy.rb

@@ -102,4 +102,40 @@ def self.publish_targets
   # JS Importmap instance
   singleton_class.attr_accessor :importmap
   self.importmap = Importmap::Map.new
+
+  # Configure tabs in the link dialog
+  #
+  # With this configuration that tabs in the link dialog can be extended
+  # without overwriting or defacing the Admin Interface.
+  #
+  # == Example
+  #
+  #    # components/acme/link_tab.rb
+  #    module Acme
+  #      class LinkTab < ::Alchemy::Admin::LinkDialog::BaseTab
+  #        def title
+  #          "Awesome Tab Title"
+  #        end
+  #
+  #        def name
+  #          :unique_name
+  #        end
+  #
+  #        def fields
+  #           [ title_input, target_select ]
+  #        end
+  #      end
+  #    end
+  #
+  #    # config/initializers/alchemy.rb
+  #    Alchemy.link_dialog_tabs << Acme::LinkTab
+  #
+  def self.link_dialog_tabs
+    @_link_dialog_tabs ||= Set.new([
+      Alchemy::Admin::LinkDialog::InternalTab,
+      Alchemy::Admin::LinkDialog::AnchorTab,
+      Alchemy::Admin::LinkDialog::ExternalTab,
+      Alchemy::Admin::LinkDialog::FileTab
+    ])
+  end
 end

spec/features/admin/link_overlay_spec.rb

@@ -2,6 +2,20 @@
 
 require "rails_helper"
 
+class TestTab < Alchemy::Admin::LinkDialog::BaseTab
+  def title
+    "Test Tab"
+  end
+
+  def name
+    :test_tab
+  end
+
+  def fields
+    [title_input, target_select]
+  end
+end
+
 RSpec.describe "Link overlay", type: :system do
   let!(:language) { create(:alchemy_language) }
 
@@ -29,6 +43,17 @@
       visit link_admin_pages_path
       within("#overlay_tabs") { expect(page).to have_content("File") }
     end
+
+    context "add new tab" do
+      before do
+        Alchemy.link_dialog_tabs << TestTab
+      end
+
+      it "has a new tab" do
+        visit link_admin_pages_path
+        within("#overlay_tabs") { expect(page).to have_content("Test Tab") }
+      end
+    end
   end
 
   context "linking pages", js: true do