Support referencing theme assets from shared theme directory

REDMINE-20841

entry_types/scrolled/app/helpers/pageflow_scrolled/themes_helper.rb

@@ -6,9 +6,11 @@ def scrolled_theme_asset_path(theme,
                                   theme_file_role: nil,
                                   theme_file_style: :resized,
                                   relative_url: false)
+      theme_directory, path = extract_theme_directory_from_scrolled_theme_asset_path(theme, path)
+
       path =
         theme.files.dig(theme_file_role, theme_file_style) ||
-        asset_pack_path("static/pageflow-scrolled/themes/#{theme.name}/#{path}")
+        asset_pack_path("static/pageflow-scrolled/themes/#{theme_directory}/#{path}")
 
       if relative_url
         URI.parse(path).path
@@ -122,5 +124,17 @@ def scrolled_theme_deep_declarations(hash, suffix = nil, prefix = [])
         end
       end
     end
+
+    def extract_theme_directory_from_scrolled_theme_asset_path(theme, path)
+      if path.starts_with?('../shared/')
+        ['shared', path.gsub!('../shared/', '')]
+      elsif path.starts_with?('../')
+        raise(ArgumentError,
+              'Upward navigation to other directory than the shared ' \
+              'theme directory not allowed in theme asset path.')
+      else
+        [theme.name, path]
+      end
+    end
   end
 end

entry_types/scrolled/spec/helpers/pageflow_scrolled/entry_json_seed_helper_spec.rb

@@ -737,6 +737,34 @@ def render(helper, entry, options = {})
                                        })
       end
 
+      it 'supports shared theme directory in custom icons directories' do
+        pageflow_configure do |config|
+          config.themes.register(:default,
+                                 custom_icons: [:share],
+                                 custom_icons_directory: '../shared/icons')
+        end
+        entry = create(:published_entry, type_name: 'scrolled')
+        default_theme_directory = Rails.root.join('app/javascript/pageflow-scrolled/themes/default')
+        shared_theme_directory = Rails.root.join('app/javascript/pageflow-scrolled/themes/shared')
+        FileUtils.mkdir_p(shared_theme_directory.join('icons'))
+        FileUtils.cp(
+          default_theme_directory.join('icons/share.svg'),
+          shared_theme_directory.join('icons/share.svg')
+        )
+
+        result = render(helper, entry)
+
+        expect(result).to include_json(config: {
+                                         theme: {
+                                           assets: {
+                                             icons: {
+                                               share: %r{themes/shared/icons/share.*svg$}
+                                             }
+                                           }
+                                         }
+                                       })
+      end
+
       it 'does not use asset host in icon paths to allow xlink:href usage' do
         controller.config.asset_host = 'some-asset-host'
         pageflow_configure do |config|

entry_types/scrolled/spec/helpers/pageflow_scrolled/themes_helper_spec.rb

@@ -2,6 +2,42 @@
 
 module PageflowScrolled
   RSpec.describe ThemesHelper, type: :helper do
+    describe '#scrolled_theme_asset_path' do
+      it 'retrieves asset pack path from theme directory' do
+        entry = create(:entry)
+        theme = Pageflow::Theme.new(:test)
+        customized_theme = Pageflow::CustomizedTheme.find(entry: , theme:)
+
+        expect(helper).to receive(:asset_pack_path).with(
+          'static/pageflow-scrolled/themes/test/icons/muted.svg'
+        )
+
+        helper.scrolled_theme_asset_path(customized_theme, 'icons/muted.svg')
+      end
+
+      it 'expands relative path to shared theme directory' do
+        entry = create(:entry)
+        theme = Pageflow::Theme.new(:test)
+        customized_theme = Pageflow::CustomizedTheme.find(entry: , theme:)
+
+        expect(helper).to receive(:asset_pack_path).with(
+          'static/pageflow-scrolled/themes/shared/icons/muted.svg'
+        )
+
+        helper.scrolled_theme_asset_path(customized_theme, '../shared/icons/muted.svg')
+      end
+
+      it 'raises helpful error for relative paths to other sibling or parent directory' do
+        entry = create(:entry)
+        theme = Pageflow::Theme.new(:test)
+        customized_theme = Pageflow::CustomizedTheme.find(entry: , theme:)
+
+        expect {
+          helper.scrolled_theme_asset_path(customized_theme, '../other/icons/muted.svg')
+        }.to raise_error(/not allowed in theme asset path/)
+      end
+    end
+
     describe '#scrolled_theme_stylesheet_pack_tags' do
       it 'renders stylesheet pack tags for theme' do
         theme = Pageflow::Theme.new(:test, stylesheet_packs: ['fonts/sourceSansPro'])