DEV: Allow plugins to add theme modifiers via db migrations (#9192)

app/models/remote_theme.rb

@@ -145,7 +145,7 @@ class RemoteTheme < ActiveRecord::Base
       raise ImportError, I18n.t("themes.import_error.about_json_values", errors: self.errors.full_messages.join(","))
     end
 
-    ThemeModifierSet::MODIFIERS.keys.each do |modifier_name|
+    ThemeModifierSet.modifiers.keys.each do |modifier_name|
       theme.theme_modifier_set.public_send(:"#{modifier_name}=", theme_info.dig("modifiers", modifier_name.to_s))
     end
     if !theme.theme_modifier_set.valid?

app/models/theme.rb

@@ -538,7 +538,7 @@ class Theme < ActiveRecord::Base
       end
 
       meta[:modifiers] = {}.tap do |hash|
-        ThemeModifierSet::MODIFIERS.keys.each do |modifier|
+        ThemeModifierSet.modifiers.keys.each do |modifier|
           value = self.theme_modifier_set.public_send(modifier)
           hash[modifier] = value if !value.nil?
         end

app/models/theme_modifier_set.rb

@@ -4,16 +4,14 @@ class ThemeModifierSet < ActiveRecord::Base
 
   belongs_to :theme
 
-  MODIFIERS ||= {
-    serialize_topic_excerpts: { combine_mode: :any, type: :boolean },
-    csp_extensions: { combine_mode: :flatten, type: :string_array },
-    svg_icons: { combine_mode: :flatten, type: :string_array },
-  }
+  def self.modifiers
+    @modifiers ||= self.load_modifiers
+  end
 
   validate :type_validator
 
   def type_validator
-    MODIFIERS.each do |k, config|
+    ThemeModifierSet.modifiers.each do |k, config|
       value = public_send(k)
       next if value.nil?
 
@@ -39,18 +37,41 @@ class ThemeModifierSet < ActiveRecord::Base
   # Given the ids of multiple active themes / theme components, this function
   # will combine them into a 'resolved' behavior
   def self.resolve_modifier_for_themes(theme_ids, modifier_name)
-    return nil if !(config = MODIFIERS[modifier_name])
+    return nil if !(config = self.modifiers[modifier_name])
 
     all_values = self.where(theme_id: theme_ids).where.not(modifier_name => nil).pluck(modifier_name)
-    case config[:combine_mode]
-    when :any
+    case config[:type]
+    when :boolean
       all_values.any?
-    when :flatten
+    when :string_array
       all_values.flatten(1)
     else
       raise ThemeModifierSetError "Invalid theme modifier combine_mode"
     end
   end
+
+  private
+
+  # Build the list of modifiers from the DB schema.
+  # This allows plugins to introduce new modifiers by adding columns to the table
+  def self.load_modifiers
+    hash = {}
+    columns_hash.each do |column_name, info|
+      next if ["id", "theme_id"].include?(column_name)
+
+      type = nil
+      if info.type == :string && info.array?
+        type = :string_array
+      elsif info.type == :boolean && !info.array?
+        type = :boolean
+      else
+        raise ThemeModifierSetError "Invalid theme modifier column type" if ![:boolean, :string].include?(info.type)
+      end
+
+      hash[column_name.to_sym] = { type: type }
+    end
+    hash
+  end
 end
 
 # == Schema Information

lib/theme_modifier_helper.rb

@@ -4,7 +4,7 @@ class ThemeModifierHelper
     @theme_ids = theme_ids || request&.env&.[](:resolved_theme_ids)
   end
 
-  ThemeModifierSet::MODIFIERS.keys.each do |modifier|
+  ThemeModifierSet.modifiers.keys.each do |modifier|
     define_method(modifier) do
       Theme.lookup_modifier(@theme_ids, modifier)
     end

spec/models/theme_modifier_set_spec.rb

@@ -20,5 +20,11 @@ describe ThemeModifierSet do
 
       expect(ThemeModifierSet.resolve_modifier_for_themes([t1.id, t2.id], :serialize_topic_excerpts)).to eq(false)
     end
+
+    it "builds modifiers list from database" do
+      expect(ThemeModifierSet.modifiers.keys).to include(:serialize_topic_excerpts, :csp_extensions)
+      expect(ThemeModifierSet.modifiers[:serialize_topic_excerpts][:type]).to eq(:boolean)
+      expect(ThemeModifierSet.modifiers[:csp_extensions][:type]).to eq(:string_array)
+    end
   end
 end