FEATURE: Allow themes to specify modifiers in their about.json file (#9097)

There are three modifiers:
- serialize_topic_excerpts (boolean)
- csp_extensions (array of strings)
- svg_icons (array of strings)

When multiple themes are active, the values will be combined. The combination method varies based on the setting. CSP/SVG arrays will be combined. serialize_topic_excerpts will use `Enumerable#any`.

app/models/remote_theme.rb

@@ -145,6 +145,13 @@ 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|
+      theme.theme_modifier_set.public_send(:"#{modifier_name}=", theme_info.dig("modifiers", modifier_name.to_s))
+    end
+    if !theme.theme_modifier_set.valid?
+      raise ImportError, I18n.t("themes.import_error.modifier_values", errors: theme.theme_modifier_set.errors.full_messages.join(","))
+    end
+
     importer.all_files.each do |filename|
       next unless opts = ThemeField.opts_from_file_path(filename)
       value = importer[filename]

app/models/theme.rb

@@ -17,6 +17,7 @@ class Theme < ActiveRecord::Base
   has_many :parent_themes, -> { order(:name) }, through: :parent_theme_relation, source: :parent_theme
   has_many :color_schemes
   belongs_to :remote_theme, dependent: :destroy
+  has_one :theme_modifier_set, dependent: :destroy
 
   has_one :settings_field, -> { where(target_id: Theme.targets[:settings], name: "yaml") }, class_name: 'ThemeField'
   has_one :javascript_cache, dependent: :destroy
@@ -34,6 +35,10 @@ class Theme < ActiveRecord::Base
     changed_schemes << scheme if scheme
   end
 
+  def theme_modifier_set
+    super || build_theme_modifier_set
+  end
+
   after_save do
     changed_colors.each(&:save!)
     changed_schemes.each(&:save!)
@@ -44,6 +49,8 @@ class Theme < ActiveRecord::Base
     changed_fields.each(&:save!)
     changed_fields.clear
 
+    theme_modifier_set.save!
+
     if saved_change_to_name?
       theme_fields.select(&:basic_html_field?).each(&:invalidate_baked!)
     end
@@ -112,8 +119,8 @@ class Theme < ActiveRecord::Base
   end
 
   def self.get_set_cache(key, &blk)
-    if val = @cache[key]
-      return val
+    if @cache.hash.key? key.to_s
+      return @cache[key]
     end
     @cache[key] = blk.call
   end
@@ -247,6 +254,15 @@ class Theme < ActiveRecord::Base
     (@cache[cache_key] = val || "").html_safe
   end
 
+  def self.lookup_modifier(theme_ids, modifier_name)
+    theme_ids = [theme_ids] unless Array === theme_ids
+
+    theme_ids = transform_ids(theme_ids)
+    get_set_cache("#{theme_ids.join(",")}:modifier:#{modifier_name}:#{ThemeField::COMPILER_VERSION}") do
+      ThemeModifierSet.resolve_modifier_for_themes(theme_ids, modifier_name)
+    end
+  end
+
   def self.remove_from_cache!
     clear_cache!
   end
@@ -521,6 +537,13 @@ class Theme < ActiveRecord::Base
         end
       end
 
+      meta[:modifiers] = {}.tap do |hash|
+        ThemeModifierSet::MODIFIERS.keys.each do |modifier|
+          value = self.theme_modifier_set.public_send(modifier)
+          hash[modifier] = value if !value.nil?
+        end
+      end
+
       meta[:learn_more] = "https://meta.discourse.org/t/beginners-guide-to-using-discourse-themes/91966"
 
     end

app/models/theme_modifier_set.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+class ThemeModifierSet < ActiveRecord::Base
+  class ThemeModifierSetError < StandardError; end
+
+  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 },
+  }
+
+  validate :type_validator
+
+  def type_validator
+    MODIFIERS.each do |k, config|
+      value = public_send(k)
+      next if value.nil?
+
+      case config[:type]
+      when :boolean
+        next if [true, false].include?(value)
+      when :string_array
+        next if value.is_a?(Array) && value.all? { |v| v.is_a?(String) }
+      end
+      errors.add(k, :invalid)
+    end
+  end
+
+  after_save do
+    if saved_change_to_svg_icons?
+      SvgSprite.expire_cache
+    end
+    if saved_change_to_csp_extensions?
+      CSP::Extension.clear_theme_extensions_cache!
+    end
+  end
+
+  # 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])
+
+    all_values = self.where(theme_id: theme_ids).where.not(modifier_name => nil).pluck(modifier_name)
+    case config[:combine_mode]
+    when :any
+      all_values.any?
+    when :flatten
+      all_values.flatten(1)
+    else
+      raise ThemeModifierSetError "Invalid theme modifier combine_mode"
+    end
+  end
+end
+
+# == Schema Information
+#
+# Table name: theme_modifier_sets
+#
+#  id                       :bigint           not null, primary key
+#  theme_id                 :bigint           not null
+#  serialize_topic_excerpts :boolean
+#  csp_extensions           :string           is an Array
+#  svg_icons                :string           is an Array
+#
+# Indexes
+#
+#  index_theme_modifier_sets_on_theme_id  (theme_id) UNIQUE
+#

app/serializers/listable_topic_serializer.rb

@@ -111,7 +111,7 @@ class ListableTopicSerializer < BasicTopicSerializer
   alias :include_new_posts? :has_user_data
 
   def include_excerpt?
-    pinned || SiteSetting.always_include_topic_excerpts
+    pinned || SiteSetting.always_include_topic_excerpts || ThemeModifierHelper.new(request: scope.request).serialize_topic_excerpts
   end
 
   def pinned

config/locales/server.en.yml

@@ -83,6 +83,7 @@ en:
       generic: An error occured while importing that theme
       about_json: "Import Error: about.json does not exist, or is invalid"
       about_json_values: "about.json contains invalid values: %{errors}"
+      flag_values: "about.json flags contain invalid values: %{errors}"
       git: "Error cloning git repository, access is denied or repository is not found"
       unpack_failed: "Failed to unpack file"
       file_too_big: "The uncompressed file is too big."

db/migrate/20200302120829_add_theme_modifier_set.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+class AddThemeModifierSet < ActiveRecord::Migration[6.0]
+  def change
+    create_table(:theme_modifier_sets) do |t|
+      t.references :theme, index: { unique: true }, null: false
+      t.column :serialize_topic_excerpts, :boolean
+      t.column :csp_extensions, :string, array: true
+      t.column :svg_icons, :string, array: true
+    end
+  end
+end

lib/content_security_policy/extension.rb

@@ -44,16 +44,18 @@ class ContentSecurityPolicy
 
       Theme.where(id: Theme.transform_ids(theme_ids)).find_each do |theme|
         theme.cached_settings.each do |setting, value|
-          extensions << build_theme_extension(value) if setting.to_s == THEME_SETTING
+          extensions << build_theme_extension(value.split("|")) if setting.to_s == THEME_SETTING
         end
       end
 
+      extensions << build_theme_extension(ThemeModifierHelper.new(theme_ids: theme_ids).csp_extensions)
+
       extensions
     end
 
-    def build_theme_extension(raw)
+    def build_theme_extension(entries)
       {}.tap do |extension|
-        raw.split('|').each do |entry|
+        entries.each do |entry|
           directive, source = entry.split(':', 2).map(&:strip)
 
           extension[directive] ||= []

lib/svg_sprite/svg_sprite.rb

@@ -399,6 +399,8 @@ License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL
       end
     end
 
+    theme_icon_settings |= ThemeModifierHelper.new(theme_ids: theme_ids).svg_icons
+
     theme_icon_settings
   end
 

lib/theme_modifier_helper.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+class ThemeModifierHelper
+  def initialize(request: nil, theme_ids: nil)
+    @theme_ids = theme_ids || request&.env&.[](:resolved_theme_ids)
+  end
+
+  ThemeModifierSet::MODIFIERS.keys.each do |modifier|
+    define_method(modifier) do
+      Theme.lookup_modifier(@theme_ids, modifier)
+    end
+  end
+end

spec/components/svg_sprite/svg_sprite_spec.rb

@@ -142,6 +142,16 @@ describe SvgSprite do
     expect(SvgSprite.all_icons([parent_theme.id])).to include("dragon")
   end
 
+  it 'includes icons defined in theme flags' do
+    theme = Fabricate(:theme)
+
+    expect(SvgSprite.all_icons([theme.id])).not_to include("dragon")
+
+    theme.theme_modifier_set.svg_icons = ["dragon"]
+    theme.save!
+    expect(SvgSprite.all_icons([theme.id])).to include("dragon")
+  end
+
   it 'includes custom icons from a sprite in a theme' do
     theme = Fabricate(:theme)
     fname = "custom-theme-icon-sprite.svg"

spec/components/theme_store/zip_exporter_spec.rb

@@ -100,6 +100,7 @@ describe ThemeStore::ZipExporter do
             "tertiary": "858585"
           }
         },
+        "modifiers": {},
         "learn_more": "https://meta.discourse.org/t/beginners-guide-to-using-discourse-themes/91966"
       )
 

spec/lib/content_security_policy_spec.rb

@@ -165,6 +165,21 @@ describe ContentSecurityPolicy do
       expect(parse(theme_policy)['script-src']).to_not include('https://from-theme.net')
       expect(parse(theme_policy)['worker-src']).to_not include('from-theme.com')
     end
+
+    it 'can be extended by theme flags' do
+      policy # call this first to make sure further actions clear the cache
+
+      theme.theme_modifier_set.csp_extensions = ["script-src: https://from-theme-flag.script", "worker-src: from-theme-flag.worker"]
+      theme.save!
+
+      expect(parse(theme_policy)['script-src']).to include('https://from-theme-flag.script')
+      expect(parse(theme_policy)['worker-src']).to include('from-theme-flag.worker')
+
+      theme.destroy!
+
+      expect(parse(theme_policy)['script-src']).to_not include('https://from-theme-flag.script')
+      expect(parse(theme_policy)['worker-src']).to_not include('from-theme-flag.worker')
+    end
   end
 
   it 'can be extended by site setting' do

spec/lib/theme_flag_modifier_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+require 'rails_helper'
+
+describe ThemeModifierHelper do
+  fab!(:theme) { Fabricate(:theme).tap { |t| t.theme_modifier_set.update!(serialize_topic_excerpts: true) } }
+
+  it "defines a getter for modifiers" do
+    tmh = ThemeModifierHelper.new(theme_ids: [theme.id])
+    expect(tmh.serialize_topic_excerpts).to eq(true)
+  end
+
+  it "can extract theme ids from a request object" do
+    request = Rack::Request.new({ resolved_theme_ids: [theme.id] })
+    tmh = ThemeModifierHelper.new(request: request)
+    expect(tmh.serialize_topic_excerpts).to eq(true)
+  end
+end

spec/models/remote_theme_spec.rb

@@ -37,6 +37,9 @@ describe RemoteTheme do
               "love": "#{love_color}",
               "tertiary-low": "#{tertiary_low_color}"
             }
+          },
+          "modifiers": {
+            "serialize_topic_excerpts": true
           }
         }
       JSON
@@ -85,6 +88,8 @@ describe RemoteTheme do
       expect(remote.theme_version).to eq("1.0")
       expect(remote.minimum_discourse_version).to eq("1.0.0")
 
+      expect(@theme.theme_modifier_set.serialize_topic_excerpts).to eq(true)
+
       expect(@theme.theme_fields.length).to eq(9)
 
       mapped = Hash[*@theme.theme_fields.map { |f| ["#{f.target_id}-#{f.name}", f.value] }.flatten]

spec/models/theme_modifier_set_spec.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+require 'rails_helper'
+
+describe ThemeModifierSet do
+  describe "#resolve_modifiers_for_themes" do
+    it "returns nil for unknown modifier" do
+      expect(ThemeModifierSet.resolve_modifier_for_themes([1, 2], :unknown_modifier)).to eq(nil)
+    end
+
+    it "resolves serialize_topic_excerpts correctly" do
+      t1 = Fabricate(:theme)
+      t1.theme_modifier_set.update!(serialize_topic_excerpts: true)
+      t2 = Fabricate(:theme)
+      t2.theme_modifier_set.update!(serialize_topic_excerpts: false)
+
+      expect(ThemeModifierSet.resolve_modifier_for_themes([t1.id, t2.id], :serialize_topic_excerpts)).to eq(true)
+
+      t1 = Fabricate(:theme)
+      t1.theme_modifier_set.update!(serialize_topic_excerpts: nil)
+
+      expect(ThemeModifierSet.resolve_modifier_for_themes([t1.id, t2.id], :serialize_topic_excerpts)).to eq(false)
+    end
+  end
+end