FIX: When running the wizard and using a custom theme, fallback to the color_scheme name if the base_scheme_id is nil (#8236)

app/models/color_scheme.rb

@@ -187,6 +187,10 @@ class ColorScheme < ActiveRecord::Base
     @base_color_scheme
   end
 
+  def self.is_base?(scheme_name)
+    base_color_scheme_colors.map { |c| c[:id] }.include?(scheme_name)
+  end
+
   # create_from_base will create a new ColorScheme that overrides Discourse's base color scheme with the given colors.
   def self.create_from_base(params)
     new_color_scheme = new(name: params[:name])

lib/wizard/builder.rb

@@ -146,12 +146,10 @@ class Wizard
         default_theme = Theme.find_by(id: SiteSetting.default_theme_id)
         default_theme_override = SiteSetting.exists?(name: "default_theme_id")
 
-        scheme_id =
-          if default_theme_override
-            default_theme&.color_scheme&.base_scheme_id
-          else
-            ColorScheme::LIGHT_THEME_ID
-          end
+        base_scheme = default_theme&.color_scheme&.base_scheme_id
+        color_scheme_name = default_theme&.color_scheme&.name
+
+        scheme_id = default_theme_override ? (base_scheme || color_scheme_name) : ColorScheme::LIGHT_THEME_ID
 
         themes = step.add_field(
           id: 'theme_previews',
@@ -160,6 +158,14 @@ class Wizard
           value: scheme_id
         )
 
+        # fix for the case when base_scheme is nil
+        if scheme_id && default_theme_override && base_scheme.nil?
+          scheme = default_theme.color_scheme
+          default_colors = scheme.colors.select(:name, :hex)
+          choice_hash = default_colors.reduce({}) { |choice, color| choice[color.name] = "##{color.hex}"; choice }
+          themes.add_choice(scheme_id, data: { colors: choice_hash })
+        end
+
         ColorScheme.base_color_scheme_colors.each do |t|
           with_hash = t[:colors].dup
           with_hash.map { |k, v| with_hash[k] = "##{v}" }
@@ -172,7 +178,7 @@ class Wizard
             ColorScheme::LIGHT_THEME_ID
           )
 
-          next unless scheme_name.present?
+          next unless scheme_name.present? && ColorScheme.is_base?(scheme_name)
 
           name = I18n.t("color_schemes.#{scheme_name.downcase.gsub(' ', '_')}_theme_name")
 

spec/components/wizard/wizard_builder_spec.rb

@@ -162,7 +162,21 @@ describe Wizard::Builder do
       end
     end
 
-    describe "when the default them hass been override" do
+    describe "when the default theme has been override and the color scheme doesn't have a base scheme" do
+      let(:color_scheme) { Fabricate(:color_scheme, base_scheme_id: nil) }
+
+      before do
+        SiteSetting.default_theme_id = theme.id
+        theme.update(color_scheme: color_scheme)
+      end
+
+      it 'fallbacks to the color scheme name' do
+        expect(field.required).to eq(false)
+        expect(field.value).to eq(color_scheme.name)
+      end
+    end
+
+    describe "when the default theme has been override" do
       before do
         theme.set_default!
       end