FIX: Child themes being precompiled multiple times take 2. (#13599)

This fix was reverted in 128fdf9d9ce92275ecb0a2bdb12bdf038a811a45 but
fix is still relevant.

lib/stylesheet/manager.rb

@@ -42,7 +42,7 @@ class Stylesheet::Manager
   end
 
   def self.precompile_css
-    themes = Theme.where('user_selectable OR id = ?', SiteSetting.default_theme_id).pluck(:id, :name, :color_scheme_id)
+    themes = Theme.where('user_selectable OR id = ?', SiteSetting.default_theme_id).pluck(:id, :color_scheme_id)
     themes << nil
 
     color_schemes = ColorScheme.where(user_selectable: true).to_a
@@ -51,8 +51,9 @@ class Stylesheet::Manager
 
     targets = [:desktop, :mobile, :desktop_rtl, :mobile_rtl, :desktop_theme, :mobile_theme, :admin, :wizard]
     targets += Discourse.find_plugin_css_assets(include_disabled: true, mobile_view: true, desktop_view: true)
+    compiled = Set.new
 
-    themes.each do |id, name, color_scheme_id|
+    themes.each do |id, color_scheme_id|
       theme_id = id || SiteSetting.default_theme_id
       manager = self.new(theme_id: theme_id)
 
@@ -63,16 +64,19 @@ class Stylesheet::Manager
           scss_checker = ScssChecker.new(target, manager.theme_ids)
 
           manager.load_themes(manager.theme_ids).each do |theme|
+            next if compiled.include?("#{target}_#{theme.id}")
+
             builder = Stylesheet::Manager::Builder.new(
               target: target, theme: theme, manager: manager
             )
 
-            STDERR.puts "precompile target: #{target} #{builder.theme.name}"
             next if theme.component && !scss_checker.has_scss(theme.id)
+            $stderr.puts "precompile target: #{target} #{theme.name}"
             builder.compile(force: true)
+            compiled << "#{target}_#{theme.id}"
           end
         else
-          STDERR.puts "precompile target: #{target} #{name}"
+          $stderr.puts "precompile target: #{target} #{name}"
 
           Stylesheet::Manager::Builder.new(
             target: target, theme: manager.get_theme(theme_id), manager: manager
@@ -81,17 +85,19 @@ class Stylesheet::Manager
       end
 
       theme_color_scheme = ColorScheme.find_by_id(color_scheme_id) || ColorScheme.base
+      theme = manager.get_theme(theme_id)
 
       [theme_color_scheme, *color_schemes].uniq.each do |scheme|
-        STDERR.puts "precompile target: #{COLOR_SCHEME_STYLESHEET} #{name} (#{scheme.name})"
+        $stderr.puts "precompile target: #{COLOR_SCHEME_STYLESHEET} (#{scheme.name}) #{theme&.name}"
 
         Stylesheet::Manager::Builder.new(
           target: COLOR_SCHEME_STYLESHEET,
-          theme: manager.get_theme(theme_id),
+          theme: theme,
           color_scheme: scheme,
           manager: manager
         ).compile(force: true)
       end
+
       clear_color_scheme_cache!
     end
 

spec/components/stylesheet/manager_spec.rb

@@ -650,13 +650,19 @@ describe Stylesheet::Manager do
         t.save!
 
         user_theme.add_relative_theme!(:child, t)
+        default_theme.add_relative_theme!(:child, t)
       end
 
       default_theme.set_default!
 
       StylesheetCache.destroy_all
 
-      Stylesheet::Manager.precompile_css
+      output = capture_output(:stderr) do
+        Stylesheet::Manager.precompile_css
+      end
+
+      # Ensure we force compile each theme only once
+      expect(output.scan(/#{child_theme_with_css.name}/).length).to eq(2)
       results = StylesheetCache.pluck(:target)
 
       expect(results.size).to eq(24) # (2 themes x 8 targets) + (1 child Theme x 2 targets) + 6 color schemes (2 custom theme schemes, 4 base schemes)