PERF: don't recompile css files that have already been compiled

lib/sass/discourse_stylesheets.rb

@@ -33,9 +33,9 @@ class DiscourseStylesheets
 
   def self.compile(target = :desktop, opts={})
     @lock.synchronize do
-      FileUtils.rm(MANIFEST_FULL_PATH, force: true) if opts[:force] # Force a recompile, even in production env
+      FileUtils.rm(MANIFEST_FULL_PATH, force: true) if opts[:force]
       builder = self.new(target)
-      builder.compile
+      builder.compile(opts)
       builder.stylesheet_filename
     end
   end
@@ -76,7 +76,20 @@ class DiscourseStylesheets
     @target = target
   end
 
-  def compile
+  def compile(opts={})
+    unless opts[:force]
+      if File.exists?(stylesheet_fullpath)
+        unless StylesheetCache.where(target: @target, digest: digest).exists?
+          begin
+            StylesheetCache.add(@target, digest, File.read(stylesheet_fullpath))
+          rescue => e
+            Rails.logger.warn "Completely unexpected error adding contents of '#{stylesheet_fullpath}' to cache #{e}"
+          end
+        end
+        return true
+      end
+    end
+
     scss = File.read("#{Rails.root}/app/assets/stylesheets/#{@target}.scss")
     css = begin
       DiscourseSassCompiler.compile(scss, @target)

lib/tasks/assets.rake

@@ -72,16 +72,18 @@ task 'assets:precompile:before' do
 end
 
 task 'assets:precompile:css' => 'environment' do
+  puts "Start compiling CSS: #{Time.zone.now}"
   RailsMultisite::ConnectionManagement.each_connection do |db|
     # Heroku precompiles assets before db migration, so tables may not exist.
     # css will get precompiled during first request instead in that case.
     if ActiveRecord::Base.connection.table_exists?(ColorScheme.table_name)
       puts "Compiling css for #{db}"
       [:desktop, :mobile].each do |target|
-        puts DiscourseStylesheets.compile(target, force: true)
+        puts DiscourseStylesheets.compile(target)
       end
     end
   end
+  puts "Done compiling CSS: #{Time.zone.now}"
 end
 
 def assets_path

spec/components/discourse_stylesheets_spec.rb

@@ -7,14 +7,14 @@ describe DiscourseStylesheets do
     it "can compile desktop bundle" do
       DiscoursePluginRegistry.stubs(:stylesheets).returns(["#{Rails.root}/spec/fixtures/scss/my_plugin.scss"])
       builder = described_class.new(:desktop)
-      expect(builder.compile).to include('my-plugin-thing')
+      expect(builder.compile(force: true)).to include('my-plugin-thing')
       FileUtils.rm builder.stylesheet_fullpath
     end
 
     it "can compile mobile bundle" do
       DiscoursePluginRegistry.stubs(:mobile_stylesheets).returns(["#{Rails.root}/spec/fixtures/scss/my_plugin.scss"])
       builder = described_class.new(:mobile)
-      expect(builder.compile).to include('my-plugin-thing')
+      expect(builder.compile(force: true)).to include('my-plugin-thing')
       FileUtils.rm builder.stylesheet_fullpath
     end
 
@@ -24,7 +24,7 @@ describe DiscourseStylesheets do
         "#{Rails.root}/spec/fixtures/scss/broken.scss"
       ])
       builder = described_class.new(:desktop)
-      expect(builder.compile).not_to include('my-plugin-thing')
+      expect(builder.compile(force: true)).not_to include('my-plugin-thing')
       FileUtils.rm builder.stylesheet_fullpath
     end
   end