update webpack manifest integration to recognize multi-chunk entrypoints

app/helpers/webpack_helper.rb

-require 'webpack/rails/manifest'
+require 'gitlab/webpack/manifest'
 
 module WebpackHelper
   def webpack_bundle_tag(bundle, force_same_domain: false)
-    javascript_include_tag(*gitlab_webpack_asset_paths(bundle, force_same_domain: force_same_domain))
+    javascript_include_tag(*entrypoint_paths(bundle, force_same_domain: force_same_domain))
   end
 
   def webpack_controller_bundle_tags
@@ -18,23 +18,22 @@ module WebpackHelper
 
     until route.empty?
       begin
-        asset_paths = gitlab_webpack_asset_paths("pages.#{route.join('.')}", extension: 'js')
+        asset_paths = entrypoint_paths("pages.#{route.join('.')}", extension: 'js')
         bundles.unshift(*asset_paths)
-      rescue Webpack::Rails::Manifest::EntryPointMissingError
+      rescue Gitlab::Webpack::Manifest::AssetMissingError
         # no bundle exists for this path
       end
 
       route.pop
     end
 
-    javascript_include_tag(*bundles)
+    javascript_include_tag(*bundles.uniq)
   end
 
-  # override webpack-rails gem helper until changes can make it upstream
-  def gitlab_webpack_asset_paths(source, extension: nil, force_same_domain: false)
+  def entrypoint_paths(source, extension: nil, force_same_domain: false)
     return "" unless source.present?
 
-    paths = Webpack::Rails::Manifest.asset_paths(source)
+    paths = Gitlab::Webpack::Manifest.entrypoint_paths(source)
     if extension
       paths.select! { |p| p.ends_with? ".#{extension}" }
     end

app/views/layouts/_head.html.haml

@@ -38,9 +38,6 @@
     = yield :library_javascripts
 
   = javascript_include_tag locale_path unless I18n.locale == :en
-  = webpack_bundle_tag "webpack_runtime"
-  = webpack_bundle_tag "common"
-  = webpack_bundle_tag "main"
   = webpack_bundle_tag "raven" if Gitlab::CurrentSettings.clientside_sentry_enabled
 
   - if content_for?(:page_specific_javascripts)

lib/gitlab/webpack/manifest.rb

+require 'webpack/rails/manifest'
+
+module Gitlab
+  module Webpack
+    class Manifest < ::Webpack::Rails::Manifest
+      # Raised if webpack couldn't build one of your assets
+      class WebpackError < StandardError
+        def initialize(errors)
+          super "Error in webpack compile, details follow below:\n#{errors.join("\n\n")}"
+        end
+      end
+
+      # Raised if a supplied asset does not exist in the webpack manifest
+      AssetMissingError = Class.new(StandardError)
+
+      class << self
+        def asset_paths(source)
+          raise ::Webpack::Rails::Manifest::WebpackError, manifest["errors"] unless manifest_bundled?
+
+          paths = manifest["assetsByChunkName"][source]
+          if paths
+            # Can be either a string or an array of strings.
+            # Do not include source maps as they are not javascript
+            [paths].flatten.reject { |p| p =~ /.*\.map$/ }.map do |p|
+              "/#{::Rails.configuration.webpack.public_path}/#{p}"
+            end
+          else
+            raise AssetMissingError, "Can't find asset '#{source}' in webpack manifest"
+          end
+        end
+
+        def entrypoint_paths(source)
+          raise ::Webpack::Rails::Manifest::WebpackError, manifest["errors"] unless manifest_bundled?
+
+          entrypoint = manifest["entrypoints"][source]
+          if entrypoint && entrypoint["assets"]
+            # Can be either a string or an array of strings.
+            # Do not include source maps as they are not javascript
+            [entrypoint["assets"]].flatten.reject { |p| p =~ /.*\.map$/ }.map do |p|
+              "/#{::Rails.configuration.webpack.public_path}/#{p}"
+            end
+          else
+            raise AssetMissingError, "Can't find entry point '#{source}' in webpack manifest"
+          end
+        end
+      end
+    end
+  end
+end