diff --git a/middleman-core/features/custom_layouts.feature b/middleman-core/features/custom_layouts.feature
index 27f7df08..dfe52344 100644
--- a/middleman-core/features/custom_layouts.feature
+++ b/middleman-core/features/custom_layouts.feature
@@ -11,6 +11,22 @@ Feature: Custom layouts
     When I go to "/custom-layout.html"
     Then I should see "Custom Layout"
 
+  Scenario: Using custom :layout attribute with proxy
+    Given a fixture app "custom-layout-app2"
+    And a file named "config.rb" with:
+      """
+      page '/test/*', layout: :custom
+      proxy "/test/me.html", "/custom-layout.html"
+      live { %w(you) }.each do |who|
+        proxy "/test/#{who}.html", "/custom-layout.html"
+      end
+      """
+    And the Server is running at "custom-layout-app2"
+    When I go to "/test/me.html"
+    Then I should see "Custom Layout"
+    When I go to "/test/you.html"
+    Then I should see "Custom Layout"
+
   Scenario: Using custom :layout attribute with folders
     Given a fixture app "custom-layout-app2"
     And a file named "config.rb" with:
@@ -65,4 +81,4 @@ Feature: Custom layouts
     When I go to "/path/index.html"
     Then I should see "Alt"
     And I should see "Monde"
-    And I should not see "Hello"
\ No newline at end of file
+    And I should not see "Hello"
diff --git a/middleman-core/lib/middleman-core/builder.rb b/middleman-core/lib/middleman-core/builder.rb
index 9bb3c031..d2235c5f 100644
--- a/middleman-core/lib/middleman-core/builder.rb
+++ b/middleman-core/lib/middleman-core/builder.rb
@@ -97,7 +97,7 @@ module Middleman
 
       ::Middleman::Util.instrument 'builder.prerender.check-files' do
         # Double-check for compass sprites
-        if @app.files.find_new_files!.length > 0
+        unless @app.files.find_new_files!.empty?
           logger.debug '== Checking for Compass sprites'
           @app.sitemap.ensure_resource_list_updated!
         end
diff --git a/middleman-core/lib/middleman-core/configuration.rb b/middleman-core/lib/middleman-core/configuration.rb
index 3f889c00..c916fc90 100644
--- a/middleman-core/lib/middleman-core/configuration.rb
+++ b/middleman-core/lib/middleman-core/configuration.rb
@@ -40,7 +40,7 @@ module Middleman
 
       # Allow configuration settings to be read and written via methods
       def method_missing(method, *args)
-        if defines_setting?(method) && args.size == 0
+        if defines_setting?(method) && args.empty?
           self[method]
         elsif method.to_s =~ /^(\w+)=$/ && args.size == 1
           self[$1.to_sym] = args[0]
diff --git a/middleman-core/lib/middleman-core/core_extensions/i18n.rb b/middleman-core/lib/middleman-core/core_extensions/i18n.rb
index 9f7503b8..ac86d9a0 100644
--- a/middleman-core/lib/middleman-core/core_extensions/i18n.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/i18n.rb
@@ -102,7 +102,7 @@ class Middleman::CoreExtensions::Internationalization < ::Middleman::Extension
       locale_suffix = ::I18n.locale
 
       extname = File.extname(partial_name)
-      maybe_static = extname.length > 0
+      maybe_static = !extname.empty?
       suffixed_partial_name = if maybe_static
         partial_name.sub(extname, ".#{locale_suffix}#{extname}")
       else
diff --git a/middleman-core/lib/middleman-core/core_extensions/routing.rb b/middleman-core/lib/middleman-core/core_extensions/routing.rb
index b10fba53..f47ac16b 100644
--- a/middleman-core/lib/middleman-core/core_extensions/routing.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/routing.rb
@@ -4,7 +4,7 @@ module Middleman
     class Routing < ConfigExtension
       # This should always run late, but not as late as :directory_indexes,
       # so it can add metadata to any pages generated by other extensions
-      self.resource_list_manipulator_priority = 10
+      self.resource_list_manipulator_priority = [10, 130]
 
       # Expose the `page` method to config.
       expose_to_config :page
@@ -25,7 +25,7 @@ module Middleman
 
           resources
             .select { |r| ::Middleman::Util.path_match(normalized_path, "/#{r.path}") }
-            .each { |r| r.add_metadata(metadata) }
+            .each { |r| r.add_metadata(metadata, true) }
 
           resources
         end
diff --git a/middleman-core/lib/middleman-core/extension.rb b/middleman-core/lib/middleman-core/extension.rb
index e8e36af0..d9dc01ca 100644
--- a/middleman-core/lib/middleman-core/extension.rb
+++ b/middleman-core/lib/middleman-core/extension.rb
@@ -402,11 +402,11 @@ module Middleman
         ext.after_configuration if ext.respond_to?(:after_configuration)
 
         if ext.respond_to?(:manipulate_resource_list)
-          ext.app.sitemap.register_resource_list_manipulator(ext.class.ext_name, ext, ext.class.resource_list_manipulator_priority)
+          ext.app.sitemap.register_resource_list_manipulators(ext.class.ext_name, ext, ext.class.resource_list_manipulator_priority)
         end
 
         if ext.class.resources_generators && !ext.class.resources_generators.empty?
-          ext.app.sitemap.register_resource_list_manipulator(
+          ext.app.sitemap.register_resource_list_manipulators(
             :"#{ext.class.ext_name}_generator",
             ext,
             ext.class.resource_list_manipulator_priority,
diff --git a/middleman-core/lib/middleman-core/extensions/external_pipeline.rb b/middleman-core/lib/middleman-core/extensions/external_pipeline.rb
index 0e09dc17..d4a5aab5 100644
--- a/middleman-core/lib/middleman-core/extensions/external_pipeline.rb
+++ b/middleman-core/lib/middleman-core/extensions/external_pipeline.rb
@@ -30,7 +30,7 @@ class Middleman::Extensions::ExternalPipeline < ::Middleman::Extension
     ::IO.popen(options[:command], 'r') do |pipe|
       while buf = pipe.gets
         without_newline = buf.sub(/\n$/, '')
-        logger.info "== External: #{without_newline}" if without_newline.length > 0
+        logger.info "== External: #{without_newline}" unless without_newline.empty?
       end
     end
 
diff --git a/middleman-core/lib/middleman-core/logger.rb b/middleman-core/lib/middleman-core/logger.rb
index 30e28307..1c0170d1 100644
--- a/middleman-core/lib/middleman-core/logger.rb
+++ b/middleman-core/lib/middleman-core/logger.rb
@@ -7,7 +7,7 @@ module Middleman
   # The Middleman Logger
   class Logger < ActiveSupport::Logger
     def self.singleton(*args)
-      if !@_logger || args.length > 0
+      if !@_logger || !args.empty?
         if args.length == 1 && (args.first.is_a?(::String) || args.first.respond_to?(:write))
           args = [0, false, args.first]
         end
diff --git a/middleman-core/lib/middleman-core/rack.rb b/middleman-core/lib/middleman-core/rack.rb
index cf241d9f..293a2e43 100644
--- a/middleman-core/lib/middleman-core/rack.rb
+++ b/middleman-core/lib/middleman-core/rack.rb
@@ -125,7 +125,7 @@ module Middleman
 
     # Halt request and return 404
     def not_found(res, path)
-      path = ::Rack::Utils::escape_html(path)
+      path = ::Rack::Utils.escape_html(path)
       res.status = 404
       res.write "<html><head></head><body><h1>File Not Found</h1><p>#{path}</p></body></html>"
       res.finish
diff --git a/middleman-core/lib/middleman-core/renderers/redcarpet.rb b/middleman-core/lib/middleman-core/renderers/redcarpet.rb
index 122de759..1542489c 100644
--- a/middleman-core/lib/middleman-core/renderers/redcarpet.rb
+++ b/middleman-core/lib/middleman-core/renderers/redcarpet.rb
@@ -76,7 +76,7 @@ module Middleman
           scope.image_tag(link, title: title, alt: alt_text)
         else
           link_string = link.dup
-          link_string << %("#{title}") if title && title.length > 0 && title != alt_text
+          link_string << %("#{title}") if title && !title.empty? && title != alt_text
           "![#{alt_text}](#{link_string})"
         end
       end
@@ -89,7 +89,7 @@ module Middleman
           scope.link_to(content, link, attributes)
         else
           link_string = link.dup
-          link_string << %("#{title}") if title && title.length > 0 && title != alt_text
+          link_string << %("#{title}") if title && !title.empty? && title != alt_text
           "[#{content}](#{link_string})"
         end
       end
diff --git a/middleman-core/lib/middleman-core/sitemap/resource.rb b/middleman-core/lib/middleman-core/sitemap/resource.rb
index 22213c21..fd236f3f 100644
--- a/middleman-core/lib/middleman-core/sitemap/resource.rb
+++ b/middleman-core/lib/middleman-core/sitemap/resource.rb
@@ -96,10 +96,15 @@ module Middleman
       #   Locals are local variables for rendering this resource's template
       #   Page are data that is exposed through this resource's data member.
       #   Note: It is named 'page' for backwards compatibility with older MM.
-      Contract METADATA_HASH => METADATA_HASH
-      def add_metadata(meta={})
+      Contract METADATA_HASH, Maybe[Bool] => METADATA_HASH
+      def add_metadata(meta={}, reverse=false)
         @page_data = nil
-        @metadata.deep_merge!(meta)
+
+        @metadata = if reverse
+          meta.deep_merge(@metadata)
+        else
+          @metadata.deep_merge(meta)
+        end
       end
 
       # Data about this resource, populated from frontmatter or extensions.
diff --git a/middleman-core/lib/middleman-core/sitemap/store.rb b/middleman-core/lib/middleman-core/sitemap/store.rb
index a7ade5fc..4667936d 100644
--- a/middleman-core/lib/middleman-core/sitemap/store.rb
+++ b/middleman-core/lib/middleman-core/sitemap/store.rb
@@ -87,6 +87,13 @@ module Middleman
         @app.config_context.class.send :def_delegator, :app, :sitemap
       end
 
+      Contract Symbol, RespondTo[:manipulate_resource_list], Maybe[Or[Num, ArrayOf[Num]]], Maybe[Symbol] => Any
+      def register_resource_list_manipulators(name, manipulator, priority=50, custom_name=nil)
+        Array(priority || 50).each do |p|
+          register_resource_list_manipulator(name, manipulator, p, custom_name)
+        end
+      end
+
       # Register an object which can transform the sitemap resource list. Best to register
       # these in a `before_configuration` or `after_configuration` hook.
       #
@@ -221,7 +228,7 @@ module Middleman
 
             @resource_list_manipulators.each do |m|
               ::Middleman::Util.instrument 'sitemap.manipulator', name: m[:name] do
-                @app.logger.debug "== Running manipulator: #{m[:name]}"
+                @app.logger.debug "== Running manipulator: #{m[:name]} (#{m[:priority]})"
                 @resources = m[:manipulator].send(m[:custom_name] || :manipulate_resource_list, @resources)
 
                 # Reset lookup cache
diff --git a/middleman-core/lib/middleman-core/util/files.rb b/middleman-core/lib/middleman-core/util/files.rb
index f8fb1316..4422b3ef 100644
--- a/middleman-core/lib/middleman-core/util/files.rb
+++ b/middleman-core/lib/middleman-core/util/files.rb
@@ -104,30 +104,19 @@ module Middleman
       sass_type_aliasing = ['.scss', '.sass']
       erb_type_aliasing = ['.erb', '.haml', '.slim']
 
-      if (all_extensions & sass_type_aliasing).length > 0
-        all_extensions |= sass_type_aliasing
-      end
-
-      if (all_extensions & erb_type_aliasing).length > 0
-        all_extensions |= erb_type_aliasing
-      end
+      all_extensions |= sass_type_aliasing unless (all_extensions & sass_type_aliasing).empty?
+      all_extensions |= erb_type_aliasing unless (all_extensions & erb_type_aliasing).empty?
 
       all_extensions.uniq!
 
       app.sitemap.resources.select(&:file_descriptor).select { |r|
         local_extensions = collect_extensions(r.file_descriptor[:full_path].to_s)
-
-        if (local_extensions & sass_type_aliasing).length > 0
-          local_extensions |= sass_type_aliasing
-        end
-
-        if (local_extensions & erb_type_aliasing).length > 0
-          local_extensions |= erb_type_aliasing
-        end
+        local_extensions |= sass_type_aliasing unless (local_extensions & sass_type_aliasing).empty?
+        local_extensions |= erb_type_aliasing unless (local_extensions & erb_type_aliasing).empty?
 
         local_extensions.uniq!
 
-        ((all_extensions & local_extensions).length > 0) && files.none? { |f| f == r.file_descriptor[:full_path] }
+        !(all_extensions & local_extensions).empty? && files.none? { |f| f == r.file_descriptor[:full_path] }
       }.map(&:file_descriptor)
     end
   end