LayoutReader#read: read in Theme layouts if they aren't already registered

lib/jekyll/readers/layout_reader.rb

@@ -7,8 +7,12 @@ module Jekyll
     end
 
     def read
-      layout_entries.each do |f|
-        @layouts[layout_name(f)] = Layout.new(site, layout_directory, f)
+      layout_entries.each do |layout_file|
+        @layouts[layout_name(layout_file)] = Layout.new(site, layout_directory, layout_file)
+      end
+
+      theme_layout_entries.each do |layout_file|
+        @layouts[layout_name(layout_file)] ||= Layout.new(site, theme_layout_directory, layout_file)
       end
 
       @layouts
@@ -18,11 +22,23 @@ module Jekyll
       @layout_directory ||= (layout_directory_in_cwd || layout_directory_inside_source)
     end
 
+    def theme_layout_directory
+      @theme_layout_directory ||= site.theme.layout_dir if site.theme
+    end
+
     private
 
     def layout_entries
+      entries_in layout_directory
+    end
+
+    def theme_layout_entries
+      theme_layout_directory ? entries_in(theme_layout_directory) : []
+    end
+
+    def entries_in(dir)
       entries = []
-      within(layout_directory) do
+      within(dir) do
         entries = EntryFilter.new(site).filter(Dir['**/*.*'])
       end
       entries