Pass the filename as an argument to Document#slug

lib/jekyll/document.rb

@@ -45,13 +45,15 @@ module Jekyll
       File.basename(path, suffix)
     end
 
-    # The sluggified base filename of the document.
+    # A sluggified filename or title.
     #
-    # Returns the base filename of the document in lowercase, with every
+    # name - the filename or title to sluggify
+    #
+    # Returns the given filename or title in lowercase, with every
     # sequence of spaces and non-alphanumeric characters replaced with a
     # hyphen.
-    def slug
+    def slug(name)
-      File.basename(path, ".*").downcase.gsub(/[\W\s]+/, '-')
+      name.downcase.gsub(/[\W\s]+/, '-')
     end
 
     # The extension name of the document.
@@ -138,7 +140,7 @@ module Jekyll
         collection: collection.label,
         path:       cleaned_relative_path,
         output_ext: Jekyll::Renderer.new(site, self).output_ext,
-        name:       slug
+        name:       slug(File.basename(path, ".*"))
       }
     end