prevent Gollum::Wiki instances from creating new pages that overwrite pages with the same name.

lib/gollum.rb

@@ -58,5 +58,19 @@ module Gollum
       'img' => {'href' => ['http', 'https', :relative]}
     }
   }
+
+  class Error < StandardError; end
+  class DuplicatePageError < Error
+    attr_accessor :dir
+    attr_accessor :existing_path
+    attr_accessor :attempted_path
+
+    def initialize(dir, existing, attempted, message = nil)
+      @dir            = dir
+      @existing_path  = existing
+      @attempted_path = attempted
+      super(message || "Cannot write #{@dir}/#{@attempted_path}, found #{@dir}/#{@existing_path}.")
+    end
+  end
 end