Fix implication antecedents with aliases

app/models/tag_implication.rb

@@ -8,6 +8,7 @@ class TagImplication < ActiveRecord::Base
   validates_presence_of :creator_id, :antecedent_name, :consequent_name
   validates_uniqueness_of :antecedent_name, :scope => :consequent_name
   validate :absence_of_circular_relation
+  validate :antecedent_is_not_aliased
   validate :consequent_is_not_aliased
 
   module DescendantMethods
@@ -126,6 +127,14 @@ class TagImplication < ActiveRecord::Base
     end
   end
 
+  def antecedent_is_not_aliased
+    # We don't want to implicate a -> b if a is already aliased to c
+    if TagAlias.exists?(["antecedent_name = ?", antecedent_name])
+      self.errors[:base] << "Antecedent tag must not be aliased to another tag"
+      false
+    end
+  end
+
   def consequent_is_not_aliased
     # We don't want to implicate a -> b if b is already aliased to c
     if TagAlias.exists?(["antecedent_name = ?", consequent_name])