aliases: warn about conflicting wikis when alias is requested.

* Warn about conflicting wiki pages during secondary validation.

* Only warn about missing wiki if both tags are missing a wiki page.

app/models/tag_alias.rb

@@ -5,7 +5,7 @@ class TagAlias < TagRelationship
   after_save :create_mod_action
   validates_uniqueness_of :antecedent_name
   validate :absence_of_transitive_relation
-  validate :consequent_has_wiki_page, on: :create, unless: :skip_secondary_validations
+  validate :wiki_pages_present, on: :create, unless: :skip_secondary_validations
   validate :mininum_antecedent_count, on: :create, unless: :skip_secondary_validations
 
   module CacheMethods
@@ -195,8 +195,10 @@ class TagAlias < TagRelationship
     destroy
   end
 
-  def consequent_has_wiki_page
+  def wiki_pages_present
-    if consequent_wiki.nil?
+    if antecedent_wiki.present? && consequent_wiki.present?
+      errors[:base] << conflict_message
+    elsif antecedent_wiki.blank? && consequent_wiki.blank?
       errors[:base] << "The #{consequent_name} tag needs a corresponding wiki page"
     end
   end

test/unit/tag_alias_test.rb

@@ -42,6 +42,25 @@ class TagAliasTest < ActiveSupport::TestCase
 
       should_not allow_value(nil).for(:creator_id)
       should_not allow_value(-1).for(:creator_id).with_message("must exist", against: :creator)
+
+    end
+
+    context "on secondary validation" do
+      should "warn about missing wiki pages" do
+        ti = FactoryBot.build(:tag_alias, antecedent_name: "aaa", consequent_name: "bbb", skip_secondary_validations: false)
+
+        assert(ti.invalid?)
+        assert_includes(ti.errors[:base], "The bbb tag needs a corresponding wiki page")
+      end
+
+      should "warn about conflicting wiki pages" do
+        FactoryBot.create(:wiki_page, title: "aaa", body: "aaa")
+        FactoryBot.create(:wiki_page, title: "bbb", body: "bbb")
+        ti = FactoryBot.build(:tag_alias, antecedent_name: "aaa", consequent_name: "bbb", skip_secondary_validations: false)
+
+        assert(ti.invalid?)
+        assert_includes(ti.errors[:base], "The tag alias [[aaa]] -> [[bbb]]  has conflicting wiki pages. [[bbb]] should be updated to include information from [[aaa]] if necessary.")
+      end
     end
 
     should "populate the creator information" do