BURs: refactor implication wiki page validations.

Move the validation that the tags in an implication must have wiki pages
back into the TagImplication model. Use validation contexts to only run
the validation when the BUR is created, not when the BUR is approved.

app/models/bulk_update_request.rb

@@ -73,6 +73,7 @@ class BulkUpdateRequest < ApplicationRecord
     def approve!(approver)
       transaction do
         CurrentUser.scoped(approver) do
+          processor.validate!(:approval)
           processor.process!(approver)
           update!(status: "approved", approver: approver)
           forum_updater.update("The #{bulk_update_request_link} (forum ##{forum_post.id}) has been approved by @#{approver.name}.")
@@ -107,7 +108,7 @@ class BulkUpdateRequest < ApplicationRecord
   end
 
   def validate_script
-    if processor.invalid?
+    if processor.invalid?(:request)
       errors[:base] << processor.errors.full_messages.join("; ")
     end
   end

app/models/tag_implication.rb

@@ -7,6 +7,7 @@ class TagImplication < TagRelationship
   validate :absence_of_transitive_relation
   validate :antecedent_is_not_aliased
   validate :consequent_is_not_aliased
+  validate :has_wiki_page, on: :request
 
   concerning :HierarchyMethods do
     class_methods do
@@ -91,6 +92,16 @@ class TagImplication < TagRelationship
         errors[:base] << "Consequent tag must not be aliased to another tag"
       end
     end
+
+    def has_wiki_page
+      if !antecedent_tag.empty? && antecedent_wiki.blank?
+        errors[:base] << "'#{antecedent_name}' must have a wiki page"
+      end
+
+      if !consequent_tag.empty? && consequent_wiki.blank?
+        errors[:base] << "'#{consequent_name}' must have a wiki page"
+      end
+    end
   end
 
   concerning :ApprovalMethods do