implications: don't update posts that already have the new tag.

When approving an implication, only retag posts that are missing the new
tag. Don't try to update posts that already have the tag. This makes
large implication requests faster to process when most of the posts
already have the implied tag.

app/models/tag_implication.rb

@@ -110,8 +110,15 @@ class TagImplication < TagRelationship
 
   module ApprovalMethods
     def process!
+      update_posts!
+    end
+
+    def update_posts!
       CurrentUser.scoped(User.system) do
-        update_posts
+        Post.system_tag_match("#{antecedent_name} -#{consequent_name}").find_each do |post|
+          post.lock!
+          post.save!
+        end
       end
     end
 

app/models/tag_relationship.rb

@@ -118,16 +118,6 @@ class TagRelationship < ApplicationRecord
     end
   end
 
-  def update_posts
-    Post.without_timeout do
-      Post.raw_tag_match(antecedent_name).find_each do |post|
-        post.with_lock do
-          post.save!
-        end
-      end
-    end
-  end
-
   def self.approve!(antecedent_name:, consequent_name:, approver:, forum_topic: nil)
     ProcessTagRelationshipJob.perform_later(class_name: self.name, approver: approver, antecedent_name: antecedent_name, consequent_name: consequent_name, forum_topic: forum_topic)
   end

test/unit/tag_implication_test.rb

@@ -116,13 +116,14 @@ class TagImplicationTest < ActiveSupport::TestCase
     end
 
     should "update any affected post upon save" do
-      p1 = FactoryBot.create(:post, :tag_string => "aaa bbb ccc")
+      p1 = create(:post, tag_string: "sword")
+      p2 = create(:post, tag_string: "sword weapon")
 
-      TagImplication.approve!(antecedent_name: "aaa", consequent_name: "xxx", approver: @admin)
+      TagImplication.approve!(antecedent_name: "sword", consequent_name: "weapon", approver: @admin)
-      TagImplication.approve!(antecedent_name: "aaa", consequent_name: "yyy", approver: @admin)
       perform_enqueued_jobs
 
-      assert_equal("aaa bbb ccc xxx yyy", p1.reload.tag_string)
+      assert_equal("sword weapon", p1.reload.tag_string)
+      assert_equal("sword weapon", p2.reload.tag_string)
     end
 
     context "when calculating implied tags" do