FIX: Don't run post validations when hiding post (#23139)

When hiding a post (essentially updating hidden, hidden_at, and hidden_reason_id) our callbacks are running the whole battery of post validations. This can cause the hiding to fail in a number of edge cases. The issue is similar to the one fixed in #11680, but applies to all post validations, none of which should apply when hiding a post.

After some code reading and discussion, none of the validations in PostValidator seem to be relevant when hiding posts, so instead of just skipping unique check, we skip all post validator checks.

app/models/post.rb

@@ -585,13 +585,10 @@ class Post < ActiveRecord::Base
 
     hiding_again = hidden_at.present?
 
-    self.hidden = true
-    self.hidden_at = Time.zone.now
-    self.hidden_reason_id = reason
-    self.skip_unique_check = true
-
     Post.transaction do
-      save!
+      self.skip_validation = true
+
+      update!(hidden: true, hidden_at: Time.zone.now, hidden_reason_id: reason)
 
       Topic.where(
         "id = :topic_id AND NOT EXISTS(SELECT 1 FROM POSTS WHERE topic_id = :topic_id AND NOT hidden)",

spec/models/post_spec.rb

@@ -1441,17 +1441,12 @@ RSpec.describe Post do
 
     after { Discourse.redis.flushdb }
 
-    it "should ignore the unique post validator when hiding a post with similar content as a recent post" do
-      post_2 = Fabricate(:post, user: post.user)
-      SiteSetting.unique_posts_mins = 10
-      post.store_unique_post_key
+    it "should not run post validations" do
+      PostValidator.any_instance.expects(:validate).never
 
-      expect(post_2.valid?).to eq(false)
-      expect(post_2.errors.full_messages.to_s).to include(I18n.t(:just_posted_that))
-
-      post_2.hide!(PostActionType.types[:off_topic])
-
-      expect(post_2.reload.hidden).to eq(true)
+      expect { post.hide!(PostActionType.types[:off_topic]) }.to change { post.reload.hidden }.from(
+        false,
+      ).to(true)
     end
 
     it "should decrease user_stat topic_count for first post" do