UX: Exclude search ignored and user muted categories in similarity search (#19349)

When finding the candidates for `Topic.similar_to`, we will now ignore
topics in categories where `Category#search_priority` has been set to
ignore and also topics in categories which the user has specifically
muted.

Internal Ref: /t/87132

app/models/topic.rb

@@ -634,14 +634,27 @@ class Topic < ActiveRecord::Base
 
     tsquery = Search.to_tsquery(term: tsquery, joiner: "|")
 
+    guardian = Guardian.new(user)
+
+    excluded_category_ids_sql = Category.secured(guardian).where(search_priority: Searchable::PRIORITIES[:ignore]).select(:id).to_sql
+
+    if user
+      excluded_category_ids_sql = <<~SQL
+      #{excluded_category_ids_sql}
+      UNION
+      #{CategoryUser.where(notification_level: CategoryUser.notification_levels[:muted], user: user).select(:category_id).to_sql}
+      SQL
+    end
+
     candidates = Topic
       .visible
       .listable_topics
-      .secured(Guardian.new(user))
+      .secured(guardian)
       .joins("JOIN topic_search_data s ON topics.id = s.topic_id")
       .joins("LEFT JOIN categories c ON topics.id = c.topic_id")
       .where("search_data @@ #{tsquery}")
       .where("c.topic_id IS NULL")
+      .where("topics.category_id NOT IN (#{excluded_category_ids_sql})")
       .order("ts_rank(search_data, #{tsquery}) DESC")
       .limit(SiteSetting.max_similar_results * 3)
 

spec/models/topic_spec.rb

@@ -685,10 +685,28 @@ RSpec.describe Topic do
         expect(topics).to eq([])
       end
 
+      it 'does not return topics from categories with search priority set to ignore' do
+        expect(Topic.similar_to("has evil trout made any topics?", "")).to eq([topic])
+
+        topic.category.update!(search_priority: Searchable::PRIORITIES[:ignore])
+
+        expect(Topic.similar_to("has evil trout made any topics?", "")).to eq([])
+      end
+
+      it 'does not return topics from categories which the user has muted' do
+        expect(Topic.similar_to("has evil trout made any topics?", "", user)).to eq([topic])
+
+        CategoryUser.create!(category: topic.category, user: user, notification_level: CategoryUser.notification_levels[:muted])
+
+        expect(Topic.similar_to("has evil trout made any topics?", "", user)).to eq([])
+      end
+
       context "with secure categories" do
+        fab!(:group) { Fabricate(:group) }
+        fab!(:private_category) { Fabricate(:private_category, group: group) }
+
         before do
-          category.update!(read_restricted: true)
-          topic.update!(category: category)
+          topic.update!(category: private_category)
         end
 
         it "doesn't return topics from private categories" do
@@ -696,7 +714,8 @@ RSpec.describe Topic do
         end
 
         it "should return the cat since the user can see it" do
-          Guardian.any_instance.expects(:secure_category_ids).returns([category.id])
+          group.add(user)
+
           expect(Topic.similar_to("has evil trout made any topics?", "i am wondering has evil trout made any topics?", user)).to include(topic)
         end
       end