FEATURE: Add `in:polls` filter to search (#19885)

Allows users to filter search results to posts with polls (if the plugin is enabled).

plugins/poll/assets/javascripts/initializers/extend-for-poll.js

@@ -134,6 +134,11 @@ function initializePolls(api) {
     id: "discourse-poll",
   });
   api.cleanupStream(cleanUpPolls);
+
+  const siteSettings = api.container.lookup("site-settings:main");
+  if (siteSettings.poll_enabled) {
+    api.addSearchSuggestion("in:polls");
+  }
 }
 
 export default {

plugins/poll/plugin.rb

@@ -231,4 +231,12 @@ after_initialize do
     SiteSetting.poll_enabled && scope.user&.id.present? && preloaded_polls.present? &&
       preloaded_polls.any? { |p| p.has_voted?(scope.user) }
   end
+
+  register_search_advanced_filter(/in:polls/) do |posts, match|
+    if SiteSetting.poll_enabled
+      posts.joins(:polls)
+    else
+      posts
+    end
+  end
 end

plugins/poll/spec/lib/search_spec.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+RSpec.describe Search do
+  fab!(:topic) { Fabricate(:topic) }
+  fab!(:topic2) { Fabricate(:topic) }
+  fab!(:regular_post) { Fabricate(:post, topic: topic, raw: <<~RAW) }
+      Somewhere over the rainbow but no poll.
+    RAW
+
+  fab!(:post_with_poll) { Fabricate(:post, topic: topic2, raw: <<~RAW) }
+      Somewhere over the rainbow with a poll.
+      [poll]
+      * Like
+      * Dislike
+      [/poll]
+    RAW
+
+  before do
+    SearchIndexer.enable
+    Jobs.run_immediately!
+
+    SearchIndexer.index(topic2, force: true)
+    SearchIndexer.index(topic, force: true)
+  end
+
+  after { SearchIndexer.disable }
+
+  context "when using in:polls" do
+    it "displays only posts containing polls" do
+      results = Search.execute("rainbow in:polls", guardian: Guardian.new)
+      expect(results.posts).to contain_exactly(post_with_poll)
+    end
+  end
+
+  context "when polls are disabled" do
+    it "ignores in:polls filter" do
+      SiteSetting.poll_enabled = false
+      results = Search.execute("rainbow in:polls", guardian: Guardian.new)
+      expect(results.posts).to contain_exactly(regular_post, post_with_poll)
+    end
+  end
+end