DEV: Introduce in:pinned filter for experimental /filter route (#20974)

This commit adds support for the `in:pinned` filter to the topics filtering
query language. When the filter is present, it will filter for topics
where `Topic#pinned_until` is greater than `Topic#pinned_at`.

lib/topics_filter.rb

@@ -14,6 +14,8 @@ class TopicsFilter
       /(?<key_prefix>[-=])?(?<key>\w+):(?<value>[^\s]+)/,
     ) do |key_prefix, key, value|
       case key
+      when "in"
+        @scope = filter_state(state: value)
       when "status"
         @scope = filter_status(status: value)
       when "tags"
@@ -84,6 +86,18 @@ class TopicsFilter
 
   private
 
+  def filter_state(state:)
+    case state
+    when "pinned"
+      @scope.where(
+        "topics.pinned_at IS NOT NULL AND topics.pinned_until > topics.pinned_at AND ? < topics.pinned_until",
+        Time.zone.now,
+      )
+    else
+      @scope
+    end
+  end
+
   def filter_categories(category_slugs:, exclude_subcategories: false, or_clause: false)
     category_ids = Category.ids_from_slugs(category_slugs)
 

spec/lib/topics_filter_spec.rb

@@ -24,6 +24,40 @@ RSpec.describe TopicsFilter do
       end
     end
 
+    describe "when filtering with the `in` filter" do
+      fab!(:topic) { Fabricate(:topic) }
+
+      fab!(:pinned_topic) do
+        Fabricate(:topic, pinned_at: Time.zone.now, pinned_until: 1.hour.from_now)
+      end
+
+      fab!(:expired_pinned_topic) do
+        Fabricate(:topic, pinned_at: 2.hour.ago, pinned_until: 1.hour.ago)
+      end
+
+      describe "when query string is `in:pinned`" do
+        it "should return topics that are pinned" do
+          expect(
+            TopicsFilter
+              .new(guardian: Guardian.new)
+              .filter_from_query_string("in:pinned")
+              .pluck(:id),
+          ).to contain_exactly(pinned_topic.id)
+        end
+
+        it "should not return pinned topics that have expired" do
+          freeze_time(2.hours.from_now) do
+            expect(
+              TopicsFilter
+                .new(guardian: Guardian.new)
+                .filter_from_query_string("in:pinned")
+                .pluck(:id),
+            ).to eq([])
+          end
+        end
+      end
+    end
+
     describe "when filtering by categories" do
       fab!(:category) { Fabricate(:category, name: "category") }