Fix public timeline showing reblogs of unlisted posts

Fixes #2723

app/models/public_feed.rb

@@ -24,7 +24,11 @@ class PublicFeed
 
     scope.merge!(without_local_only_scope) unless allow_local_only?
     scope.merge!(without_replies_scope) unless with_replies?
-    scope.merge!(without_reblogs_scope) unless with_reblogs?
+    if with_reblogs?
+      scope.merge!(with_reblogs_of_public_scope)
+    else
+      scope.merge!(without_reblogs_scope)
+    end
     scope.merge!(local_only_scope) if local_only?
     scope.merge!(remote_only_scope) if remote_only?
     scope.merge!(account_filters_scope) if account?
@@ -90,6 +94,10 @@ class PublicFeed
     Status.without_reblogs
   end
 
+  def with_reblogs_of_public_scope
+    Status.left_outer_joins(:reblog).where(reblog: { visibility: [nil, :public] })
+  end
+
   def media_only_scope
     Status.joins(:media_attachments).group(:id)
   end

spec/models/public_feed_spec.rb

@@ -41,6 +41,20 @@ RSpec.describe PublicFeed do
       expect(subject).to_not include(silenced_status.id)
     end
 
+    context 'with with_reblogs option' do
+      subject { described_class.new(nil, with_reblogs: true).get(20).map(&:id) }
+
+      it 'lists public reblogs of public posts, but not public reblogs of unlisted posts' do
+        status = Fabricate(:status, visibility: :public)
+        boost = Fabricate(:status, reblog_of_id: status.id, visibility: :public)
+        unlisted_status = Fabricate(:status, visibility: :unlisted)
+        excluded_boost = Fabricate(:status, reblog_of_id: unlisted_status.id, visibility: :public)
+
+        expect(subject).to include(boost.id)
+          .and not_include(excluded_boost.id)
+      end
+    end
+
     context 'without local_only option' do
       subject { described_class.new(viewer).get(20).map(&:id) }