Ensure blocked user unfollows blocker if Block/Undo Block are processed out of order (#9687)

* Ensure blocked user unfollows blocker if Block/Undo Block are processed out of order

* Add specs for Block causing unfollow and for out-of-order Block + Undo

app/lib/activitypub/activity/block.rb

@@ -4,9 +4,10 @@ class ActivityPub::Activity::Block < ActivityPub::Activity
   def perform
     target_account = account_from_uri(object_uri)
 
-    return if target_account.nil? || !target_account.local? || delete_arrived_first?(@json['id']) || @account.blocking?(target_account)
+    return if target_account.nil? || !target_account.local? || @account.blocking?(target_account)
 
     UnfollowService.new.call(target_account, @account) if target_account.following?(@account)
-    @account.block!(target_account, uri: @json['id'])
+
+    @account.block!(target_account, uri: @json['id']) unless delete_arrived_first?(@json['id'])
   end
 end

spec/lib/activitypub/activity/block_spec.rb

@@ -14,6 +14,7 @@ RSpec.describe ActivityPub::Activity::Block do
     }.with_indifferent_access
   end
 
+  context 'when the recipient does not follow the sender' do
     describe '#perform' do
       subject { described_class.new(json, sender) }
 
@@ -25,4 +26,60 @@ RSpec.describe ActivityPub::Activity::Block do
         expect(sender.blocking?(recipient)).to be true
       end
     end
+  end
+
+  context 'when the recipient follows the sender' do
+    before do
+      recipient.follow!(sender)
+    end
+
+    describe '#perform' do
+      subject { described_class.new(json, sender) }
+
+      before do
+        subject.perform
+      end
+
+      it 'creates a block from sender to recipient' do
+        expect(sender.blocking?(recipient)).to be true
+      end
+
+      it 'ensures recipient is not following sender' do
+        expect(recipient.following?(sender)).to be false
+      end
+    end
+  end
+
+  context 'when a matching undo has been received first' do
+    let(:undo_json) do
+      {
+        '@context': 'https://www.w3.org/ns/activitystreams',
+        id: 'bar',
+        type: 'Undo',
+        actor: ActivityPub::TagManager.instance.uri_for(sender),
+        object: json,
+      }.with_indifferent_access
+    end
+
+    before do
+      recipient.follow!(sender)
+      ActivityPub::Activity::Undo.new(undo_json, sender).perform
+    end
+
+    describe '#perform' do
+      subject { described_class.new(json, sender) }
+
+      before do
+        subject.perform
+      end
+
+      it 'does not create a block from sender to recipient' do
+        expect(sender.blocking?(recipient)).to be false
+      end
+
+      it 'ensures recipient is not following sender' do
+        expect(recipient.following?(sender)).to be false
+      end
+    end
+  end
 end