Fix EE delta size check handling with annotated tags

Pushes with annotated tags would fail when the repository
size limits were enabled.

Closes #3589

changelogs/unreleased-ee/sh-delta-check-with-annotated-tags.yml

+---
+title: Fix EE delta size check handling with annotated tags
+merge_request:
+author:
+type: fixed

ee/lib/ee/gitlab/deltas.rb

@@ -7,6 +7,9 @@ module EE
         begin
           tree_a = repo.lookup(change[:oldrev])
           tree_b = repo.lookup(change[:newrev])
+
+          return size_of_deltas unless diffable?(tree_a) && diffable?(tree_b)
+
           diff = tree_a.diff(tree_b)
 
           diff.each_delta do |d|
@@ -25,6 +28,10 @@ module EE
           size_of_deltas
         end
       end
+
+      def self.diffable?(object)
+        [Rugged::Commit, Rugged::Tree].include?(object.class)
+      end
     end
   end
 end

spec/ee/spec/lib/ee/gitlab/deltas_spec.rb

@@ -12,5 +12,19 @@ describe EE::Gitlab::Deltas do
 
       expect(described_class.delta_size_check(change, project.repository)).to be > 0
     end
+
+    it 'handles annotated tags on an object' do
+      object_id = 'faaf198af3a36dbf41961466703cc1d47c61d051'
+      options = { message: 'test tag message\n',
+                  tagger: { name: 'John Smith', email: 'john@gmail.com' } }
+      result = project.repository.rugged.tags.create('annotated-tag', object_id, options)
+
+      change = {
+        oldrev: result.annotation.oid,
+        newrev: TestEnv::BRANCH_SHA['master']
+      }
+
+      expect(described_class.delta_size_check(change, project.repository)).to eq(0)
+    end
   end
 end