Make Commit#has_been_reverted? cheaper

There is no way in git to efficiently tell if a commit has been
reverted. Instead, GitLab creates system notes when we perform this
action in the web UI. These are introspected to answer the question;
doing so requires us to extract commit references from those notes.

With this change, we stop extracting commit references from the message
of the commit that is under question. This is user-controlled content
and we can't control the number of references in it. Further, since the
revert happens *after* that commit message is written, there is no way
for it to contain references to a reverting commit.

app/models/commit.rb

@@ -415,7 +415,7 @@ class Commit
   end
 
   def has_been_reverted?(current_user, notes_association = nil)
-    ext = all_references(current_user)
+    ext = Gitlab::ReferenceExtractor.new(project, current_user)
     notes_association ||= notes_with_associations
 
     notes_association.system.each do |note|

changelogs/unreleased/199197-make-has-been-reverted-check-cheaper.yml

+---
+title: Improve performance of the "has this commit been reverted?" check
+merge_request: 26784
+author:
+type: performance

spec/models/commit_range_spec.rb

@@ -137,29 +137,4 @@ describe CommitRange do
       end
     end
   end
-
-  describe '#has_been_reverted?' do
-    let(:user) { create(:user) }
-    let(:issue) { create(:issue, author: user, project: project) }
-
-    it 'returns true if the commit has been reverted' do
-      create(:note_on_issue,
-             noteable: issue,
-             system: true,
-             note: commit1.revert_description(user),
-             project: issue.project)
-
-      expect_next_instance_of(Commit) do |commit|
-        expect(commit).to receive(:reverts_commit?)
-          .with(commit1, user)
-          .and_return(true)
-      end
-
-      expect(commit1.has_been_reverted?(user, issue.notes_with_associations)).to eq(true)
-    end
-
-    it 'returns false if the commit has not been reverted' do
-      expect(commit1.has_been_reverted?(user, issue.notes_with_associations)).to eq(false)
-    end
-  end
 end

spec/models/commit_spec.rb

@@ -821,4 +821,29 @@ eos
       expect(commit.has_signature?).to be_falsey
     end
   end
+
+  describe '#has_been_reverted?' do
+    let(:user) { create(:user) }
+    let(:issue) { create(:issue, author: user, project: project) }
+
+    it 'returns true if the commit has been reverted' do
+      create(:note_on_issue,
+             noteable: issue,
+             system: true,
+             note: commit.revert_description(user),
+             project: issue.project)
+
+      expect_next_instance_of(Commit) do |revert_commit|
+        expect(revert_commit).to receive(:reverts_commit?)
+          .with(commit, user)
+          .and_return(true)
+      end
+
+      expect(commit.has_been_reverted?(user, issue.notes_with_associations)).to eq(true)
+    end
+
+    it 'returns false if the commit has not been reverted' do
+      expect(commit.has_been_reverted?(user, issue.notes_with_associations)).to eq(false)
+    end
+  end
 end