Add client support for count diverging commits

Adds the client call for the gitaly rpc CountDivergingCommits

fixing signature

simplifying commit logic

adding test for max-count

refactoring tests

6 files changed, 116 insertions, 4 deletions

diff --git a/GITALY_SERVER_VERSION b/GITALY_SERVER_VERSION
index 744068368fb..84cc529467b 100644
--- a/GITALY_SERVER_VERSION
+++ b/GITALY_SERVER_VERSION
@@ -1 +1 @@
-1.18.0
\ No newline at end of file
+1.18.0
diff --git a/app/models/repository.rb b/app/models/repository.rb
index 7c50b4488e5..ed55a6e572b 100644
--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -288,13 +288,16 @@ class Repository
       # Rugged seems to throw a `ReferenceError` when given branch_names rather
       # than SHA-1 hashes
       number_commits_behind, number_commits_ahead =
-        raw_repository.count_commits_between(
+        raw_repository.diverging_commit_count(
           @root_ref_hash,
           branch.dereferenced_target.sha,
-          left_right: true,
           max_count: MAX_DIVERGING_COUNT)
 
-      { behind: number_commits_behind, ahead: number_commits_ahead }
+      if number_commits_behind + number_commits_ahead >= MAX_DIVERGING_COUNT
+        { distance: MAX_DIVERGING_COUNT }
+      else
+        { behind: number_commits_behind, ahead: number_commits_ahead }
+      end
     end
   end
 
diff --git a/changelogs/unreleased/improve-performance-for-diverging-commit-counts.yml b/changelogs/unreleased/improve-performance-for-diverging-commit-counts.yml
new file mode 100644
index 00000000000..76ff15cba5b
--- /dev/null
+++ b/changelogs/unreleased/improve-performance-for-diverging-commit-counts.yml
@@ -0,0 +1,5 @@
+---
+title: Improve performance for diverging commit counts
+merge_request: 24287
+author:
+type: performance
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index 54bbd531398..593a3676519 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -491,6 +491,13 @@ module Gitlab
         end
       end
 
+      # Return total diverging commits count
+      def diverging_commit_count(from, to, max_count:)
+        wrapped_gitaly_errors do
+          gitaly_commit_client.diverging_commit_count(from, to, max_count: max_count)
+        end
+      end
+
       # Mimic the `git clean` command and recursively delete untracked files.
       # Valid keys that can be passed in the +options+ hash are:
       #
diff --git a/lib/gitlab/gitaly_client/commit_service.rb b/lib/gitlab/gitaly_client/commit_service.rb
index 4e46cb9f05c..ea12424eb4a 100644
--- a/lib/gitlab/gitaly_client/commit_service.rb
+++ b/lib/gitlab/gitaly_client/commit_service.rb
@@ -150,6 +150,17 @@ module Gitlab
         GitalyClient.call(@repository.storage, :commit_service, :count_commits, request, timeout: GitalyClient.medium_timeout).count
       end
 
+      def diverging_commit_count(from, to, max_count:)
+        request = Gitaly::CountDivergingCommitsRequest.new(
+          repository: @gitaly_repo,
+          from: encode_binary(from),
+          to: encode_binary(to),
+          max_count: max_count
+        )
+        response = GitalyClient.call(@repository.storage, :commit_service, :count_diverging_commits, request, timeout: GitalyClient.medium_timeout)
+        [response.left_count, response.right_count]
+      end
+
       def list_last_commits_for_tree(revision, path, offset: 0, limit: 25)
         request = Gitaly::ListLastCommitsForTreeRequest.new(
           repository: @gitaly_repo,
diff --git a/spec/lib/gitlab/git/repository_spec.rb b/spec/lib/gitlab/git/repository_spec.rb
index cf9e0cccc71..aef4e433439 100644
--- a/spec/lib/gitlab/git/repository_spec.rb
+++ b/spec/lib/gitlab/git/repository_spec.rb
@@ -283,6 +283,92 @@ describe Gitlab::Git::Repository, :seed_helper do
     end
   end
 
+  describe '#diverging_commit_count' do
+    it 'counts 0 for the same branch' do
+      expect(repository.diverging_commit_count('master', 'master', max_count: 1000)).to eq([0, 0])
+    end
+
+    context 'max count does not truncate results' do
+      where(:left, :right, :expected) do
+        1 | 1 | [1, 1]
+        4 | 4 | [4, 4]
+        2 | 2 | [2, 2]
+        2 | 4 | [2, 4]
+        4 | 2 | [4, 2]
+        10 | 10 | [10, 10]
+      end
+
+      with_them do
+        before do
+          repository.create_branch('left-branch', 'master')
+          repository.create_branch('right-branch', 'master')
+          left.times do
+            new_commit_edit_new_file_on_branch(repository_rugged, 'encoding/CHANGELOG', 'left-branch', 'some more content for a', 'some stuff')
+          end
+
+          right.times do
+            new_commit_edit_new_file_on_branch(repository_rugged, 'encoding/CHANGELOG', 'right-branch', 'some more content for b', 'some stuff')
+          end
+        end
+
+        after do
+          repository.delete_branch('left-branch')
+          repository.delete_branch('right-branch')
+        end
+
+        it 'returns the correct count bounding at max_count' do
+          branch_a_sha = repository_rugged.branches['left-branch'].target.oid
+          branch_b_sha = repository_rugged.branches['right-branch'].target.oid
+          expect(
+            repository.diverging_commit_count(
+              branch_a_sha, branch_b_sha, max_count: 1000)
+          ).to eq(expected)
+        end
+      end
+    end
+
+    context 'max count truncates results' do
+      where(:left, :right, :max_count) do
+        1 | 1 | 1
+        4 | 4 | 4
+        2 | 2 | 3
+        2 | 4 | 3
+        4 | 2 | 5
+        10 | 10 | 10
+      end
+
+      with_them do
+        before do
+          repository.create_branch('left-branch', 'master')
+          repository.create_branch('right-branch', 'master')
+          left.times do
+            new_commit_edit_new_file_on_branch(repository_rugged, 'encoding/CHANGELOG', 'left-branch', 'some more content for a', 'some stuff')
+          end
+
+          right.times do
+            new_commit_edit_new_file_on_branch(repository_rugged, 'encoding/CHANGELOG', 'right-branch', 'some more content for b', 'some stuff')
+          end
+        end
+
+        after do
+          repository.delete_branch('left-branch')
+          repository.delete_branch('right-branch')
+        end
+
+        it 'returns the correct count bounding at max_count' do
+          branch_a_sha = repository_rugged.branches['left-branch'].target.oid
+          branch_b_sha = repository_rugged.branches['right-branch'].target.oid
+          results = repository.diverging_commit_count(branch_a_sha, branch_b_sha, max_count: max_count)
+          expect(results[0] + results[1]).to eq(max_count)
+        end
+      end
+    end
+
+    it_behaves_like 'wrapping gRPC errors', Gitlab::GitalyClient::CommitService, :diverging_commit_count do
+      subject { repository.diverging_commit_count('master', 'master', max_count: 1000) }
+    end
+  end
+
   describe '#has_local_branches?' do
     context 'check for local branches' do
       it { expect(repository.has_local_branches?).to eq(true) }