Add Gitaly diff stats RPC client

This adds a basic interface to fetch diff statistics given two SHAs.
It's a requirement for #49399 #20282 and #19232.

3 files changed, 38 insertions, 0 deletions

diff --git a/lib/gitlab/git/diff_stats_collection.rb b/lib/gitlab/git/diff_stats_collection.rb
new file mode 100644
index 00000000000..84d9e46f98e
--- /dev/null
+++ b/lib/gitlab/git/diff_stats_collection.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Git
+    class DiffStatsCollection
+      include Enumerable
+
+      def initialize(diff_stats)
+        @collection = diff_stats
+      end
+
+      def each(&block)
+        @collection.each(&block)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index 74a1bfb273a..b0dfd9c213e 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -463,6 +463,16 @@ module Gitlab
         Gitlab::Git::DiffCollection.new(iterator, options)
       end
 
+      def diff_stats(left_id, right_id)
+        stats = wrapped_gitaly_errors do
+          gitaly_commit_client.diff_stats(left_id, right_id)
+        end
+
+        Gitlab::Git::DiffStatsCollection.new(stats)
+      rescue CommandError
+        Gitlab::Git::DiffStatsCollection.new([])
+      end
+
       # Returns a RefName for a given SHA
       def ref_name_for_sha(ref_path, sha)
         raise ArgumentError, "sha can't be empty" unless sha.present?
diff --git a/lib/gitlab/gitaly_client/commit_service.rb b/lib/gitlab/gitaly_client/commit_service.rb
index aa5b4f94090..667fbf4951c 100644
--- a/lib/gitlab/gitaly_client/commit_service.rb
+++ b/lib/gitlab/gitaly_client/commit_service.rb
@@ -172,6 +172,17 @@ module Gitlab
         consume_commits_response(response)
       end
 
+      def diff_stats(left_commit_sha, right_commit_sha)
+        request = Gitaly::DiffStatsRequest.new(
+          repository: @gitaly_repo,
+          left_commit_id: left_commit_sha,
+          right_commit_id: right_commit_sha
+        )
+
+        response = GitalyClient.call(@repository.storage, :diff_service, :diff_stats, request, timeout: GitalyClient.medium_timeout)
+        response.flat_map(&:stats)
+      end
+
       def find_all_commits(opts = {})
         request = Gitaly::FindAllCommitsRequest.new(
           repository: @gitaly_repo,