Use the ListCommits RPC for Gitlab::Git::Commit.between

The CommitsBetween RPC is deprecated in favour of the new ListCommits
RPC, so switch to that.

ListCommits has a working pagination implementation, so this change
helps us to reduce the number of commits we pull from Gitaly.

config/feature_flags/development/between_uses_list_commits.yml

+---
+name: between_uses_list_commits
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/67591
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/337960
+milestone: '14.2'
+type: development
+group: group::source code
+default_enabled: false

lib/gitlab/git/commit.rb

@@ -111,8 +111,18 @@ module Gitlab
         #   Commit.between(repo, '29eda46b', 'master')
         #
         def between(repo, base, head)
+          # In either of these cases, we are guaranteed to return no commits, so
+          # shortcut the RPC call
+          return [] if Gitlab::Git.blank_ref?(base) || Gitlab::Git.blank_ref?(head)
+
           wrapped_gitaly_errors do
-            repo.gitaly_commit_client.between(base, head)
+            if Feature.enabled?(:between_uses_list_commits, default_enabled: :yaml)
+              revisions = [head, "^#{base}"] # base..head
+
+              repo.gitaly_commit_client.list_commits(revisions, reverse: true)
+            else
+              repo.gitaly_commit_client.between(base, head)
+            end
           end
         end
 

lib/gitlab/gitaly_client/commit_service.rb

@@ -255,10 +255,11 @@ module Gitlab
         consume_commits_response(response)
       end
 
-      def list_commits(revisions)
+      def list_commits(revisions, reverse: false)
         request = Gitaly::ListCommitsRequest.new(
           repository: @gitaly_repo,
-          revisions: Array.wrap(revisions)
+          revisions: Array.wrap(revisions),
+          reverse: reverse
         )
 
         response = GitalyClient.call(@repository.storage, :commit_service, :list_commits, request, timeout: GitalyClient.medium_timeout)

spec/lib/gitlab/git/commit_spec.rb

@@ -369,11 +369,15 @@ RSpec.describe Gitlab::Git::Commit, :seed_helper do
         commits.map { |c| c.id }
       end
 
-      it 'has 1 element' do
-        expect(subject.size).to eq(1)
+      it { is_expected.to contain_exactly(SeedRepo::Commit::ID) }
+
+      context 'between_uses_list_commits FF disabled' do
+        before do
+          stub_feature_flags(between_uses_list_commits: false)
+        end
+
+        it { is_expected.to contain_exactly(SeedRepo::Commit::ID) }
       end
-      it { is_expected.to include(SeedRepo::Commit::ID) }
-      it { is_expected.not_to include(SeedRepo::FirstCommit::ID) }
     end
 
     describe '.shas_with_signatures' do