Merge branch 'fix/move-can-be-merged-to-lib-git' into 'master'

Move Repository#can_be_merged? to Gitlab::Git::Repository

Closes #42544

See merge request gitlab-org/gitlab-ce!16771

app/models/repository.rb

@@ -852,7 +852,7 @@ class Repository
     @root_ref_sha ||= commit(root_ref).sha
   end
 
-  delegate :merged_branch_names, to: :raw_repository
+  delegate :merged_branch_names, :can_be_merged?, to: :raw_repository
 
   def merge_base(first_commit_id, second_commit_id)
     first_commit_id = commit(first_commit_id).try(:id) || first_commit_id

lib/gitlab/git/repository.rb

@@ -1386,6 +1386,16 @@ module Gitlab
         run_git(args).first.scrub.split(/^--$/)
       end
 
+      def can_be_merged?(source_sha, target_branch)
+        gitaly_migrate(:can_be_merged) do |is_enabled|
+          if is_enabled
+            gitaly_can_be_merged?(source_sha, find_branch(target_branch, true).target)
+          else
+            rugged_can_be_merged?(source_sha, target_branch)
+          end
+        end
+      end
+
       def search_files_by_name(query, ref)
         safe_query = Regexp.escape(query.sub(/^\/*/, ""))
 
@@ -2280,6 +2290,14 @@ module Gitlab
         run_git(['fetch', remote_name], env: env).last.zero?
       end
 
+      def gitaly_can_be_merged?(their_commit, our_commit)
+        !gitaly_conflicts_client(our_commit, their_commit).conflicts?
+      end
+
+      def rugged_can_be_merged?(their_commit, our_commit)
+        !rugged.merge_commits(our_commit, their_commit).conflicts?
+      end
+
       def gitlab_projects_error
         raise CommandError, @gitlab_projects.output
       end