Ensure Rugged methods are called with a Rugged Commit

app/models/repository.rb

@@ -763,7 +763,7 @@ class Repository
       index = Gitlab::Git::Index.new(raw_repository)
 
       if start_commit
-        index.read_tree(start_commit.raw_commit.tree)
+        index.read_tree(start_commit.rugged_commit.tree)
         parents = [start_commit.sha]
       else
         parents = []

lib/gitlab/conflict/file_collection.rb

@@ -77,8 +77,8 @@ EOM
 
       def initialize(merge_request, project)
         @merge_request = merge_request
-        @our_commit = merge_request.source_branch_head.raw.raw_commit
-        @their_commit = merge_request.target_branch_head.raw.raw_commit
+        @our_commit = merge_request.source_branch_head.raw.rugged_commit
+        @their_commit = merge_request.target_branch_head.raw.rugged_commit
         @project = project
       end
     end

lib/gitlab/git/commit.rb

@@ -14,7 +14,7 @@ module Gitlab
 
       attr_accessor *SERIALIZE_KEYS # rubocop:disable Lint/AmbiguousOperator
 
-      delegate :tree, to: :raw_commit
+      delegate :tree, to: :rugged_commit
 
       def ==(other)
         return false unless other.is_a?(Gitlab::Git::Commit)
@@ -287,7 +287,7 @@ module Gitlab
       # empty repo.  See Repository#diff for keys allowed in the +options+
       # hash.
       def diff_from_parent(options = {})
-        Commit.diff_from_parent(raw_commit, options)
+        Commit.diff_from_parent(rugged_commit, options)
       end
 
       def deltas
@@ -335,7 +335,7 @@ module Gitlab
 
       def to_patch(options = {})
         begin
-          raw_commit.to_mbox(options)
+          rugged_commit.to_mbox(options)
         rescue Rugged::InvalidError => ex
           if ex.message =~ /commit \w+ is a merge commit/i
             'Patch format is not currently supported for merge commits.'
@@ -383,6 +383,14 @@ module Gitlab
         encode! @committer_email
       end
 
+      def rugged_commit
+        @rugged_commit ||= if raw_commit.is_a?(Rugged::Commit)
+                             raw_commit
+                           else
+                             @repository.rev_parse_target(id)
+                           end
+      end
+
       private
 
       def init_from_hash(hash)

spec/migrations/migrate_process_commit_worker_jobs_spec.rb

@@ -6,7 +6,7 @@ require Rails.root.join('db', 'migrate', '20161124141322_migrate_process_commit_
 describe MigrateProcessCommitWorkerJobs do
   let(:project) { create(:project, :repository) }
   let(:user) { create(:user) }
-  let(:commit) { project.commit.raw.raw_commit }
+  let(:commit) { project.commit.raw.rugged_commit }
 
   describe 'Project' do
     describe 'find_including_path' do