Use project.commit convenience method.

app/controllers/projects/commit_controller.rb

@@ -36,6 +36,6 @@ class Projects::CommitController < Projects::ApplicationController
   end
   def commit
-    @commit ||= @project.repository.commit(params[:id])
+    @commit ||= @project.commit(params[:id])
   end
 end

app/controllers/projects/merge_requests_controller.rb

@@ -146,7 +146,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   def branch_to
     @target_project = selected_target_project
-    @commit = @target_project.repository.commit(params[:ref]) if params[:ref].present?
+    @commit = @target_project.commit(params[:ref]) if params[:ref].present?
   end
   def update_branches

app/models/note.rb

@@ -290,7 +290,7 @@ class Note < ActiveRecord::Base
     # +mentioner+.
     def noteable_project_id(noteable, mentioning_project)
       if noteable.is_a?(Commit)
-        if mentioning_project.repository.commit(noteable.id)
+        if mentioning_project.commit(noteable.id)
           # The noteable commit belongs to the mentioner's project
           mentioning_project.id
         else
@@ -512,7 +512,7 @@ class Note < ActiveRecord::Base
   # override to return commits, which are not active record
   def noteable
     if for_commit?
-      project.repository.commit(commit_id)
+      project.commit(commit_id)
     else
       super
     end

app/models/project.rb

@@ -257,7 +257,7 @@ class Project < ActiveRecord::Base
     @repository ||= Repository.new(path_with_namespace, nil, self)
   end
-  def commit(id)
+  def commit(id = 'HEAD')
     repository.commit(id)
   end

app/models/protected_branch.rb

@@ -18,6 +18,6 @@ class ProtectedBranch < ActiveRecord::Base
   validates :project, presence: true
   def commit
-    project.repository.commit(self.name)
+    project.commit(self.name)
   end
 end

app/services/create_tag_service.rb

@@ -38,7 +38,7 @@ class CreateTagService < BaseService
   end
   def create_push_data(project, user, tag)
-    commits = [project.repository.commit(tag.target)].compact
+    commits = [project.commit(tag.target)].compact
     Gitlab::PushDataBuilder.
       build(project, user, Gitlab::Git::BLANK_SHA, tag.target, "#{Gitlab::Git::TAG_REF_PREFIX}#{tag.name}", commits, tag.message)
   end

app/services/git_tag_push_service.rb

@@ -25,7 +25,7 @@ class GitTagPushService
       tag_name = Gitlab::Git.ref_name(ref)
       tag = project.repository.find_tag(tag_name)
       if tag && tag.target == newrev
-        commit = project.repository.commit(tag.target)
+        commit = project.commit(tag.target)
         commits = [commit].compact
         message = tag.message
       end

app/services/projects/participants_service.rb

@@ -22,7 +22,7 @@ module Projects
           merge_request = project.merge_requests.find_by_iid(id)
           merge_request.participants(current_user) if merge_request
         when "Commit"
-          commit = project.repository.commit(id)
+          commit = project.commit(id)
           commit.participants(project, current_user) if commit
         end

lib/api/commits.rb

@@ -32,7 +32,7 @@ module API
       #   GET /projects/:id/repository/commits/:sha
       get ":id/repository/commits/:sha" do
         sha = params[:sha]
-        commit = user_project.repository.commit(sha)
+        commit = user_project.commit(sha)
         not_found! "Commit" unless commit
         present commit, with: Entities::RepoCommitDetail
       end
@@ -46,7 +46,7 @@ module API
       #   GET /projects/:id/repository/commits/:sha/diff
       get ":id/repository/commits/:sha/diff" do
         sha = params[:sha]
-        commit = user_project.repository.commit(sha)
+        commit = user_project.commit(sha)
         not_found! "Commit" unless commit
         commit.diffs
       end
@@ -60,7 +60,7 @@ module API
       #   GET /projects/:id/repository/commits/:sha/comments
       get ':id/repository/commits/:sha/comments' do
         sha = params[:sha]
-        commit = user_project.repository.commit(sha)
+        commit = user_project.commit(sha)
         not_found! 'Commit' unless commit
         notes = Note.where(commit_id: commit.id)
         present paginate(notes), with: Entities::CommitNote
@@ -81,7 +81,7 @@ module API
         required_attributes! [:note]
         sha = params[:sha]
-        commit = user_project.repository.commit(sha)
+        commit = user_project.commit(sha)
         not_found! 'Commit' unless commit
         opts = {
           note: params[:note],

lib/api/files.rb

@@ -34,7 +34,7 @@ module API
         ref = attrs.delete(:ref)
         file_path = attrs.delete(:file_path)
-        commit = user_project.repository.commit(ref)
+        commit = user_project.commit(ref)
         not_found! 'Commit' unless commit
         blob = user_project.repository.blob_at(commit.sha, file_path)

lib/api/repositories.rb

@@ -62,7 +62,7 @@ module API
         ref = params[:ref_name] || user_project.try(:default_branch) || 'master'
         path = params[:path] || nil
-        commit = user_project.repository.commit(ref)
+        commit = user_project.commit(ref)
         not_found!('Tree') unless commit
         tree = user_project.repository.tree(commit.id, path)

lib/gitlab/identifier.rb

@@ -5,7 +5,7 @@ module Gitlab
     def identify(identifier, project, newrev)
       if identifier.blank?
         # Local push from gitlab
-        email = project.repository.commit(newrev).author_email rescue nil
+        email = project.commit(newrev).author_email rescue nil
         User.find_by(email: email) if email
       elsif identifier =~ /\Auser-\d+\Z/

lib/gitlab/markdown/commit_range_reference_filter.rb

@@ -84,7 +84,7 @@ module Gitlab
       def commit(id)
         unless @commit_map[id]
-          @commit_map[id] = project.repository.commit(id)
+          @commit_map[id] = project.commit(id)
         end
         @commit_map[id]

lib/gitlab/markdown/commit_reference_filter.rb

@@ -66,7 +66,7 @@ module Gitlab
       def commit_from_ref(project, commit_ref)
         if project && project.valid_repo?
-          project.repository.commit(commit_ref)
+          project.commit(commit_ref)
         end
       end

lib/gitlab/note_data_builder.rb

@@ -69,7 +69,7 @@ module Gitlab
       def build_data_for_commit(project, user, note)
         # commit_id is the SHA hash
-        commit = project.repository.commit(note.commit_id)
+        commit = project.commit(note.commit_id)
         commit.hook_attrs(project)
       end
     end

spec/controllers/commit_controller_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Projects::CommitController do
   let(:project) { create(:project) }
   let(:user)    { create(:user) }
-  let(:commit)  { project.repository.commit("master") }
+  let(:commit)  { project.commit("master") }
   before do
     sign_in(user)

spec/features/gitlab_flavored_markdown_spec.rb

@@ -14,7 +14,7 @@ describe "GitLab Flavored Markdown", feature: true do
     Commit.any_instance.stub(title: "fix ##{issue.iid}\n\nask @#{fred.username} for details")
   end
-  let(:commit) { project.repository.commit }
+  let(:commit) { project.commit }
   before do
     login_as :user

spec/helpers/diff_helper_spec.rb

@@ -4,7 +4,7 @@ describe DiffHelper do
   include RepoHelpers
   let(:project) { create(:project) }
-  let(:commit) { project.repository.commit(sample_commit.id) }
+  let(:commit) { project.commit(sample_commit.id) }
   let(:diff) { commit.diffs.first }
   let(:diff_file) { Gitlab::Diff::File.new(diff) }

spec/helpers/gitlab_markdown_helper_spec.rb

@@ -6,7 +6,7 @@ describe GitlabMarkdownHelper do
   let!(:project) { create(:project) }
   let(:user)          { create(:user, username: 'gfm') }
-  let(:commit)        { project.repository.commit }
+  let(:commit)        { project.commit }
   let(:issue)         { create(:issue, project: project) }
   let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
   let(:snippet)       { create(:project_snippet, project: project) }

spec/helpers/tree_helper_spec.rb

@@ -6,7 +6,7 @@ describe TreeHelper do
     before {
       @repository = project.repository
-      @commit = project.repository.commit("e56497bb")
+      @commit = project.commit("e56497bb")
     }
     context "on a directory containing more than one file/directory" do