removed the #ensure_ref_fetched from all controllers

also, I refactored the MergeRequest#fetch_ref method to express
the side-effect that this method has.

  MergeRequest#fetch_ref -> MergeRequest#fetch_ref!
  Repository#fetch_source_branch -> Repository#fetch_source_branch!

app/controllers/projects/merge_requests/application_controller.rb

@@ -2,7 +2,6 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
   before_action :check_merge_requests_available!
   before_action :merge_request
   before_action :authorize_read_merge_request!
-  before_action :ensure_ref_fetched
   private
@@ -10,12 +9,6 @@ class Projects::MergeRequests::ApplicationController < Projects::ApplicationCont
     @issuable = @merge_request ||= @project.merge_requests.find_by!(iid: params[:id])
   end
-  # Make sure merge requests created before 8.0
-  # have head file in refs/merge-requests/
-  def ensure_ref_fetched
-    @merge_request.ensure_ref_fetched if Gitlab::Database.read_write?
-  end
-
   def merge_request_params
     params.require(:merge_request).permit(merge_request_params_attributes)
   end

app/controllers/projects/merge_requests/creations_controller.rb

@@ -4,7 +4,6 @@ class Projects::MergeRequests::CreationsController < Projects::MergeRequests::Ap
   include RendersCommits
   skip_before_action :merge_request
-  skip_before_action :ensure_ref_fetched
   before_action :authorize_create_merge_request!
   before_action :apply_diff_view_cookie!, only: [:diffs, :diff_for_path]
   before_action :build_merge_request, except: [:create]

app/controllers/projects/merge_requests_controller.rb

@@ -7,7 +7,6 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   include IssuableCollections
   skip_before_action :merge_request, only: [:index, :bulk_update]
-  skip_before_action :ensure_ref_fetched, only: [:index, :bulk_update]
   before_action :authorize_update_issuable!, only: [:close, :edit, :update, :remove_wip, :sort]
@@ -52,7 +51,6 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   def show
     validates_merge_request
-    ensure_ref_fetched
     close_merge_request_without_source_project
     check_if_can_be_merged

app/models/merge_request.rb

@@ -426,7 +426,7 @@ class MergeRequest < ActiveRecord::Base
   end
   def create_merge_request_diff
-    fetch_ref
+    fetch_ref!
     # n+1: https://gitlab.com/gitlab-org/gitlab-ce/issues/37435
     Gitlab::GitalyClient.allow_n_plus_1_calls do
@@ -811,29 +811,14 @@ class MergeRequest < ActiveRecord::Base
     end
   end
-  def fetch_ref
-    write_ref
-    update_column(:ref_fetched, true)
+  def fetch_ref!
+    target_project.repository.fetch_source_branch!(source_project.repository, source_branch, ref_path)
   end
   def ref_path
     "refs/#{Repository::REF_MERGE_REQUEST}/#{iid}/head"
   end
-  def ref_fetched?
-    super ||
-      begin
-        computed_value = project.repository.ref_exists?(ref_path)
-        update_column(:ref_fetched, true) if computed_value
-
-        computed_value
-      end
-  end
-
-  def ensure_ref_fetched
-    fetch_ref unless ref_fetched?
-  end
-
   def in_locked_state
     begin
       lock_mr
@@ -975,10 +960,4 @@ class MergeRequest < ActiveRecord::Base
     project.merge_requests.merged.where(author_id: author_id).empty?
   end
-
-  private
-
-  def write_ref
-    target_project.repository.fetch_source_branch(source_project.repository, source_branch, ref_path)
-  end
 end

app/models/repository.rb

@@ -982,8 +982,8 @@ class Repository
     gitlab_shell.fetch_remote(raw_repository, remote, forced: forced, no_tags: no_tags)
   end
-  def fetch_source_branch(source_repository, source_branch, local_ref)
-    raw_repository.fetch_source_branch(source_repository.raw_repository, source_branch, local_ref)
+  def fetch_source_branch!(source_repository, source_branch, local_ref)
+    raw_repository.fetch_source_branch!(source_repository.raw_repository, source_branch, local_ref)
   end
   def compare_source_branch(target_branch_name, source_repository, source_branch_name, straight:)

config/initializers/8_metrics.rb

@@ -118,8 +118,7 @@ def instrument_classes(instrumentation)
   instrumentation.instrument_instance_method(MergeRequestDiff, :load_commits)
   # Needed for https://gitlab.com/gitlab-org/gitlab-ce/issues/36061
-  instrumentation.instrument_instance_method(MergeRequest, :ensure_ref_fetched)
-  instrumentation.instrument_instance_method(MergeRequest, :fetch_ref)
+  instrumentation.instrument_instance_method(MergeRequest, :fetch_ref!)
 end
 # rubocop:enable Metrics/AbcSize

db/migrate/20171101134435_remove_ref_fetched_from_merge_requests.rb

+class RemoveRefFetchedFromMergeRequests < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # We don't need to cache this anymore: the refs are now created
+  # upon save/update and there is no more use for this flag
+  #
+  # See https://gitlab.com/gitlab-org/gitlab-ce/issues/36061
+  def change
+    remove_column :merge_requests, :ref_fetched
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20171026082505) do
+ActiveRecord::Schema.define(version: 20171101134435) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -970,7 +970,6 @@ ActiveRecord::Schema.define(version: 20171026082505) do
     t.datetime "last_edited_at"
     t.integer "last_edited_by_id"
     t.integer "head_pipeline_id"
-    t.boolean "ref_fetched"
     t.string "merge_jid"
     t.boolean "discussion_locked"
     t.integer "latest_merge_request_diff_id"

lib/github/import.rb

@@ -161,7 +161,6 @@ module Github
               iid: pull_request.iid,
               title: pull_request.title,
               description: description,
-              ref_fetched: true,
               source_project: pull_request.source_project,
               source_branch: pull_request.source_branch_name,
               source_branch_sha: pull_request.source_branch_sha,

lib/gitlab/git/repository.rb

@@ -1034,7 +1034,7 @@ module Gitlab
         delete_refs(tmp_ref) if tmp_ref
       end
-      def fetch_source_branch(source_repository, source_branch, local_ref)
+      def fetch_source_branch!(source_repository, source_branch, local_ref)
         with_repo_branch_commit(source_repository, source_branch) do |commit|
           if commit
             write_ref(local_ref, commit.sha)

spec/lib/gitlab/git/repository_spec.rb

@@ -1482,7 +1482,7 @@ describe Gitlab::Git::Repository, seed_helper: true do
     end
   end
-  describe '#fetch_source_branch' do
+  describe '#fetch_source_branch!' do
     let(:local_ref) { 'refs/merge-requests/1/head' }
     context 'when the branch exists' do
@@ -1491,11 +1491,11 @@ describe Gitlab::Git::Repository, seed_helper: true do
       it 'writes the ref' do
         expect(repository).to receive(:write_ref).with(local_ref, /\h{40}/)
-        repository.fetch_source_branch(repository, source_branch, local_ref)
+        repository.fetch_source_branch!(repository, source_branch, local_ref)
       end
       it 'returns true' do
-        expect(repository.fetch_source_branch(repository, source_branch, local_ref)).to eq(true)
+        expect(repository.fetch_source_branch!(repository, source_branch, local_ref)).to eq(true)
       end
     end
@@ -1505,11 +1505,11 @@ describe Gitlab::Git::Repository, seed_helper: true do
       it 'does not write the ref' do
         expect(repository).not_to receive(:write_ref)
-        repository.fetch_source_branch(repository, source_branch, local_ref)
+        repository.fetch_source_branch!(repository, source_branch, local_ref)
       end
       it 'returns false' do
-        expect(repository.fetch_source_branch(repository, source_branch, local_ref)).to eq(false)
+        expect(repository.fetch_source_branch!(repository, source_branch, local_ref)).to eq(false)
       end
     end
   end

spec/lib/gitlab/import_export/fork_spec.rb

@@ -46,7 +46,7 @@ describe 'forked project import' do
   end
   it 'can access the MR' do
-    project.merge_requests.first.ensure_ref_fetched
+    project.merge_requests.first.fetch_ref!
     expect(project.repository.ref_exists?('refs/merge-requests/1/head')).to be_truthy
   end

spec/models/merge_request_spec.rb

@@ -1755,39 +1755,12 @@ describe MergeRequest do
     end
   end
-  describe '#fetch_ref' do
-    it 'sets "ref_fetched" flag to true' do
-      subject.update!(ref_fetched: nil)
-      subject.fetch_ref
-
-      expect(subject.reload.ref_fetched).to be_truthy
-    end
-  end
-
-  describe '#ref_fetched?' do
-    it 'does not perform git operation when value is cached' do
-      subject.ref_fetched = true
-
-      expect_any_instance_of(Repository).not_to receive(:ref_exists?)
-      expect(subject.ref_fetched?).to be_truthy
-    end
-
-    it 'caches the value when ref exists but value is not cached' do
-      subject.update!(ref_fetched: nil)
-      allow_any_instance_of(Repository).to receive(:ref_exists?)
-        .and_return(true)
-
-      expect(subject.ref_fetched?).to be_truthy
-      expect(subject.reload.ref_fetched).to be_truthy
-    end
-
-    it 'returns false when ref does not exist' do
-      subject.update!(ref_fetched: nil)
-      allow_any_instance_of(Repository).to receive(:ref_exists?)
-        .and_return(false)
-
-      expect(subject.ref_fetched?).to be_falsey
+  describe '#fetch_ref!' do
+    it 'fetch the ref correctly' do
+      expect { subject.target_project.repository.delete_refs(subject.ref_path) }.not_to raise_error
+      subject.fetch_ref!
+      expect(subject.target_project.repository.ref_exists?(subject.ref_path)).to be_truthy
     end
   end