Gracefully recover from previously failed rebase

app/models/merge_request.rb

@@ -785,7 +785,16 @@ class MergeRequest < ActiveRecord::Base
   end
   def rebase_in_progress?
-    File.exist?(rebase_dir_path)
+    File.exist?(rebase_dir_path) && !clean_stuck_rebase
+  end
+
+  def clean_stuck_rebase
+    expiration_time = Time.now - 15.minutes
+
+    if File.new(rebase_dir_path).mtime < expiration_time
+      FileUtils.rm_rf(rebase_dir_path)
+      true
+    end
   end
   def diverged_commits_count

changelogs/unreleased-ee/1119-gracefully-recover-from-previously-failed-rebase.yml

+---
+title: Gracefully recover from previously failed rebase
+merge_request: 
+author: 

spec/models/merge_request_spec.rb

@@ -751,6 +751,25 @@ describe MergeRequest, models: true do
     subject { create :merge_request, :simple }
   end
+  describe '#rebase_in_progress?' do
+    it 'return true' do
+      allow(File).to receive(:exist?).and_return(true)
+      allow(File).to receive(:new).and_return(double(:file, mtime: Time.now))
+      expect(subject.rebase_in_progress?).to be_truthy
+    end
+
+    it 'return false' do
+      allow(File).to receive(:exist?).with(subject.rebase_dir_path).and_return(false)
+      expect(subject.rebase_in_progress?).to be_falsey
+    end
+
+    it 'return false if temporary file exists by is expired' do
+      allow(File).to receive(:exist?).and_return(true)
+      allow(File).to receive(:new).and_return(double(:file, mtime: Time.now - 2.hours))
+      expect(subject.rebase_in_progress?).to be_falsey
+    end
+  end
+
   describe '#commits_sha' do
     let(:commit0) { double('commit0', sha: 'sha1') }
     let(:commit1) { double('commit1', sha: 'sha2') }