Merge branch 'frank-west-iii/gitlab-ce-fwiii-5857-web-editor-overwrites-commits'

2 files changed, 24 insertions, 0 deletions

diff --git a/app/services/files/base_service.rb b/app/services/files/base_service.rb
index c4a206f785e..ea94818713b 100644
--- a/app/services/files/base_service.rb
+++ b/app/services/files/base_service.rb
@@ -15,6 +15,7 @@ module Files
                         else
                           params[:file_content]
                         end
+      @last_commit_sha = params[:last_commit_sha]
 
       # Validate parameters
       validate
diff --git a/app/services/files/update_service.rb b/app/services/files/update_service.rb
index 8d2b5083179..4fc3b640799 100644
--- a/app/services/files/update_service.rb
+++ b/app/services/files/update_service.rb
@@ -2,11 +2,34 @@ require_relative "base_service"
 
 module Files
   class UpdateService < Files::BaseService
+    class FileChangedError < StandardError; end
+
     def commit
       repository.update_file(current_user, @file_path, @file_content,
                              branch: @target_branch,
                              previous_path: @previous_path,
                              message: @commit_message)
     end
+
+    private
+
+    def validate
+      super
+
+      if file_has_changed?
+        raise FileChangedError.new("You are attempting to update a file that has changed since you started editing it.")
+      end
+    end
+
+    def file_has_changed?
+      return false unless @last_commit_sha && last_commit
+
+      @last_commit_sha != last_commit.sha
+    end
+
+    def last_commit
+      @last_commit ||= Gitlab::Git::Commit.
+        last_for_path(@source_project.repository, @source_branch, @file_path)
+    end
   end
 end