Implement rebase feature

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -2,7 +2,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   before_action :module_enabled
   before_action :merge_request, only: [
     :edit, :update, :show, :diffs, :commits, :merge, :merge_check,
-    :ci_status, :toggle_subscription, :approve, :ff_merge
+    :ci_status, :toggle_subscription, :approve, :ff_merge, :rebase
   ]
   before_action :closes_issues, only: [:edit, :update, :show, :diffs, :commits]
   before_action :validates_merge_request, only: [:show, :diffs, :commits]
@@ -231,6 +231,14 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     end
   end
 
+  def rebase
+    return access_denied! unless @merge_request.can_be_merged_by?(current_user)
+    return render_404 unless @merge_request.approved?
+
+    MergeRequests::RebaseService.new(merge_request.target_project, current_user).
+      execute(merge_request)
+  end
+
   protected
 
   def selected_target_project

app/services/merge_requests/rebase_service.rb

@@ -0,0 +1,54 @@
+module MergeRequests
+  # MergeService class
+  #
+  # Do git merge and in case of success
+  # mark merge request as merged and execute all hooks and notifications
+  # Executed when you do merge via GitLab UI
+  #
+  class RebaseService < MergeRequests::BaseService
+    include Gitlab::Popen
+
+    attr_reader :merge_request
+
+    def execute(merge_request)
+      @merge_request = merge_request
+
+      if rebase
+        success
+      else
+        error('Failed to rebase. Should be done manually')
+      end
+    end
+
+    def rebase
+      Gitlab::ShellEnv.set_env(current_user)
+
+      # Clone
+      output, status = popen(%W(git clone -b #{merge_request.source_branch} -- #{source_project.repository.path_to_repo} #{tree_path}))
+      raise 'Failed to clone repo' unless status.zero?
+
+      # Rebase
+      output, status = popen(%W(git pull --rebase #{target_project.repository.path_to_repo} #{merge_request.target_branch}), tree_path)
+      raise 'Failed to rebase' unless status.zero?
+
+      output, status = popen(%W(git push -f origin #{merge_request.source_branch}), tree_path)
+      raise 'Failed to push' unless status.zero?
+
+      true
+    ensure
+      Gitlab::ShellEnv.reset_env
+    end
+
+    def source_project
+      @source_project ||= merge_request.source_project
+    end
+
+    def target_project
+      @target_project ||= merge_request.target_project
+    end
+
+    def tree_path
+      @tree_path ||= Rails.root.join('tmp', 'rebase', source_project.id.to_s, SecureRandom.hex).to_s
+    end
+  end
+end

app/views/projects/merge_requests/widget/open/_ff_accept.html.haml

@@ -10,7 +10,7 @@
         Fast-forward merge without creating merge commit
 - else
   = form_for [:rebase, @project.namespace.becomes(Namespace), @project, @merge_request],
-    remote: true, method: :post, html: { class: 'accept-mr-form js-requires-input' } do |f|
+    remote: false, method: :post, html: { class: 'accept-mr-form js-requires-input' } do |f|
     = hidden_field_tag :authenticity_token, form_authenticity_token
     .accept-merge-holder.clearfix.js-toggle-container
       - if @merge_request.target_project.merge_requests_rebase_enabled && can_rebase?(@merge_request.target_project, @merge_request.target_branch)