Abstract auto merge processes

We have one auto merge strategy today - Merge When Pipeline
Succeeds.

In order to add more strategies for Merge Train feature,
we abstract the architecture to be more extensible.

Removed arguments

Fix spec

app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_merge_when_pipeline_succeeds.vue

@@ -57,7 +57,7 @@ export default {
     removeSourceBranch() {
       const options = {
         sha: this.mr.sha,
-        merge_when_pipeline_succeeds: true,
+        auto_merge_strategy: 'merge_when_pipeline_succeeds',
         should_remove_source_branch: true,
       };
 
@@ -85,7 +85,7 @@ export default {
       <h4 class="d-flex align-items-start">
         <span class="append-right-10">
           {{ s__('mrWidget|Set by') }}
-          <mr-widget-author :author="mr.setToMWPSBy" />
+          <mr-widget-author :author="mr.setToAutoMergeBy" />
           {{ s__('mrWidget|to be merged automatically when the pipeline succeeds') }}
         </span>
         <a

app/assets/javascripts/vue_merge_request_widget/components/states/ready_to_merge.vue

@@ -31,7 +31,7 @@ export default {
     return {
       removeSourceBranch: this.mr.shouldRemoveSourceBranch,
       mergeWhenBuildSucceeds: false,
-      setToMergeWhenPipelineSucceeds: false,
+      autoMergeStrategy: null,
       isMakingRequest: false,
       isMergingImmediately: false,
       commitMessage: this.mr.commitMessage,
@@ -42,7 +42,7 @@ export default {
     };
   },
   computed: {
-    shouldShowMergeWhenPipelineSucceedsText() {
+    shouldShowAutoMergeText() {
       return this.mr.isPipelineActive;
     },
     status() {
@@ -87,7 +87,7 @@ export default {
     mergeButtonText() {
       if (this.isMergingImmediately) {
         return __('Merge in progress');
-      } else if (this.shouldShowMergeWhenPipelineSucceedsText) {
+      } else if (this.shouldShowAutoMergeText) {
         return __('Merge when pipeline succeeds');
       }
 
@@ -104,7 +104,7 @@ export default {
       return enableSquashBeforeMerge && commitsCount > 1;
     },
     shouldShowMergeControls() {
-      return this.mr.isMergeAllowed || this.shouldShowMergeWhenPipelineSucceedsText;
+      return this.mr.isMergeAllowed || this.shouldShowAutoMergeText;
     },
     shouldShowSquashEdit() {
       return this.squashBeforeMerge && this.shouldShowSquashBeforeMerge;
@@ -126,12 +126,16 @@ export default {
         this.isMergingImmediately = true;
       }
 
-      this.setToMergeWhenPipelineSucceeds = mergeWhenBuildSucceeds === true;
+      if (mergeWhenBuildSucceeds === true) {
+        this.autoMergeStrategy = 'merge_when_pipeline_succeeds'
+      } else {
+        this.autoMergeStrategy = null
+      }
 
       const options = {
         sha: this.mr.sha,
         commit_message: this.commitMessage,
-        merge_when_pipeline_succeeds: this.setToMergeWhenPipelineSucceeds,
+        auto_merge_strategy: this.autoMergeStrategy,
         should_remove_source_branch: this.removeSourceBranch === true,
         squash: this.squashBeforeMerge,
         squash_commit_message: this.squashCommitMessage,

app/assets/javascripts/vue_merge_request_widget/stores/get_state_key.js

@@ -23,7 +23,7 @@ export default function deviseState(data) {
     return stateKey.pipelineBlocked;
   } else if (this.isSHAMismatch) {
     return stateKey.shaMismatch;
-  } else if (this.mergeWhenPipelineSucceeds) {
+  } else if (this.autoMergeEnabled) {
     return this.mergeError ? stateKey.autoMergeFailed : stateKey.mergeWhenPipelineSucceeds;
   } else if (!this.canMerge) {
     return stateKey.notAllowedToMerge;

app/assets/javascripts/vue_merge_request_widget/stores/mr_widget_store.js

@@ -61,7 +61,7 @@ export default class MergeRequestStore {
 
     this.updatedAt = data.updated_at;
     this.metrics = MergeRequestStore.buildMetrics(data.metrics);
-    this.setToMWPSBy = MergeRequestStore.formatUserObject(data.merge_user || {});
+    this.setToAutoMergeBy = MergeRequestStore.formatUserObject(data.merge_user || {});
     this.mergeUserId = data.merge_user_id;
     this.currentUserId = gon.current_user_id;
     this.sourceBranchPath = data.source_branch_path;
@@ -70,12 +70,13 @@ export default class MergeRequestStore {
     this.targetBranchPath = data.target_branch_commits_path;
     this.targetBranchTreePath = data.target_branch_tree_path;
     this.conflictResolutionPath = data.conflict_resolution_path;
-    this.cancelAutoMergePath = data.cancel_merge_when_pipeline_succeeds_path;
+    this.cancelAutoMergePath = data.cancel_auto_merge_path;
     this.removeWIPPath = data.remove_wip_path;
     this.sourceBranchRemoved = !data.source_branch_exists;
     this.shouldRemoveSourceBranch = data.remove_source_branch || false;
     this.onlyAllowMergeIfPipelineSucceeds = data.only_allow_merge_if_pipeline_succeeds || false;
-    this.mergeWhenPipelineSucceeds = data.merge_when_pipeline_succeeds || false;
+    this.autoMergeEnabled = data.auto_merge_enabled || false;
+    this.autoMergeStrategy = data.auto_merge_strategy;
     this.mergePath = data.merge_path;
     this.ffOnlyEnabled = data.ff_only_enabled;
     this.shouldBeRebased = !!data.should_be_rebased;
@@ -93,7 +94,7 @@ export default class MergeRequestStore {
     this.canRemoveSourceBranch = currentUser.can_remove_source_branch || false;
     this.canMerge = !!data.merge_path;
     this.canCreateIssue = currentUser.can_create_issue || false;
-    this.canCancelAutomaticMerge = !!data.cancel_merge_when_pipeline_succeeds_path;
+    this.canCancelAutomaticMerge = !!data.cancel_auto_merge_path;
     this.isSHAMismatch = this.sha !== data.diff_head_sha;
     this.canBeMerged = data.can_be_merged || false;
     this.isMergeAllowed = data.mergeable || false;

app/controllers/projects/merge_requests_controller.rb

@@ -145,14 +145,12 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     render partial: 'projects/merge_requests/widget/commit_change_content', layout: false
   end
 
-  def cancel_merge_when_pipeline_succeeds
-    unless @merge_request.can_cancel_merge_when_pipeline_succeeds?(current_user)
+  def cancel_auto_merge
+    unless @merge_request.can_cancel_auto_merge?(current_user)
       return access_denied!
     end
 
-    ::MergeRequests::MergeWhenPipelineSucceedsService
-      .new(@project, current_user)
-      .cancel(@merge_request)
+    AutoMergeService.new(project, current_user).cancel(@merge_request)
 
     render json: serialize_widget(@merge_request)
   end
@@ -229,12 +227,12 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   end
 
   def merge_params_attributes
-    [:should_remove_source_branch, :commit_message, :squash_commit_message, :squash]
+    [:should_remove_source_branch, :commit_message, :squash_commit_message, :squash, :auto_merge_strategy]
   end
 
-  def merge_when_pipeline_succeeds_active?
-    params[:merge_when_pipeline_succeeds].present? &&
-      @merge_request.head_pipeline && @merge_request.head_pipeline.active?
+  def auto_merge_requested?
+    # Support params[:merge_when_pipeline_succeeds] during the transition period
+    params[:auto_merge_strategy].present? || params[:merge_when_pipeline_succeeds].present?
   end
 
   def close_merge_request_if_no_source_project
@@ -258,9 +256,9 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   end
 
   def merge!
-    # Disable the CI check if merge_when_pipeline_succeeds is enabled since we have
+    # Disable the CI check if auto_merge_strategy is specified since we have
     # to wait until CI completes to know
-    unless @merge_request.mergeable?(skip_ci_check: merge_when_pipeline_succeeds_active?)
+    unless @merge_request.mergeable?(skip_ci_check: auto_merge_requested?)
       return :failed
     end
 
@@ -274,24 +272,10 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
 
     @merge_request.update(merge_error: nil, squash: merge_params.fetch(:squash, false))
 
-    if params[:merge_when_pipeline_succeeds].present?
-      return :failed unless @merge_request.actual_head_pipeline
-
-      if @merge_request.actual_head_pipeline.active?
-        ::MergeRequests::MergeWhenPipelineSucceedsService
-          .new(@project, current_user, merge_params)
-          .execute(@merge_request)
-
-        :merge_when_pipeline_succeeds
-      elsif @merge_request.actual_head_pipeline.success?
-        # This can be triggered when a user clicks the auto merge button while
-        # the tests finish at about the same time
-        @merge_request.merge_async(current_user.id, merge_params)
-
-        :success
-      else
-        :failed
-      end
+    if auto_merge_requested?
+      AutoMergeService.new(project, current_user, merge_params)
+        .execute(merge_request,
+                 params[:auto_merge_strategy] || AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
     else
       @merge_request.merge_async(current_user.id, merge_params)
 

app/helpers/merge_requests_helper.rb

@@ -103,7 +103,7 @@ module MergeRequestsHelper
 
   def merge_params(merge_request)
     {
-      merge_when_pipeline_succeeds: true,
+      auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
       should_remove_source_branch: true,
       sha: merge_request.diff_head_sha,
       squash: merge_request.squash

app/models/merge_request.rb

@@ -165,7 +165,7 @@ class MergeRequest < ApplicationRecord
   validates :source_branch, presence: true
   validates :target_project, presence: true
   validates :target_branch, presence: true
-  validates :merge_user, presence: true, if: :merge_when_pipeline_succeeds?, unless: :importing?
+  validates :merge_user, presence: true, if: :auto_merge_enabled?, unless: :importing?
   validate :validate_branches, unless: [:allow_broken, :importing?, :closed_without_fork?]
   validate :validate_fork, unless: :closed_without_fork?
   validate :validate_target_project, on: :create
@@ -196,6 +196,7 @@ class MergeRequest < ApplicationRecord
 
   alias_attribute :project, :target_project
   alias_attribute :project_id, :target_project_id
+  alias_attribute :auto_merge_enabled, :merge_when_pipeline_succeeds
 
   def self.reference_prefix
     '!'
@@ -391,7 +392,7 @@ class MergeRequest < ApplicationRecord
   def merge_participants
     participants = [author]
 
-    if merge_when_pipeline_succeeds? && !participants.include?(merge_user)
+    if auto_merge_enabled? && !participants.include?(merge_user)
       participants << merge_user
     end
 
@@ -782,7 +783,7 @@ class MergeRequest < ApplicationRecord
     project.ff_merge_must_be_possible? && !ff_merge_possible?
   end
 
-  def can_cancel_merge_when_pipeline_succeeds?(current_user)
+  def can_cancel_auto_merge?(current_user)
     can_be_merged_by?(current_user) || self.author == current_user
   end
 
@@ -801,6 +802,16 @@ class MergeRequest < ApplicationRecord
     Gitlab::Utils.to_boolean(merge_params['force_remove_source_branch'])
   end
 
+  def auto_merge_strategy
+    return unless auto_merge_enabled?
+
+    merge_params['auto_merge_strategy'] || AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
+  end
+
+  def auto_merge_strategy=(strategy)
+    merge_params['auto_merge_strategy'] = strategy
+  end
+
   def remove_source_branch?
     should_remove_source_branch? || force_remove_source_branch?
   end
@@ -973,15 +984,16 @@ class MergeRequest < ApplicationRecord
     end
   end
 
-  def reset_merge_when_pipeline_succeeds
-    return unless merge_when_pipeline_succeeds?
+  def reset_auto_merge
+    return unless auto_merge_enabled?
 
-    self.merge_when_pipeline_succeeds = false
+    self.auto_merge_enabled = false
     self.merge_user = nil
     if merge_params
       merge_params.delete('should_remove_source_branch')
       merge_params.delete('commit_message')
       merge_params.delete('squash_commit_message')
+      merge_params.delete('auto_merge_strategy')
     end
 
     self.save

app/presenters/merge_request_presenter.rb

@@ -22,9 +22,9 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
     end
   end
 
-  def cancel_merge_when_pipeline_succeeds_path
-    if can_cancel_merge_when_pipeline_succeeds?(current_user)
-      cancel_merge_when_pipeline_succeeds_project_merge_request_path(project, merge_request)
+  def cancel_auto_merge_path
+    if can_cancel_auto_merge?(current_user)
+      cancel_auto_merge_project_merge_request_path(project, merge_request)
     end
   end
 

app/serializers/merge_request_widget_entity.rb

@@ -9,7 +9,11 @@ class MergeRequestWidgetEntity < IssuableEntity
   expose :merge_params
   expose :merge_status
   expose :merge_user_id
-  expose :merge_when_pipeline_succeeds
+  expose :auto_merge_enabled
+  expose :auto_merge_strategy
+  expose :available_auto_merge_strategies do |merge_request|
+    AutoMergeService.new(merge_request.project, current_user).available_strategies(merge_request) # rubocop: disable CodeReuse/ServiceClass
+  end
   expose :source_branch
   expose :source_branch_protected do |merge_request|
     merge_request.source_project.present? && ProtectedBranch.protected?(merge_request.source_project, merge_request.source_branch)
@@ -182,8 +186,8 @@ class MergeRequestWidgetEntity < IssuableEntity
     presenter(merge_request).remove_wip_path
   end
 
-  expose :cancel_merge_when_pipeline_succeeds_path do |merge_request|
-    presenter(merge_request).cancel_merge_when_pipeline_succeeds_path
+  expose :cancel_auto_merge_path do |merge_request|
+    presenter(merge_request).cancel_auto_merge_path
   end
 
   expose :create_issue_to_resolve_discussions_path do |merge_request|

app/services/auto_merge/merge_when_pipeline_succeeds_service.rb

+# frozen_string_literal: true
+
+module AutoMerge
+  class MergeWhenPipelineSucceedsService < BaseService
+    def execute(merge_request)
+      return :failed unless merge_request.actual_head_pipeline
+
+      if merge_request.actual_head_pipeline.active?
+        merge_request.merge_params.merge!(params)
+
+        unless merge_request.auto_merge_enabled?
+          merge_request.auto_merge_enabled = true
+          merge_request.merge_user = @current_user
+          merge_request.auto_merge_strategy = AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
+
+          SystemNoteService.merge_when_pipeline_succeeds(merge_request, @project, @current_user, merge_request.diff_head_commit)
+        end
+
+        return :failed unless merge_request.save
+
+        :merge_when_pipeline_succeeds
+      elsif merge_request.actual_head_pipeline.success?
+        # This can be triggered when a user clicks the auto merge button while
+        # the tests finish at about the same time
+        merge_request.merge_async(current_user.id, merge_params)
+
+        :success
+      else
+        :failed
+      end
+    end
+
+    def process(merge_request)
+      return unless merge_request.actual_head_pipeline&.success?
+      return unless merge_request.mergeable?
+
+      merge_request.merge_async(merge_request.merge_user_id, merge_request.merge_params)
+    end
+
+    def cancel(merge_request)
+      if merge_request.reset_auto_merge
+        SystemNoteService.cancel_merge_when_pipeline_succeeds(merge_request, @project, @current_user)
+
+        success
+      else
+        error("Can't cancel the automatic merge", 406)
+      end
+    end
+
+    def available_for?(merge_request)
+      merge_request.actual_head_pipeline&.active?
+    end
+  end
+end

app/services/auto_merge_service.rb

+# frozen_string_literal: true
+
+class AutoMergeService < BaseService
+  STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS = 'merge_when_pipeline_succeeds'.freeze
+  STRATEGIES = [STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS].freeze
+
+  class << self
+    def all_strategies
+      STRATEGIES
+    end
+
+    def get_service_class(strategy)
+      return unless all_strategies.include?(strategy)
+
+      "::AutoMerge::#{strategy.camelize}Service".constantize
+    end
+  end
+
+  def execute(merge_request, strategy)
+    service = get_service_instance(strategy)
+
+    return :failed unless service&.available_for?(merge_request)
+
+    service.execute(merge_request)
+  end
+
+  def process(merge_request)
+    return unless merge_request.auto_merge_enabled?
+
+    get_service_instance(merge_request.auto_merge_strategy).process(merge_request)
+  end
+
+  def cancel(merge_request)
+    return error("Can't cancel the automatic merge", 406) unless merge_request.auto_merge_enabled?
+
+    get_service_instance(merge_request.auto_merge_strategy).cancel(merge_request)
+  end
+
+  def available_strategies(merge_request)
+    self.class.all_strategies.select do |strategy|
+      get_service_instance(strategy).available_for?(merge_request)
+    end
+  end
+
+  private
+
+  def get_service_instance(strategy)
+    self.class.get_service_class(strategy)&.new(project, current_user, params)
+  end
+end

app/services/merge_requests/merge_when_pipeline_succeeds_service.rb

-# frozen_string_literal: true
-
-module MergeRequests
-  class MergeWhenPipelineSucceedsService < MergeRequests::BaseService
-    # Marks the passed `merge_request` to be merged when the pipeline succeeds or
-    # updates the params for the automatic merge
-    def execute(merge_request)
-      merge_request.merge_params.merge!(params)
-
-      # The service is also called when the merge params are updated.
-      already_approved = merge_request.merge_when_pipeline_succeeds?
-
-      unless already_approved
-        merge_request.merge_when_pipeline_succeeds = true
-        merge_request.merge_user = @current_user
-
-        SystemNoteService.merge_when_pipeline_succeeds(merge_request, @project, @current_user, merge_request.diff_head_commit)
-      end
-
-      merge_request.save
-    end
-
-    # Triggers the automatic merge of merge_request once the pipeline succeeds
-    def trigger(pipeline)
-      return unless pipeline.success?
-
-      pipeline_merge_requests(pipeline) do |merge_request|
-        next unless merge_request.merge_when_pipeline_succeeds?
-        next unless merge_request.mergeable?
-
-        merge_request.merge_async(merge_request.merge_user_id, merge_request.merge_params)
-      end
-    end
-
-    # Cancels the automatic merge
-    def cancel(merge_request)
-      if merge_request.merge_when_pipeline_succeeds? && merge_request.open?
-        merge_request.reset_merge_when_pipeline_succeeds
-        SystemNoteService.cancel_merge_when_pipeline_succeeds(merge_request, @project, @current_user)
-
-        success
-      else
-        error("Can't cancel the automatic merge", 406)
-      end
-    end
-  end
-end

app/services/merge_requests/refresh_service.rb

@@ -24,7 +24,7 @@ module MergeRequests
       reload_merge_requests
       outdate_suggestions
       refresh_pipelines_on_merge_requests
-      reset_merge_when_pipeline_succeeds
+      cancel_auto_merge
       mark_pending_todos_done
       cache_merge_requests_closing_issues
 
@@ -142,8 +142,10 @@ module MergeRequests
       end
     end
 
-    def reset_merge_when_pipeline_succeeds
-      merge_requests_for_source_branch.each(&:reset_merge_when_pipeline_succeeds)
+    def cancel_auto_merge
+      merge_requests_for_source_branch.each do |merge_request|
+        AutoMergeService.new(project, current_user).cancel(merge_request)
+      end
     end
 
     def mark_pending_todos_done

app/services/merge_requests/update_service.rb

@@ -89,7 +89,7 @@ module MergeRequests
       merge_request.update(merge_error: nil)
 
       if merge_request.head_pipeline && merge_request.head_pipeline.active?
-        MergeRequests::MergeWhenPipelineSucceedsService.new(project, current_user).execute(merge_request)
+        AutoMergeService.new(project, current_user).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
       else
         merge_request.merge_async(current_user.id, {})
       end

app/services/notification_service.rb

@@ -238,7 +238,7 @@ class NotificationService
       merge_request,
       current_user,
       :merged_merge_request_email,
-      skip_current_user: !merge_request.merge_when_pipeline_succeeds?
+      skip_current_user: !merge_request.auto_merge_enabled?
     )
   end
 

app/workers/pipeline_success_worker.rb

@@ -9,9 +9,10 @@ class PipelineSuccessWorker
   # rubocop: disable CodeReuse/ActiveRecord
   def perform(pipeline_id)
     Ci::Pipeline.find_by(id: pipeline_id).try do |pipeline|
-      MergeRequests::MergeWhenPipelineSucceedsService
-        .new(pipeline.project, nil)
-        .trigger(pipeline)
+      pipeline.all_merge_requests.preload(:merge_user).each do |merge_request|
+        AutoMergeService.new(pipeline.project, merge_request.merge_user)
+                        .process(merge_request)
+      end
     end
   end
   # rubocop: enable CodeReuse/ActiveRecord

changelogs/unreleased/abstract-auto-merge.yml

+---
+title: Refactor and abstract Auto Merge Processes
+merge_request: 28595
+author:
+type: other

config/routes/project.rb

@@ -208,7 +208,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
         member do
           get :commit_change_content
           post :merge
-          post :cancel_merge_when_pipeline_succeeds
+          post :cancel_auto_merge
           get :pipeline_status
           get :ci_environments_status
           post :toggle_subscription

lib/api/merge_requests.rb

@@ -386,9 +386,8 @@ module API
         )
 
         if merge_when_pipeline_succeeds && merge_request.head_pipeline && merge_request.head_pipeline.active?
-          ::MergeRequests::MergeWhenPipelineSucceedsService
-            .new(merge_request.target_project, current_user, merge_params)
-            .execute(merge_request)
+          AutoMergeService.new(merge_request.target_project, current_user, merge_params)
+            .execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
         else
           ::MergeRequests::MergeService
             .new(merge_request.target_project, current_user, merge_params)
@@ -429,11 +428,9 @@ module API
       post ':id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds' do
         merge_request = find_project_merge_request(params[:merge_request_iid])
 
-        unauthorized! unless merge_request.can_cancel_merge_when_pipeline_succeeds?(current_user)
+        unauthorized! unless merge_request.can_cancel_auto_merge?(current_user)
 
-        ::MergeRequests::MergeWhenPipelineSucceedsService
-          .new(merge_request.target_project, current_user)
-          .cancel(merge_request)
+        AutoMergeService.new(merge_request.target_project, current_user).cancel(merge_request)
       end
 
       desc 'Rebase the merge request against its target branch' do

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -429,8 +429,9 @@ describe Projects::MergeRequestsController do
 
         it 'sets the MR to merge when the pipeline succeeds' do
           service = double(:merge_when_pipeline_succeeds_service)
+          allow(service).to receive(:available_for?) { true }
 
-          expect(MergeRequests::MergeWhenPipelineSucceedsService)
+          expect(AutoMerge::MergeWhenPipelineSucceedsService)
             .to receive(:new).with(project, anything, anything)
             .and_return(service)
           expect(service).to receive(:execute).with(merge_request)
@@ -713,9 +714,9 @@ describe Projects::MergeRequestsController do
     end
   end
 
-  describe 'POST cancel_merge_when_pipeline_succeeds' do
+  describe 'POST cancel_auto_merge' do
     subject do
-      post :cancel_merge_when_pipeline_succeeds,
+      post :cancel_auto_merge,
         params: {
           format: :json,
           namespace_id: merge_request.project.namespace.to_param,
@@ -725,14 +726,15 @@ describe Projects::MergeRequestsController do
         xhr: true
     end
 
-    it 'calls MergeRequests::MergeWhenPipelineSucceedsService' do
-      mwps_service = double
+    it 'calls AutoMergeService' do
+      auto_merge_service = double
 
-      allow(MergeRequests::MergeWhenPipelineSucceedsService)
+      allow(AutoMergeService)
         .to receive(:new)
-        .and_return(mwps_service)
+        .and_return(auto_merge_service)
 
-      expect(mwps_service).to receive(:cancel).with(merge_request)
+      allow(auto_merge_service).to receive(:available_strategies).with(merge_request)
+      expect(auto_merge_service).to receive(:cancel).with(merge_request)
 
       subject
     end

spec/factories/merge_requests.rb

@@ -95,7 +95,8 @@ FactoryBot.define do
     end
 
     trait :merge_when_pipeline_succeeds do
-      merge_when_pipeline_succeeds true
+      auto_merge_enabled true
+      auto_merge_strategy AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
       merge_user { author }
     end
 

spec/features/merge_request/user_merges_when_pipeline_succeeds_spec.rb

@@ -74,11 +74,12 @@ describe 'Merge request > User merges when pipeline succeeds', :js do
                    source_project: project,
                    title: 'Bug NS-04',
                    author: user,
-                   merge_user: user,
-                   merge_params: { force_remove_source_branch: '1' })
+                   merge_user: user)
         end
 
         before do
+          merge_request.merge_params['force_remove_source_branch'] = '0'
+          merge_request.save!
           click_link "Cancel automatic merge"
         end
 
@@ -102,11 +103,11 @@ describe 'Merge request > User merges when pipeline succeeds', :js do
 
   context 'when merge when pipeline succeeds is enabled' do
     let(:merge_request) do
-      create(:merge_request_with_diffs, :simple,  source_project: project,
+      create(:merge_request_with_diffs, :simple, :merge_when_pipeline_succeeds,
+        source_project: project,
         author: user,
         merge_user: user,
-                                                  title: 'MepMep',
-                                                  merge_when_pipeline_succeeds: true)
+        title: 'MepMep')
     end
     let!(:build) do
       create(:ci_build, pipeline: pipeline)

spec/features/merge_request/user_sees_merge_widget_spec.rb

@@ -314,7 +314,8 @@ describe 'Merge request > User sees merge widget', :js do
   context 'view merge request with MWPS enabled but automatically merge fails' do
     before do
       merge_request.update(
-        merge_when_pipeline_succeeds: true,
+        auto_merge_enabled: true,
+        auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
         merge_user: merge_request.author,
         merge_error: 'Something went wrong'
       )

spec/frontend/vue_mr_widget/stores/get_state_key_spec.js

@@ -31,7 +31,7 @@ describe('getStateKey', () => {
 
     expect(bound()).toEqual('notAllowedToMerge');
 
-    context.mergeWhenPipelineSucceeds = true;
+    context.autoMergeEnabled = true;
 
     expect(bound()).toEqual('mergeWhenPipelineSucceeds');
 

spec/javascripts/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js

@@ -80,7 +80,7 @@ describe('ReadyToMerge', () => {
     it('should have default data', () => {
       expect(vm.mergeWhenBuildSucceeds).toBeFalsy();
       expect(vm.useCommitMessageWithDescription).toBeFalsy();
-      expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+      expect(vm.setToAutoMerge).toBeFalsy();
       expect(vm.showCommitMessageEditor).toBeFalsy();
       expect(vm.isMakingRequest).toBeFalsy();
       expect(vm.isMergingImmediately).toBeFalsy();
@@ -91,17 +91,17 @@ describe('ReadyToMerge', () => {
   });
 
   describe('computed', () => {
-    describe('shouldShowMergeWhenPipelineSucceedsText', () => {
+    describe('shouldShowAutoMergeText', () => {
       it('should return true with active pipeline', () => {
         vm.mr.isPipelineActive = true;
 
-        expect(vm.shouldShowMergeWhenPipelineSucceedsText).toBeTruthy();
+        expect(vm.shouldShowAutoMergeText).toBeTruthy();
       });
 
       it('should return false with inactive pipeline', () => {
         vm.mr.isPipelineActive = false;
 
-        expect(vm.shouldShowMergeWhenPipelineSucceedsText).toBeFalsy();
+        expect(vm.shouldShowAutoMergeText).toBeFalsy();
       });
     });
 
@@ -325,7 +325,7 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick(true);
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeTruthy();
+          expect(vm.setToAutoMerge).toBeTruthy();
           expect(vm.isMakingRequest).toBeTruthy();
           expect(eventHub.$emit).toHaveBeenCalledWith('MRWidgetUpdateRequested');
 
@@ -345,7 +345,7 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick(false, true);
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+          expect(vm.setToAutoMerge).toBeFalsy();
           expect(vm.isMakingRequest).toBeTruthy();
           expect(eventHub.$emit).toHaveBeenCalledWith('FailedToMerge', undefined);
 
@@ -363,7 +363,7 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick();
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+          expect(vm.setToAutoMerge).toBeFalsy();
           expect(vm.isMakingRequest).toBeTruthy();
           expect(vm.initiateMergePolling).toHaveBeenCalled();
 

spec/models/merge_request_spec.rb

@@ -1038,14 +1038,28 @@ describe MergeRequest do
     end
   end
 
-  describe "#reset_merge_when_pipeline_succeeds" do
+  describe "#auto_merge_strategy" do
+    subject { merge_request.auto_merge_strategy }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it { is_expected.to eq('merge_when_pipeline_succeeds') }
+
+    context 'when auto merge is disabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it { is_expected.to be_nil }
+    end
+  end
+
+  describe "#reset_auto_merge" do
     let(:merge_if_green) do
       create :merge_request, merge_when_pipeline_succeeds: true, merge_user: create(:user),
                              merge_params: { "should_remove_source_branch" => "1", "commit_message" => "msg" }
     end
 
     it "sets the item to false" do
-      merge_if_green.reset_merge_when_pipeline_succeeds
+      merge_if_green.reset_auto_merge
       merge_if_green.reload
 
       expect(merge_if_green.merge_when_pipeline_succeeds).to be_falsey

spec/presenters/merge_request_presenter_spec.rb

@@ -207,25 +207,25 @@ describe MergeRequestPresenter do
     end
   end
 
-  describe '#cancel_merge_when_pipeline_succeeds_path' do
+  describe '#cancel_auto_merge_path' do
     subject do
       described_class.new(resource, current_user: user)
-        .cancel_merge_when_pipeline_succeeds_path
+        .cancel_auto_merge_path
     end
 
     context 'when can cancel mwps' do
       it 'returns path' do
-        allow(resource).to receive(:can_cancel_merge_when_pipeline_succeeds?)
+        allow(resource).to receive(:can_cancel_auto_merge?)
           .with(user)
           .and_return(true)
 
-        is_expected.to eq("/#{resource.project.full_path}/merge_requests/#{resource.iid}/cancel_merge_when_pipeline_succeeds")
+        is_expected.to eq("/#{resource.project.full_path}/merge_requests/#{resource.iid}/cancel_auto_merge")
       end
     end
 
     context 'when cannot cancel mwps' do
       it 'returns nil' do
-        allow(resource).to receive(:can_cancel_merge_when_pipeline_succeeds?)
+        allow(resource).to receive(:can_cancel_auto_merge?)
           .with(user)
           .and_return(false)
 

spec/requests/api/merge_requests_spec.rb

@@ -1473,7 +1473,7 @@ describe API::MergeRequests do
     end
 
     it "enables merge when pipeline succeeds if the pipeline is active" do
-      allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(pipeline)
+      allow_any_instance_of(MergeRequest).to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
       allow(pipeline).to receive(:active?).and_return(true)
 
       put api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/merge", user), params: { merge_when_pipeline_succeeds: true }
@@ -1484,7 +1484,7 @@ describe API::MergeRequests do
     end
 
     it "enables merge when pipeline succeeds if the pipeline is active and only_allow_merge_if_pipeline_succeeds is true" do
-      allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(pipeline)
+      allow_any_instance_of(MergeRequest).to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
       allow(pipeline).to receive(:active?).and_return(true)
       project.update_attribute(:only_allow_merge_if_pipeline_succeeds, true)
 
@@ -1950,7 +1950,7 @@ describe API::MergeRequests do
 
   describe 'POST :id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds' do
     before do
-      ::MergeRequests::MergeWhenPipelineSucceedsService.new(merge_request.target_project, user).execute(merge_request)
+      ::AutoMergeService.new(merge_request.target_project, user).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
     end
 
     it 'removes the merge_when_pipeline_succeeds status' do

spec/serializers/merge_request_widget_entity_spec.rb

@@ -297,4 +297,50 @@ describe MergeRequestWidgetEntity do
       end
     end
   end
+
+  describe 'auto merge' do
+    context 'when auto merge is enabled' do
+      let(:resource) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+      it 'returns auto merge related information' do
+        expect(subject[:auto_merge_enabled]).to be_truthy
+        expect(subject[:auto_merge_strategy]).to eq('merge_when_pipeline_succeeds')
+      end
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:resource) { create(:merge_request) }
+
+      it 'returns auto merge related information' do
+        expect(subject[:auto_merge_enabled]).to be_falsy
+        expect(subject[:auto_merge_strategy]).to be_nil
+      end
+    end
+
+    context 'when head pipeline is running' do
+      before do
+        create(:ci_pipeline, :running, project: project,
+                                       ref: resource.source_branch,
+                                       sha: resource.diff_head_sha)
+        resource.update_head_pipeline
+      end
+
+      it 'returns available auto merge strategies' do
+        expect(subject[:available_auto_merge_strategies]).to eq(%w[merge_when_pipeline_succeeds])
+      end
+    end
+
+    context 'when head pipeline is finished' do
+      before do
+        create(:ci_pipeline, :success, project: project,
+                                       ref: resource.source_branch,
+                                       sha: resource.diff_head_sha)
+        resource.update_head_pipeline
+      end
+
+      it 'returns available auto merge strategies' do
+        expect(subject[:available_auto_merge_strategies]).to be_empty
+      end
+    end
+  end
 end

spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb → spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-describe MergeRequests::MergeWhenPipelineSucceedsService do
+describe AutoMerge::MergeWhenPipelineSucceedsService do
   let(:user) { create(:user) }
   let(:project) { create(:project, :repository) }
 
@@ -21,6 +21,27 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     described_class.new(project, user, commit_message: 'Awesome message')
   end
 
+  describe "#available_for?" do
+    subject { service.available_for?(mr_merge_if_green_enabled) }
+
+    let(:pipeline_status) { :running }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: mr_merge_if_green_enabled.source_branch,
+                                            sha: mr_merge_if_green_enabled.diff_head_sha,
+                                            project: mr_merge_if_green_enabled.source_project)
+      mr_merge_if_green_enabled.update_head_pipeline
+    end
+
+    it { is_expected.to be_truthy }
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it { is_expected.to be_falsy }
+    end
+  end
+
   describe "#execute" do
     let(:merge_request) do
       create(:merge_request, target_project: project, source_project: project,
@@ -30,8 +51,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     context 'first time enabling' do
       before do
         allow(merge_request)
-          .to receive(:head_pipeline)
-          .and_return(pipeline)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
 
         service.execute(merge_request)
       end
@@ -39,7 +59,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       it 'sets the params, merge_user, and flag' do
         expect(merge_request).to be_valid
         expect(merge_request.merge_when_pipeline_succeeds).to be_truthy
-        expect(merge_request.merge_params).to eq commit_message: 'Awesome message'
+        expect(merge_request.merge_params).to include commit_message: 'Awesome message'
         expect(merge_request.merge_user).to be user
       end
 
@@ -54,8 +74,8 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       let(:build)   { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch) }
 
       before do
-        allow(mr_merge_if_green_enabled).to receive(:head_pipeline)
-          .and_return(pipeline)
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
 
         allow(mr_merge_if_green_enabled).to receive(:mergeable?)
           .and_return(true)
@@ -72,7 +92,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     end
   end
 
-  describe "#trigger" do
+  describe "#process" do
     let(:merge_request_ref) { mr_merge_if_green_enabled.source_branch }
     let(:merge_request_head) do
       project.commit(mr_merge_if_green_enabled.source_branch).id
@@ -86,8 +106,11 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       end
 
       it "merges all merge requests with merge when the pipeline succeeds enabled" do
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: triggering_pipeline, actual_head_pipeline: triggering_pipeline)
+
         expect(MergeWorker).to receive(:perform_async)
-        service.trigger(triggering_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -99,7 +122,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
 
       it 'does not merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(old_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -111,7 +134,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
 
       it 'does not merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(unrelated_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -125,8 +148,11 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       end
 
       it 'merges the associated merge request' do
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
+
         expect(MergeWorker).to receive(:perform_async)
-        service.trigger(pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
   end

spec/services/auto_merge_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe AutoMergeService do
+  set(:project) { create(:project) }
+  set(:user) { create(:user) }
+  let(:service) { described_class.new(project, user) }
+
+  describe '.all_strategies' do
+    subject { described_class.all_strategies }
+
+    it 'returns all strategies' do
+      is_expected.to eq(AutoMergeService::STRATEGIES)
+    end
+  end
+
+  describe '#available_strategies' do
+    subject { service.available_strategies(merge_request) }
+
+    let(:merge_request) { create(:merge_request) }
+    let(:pipeline_status) { :running }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: merge_request.source_branch,
+                                            sha: merge_request.diff_head_sha,
+                                            project: merge_request.source_project)
+
+      merge_request.update_head_pipeline
+    end
+
+    it 'returns available strategies' do
+      is_expected.to include('merge_when_pipeline_succeeds')
+    end
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it 'returns available strategies' do
+        is_expected.to be_empty
+      end
+    end
+  end
+
+  describe '.get_service_class' do
+    subject { described_class.get_service_class(strategy) }
+
+    let(:strategy) { AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS }
+
+    it 'returns service instance' do
+      is_expected.to eq(AutoMerge::MergeWhenPipelineSucceedsService)
+    end
+
+    context 'when strategy is not present' do
+      let(:strategy) { }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#execute' do
+    subject { service.execute(merge_request, strategy) }
+
+    let(:merge_request) { create(:merge_request) }
+    let(:pipeline_status) { :running }
+    let(:strategy) { AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: merge_request.source_branch,
+                                            sha: merge_request.diff_head_sha,
+                                            project: merge_request.source_project)
+
+      merge_request.update_head_pipeline
+    end
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:execute).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it 'returns failed' do
+        is_expected.to eq(:failed)
+      end
+    end
+  end
+
+  describe '#process' do
+    subject { service.process(merge_request) }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:process).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#cancel' do
+    subject { service.cancel(merge_request) }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:cancel).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns error' do
+        expect(subject[:message]).to eq("Can't cancel the automatic merge")
+        expect(subject[:status]).to eq(:error)
+        expect(subject[:http_status]).to eq(406)
+      end
+    end
+  end
+end

spec/services/merge_requests/push_options_handler_service_spec.rb

@@ -76,10 +76,11 @@ describe MergeRequests::PushOptionsHandlerService do
   shared_examples_for 'a service that can set the merge request to merge when pipeline succeeds' do
     subject(:last_mr) { MergeRequest.last }
 
-    it 'sets merge_when_pipeline_succeeds' do
+    it 'sets auto_merge_enabled' do
       service.execute
 
-      expect(last_mr.merge_when_pipeline_succeeds).to eq(true)
+      expect(last_mr.auto_merge_enabled).to eq(true)
+      expect(last_mr.auto_merge_strategy).to eq(AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
     end
 
     it 'sets merge_user to the user' do

spec/services/merge_requests/refresh_service_spec.rb

@@ -23,7 +23,8 @@ describe MergeRequests::RefreshService do
                               source_branch: 'master',
                               target_branch: 'feature',
                               target_project: @project,
-                              merge_when_pipeline_succeeds: true,
+                              auto_merge_enabled: true,
+                              auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
                               merge_user: @user)
 
       @another_merge_request = create(:merge_request,
@@ -31,7 +32,8 @@ describe MergeRequests::RefreshService do
                                       source_branch: 'master',
                                       target_branch: 'test',
                                       target_project: @project,
-                                      merge_when_pipeline_succeeds: true,
+                                      auto_merge_enabled: true,
+                                      auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
                                       merge_user: @user)
 
       @fork_merge_request = create(:merge_request,
@@ -83,7 +85,7 @@ describe MergeRequests::RefreshService do
 
         expect(@merge_request.notes).not_to be_empty
         expect(@merge_request).to be_open
-        expect(@merge_request.merge_when_pipeline_succeeds).to be_falsey
+        expect(@merge_request.auto_merge_enabled).to be_falsey
         expect(@merge_request.diff_head_sha).to eq(@newrev)
         expect(@fork_merge_request).to be_open
         expect(@fork_merge_request.notes).to be_empty
@@ -292,7 +294,7 @@ describe MergeRequests::RefreshService do
 
         expect(@merge_request.notes).not_to be_empty
         expect(@merge_request).to be_open
-        expect(@merge_request.merge_when_pipeline_succeeds).to be_falsey
+        expect(@merge_request.auto_merge_enabled).to be_falsey
         expect(@merge_request.diff_head_sha).to eq(@newrev)
         expect(@fork_merge_request).to be_open
         expect(@fork_merge_request.notes).to be_empty

spec/services/merge_requests/update_service_spec.rb

@@ -217,8 +217,9 @@ describe MergeRequests::UpdateService, :mailer do
             head_pipeline_of: merge_request
           )
 
-          expect(MergeRequests::MergeWhenPipelineSucceedsService).to receive(:new).with(project, user)
+          expect(AutoMerge::MergeWhenPipelineSucceedsService).to receive(:new).with(project, user, {})
             .and_return(service_mock)
+          allow(service_mock).to receive(:available_for?) { true }
           expect(service_mock).to receive(:execute).with(merge_request)
         end
 

spec/workers/pipeline_success_worker_spec.rb

@@ -5,12 +5,13 @@ require 'spec_helper'
 describe PipelineSuccessWorker do
   describe '#perform' do
     context 'when pipeline exists' do
-      let(:pipeline) { create(:ci_pipeline, status: 'success') }
+      let(:pipeline) { create(:ci_pipeline, status: 'success', ref: merge_request.source_branch, project: merge_request.source_project) }
+      let(:merge_request) { create(:merge_request) }
 
       it 'performs "merge when pipeline succeeds"' do
-        expect_any_instance_of(
-          MergeRequests::MergeWhenPipelineSucceedsService
-        ).to receive(:trigger)
+        expect_next_instance_of(AutoMergeService) do |auto_merge|
+          expect(auto_merge).to receive(:process)
+        end
 
         described_class.new.perform(pipeline.id)
       end