Slash command support for merge train

This commit adds slash command support for merge train

app/services/auto_merge/base_service.rb

@@ -49,6 +49,14 @@ module AutoMerge
       end
     end
 
+    def available_for?(merge_request)
+      strong_memoize("available_for_#{merge_request.id}") do
+        merge_request.can_be_merged_by?(current_user) &&
+          merge_request.mergeable_state?(skip_ci_check: true) &&
+          yield
+      end
+    end
+
     private
 
     def strategy

app/services/auto_merge/merge_when_pipeline_succeeds_service.rb

@@ -30,7 +30,9 @@ module AutoMerge
     end
 
     def available_for?(merge_request)
-      merge_request.actual_head_pipeline&.active?
+      super do
+        merge_request.actual_head_pipeline&.active?
+      end
     end
   end
 end

app/services/auto_merge_service.rb

 # frozen_string_literal: true
 
 class AutoMergeService < BaseService
+  include Gitlab::Utils::StrongMemoize
+
   STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS = 'merge_when_pipeline_succeeds'
   STRATEGIES = [STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS].freeze
 
   class << self
-    def all_strategies
+    def all_strategies_ordered_by_preference
       STRATEGIES
     end
 
     def get_service_class(strategy)
-      return unless all_strategies.include?(strategy)
+      return unless all_strategies_ordered_by_preference.include?(strategy)
 
       "::AutoMerge::#{strategy.camelize}Service".constantize
     end
   end
 
-  def execute(merge_request, strategy)
-    service = get_service_instance(strategy)
+  def execute(merge_request, strategy = nil)
+    strategy ||= preferred_strategy(merge_request)
+    service = get_service_instance(merge_request, strategy)
 
     return :failed unless service&.available_for?(merge_request)
 
@@ -27,37 +30,47 @@ class AutoMergeService < BaseService
   def update(merge_request)
     return :failed unless merge_request.auto_merge_enabled?
 
-    get_service_instance(merge_request.auto_merge_strategy).update(merge_request)
+    strategy = merge_request.auto_merge_strategy
+    get_service_instance(merge_request, strategy).update(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)
+    strategy = merge_request.auto_merge_strategy
+    get_service_instance(merge_request, 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)
+    strategy = merge_request.auto_merge_strategy
+    get_service_instance(merge_request, strategy).cancel(merge_request)
   end
 
   def abort(merge_request, reason)
     return error("Can't abort the automatic merge", 406) unless merge_request.auto_merge_enabled?
 
-    get_service_instance(merge_request.auto_merge_strategy).abort(merge_request, reason)
+    strategy = merge_request.auto_merge_strategy
+    get_service_instance(merge_request, strategy).abort(merge_request, reason)
   end
 
   def available_strategies(merge_request)
-    self.class.all_strategies.select do |strategy|
-      get_service_instance(strategy).available_for?(merge_request)
+    self.class.all_strategies_ordered_by_preference.select do |strategy|
+      get_service_instance(merge_request, strategy).available_for?(merge_request)
     end
   end
 
+  def preferred_strategy(merge_request)
+    available_strategies(merge_request).first
+  end
+
   private
 
-  def get_service_instance(strategy)
-    self.class.get_service_class(strategy)&.new(project, current_user, params)
+  def get_service_instance(merge_request, strategy)
+    strong_memoize("service_instance_#{merge_request.id}_#{strategy}") do
+      self.class.get_service_class(strategy)&.new(project, current_user, params)
+    end
   end
 end
 

app/services/merge_requests/merge_orchestration_service.rb

+# frozen_string_literal: true
+
+module MergeRequests
+  class MergeOrchestrationService < ::BaseService
+    def execute(merge_request)
+      return unless can_merge?(merge_request)
+
+      merge_request.update(merge_error: nil)
+
+      if can_merge_automatically?(merge_request)
+        auto_merge_service.execute(merge_request)
+      else
+        merge_request.merge_async(current_user.id, params)
+      end
+    end
+
+    def can_merge?(merge_request)
+      can_merge_automatically?(merge_request) || can_merge_immediately?(merge_request)
+    end
+
+    def preferred_auto_merge_strategy(merge_request)
+      auto_merge_service.preferred_strategy(merge_request)
+    end
+
+    private
+
+    def can_merge_immediately?(merge_request)
+      merge_request.can_be_merged_by?(current_user) &&
+        merge_request.mergeable_state?
+    end
+
+    def can_merge_automatically?(merge_request)
+      auto_merge_service.available_strategies(merge_request).any?
+    end
+
+    def auto_merge_service
+      @auto_merge_service ||= AutoMergeService.new(project, current_user, params)
+    end
+  end
+end

app/services/merge_requests/update_service.rb

@@ -79,14 +79,21 @@ module MergeRequests
 
     def merge_from_quick_action(merge_request)
       last_diff_sha = params.delete(:merge)
-      return unless merge_request.mergeable_with_quick_action?(current_user, last_diff_sha: last_diff_sha)
 
-      merge_request.update(merge_error: nil)
-
-      if merge_request.head_pipeline_active?
-        AutoMergeService.new(project, current_user, { sha: last_diff_sha }).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+      if Feature.enabled?(:merge_orchestration_service, merge_request.project, default_enabled: true)
+        MergeRequests::MergeOrchestrationService
+          .new(project, current_user, { sha: last_diff_sha })
+          .execute(merge_request)
       else
-        merge_request.merge_async(current_user.id, { sha: last_diff_sha })
+        return unless merge_request.mergeable_with_quick_action?(current_user, last_diff_sha: last_diff_sha)
+
+        merge_request.update(merge_error: nil)
+
+        if merge_request.head_pipeline_active?
+          AutoMergeService.new(project, current_user, { sha: last_diff_sha }).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+        else
+          merge_request.merge_async(current_user.id, { sha: last_diff_sha })
+        end
       end
     end
 

changelogs/unreleased/slash-command-support-for-merge-train.yml

+---
+title: Add slash command support for merge train
+merge_request: 28532
+author:
+type: added

doc/user/project/quick_actions.md

@@ -70,7 +70,7 @@ The following quick actions are applicable to descriptions, discussions and thre
 | `/wip`                                |       | ✓             |      | Toggle the Work In Progress status |
 | `/approve`                            |       | ✓             |      | Approve the merge request **(STARTER)** |
 | `/submit_review`                      |       | ✓             |      | Submit a pending review. ([Introduced in GitLab 12.7](https://gitlab.com/gitlab-org/gitlab/issues/8041)) **(PREMIUM)** |
-| `/merge`                              |       | ✓             |      | Merge (when pipeline succeeds) |
+| `/merge`                              |       | ✓             |      | Merge changes. Depending on the project setting, this may be [when the pipeline succeeds](merge_requests/merge_when_pipeline_succeeds.md), adding to a [Merge Train](../../ci/merge_request_pipelines/pipelines_for_merged_results/merge_trains/index.md), etc).  |
 | `/child_epic <epic>`                  |       |               | ✓    | Add child epic to `<epic>`. The `<epic>` value should be in the format of `&epic`, `group&epic`, or a URL to an epic. ([Introduced in GitLab 12.0](https://gitlab.com/gitlab-org/gitlab/issues/7330)) **(ULTIMATE)** |
 | `/remove_child_epic <epic>`           |       |               | ✓    | Remove child epic from `<epic>`. The `<epic>` value should be in the format of `&epic`, `group&epic`, or a URL to an epic. ([Introduced in GitLab 12.0](https://gitlab.com/gitlab-org/gitlab/issues/7330)) **(ULTIMATE)** |
 | `/parent_epic <epic>`                 |       |               | ✓    | Set parent epic to `<epic>`. The `<epic>` value should be in the format of `&epic`, `group&epic`, or a URL to an epic. ([introduced in GitLab 12.1](https://gitlab.com/gitlab-org/gitlab/issues/10556)) **(ULTIMATE)** |

ee/app/services/auto_merge/add_to_merge_train_when_pipeline_succeeds_service.rb

@@ -31,10 +31,11 @@ module AutoMerge
     end
 
     def available_for?(merge_request)
-      merge_request.project.merge_trains_enabled? &&
-        !merge_request.for_fork? &&
-        merge_request.actual_head_pipeline&.active? &&
-        merge_request.mergeable_state?(skip_ci_check: true)
+      super do
+        merge_request.project.merge_trains_enabled? &&
+          !merge_request.for_fork? &&
+          merge_request.actual_head_pipeline&.active?
+      end
     end
   end
 end

ee/app/services/auto_merge/merge_train_service.rb

@@ -45,12 +45,11 @@ module AutoMerge
     end
 
     def available_for?(merge_request)
-      return false unless merge_request.project.merge_trains_enabled?
-      return false if merge_request.for_fork?
-      return false unless merge_request.actual_head_pipeline&.complete?
-      return false unless merge_request.mergeable_state?(skip_ci_check: true)
-
-      true
+      super do
+        merge_request.project.merge_trains_enabled? &&
+          !merge_request.for_fork? &&
+          merge_request.actual_head_pipeline&.complete?
+      end
     end
   end
 end

ee/app/services/ee/auto_merge_service.rb

@@ -12,10 +12,10 @@ module EE
       extend ::Gitlab::Utils::Override
       include ::Gitlab::Utils::StrongMemoize
 
-      override :all_strategies
-      def all_strategies
-        strong_memoize(:all_strategies) do
-          super + EE_STRATEGIES
+      override :all_strategies_ordered_by_preference
+      def all_strategies_ordered_by_preference
+        strong_memoize(:all_strategies_ordered_by_preference) do
+          EE_STRATEGIES + super
         end
       end
     end

ee/spec/services/auto_merge/add_to_merge_train_when_pipeline_succeeds_service_spec.rb

@@ -41,6 +41,10 @@ describe AutoMerge::AddToMergeTrainWhenPipelineSucceedsService do
   describe '#process' do
     subject { service.process(merge_request) }
 
+    before do
+      service.execute(merge_request)
+    end
+
     context 'when the latest pipeline in the merge request has succeeded' do
       before do
         pipeline.succeed!
@@ -119,6 +123,12 @@ describe AutoMerge::AddToMergeTrainWhenPipelineSucceedsService do
 
     it { is_expected.to eq(true) }
 
+    it 'memoizes the result' do
+      expect(merge_request).to receive(:can_be_merged_by?).once.and_call_original
+
+      2.times { is_expected.to be_truthy }
+    end
+
     context 'when merge trains option is disabled' do
       before do
         expect(merge_request.project).to receive(:merge_trains_enabled?) { false }
@@ -150,5 +160,13 @@ describe AutoMerge::AddToMergeTrainWhenPipelineSucceedsService do
 
       it { is_expected.to eq(false) }
     end
+
+    context 'when the user does not have permission to merge' do
+      before do
+        allow(merge_request).to receive(:can_be_merged_by?) { false }
+      end
+
+      it { is_expected.to be_falsy }
+    end
   end
 end

ee/spec/services/auto_merge/merge_train_service_spec.rb

@@ -262,6 +262,12 @@ describe AutoMerge::MergeTrainService do
 
     it { is_expected.to be_truthy }
 
+    it 'memoizes the result' do
+      expect(merge_request).to receive(:can_be_merged_by?).once.and_call_original
+
+      2.times { is_expected.to be_truthy }
+    end
+
     context 'when merge trains project option is disabled' do
       before do
         stub_feature_flags(disable_merge_trains: true)
@@ -278,6 +284,14 @@ describe AutoMerge::MergeTrainService do
       it { is_expected.to be_falsy }
     end
 
+    context 'when the user does not have permission to merge' do
+      before do
+        allow(merge_request).to receive(:can_be_merged_by?) { false }
+      end
+
+      it { is_expected.to be_falsy }
+    end
+
     context 'when merge request is submitted from a forked project' do
       before do
         allow(merge_request).to receive(:for_fork?) { true }

ee/spec/services/ee/auto_merge_service_spec.rb

@@ -3,12 +3,13 @@
 require 'spec_helper'
 
 describe AutoMergeService do
-  describe '.all_strategies' do
-    subject { described_class.all_strategies }
+  describe '.all_strategies_ordered_by_preference' do
+    subject { described_class.all_strategies_ordered_by_preference }
 
-    it 'includes all strategies' do
-      is_expected.to include(AutoMergeService::STRATEGY_MERGE_TRAIN,
-                             AutoMergeService::STRATEGY_ADD_TO_MERGE_TRAIN_WHEN_PIPELINE_SUCCEEDS)
+    it 'returns all strategies in preference order' do
+      is_expected.to eq([AutoMergeService::STRATEGY_MERGE_TRAIN,
+                         AutoMergeService::STRATEGY_ADD_TO_MERGE_TRAIN_WHEN_PIPELINE_SUCCEEDS,
+                         AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS])
     end
   end
 end

lib/gitlab/quick_actions/merge_request_actions.rb

@@ -8,14 +8,49 @@ module Gitlab
 
       included do
         # MergeRequest only quick actions definitions
-        desc _('Merge (when the pipeline succeeds)')
-        explanation _('Merges this merge request when the pipeline succeeds.')
-        execution_message _('Scheduled to merge this merge request when the pipeline succeeds.')
+        desc do
+          if Feature.enabled?(:merge_orchestration_service, quick_action_target.project, default_enabled: true)
+            if preferred_strategy = preferred_auto_merge_strategy(quick_action_target)
+              _("Merge automatically (%{strategy})") % { strategy: preferred_strategy.humanize }
+            else
+              _("Merge immediately")
+            end
+          else
+            _('Merge (when the pipeline succeeds)')
+          end
+        end
+        explanation do
+          if Feature.enabled?(:merge_orchestration_service, quick_action_target.project, default_enabled: true)
+            if preferred_strategy = preferred_auto_merge_strategy(quick_action_target)
+              _("Schedules to merge this merge request (%{strategy}).") % { strategy: preferred_strategy.humanize }
+            else
+              _('Merges this merge request immediately.')
+            end
+          else
+            _('Merges this merge request when the pipeline succeeds.')
+          end
+        end
+        execution_message do
+          if Feature.enabled?(:merge_orchestration_service, quick_action_target.project, default_enabled: true)
+            if preferred_strategy = preferred_auto_merge_strategy(quick_action_target)
+              _("Scheduled to merge this merge request (%{strategy}).") % { strategy: preferred_strategy.humanize }
+            else
+              _('Merged this merge request.')
+            end
+          else
+            _('Scheduled to merge this merge request when the pipeline succeeds.')
+          end
+        end
         types MergeRequest
         condition do
-          last_diff_sha = params && params[:merge_request_diff_head_sha]
-          quick_action_target.persisted? &&
-            quick_action_target.mergeable_with_quick_action?(current_user, autocomplete_precheck: !last_diff_sha, last_diff_sha: last_diff_sha)
+          if Feature.enabled?(:merge_orchestration_service, quick_action_target.project, default_enabled: true)
+            quick_action_target.persisted? &&
+              merge_orchestration_service.can_merge?(quick_action_target)
+          else
+            last_diff_sha = params && params[:merge_request_diff_head_sha]
+            quick_action_target.persisted? &&
+              quick_action_target.mergeable_with_quick_action?(current_user, autocomplete_precheck: !last_diff_sha, last_diff_sha: last_diff_sha)
+          end
         end
         command :merge do
           @updates[:merge] = params[:merge_request_diff_head_sha]
@@ -70,6 +105,14 @@ module Gitlab
           @updates[:target_branch] = branch_name if project.repository.branch_exists?(branch_name)
         end
       end
+
+      def merge_orchestration_service
+        @merge_orchestration_service ||= MergeRequests::MergeOrchestrationService.new(project, current_user)
+      end
+
+      def preferred_auto_merge_strategy(merge_request)
+        merge_orchestration_service.preferred_auto_merge_strategy(merge_request)
+      end
     end
   end
 end

locale/gitlab.pot

@@ -12704,6 +12704,9 @@ msgstr ""
 msgid "Merge Requests in Review"
 msgstr ""
 
+msgid "Merge automatically (%{strategy})"
+msgstr ""
+
 msgid "Merge commit message"
 msgstr ""
 
@@ -12857,6 +12860,12 @@ msgstr ""
 msgid "Merged branches are being deleted. This can take some time depending on the number of branches. Please refresh the page to see changes."
 msgstr ""
 
+msgid "Merged this merge request."
+msgstr ""
+
+msgid "Merges this merge request immediately."
+msgstr ""
+
 msgid "Merges this merge request when the pipeline succeeds."
 msgstr ""
 
@@ -17681,12 +17690,18 @@ msgstr ""
 msgid "Scheduled"
 msgstr ""
 
+msgid "Scheduled to merge this merge request (%{strategy})."
+msgstr ""
+
 msgid "Scheduled to merge this merge request when the pipeline succeeds."
 msgstr ""
 
 msgid "Schedules"
 msgstr ""
 
+msgid "Schedules to merge this merge request (%{strategy})."
+msgstr ""
+
 msgid "Scheduling"
 msgstr ""
 

spec/serializers/merge_request_poll_widget_entity_spec.rb

@@ -94,6 +94,10 @@ describe MergeRequestPollWidgetEntity do
   end
 
   describe 'auto merge' do
+    before do
+      project.add_maintainer(user)
+    end
+
     context 'when auto merge is enabled' do
       let(:resource) { create(:merge_request, :merge_when_pipeline_succeeds) }
 

spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb

@@ -3,8 +3,8 @@
 require 'spec_helper'
 
 describe AutoMerge::MergeWhenPipelineSucceedsService do
-  let(:user) { create(:user) }
-  let(:project) { create(:project, :repository) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project, :repository) }
 
   let(:mr_merge_if_green_enabled) do
     create(:merge_request, merge_when_pipeline_succeeds: true, merge_user: user,
@@ -20,6 +20,10 @@ describe AutoMerge::MergeWhenPipelineSucceedsService do
     described_class.new(project, user, commit_message: 'Awesome message')
   end
 
+  before_all do
+    project.add_maintainer(user)
+  end
+
   describe "#available_for?" do
     subject { service.available_for?(mr_merge_if_green_enabled) }
 
@@ -34,11 +38,25 @@ describe AutoMerge::MergeWhenPipelineSucceedsService do
 
     it { is_expected.to be_truthy }
 
+    it 'memoizes the result' do
+      expect(mr_merge_if_green_enabled).to receive(:can_be_merged_by?).once.and_call_original
+
+      2.times { is_expected.to be_truthy }
+    end
+
     context 'when the head pipeline succeeded' do
       let(:pipeline_status) { :success }
 
       it { is_expected.to be_falsy }
     end
+
+    context 'when the user does not have permission to merge' do
+      before do
+        allow(mr_merge_if_green_enabled).to receive(:can_be_merged_by?) { false }
+      end
+
+      it { is_expected.to be_falsy }
+    end
   end
 
   describe "#execute" do

spec/services/auto_merge_service_spec.rb

@@ -3,22 +3,36 @@
 require 'spec_helper'
 
 describe AutoMergeService do
-  let_it_be(:project) { create(:project) }
+  let_it_be(:project) { create(:project, :repository) }
   let_it_be(:user) { create(:user) }
   let(:service) { described_class.new(project, user) }
 
-  describe '.all_strategies' do
-    subject { described_class.all_strategies }
+  before_all do
+    project.add_maintainer(user)
+  end
 
-    it 'includes merge when pipeline succeeds' do
-      is_expected.to include(AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+  describe '.all_strategies_ordered_by_preference' do
+    subject { described_class.all_strategies_ordered_by_preference }
+
+    it 'returns all strategies in preference order' do
+      if Gitlab.ee?
+        is_expected.to eq(
+          [AutoMergeService::STRATEGY_MERGE_TRAIN,
+           AutoMergeService::STRATEGY_ADD_TO_MERGE_TRAIN_WHEN_PIPELINE_SUCCEEDS,
+           AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS])
+      else
+        is_expected.to eq([AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS])
+      end
     end
   end
 
   describe '#available_strategies' do
     subject { service.available_strategies(merge_request) }
 
-    let(:merge_request) { create(:merge_request) }
+    let(:merge_request) do
+      create(:merge_request, source_project: project)
+    end
+
     let(:pipeline_status) { :running }
 
     before do
@@ -42,6 +56,36 @@ describe AutoMergeService do
     end
   end
 
+  describe '#preferred_strategy' do
+    subject { service.preferred_strategy(merge_request) }
+
+    let(:merge_request) do
+      create(:merge_request, source_project: project)
+    end
+
+    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 preferred strategy' do
+      is_expected.to eq('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_nil
+      end
+    end
+  end
+
   describe '.get_service_class' do
     subject { described_class.get_service_class(strategy) }
 
@@ -63,7 +107,10 @@ describe AutoMergeService do
   describe '#execute' do
     subject { service.execute(merge_request, strategy) }
 
-    let(:merge_request) { create(:merge_request) }
+    let(:merge_request) do
+      create(:merge_request, source_project: project)
+    end
+
     let(:pipeline_status) { :running }
     let(:strategy) { AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS }
 
@@ -90,6 +137,14 @@ describe AutoMergeService do
         is_expected.to eq(:failed)
       end
     end
+
+    context 'when strategy is not specified' do
+      let(:strategy) { }
+
+      it 'chooses the most preferred strategy' do
+        is_expected.to eq(:merge_when_pipeline_succeeds)
+      end
+    end
   end
 
   describe '#update' do

spec/services/merge_requests/merge_orchestration_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MergeRequests::MergeOrchestrationService do
+  let_it_be(:maintainer) { create(:user) }
+  let(:merge_params) { { sha: merge_request.diff_head_sha } }
+  let(:user) { maintainer }
+  let(:service) { described_class.new(project, user, merge_params) }
+
+  let!(:merge_request) do
+    create(:merge_request, source_project: project, source_branch: 'feature',
+                           target_project: project, target_branch: 'master')
+  end
+
+  shared_context 'fresh repository' do
+    let_it_be(:project) { create(:project, :repository) }
+
+    before_all do
+      project.add_maintainer(maintainer)
+    end
+  end
+
+  describe '#execute' do
+    subject { service.execute(merge_request) }
+
+    include_context 'fresh repository'
+
+    context 'when merge request is mergeable' do
+      context 'when merge request can be merged automatically' do
+        before do
+          create(:ci_pipeline, :detached_merge_request_pipeline, project: project, merge_request: merge_request)
+          merge_request.update_head_pipeline
+        end
+
+        it 'schedules auto merge' do
+          expect_next_instance_of(AutoMergeService, project, user, merge_params) do |service|
+            expect(service).to receive(:execute).with(merge_request).and_call_original
+          end
+
+          subject
+
+          expect(merge_request).to be_auto_merge_enabled
+          expect(merge_request.auto_merge_strategy).to eq(AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+          expect(merge_request).not_to be_merged
+        end
+      end
+
+      context 'when merge request cannot be merged automatically' do
+        it 'merges immediately', :sidekiq_inline do
+          expect(merge_request)
+            .to receive(:merge_async).with(user.id, merge_params)
+            .and_call_original
+
+          subject
+
+          merge_request.reset
+          expect(merge_request).to be_merged
+          expect(merge_request).not_to be_auto_merge_enabled
+        end
+      end
+    end
+
+    context 'when merge request is not mergeable' do
+      before do
+        allow(merge_request).to receive(:mergeable_state?) { false }
+      end
+
+      it 'does nothing' do
+        subject
+
+        expect(merge_request).not_to be_auto_merge_enabled
+        expect(merge_request).not_to be_merged
+      end
+    end
+  end
+
+  describe '#can_merge?' do
+    subject { service.can_merge?(merge_request) }
+
+    include_context 'fresh repository'
+
+    context 'when merge request is mergeable' do
+      it { is_expected.to eq(true) }
+    end
+
+    context 'when merge request is not mergeable' do
+      before do
+        allow(merge_request).to receive(:mergeable_state?) { false }
+      end
+
+      it { is_expected.to eq(false) }
+    end
+  end
+
+  describe '#preferred_auto_merge_strategy' do
+    subject { service.preferred_auto_merge_strategy(merge_request) }
+
+    include_context 'fresh repository'
+
+    context 'when merge request can be merged automatically' do
+      before do
+        create(:ci_pipeline, :detached_merge_request_pipeline, project: project, merge_request: merge_request)
+        merge_request.update_head_pipeline
+      end
+
+      it 'fetches perferred auto merge strategy' do
+        is_expected.to eq(AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
+      end
+    end
+
+    context 'when merge request cannot be merged automatically' do
+      it { is_expected.to be_nil }
+    end
+  end
+end

spec/services/merge_requests/update_service_spec.rb

@@ -208,7 +208,7 @@ describe MergeRequests::UpdateService, :mailer do
       end
     end
 
-    context 'merge' do
+    shared_examples_for 'correct merge behavior' do
       let(:opts) do
         {
           merge: merge_request.diff_head_sha
@@ -311,6 +311,18 @@ describe MergeRequests::UpdateService, :mailer do
       end
     end
 
+    describe 'merge' do
+      it_behaves_like 'correct merge behavior'
+
+      context 'when merge_orchestration_service feature flag is disabled' do
+        before do
+          stub_feature_flags(merge_orchestration_service: false)
+        end
+
+        it_behaves_like 'correct merge behavior'
+      end
+    end
+
     context 'todos' do
       let!(:pending_todo) { create(:todo, :assigned, user: user, project: project, target: merge_request, author: user2) }
 

spec/services/quick_actions/interpret_service_spec.rb

@@ -492,7 +492,7 @@ describe QuickActions::InterpretService do
       end
     end
 
-    shared_examples 'merge command' do
+    shared_examples 'merge immediately command' do
       let(:project) { create(:project, :repository) }
 
       it 'runs merge command if content contains /merge' do
@@ -504,7 +504,18 @@ describe QuickActions::InterpretService do
       it 'returns them merge message' do
         _, _, message = service.execute(content, issuable)
 
-        expect(message).to eq('Scheduled to merge this merge request when the pipeline succeeds.')
+        expect(message).to eq('Merged this merge request.')
+      end
+    end
+
+    shared_examples 'merge automatically command' do
+      let(:project) { create(:project, :repository) }
+
+      it 'runs merge command if content contains /merge and returns merge message' do
+        _, updates, message = service.execute(content, issuable)
+
+        expect(updates).to eq(merge: merge_request.diff_head_sha)
+        expect(message).to eq('Scheduled to merge this merge request (Merge when pipeline succeeds).')
       end
     end
 
@@ -675,11 +686,23 @@ describe QuickActions::InterpretService do
     context 'merge command' do
       let(:service) { described_class.new(project, developer, { merge_request_diff_head_sha: merge_request.diff_head_sha }) }
 
-      it_behaves_like 'merge command' do
+      it_behaves_like 'merge immediately command' do
         let(:content) { '/merge' }
         let(:issuable) { merge_request }
       end
 
+      context 'when the head pipeline of merge request is running' do
+        before do
+          create(:ci_pipeline, :detached_merge_request_pipeline, merge_request: merge_request)
+          merge_request.update_head_pipeline
+        end
+
+        it_behaves_like 'merge automatically command' do
+          let(:content) { '/merge' }
+          let(:issuable) { merge_request }
+        end
+      end
+
       context 'can not be merged when logged user does not have permissions' do
         let(:service) { described_class.new(project, create(:user)) }
 

spec/support/shared_examples/quick_actions/merge_request/merge_quick_action_shared_examples.rb

@@ -10,10 +10,27 @@ RSpec.shared_examples 'merge quick action' do
     it 'merges the MR', :sidekiq_might_not_need_inline do
       add_note("/merge")
 
-      expect(page).to have_content 'Scheduled to merge this merge request when the pipeline succeeds.'
+      expect(page).to have_content 'Merged this merge request.'
 
       expect(merge_request.reload).to be_merged
     end
+
+    context 'when auto merge is avialable' do
+      before do
+        create(:ci_pipeline, :detached_merge_request_pipeline,
+          project: project, merge_request: merge_request)
+        merge_request.update_head_pipeline
+      end
+
+      it 'schedules to merge the MR' do
+        add_note("/merge")
+
+        expect(page).to have_content "Scheduled to merge this merge request (Merge when pipeline succeeds)."
+
+        expect(merge_request.reload).to be_auto_merge_enabled
+        expect(merge_request.reload).not_to be_merged
+      end
+    end
   end
 
   context 'when the head diff changes in the meanwhile' do