Introduce Pipeline#merge_requests_with_active_first,

app/mailers/emails/pipelines.rb

@@ -13,10 +13,7 @@ module Emails
     def pipeline_mail(pipeline, to, status)
       @project = pipeline.project
       @pipeline = pipeline
-      @merge_request = @project.merge_requests.opened.
-        find_by(source_project: @project,
-                source_branch: @pipeline.ref,
-                target_branch: @project.default_branch)
+      @merge_request = pipeline.merge_requests_with_active_first.first
       add_headers
 
       mail(to: to, subject: pipeline_subject(status), skip_premailer: true) do |format|

app/models/ci/pipeline.rb

@@ -293,10 +293,14 @@ module Ci
     # the merge request's latest commit.
     def merge_requests
       @merge_requests ||=
-        begin
-          project.merge_requests.where(source_branch: self.ref).
-            select { |merge_request| merge_request.pipeline.try(:id) == self.id }
-        end
+        project.merge_requests.where(source_branch: ref).
+          select { |merge_request| merge_request.pipeline.try(:id) == id }
+    end
+
+    def merge_requests_with_active_first
+      merge_requests.sort_by do |merge_request|
+        [merge_request.state_priority, -merge_request.updated_at.to_i]
+      end
     end
 
     private

app/models/merge_request.rb

@@ -169,6 +169,10 @@ class MergeRequest < ActiveRecord::Base
     work_in_progress?(title) ? title : "WIP: #{title}"
   end
 
+  def state_priority
+    %w[opened reopened closed merged locked].index(state)
+  end
+
   def to_reference(from_project = nil)
     reference = "#{self.class.reference_prefix}#{iid}"
 

spec/models/ci/pipeline_spec.rb

@@ -523,4 +523,35 @@ describe Ci::Pipeline, models: true do
       expect(pipeline.merge_requests).to be_empty
     end
   end
+
+  describe '#merge_requests_with_active_first' do
+    let(:project) { create(:project) }
+
+    let(:pipeline) do
+      create(:ci_empty_pipeline,
+             status: 'created',
+             project: project,
+             ref: 'master',
+             sha: project.repository.commit('master').sha)
+    end
+
+    let!(:merge_requests) do
+      [create_merge_request(:merged, Time.at(0)),
+       create_merge_request(:merged, Time.at(9)),
+       create_merge_request(:opened, Time.at(0))]
+    end
+
+    it 'returns opened/recent merge requests first, then closed ones' do
+      expect(pipeline.merge_requests_with_active_first).
+        to eq(merge_requests.reverse)
+    end
+
+    def create_merge_request(state, updated_at)
+      create(:merge_request,
+             source_project: project,
+             source_branch: pipeline.ref,
+             state: state,
+             updated_at: updated_at)
+    end
+  end
 end

spec/models/merge_request_spec.rb

@@ -58,6 +58,14 @@ describe MergeRequest, models: true do
     it { is_expected.to respond_to(:merge_when_build_succeeds) }
   end
 
+  describe '#state_priority' do
+    it 'returns the priority of state' do
+      %w[opened reopened closed merged locked].each.with_index do |state, idx|
+        expect(MergeRequest.new(state: state).state_priority).to eq(idx)
+      end
+    end
+  end
+
   describe '.in_projects' do
     it 'returns the merge requests for a set of projects' do
       expect(described_class.in_projects(Project.all)).to eq([subject])
@@ -334,7 +342,7 @@ describe MergeRequest, models: true do
       wip_title = "WIP: #{subject.title}"
 
       expect(subject.wip_title).to eq wip_title
-    end 
+    end
 
     it "does not add the WIP: prefix multiple times" do
       wip_title = "WIP: #{subject.title}"