Add a FF for ES default_operator change

ee/config/feature_flags/development/elasticsearch_use_or_default_operator.yml

+---
+name: elasticsearch_use_or_default_operator
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/41664
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/246500
+group: group::global search
+type: development
+default_enabled: false

ee/lib/elastic/latest/application_class_proxy.rb

@@ -33,6 +33,12 @@ module Elastic
 
       private
 
+      def default_operator
+        return :or if Feature.enabled?(:elasticsearch_use_or_default_operator)
+
+        :and
+      end
+
       def highlight_options(fields)
         es_fields = fields.map { |field| field.split('^').first }.each_with_object({}) do |field, memo|
           memo[field.to_sym] = {}
@@ -51,7 +57,7 @@ module Elastic
                     simple_query_string: {
                       fields: fields,
                       query: query,
-                      default_operator: :and
+                      default_operator: default_operator
                     }
                   }],
                   filter: [{

ee/spec/models/concerns/elastic/project_spec.rb

@@ -8,7 +8,7 @@ RSpec.describe Project, :elastic do
   end
 
   context 'when limited indexing is on' do
-    let_it_be(:project) { create :project, name: 'test1' }
+    let_it_be(:project) { create :project, name: 'main_project' }
 
     before do
       stub_ee_application_setting(elasticsearch_limit_indexing: true)
@@ -47,14 +47,14 @@ RSpec.describe Project, :elastic do
 
       it 'only indexes enabled projects' do
         Sidekiq::Testing.inline! do
-          create :project, path: 'test2', description: 'awesome project'
+          create :project, path: 'test_two', description: 'awesome project'
           create :project
 
           ensure_elasticsearch_index!
         end
 
-        expect(described_class.elastic_search('test*', options: { project_ids: :any }).total_count).to eq(1)
-        expect(described_class.elastic_search('test2', options: { project_ids: :any }).total_count).to eq(0)
+        expect(described_class.elastic_search('main_pro*', options: { project_ids: :any }).total_count).to eq(1)
+        expect(described_class.elastic_search('test_two', options: { project_ids: :any }).total_count).to eq(0)
       end
     end
 
@@ -84,9 +84,60 @@ RSpec.describe Project, :elastic do
         end
 
         expect(described_class.elastic_search('group_test*', options: { project_ids: :any }).total_count).to eq(2)
-        expect(described_class.elastic_search('group_test3', options: { project_ids: :any }).total_count).to eq(1)
-        expect(described_class.elastic_search('group_test2', options: { project_ids: :any }).total_count).to eq(0)
-        expect(described_class.elastic_search('group_test4', options: { project_ids: :any }).total_count).to eq(0)
+        expect(described_class.elastic_search('"group_test3"', options: { project_ids: :any }).total_count).to eq(1)
+        expect(described_class.elastic_search('"group_test2"', options: { project_ids: :any }).total_count).to eq(0)
+        expect(described_class.elastic_search('"group_test4"', options: { project_ids: :any }).total_count).to eq(0)
+      end
+
+      context 'default_operator' do
+        RSpec.shared_examples 'use correct default_operator' do |operator|
+          before do
+            Sidekiq::Testing.inline! do
+              create :project, name: 'project1', group: group, description: 'test foo'
+              create :project, name: 'project2', group: group, description: 'test'
+              create :project, name: 'project3', group: group, description: 'foo'
+
+              ensure_elasticsearch_index!
+            end
+          end
+
+          it 'uses correct operator' do
+            count_for_or = described_class.elastic_search('test | foo', options: { project_ids: :any }).total_count
+            expect(count_for_or).to be > 0
+
+            count_for_and = described_class.elastic_search('test + foo', options: { project_ids: :any }).total_count
+            expect(count_for_and).to be > 0
+
+            expect(count_for_or).not_to be equal(count_for_and)
+
+            expected_count = case operator
+                             when :or
+                               count_for_or
+                             when :and
+                               count_for_and
+                             else
+                               raise ArgumentError, 'Invalid operator'
+                             end
+
+            expect(described_class.elastic_search('test foo', options: { project_ids: :any }).total_count).to eq(expected_count)
+          end
+        end
+
+        context 'feature flag is enabled' do
+          before do
+            stub_feature_flags(elasticsearch_use_or_default_operator: true)
+          end
+
+          include_examples 'use correct default_operator', :or
+        end
+
+        context 'feature flag is disabled' do
+          before do
+            stub_feature_flags(elasticsearch_use_or_default_operator: false)
+          end
+
+          include_examples 'use correct default_operator', :and
+        end
       end
     end
   end
@@ -125,12 +176,12 @@ RSpec.describe Project, :elastic do
       ensure_elasticsearch_index!
     end
 
-    expect(described_class.elastic_search('test1', options: { project_ids: project_ids }).total_count).to eq(1)
-    expect(described_class.elastic_search('test2', options: { project_ids: project_ids }).total_count).to eq(1)
-    expect(described_class.elastic_search('awesome', options: { project_ids: project_ids }).total_count).to eq(1)
+    expect(described_class.elastic_search('"test1"', options: { project_ids: project_ids }).total_count).to eq(1)
+    expect(described_class.elastic_search('"test2"', options: { project_ids: project_ids }).total_count).to eq(1)
+    expect(described_class.elastic_search('"awesome"', options: { project_ids: project_ids }).total_count).to eq(1)
     expect(described_class.elastic_search('test*', options: { project_ids: project_ids }).total_count).to eq(2)
     expect(described_class.elastic_search('test*', options: { project_ids: :any }).total_count).to eq(3)
-    expect(described_class.elastic_search('someone_elses_project', options: { project_ids: project_ids }).total_count).to eq(0)
+    expect(described_class.elastic_search('"someone_elses_project"', options: { project_ids: project_ids }).total_count).to eq(0)
   end
 
   it "finds partial matches in project names" do

ee/spec/services/search/group_service_spec.rb

@@ -20,13 +20,13 @@ RSpec.describe Search::GroupService, :elastic do
   end
 
   describe 'group search' do
-    let(:term) { "Project Name" }
+    let(:term) { "RandomName" }
     let(:nested_group) { create(:group, :nested) }
 
     # These projects shouldn't be found
     let(:outside_project) { create(:project, :public, name: "Outside #{term}") }
     let(:private_project) { create(:project, :private, namespace: nested_group, name: "Private #{term}" )}
-    let(:other_project)   { create(:project, :public, namespace: nested_group, name: term.reverse) }
+    let(:other_project)   { create(:project, :public, namespace: nested_group, name: 'OtherProject') }
 
     # These projects should be found
     let(:project1) { create(:project, :internal, namespace: nested_group, name: "Inner #{term} 1") }