Always index with last_commit if exists

This ensures index in sync when indexing gap occurs,
see https://gitlab.com/gitlab-org/gitlab-ee/issues/5299

ee/app/workers/elastic_batch_project_indexer_worker.rb

@@ -28,9 +28,7 @@ class ElasticBatchProjectIndexerWorker
 
     logger.info "Indexing #{project.full_name} (ID=#{project.id})..."
 
-    # Get the last commit if we're updating indexed projects - otherwise we'll want to index everything
-    last_commit = project.index_status.try(:last_commit) if update_index
-    Gitlab::Elastic::Indexer.new(project).run(last_commit)
+    Gitlab::Elastic::Indexer.new(project).run
 
     logger.info "Indexing #{project.full_name} (ID=#{project.id}) is done!"
   rescue => err

ee/app/workers/elastic_commit_indexer_worker.rb

@@ -12,6 +12,6 @@ class ElasticCommitIndexerWorker
 
     return true unless project.use_elasticsearch?
 
-    Gitlab::Elastic::Indexer.new(project).run(oldrev, newrev)
+    Gitlab::Elastic::Indexer.new(project).run(newrev)
   end
 end

ee/lib/gitlab/elastic/indexer.rb

@@ -38,12 +38,9 @@ module Gitlab
         @index_status = project.index_status
       end
 
-      def run(from_sha = nil, to_sha = nil)
+      def run(to_sha = nil)
         to_sha = nil if to_sha == Gitlab::Git::BLANK_SHA
 
-        # Project has not been indexed before, therefore index from beginning
-        from_sha = nil unless @index_status
-
         head_commit = repository.try(:commit)
 
         if repository.nil? || !repository.exists? || repository.empty? || head_commit.nil?
@@ -51,7 +48,7 @@ module Gitlab
           return
         end
 
-        run_indexer!(from_sha, to_sha)
+        run_indexer!(to_sha)
         update_index_status(to_sha)
 
         true
@@ -77,7 +74,7 @@ module Gitlab
         end
       end
 
-      def run_indexer!(from_sha, to_sha)
+      def run_indexer!(to_sha)
         command = [path_to_indexer, project.id.to_s, repository_path]
 
         vars = @vars.merge('FROM_SHA' => from_sha, 'TO_SHA' => to_sha)
@@ -87,6 +84,20 @@ module Gitlab
         raise Error, output unless status&.zero?
       end
 
+      def last_commit
+        @index_status&.last_commit
+      end
+
+      def from_sha
+        repository_contains_last_indexed_commit? ? last_commit : Gitlab::Git::EMPTY_TREE_ID
+      end
+
+      def repository_contains_last_indexed_commit?
+        strong_memoize(:repository_contains_last_indexed_commit) do
+          last_commit.present? && repository.commit(last_commit).present?
+        end
+      end
+
       def repository_path
         # Go indexer needs relative path while ruby indexer needs absolute one
         if use_experimental_indexer?

ee/spec/lib/gitlab/elastic/indexer_spec.rb

@@ -5,12 +5,14 @@ describe Gitlab::Elastic::Indexer do
 
   before do
     stub_env('IN_MEMORY_APPLICATION_SETTINGS', 'true')
-    stub_ee_application_setting(elasticsearch_url: ['http://localhost:9200'])
+    stub_ee_application_setting(ee_application_setting) if ee_application_setting.present?
   end
 
+  let(:ee_application_setting) { { elasticsearch_url: ['http://localhost:9200'] } }
   let(:project) { create(:project, :repository) }
-  let(:from_sha) { Gitlab::Git::BLANK_SHA }
-  let(:to_sha)   { project.commit.try(:sha) }
+  let(:expected_from_sha) { Gitlab::Git::EMPTY_TREE_ID }
+  let(:to_commit) { project.commit }
+  let(:to_sha) { to_commit.try(:sha) }
   let(:indexer) { described_class.new(project) }
 
   let(:popen_success) { [[''], 0] }
@@ -53,18 +55,50 @@ describe Gitlab::Elastic::Indexer do
         hash_including(
           'ELASTIC_CONNECTION_INFO' => Gitlab::CurrentSettings.elasticsearch_config.to_json,
           'RAILS_ENV'               => Rails.env,
-          'FROM_SHA'                => from_sha,
+          'FROM_SHA'                => expected_from_sha,
           'TO_SHA'                  => to_sha
         )
       ).and_return(popen_success)
 
-      indexer.run(from_sha, to_sha)
+      indexer.run(to_sha)
+    end
+
+    context 'when IndexStatus exists' do
+      context 'when last_commit exists' do
+        let(:last_commit) { to_commit.parent_ids.first }
+
+        before do
+          project.create_index_status!(last_commit: last_commit)
+        end
+
+        it 'uses last_commit as from_sha' do
+          expect_popen.and_return(popen_success)
+
+          indexer.run(to_sha)
+
+          expect_index_status(to_sha)
+        end
+      end
+
+      context 'when last_commit no longer exists' do
+        before do
+          project.create_index_status!(last_commit: '51749675fc22nononononononono343bd54a3c95')
+        end
+
+        it 'use nil as from_sha' do
+          expect_popen.and_return(popen_success)
+
+          indexer.run(to_sha)
+
+          expect_index_status(to_sha)
+        end
+      end
     end
 
     it 'updates the index status when the indexing is a success' do
       expect_popen.and_return(popen_success)
 
-      indexer.run(from_sha, to_sha)
+      indexer.run(to_sha)
 
       expect_index_status(to_sha)
     end
@@ -72,7 +106,7 @@ describe Gitlab::Elastic::Indexer do
     it 'leaves the index status untouched when indexing a non-HEAD commit' do
       expect_popen.and_return(popen_success)
 
-      indexer.run(from_sha, project.repository.commit('HEAD~1'))
+      indexer.run(project.repository.commit('HEAD~1'))
 
       expect(project.index_status).to be_nil
     end
@@ -125,12 +159,82 @@ describe Gitlab::Elastic::Indexer do
             'GITALY_CONNECTION_INFO'  => gitaly_connection_data.to_json,
             'ELASTIC_CONNECTION_INFO' => Gitlab::CurrentSettings.elasticsearch_config.to_json,
             'RAILS_ENV'               => Rails.env,
-            'FROM_SHA'                => from_sha,
+            'FROM_SHA'                => expected_from_sha,
             'TO_SHA'                  => to_sha
           )
         ).and_return(popen_success)
 
-        indexer.run(from_sha, to_sha)
+        indexer.run(to_sha)
+      end
+    end
+  end
+
+  context 'reverting a change', :elastic do
+    let(:user) { project.owner }
+    let!(:initial_commit) { project.repository.commit('master').sha }
+    let(:ee_application_setting) { nil }
+
+    def change_repository_and_index(project, &blk)
+      yield blk
+
+      current_commit = project.repository.commit('master').sha
+
+      described_class.new(project).run(current_commit)
+      Gitlab::Elastic::Helper.refresh_index
+    end
+
+    def indexed_file_paths_for(term)
+      blobs = Repository.search(
+        term,
+        type: :blob
+      )[:blobs][:results].response
+
+      blobs.map do |blob|
+        blob['_source']['blob']['path']
+      end
+    end
+
+    context 'when IndexStatus#last_commit is no longer in repository', :pending do
+      before do
+        change_repository_and_index(project) do
+          project.repository.create_file(user, '12', '', message: '12', branch_name: 'master')
+          project.repository.create_file(user, '23', '', message: '23', branch_name: 'master')
+        end
+
+        expect(indexed_file_paths_for('12')).to include('12')
+        expect(indexed_file_paths_for('23')).to include('23')
+
+        project.index_status.update(last_commit: 'ABCDABCDABCD')
+      end
+
+      it 'reindexes from scratch if IndexStatus#last_commit is no longer in repository' do
+        change_repository_and_index(project) do
+          project.repository.write_ref('master', initial_commit)
+        end
+
+        expect(indexed_file_paths_for('12')).not_to include('12')
+        expect(indexed_file_paths_for('23')).not_to include('23')
+      end
+    end
+
+    context 'when branch is reset to an earlier commit' do
+      before do
+        change_repository_and_index(project) do
+          project.repository.create_file(user, '12', '', message: '12', branch_name: 'master')
+          project.repository.create_file(user, '23', '', message: '23', branch_name: 'master')
+        end
+
+        expect(indexed_file_paths_for('12')).to include('12')
+        expect(indexed_file_paths_for('23')).to include('23')
+      end
+
+      it 'reverses already indexed commits' do
+        change_repository_and_index(project) do
+          project.repository.write_ref('master', initial_commit)
+        end
+
+        expect(indexed_file_paths_for('12')).not_to include('12')
+        expect(indexed_file_paths_for('23')).not_to include('23')
       end
     end
   end

ee/spec/workers/elastic_batch_project_indexer_worker_spec.rb

@@ -43,7 +43,7 @@ describe ElasticBatchProjectIndexerWorker do
 
       expect_index(projects.first, false).and_call_original
       expect_next_instance_of(Gitlab::Elastic::Indexer) do |indexer|
-        expect(indexer).to receive(:run).with(nil)
+        expect(indexer).to receive(:run)
       end
 
       expect { worker.perform(projects.first.id, projects.first.id) }
@@ -56,7 +56,7 @@ describe ElasticBatchProjectIndexerWorker do
 
         expect_index(projects.first, false).and_call_original
         expect_next_instance_of(Gitlab::Elastic::Indexer) do |indexer|
-          expect(indexer).to receive(:run).with(nil)
+          expect(indexer).to receive(:run)
         end
 
         worker.perform(projects.first.id, projects.first.id)
@@ -75,7 +75,7 @@ describe ElasticBatchProjectIndexerWorker do
         projects.first.index_status.update!(last_commit: 'foo')
 
         expect_index(projects.first, true).and_call_original
-        expect_any_instance_of(Gitlab::Elastic::Indexer).to receive(:run).with('foo')
+        expect_any_instance_of(Gitlab::Elastic::Indexer).to receive(:run)
 
         worker.perform(projects.first.id, projects.first.id, true)
       end