Add setting for gitlab-elasticsearch-indexer path

The indexer is now setup by GDK, which needs to provide the path so it
can be used in all Rails processes, including those not started through
GDK like the console and Rake tasks.

By default it will be resolved through `$PATH`, as before.

config/initializers/1_settings.rb

@@ -217,6 +217,7 @@ Gitlab.ee do
   Settings['elasticsearch'] ||= Settingslogic.new({})
   Settings.elasticsearch['enabled'] = false if Settings.elasticsearch['enabled'].nil?
   Settings.elasticsearch['url'] = ENV['ELASTIC_URL'] || "http://localhost:9200"
+  Settings.elasticsearch['indexer_path'] ||= Gitlab::Utils.which('gitlab-elasticsearch-indexer')
 end
 
 #

ee/lib/gitlab/elastic/indexer.rb

@@ -8,13 +8,12 @@ module Gitlab
     class Indexer
       include Gitlab::Utils::StrongMemoize
 
-      EXPERIMENTAL_INDEXER = 'gitlab-elasticsearch-indexer'.freeze
-
       Error = Class.new(StandardError)
 
       class << self
         def experimental_indexer_present?
-          Gitlab::Utils.which(EXPERIMENTAL_INDEXER).present?
+          path = Gitlab.config.elasticsearch.indexer_path
+          path.present? && File.executable?(path)
         end
 
         def experimental_indexer_version
@@ -73,7 +72,7 @@ module Gitlab
 
       def path_to_indexer
         if use_experimental_indexer?
-          EXPERIMENTAL_INDEXER
+          Gitlab.config.elasticsearch.indexer_path
         else
           Rails.root.join('bin', 'elastic_repo_indexer').to_s
         end

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

@@ -49,7 +49,7 @@ describe Gitlab::Elastic::Indexer do
 
       expect_popen.with(
         [
-          'gitlab-elasticsearch-indexer',
+          'tmp/tests/gitlab-elasticsearch-indexer/bin/gitlab-elasticsearch-indexer',
           '--blob-type=wiki_blob',
           '--skip-commits',
           project.id.to_s,
@@ -149,6 +149,26 @@ describe Gitlab::Elastic::Indexer do
       stub_ee_application_setting(elasticsearch_experimental_indexer: true)
     end
 
+    describe '.experimental_indexer_present?' do
+      it 'returns true for an executable path' do
+        stub_elasticsearch_setting(indexer_path: 'tmp/tests/gitlab-elasticsearch-indexer/bin/gitlab-elasticsearch-indexer')
+
+        expect(described_class.experimental_indexer_present?).to eq(true)
+      end
+
+      it 'returns false for a non-executable path' do
+        stub_elasticsearch_setting(indexer_path: '/foo/bar')
+
+        expect(described_class.experimental_indexer_present?).to eq(false)
+      end
+
+      it 'returns false for a blank path' do
+        stub_elasticsearch_setting(indexer_path: '')
+
+        expect(described_class.experimental_indexer_present?).to eq(false)
+      end
+    end
+
     it 'uses the normal indexer when not present' do
       expect(described_class).to receive(:experimental_indexer_present?).and_return(false)
       expect_popen.with([Rails.root.join('bin/elastic_repo_indexer').to_s, anything, anything], anything, anything).and_return(popen_success)
@@ -158,7 +178,13 @@ describe Gitlab::Elastic::Indexer do
 
     it 'uses the experimental indexer when present' do
       expect(described_class).to receive(:experimental_indexer_present?).and_return(true)
-      expect_popen.with(['gitlab-elasticsearch-indexer', anything, anything], anything, anything).and_return(popen_success)
+      expect_popen.with(
+        [
+          'tmp/tests/gitlab-elasticsearch-indexer/bin/gitlab-elasticsearch-indexer',
+          anything, anything
+        ],
+        anything, anything
+      ).and_return(popen_success)
 
       indexer.run
     end
@@ -174,7 +200,7 @@ describe Gitlab::Elastic::Indexer do
 
         expect_popen.with(
           [
-            'gitlab-elasticsearch-indexer',
+            'tmp/tests/gitlab-elasticsearch-indexer/bin/gitlab-elasticsearch-indexer',
             project.id.to_s,
             "#{project.repository.disk_path}.git"
           ],

ee/spec/support/helpers/ee/stub_configuration.rb

@@ -33,5 +33,9 @@ module EE
     def stub_smartcard_setting(messages)
       allow(::Gitlab.config.smartcard).to receive_messages(to_settings(messages))
     end
+
+    def stub_elasticsearch_setting(messages)
+      allow(::Gitlab.config.elasticsearch).to receive_messages(to_settings(messages))
+    end
   end
 end

ee/spec/support/helpers/ee/test_env.rb

@@ -18,8 +18,7 @@ module EE
         task: "gitlab:indexer:install[#{indexer_args}]"
       )
 
-      ENV['PATH'] = # rubocop:disable RSpec/EnvAssignment
-        [indexer_bin_path, ENV['PATH']].join(File::PATH_SEPARATOR)
+      Settings.elasticsearch['indexer_path'] = indexer_bin_path
     end
 
     def indexer_path
@@ -27,7 +26,7 @@ module EE
     end
 
     def indexer_bin_path
-      @indexer_bin_path ||= File.join(indexer_path, 'bin')
+      @indexer_bin_path ||= File.join(indexer_path, 'bin', 'gitlab-elasticsearch-indexer')
     end
 
     def indexer_version