Only use the experimental elasticsearch indexer if it is present

app/views/admin/application_settings/_elasticsearch_form.html.haml

@@ -7,12 +7,15 @@
           = f.check_box :elasticsearch_indexing
           Elasticsearch indexing
 
+  - missing = !Gitlab::Elastic::Indexer.experimental_indexer_present?
   .form-group
     .col-sm-offset-2.col-sm-10
       .checkbox
         = f.label :elasticsearch_experimental_indexer do
-          = f.check_box :elasticsearch_experimental_indexer
-          Use experimental repository indexer
+          = f.check_box :elasticsearch_experimental_indexer, disabled: missing
+          Use <a href="https://gitlab.com/gitlab-org/gitlab-elasticsearch-indexer">experimental repository indexer</a>
+          - if missing
+            (not installed)
 
   .form-group
     .col-sm-offset-2.col-sm-10

lib/gitlab/elastic/indexer.rb

@@ -10,6 +10,10 @@ module Gitlab
 
       Error = Class.new(StandardError)
 
+      def self.experimental_indexer_present?
+        Gitlab::Utils.which(EXPERIMENTAL_INDEXER).present?
+      end
+
       attr_reader :project
 
       def initialize(project)
@@ -46,7 +50,7 @@ module Gitlab
       end
 
       def path_to_indexer
-        if current_application_settings.elasticsearch_experimental_indexer?
+        if current_application_settings.elasticsearch_experimental_indexer? && self.class.experimental_indexer_present?
           EXPERIMENTAL_INDEXER
         else
           Rails.root.join('bin', 'elastic_repo_indexer').to_s

lib/gitlab/utils.rb

@@ -27,5 +27,22 @@ module Gitlab
     rescue ArgumentError
       size
     end
+
+    # See: http://stackoverflow.com/questions/2108727/which-in-ruby-checking-if-program-exists-in-path-from-ruby
+    # Cross-platform way of finding an executable in the $PATH.
+    #
+    #   which('ruby') #=> /usr/bin/ruby
+    def which(cmd, env = ENV)
+      exts = env['PATHEXT'] ? env['PATHEXT'].split(';') : ['']
+
+      env['PATH'].split(File::PATH_SEPARATOR).each do |path|
+        exts.each do |ext|
+          exe = File.join(path, "#{cmd}#{ext}")
+          return exe if File.executable?(exe) && !File.directory?(exe)
+        end
+      end
+
+      nil
+    end
   end
 end

spec/lib/gitlab/elastic/indexer_spec.rb

@@ -86,12 +86,20 @@ describe Gitlab::Elastic::Indexer do
     end
   end
 
-  context 'experimental indexer present' do
+  context 'experimental indexer enabled' do
     before do
       stub_application_setting(elasticsearch_experimental_indexer: true)
     end
 
-    it 'uses the experimental indexer' do
+    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)
+
+      indexer.run
+    end
+
+    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)
 
       indexer.run

spec/lib/gitlab/utils_spec.rb

+require 'spec_helper'
+
 describe Gitlab::Utils, lib: true do
-  delegate :to_boolean, to: :described_class
+  delegate :to_boolean, :which, to: :described_class
 
   describe '.to_boolean' do
     it 'accepts booleans' do
@@ -30,4 +32,12 @@ describe Gitlab::Utils, lib: true do
       expect(to_boolean(nil)).to be_nil
     end
   end
+
+  describe '.which' do
+    it 'finds the full path to an executable binary' do
+      expect(File).to receive(:executable?).with('/bin/sh').and_return(true)
+
+      expect(which('sh', 'PATH' => '/bin')).to eq('/bin/sh')
+    end
+  end
 end