Fix mappings errors for ES6.8

See https://gitlab.com/gitlab-org/gitlab/-/merge_requests/85633

EE: true
Changelog: fixed

ee/elastic/migrate/20210623081800_add_upvotes_to_issues.rb

@@ -46,11 +46,7 @@ class AddUpvotesToIssues < Elastic::Migration
   private
 
   def update_mappings!
-    client.indices.put_mapping index: index_name, body: {
-      properties: {
-        upvotes: { type: 'integer' }
-      }
-    }
+    helper.update_mapping(index_name: index_name, mappings: { properties: { upvotes: { type: 'integer' } } })
   end
 
   def process_batch!

ee/lib/gitlab/elastic/helper.rb

@@ -261,16 +261,28 @@ module Gitlab
 
       def get_mapping(index_name: nil)
         index = target_index_name(target: index_name)
-        mappings = client.indices.get_mapping(index: index)
+        mappings = client.indices.get_mapping({ index: index })
+
+        # The check for version 6 (and the spec testing this code) should be removed when support for
+        # Elasticsearch v6.8 is removed
+        if Gitlab::VersionInfo.parse(client.info['version']['number']).major == 6
+          mappings.dig(index, 'mappings', 'doc', 'properties')
+        else
           mappings.dig(index, 'mappings', 'properties')
         end
+      end
 
       def update_settings(index_name: nil, settings:)
         client.indices.put_settings(index: index_name || target_index_name, body: settings)
       end
 
       def update_mapping(index_name: nil, mappings:)
-        client.indices.put_mapping(index: index_name || target_index_name, body: mappings)
+        options = {
+          index: index_name || target_index_name,
+          body: mappings
+        }
+        options[:type] = 'doc' if Gitlab::VersionInfo.parse(client.info['version']['number']).major == 6
+        client.indices.put_mapping(options)
       end
 
       def get_meta(index_name: nil)

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

@@ -520,4 +520,34 @@ RSpec.describe Gitlab::Elastic::Helper, :request_store do
       end
     end
   end
+
+  describe '#get_mapping' do
+    let(:index_name) { Issue.__elasticsearch__.index_name }
+
+    subject { helper.get_mapping(index_name: index_name) }
+
+    it 'reads mappings from client', :elastic do
+      is_expected.not_to be_nil
+    end
+
+    context 'when using elasticsearch version 6.8' do
+      before do
+        info = {
+          'version' => {
+            'number' => '6.8.1',
+            'build_type' => 'docker',
+            'lucene_version' => '8.6.2'
+          }
+        }
+        mapping = { "#{index_name}": { mappings: { doc: { properties: { test: 1 } } } } }.with_indifferent_access
+
+        allow(Gitlab::Elastic::Helper.default.client).to receive(:info).and_return(info)
+        allow(helper.client.indices).to receive(:get_mapping).and_return(mapping)
+      end
+
+      it 'reads mappings from client' do
+        is_expected.not_to be_nil
+      end
+    end
+  end
 end