Support elastic search for code search (#10273)

* Support elastic search for code search

* Finished elastic search implementation and add some tests

* Enable test on drone and added docs

* Add new fields to elastic search

* Fix bug

* remove unused changes

* Use indexer alias to keep the gitea indexer version

* Improve codes

* Some code improvements

* The real indexer name changed to xxx.v1

Co-authored-by: zeripath <art27@cantab.net>

modules/indexer/code/elastic_search_test.go

@@ -0,0 +1,36 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package code
+
+import (
+	"os"
+	"testing"
+
+	"code.gitea.io/gitea/models"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestESIndexAndSearch(t *testing.T) {
+	models.PrepareTestEnv(t)
+
+	u := os.Getenv("TEST_INDEXER_CODE_ES_URL")
+	if u == "" {
+		t.SkipNow()
+		return
+	}
+
+	indexer, _, err := NewElasticSearchIndexer(u, "gitea_codes")
+	if err != nil {
+		assert.Fail(t, "Unable to create ES indexer Error: %v", err)
+		if indexer != nil {
+			indexer.Close()
+		}
+		return
+	}
+	defer indexer.Close()
+
+	testIndexer("elastic_search", t, indexer)
+}