Support usage of custom builders without hints and mappers (#13839)

* Support usage of custom builders without hints and mappers

CHANGELOG.next.asciidoc

@@ -116,6 +116,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Kubernetes watcher at `add_kubernetes_metadata` fails with StatefulSets {pull}13905[13905]
 - Fix panics that could result from invalid TLS certificates. This can affect Beats that connect over
   TLS or Beats that accept connections over TLS and validate client certificates. {pull}14146[14146]
+- Support usage of custom builders without hints and mappers {pull}13839[13839]
 
 *Auditbeat*
 

libbeat/autodiscover/providers/kubernetes/config.go

@@ -20,6 +20,7 @@
 package kubernetes
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/elastic/beats/libbeat/autodiscover/template"
@@ -50,9 +51,15 @@ func defaultConfig() *Config {
 }
 
 // Validate ensures correctness of config
-func (c *Config) Validate() {
+func (c *Config) Validate() error {
 	// Make sure that prefix doesn't ends with a '.'
 	if c.Prefix[len(c.Prefix)-1] == '.' && c.Prefix != "." {
 		c.Prefix = c.Prefix[:len(c.Prefix)-2]
 	}
+
+	if len(c.Templates) == 0 && !c.Hints.Enabled() && len(c.Builders) == 0 {
+		return fmt.Errorf("no configs or hints defined for autodiscover provider")
+	}
+
+	return nil
 }

libbeat/autodiscover/providers/kubernetes/config_test.go

@@ -0,0 +1,65 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package kubernetes
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/elastic/beats/libbeat/autodiscover"
+	"github.com/elastic/beats/libbeat/common"
+	"github.com/elastic/beats/libbeat/common/bus"
+)
+
+func TestConfigWithCustomBuilders(t *testing.T) {
+	autodiscover.Registry.AddBuilder("mock", newMockBuilder)
+
+	cfg := common.MapStr{
+		"hints.enabled": false,
+		"builders": []common.MapStr{
+			{
+				"mock": common.MapStr{},
+			},
+		},
+	}
+
+	config := common.MustNewConfigFrom(&cfg)
+	c := defaultConfig()
+	err := config.Unpack(&c)
+	assert.Nil(t, err)
+
+	cfg1 := common.MapStr{
+		"hints.enabled": false,
+	}
+	config, err = common.NewConfigFrom(&cfg1)
+	c = defaultConfig()
+	err = config.Unpack(&c)
+	assert.NotNil(t, err)
+}
+
+type mockBuilder struct {
+}
+
+func newMockBuilder(_ *common.Config) (autodiscover.Builder, error) {
+	return &mockBuilder{}, nil
+}
+
+func (m *mockBuilder) CreateConfig(event bus.Event) []*common.Config {
+	return nil
+}

libbeat/autodiscover/providers/kubernetes/kubernetes.go

@@ -96,9 +96,6 @@ func AutodiscoverBuilder(bus bus.Bus, uuid uuid.UUID, c *common.Config) (autodis
 	if err != nil {
 		return nil, errWrap(err)
 	}
-	if len(mapper) == 0 && !config.Hints.Enabled() {
-		return nil, errWrap(fmt.Errorf("no configs or hints defined for autodiscover provider"))
-	}
 
 	builders, err := autodiscover.NewBuilders(config.Builders, config.Hints)
 	if err != nil {