Add plugin support for autodiscover builders, providers

CHANGELOG.asciidoc

@@ -179,6 +179,7 @@ https://github.com/elastic/beats/compare/v6.0.0-beta2...master[Check the HEAD di
 - The node name can be discovered automatically by machine-id matching when beat deployed outside kubernetes cluster. {pull}6146[6146]
 - Panics will be written to the logger before exiting. {pull}6199[6199]
 - Add builder support for autodiscover and annotations builder {pull}6408[6408]
+- Add plugin support for autodiscover builders, providers {pull}6457[6457]
 
 *Auditbeat*
 

libbeat/autodiscover/builder/plugin.go

@@ -0,0 +1,31 @@
+package builder
+
+import (
+	"errors"
+
+	"github.com/elastic/beats/libbeat/autodiscover"
+	p "github.com/elastic/beats/libbeat/plugin"
+)
+
+type builderPlugin struct {
+	name    string
+	builder autodiscover.BuilderConstructor
+}
+
+var pluginKey = "libbeat.autodiscover.builder"
+
+// Plugin accepts a BuilderConstructor to be registered as a plugin
+func Plugin(name string, b autodiscover.BuilderConstructor) map[string][]interface{} {
+	return p.MakePlugin(pluginKey, builderPlugin{name, b})
+}
+
+func init() {
+	p.MustRegisterLoader(pluginKey, func(ifc interface{}) error {
+		b, ok := ifc.(builderPlugin)
+		if !ok {
+			return errors.New("plugin does not match processor plugin type")
+		}
+
+		return autodiscover.Registry.AddBuilder(b.name, b.builder)
+	})
+}

libbeat/autodiscover/providers/plugin.go

@@ -0,0 +1,31 @@
+package providers
+
+import (
+	"errors"
+
+	"github.com/elastic/beats/libbeat/autodiscover"
+	p "github.com/elastic/beats/libbeat/plugin"
+)
+
+type providerPlugin struct {
+	name     string
+	provider autodiscover.ProviderBuilder
+}
+
+var pluginKey = "libbeat.autodiscover.provider"
+
+// Plugin accepts a ProviderBuilder to be registered as a plugin
+func Plugin(name string, provider autodiscover.ProviderBuilder) map[string][]interface{} {
+	return p.MakePlugin(pluginKey, providerPlugin{name, provider})
+}
+
+func init() {
+	p.MustRegisterLoader(pluginKey, func(ifc interface{}) error {
+		prov, ok := ifc.(providerPlugin)
+		if !ok {
+			return errors.New("plugin does not match processor plugin type")
+		}
+
+		return autodiscover.Registry.AddProvider(prov.name, prov.provider)
+	})
+}