Allow config.Load to load partial config (#910)

config/config.go

@@ -123,6 +123,7 @@ func NewViper() *viper.Viper {
 }
 
 // Load loads a Config from Viper.
+// After loading the config, need to check if it is valid by calling `ValidateConfig`.
 func Load(
 	v *viper.Viper,
 	factories Factories,
@@ -349,15 +350,6 @@ func loadReceivers(v *viper.Viper, factories map[configmodels.Type]component.Rec
 	// Get the map of "receivers" sub-keys.
 	keyMap := v.GetStringMap(receiversKeyName)
 
-	// Currently there is no default receiver enabled. The configuration must specify at least one receiver to enable
-	// functionality.
-	if len(keyMap) == 0 {
-		return nil, &configError{
-			code: errMissingReceivers,
-			msg:  "no receivers specified in config",
-		}
-	}
-
 	// Prepare resulting map
 	receivers := make(configmodels.Receivers)
 
@@ -408,14 +400,6 @@ func loadExporters(v *viper.Viper, factories map[configmodels.Type]component.Exp
 	// Get the map of "exporters" sub-keys.
 	keyMap := v.GetStringMap(exportersKeyName)
 
-	// There is no default exporter. The configuration must specify at least one exporter to enable functionality.
-	if len(keyMap) == 0 {
-		return nil, &configError{
-			code: errMissingExporters,
-			msg:  "no exporters specified in config",
-		}
-	}
-
 	// Prepare resulting map
 	exporters := make(configmodels.Exporters)
 
@@ -602,6 +586,7 @@ func ValidateConfig(cfg *configmodels.Config, logger *zap.Logger) error {
 	if err := validateReceivers(cfg); err != nil {
 		return err
 	}
+
 	if err := validateExporters(cfg); err != nil {
 		return err
 	}
@@ -610,25 +595,24 @@ func ValidateConfig(cfg *configmodels.Config, logger *zap.Logger) error {
 		return err
 	}
 
-	if err := validatePipelines(cfg); err != nil {
-		return err
-	}
-
 	return nil
 }
 
 func validateService(cfg *configmodels.Config) error {
-	// Currently only to validate extensions.
-	return validateServiceExtensions(cfg, &cfg.Service)
+	if err := validatePipelines(cfg); err != nil {
+		return err
+	}
+
+	return validateServiceExtensions(cfg)
 }
 
-func validateServiceExtensions(cfg *configmodels.Config, service *configmodels.Service) error {
+func validateServiceExtensions(cfg *configmodels.Config) error {
 	if len(cfg.Service.Extensions) == 0 {
 		return nil
 	}
 
 	// Validate extensions.
-	for _, ref := range service.Extensions {
+	for _, ref := range cfg.Service.Extensions {
 		// Check that the name referenced in the service extensions exists in the top-level extensions
 		if cfg.Extensions[ref] == nil {
 			return &configError{

config/config_test.go

@@ -20,13 +20,14 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/open-telemetry/opentelemetry-collector/config/configmodels"
 )
 
 func TestDecodeConfig(t *testing.T) {
 	factories, err := ExampleComponents()
-	assert.Nil(t, err)
+	assert.NoError(t, err)
 
 	// Load the config
 	config, err := LoadConfigFile(t, path.Join(".", "testdata", "valid-config.yaml"), factories)
@@ -192,7 +193,7 @@ func TestSimpleConfig(t *testing.T) {
 	for _, test := range testCases {
 		t.Logf("TEST[%s]", test.name)
 		factories, err := ExampleComponents()
-		assert.Nil(t, err)
+		assert.NoError(t, err)
 
 		// Load the config
 		config, err := LoadConfigFile(t, path.Join(".", "testdata", test.name+".yaml"), factories)
@@ -287,7 +288,7 @@ func TestSimpleConfig(t *testing.T) {
 
 func TestDecodeConfig_MultiProto(t *testing.T) {
 	factories, err := ExampleComponents()
-	assert.Nil(t, err)
+	assert.NoError(t, err)
 
 	// Load the config
 	config, err := LoadConfigFile(t, path.Join(".", "testdata", "multiproto-config.yaml"), factories)
@@ -383,7 +384,7 @@ func TestDecodeConfig_Invalid(t *testing.T) {
 	}
 
 	factories, err := ExampleComponents()
-	assert.Nil(t, err)
+	assert.NoError(t, err)
 
 	for _, test := range testCases {
 		_, err := LoadConfigFile(t, path.Join(".", "testdata", test.name+".yaml"), factories)
@@ -407,3 +408,25 @@ func TestDecodeConfig_Invalid(t *testing.T) {
 		}
 	}
 }
+
+func TestLoadEmptyConfig(t *testing.T) {
+	factories, err := ExampleComponents()
+	assert.NoError(t, err)
+
+	// Open the file for reading.
+	file, err := os.Open(path.Join(".", "testdata", "empty-config.yaml"))
+	require.NoError(t, err)
+
+	defer func() {
+		require.NoError(t, file.Close())
+	}()
+
+	// Read yaml config from file
+	v := NewViper()
+	v.SetConfigType("yaml")
+	require.NoError(t, v.ReadConfig(file))
+
+	// Load the config from viper using the given factories.
+	_, err = Load(v, factories)
+	assert.NoError(t, err)
+}