Don't consider unset env var to be an error during resource detection (#1170)

* Don't consider unset env var an error during detection

* update CHANGELOG

CHANGELOG.md

@@ -39,6 +39,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The [configuration style guide](https://github.com/open-telemetry/opentelemetry-go/blob/master/CONTRIBUTING.md#config) has been updated to
    recommend the use of `newConfig()` instead of `configure()`. (#1163)
 - The `otlp.Config` type has been unexported and changed to `otlp.config`, along with its initializer. (#1163)
+- Don't consider unset environment variable for resource detection to be an error. (#1170)
 
 ### Fixed
 

sdk/resource/auto.go

@@ -21,9 +21,6 @@ import (
 )
 
 var (
-	// ErrMissingResource is returned by a detector when source information
-	// is unavailable for a Resource.
-	ErrMissingResource = errors.New("missing resource")
 	// ErrPartialResource is returned by a detector when complete source
 	// information for a Resource is unavailable or the source information
 	// contains invalid values that are omitted from the returned Resource.
@@ -33,13 +30,10 @@ var (
 // Detector detects OpenTelemetry resource information
 type Detector interface {
 	// Detect returns an initialized Resource based on gathered information.
-	// If source information to construct a Resource is inaccessible, an
-	// uninitialized Resource is returned with an appropriately wrapped
-	// ErrMissingResource error is returned. If the source information to
-	// construct a Resource contains invalid values, a Resource is returned
-	// with the valid parts of the source information used for
-	// initialization along with an appropriately wrapped ErrPartialResource
-	// error.
+	// If the source information to construct a Resource contains invalid
+	// values, a Resource is returned with the valid parts of the source
+	// information used for initialization along with an appropriately
+	// wrapped ErrPartialResource error.
 	Detect(ctx context.Context) (*Resource, error)
 }
 

sdk/resource/env.go

@@ -43,7 +43,7 @@ func (d *FromEnv) Detect(context.Context) (*Resource, error) {
 	labels := strings.TrimSpace(os.Getenv(envVar))
 
 	if labels == "" {
-		return Empty(), ErrMissingResource
+		return Empty(), nil
 	}
 	return constructOTResources(labels)
 }

sdk/resource/env_test.go

@@ -55,8 +55,7 @@ func TestEmpty(t *testing.T) {
 
 	detector := &FromEnv{}
 	res, err := detector.Detect(context.Background())
-	require.Error(t, err)
-	assert.Equal(t, err, ErrMissingResource)
+	require.NoError(t, err)
 	assert.Equal(t, Empty(), res)
 }