Wrap errors returned from `Detect` and `New` in `sdk/resource` (#3844)

* Update Detect and New to wrap errors

* Add TestNewWrapedError

Test that New returns an error that can be unwrapped.

* Add changes to changelog

* Clarify and simplify errors

CHANGELOG.md

@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Changed
 
 - Avoid creating new objects on all calls to `WithDeferredSetup` and `SkipContextSetup` in OpenTracing bridge. (#3833)
+- The `New` and `Detect` functions from `go.opentelemetry.io/otel/sdk/resource` return errors that wrap underlying errors instead of just containing the underlying error strings. (#3844)
 
 ### Removed
 

sdk/resource/auto.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 )
 
 var (
@@ -45,28 +46,65 @@ type Detector interface {
 // Detect calls all input detectors sequentially and merges each result with the previous one.
 // It returns the merged error too.
 func Detect(ctx context.Context, detectors ...Detector) (*Resource, error) {
-	var autoDetectedRes *Resource
-	var errInfo []string
+	r := new(Resource)
+	return r, detect(ctx, r, detectors)
+}
+
+// detect runs all detectors using ctx and merges the result into res. This
+// assumes res is allocated and not nil, it will panic otherwise.
+func detect(ctx context.Context, res *Resource, detectors []Detector) error {
+	var (
+		r    *Resource
+		errs detectErrs
+		err  error
+	)
+
 	for _, detector := range detectors {
 		if detector == nil {
 			continue
 		}
-		res, err := detector.Detect(ctx)
+		r, err = detector.Detect(ctx)
 		if err != nil {
-			errInfo = append(errInfo, err.Error())
+			errs = append(errs, err)
 			if !errors.Is(err, ErrPartialResource) {
 				continue
 			}
 		}
-		autoDetectedRes, err = Merge(autoDetectedRes, res)
+		r, err = Merge(res, r)
 		if err != nil {
-			errInfo = append(errInfo, err.Error())
+			errs = append(errs, err)
 		}
+		*res = *r
 	}
 
-	var aggregatedError error
-	if len(errInfo) > 0 {
-		aggregatedError = fmt.Errorf("detecting resources: %s", errInfo)
+	if len(errs) == 0 {
+		return nil
 	}
-	return autoDetectedRes, aggregatedError
+	return errs
+}
+
+type detectErrs []error
+
+func (e detectErrs) Error() string {
+	errStr := make([]string, len(e))
+	for i, err := range e {
+		errStr[i] = fmt.Sprintf("* %s", err)
+	}
+
+	format := "%d errors occurred detecting resource:\n\t%s"
+	return fmt.Sprintf(format, len(e), strings.Join(errStr, "\n\t"))
+}
+
+func (e detectErrs) Unwrap() error {
+	switch len(e) {
+	case 0:
+		return nil
+	case 1:
+		return e[0]
+	}
+	return e[1:]
+}
+
+func (e detectErrs) Is(target error) bool {
+	return len(e) != 0 && errors.Is(e[0], target)
 }

sdk/resource/resource.go

@@ -17,7 +17,6 @@ package resource // import "go.opentelemetry.io/otel/sdk/resource"
 import (
 	"context"
 	"errors"
-	"fmt"
 	"sync"
 
 	"go.opentelemetry.io/otel"
@@ -51,17 +50,8 @@ func New(ctx context.Context, opts ...Option) (*Resource, error) {
 		cfg = opt.apply(cfg)
 	}
 
-	resource, err := Detect(ctx, cfg.detectors...)
-
-	var err2 error
-	resource, err2 = Merge(resource, &Resource{schemaURL: cfg.schemaURL})
-	if err == nil {
-		err = err2
-	} else if err2 != nil {
-		err = fmt.Errorf("detecting resources: %s", []string{err.Error(), err2.Error()})
-	}
-
-	return resource, err
+	r := &Resource{schemaURL: cfg.schemaURL}
+	return r, detect(ctx, r, cfg.detectors)
 }
 
 // NewWithAttributes creates a resource from attrs and associates the resource with a

sdk/resource/resource_test.go

@@ -452,6 +452,25 @@ func TestNew(t *testing.T) {
 	}
 }
 
+func TestNewWrapedError(t *testing.T) {
+	localErr := errors.New("local error")
+	_, err := resource.New(
+		context.Background(),
+		resource.WithDetectors(
+			resource.StringDetector("", "", func() (string, error) {
+				return "", localErr
+			}),
+			resource.StringDetector("", "", func() (string, error) {
+				return "", assert.AnError
+			}),
+		),
+	)
+
+	assert.ErrorIs(t, err, localErr)
+	assert.ErrorIs(t, err, assert.AnError)
+	assert.NotErrorIs(t, err, errors.New("false positive error"))
+}
+
 func TestWithOSType(t *testing.T) {
 	mockRuntimeProviders()
 	t.Cleanup(restoreAttributesProviders)