Support nesting of errors

fields_error_test.go

@@ -22,6 +22,7 @@ package zap
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -30,20 +31,35 @@ import (
 
 func TestErrorWithFields(t *testing.T) {
 	rootErr := errors.New("root err")
-	wrapped := WrapError(rootErr,
+	wrap1 := fmt.Errorf("wrap1: %w", rootErr)
+	wrap2 := WrapError(wrap1,
 		String("user", "foo"),
 		Int("count", 12),
 	)
 
-	assert.True(t, errors.Is(wrapped, rootErr), "errors.Is")
+	assert.True(t, errors.Is(wrap2, rootErr), "errors.Is")
+	assert.True(t, errors.Is(wrap2, wrap1), "errors.Is")
 
 	enc := zapcore.NewMapObjectEncoder()
-	Error(wrapped).AddTo(enc)
+	Error(wrap2).AddTo(enc)
 	assert.Equal(t, map[string]any{
-		"error": rootErr.Error(),
+		"error": "wrap1: root err",
 		"errorFields": map[string]any{
 			"user":  "foo",
 			"count": int64(12),
 		},
 	}, enc.Fields)
+
+	wrap3 := fmt.Errorf("wrap3: %w", wrap2)
+	wrap4 := WrapError(wrap3, Bool("wrap4", true))
+
+	Error(wrap4).AddTo(enc)
+	assert.Equal(t, map[string]any{
+		"error": "wrap3: wrap1: root err",
+		"errorFields": map[string]any{
+			"user":  "foo",
+			"count": int64(12),
+			"wrap4": true,
+		},
+	}, enc.Fields)
 }

zapcore/error.go

@@ -21,9 +21,11 @@
 package zapcore
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 
+	"go.uber.org/multierr"
 	"go.uber.org/zap/internal/pool"
 )
 
@@ -76,15 +78,40 @@ func encodeError(key string, err error, enc ObjectEncoder) (retErr error) {
 		}
 	}
 
-	if errObj, ok := err.(ObjectMarshaler); ok {
-		if err := enc.AddObject(key+"Fields", errObj); err != nil {
+	// Unwrap the error and marshal any ObjectMarshalers in the error chain.
+
+	marshalers := make(mergedMarshalers, 0, 1)
+	for e := err; e != nil; e = errors.Unwrap(e) {
+		errObj, ok := e.(ObjectMarshaler)
+		if ok {
+			marshalers = append(marshalers, errObj)
+		}
+	}
+
+	switch {
+	case len(marshalers) == 1:
+		if err := enc.AddObject(key+"Fields", marshalers[0]); err != nil {
+			return err
+		}
+	case len(marshalers) > 1:
+		if err := enc.AddObject(key+"Fields", marshalers); err != nil {
 			return err
 		}
 	}
 
 	return nil
 }
 
+type mergedMarshalers []ObjectMarshaler
+
+func (ms mergedMarshalers) MarshalLogObject(enc ObjectEncoder) error {
+	var errs error
+	for _, m := range ms {
+		errs = multierr.Append(errs, m.MarshalLogObject(enc))
+	}
+	return errs
+}
+
 type errorGroup interface {
 	// Provides read-only access to the underlying list of errors, preferably
 	// without causing any allocs.