Store verbose error under a separate key

field.go

@@ -175,6 +175,10 @@ func Time(key string, val time.Time) zapcore.Field {
 // "error". If passed a nil error, the field is a no-op. This is purely a
 // convenience for a common error-logging idiom; use String("someFieldName",
 // err.Error()) to customize the key.
+//
+// Errors which also implement fmt.Formatter (like those produced by
+// github.com/pkg/errors) will also have their verbose representation stored
+// under "errorVerbose".
 func Error(err error) zapcore.Field {
 	if err == nil {
 		return Skip()

zapcore/field.go

@@ -155,10 +155,9 @@ func (f Field) AddTo(enc ObjectEncoder) {
 		if fancy, ok := val.(fmt.Formatter); ok {
 			// This is a rich error type, like those produced by
 			// github.com/pkg/errors.
-			enc.AddString(f.Key, fmt.Sprintf("%+v", fancy))
-		} else {
-			enc.AddString(f.Key, val.Error())
+			enc.AddString(f.Key+"Verbose", fmt.Sprintf("%+v", fancy))
 		}
+		enc.AddString(f.Key, val.Error())
 	case SkipType:
 		break
 	default:

zapcore/field_test.go

@@ -126,6 +126,9 @@ func TestFields(t *testing.T) {
 		f := Field{Key: "k", Type: tt.t, Integer: tt.i, Interface: tt.iface, String: tt.s}
 		f.AddTo(enc)
 		assert.Equal(t, tt.want, enc.Fields["k"], "Unexpected output from field %+v.", f)
+
+		delete(enc.Fields, "k")
+		assert.Equal(t, 0, len(enc.Fields), "Unexpected extra fields present.")
 	}
 }
 
@@ -137,7 +140,9 @@ func TestRichErrorSupport(t *testing.T) {
 	}
 	enc := NewMapObjectEncoder()
 	f.AddTo(enc)
-	serialized := enc.Fields["k"]
+	assert.Equal(t, "failed: egad", enc.Fields["k"], "Unexpected basic error message.")
+
+	serialized := enc.Fields["kVerbose"]
 	// Don't assert the exact format used by a third-party package, but ensure
 	// that some critical elements are present.
 	assert.Regexp(t, `egad`, serialized, "Expected original error message to be present.")