Prevent nil-dereference in format.Object for boxed nil error (#681)

Author: matthchr

format/format.go

@@ -259,7 +259,7 @@ func Object(object interface{}, indentation uint) string {
 	indent := strings.Repeat(Indent, int(indentation))
 	value := reflect.ValueOf(object)
 	commonRepresentation := ""
-	if err, ok := object.(error); ok {
+	if err, ok := object.(error); ok && !isNilValue(value) { // isNilValue check needed here to avoid nil deref due to boxed nil
 		commonRepresentation += "\n" + IndentString(err.Error(), indentation) + "\n" + indent
 	}
 	return fmt.Sprintf("%s<%s>: %s%s", indent, formatType(value), commonRepresentation, formatValue(value, indentation))

format/format_test.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	. "github.com/onsi/ginkgo/v2"
+
 	. "github.com/onsi/gomega"
 	. "github.com/onsi/gomega/format"
 	"github.com/onsi/gomega/types"
@@ -73,6 +74,16 @@ type NotCustomFormatted struct {
 	Count int
 }
 
+type CustomError struct {
+	Details string
+}
+
+var _ error = &CustomError{}
+
+func (c *CustomError) Error() string {
+	return c.Details
+}
+
 func customFormatter(obj interface{}) (string, bool) {
 	cf, ok := obj.(CustomFormatted)
 	if !ok {
@@ -626,6 +637,11 @@ var _ = Describe("Format", func() {
         \},
     \}`))
 			})
+
+			It("should not panic if the error is a boxed nil", func() {
+				var err *CustomError
+				Expect(Object(err, 1)).Should(Equal("    <*format_test.CustomError | 0x0>: nil"))
+			})
 		})
 	})