fix: treat typed nils as nil in Wrap/WrapPrefix

error.go

@@ -93,8 +93,25 @@ func New(e interface{}) *Error {
 // explicitly wrap an *Error with a new stacktrace use Errorf. The skip
 // parameter indicates how far up the stack to start the stacktrace. 0 is from
 // the current call, 1 from its caller, etc.
-func Wrap(e interface{}, skip int) *Error {
+
+// isNil reports whether e is a nil interface value or a typed nil
+// (nil pointer/slice/map/func/chan/interface). Zero-value structs that
+// implement error are not considered nil.
+func isNil(e interface{}) bool {
 	if e == nil {
+		return true
+	}
+	v := reflect.ValueOf(e)
+	switch v.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
+		return v.IsNil()
+	default:
+		return false
+	}
+}
+
+func Wrap(e interface{}, skip int) *Error {
+	if isNil(e) {
 		return nil
 	}
 
@@ -127,7 +144,7 @@ func Wrap(e interface{}, skip int) *Error {
 // the stack to start the stacktrace. 0 is from the current call, 1 from its
 // caller, etc.
 func WrapPrefix(e interface{}, prefix string, skip int) *Error {
-	if e == nil {
+	if isNil(e) {
 		return nil
 	}
 

error_test.go

@@ -345,3 +345,24 @@ type errorString string
 func (e errorString) Error() string {
 	return string(e)
 }
+
+type typedNilError struct{ message string }
+
+func (e *typedNilError) Error() string { return e.message }
+
+func TestWrapTypedNil(t *testing.T) {
+	var ptr *typedNilError
+	if Wrap(ptr, 0) != nil {
+		t.Errorf("Wrap typed nil pointer should return nil")
+	}
+	if WrapPrefix(ptr, "prefix", 0) != nil {
+		t.Errorf("WrapPrefix typed nil pointer should return nil")
+	}
+	if Wrap(nil, 0) != nil || WrapPrefix(nil, "p", 0) != nil {
+		t.Errorf("Wrap/WrapPrefix nil should return nil")
+	}
+	nonNil := &typedNilError{message: "x"}
+	if Wrap(nonNil, 0) == nil {
+		t.Errorf("Wrap non-nil pointer should wrap")
+	}
+}