From a611f9fd7cd971ab4ebf04e3fa76377af442e992 Mon Sep 17 00:00:00 2001
From: gutmet <me.git@gutmet.org>
Date: Mon, 27 Apr 2020 20:09:58 +0200
Subject: [PATCH] better error message for byte field of unknown size

---
 laymanshex.go | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/laymanshex.go b/laymanshex.go
index 84d71c6..21d1f88 100644
--- a/laymanshex.go
+++ b/laymanshex.go
@@ -16,7 +16,11 @@ import (
 
 func optPanic(msg string, err error) {
 	if err != nil {
-		panic(errors.New(msg + ": " + err.Error()))
+		if msg != "" {
+			panic(msg + ": " + err.Error())
+		} else {
+			panic(err)
+		}
 	}
 }
 
@@ -174,7 +178,11 @@ func (part *filePart) setByteFieldHandling(assignments map[string]*formatAssignm
 			ass.used = true
 			err = nil
 		} else {
-			err = errors.New("Could neither parse size to int64 nor obtain value from -fvar")
+			msg := "byte field: could neither parse size to int64 nor obtain value from -fvar"
+			if part.name != "" {
+				msg += " definition " + part.name
+			}
+			err = errors.New(msg)
 		}
 	}
 	optPanic(part.name, err)