tree-wide: Audit panic error messages

These shouldn't happen, but if they do, then let's make it easier to
debug.

1 files changed, 2 insertions, 1 deletions

diff --git a/encode_string.go b/encode_string.go
index 328b07a..208aef4 100644
--- a/encode_string.go
+++ b/encode_string.go
@@ -5,6 +5,7 @@
 package lowmemjson
 
 import (
+	"fmt"
 	"io"
 	"unicode/utf8"
 
@@ -40,7 +41,7 @@ func writeStringShortEscape(w io.Writer, c rune) (int, error) {
 	case '\t':
 		b = 't'
 	default:
-		panic("should not happen")
+		panic(fmt.Errorf("should not happen: writeStringShortEscape called with invalid rune: %q", c))
 	}
 	buf := [2]byte{'\\', b}
 	return w.Write(buf[:])