From 51a1ea979a88383a62d176161b8503a8045cb46c Mon Sep 17 00:00:00 2001
From: Alec Thomas <alec@swapoff.org>
Date: Mon, 27 Apr 2020 09:10:44 +1000
Subject: [PATCH] Ensure "existingfile" doesn't choke on "-".

---
 mapper.go | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mapper.go b/mapper.go
index 0291184..a605dea 100644
--- a/mapper.go
+++ b/mapper.go
@@ -555,13 +555,15 @@ func existingFileMapper(r *Registry) MapperFunc {
 		if err != nil {
 			return err
 		}
-		path = ExpandPath(path)
-		stat, err := os.Stat(path)
-		if err != nil {
-			return err
-		}
-		if stat.IsDir() {
-			return errors.Errorf("%q exists but is a directory", path)
+		if path != "-" {
+			path = ExpandPath(path)
+			stat, err := os.Stat(path)
+			if err != nil {
+				return err
+			}
+			if stat.IsDir() {
+				return errors.Errorf("%q exists but is a directory", path)
+			}
 		}
 		target.SetString(path)
 		return nil