From 6ebb665a622d5d5dc33885f7c07d78a8174cf068 Mon Sep 17 00:00:00 2001
From: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Date: Wed, 29 Jul 2026 14:05:50 +0900
Subject: [PATCH] Close merge destination before removing the source

---
 upgrade/upgrade.go | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/upgrade/upgrade.go b/upgrade/upgrade.go
index aa862e3..4a65531 100644
--- a/upgrade/upgrade.go
+++ b/upgrade/upgrade.go
@@ -83,21 +83,29 @@ func mergeFile(src string, dst string) error {
 	if err != nil {
 		return err
 	}
-	defer fdst.Close()
 
 	// Read source content
 	content, err := ioutil.ReadFile(src)
 	if err != nil {
+		fdst.Close()
 		return err
 	}
 
 	// Add Additional newline
 	if _, err := fdst.WriteString("\n"); err != nil {
+		fdst.Close()
 		return err
 	}
 
 	fmt.Printf("Merging: %s into %s\n", src, dst)
 	if _, err = fdst.Write(content); err != nil {
+		fdst.Close()
+		return err
+	}
+
+	// Close may surface deferred write errors; the source must survive
+	// unless the merge fully reached the destination.
+	if err := fdst.Close(); err != nil {
 		return err
 	}