save: Create temporary file only in case the target file already exists

internal/buffer/save.go

@@ -31,10 +31,16 @@ func overwriteFile(name string, enc encoding.Encoding, fn func(io.Writer) error,
 	var writeCloser io.WriteCloser
 	var screenb bool
 	var cmd *exec.Cmd
-	tmpName := name + ".tmp"
+	potentialName := name
+	rename := false
+
+	if _, statErr := os.Stat(potentialName); os.IsNotExist(statErr) {
+		potentialName = name + ".tmp"
+		rename = true
+	}
 
 	if withSudo {
-		cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "dd", "bs=4k", "of="+tmpName)
+		cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "dd", "bs=4k", "of="+potentialName)
 
 		if writeCloser, err = cmd.StdinPipe(); err != nil {
 			return
@@ -55,7 +61,7 @@ func overwriteFile(name string, enc encoding.Encoding, fn func(io.Writer) error,
 			screen.TempStart(screenb)
 			return err
 		}
-	} else if writeCloser, err = os.OpenFile(tmpName, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666); err != nil {
+	} else if writeCloser, err = os.OpenFile(potentialName, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666); err != nil {
 		return
 	}
 
@@ -85,28 +91,31 @@ func overwriteFile(name string, enc encoding.Encoding, fn func(io.Writer) error,
 			return err
 		}
 
-		cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "mv", tmpName, name)
+		if rename {
+			cmd = exec.Command(config.GlobalSettings["sucmd"].(string), "mv", potentialName, name)
 
-		c := make(chan os.Signal, 1)
-		signal.Notify(c, os.Interrupt)
-		go func() {
-			<-c
-			cmd.Process.Kill()
-		}()
+			c := make(chan os.Signal, 1)
+			signal.Notify(c, os.Interrupt)
+			go func() {
+				<-c
+				cmd.Process.Kill()
+			}()
 
-		if e := cmd.Start(); e != nil && err == nil {
-			screen.TempStart(screenb)
-			return err
+			if e := cmd.Start(); e != nil && err == nil {
+				screen.TempStart(screenb)
+				return err
+			}
+
+			err = cmd.Wait()
 		}
 
-		err = cmd.Wait()
 		screen.TempStart(screenb)
 		if err != nil {
 			return err
 		}
-	} else {
+	} else if rename {
 		if err == nil {
-			err = os.Rename(tmpName, name)
+			err = os.Rename(potentialName, name)
 		}
 	}