Now can join multiple errors.

error.go

@@ -18,11 +18,37 @@ func isUnwrapable(err error) bool {
     return ok1 || ok2
 }
 
-func errStack(err1 error, err2 error) error {
-    if isUnwrapable(err2) {
-        return fmt.Errorf("%w: %w", err1, err2)
-    }
-    return fmt.Errorf("%w: %v", err1, err2)
+func enshureUnwrapable(err error) error {
+	if isUnwrapable(err) {
+		return err
+	}
+	return fmt.Errorf(err.Error())
+}
+
+func filterNilErrors(errs []error) (notNilErrs []error) {
+	for _, err := range errs {
+		if err != nil {
+			notNilErrs = append(notNilErrs, err)
+		}
+	}
+	return notNilErrs
+}
+
+func Join(errs ...error) (result error) {
+	errs = filterNilErrors(errs)
+	if len(errs) == 0 {
+		return nil
+	}
+	
+	for index, err := range errs {
+		err = enshureUnwrapable(err)
+		if index == 0 {
+			result = err
+		} else {
+			result = fmt.Errorf("%w: %w", result, err)
+		}
+	}
+    return result
 }
 
 func ERR_NOT_TTY() error {

real.go

@@ -12,7 +12,7 @@ func (r *real) SetBaudRate(portPath string, baudrate int) error {
 	setBaudRateCMD := exec.Command("stty", "-F", portPath, fmt.Sprint(baudrate))
 	_, err := setBaudRateCMD.Output()
     if err != nil {
-        return errStack(ERR_SET_BAUDRATE_FAILED(), err)
+        return Join(ERR_SET_BAUDRATE_FAILED(), err)
     }
     return nil
 }
@@ -39,7 +39,7 @@ func (r *real) TestBaudRate(portPath string, baudrate int) error {
 
 	newBaudRate, err := r.CheckBaudRate(portPath)
 	if err != nil {
-		return errStack(ERR_CHECK_BAUDRATE_FAILED(), err)
+		return Join(ERR_CHECK_BAUDRATE_FAILED(), err)
 	}
 
 	if newBaudRate == baudrate {

stty.go

@@ -25,7 +25,7 @@ func init() {
 	checkSttyCMD := exec.Command("stty", "--version")
 	sttyOutput, err := checkSttyCMD.Output()
 	if err != nil || len(sttyOutput) == 0 {
-        cmd = &dummy{errStack(ERR_STTY_MISSING(),err)}
+        cmd = &dummy{Join(ERR_STTY_MISSING(),err)}
 	}
 	cmd = &real{}
 }
@@ -33,13 +33,13 @@ func init() {
 func ValidateTtyFile(filepath string) error {
     file, err := os.Open(filepath)
 	if err != nil {
-        return errStack(ERR_CANNOT_OPEN_FILE(), fmt.Errorf(err.Error()))
+        return Join(ERR_CANNOT_OPEN_FILE(), fmt.Errorf(err.Error()))
 	}
 	defer file.Close()
 
 	err = unix.Access(filepath, unix.W_OK)
 	if err != nil {
-		return errStack(ERR_NO_WRITE_ACCESS(), err)
+		return Join(ERR_NO_WRITE_ACCESS(), err)
 	}
 
 	if term.IsTerminal(int(file.Fd())) {