func checkElem()

in module/module.go [416:481]
56 lines of code
20 McCabe index (conditional complexity)

func checkElem(elem string, kind pathKind) error {
	if elem == "" {
		return fmt.Errorf("empty path element")
	}
	if strings.Count(elem, ".") == len(elem) {
		return fmt.Errorf("invalid path element %q", elem)
	}
	if elem[0] == '.' && kind == modulePath {
		return fmt.Errorf("leading dot in path element")
	}
	if elem[len(elem)-1] == '.' {
		return fmt.Errorf("trailing dot in path element")
	}
	for _, r := range elem {
		ok := false
		switch kind {
		case modulePath:
			ok = modPathOK(r)
		case importPath:
			ok = importPathOK(r)
		case filePath:
			ok = fileNameOK(r)
		default:
			panic(fmt.Sprintf("internal error: invalid kind %v", kind))
		}
		if !ok {
			return fmt.Errorf("invalid char %q", r)
		}
	}

	// Windows disallows a bunch of path elements, sadly.
	// See https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file
	short := elem
	if i := strings.Index(short, "."); i >= 0 {
		short = short[:i]
	}
	for _, bad := range badWindowsNames {
		if strings.EqualFold(bad, short) {
			return fmt.Errorf("%q disallowed as path element component on Windows", short)
		}
	}

	if kind == filePath {
		// don't check for Windows short-names in file names. They're
		// only an issue for import paths.
		return nil
	}

	// Reject path components that look like Windows short-names.
	// Those usually end in a tilde followed by one or more ASCII digits.
	if tilde := strings.LastIndexByte(short, '~'); tilde >= 0 && tilde < len(short)-1 {
		suffix := short[tilde+1:]
		suffixIsDigits := true
		for _, r := range suffix {
			if r < '0' || r > '9' {
				suffixIsDigits = false
				break
			}
		}
		if suffixIsDigits {
			return fmt.Errorf("trailing tilde and digits in path element")
		}
	}

	return nil
}