rule/rule.go
func (l *Load) Add(sym string) {
	if _, ok := l.symbols[sym]; !ok {
		i := &bzl.Ident{Name: sym}
		l.symbols[sym] = identPair{to: i, from: i}
		l.updated = true
	}
}
func (l *Load) Add(sym string) {
	if _, ok := l.symbols[sym]; !ok {
		i := &bzl.Ident{Name: sym}
		l.symbols[sym] = identPair{to: i, from: i}
		l.updated = true
	}
}
// Add inserts a new symbol into the load statement. This has no effect if
// the symbol is already loaded. Symbols will be sorted, so the order
// doesn't matter.