demangle.go
func (st *state) baseUnresolvedName() AST {
	var n AST
	if len(st.str) >= 2 && st.str[:2] == "on" {
		st.advance(2)
		n, _ = st.operatorName(true)
	} else if len(st.str) >= 2 && st.str[:2] == "dn" {
		st.advance(2)
		if len(st.str) > 0 && isDigit(st.str[0]) {
			n = st.sourceName()
		} else {
			n = st.demangleType(false)
		}
		n = &Destructor{Name: n}
	} else if len(st.str) > 0 && isDigit(st.str[0]) {
		n = st.sourceName()
	} else {
		// GCC seems to not follow the ABI here: it can have
		// an operator name without on.
		// See https://gcc.gnu.org/PR70182.
		n, _ = st.operatorName(true)
	}
	if len(st.str) > 0 && st.str[0] == 'I' {
		args := st.templateArgs()
		n = &Template{Name: n, Args: args}
	}
	return n
}
func (st *state) baseUnresolvedName() AST {
	var n AST
	if len(st.str) >= 2 && st.str[:2] == "on" {
		st.advance(2)
		n, _ = st.operatorName(true)
	} else if len(st.str) >= 2 && st.str[:2] == "dn" {
		st.advance(2)
		if len(st.str) > 0 && isDigit(st.str[0]) {
			n = st.sourceName()
		} else {
			n = st.demangleType(false)
		}
		n = &Destructor{Name: n}
	} else if len(st.str) > 0 && isDigit(st.str[0]) {
		n = st.sourceName()
	} else {
		// GCC seems to not follow the ABI here: it can have
		// an operator name without on.
		// See https://gcc.gnu.org/PR70182.
		n, _ = st.operatorName(true)
	}
	if len(st.str) > 0 && st.str[0] == 'I' {
		args := st.templateArgs()
		n = &Template{Name: n, Args: args}
	}
	return n
}
// <base-unresolved-name> ::= <simple-id>
//                        ::= on <operator-name>
//                        ::= on <operator-name> <template-args>
//                        ::= dn <destructor-name>
//
//<simple-id> ::= <source-name> [ <template-args> ]