demangle.go
func (st *state) fail(err string) {
	panic(demangleErr{err: err, off: st.off})
}
func (st *state) fail(err string) {
	panic(demangleErr{err: err, off: st.off})
}
func ( st * state ) fail ( err string ) { panic ( demangleErr { err : err , off : st . off } ) }
// fail panics with demangleErr, to be caught in doDemangle.
fail panics with demangleErr to be caught in doDemangle .