A trait for types that are parsed from a pest::iterators::Pair<Rule> that
depends on the context - e.g. extension lookups or other contextual
information. This is used for types that are not directly parsed from the
grammar, but rather require additional context to parse correctly.
Map a sort-direction enum identifier (without the leading &) to a
SortDirection. Shared by the Sort relationβs sort_field parser and
the window functionβs order= parser, which reach it from different grammar
rules (sort_direction vs a generic enum_value) but accept the same set
of variant names. Lives in common so neither relations nor
expressions depends on the other for it.