tamer: nir::desugar::interp: Generalize without NIR symbol typesmain

This is a shift in approach.

My original idea was to try to keep NIR parsing the way it was, since it's
already hard enough to reason about with the `ele_parse!` parser-generator
macro mess.  The idea was to produce an IR that would explicitly be denoted
as "maybe sugared", and have a desugaring operation as part of the lowering
pipeline that would perform interpolation and lower the symbol into a plain
version.

The problem with that is:

  1. The use of the type was going to introduce a lot of mapping for all the
     NIR token variants there are going to be; and
  2. _The types weren't even utilized for interpolation._

Instead, if we interpolated _as attributes are encountered_ while parsing
NIR, then we'd be able to expand directly into that NIR token stream and
handle _all_ symbols in a generic way, without any mapping beyond the
definition of NIR's grammar using `ele_parse!`.

This is a step in that direction---it removes `NirSymbolTy` and introduces a
generic abstraction for the concept of expansion, which will be utilized
soon by the attribute parser to allow replacing `TryFrom` with something
akin to `ParseFrom`, or something like that, which is able to produce a
token stream before finally yielding the value of the attribute (which will
be either the original symbol or the replacement metavariable, in the case
of interpolation).

(Note that interpolation isn't yet finished---errors still need to be
implemented.  But I want a working vertical slice first.)

DEV-13156

0 files changed, 0 insertions, 0 deletions