The parsing framework originally created for XIR is now more general and
useful to other things. We'll see how this evolves.
This needs additional documentation, but I'd like to see how it changes as
I implement XmloReader and then some of the source readers first.
DEV-10863
This adds a `Token` type to `ParseState`. Everything uses `xir::Token`
currently, but `XmloReader` will use `xir::flat::Object`.
Now that this has been generalized beyond XIR, the parser ought to be
hoisted up a level.
DEV-10863
This does a couple of things: it ensures that documents one and only one
root note, and it properly handles dead transitions once parsing is
complete (allowing it to be composed).
This should make XIRF feature-complete for the time being. It does rely on
the assumption that the reader is stripping out any trailing whitespace, so
I guess we'll see if that's true as we proceed.
DEV-10863
XIRF introduced the concept of `Transition` to help document code and
provide mental synchronization points that make it easier to reason about
the system. I decided to hoist this into XIR's parser itself, and have
`parse_token` accept an owned state and require a new state to be returned,
utilizing `Transition`.
Together with the convenience methods introduced on `Transition` itself,
this produces much clearer code, as is evidenced by tree::Stack (XIRT's
parser). Passing an owned state is something that I had wanted to do
originally, but I thought it'd lead to more concise code to use a mutable
reference. Unfortunately, that concision lead to code that was much more
difficult than necessary to understand, and ended up having a net negative
benefit by leading to some more boilerplate for the nested types (granted,
that could have been alleviated in other ways).
This also opens up the possibility to do something that I wasn't able to
before, which was continue to abstract away parser composition by stitching
their state machines together. I don't know if this'll be done immediately,
but because the actual parsing operations are now able to compose
functionally without mutability getting the way, the previous state coupling
issues with the parent parser go away.
DEV-10863
This introduces XIR Flat (XIRF), which is conceptually between XIR and
XIRT. This provides a more appropriate level of abstraction for further
lowering operations to parse against, and removes the need for other parsers
to perform their own validations (inappropriately) to ensure well-formed
XML.
There is still some cleanup worth doing, including moving some of the
parsing responsibility up a level back into the XIR parser.
DEV-10863
Mike Gerwitz