This makes the necessary tweaks to have the entire linker work end-to-end
and produce a compatible xmle file (that is, identical except for
nondeterministic topological ordering). That's good, and finally that can
get off of my plate.
What's disappointing, and what I'll have more information on in future
commits, is how slow it is.
The linking of our largest package goes from ~1s -> ~15s with this
change. The reason is because of tens of millions of `memcpy` calls. Why?
The ParseState abstraction is pure and passes an owned `self` around, and
Parser replaces its own reference using this:
let result;
TransitionResult(Transition(self.state), result) =
take(&mut self.state).parse_token(tok);
Naively, this would store a copy of the old state in `result`, allocate a
new ParseState for `self.state`, pass the original or a copy to
`parse_token`, and then overwrite `self.state` with the new ParseState that
is returned once it is all over.
Of course, that'd be devastating. What we want to happen is for Rust to
realize that it can just pass a reference to `self.state` and perform no
copying at all.
For certain parsers, this is exactly what happens. Great!
But for XIRF, it we have this:
/// Stack of element [`QName`] and [`Span`] pairs,
/// representing the current level of nesting.
///
/// This storage is statically allocated,
/// allowing XIRF's parser to avoid memory allocation entirely.
type ElementStack<const MAX_DEPTH: usize> = ArrayVec<(QName, Span), MAX_DEPTH>;
/// XIRF document parser state.
///
/// This parser is a pushdown automaton that parses a single XML document.
#[derive(Debug, Default, PartialEq, Eq)]
pub enum State<const MAX_DEPTH: usize, SA = AttrParseState>
where
SA: FlatAttrParseState,
{
/// Document parsing has not yet begun.
#[default]
PreRoot,
/// Parsing nodes.
NodeExpected(ElementStack<MAX_DEPTH>),
/// Delegating to attribute parser.
AttrExpected(ElementStack<MAX_DEPTH>, SA),
/// End of document has been reached.
Done,
}
ParseState contains an ArrayVec, and its implementation details are causes
LLVM _not_ to elide the `memcpy`. And there's a lot of them.
Considering that ParseState is supposed to use only statically allocated
memory and be zero-copy, this is rather ironic.
Now, this _could_ be potentially fixed by not using ArrayVec; removing
it (and the corresponding checks for balanced tags) gets us down to
2s (which still needs improvement), but we can't have a core abstraction in
our system resting on a house of cards. What if the optimization changes
between releases and suddenly linking / building becomes shit slow? That's
too much of a risk.
Further, having to limit what abstractions we use just to appease the
compiler to optimize away moves is very restrictive.
The better option seems like to go back to what I used to do: pass around
`&mut self`. I had moved to an owned `self` to force consideration of _all_
state transitions, but I can try to do the same thing in a different type of
way using mutable references, and then we avoid this problem. The
abstraction isn't pure (in the functional sense) anymore, but it's safe and
isn't relying on delicate inlining and optimizer implementation details to
have a performant system.
More information to come.
DEV-10863
This concludes the bulk of the header parsing, though there are surely going
to be other issues when I try to read a real xmlo file, such as
whitespace. That is something I expect that I'd rather handle as part of
XIRF, but maybe I'll initially ignore it here just to get it working. We'll
see.
DEV-10863
This parses the symbol dependency list (adjacency list).
I'm noticing some glaring issues in error handling, particularly that the
token being parsed while an error occurs is not returned and so recovery is
impossible. I'll have to address that later on, after I get this parser
completed.
Another previous question that I had a hard time answering in prior months
was how I was going to compose boilerplate parsers, e.g. handling the
parsing of single-attribute elements and such. A pattern is clearly taking
shape, and with the composition of parsers more formalized, that'll be able
to be abstracted away. But again, that's going to wait until after this
parser is actually functioning. Too many delays so far.
DEV-10863
Ideally this would just be an attribute, but I guess I never got around to
making that change in the compiler and I don't want a detour right now.
DEV-10863
I clearly was not paying attention to what was correct behavior here, since
the tests also verified the wrong behavior: rather than taking the last
processed attribute span, we should be taking the span of the opening
tag for the `preproc:sym` node.
DEV-10863
This simply removes boilerplate.
This will receive concrete examples once I come up with docs for the entire
module; there's boilerplate involved in testing and documenting this in
isolation and the time investment is not worth it yet until I'm certain that
this will not be changed.
DEV-10863
This integrates much of the work done so far to parse into a
`XmloEvent::SymDecl`. The attribute parsing _is_ verbose, and I do intend
to abstract it away later on, but I'm going to wait on that for now.
The new reader should be finishing up soon, which is really exciting, since
I started working on this months ago (before having to take a break on
TAMER); I'm anticipating strong performance gains in the reader, and this is
a test that will tell us how the compiler will perform moving forward with
the abstractions that I've spent so much time on.
DEV-10863
This introduces a new method similar to the previous `delegate`, but with
another closure that allows for handling lookahead tokens from the child
parser.
Admittedly, this isn't exactly what I was going for---a list of arguments
isn't exactly self-documenting, especially with the brevity when the
arguments line up---but this was easy to do and so I'll run with this for
now.
This also modified `delegate` to accept a context, even though it wasn't
necessary, both for consistency with its lookup counterpart and for brevity
with the `into` argument (allowing, in our case, to just pass the name of
the variant, rather than a closure).
I'm not going to handle the actual starting and accepting state stitching
abstraction for now; I'd like to observe future boilerplate more before I
consider the best way to handle it, though I do have some ideas.
DEV-10863
This is the delegation portion of what I've come to call "state
stitching"---wiring together two state machines that recognize the same
input tokens.
This handles the delegation of tokens once the parser has been entered, but
does not yet handle the actual stitching part of it: wiring the start and
accepting states of the child parser to the parent.
This is indirectly tested by the XmloReader, but it will receive its own
tests once I further finalize this concept. I'm playing around with some
ideas. With that said, a quick visual inspection together with the
guarantees provided by the type system should convince any familiar reader
of its correctness.
DEV-10863
This wasn't the simplest thing to start with, but I wanted to explore
something with a higher level of complexity. There is some boilerplate to
observe here, including:
1. The state stitching (as I guess I'm calling it now) of SymtableState
with XmloReaderState is all boilerplate and requires no lookahead,
presenting an abstraction opportunity that I was holding off on
previously (attr parsing for XIRF requires lookahead).
2. This is simply collecting attributes into a struct. This can be
abstracted away in the future.
3. Creating stub parsers to verify that generics are stitched rather than
being tightly coupled with another state is boilerplate that maybe can
be abstracted away after a pattern is observed in future tests.
DEV-10863
This does some cleanup and adds `parse::Object` for use in disambiguating
`From` for `ParseStatus`, allowing the `Transition` API to be much more
flexible in the data it accepts and automatically converts. This allows us
to concisely provide raw output data to be wrapped, or provide `ParseStatus`
directly when more convenient.
There aren't yet examples in the docs; I'll do so once I make sure this API
is actually utilized as intended.
DEV-10863
This replaces u8 and will be used for the new XmloReader.
Previously I wasn't sure what direction TAMER was going to go in with
regards to dimensionality, but I do not expect that higher dimensions will
be supported, and if they are, they'd very likely compile down to lower ones
and create an illusion of higher-dimensionality.
Whatever the future holds, it's not used today, and I'd rather these types
be correct.
ASG needs changing too, but one step at a time.
DEV-10863
This converts the tuple type alias into a newtype, so that we may provide
our own implementations.
This differs from a previous approach that I took, which involved making
this type `Result<(S, T), (S, E)>` so that the return values composed well
with other functions. But the reality is that this is used only by other
`ParseState`s and `Parser`, so it's unnecessary.
However, this is also an attempt to utilize the new Try and FromResidual
traits; note how the Try associated types match precisely what I was trying
to do before, though they're used as intermediate types. I'll see how this
evolves.
DEV-10863
This allows the Results to compose and, importantly, is compatible with
`?` without having to put in any extra effort.
This makes puts the caller in an awkward spot, so I introduced a utility
function `result_tup0_invert` for now; we'll see if that stays or evolves
differently.
DEV-10863
Since this is the object produced by this parser, this is likely the most
useful first thing to present as a summary of what `XmloReader` actually
does.
DEV-10863
This removes the flag from most of the code, which also resolves the
indentation. Not only was it bothering me, but I don't want (a) every line
modified when the module body is hoisted and (b) `rustfmt` to reformat
everything when that happens.
This means that everything will be built, even though it's not used, when
the flag is off, but I see that as a good thing.
DEV-10863
Finally we get to do some actual parsing with all of the preparatory work!
This means that we're finally ready to fully replace the old XmloReader,
provided that I'm okay with some boilerplate / lack of abstractions for
now (and I am, because all I've been doing is working on abstractions to
prepare lowering operations).
DEV-10863
This makes more sense for pattern matching. Encapsulation of these fields
is not necessary, given that it's passed around as an owned value and its
`new` method constructs it verbatim; the individual fields are
self-validating.
DEV-10863
This introduces a WIP lowering operation, abstracting away quite a bit of
the manual wiring work, which is really important to providing an API that
provides the proper level of abstraction for actually understanding what the
system is doing.
This does not yet have tests associated with it---I had started, but it's a
lot of work and boilerplate for something that is going to
evolve. Generally, I wouldn't use that as an excuse, but the robust type
definitions in play, combined with the tiny amount of actual logic, provide
a pretty high level of confidence. It's very difficult to wire these types
together and produce something incorrect without doing something obviously
bad.
Similarly, I'm holding off on proper docs too, though I did write some
information here.
More to come, after I actually get to work on the XmloReader.
On a side note: I'm happy to have made progress on this, since this wiring
is something I've been dreading and wondering about since before the Parser
abstraction even existed.
Note also that this makes parser::feed_toks private again---I don't intend
to support push parsers yet, since they're only needed internally. Maybe
for error recovery, but I'll wait to decide until it's actually needed.
DEV-10863
This begins to transition XmloReader into a ParseState. Unlike previous
changes where ParseStates were composed into a single ParseState, this is
instead a lowering operation that will take the output of one Parser and
provide it to another.
The mess in ld::poc (...which still needs to be refactored and removed)
shows the concept, which will be abstracted away. This won't actually get
to the ASG in order to test that that this works with the
wip-xmlo-xir-reader flag on (development hasn't gotten that far yet), but
since it type-checks, it should conceptually work.
Wiring lowering operations together is something that I've been dreading for
months, but my approach of only abstracting after-the-fact has helped to
guide a sane approach for this. For some definition of "sane".
It's also worth noting that AsgBuilder will too become a ParseState
implemented as another lowering operation, so:
XIR -> XIRF -> XMLO -> ASG
These steps will all be streaming, with iteration happening only at the
topmost level. For this reason, it's important that ASG not be responsible
for doing that pull, and further we should propagate Parsed::Incomplete
rather than filtering it out and looping an indeterminate number of times
outside of the toplevel.
One final note: the choice of 64 for the maximum depth is entirely
arbitrary and should be more than generous; it'll be finalized at some point
in the future once I actually evaluate what maximum depth is reasonable
based on how the system is used, with some added growing room.
DEV-10863
This introduces a (still-private) way to _push_ tokens into the parser,
rather than relying purely on a pull-based interface. Not only does this
simplify the iterator, but this is also preparing to make the new `feed_tok`
public so that parsers can be composed in more contexts. I suspect that
this method may also be useful for error recovery, since it can be used to
inject tokens into arbitrary points of a token stream.
I kept the new method private for now so that I can introduce the new API
and docs separate from this refactoring.
DEV-10863
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
I'm not rendering errors yet in practice, so this wouldn't have been
noticed, but we want error messages to reference the final byte in a file on
EOF, not the offset of the last-encountered token, which would be confusing.
This doesn't _directly_ pertain to what I'm working on; I just happened to
notice it.
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
This behavior is unchanged, but it allows us to create more constant spans
for testing. For example:
const S = DUMMY_SPAN.offset_add(1).unwrap();
This, in turn, will allow for removing lazy_static! for tests that use it
for span generation.
DEV-10863
Petgraph was previously held back due to petgraph-graphml. I'd like to
transition away from that at some point, given that it's tied to petgraph
and also pulls in xmlns, on top of quick-xml and our XIR, but that can come
down the line.
The Options here are awkward and will be able to go away in the new reader
and in AsgBuilder once it has a proper state machine.
This gets rid of some of the initial migratory work for the new reader,
because PackageAttrs is gone. I'm going to wait to update this to the new
way until I get further into this.
DEV-11449
I'm finally back to TAMER development.
The original plan, some time ago, was to gate an entirely new XmloReader
behind a feature flag (wip-xmlo-xir-reader), and go from there, leaving the
existing implementation untouched. Unfortunately, it became too difficult
and confusing to marry the old aggregate API with the new streaming one.
AsgBuilder is the only system interacting with XmloReader, so I decided (see
previous commits) to just go the route of refactoring the existing
one. I'm not yet sure if I'll continue to progressively refactor this one
and eliminate the two separate implementations behind the flag, or if I'll
get this API similar and then keep the flag and reimplement it. But I'll
know soon.
DEV-11449
This is simply not worth it; the size is not going to be the bottleneck (at
least any time soon) and the generic not only pollutes all the things that
will use ASG in the near future, but is also incompatible with the SymbolId
default that is used everywhere; if we have to force it to 32 bits anyway,
then we may as well just default it right off the bat.
I thought that this seemed like a good idea at the time, and saving bits is
certainly tempting, but it was premature.
It's a bit odd that I've done next to nothing with TAMER for the past week
or so, and decided to do this one small thing before I go on break for the
holidays, but I felt compelled to do _something_. Besides, this gets me in
a better spot for the inevitable mental planning and writing I'll be doing
over the holidays.
This move was natural, given what this has evolved into---it has nothing to
do with the concept of a "tree", and the modules imports emphasized that
fact given the level of inappropriate nesting.
Now that the parser has been simplified by removing attributes, we can
further simplify the state transitions to make it more clear what further
refactoring can be done.
DEV-11339
More information can be found in the prior commit message, but I'll
summarize here.
This token was introduced to create a LL(0) parser---no tokens of
lookahead. This allowed the underlying TokenStream to be freely passed to
the next system that needed it.
Since then, Parser and ParseState were introduced, along with
ParseStatus::Dead, which introduces the concept of lookahead for a single
token---an LL(1) grammar.
I had always suspected that this would happen, given the awkwardness of
AttrEnd; it was just a matter of time before the right abstraction
manifested itself to handle lookahead.
DEV-11339
Note that AttrParse{r=>}State needs renaming, and Stack will get a better
name down the line too. This commit message is accurate, but confusing.
This performs the long-awaited task of trying to observe, concretely, how to
combine two automata. This has the effect of stitching together the state
machines, such that the union of the two is equivalent to the original
monolith.
The next step will be to abstract this away.
There are some important things to note here. First, this introduces a new
"dead" state concept, where here a dead state is defined as an _accepting_
state that has no state transitions for the given input token. This is more
strict than a dead state as defined in, for example, the Dragon Book, where
backtracking may occur.
The reason I chose for a Dead state to be accepting is simple: it represents
a lookahead situation. It says, "I don't know what this token is, but I've
done my job, so it may be useful in a parent context". The "I've done my
job" part is only applicable in an accepting state.
If the parser is _not_ in an accepting state, then an unknown token is
simply an error; we should _not_ try to backtrack or anything of the sort,
because we want only a single token of lookahead.
The reason this was done is because it's otherwise difficult to compose the
two parsers without requiring that AttrEnd exist in every XIR stream; this
has always been an awkward delimiter that was introduced to make the parser
LL(0), but I tried to compromise by saying that it was optional. Of course,
I knew that decision caused awkward inconsistencies, I had just hoped that
those inconsistencies wouldn't manifest in practical issues.
Well, now it did, and the benefits of AttrEnd that we had in the previous
construction do not exist in this one. Consequently, it makes more sense to
simply go from LL(0) to LL(1), which makes AttrEnd unnecessary, and a future
commit will remove it entirely.
All of this information will be documented, but I want to get further in
the implementation first to make sure I don't change course again and
therefore waste my time on docs.
DEV-11268
These were missed from a couple of commits ago, after I recalled that I
could now simplify the Stack variants; they were made more complicated due
to isolated attribute parsing.
These progressive refactorings do a good job illustrating why composing
parsers is better than a monolith---the complexity of the parsers is
significantly reduced, and the number of combinations of states are also
greatly reduced, which allows us to reason about them in isolation.
DEV-11268
This was added only for isolated attribute parsing. Of course, this does
mean that a new union type will be needed when combining the two parsers,
depending on the desired resolution, but that'll come at a later time and
possibly in a more general way.
DEV-11268
This nearly completely integrates the new Parser with xir::tree, but does
not yet compose AttrParseState. I also need to determine what to do with
`parse()` and, further, make `parser_from` generic as part of mod parse.
If we take a moment to reflect on all of the changes, this struggle has been
a roundabout way of converting tree's parser into parse::Parser; providing
a trait for Stack (as ParseState); beginning parser decomposition; and
moving some common logic into Parser. The composition of parsers is the
final piece to be realized.
This could have been a lot less work if I really understood exactly what I
wanted to do up front, but as was mentioned in previous commits, I was
really confusing myself trying to maintain API BC in ways that I should not
have for XmloReader. More on that will be coming soon as well.
DEV-11268
This will allow Parser to operate on both owned and &mut values, and is the
same approach that Rust's built-in iterators take.
This is at first quite surprising, and I often forget that this is a
feature, and, as a bonus, an attractive way to avoid lifetimes in struct
definitions when generics are used for the type that may become a
reference.
DEV-11268
This isn't currently used by anything, and this is collecting, which does
not fit well with the streaming model. AttrList was originally written for
Element parsing, and the isolated attr parser was written for test cases,
before it was fully decided how this system ought to work.
Instead, if AttrList is in fact needed, we can either collect (ideally not)
or implement Extend for AttrList. (Or create TryExtend.)
DEV-11268
This removes the layer of encapsulation that was hiding Stack, which is the
actual parser. The new layer of encapsulation is parse::Parser, which will
be introduced here soon. Baby steps, so it's clear how this evolves.
DEV-11268
The old Parsed was renamed to ParseStatus to be used by Parser, and Parser
converts it into Parsed, which has the same variants as it did before and
has all but the Done variant, since it's not possible for Parser to yield
it.
DEV-11268
This removes Option from ParseState, as mentioned in previous commits.
This is ideal because it not only removes a layer of abstraction, but also
makes the intent very clear; the use of None was too tied to the concept of
an Iterator, which is the concern of Parser, _not_ ParseState.
This is now similar to tree::Parsed, which will help with that refactoring
shortly.
The Done variant is not accessible outside of Parser, since it always
coverts it to None (to halt iteration); given that, we should have another
public-facing type, as was also mentioned in a previous commit.
DEV-11268
This also renames related types.
See previous commits for more in formation. In essence, this trait
represents the reification of all parser state. The omission of "r" in the
name ParseState is intentional, since it indicates the state of a current
parse. We'll see whether that naming ends up being too confusing; it's easy
enough to change.
DEV-11268
This just leaves Parser, which is what I started with, but I wasn't sure how
far I was going to take this. I went against my usual judgment in creating
a trait that I may not need, in an attempt to try to reason about the API
that I wanted, because it wasn't yet clear at the time whether the Parser
ought to be generic.
Since then (as detailed in the last commit), this has become more of a
coordinator/mediator, and the real parser is actually TokenStreamState,
which will be renamed shortly.
DEV-11268
This begins to integrate the isolated AttrParser. The next step will be
integrating it into the larger XIRT parser.
There's been considerable delay in getting this committed, because I went
through quite the struggle with myself trying to determine what balance I
want to strike between Rust's type system; convenience with parser
combinators; iterators; and various other abstractions. I ended up being
confounded by trying to maintain the current XmloReader abstraction, which
is fundamentally incompatible with the way the new parsing system
works (streaming iterators that do not collect or perform heap
allocations).
There'll be more information on this to come, but there are certain things
that will be changing.
There are a couple problems highlighted by this commit (not in code, but
conceptually):
1. Introducing Option here for the TokenParserState doesn't feel right, in
the sense that the abstraction is inappropriate. We should perhaps
introduce a new variant Parsed::Done or something to indicate intent,
rather than leaving the reader to have to read about what None actually
means.
2. This turns Parsed into more of a statement influencing control
flow/logic, and so should be encapsulated, with an external equivalent
of Parsed that omits variants that ought to remain encapsulated.
3. TokenStreamState is true, but these really are the actual parsers;
TokenStreamParser is more of a coordinator, and helps to abstract away
some of the common logic so lower-level parsers do not have to worry
about it. But calling it TokenStreamState is both a bit
confusing and is an understatement---it _does_ hold the state, but it
also holds the current parsing stack in its variants.
Another thing that is not yet entirely clear is whether this AttrParser
ought to care about detection of duplicate attributes, or if that should be
done in a separate parser, perhaps even at the XIR level. The same can be
said for checking for balanced tags. By pushing it to TokenStream in XIR,
we would get a guaranteed check regardless of what parsers are used, which
is attractive because it reduces the (almost certain-to-otherwise-occur)
risk that individual parsers will not sufficiently check for semantically
valid XML. But it does _potentially_ match error recovery more
complicated. But at the same time, perhaps more specific parsers ought not
care about recovery at that level.
Anyway, point being, more to come, but I am disappointed how much time I'm
spending considering parsing, given that there are so many things I need to
move onto. I just want this done right and in a way that feels like it's
working well with Rust while it's all in working memory, otherwise it's
going to be a significant effort to get back into.
DEV-11268
This stores the last seen Span and uses that when reporting EOF, so that the
user will be able to be notified of where exactly the problem occurred.
When I get into creating combinators, it'll be the responsibility of those
combinators to ensure that any None return value will be supplemented by its
own last span.
DEV-11268
This permits retrieving a Span from any Token variant. To support this,
rather than having this return an Option, Token::AttrEnd was augmented with
a Span; this results in a much simpler and friendlier API.
DEV-11268
This removes XIRT support for attribute fragments. The reason is that
because this is a write-only operation---fragments are used to concatenate
SymbolIds without reallocation, which can only happen if we are generating
XIR internally.
Given that this cannot happen during read, it was a mistake to complicate
the parsers. But it makes sense why I did originally, given that the XIRT
parser was written for simplifying test cases. But now that we want parsers
for real, and are writing production-quality parsers, this extra complexity
is very undesirable.
As a bonus, we also avoid any potential for heap allocations related to
attributes. Granted, they didn't _really_ exist to begin with, but it was
part of XIRT, and was ugly.
DEV-11268
The XIRT parser was initially written for test cases, so that unit tests
should assert more easily on generated token streams (XIR). While it was
planned, it wasn't clear what the eventual needs would be, which were
expected to differ. Indeed, loading everything into a generic tree
representation in memory is not appropriate---we should prefer streaming and
avoiding heap allocations when they’re not necessary, and we should parse
into an IR rather than a generic format, which ensures that the data follow
a proper grammar and are semantically valid.
When parsing attributes in an isolated context became necessary for the
aforementioned task, the state machine of the XIRT parser was modified to
accommodate. The opposite approach should have been taken---instead of
adding complexity and special cases to the parser, and from a complex parser
extracting a simple one (an attribute parser), we should be composing the
larger (full XIRT) parser from smaller ones (e.g. attribute, child
elements).
A combinator, when used in a functional sense, refers not to combinatory
logic but to the composition of more complex systems from smaller ones. The
changes made as part of this commit begin to work toward combinators, though
it's not necessarily evident yet (to you, the reader) how that'll work,
since the code for it hasn't yet been written; this is commit is simply
getting my work thusfar introduced so I can do some light refactoring before
continuing on it.
TAMER does not aim to introduce a parser combinator framework in its usual
sense---it favors, instead, striking a proper balance with Rust’s type
system that permits the convenience of combinators only in situations where
they are needed, to avoid having to write new parser
boilerplate. Specifically:
1. Rust’s type system should be used as combinators, so that parsers are
automatically constructed from the type definition.
2. Primitive parsers are written as explicit automata, not as primitive
combinators.
3. Parsing should directly produce IRs as a lowering operation below XIRT,
rather than producing XIRT itself. That is, target IRs should consume
XIRT and produce parse themselves immediately, during streaming.
In the future, if more combinators are needed, they will be added; maybe
this will eventually evolve into a more generic parser combinator framework
for TAME, but that is certainly a waste of time right now. And, to be
honest, I’m hoping that won’t be necessary.
There are a number of reasons for this, where the benefits do not make up
for the losses.
First: this is actually invoking cargo. Not only is this not necessary, but
it's not desirable: cargo by default hits the network and does all sorts of
other stuff, when all we want to do is invoke the executable. So the tests
aren't really testing the right thing in that sense. See the previous
commit for more information.
The way it invokes cargo is different than the way the Makefile invokes
cargo, so on my system, it's actually invoking a _different cargo_! This is
causing problems, in particular with lock files, which causes my tests to
fail.
Importantly, this also removes a _lot_ of dependencies, which removes a lot
of supplier chain risk and a lot of code to audit. This provides
significant security benefits, especially given that what was being tested
was rather small, and could be done in a shell script.
TAMER will receive significant system testing later on. But for now, none
of this was worth it.
Further audits of dependencies will come later on. I've always been fairly
insistent on keeping the dependency graph small and auditable, but recent
supply chain attacks have given me a better way to rationalize the security
risk. Further, I'm the only one on this project right now.
Cargo's default behavior is unfortunately to issue network calls each time
it is invoke in order to check for dependencies updates. This is not only
bad for reproducibility and privacy, but it's also a concern for supply
chain attacks, since most developers are unaware that this is occurring.
Instead, we pin to the lockfile. Installing dependencies can be done with
`cargo fetch` and updating dependencies must be explicitly done by the
developer, with the lockfile updated.
Well, parse to the extent that it was being parsed before, anyway.
The core of this change demonstrates how well TAMER's abstractions work well
together. (As long as you have an e.g. LSP to help you make sense of all of
the inference, I suppose.)
Token::Open(QN_LV_PACKAGE | QN_PACKAGE, _) => {
return Ok(XmloEvent::Package(
attr_parser_from(&mut self.reader)
.try_collect_ok()??,
));
}
This finally makes use of `attr_parser_from` and `try_collect_ok`. All of
the types are inferred---from the iterator transformations, to the error
conversions, to the destination PackageAttrs type.
DEV-10863
This was forgotten when the attribute parser was introduced, and led to the
parser continuing to the token following AttrEnd, which properly caused a
failure given that the parser was in the Done state.
There is a future task I have in my backlog to properly address the Done
state, but this is sufficient for now.
To maintain a proper abstraction, this cannot be the responsibility of the
caller; most callers should not know that fragments exist, letalone how to
handle them.
Like previous commits, this replaces the explicit escaping context with the
convention that all values retrieved from `xir` are unescaped on read and
escaped on write.
Comments are a notable TODO, since we must escape only `--`.
CData is also an issue. I had _expected_ to use it as a means to avoid
unescaping fragments, but I had forgotten that quick_xml hard-codes escaping
on read, so that it can re-use BytesStart! That is terribly unfortunate,
and may result in us having to re-implement our own read method in the
future to avoid this nonsense. So I'm just leaving it as a TODO for now.
DEV-11081
This adds a constant `ST_COUNT` representing the number of statically
allocated symbols, and uses that to estimate an initial capacity for the
`CachingEscaper`.
This is just a guess (and is certainly too low), but we can adjust later on
after profiling, if it ever comes up.
This rewrites a good portion of the previous commit.
Rather than explicitly storing whether a given string has been escaped, we
can instead assume that all SymbolIds leaving or entering XIR are unescaped,
because there is no reason for any other part of the system to deal with
such details of XML documents.
Given that, we need only unescape on read and escape on write. This is
customary, so why didn't I do that to begin with?
The previous commit outlines the reason, mainly being an optimization for
the echo writer that is upcoming. However, this solution will end up being
better---it's not implemented yet, but we can have a caching layer, such
that the Escaper records a mapping between escaped and unescaped SymbolIds
to avoid work the next time around. If we share the Escaper between _all_
readers and the writer, the result is that
1. Duplicate strings between source files and object files (many of which
are read by both the linker and compiler) avoid re-unescaping; and
2. Writers can use this cache to avoid re-escaping when we've already seen
the escaped variant of the string during read.
The alternative would be a global cache, like the internment system, but I
did not find that to be appropriate here, since this is far less
fundamental and is much easier to compose.
DEV-11081
I'm not fond of this implementation, which is why it's not fully
completed. I wanted to commit this for future reference, and take the
opportunity to explain why I don't like it.
First: this task started as an idea to implement a third variant to
AttrValue and friends that indicates that a value is fixed, in the sense of
a fixed-point function: escaped or unescaped, its value is the same. This
would allow us to skip wasteful escape/unescape operations.
In doing so, it became obvious that there's no need to leak this information
through the API, and indeed, no part of the system should care. When we
read XML, it should be unescaped, and when we write, it should be
escaped. The reason that this didn't quite happen to begin with was an
optimization: I'll be creating an echo writer in place of the current
filesystem-based copy in tamec shortly, and this would allow streaming XIR
directly from the reader to the writer without any unescaping or
re-escaping.
When we unescape, we know the value that it came from, so we could simply
store both symbols---they're 32-bit, so it results in a nicely compressed
64-bit value, so it's essentially cost-free, as long as we accept the
expense of internment. This is `XirString`. Then, when we want to escape
or unescape, we first check to see whether a symbol already exists and, if
so, use it.
While this works well for echoing streams, it won't work all that well in
practice: the unescaped SymbolId will be taken and the XirString discarded,
since nothing after XIR should be coupled with it. Then, when we later
construct a XIR stream for writting, XirString will no longer be available
and our previously known escape is lost, so the writer will have to
re-escape.
Further, if we look at XirString's generic for the XirStringEscaper---it
uses phantom, which hints that maybe it's not in the best place. Indeed,
I've already acknowledged that only a reader unescapes and only a writer
escapes, and that the rest of the system works with normal (unescaped)
values, so only readers and writers should be part of this process. I also
already acknowledged that XirString would be lost and only the unescaped
SymbolId would be used.
So what's the point of XirString, then, if it won't be a useful optimization
beyond the temporary echo writer?
Instead, we can take the XirStringWriter and implement two caches on that:
mapping SymbolId from escaped->unescaped and vice-versa. These can be
simple vectors, since SymbolId is a 32-bit value we will not have much
wasted space for symbols that never get read or written. We could even
optimize for preinterned symbols using markers, though I'll probably not do
so, and I'll explain why later.
If we do _that_, we get even _better_ optimizations through caching that
_will_ apply in the general case (so, not just for echo), and we're able to
ditch XirString entirely and simply use a SymbolId. This makes for a much
more friendly API that isn't leaking implementation details, though it
_does_ put an onus on the caller to pass the encoder to both the reader and
the writer, _if_ it wants to take advantage of a cache. But that burden is
not significant (and is, again, optional if we don't want it).
So, that'll be the next step.
This is intended to alleviate what will be some common boilerplate because
of the Rust compiler error described therein.
This will evolve over time, I'm sure.
DEV-10863
This provides convenience methods atop of the already-existing
functions. These are a bit more ergonomic since they (a) remove a variable
and its generics and (b) are conveniently suggested via LSP (with
e.g. rust-analyzer) if the iterator is of the right type, even if the trait
is not yet imported. This should help with discoverability as well.
These traits augment Rust's built-in traits to handle failure scenarios,
which will allow us to encapsulate lowering logic into discrete,
self-parsing units that enforce e.g. schemas (the example alludes to my
intentions).
The previous implementation took ownership over the provided iterator, which
was an oversight, considering that this is intended to be used in contexts
where doing so is not possible. A good example where isolated test cases
aren't necessarily painting the correct picture.
`scan` takes owned values, so this instead uses the same parsing method as
`parse_attrs`, but using a `FromFn` iterator to avoid having to create a
whole new iterator type. This will work well so long as we don't need to
store the type returned by this (while also wanting to avoid boxing).
DEV-11062
See the previous commit. There is no sense in some common "IR" namespace,
since those IRs should live close to whatever system whose data they
represent.
In the case of these, they are general IRs that can apply to many different
parts of the system. If that proves to be a false statement, they'll be
moved.
DEV-10863
Calling it "legacyir" is just confusing. The original hope, when beginning
TAMER, was that I'd be able to use a new object format in the near future to
help speed up the compilation process. But that's far from our list of
priorities now, and so seeing "legacy" all over the place is really
confusing considering that it implies that perhaps it shouldn't be used for
new code.
This helps to clear up that cognitive dissonance by remaining neutral on the
topic. And the reality is that it won't be "legacy" for some time.
DEV-10863
The IRs really ought to live where they are owned, especially given that
"IR" is so generic that it makes no sense for there to be a single location
for them; they're just data structures coupled with different phases of
compilation.
This will be renamed next commit; see that for details.
This also removes some documentation describing the lowering process,
because it's undergone a number of changes and needs to be accurately
re-summarized in another location. That will come at a later time after the
work is further along so that I don't have to keep spending the time
rewriting it.
DEV-10863
This was previous gated behind the negation of the wip-xmlo-xir-reader flag,
which meant that it was not being compiled or picked up by LSP. Both of
those things are inconvenient and unideal.
DEV-10863
This allows for the lazy parsing of attributes, and makes the necessary
changes to the parser to be able to do so safely without getting into a bad
context.
When XIRT was originally conceived, this concept existed somewhat, but it
was done in a way that would allow the parser to accept invalid input. This
avoids that problem.
This also introduces the concept of "Done", primarily because we had to for
the AttrEnd token. This will evolve in following commit(s), which will
allow carrying out the important check of ensuring that the parser has ended
parsing in a valid accepting state (in terms of a state machine).
DEV-11062
This produces an `AttrList` independent from a containing
`Element`. Upcoming changes may further permit the parser to yield smaller
components that are not part of an aggregate.
DEV-10863
This allows Rust to carry out its exhaustiveness check for when we add new
tokens. It further ensure that we understand what we missed, or chose not
to handle.
DEV-10863
This allows AttrList not only to be lazily initialized (which is less of a
problem at the moment with Vec, but may become one in the future), but also
leaves a space open for attributes to be added _after_ having been
parsed. It further leaves room to _take_ attributes from their `Element`.
This is important because the next commit will re-introduce the ability to
parse attributes independently, allowing us to put the parser in a state
where we can parse AttrList without an Element context. To re-use that
parsing under an Element context, we can simply attach an AttrList after it
has been parsed.
Option adds no additional size cost to Vec, so we get this for free (except
for the tiny change that initializes the attribute list when we try to push
to it).
I also think this reads better ("attrs: None"). Though it makes the API
slightly more of a pain to work with.
DEV-10863
The purpose of this token is to implement a lazy streaming attribute
collection operation without a token of lookup, which would complicate
parsing or require that a TokenStream provide a `peek` method.
This is only required for readers to produce, since readers will be feeding
data to parsers. I have the writer ignoring it. If you're looking back at
this commit, the question is whether this was a bad idea: it introduces
inconsistencies into the token stream depending on the context, which can be
confusing and error-prone.
The intent is to have the parser throw an explicit error if the new token is
missing in the context in which it is required, which will safely handle the
issue, but does defer it to runtime. But only readers need auditing, and
there's only one XIR reader at the moment.
DEV-10863
There isn't a whole lot here, but there is additional work needed in various
places to support upcoming changes and so I want to get this commited to
ease the cognitive burden of what I have thusfar. And to stop stashing. We
have a feature flag for a reason.
DEV-10863
This macro was previously using the path of wherever the template expanded
into, which I found to be unexpected considering that I thought the macros
were hygenic and the names bound to the environment in which they were
defined.
In any case, this solves the problem in all cases.
DEV-10863
This was forgotten in the previous commit and exists simply to ensure that
the TripIter doesn't add any significant overhead. The tests are
a handful of nanoseconds apart, on my machine.
See the documentation in this commit for more information.
This is pretty significant, in that it's been a long-standing question for
me how I'd like to join together `Result` iterators without having
unnecessarily complex APIs, and also allow for error recovery. This solves
both of those problems.
It should be noted, however, that this does not yet explicitly implement
error recovery, beyond being able to observe the failure as the result of
the provided callback function. Proper recovery will be implemented once
there's a use-case.
DEV-11006
This moves the Iterator impl and From<B> back into `quickxml`. The type of
the new reader is different, taking an iterator instead of a BufRead. This
will allow us to easily mock for unit tests, without the clustfuckery that
has ensued previously with quick-xml mocking.
DEV-10863
The original plan was to modify the existing reader to use the new
XmlXirReader, but that's going to be a lot of ongoing uncommitted work, with
both tests and implementation. The better option seems to be to reimplement
it, since so many things are changing.
This flag will be short-lived and removed as soon as the implementation is
complete.
DEV-10863
Comments re-use Text, but they are _not_ escaped, so we need to take care
with the type to ensure that, if the value were ever used with a
Token::Text, that we don't end up injecting XML.
quick_xml provides us the value escaped, so we can just handle this the same
way as Text for now.
In the future, we may want to distinguish between the two so that we can
reconstruct an identical XML document, but at the moment CData isn't used at
all in TAME sources or outputs, and so I'm not going to worry about it for
now.
DEV-10863
It's nice being able to breeze through changes, since that's been a pretty
rare thing so far, given all the foundational work that has been needed.
This should get us pretty damn close to being able to parse the `xmlo` files
for the reader linker, if we're not there already.
DEV-10863
This is quick-and-dirty; refactoring can be done later on. This is also
intended to demonstrate the ease with which additional events can be
added---the hard work is done.
This is an initial working concept for the reader which handles, so far,
just a single attribute. But extending it to completion will not be all
that much more work.
This does not have namespace support---that will be added later as part of
XIRT, which is responsible for semantic analysis. This allows XIR to stay
wonderfully simple, and won't have any impact on the writer (which expects
that QNames are unresolved and contain the namespace prefix to be written).
This is the safe version of the existing intern_utf8_unchecked, and exists
as a performance optimization.
We're about to introduce a XIR reader, which is going to intern a _lot_ of
duplicate strings, since it will intern node and attribute names as
well. Given that, we do not want to spent a lot of time performing UTF-8
checks that have already been performed.
We know that, if an intern is in the pool, it's either already UTF-8 or that
check was bypassed when it was initially interned. Therefore, if we find an
existing symbol, that can be returned without having to perform any
check. Otherwise, we intern as we usually would after attempting to convert
the byte slice into a string.
This allows us to continue to have good performance for interning without
sacrificing safety for strings.
The intent of this is to demonstrate how significant of an impact checking
byte arrays for UTF-8 validity will have, since the existing tests do not
make that clear (a static string in Rust is always valid UTF-8).
These benchmarks show that the cost when re-interning an already existing
value is +50%.
This is important, because the new reader will be interning a _lot_ of
duplicate strings, whereas the existing reader operates on byte arrays
without interning unless necessary. And, when it does, it does so
unchecked. But we'd rather not do that, since we cannot guarantee that
those XML files are valid (and not modified in some way).
Upcoming commits will have what I think is a reasonable compromise to this,
based on the fact that we'll be encountering _many_ duplicate strings in
parsing XML files.
DEV-10920
This provides a child `raw` module that exposes a SymbolId representing the
inner value of each of the static newtypes. This is needed in situations
where the type must match and the type of the static symbol is not
important.
In particular, when comparing against runtime-allocated symbols in `match`
expressions.
It is also worth noting that this commit managed to hit a bug in Rustc that
was fixed on 10/1/2021. We use nightly, and it doesn't seem that this
occurred in stable, from bug reports.
- https://github.com/rust-lang/rust/issues/89393
- 5ab1245303
- Original issue: https://github.com/rust-lang/rust/issues/72476
The error was:
compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs:1191:22:
Unexpected type for `Single` constructor: <u32 as sym::symbol::SymbolIndexSize>::NonZero
thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1146:9
This occurred because we were trying to use `SymbolId` as the type, which
uses a projected type as its inner value: `SymbolId<Ix: SymbolIndexSize>(Ix::NonZero)`.
This was not a problem with the static newtypes because their inner type was
simply `SymbolId<Ix>`, which is not projected.
This is one of the risks of using nightly.
But, the point is: if you receive this error, upgrade your toolchain.
Tbh, I was unaware that this was supported by tuple variants until reading
over the Rustc source code for something. (Which I had previously read, but
I must have missed it.)
This is more proper, in the sense that in a lot of cases we not only care
about how many values a tuple has, but if we explicitly match on them using
`_`, then any time we modify the number of values, it would _break_ any code
doing so. Using this method, we improve maintainability by not causing
breakages under those circumstances.
But, consequently, it's important that we use this only when we _really_
don't care and don't want to be notified by the compiler.
I did not use `..` as a prefix, even where supported, because the intent is
to append additional information to tuples. Consequently, I also used `..`
in places where no additional fields currently exist, since they may in the
future (e.g. introducing `Span` for `IdentObject`).
In particular, `name` needn't return an `Option`. `fragment` also returns a
copy, since it's just a `SymbolId`. (It really ought to be a newtype rather
than an alias, but we'll worry about that some other time.)
These changes allow us to remove some runtime panics.
DEV-10859
This moves the logic that sorts identifiers into sections into Sections
itself, and introduces XmleSections to allow for mocking for testing.
This then allows us to narrow the types significantly, eliminating some
runtime checks. The types can be narrowed further, but I'll be limiting the
work I'll be doing now; this'll be inevitably addressed as we use the ASG
for the compiler.
This also handles moving Sections tests, which was a TODO from the previous
commit.
DEV-10859
This is the appropriate place to be, now that we've begun narrowing the
types. We'll be able to do so further; this is just the first step.
This does not yet move the tests, but the code is still tested because it's
tightly coupled with `sort`. Those will move in the next commit(s).
DEV-10859
xmle sections will only ever contain an object of one type, so there is no
use in making this generic.
I think the original plan was to have this represent, generically, sections
of some object file (like ELF), but doing so would require a significant
redesign anyway, so it makes no sense. This is easier to reason about.
DEV-10859
This has always been a lowering operation, but it was not phrased in terms
of it, which made the process a bit more confusing to understand.
The implementation hasn't changed, but this is an incremental refactoring
and so exposes BaseAsg and its `graph` field temporarily.
DEV-10859
Sections, as written, are specific to xmle files.
I think the intent originally was to have this be more generic, but that
doesn't really make sense.
By explicitly coupling it with `xmle` files, that will allow us to turn this
into a proper lowering operation with its own validations that will allow
`xmle::xir` to do its job without having to validate anything itself.
This outputs enough information to be a little bit useful in the event of an
error. In the future, we'll want to provide a (likely non-Display)
implementation that provides line number and source file context with
the problem characters indicated, like Rust.
This is a significant departure from my original plans---this makes it
_easy_ to display symbol values, despite me not wanting that to occur unless
absolutely necessary.
The reality is, based on the design of the system, they will only occur in
these situations:
1. Writing to files;
2. Displaying errors;
3. Tests; or
4. People not following the design of the system.
The fourth one is the most risky as people begin to contribute in the
future, but the reality is that those can be fixed as they are encountered,
since if they're not showing up in a profiler, then they must not be causing
much of a problem.
This removes `SymbolStr` in favor of, simply, `&'static str`.
The abstraction provided no additional safety since the slice was trivially
extracted (and commonly, in practice), and was inconvenient to work with.
This is part of a process of relaxing lookups so that symbols can be
conveniently displayed in errors; rather than trying to prevent the
developer from doing something bad, we'll just rely on conventions, hope
that it doesn't happen, and if it does, address it either at that time or
when it shows up in the profiler.
The docs still need to be improved, but they can be touched as we go.
This concludes the initial development of XIR. That was much more involved
that I had originally intended, but the result is good.
DEV-10561
This generalizes it a bit and provides tests, which was always the intent;
the existing code was POC to determine if this could be done without
performance degradation (see that commit for more information).
The intent is to support the composition and decomposition of spans such
that (A, B) is as documented here. This only performs the trivial case for
the sake of providing a convenient API when the developer would otherwise
just type (S, S).
This is intended to represent the sections written to the final xmle file,
and there was unnecessary complexity in separating everything.
By reducing this IR further, we can begin to constrain its types to
eliminate some of the runtime panics and error checking we have/had in the
writer.
The new writer has reached parity of the old, with the exception of some
edge case explicit error handling that should never occur (which will be
added), and cleanup/docs.
Removing this flag now allows me to perform that cleanup without having to
worry about updating the now-old implementation.
I ran `tameld` with the new writer against our production system with
numerous programs and a significant number of test cases, and diff'd the old
and new xmle files, and everything looks good.
This is a significant milestone, in the sense that it is the culmination of
the past month or so of work to prove that an Iterator-based XIR will be
viable for the system.
This barely had any impact on the performance from the previous commit
reporting the profiling. This performs at least as well as the quick-xml
based writer. In isolated benchmarks, it performs better, but in the real
world, the linker spends most of its time reading xmlo files, and so minor
differences in writing do not have a significant overall impact.
With that said, a lot of cleanup and documentation is still needed. That is
the subject of the upcoming commits, before this writer can finalized.
Mike Gerwitz