I need to move on, and there are (a) a couple different ways to proceed that
I want to mull over and (b) upcoming changes that may influence my decision
one way or another.
DEV-7145
This will utilize the superstate's error object in place of nested errors,
which was the result of the previous composition-based delegation.
As you can see, all we had to do was remove the special handling of these
errors; the existing delegation setup continues to handle the types properly
with no change. The composition continues to work for `*Attr_`.
The alternative was to box inner errors, since they're far from the hot code
path, but that's clearly unnecessary.
To be clear: this is necessary to allow for recursive grammars in
`ele_parse` without creating recursive data structures in Rust.
DEV-7145
Comments ought not have any more semantic meaning than whitespace. Other
languages may have conventions that allow for various types of things in
comments, like annotations, but those are symptoms of language
limitations---we control the source language here.
DEV-7145
This properly integrates the trampoline into `ele_parse!`. The
implementation leaves some TODOs, most notably broken mixed text handling
since we can no longer intercept those tokens before passing to the
child. That is temporarily marked as incomplete; see a future commit.
The introduced test `ParseState`s were to help me reason about the system
intuitively as I struggled to track down some type errors in the monstrosity
that is `ele_parse!`. It will fail to compile if those invariants are
violated. (In the end, the problems were pretty simple to resolve, and the
struggle was the type system doing its job in telling me that I needed to
step back and try to reason about the problem again until it was intuitive.)
This keeps around the NT states for now, which are quickly used to
transition to the next NT state, like a couple of bounces on a trampoline:
NT -> Dead -> Parent -> Next NT
This could be optimized in the future, if it's worth doing.
This also makes no attempt to implement tail calls; that would have to come
after fixing mixed content and really isn't worth the added complexity
now. I (desperately) need to move on, and still have a bunch of cleanup to
do.
I had hoped for a smaller commit, but that was too difficult to do with all
the types involved.
DEV-7145
I had previously used `Context` to hold the parser configuration for
repetition, since that was the easier option. But I now want to utilize the
`Context` for a stack for the superstate trampoline, and I don't want to
have to deal with the awkwardness of the repetition in doing so, since it
requires that the configuration be created during delegation, rather than
just being passed through to all child parsers.
This adds to a mess that needs cleaning up, but I'll do that after
everything is working.
DEV-7145
And here's the thing that I've been dreading, partly because of the
`macro_rules` issues involved. But, it's not too terrible.
This module was already large and complex, and this just adds to it---it's
in need of refactoring, but I want to be sure it's fully working and capable
of handling NIR before I go spending time refactoring only to undo it.
_This does not yet use trampolining in place of the call stack._ That'll
come next; I just wanted to get the macro updated, the superstate generated,
and tests passing. This does convert into the
superstate (`ParseState::Super`), but then converts back to the original
`ParseState` for BC with the existing composition-based delegation. That
will go away and will then use the equivalent of CPS, using the
superstate+`Parser` as a trampoline. This will require an explicit stack
via `Context`, like XIRF. And it will allow for tail calls, with respect to
parser delegation, if I decide it's worth doing.
The root problem is that source XML requires recursive parsing (for
expressions and statements like `<section>`), which results in recursive
data structures (`ParseState` enum variants). Resolving this with boxing is
not appropriate, because that puts heap indirection in an extremely hot code
path, and may also inhibit the aggressive optimizations that I need Rust to
perform to optimize away the majority of the lowering pipeline.
Once this is sorted out, this should be the last big thing for the
parser. This unfortunately has been a nagging and looming issue for months,
that I was hoping to avoid, and in retrospect that was naive.
DEV-7145
I'm disappointed that I keep having to implement features that I had hoped
to avoid implementing.
This introduces a "superstate" feature, which is intended really just to be
a sum type that is able to delegate to stitched `ParseState`s. This then
allows a `ParseState` to transition directly to another `ParseState` and
have the parent `ParseState` handle the delegation---a trampoline.
This issue naturally arises out of the recursive nature of parsing a TAME
XML document, where certain statements can be nested (like `<section>`), and
where expressions can be nested. I had gotten away with composition-based
delegation for now because `xmlo` headers do not have such nesting.
The composition-based approach falls flat for recursive structures. The
typical naive solution is boxing, which I cannot do, because not only is
this on an extremely hot code path, but I require that Rust be able to
deeply introspect and optimize away the lowering pipeline as much as
possible.
Many months ago, I figured that such a solution would require a trampoline,
as it typically does in stack-based languages, but I was hoping to avoid
it. Well, no longer; let's just get on with it.
This intends to implement trampolining in a `ParseState` that serves as that
sum type, rather than introducing it as yet another feature to `Parser`; the
latter would provide a more convenient API, but it would continue to bloat
`Parser` itself. Right now, only the element parser generator will require
use of this, so if it's needed beyond that, then I'll debate whether it's
worth providing a better abstraction. For now, the intent will be to use
the `Context` to store a stack that it can pop off of to restore the
previous `ParseState` before delegation.
DEV-7145
"Mixed content" is the XML term representing element nodes mixed with text
nodes. For example, `foo <strong>bar</strong> baz` is mixed.
TAME supports text nodes as documentation, intended to be in a literate
style but never fully realized. In any case, we need to permit them, and I
wanted to do more than just ignore the nodes.
This takes a different approach than typical parser delegation---it has the
parent parser _preempt_ the child by intercepting text before delegation
takes place, rather than having the child reject the token (or possibly
interpret it itself!) and have to handle an error or dead state.
And while this makes it more confusing in terms of state machine stitching,
it does make sense, in the sense that the parent parser is really what
"owns" the text node---the parser is delegating _element_ parsing only, take
asserts authority when necessary to take back control where it shouldn't be
delegated.
DEV-7145
Previously a `Depth` was provided only for `Open` and `Close`. This depth
information, for example, will be used by NIR to quickly determine whether a
given parser ought to assert ownership of a text/comment token rather than
delegating it.
This involved modifying a number of test cases, but it's worth repeating in
these commits that this is intentional---I've been bit in the past using
`..` in contexts where I really do want to know if variant fields change so
that I can consider whether and how that change may affect the code
utilizing that variant.
DEV-7145
Recent changes regarding whitespace were all to support this change (though
it was also needed for XIRF, pre- and post-root).
Now I'll have to conted with how I want to handle text nodes in various
circumstances, in terms of `ele_parse!`.
DEV-7145
Various DUMMY_SPAN-derived spans are used by many test cases, so this
finally extracts them---something I've been meaning to do for some time.
This also places DUMMY_SPAN behind a `cfg(test)` directive to ensure that it
is _only_ used in tests; UNKNOWN_SPAN should be used when a span is actually
unknown, which may also be the case during development.
DEV-7145
Whether or not quoting is appropriate depends on context, and that parent
context is already performing the quoting. For example:
error: expected `</rater>`, but found `<import>`
--> /home/[...]/foo.xml:2:1
|
2 | <rater xmlns="http://www.lovullo.com/rater"
| ------ note: element starts here
--> /home/[...]/foo.xml:7:3
|
7 | <import package="/rater/core/base" />
| ^^^^^^^ error: expected `</rater>`
In these cases (obviously I'm still working on the parser, since this is
nonsense), the parser is responsible for quoting the token "<import>".
DEV-7145
There were two problem errors: one showing "element element" and one showing
the value along with the name of the attribute.
The change for `<Attr as Display>::fmt` is debatable. I'm going to do this
for now (only show `@name`) and adjust later if necessary.
I'll need to go use `crate::fmt` consistently in previously-existing format
strings at some point, too.
DEV-7145
This teaches XIRF to optionally refine Text into RefinedText, which
determines whether the given SymbolId represents entirely whitespace.
This is something I've been putting off for some time, but now that I'm
parsing source language for NIR, it is necessary, in that we can only permit
whitespace Text nodes in certain contexts.
The idea is to capture the most common whitespace as preinterned
symbols. Note that this heuristic ought to be determined from scanning a
codebase, which I haven't done yet; this is just an initial list.
The fallback is to look up the string associated with the SymbolId and
perform a linear scan, aborting on the first non-whitespace character. This
combination of checks should be sufficiently performant for now considering
that this is only being run on source files, which really are not all that
large. (They become large when template-expanded.) I'll optimize further
if I notice it show up during profiling.
This also frees XIR itself from being concerned by Whitespace. Initially I
had used quick-xml's whitespace trimming, but it messed up my span
calculations, and those were a pain in the ass to implement to begin with,
since I had to resort to pointer arithmetic. I'd rather avoid tweaking it.
tameld will not check for whitespace, since it's not important---xmlo files,
if malformed, are the fault of the compiler; we can ignore text nodes except
in the context of code fragments, where they are never whitespace (unless
that's also a compiler bug).
Onward and yonward.
DEV-7145
Because of recovery, the trace otherwise paints a really confusing-looking
picture when given unexpected input.
This is large enough now that it really ought to be extracted from
`feed_tok`, but I'll wait to see how this evolves further. I considered
adding color too, but it's not yet clear to me that the visual noise will be
all that helpful.
DEV-7145
impl for `&Token` instead of Token; the writer is just copying data into the
destination stream anyway.
This will allow us to continue writing the token while also using it for
further processing, like `tee`.
DEV-7145
We need to be able to export generated identifiers. Trying to figure out a
syntax for this was a bit tricky considering how much is generated, so I
just settled on something that's reasonably clear and easy to parse with
`macro_rules!`.
I had intended to just make everything public by default and encapsulate
using private modules, but that then required making everything else that it
uses public (e.g. error and token objects), which would have been a bizarre
thing to do in e.g. test cases.
DEV-7145
Values can be parsed using `TryFrom<Attr>`. Previously only `From<Attr>`
was supported, which could not fail.
This is critical for parsing values into types, which will wrap `SymbolId`
to provide data assurances.
DEV-7145
The tests had certain things in scope, but now that I'm trying to use it
outside of those modules, some fixes are needed.
This is admittedly a sloppy commit, with a number of miscellaneous fixes. I
didn't bother separating it more because most of them are type fixes, and
the `From<Attr>` stuff is going to have to change into, likely,
`TryFrom<Attr>` so that parse failures can occur when attributes do not
match certain patterns.
DEV-7145
The only additional information needed was opening spans so that we can
provide useful information regarding closing tags.
This uses a generic Span in place of {Open,Close}Span because the latter
wasn't necessary, but more descriptive types would be nice; it may be
beneficial later on to introduce newtypes for each of the span generated by
{Open,Close}Span.
DEV-7145
This was a TODO for the attribute parser generator. The first attribute
will be kept and later ones will be ignored, producing an error. Recovery
permits further attribute parsing having ignored the duplicate.
DEV-7145
This allows an element to be repeated by the parent NT. The easiest way I
saw to implement this for now was to abuse the Context to provide a runtime
configuration that would allow the state machine to reset after it has
completed parsing.
This also influences error recovery, in that if we're expecting zero or more
of something, we cannot provide an error for an unexpected name, and instead
must emit a dead state so that the caller can determine what to do.
DEV-7145
This produces useful parse traces that are output as part of a failing test
case. The parser generator macros can be a bit confusing to deal with when
things go wrong, so this helps to clarify matters.
This is _not_ intended to be machine-readable, but it does show that it
would be possible to generate machine-readable output to visualize the
entire lowering pipeline. Perhaps something for the future.
I left these inline in Parser::feed_tok because they help to elucidate what
is going on, just by reading what the trace would output---that is, it helps
to make the method more self-documenting, albeit a tad bit more
verbose. But with that said, it should probably be extracted at some point;
I don't want this to set a precedent where composition is feasible.
Here's an example from test cases:
[Parser::feed_tok] (input IR: XIRF)
| ==> Parser before tok is parsing attributes for `package`.
| | Attrs_(SutAttrsState_ { ___ctx: (QName(None, LocalPart(NCName(SymbolId(46 "package")))), OpenSpan(Span { len: 0, offset: 0, ctx: Context(SymbolId(1 "#!DUMMY")) }, 10)), ___done: false })
|
| ==> XIRF tok: `<unexpected>`
| | Open(QName(None, LocalPart(NCName(SymbolId(82 "unexpected")))), OpenSpan(Span { len: 0, offset: 1, ctx: Context(SymbolId(1 "#!DUMMY")) }, 10), Depth(1))
|
| ==> Parser after tok is expecting opening tag `<classify>`.
| | ChildA(Expecting_)
| | Lookahead: Some(Lookahead(Open(QName(None, LocalPart(NCName(SymbolId(82 "unexpected")))), OpenSpan(Span { len: 0, offset: 1, ctx: Context(SymbolId(1 "#!DUMMY")) }, 10), Depth(1))))
= note: this trace was output as a debugging aid because `cfg(test)`.
[Parser::feed_tok] (input IR: XIRF)
| ==> Parser before tok is expecting opening tag `<classify>`.
| | ChildA(Expecting_)
|
| ==> XIRF tok: `<unexpected>`
| | Open(QName(None, LocalPart(NCName(SymbolId(82 "unexpected")))), OpenSpan(Span { len: 0, offset: 1, ctx: Context(SymbolId(1 "#!DUMMY")) }, 10), Depth(1))
|
| ==> Parser after tok is attempting to recover by ignoring element with unexpected name `unexpected` (expected `classify`).
| | ChildA(RecoverEleIgnore_(QName(None, LocalPart(NCName(SymbolId(82 "unexpected")))), OpenSpan(Span { len: 0, offset: 1, ctx: Context(SymbolId(1 "#!DUMMY")) }, 10), Depth(1)))
| | Lookahead: None
= note: this trace was output as a debugging aid because `cfg(test)`.
DEV-7145
This resolves a TODO by including the name of the element whose attributes
are currently being parsed.
This also frees a parent from having to provide additional context, allowing
Display to be fully delegated when stitching.
DEV-7145
This introduces `Nt := (A | ... | Z);`, where `Nt` is the name of the
nonterminal and `A ... Z` are the inner nonterminals---it produces a parser
that provides a choice between a set of nonterminals.
This is implemented efficiently by understanding the QName that is accepted
by each of the inner nonterminals and delegating that token immediately to
the appropriate parser. This is a benefit of using a parser generator macro
over parser combinators---we do not need to implement backtracking by
letting inner parsers fail, because we know ahead of time exactly what
parser we need.
This _does not_ verify that each of the inner parsers accept a unique QName;
maybe at a later time I can figure out something for that. However, because
this compiles into a `match`, there is no ambiguity---like a PEG parser,
there is precedence in the face of an ambiguous token, and the first one
wins. Consequently, tests would surely fail, since the latter wouldn't be
able to be parsed.
This also demonstrates how we can have good error suggestions for this
parsing framework: because the inner nonterminals and their QNames are known
at compile time, error messages simply generate a list of QNames that are
expected.
The error recovery strategy is the same as previously noted, and subject to
the same concerns, though it may be more appropriate here: it is desirable
for the inner parser to fail rather than retrying, so that the sum parser is
able to fail and, once the Kleene operator is introduced, retry on another
potential element. But again, that recovery strategy may happen to work in
some cases, but'll fail miserably in others (e.g. placing an unknown element
at the head of a block that expects a sequence of elements would potentially
fail the entire block rather than just the invalid one). But more to come
on that later; it's not critical at this point. I need to get parsing
completed for TAME's input language.
DEV-7145
This adds the ability to bind identifiers to represent `OpenSpan` and
`CloseSpan`, available to the `@` and `/` maps. Since identifiers in TAME
originate from attributes, this may not get a whole lot of use, but it's
important to be available.
There is some awkwardness in that the opening span appears to be scoped to
the entire nonterminal, but it's actually only available in the `@`
mapping. I'll change this if it's actually needed; this keeps things simple
for now.
DEV-7145
Since the parsers produce streaming IRs, we need to be able to emit tokens
representing closing delimiters, where they are important.
This notably doesn't use spans; I'll add those next, since they're also
needed for the previous work.
DEV-7145
The comment explains the issue. I don't think the strategy is going to be a
desirable one, but I want to move on and observe in retrospect how it ought
to be handled.
The important part right now is that recovery is accounted for and possible,
which was a long-standing concern.
DEV-7145
This begins generating parsers that are capable of parsing elements. I need
to move on, so this abstraction isn't going to go as far as it could, but
let's see where it takes me.
This was the work that required the recent lookahead changes, which has been
detailed in previous commits.
This initial support is basic, but robust. It supports parsing elements
with attributes and children, but it does not yet support the equivalent of
the Kleene star (`*`). Such support will likely be added by supporting
parsers that are able to recurse on their own definition in tail position,
which will also require supporting parsers that do not add to the stack.
This generates parsers that, like all the other parsers, use enums to
provide a typed stack. Stitched parsers produce a nested stack that is
always bounded in size. Fortunately, expressions---which can nest
deeply---do not need to maintain ancestor context on the stack, and so this
should work fine; we can get away with this because XIRF ensures proper
nesting for us. Statements that _do_ need to maintain such context are not
nested.
This also does not yet support emitting an object on closing tag, which
will be necessary for NIR, which will be a streaming IR that is "near" to
the source XML in structure. This will then be used to lower into AIR for
the ASG, which gives structure needed for further analysis.
More information to come; I just want to get this committed to serve as a
mental synchronization point and clear my head, since I've been sitting on
these changes for so long and have to keep stashing them as I tumble down
rabbit holes covered in yak hair.
DEV-7145
Oh what a tortured journey. I had originally tried to avoid formalizing
lookahead for all parsers by pretending that it was only needed for dead
state transitions (that is---states that have no transitions for a given
input token), but then I needed to yield information for aggregation. So I
added the ability to override the token for `Dead` to yield that, in
addition to the token. But then I also needed to yield lookahead for error
conditions. It was a mess that didn't make sense.
This eliminates `ParseStatus::Dead` entirely and fully integrates the
lookahead token in `Parser` that was previously implemented.
Notably, the lookahead token is encapsulated in `TransitionResult` and
unavailable to `ParseState` implementations, forcing them to rely on
`Parser` for recursion. This not only prevents `ParseState` from recursing,
but also simplifies delegation by removing the need to manually handle
tokens of lookahead.
The awkward case here is XIRT, which does not follow the streaming parsing
convention, because it was conceived before the parsing framework. It needs
to go away, but doing so right now would be a lot of work, so it has to
stick around for a little bit longer until the new parser generators can be
used instead. It is a persistent thorn in my side, going against the grain.
`Parser` will immediately recurse if it sees a token of lookahead with an
incomplete parse. This is because stitched parsers will frequently yield a
dead state indication when they're done parsing, and there's no use in
propagating an `Incomplete` status down the entire lowering pipeline. But,
that does mean that the toplevel is not the only thing recursing. _But_,
the behavior doesn't really change, in the sense that it would infinitely
recurse down the entire lowering stack (though there'd be an opportunity to
detect that). This should never happen with a correct parser, but it's not
worth the effort right now to try to force such a thing with Rust's type
system. Something like TLA+ is better suited here as an aid, but it
shouldn't be necessary with clear implementations and proper test
cases. Parser generators will also ensure such a thing cannot occur.
I had hoped to remove ParseStatus entirely in favor of Parsed, but there's a
lot of type inference that happens based on the fact that `ParseStatus` has
a `ParseState` type parameter; `Parsed` has only `Object`. It is desirable
for a public-facing `Parsed` to not be tied to `ParseState`, since consumers
need not be concerned with such a heavy type; however, we _do_ want that
heavy type internally, as it carries a lot of useful information that allows
for significant and powerful type inference, which in turn creates
expressive and convenient APIs.
DEV-7145
There was only one test outside of the `parse` module using these
fields. The next commit will be introducing lookahead, and I do not want to
have to trust callers to ensure invariants are met.
DEV-7145
This reverts commit b973d36862.
Alright, I'm getting sick of fighting with myself on this. But rather than
just removing the last commit, I'm going to keep it around, so that my
thoughts are clearly documented for my future quarrels with myself.
Firstly: this added more overhead than I wanted it to. While it wasn't
significant, it did add 100--150ms to one of our largest systems, up from
~2.8s, which seems a bit much for a token that's really just meant to make
life easier for the parser.
Further, it seems that all I've managed to do is push my original problem to
a different layer---this started as a means to resolve having to emit both
an object and an error simultaneously in the case where aggregate attribute
parsing has completed, but we encounter an error on the next token (e.g. an
unexpected element). But XIRF, if it's missing AttrEnd, should throw an
error, but should also recover. Recovery is easy---just assume that it was
present---_but then we don't emit a XIRF `AttrEnd` token_, which is
necessary for downstream systems. So we'd need to either:
(a) emit both a token and an error; or
(b) panic.
But if we're doing (a), then the need for `AttrEnd` goes away, because it
solves the original problem (though the other concerns of the previous
commit still stand). (b) is not ideal at all, even though the missing token
does represent an internal system error; it's not something the user can
correct. But, given that it's something that the user cannot correct,
doesn't that imply that it's an awkward thing to include in the token
stream? So back to `AttrEnd` being an awkward PITA to have.
So, given (a), I'll just do that: errors will become more of a "hey, this
error just occurred, but I'm trying to recover---here's an object that you
should use if you choose to continue parsing, but it may or may not be what
you're looking for; proceed with caution". That flips the original script:
I imagined having external systems feed recovery tokens, but this
encapsulates recovery within the parser, which really is more appropriate,
though less flexible than having an omniscient external recovery system;
such a monolith was always an awkward concept and would be difficult to
implement cleanly.
This can also potentially be implemented as a generalization of the Dead
state change that allowed an object to be emitted alongside the
lookahead/error.
Anyway, back to where I was...I'm sure I'll look back on this in the future
shaking my head, reflecting on how naive I was.
DEV-7145
AttrEnd was initially removed in
0cc0bc9d5a (and the commit prior), because
there was not a compelling reason to use it over a lookahead
operation (returning a token via the a dead state transition); `AttrEnd`
simply introduced inconsistencies between the XIR reader (which produced
AttrEnd) and internal XIR stream generators (e.g. the lowering operations
into XIR->XML, which do not).
But now that parsers are performing aggregation---in particular the
attribute parser-generator `xir::parse::attr`---this has become quite a
pain, because the dead state is an actionable token. For example:
1. Open
2. Attr
3. Attr
4. Open
5. ...
In the happy case, token #4 results in `Parsed::Incomplete`, and so can just
be transformed into the object representing the aggregated attributes. But
even in this happy path, it's ugly, and it requires non-tail recursion on
the parser which requires a duplicate stack allocation for the
`ParserState`. That violates a core principle of the system.
But if there is an error at #4---e.g. an unexpected element---then we no
longer have a `Parsed::Incomplete` to hijack for our own uses, and we'd have
to introduce the ability to return both an error and a token, or we'd have
to introduce the ability to keep a token of lookahead instead of reading
from the underlying token stream, but that's complicated with push parsers,
which are used for parser composition. Yikes.
And furthermore, the aggregation has caused me to introduce the ability to
override the dead state type to introduce both a token of lookahead and
aggregation information. This complicates the system and is going to be
confusing to others.
Given all of this, AttrEnd does now seem appropriate to reintroduce, since
it will allow processing of aggregate operations when encountering that
token without having to worry about the above scenario; without having to
duplicate a `ParseState` stack; without having to hijack dead state
transitions for producing our aggregate object; and everything else
mentioned above.
This commit does not modify those abstractions to use AttrEnd yet; it
re-introduces the token to the core system, not the parser-generators, and
it doesn't yet replace lookahead operations in the parsers that use
them. That'll come next. Unlike the commit that removed it, though, we are
now generating proper spans, so make note of that here. This also does not
introduce the concept to XIRF yet, which did not exist at the time that it
was removed, so XIRF is filtering it out until a following commit.
DEV-7145
This isn't conceptally all that significant of a change, but there was a lot
of modify to get it working. I would generally separate this into a commit
for the implementation and another commit for the integration, but I decided
to keep things together.
This serves a role similar to AttrSpan---this allows deriving a span
representing the element name from a span representing the entire XIR
token. This will provide more useful context for errors---including the tag
delimiter(s) means that we care about the fact that an element is in that
position (as opposed to some other type of node) within the context of an
error. However, if we are expecting an element but take issue with the
element name itself, we want to place emphasis on that instead.
This also starts to consider the issue of span contexts---a blob of detached
data that is `Span` is useful for error context, but it's not useful for
manipulation or deriving additional information. For that, we need to
encode additional context, and this is an attempt at that.
I am interested in the concept of providing Spans that are guaranteed to
actually make sense---that are instantiated and manipulated with APIs that
ensure consistency. But such a thing buys us very little, practically
speaking, over what I have now for TAMER, and so I don't expect to actually
implement that for this project; I'll leave that for a personal
project. TAMER's already take a lot of my personal interests and it can
cause me a lot of grief sometimes (with regards to letting my aspirations
cause me more work).
DEV-7145
Non-attribute and non-empty start/end tags will have their whitespace
as part of the produced span. This sets us up for a following change that
will allow for deriving the name span from this span given a QName, which
gives us a span that both represents the entire XIR token and allows
deriving the element name.
An accurate token span is necessary for parsing errors where an element was
not expected, while an element name span is more appropriate for issues of
grammar and semantic errors that deal not with the fact that an element was
encountered, but _what_ element was encountered.
DEV-7145
This both adds clarifying tests and corrects the case of `<foo/>`, where the
offset was erroneously off by one---it saw that there were no attributes and
added a byte thinking it'd include `>`, as in `<foo>`.
DEV-7145
This is the first parser generator for the parsing framework. I've been
waiting quite a while to do this because I wanted to be sure that I
understood how I intended to write the attribute parsers manually. Now that
I'm about to start parsing source XML files, it is necessary to have a
parser generator.
Typically one thinks of a parser generator as a separate program that
generates code for some language, but that is not always the case---that
represents a lack of expressiveness in the language itself (e.g. C). Here,
I simply use Rust's macro system, which should be a concept familiar to
someone coming from a language like Lisp.
This also resolves where I stand on parser combinators with respect to this
abstraction: they both accomplish the exact same thing (composition of
smaller parsers), but this abstraction doesn't do so in the typical
functional way. But the end result is the same.
The parser generated by this abstraction will be optimized an inlined in the
same manner as the hand-written parsers. Since they'll be tightly coupled
with an element parser (which too will have a parser generator), I expect
that most attribute parsers will simply be inlined; they exist as separate
parsers conceptually, for the same reason that you'd use parser combinators.
It's worth mentioning that this awkward reliance on dead state for a
lookahead token to determine when aggregation is complete rubs me the wrong
way, but resolving it would involve reintroducing the XIR AttrEnd that I had
previously removed. I'll keep fighting with myself on this, but I want to
get a bit further before I determine if it's worth the tradeoff of
reintroducing (more complex IR but simplified parsing).
DEV-7145
This was missed. It was not possible, using the documentation
alone (without looking at the linked source) to tell what the QName actually
represented, though you could assume by the name.
DEV-7145
This is partly an experiment, but is designed to simplify producing English
sentences in various contexts. It makes use of a not only unstable, but
incomplete, Rust feature---adt_const_params, for a static str const type
parameter. Hopefully that ends up being stabalized.
This uses types, but it's the same as function composition due to Rust's
monomorphization.
DEV-7145
`ParseState` originally required `Default` for use with `mem::take` in
`Parser::feed_tok`. This unfortunately cannot last, since more specialized
parsers require context during initialization in order to provide useful
diagnostic information. (The other option is to require the caller to
augment errors with diagnostic information, but that would have to be
duplicated by every caller and complicates parser composition; I'd prefer
those diagnostic details remain encapsulated.)
Replacing `Default` with `Option` is uglier, but it ends up producing the
same assembly as `mem::take` did, at least at the time of writing. Because
Rust is able to elide unnecessary moves using this implementation, there is
no need for `unwrap_unchecked` or other unsafe methods, which is great,
since it shows that this parsing methodology is viable entirely in safe
Rust.
DEV-7145
Previously, `ParseStatus::Dead` always yielded
`ParseState::Token`. However, I'm working on introducing parsers that
aggregate (parsing XML attributes into structs), and those parsers do not
know that they have completed aggregation until they reach a dead state;
given that, I need to yield additional information at that time.
I played around with a number of alternative ideas, but this ended up being
the cleanest, relative to the effort involved. For example, introducing
another parameter to `ParseStatus::Dead` was too burdensome on APIs that
ought not concern themselves with the possibility of receiving an object in
addition to a lookahead token, since many parsers are not capable of doing
so (given that they map M:(N<=M)).
Another option that I abandoned fairly quickly was having
`is_accepting` (potentially renamed) return an aggregate object, since
that's on the side and didn't feel like it was part of the parsing pipeline.
The intent is to abstract this some in a new `ParseState` method for
delegation + aggregation.
DEV-7145
I'll document it more formally eventually, but this settles on a mix of the
two: square brackets and dashes for intervals, `+` for intersecting lines,
byte offsets below interval endpoints, and names below that.
The docblock for `Span` itself iss still off; I'll probably just take one of
the test cases and paste it there at some point.
DEV-7145
This replaces a tuple with a tuple struct that allows for calculating more
complete span information, such as the span encompassing the entire
attribute and the value span including the surrounding quotes.
This includes logic that ought to be abstracted into `Span` itself, and it's
not as formal as I'd like it to be (e.g. not ensuring context), but this is
a good starting point.
Note that parsers call `Token::span`, which in turn calculates the attribute
span, each time an attribute is encountered during lowering. But Rust does
a good job at optimizing away unnecessary operations, so this didn't have an
observable impact on time.
DEV-7145
This allows `XmlXirReader` to be used in a `Lower` operation, just as
everything else, bringing me one step closer to a pipeline that can be
concisely represented; this is finally beginning to unify in a clear way,
though it is still a bit of a mess.
This causes `XmlXirReader` to _act_ like a `parse::Parser` in that it yields
a `ParsedResult`, but it does not use `parse::Parser` itself; that was the
_original_ plan: convert it into a `ParseState` where `XmlXirReader` became
a context, and force `Parser` to yield by feeding it a stream of tokens with
`repeat`, but that ended up performing poorly relative to this change. I
did some investigation, which I might write about in the future, but for
now, this solution works just fine.
DEV-7145
This finally uses `parse` all the way up to aggregation into the ASG, as can
be seen by the mess in `poc`. This will be further simplified---I just need
to get this committed so that I can mentally get it off my plate. I've been
separating this commit into smaller commits, but there's a point where it's
just not worth the effort anymore. I don't like making large changes such
as this one.
There is still work to do here. First, it's worth re-mentioning that
`poc` means "proof-of-concept", and represents things that still need a
proper home/abstraction.
Secondly, `poc` is retrieving the context of two parsers---`LowerContext`
and `Asg`. The latter is desirable, since it's the final aggregation point,
but the former needs to be eliminated; in particular, packages need to be
worked into the ASG so that `found` can be removed.
Recursively loading `xmlo` files still happens in `poc`, but the compiler
will need this as well. Once packages are on the ASG, along with their
state, that responsibility can be generalized as well.
That will then simplify lowering even further, to the point where hopefully
everything has the same shape (once final aggregation has an abstraction),
after which we can then create a final abstraction to concisely stitch
everything together. Right now, Rust isn't able to infer `S` for
`Lower<S, LS>`, which is unfortunate, but we'll be able to help it along
with a more explicit abstraction.
DEV-11864
This is intended to describe, to the user, the state that the parser is
in. This will be used to convey additional information for general parser
errors, but it should also probably be integrated into parsers' individual
errors as well when appropriate.
This is something I expected to add at some point, but I wanted to add them
because, when dealing with lowering errors, it can be difficult to tell
what parser the error originated from.
DEV-11864
RSG (Ryan Specialty Group) recently announced a rename to Ryan Specialty (no
"Group"), but I'm not sure if the legal name has been changed yet or not, so
I'll wait on that.
This is now visible in the diagnostic output. Example at this point in
time, on an xmlo file for one of our smallest systems:
error: expected closing tag for `preproc:symtable`
--> /home/.../foo.xmlo:16:4
|
| <preproc:symtable xmlns:map="http://www.w3.org/2005/xpath-functions/map">
| -----------------
= note: element `preproc:symtable` is opened here
--> /home/.../foo.xmlo:11326:4
|
| </preproc:wrong>
| ^^^^^^^^^^^^^^^^
= error: expected `</preproc:symtable>`
DEV-12151
This is a working concept that will continue to evolve. I wanted to start
with some basic output before getting too carried away, since there's a lot
of potential here.
This is heavily influenced by Rust's helpful diagnostic messages, but will
take some time to realize a lot of the things that Rust does. The next step
will be to resolve line and column numbers, and then possibly include
snippets and underline spans, placing the labels alongside them. I need to
balance this work with everything else I have going on.
This is a large commit, but it converts the existing Error Display impls
into Diagnostic. This separation is a bit verbose, so I'll see how this
ends up evolving.
Diagnostics are tied to Error at the moment, but I imagine in the future
that any object would be able to describe itself, error or not, which would
be useful in the future both for the Summary Page and for query
functionality, to help developers understand the systems they are writing
using TAME.
Output is integrated into tameld only in this commit; I'll add tamec
next. Examples of what this outputs are available in the test cases in this
commit.
DEV-10935
There's no use in complicating the error handling here when we'd just
default to `UNKNOWN_SPAN` anyway when trying to render it. `UNKNOWN_SPAN`
didn't exist at the time of writing.
DEV-10935
This entirely removes the old XmloReader that has since been replaced with a
XIR-based reader.
I had been holding off on this because the new reader is slower, pending
performance optimizations (which I'll do a little later on), however the
performance loss is of no practical consideration and only affects the
linker, which is still fast.
Therefore, it's better to get this old code out of the way to simplify
refactoring going forward. In particular, I'm working on the diagnostic
system.
This is a little sad, in a way---this is some of my first Rust code that I'm
deleting.
DEV-10935
tamec and tameld will now both introduce a `Context` to XIR, which will use
it to create spans.
Here's an example of an error, now that it's all working well together:
$ target/release/tameld --emit xmle -o /dev/null path/to/package.xmlo
error: invalid preproc:sym/@dim `9` at [/../path/to/package.xmlo offset 1175451-1175452]
A future task will make this human-readable by producing line and column
numbers, and perhaps even a snippet (if not now, then eventually).
It's exciting to see this coming together finally.
DEV-10934
There's a bit to unpack here. Some of the spans originate from quick-xml's
error handling, but in coming up with test cases to try to trigger errors, I
found that quick-xml is far too permissive in what it accepts, and
oughtright dangerous in some situations.
I feel like the writing is on the wall for quick-xml, but I'll probably wait
until replacing `xmlo` with a more efficient format before deciding whether
to use a different library or implement parsing ourselves. There's a lot of
factors to consider, and a library would have to not only be correct and
performant, but provide useful information for span generation.
But for now, I have other more important things to work on, like a
functioning compiler. So while quick-xml is around, I'll just have to do
the best I can to provide a correct parser with useful errors.
DEV-10934
This is a large change, and was a bit of a tedious one, given the
comprehensive tests.
This introduces proper offsets and lengths for spans, with the exception of
some quick-xml errors that still need proper mapping. Further, this still
uses `UNKNOWN_CONTEXT`, which will be resolved shortly.
This also introduces `SpanlessError`, which `Error` explicitly _does not_
implement `From<SpanlessError>` for---this forces the caller to provide a
span before the error is compatable with the return value, ensuring that
spans will actually be available rather than forgotten for errors. This is
important, given that errors are generally less tested than the happy path,
and errors are when users need us the most (so, need span information).
Further, I had to use pointer arithmetic in order to calculate many of the
spans, because quick-xml does not provide enough information. There's no
safety considerations here, and the comprehensive unit test will ensure
correct behavior if the implementation changes in the future.
I would like to introduce typed spans at some point---I made some
opinionated choices when it comes to what the spans ought to
represent. Specifically, whether to include the `<` or `>` with the open
span (depends), whether to include quotes with attribute values (no),
and some other details highlighted in the test cases. If we provide typed
spans, then we could, knowing the type of span, calculate other spans on
request, e.g. to include or omit quotes for attributes. Different such
spans may be useful in different situations when presenting information to
the user.
This also highlights gaps in the tokens emitted by XIR, such as whitespace
between attributes, the `=` between name and value, and so on. These are
important when it comes to code formatting, so that we can reliably
reconstruct the XML tree, but it's not important right now. I anticipate
future changes would allow the XIR reader to be configured (perhaps via
generics, like a strategy-type pattern) to optionally omit these tokens if
desired.
Anyway, more to come.
DEV-10934
When wip-frontends is on, this will parse the input file using XIR and then
immediately output it again. This makes the necessary changes to be able to
read every source file we have in our largest project, such that the output
is identical after having been formatted with `xmllint --format -` (there
are differences because e.g. whitespace between attributes is not yet
maintained).
This is performant too, with times remaining essentially identical despite
the additional work.
DEV-10413
This resolves the performance issues caused by Rust's failure to elide the
ElementStack (ArrayVec) memcpys on move.
Since XIRF is invoked tens of millions of times in some cases for larger
systems, prior to this change, failure to optimize away moves for XIRF
resulted in tens of millions of memcpys. This resulted in linking of one
program going from 1s -> ~15s. This change reduces it to ~2.5s with the
wip-xmlo-xir-reader flag on, with the extra time coming from elsewhere (the
subject of future changes).
In particular, this change introduces a new mutable reference to
`ParseState::parse_token`, which is a reference to a `Context` owned by the
caller (e.g. `Parser`). In the case of XIRF, this means that
`Parser<flat::State, _>` will own the `ElementStack`/`ArrayVec` instead of
`flat::State`; this allows the latter to remain pure and benefit from Rust's
move optimizations, without sacrificing the otherwise-pure implementation.
ParseStates that do not need a mutable context can use `NoContext` and
remain pure.
DEV-12024
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 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
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 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
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
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
Mike Gerwitz