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.
The previous iterators had to be used in a certain order because they mixed
concerns, out of concern for performance. This attempts to chain even more
iterators to see how it may perform.
To be clear: this will be cleaned up. This was just an experiment.
Here were profiles on the average of 50 runs of linking our largest program:
Baseline, pre-XIR (with fragments removed from output) 0.8082
XIR writer, pre-ElemWrap, no #[inline] 0.7844s
XIR writer, ElemWrap, no #[inline] 0.7918s
XIR writer, ElemWrap, inlines in obj::xmle::xir 0.7892s
XIR writer, ElemWrap, inlines in obj::xmle::xir and ir::asg::section 0.7858s
XIR writer, ElemWrap, inline in only ir::asg::section 0.781s
Pre-ElemWrap, inlines in ir::asg::section 0.7772s
These profiles are difficult, because they hit the filesystem so much. I
write to /dev/null, but it reads 100s of xmlo files from disk.
It's clear that the impact is fairly modest and within a margin of error; as
such, I will continue down the path of writing code that's easier to grok
and maintain, since not doing so would be a micro-optimization relative to
the concerns of the rest of the system at this point.
But the purpose of all of this work was to determine whether an
iterator-based XIR would be viable. It seems to be competitive. I'll
finish up the writer reimplementation and move on.
This contains some awkward coupling for opening and closing tags to reduce
the complexity of the `Iterator` types that must be manually
specified. That may be addressed shortly.
This was creating a heap-allocated `Vec` for each map symbol despite not
actually needing it. We do have multiple froms for return map values.
But by the time we may want this type of thing, we'll have a different IR
for it anyway.
See the docs for a much deeper discussion. In summary: traits do not
support static methods, and this is the workaround, which relies on unstable
nightly constant function features.
This implementation is tested using `qname_const!`, and will be utilized
with a new static type in a following commit.
This is to support two things:
1. Early switch to 2021 Edition, which is stable Oct 21; and
2. To make use of unstable const features.
The rationale is that switching to nightly does not really have any
significant downside for us, given that TAMER is used only by us and
the only risk is that unstable features may change a bit, which can be
mitigated with certain precautions.
The rationale for each unstable feature will be documented as they are used,
including documentation on what would be required to remove it and what
functionality would be lost / need to change in doing so.
This is far from fully documented; it's just a start. I'll document fully
once the implementation is done, to ensure I don't waste time documenting
things that may change.
These are getting large and messy.
And I now notice that I never completed the header test after
prototyping. Shame on me.
Also, errata from the previous commit message: the diffs are identical
_except for attribute escaping_ that is unnecessary; we're outputting data
read directly from existing XML files (output by Saxon), so characters are
already escaped as needed.
DEV-10561
The `l:dep` section of the `xmle` file, after formatting (since XIR writes
without newlines and indentation), is now identical to the existing xmle
writer. I can now move on to the other sections.
Note that the attribute movement in this commit is simply to get the diff to
properly align. Once the current xmle writer is removed, I'll organize them
a bit more sensibly.
`obj::xmle::xir` also needs documentation, now that it's shown to be viable.
The new xmle writer was having to intern before write, which did not make
sense.
This continues with consistently using symbols throughout the system, and
is a smaller size than `String` as a bonus.
`IdentKind` needs to be written to `xmle` files and displayed in error
messages. String slices were used when quick-xml was used for writing,
which will be going away with the new writer.
This has been a long time coming, and has been repeatedly stashed as other
parts of the system have evolved to support it. The introduction of the XIR
tree was to write tests for this (which are sloppy atm).
This currently writes out the `xmle` header and _most_ of the `l:dep`
section; it's missing the object-type-specific attributes. There is,
relatively speaking, not much more work to do here.
The feature flag `wip-xir-xmle-writer` was introduced to toggle this system
in place of `XmleWriter`. Initial benchmarks show that it will be
competitive with the quick-xml-based writer, but remember that is not the
goal: the purpose of this is to test XIR in a production system before we
continue to implement it for a frontend, and to refactor so that we do not
have multiple implementations writing XML files (once we echo the source XML
files).
I'm excited to get this done with so that I can move on. This has been
rather exhausting.
The 16-bit interner at present will be used only for span contexts. In the
future, this interner may become specialized specifically for that, but for
now let's just re-use what we already have so that I can move on.
DEV-10733
I want to make it clear in the assertion that the problem could be caused by
duplicate strings. We do not sort by string, because in part we may in the
future want to group certain symbols together in some arbitrary way so we
can compare ranges (using the markers).
If that doesn't end up happening, it may be better to just sort by string
to obviate the problem.
It's really awkward not having them caps, when not only are constants
expected to be, but also that we cannot maintain consistency between the
string and the identifier name in even the simplest of cases.
(We could use `r#`, but that's too cumbersome.)
Mike Gerwitz
Austin Schaffer