// XIR element parser generator
//
// Copyright (C) 2014-2022 Ryan Specialty Group, LLC.
//
// This file is part of TAME.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see .
//! Element parser generator for parsing of [XIRF](super::super::flat).
use arrayvec::ArrayVec;
use std::{
error::Error,
fmt::{Debug, Display},
marker::PhantomData,
};
use crate::{
diagnose::Diagnostic,
diagnostic_panic,
fmt::{DisplayWrapper, TtQuote},
parse::{
ClosedParseState, Context, ParseState, Transition, TransitionResult,
},
span::Span,
xir::{Prefix, QName},
};
#[cfg(doc)]
use crate::{ele_parse, parse::Parser};
/// A parser accepting a single element.
pub trait EleParseState: ParseState {}
/// Maximum level of parser nesting.
///
/// Unfortunately,
/// this limit _does not_ correspond to the level of XML nesting;
/// parsers composed of Sum NTs,
/// in particular,
/// push multiple parsers onto the stack for a single element.
///
/// Note that this is assuming that this parser is used only for TAME
/// sources.
/// If that's not the case,
/// this can be made to be configurable like XIRF.
pub const MAX_DEPTH: usize = 64;
/// Parser stack for trampoline.
///
/// This can be used as a call stack for parsers while avoiding creating
/// otherwise-recursive data structures with composition-based delegation.
/// However,
/// it is more similar to CPS,
/// in that the parser popped off the stack need not be the parser that
/// initiated the request and merely represents the next step in
/// a delayed computation.
/// If such a return context is unneeded,
/// a [`ParseState`] may implement tail calls by simply not pushing itself
/// onto the stack before requesting transfer to another [`ParseState`].
#[derive(Debug, Default)]
pub struct StateStack(ArrayVec);
pub type StateStackContext = Context>;
// Note that public visibility is needed because `ele_parse` expands outside
// of this module.
impl StateStack {
/// Request a transfer to another [`ParseState`],
/// expecting that control be returned to `ret` after it has
/// completed.
///
/// This can be reasoned about like calling a thunk:
/// the return [`ParseState`] is put onto the stack,
/// the target [`ParseState`] is used for the state transition to
/// cause [`Parser`] to perform the call to it,
/// and when it is done
/// (e.g. a dead state),
/// `ret` will be pop'd from the stack and we'll transition back to
/// it.
/// Note that this method is not responsible for returning;
/// see [`Self::ret_or_dead`] to perform a return.
///
/// However,
/// the calling [`ParseState`] is not responsible for its return,
/// unlike a typical function call.
/// Instead,
/// this _actually_ more closely resembles CPS
/// (continuation passing style),
/// and so [`ele_parse!`] must be careful to ensure that stack
/// operations are properly paired.
/// On the upside,
/// if something is erroneously `ret`'d,
/// the parser is guaranteed to be in a consistent state since the
/// entire state has been reified
/// (but the input would then be parsed incorrectly).
///
/// Note that tail calls can be implemented by transferring control
/// without pushing an entry on the stack to return to,
/// but that hasn't been formalized \[yet\] and requires extra care.
pub fn transfer_with_ret(
&mut self,
Transition(ret): Transition,
target: TransitionResult,
) -> TransitionResult
where
SA: ParseState,
ST: ParseState,
{
let Self(stack) = self;
// TODO: Global configuration to (hopefully) ensure that XIRF will
// actually catch this.
if stack.is_full() {
// TODO: We need some spans here and ideally convert the
// parenthetical error message into a diagnostic footnote.
// TODO: Or should we have a special error type that tells the
// parent `Parser` to panic with context?
diagnostic_panic!(
vec![],
"maximum parsing depth of {} exceeded while attempting \
to push return state {} \
(try reducing XML nesting as a workaround)",
MAX_DEPTH,
TtQuote::wrap(ret),
);
}
stack.push(ret.into());
target
}
/// Attempt to return to a previous [`ParseState`] that transferred
/// control away from itself,
/// otherwise yield a dead state transition to `deadst`.
///
/// Conceptually,
/// this is like returning from a function call,
/// where the function was invoked using [`Self::transfer_with_ret`].
/// However,
/// this system is more akin to CPS
/// (continuation passing style);
/// see [`Self::transfer_with_ret`] for important information.
///
/// If there is no state to return to on the stack,
/// then it is assumed that we have received more input than expected
/// after having completed a full parse.
pub fn ret_or_dead(
&mut self,
lookahead: S::Token,
deadst: S,
) -> TransitionResult {
let Self(stack) = self;
// This should certainly never happen unless there is a bug in the
// `ele_parse!` parser-generator,
// since it means that we're trying to return to a caller that
// does not exist.
match stack.pop() {
Some(st) => Transition(st).incomplete().with_lookahead(lookahead),
None => Transition(deadst).dead(lookahead),
}
}
/// Test every [`ParseState`] on the stack against the predicate `f`.
pub fn all(&self, f: impl Fn(&S) -> bool) -> bool {
let Self(stack) = self;
stack[..].iter().all(f)
}
}
/// Match some type of node.
#[derive(Debug, PartialEq, Eq)]
pub enum NodeMatcher {
/// Static [`QName`] with a simple equality check.
QName(QName),
/// Any element with a matching [`Prefix`].
Prefix(Prefix),
}
impl NodeMatcher {
/// Match against the provided [`QName`].
pub fn matches(&self, qname: QName) -> bool {
match self {
Self::QName(qn_match) if qn_match == &qname => true,
Self::Prefix(prefix) if Some(*prefix) == qname.prefix() => true,
_ => false,
}
}
}
impl From for NodeMatcher {
fn from(qname: QName) -> Self {
Self::QName(qname)
}
}
impl From for NodeMatcher {
fn from(prefix: Prefix) -> Self {
Self::Prefix(prefix)
}
}
impl Display for NodeMatcher {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
use crate::xir::fmt::XmlPrefixAnyLocal;
match self {
Self::QName(qname) => Display::fmt(qname, f),
Self::Prefix(prefix) => XmlPrefixAnyLocal::fmt(prefix, f),
}
}
}
#[macro_export]
macro_rules! ele_parse {
(
$(#[$super_attr:meta])*
$vis:vis enum $super:ident;
// Attr has to be first to avoid ambiguity with `$rest`.
$(type AttrValueError = $evty:ty;)?
type Object = $objty:ty;
$(
[super] {
$($super_body:tt)*
};
)?
// Combination of square brackets above and the prefix here are
// needed for disambiguation.
$(#[$nt_first_attr:meta])*
$nt_first:ident := $($nt_defs:tt)*
) => {
ele_parse! {@!next $vis $super
$(type AttrValueError = $evty;)?
type Object = $objty;
$(#[$nt_first_attr])*
$nt_first := $($nt_defs)*
}
ele_parse!(@!super_sum <$objty> $(#[$super_attr])* $vis $super
$([super] { $($super_body)* })?
$nt_first := $($nt_defs)*
);
};
(@!next $vis:vis $super:ident
// Attr has to be first to avoid ambiguity with `$rest`.
$(type AttrValueError = $evty:ty;)?
type Object = $objty:ty;
$($rest:tt)*
) => {
ele_parse!(@!nonterm_decl <$objty, $($evty)?> $vis $super $($rest)*);
};
(@!nonterm_decl <$objty:ty, $($evty:ty)?>
$vis:vis $super:ident $(#[$nt_attr:meta])* $nt:ident := $($rest:tt)*
) => {
ele_parse!(@!nonterm_def <$objty, $($evty)?>
$vis $super $(#[$nt_attr])* $nt $($rest)*
);
};
(@!nonterm_def <$objty:ty, $($evty:ty)?>
$vis:vis $super:ident $(#[$nt_attr:meta])* $nt:ident $qname:ident $(($($ntp:tt)*))?
{ $($matches:tt)* }; $($rest:tt)*
) => {
ele_parse!(@!ele_expand_body <$objty, $($evty)?>
$vis $super $(#[$nt_attr])* $nt $qname ($($($ntp)*)?) $($matches)*
);
ele_parse! {@!next $vis $super
$(type AttrValueError = $evty;)?
type Object = $objty;
$($rest)*
}
};
(@!nonterm_def <$objty:ty, $($evty:ty)?>
$vis:vis $super:ident $(#[$nt_attr:meta])* $nt:ident
($ntref_first:ident $(| $ntref:ident)+); $($rest:tt)*
) => {
ele_parse!(@!ele_dfn_sum <$objty>
$vis $super $(#[$nt_attr])* $nt [$ntref_first $($ntref)*]
);
ele_parse! {@!next $vis $super
$(type AttrValueError = $evty;)?
type Object = $objty;
$($rest)*
}
};
(@!nonterm_decl <$objty:ty, $($evty:ty)?> $vis:vis $super:ident) => {};
// Expand the provided data to a more verbose form that provides the
// context necessary for state transitions.
(@!ele_expand_body <$objty:ty, $($evty:ty)?>
$vis:vis $super:ident
$(#[$nt_attr:meta])* $nt:ident $qname:ident ($($ntp:tt)*)
@ { $($attrbody:tt)* } => $attrmap:expr,
$(/$(($close_span:ident))? => $closemap:expr,)?
// Special forms (`[sp](args) => expr`).
$(
[$special:ident]$(($($special_arg:ident),*))?
=> $special_map:expr,
)?
// Nonterminal references are provided as a list.
// A configuration specifier can be provided,
// currently intended to support the Kleene star.
$(
$ntref:ident,
)*
) => {
ele_parse! {
@!ele_dfn_body <$objty, $($evty)?>
$vis $super $(#[$nt_attr])*$nt $qname ($($ntp)*)
@ { $($attrbody)* } => $attrmap,
/$($($close_span)?)? => ele_parse!(@!ele_close $($closemap)?),
$([$special]$(($($special_arg),*))? => $special_map,)?
<> {
$(
$ntref,
)*
}
// Generate state transitions of the form `(S) -> (S')`.
-> {
@ ->
$(
($nt::$ntref, $ntref),
($nt::$ntref, $ntref) ->
)* ($nt::ExpectClose_, ()),
}
}
};
// No explicit Close mapping defaults to doing nothing at all
// (so yield Incomplete).
(@!ele_close) => {
crate::parse::ParseStatus::Incomplete
};
(@!ele_close $close:expr) => {
crate::parse::ParseStatus::Object($close)
};
// Delegation when the destination type is `()`,
// indicating that the next state is not a child NT
// (it is likely the state expecting a closing tag).
(@!ntref_delegate
$stack:ident, $ret:expr, (), $_target:expr, $done:expr
) => {
$done
};
// Delegate to a child parser by pushing self onto the stack and
// yielding to one of the child's states.
// This uses a trampoline,
// which avoids recursive data structures
// (due to `ParseState` composition/stitching)
// and does not grow the call stack.
(@!ntref_delegate
$stack:ident, $ret:expr, $ntnext_st:ty, $target:expr, $_done:expr
) => {
$stack.transfer_with_ret(
Transition($ret),
$target,
)
};
(@!ele_dfn_body <$objty:ty, $($evty:ty)?>
$vis:vis $super:ident $(#[$nt_attr:meta])* $nt:ident $qname:ident
($($qname_matched:pat, $open_span:pat)?)
// Attribute definition special form.
@ {
// We must lightly parse attributes here so that we can retrieve
// the field identifiers that may be later used as bindings in
// `$attrmap`.
$(
$(#[$fattr:meta])*
$field:ident: ($($fmatch:tt)+) => $fty:ty,
)*
} => $attrmap:expr,
// Close expression
// (defaulting to Incomplete via @!ele_expand_body).
/$($close_span:ident)? => $closemap:expr,
// Streaming (as opposed to aggregate) attribute parsing.
$([attr]($attr_stream_binding:ident) => $attr_stream_map:expr,)?
// Nonterminal references.
<> {
$(
$ntref:ident,
)*
}
-> {
@ -> ($ntfirst:path, $ntfirst_st:ty),
$(
($ntprev:path, $ntprev_st:ty) -> ($ntnext:path, $ntnext_st:ty),
)*
}
) => {
paste::paste! {
crate::attr_parse! {
vis($vis);
$(type ValueError = $evty;)?
struct [<$nt AttrsState_>] -> [<$nt Attrs_>] {
$(
$(#[$fattr])*
$field: ($($fmatch)+) => $fty,
)*
}
}
$(#[$nt_attr])*
///
#[doc=concat!("Parser for element [`", stringify!($qname), "`].")]
#[derive(Debug, PartialEq, Eq, Default)]
$vis enum $nt {
#[doc=concat!(
"Expecting opening tag for element [`",
stringify!($qname),
"`]."
)]
#[doc(hidden)]
#[default]
Expecting_,
/// Non-preemptable [`Self::Expecting_`].
#[doc(hidden)]
#[allow(dead_code)] // used by sum parser
NonPreemptableExpecting_,
/// Recovery state ignoring all remaining tokens for this
/// element.
#[doc(hidden)]
RecoverEleIgnore_(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth
),
// Recovery completed because end tag corresponding to the
// invalid element has been found.
#[doc(hidden)]
RecoverEleIgnoreClosed_(
crate::xir::QName,
crate::xir::CloseSpan
),
/// Recovery state ignoring all tokens when a `Close` is
/// expected.
///
/// This is token-agnostic---it
/// may be a child element,
/// but it may be text,
/// for example.
#[doc(hidden)]
CloseRecoverIgnore_(
(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth
),
crate::span::Span
),
/// Parsing element attributes.
#[doc(hidden)]
Attrs_(
(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth
),
[<$nt AttrsState_>]
),
$(
#[doc(hidden)]
$ntref(
(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth
),
),
)*
#[doc(hidden)]
ExpectClose_(
(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth
),
),
/// Closing tag found and parsing of the element is
/// complete.
#[doc(hidden)]
Closed_(
Option,
crate::span::Span
),
}
impl $nt {
/// Matcher describing the node recognized by this parser.
#[allow(dead_code)] // used by sum parser
#[inline]
fn matcher() -> crate::xir::parse::NodeMatcher {
crate::xir::parse::NodeMatcher::from($qname)
}
/// Whether the given QName would be matched by any of the
/// parsers associated with this type.
#[inline]
fn matches(qname: crate::xir::QName) -> bool {
Self::matcher().matches(qname)
}
/// Number of
/// [`NodeMatcher`](crate::xir::parse::NodeMatcher)s
/// considered by this parser.
///
/// This is always `1` for this parser.
#[allow(dead_code)] // used by Sum NTs
const fn matches_n() -> usize {
1
}
/// Format [`Self::matcher`] for display.
///
/// This value may be rendered singularly or as part of a
/// list of values joined together by Sum NTs.
/// This function receives the number of values to be
/// formatted as `n` and the current 0-indexed offset
/// within that list as `i`.
/// This allows for zero-copy rendering of composable NTs.
///
/// `i` must be incremented after the operation.
#[allow(dead_code)] // used by Sum NTs
fn fmt_matches(
n: usize,
i: &mut usize,
f: &mut std::fmt::Formatter
) -> std::fmt::Result {
use crate::{
fmt::ListDisplayWrapper,
xir::fmt::EleSumList,
};
EleSumList::fmt_nth(n, *i, &Self::matcher(), f)?;
*i += 1;
Ok(())
}
/// Whether the parser is in a state that can tolerate
/// superstate node preemption.
///
/// For more information,
/// see the superstate
#[doc=concat!(
" [`", stringify!($super), "::can_preempt_node`]."
)]
fn can_preempt_node(&self) -> bool {
use $nt::*;
match self {
// Preemption before the opening tag is safe,
// since we haven't started processing yet.
Expecting_ => true,
// The name says it all.
// Instantiated by the superstate.
NonPreemptableExpecting_ => false,
// Preemption during recovery would cause tokens to
// be parsed when they ought to be ignored,
// so we must process all tokens during recovery.
RecoverEleIgnore_(..)
| CloseRecoverIgnore_(..) => false,
// It is _not_ safe to preempt attribute parsing
// since attribute parsers aggregate until a
// non-attribute token is encountered;
// we must allow attribute parsing to finish its
// job _before_ any preempted nodes are emitted
// since the attributes came _before_ that node.
Attrs_(..) => false,
// These states represent jump states where we're
// about to transition to the next child parser.
// It's safe to preempt here,
// since we're not in the middle of parsing.
//
// Note that this includes `ExpectClose_` because of
// the macro preprocessing,
// and Rust's exhaustiveness check will ensure
// that it is accounted for if that changes.
// If we're expecting that the next token is a
// `Close`,
// then it must be safe to preempt other nodes
// that may appear in this context as children.
$ntfirst(..) => true,
$(
$ntnext(..) => true,
)*
// If we're done,
// we want to be able to yield a dead state so
// that we can transition away from this parser.
RecoverEleIgnoreClosed_(..)
| Closed_(..) => false,
}
}
#[allow(dead_code)] // used only when there are child NTs
/// Whether the current state represents the last child NT.
fn is_last_nt(&self) -> bool {
// This results in `Self::$ntref(..) => true,` for the
// _last_ NT,
// and `=> false` for all others.
// If there are no NTs,
// it results in `Self::Attrs(..) => true,`,
// which is technically true but will never be
// called in that context.
match self {
Self::Attrs_(..) => $(
false,
Self::$ntref(..) =>
)* true,
_ => false,
}
}
}
impl std::fmt::Display for $nt {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
use crate::{
fmt::{DisplayWrapper, TtQuote},
xir::fmt::{TtOpenXmlEle, TtCloseXmlEle},
};
match self {
Self::Expecting_
| Self::NonPreemptableExpecting_ => write!(
f,
"expecting opening tag {}",
TtOpenXmlEle::wrap(Self::matcher()),
),
Self::RecoverEleIgnore_(name, _, _)
| Self::RecoverEleIgnoreClosed_(name, _) => write!(
f,
"attempting to recover by ignoring element \
with unexpected name {given} \
(expected {expected})",
given = TtQuote::wrap(name),
expected = TtQuote::wrap(Self::matcher()),
),
Self::CloseRecoverIgnore_((qname, _, depth), _) => write!(
f,
"attempting to recover by ignoring input \
until the expected end tag {expected} \
at depth {depth}",
expected = TtCloseXmlEle::wrap(qname),
),
Self::Attrs_(_, sa) => std::fmt::Display::fmt(sa, f),
Self::ExpectClose_((qname, _, depth)) => write!(
f,
"expecting closing element {} at depth {depth}",
TtCloseXmlEle::wrap(qname)
),
Self::Closed_(Some(qname), _) => write!(
f,
"done parsing element {}",
TtQuote::wrap(qname),
),
// Should only happen on an unexpected `Close`.
Self::Closed_(None, _) => write!(
f,
"skipped parsing element {}",
TtQuote::wrap(Self::matcher()),
),
$(
// TODO: A better description.
Self::$ntref(_) => {
write!(
f,
"preparing to transition to \
parser for next child element(s)"
)
},
)*
}
}
}
#[derive(Debug, PartialEq)]
$vis enum [<$nt Error_>] {
/// An element was expected,
/// but the name of the element was unexpected.
UnexpectedEle(crate::xir::QName, crate::span::Span),
/// Unexpected input while expecting an end tag for this
/// element.
///
/// The span corresponds to the opening tag.
CloseExpected(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::XirfToken,
),
Attrs(crate::xir::parse::AttrParseError<[<$nt AttrsState_>]>),
}
impl From]>>
for [<$nt Error_>]
{
fn from(
e: crate::xir::parse::AttrParseError<[<$nt AttrsState_>]>
) -> Self {
[<$nt Error_>]::Attrs(e)
}
}
impl std::error::Error for [<$nt Error_>] {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
// TODO
None
}
}
impl std::fmt::Display for [<$nt Error_>] {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
use crate::{
fmt::{DisplayWrapper, TtQuote},
xir::fmt::{TtOpenXmlEle, TtCloseXmlEle},
};
match self {
Self::UnexpectedEle(name, _) => write!(
f,
"unexpected {unexpected} (expecting {expected})",
unexpected = TtOpenXmlEle::wrap(name),
expected = TtOpenXmlEle::wrap($nt::matcher()),
),
Self::CloseExpected(qname, _, tok) => write!(
f,
"expected {}, but found {}",
TtCloseXmlEle::wrap(qname),
TtQuote::wrap(tok)
),
Self::Attrs(e) => std::fmt::Display::fmt(e, f),
}
}
}
impl crate::diagnose::Diagnostic for [<$nt Error_>] {
fn describe(&self) -> Vec {
use crate::{
diagnose::Annotate,
fmt::{DisplayWrapper, TtQuote},
parse::Token,
xir::{
EleSpan,
fmt::TtCloseXmlEle,
},
};
match self {
Self::UnexpectedEle(_, ospan) => ospan.error(
format!(
"expected {ele_name} here",
ele_name = TtQuote::wrap($nt::matcher())
)
).into(),
Self::CloseExpected(qname, ospan, tok) => vec![
ospan.span().note("element starts here"),
tok.span().error(format!(
"expected {}",
TtCloseXmlEle::wrap(qname),
)),
],
Self::Attrs(e) => e.describe(),
}
}
}
impl crate::parse::ParseState for $nt {
type Token = crate::xir::flat::XirfToken<
crate::xir::flat::RefinedText
>;
type Object = $objty;
type Error = [<$nt Error_>];
type Context = crate::xir::parse::StateStackContext;
type Super = $super;
fn parse_token(
self,
tok: Self::Token,
#[allow(unused_variables)] // used only if child NTs
stack: &mut Self::Context,
) -> crate::parse::TransitionResult {
use crate::{
parse::{EmptyContext, Transition, Transitionable},
xir::{
EleSpan,
flat::XirfToken,
parse::parse_attrs,
},
};
use $nt::{
Attrs_, Expecting_, NonPreemptableExpecting_,
RecoverEleIgnore_, CloseRecoverIgnore_,
RecoverEleIgnoreClosed_, ExpectClose_, Closed_
};
match (self, tok) {
(
Expecting_ | NonPreemptableExpecting_,
XirfToken::Open(qname, span, depth)
) if $nt::matches(qname) => {
let transition = Transition(Attrs_(
(qname, span, depth),
parse_attrs(qname, span)
));
// Streaming attribute parsing will cause the
// attribute map to be yielded immediately as
// the opening object,
// since we will not be aggregating attrs.
$(
// Used only to match on `[attr]`.
let [<_ $attr_stream_binding>] = ();
return transition.ok($attrmap);
)?
// If the `[attr]` special form was _not_
// provided,
// we'll be aggregating attributes.
#[allow(unreachable_code)]
transition.incomplete()
},
(
Closed_(..),
XirfToken::Open(qname, span, depth)
) if Self::matches(qname) => {
Transition(Attrs_(
(qname, span, depth),
parse_attrs(qname, span)
)).incomplete()
},
// We only attempt recovery when encountering an
// unknown token if we're forced to accept that
// token.
(
NonPreemptableExpecting_,
XirfToken::Open(qname, span, depth)
) => {
Transition(RecoverEleIgnore_(qname, span, depth)).err(
[<$nt Error_>]::UnexpectedEle(qname, span.name_span())
)
},
(
RecoverEleIgnore_(qname, _, depth_open),
XirfToken::Close(_, span, depth_close)
) if depth_open == depth_close => {
Transition(
RecoverEleIgnoreClosed_(qname, span)
).incomplete()
},
// Streaming attribute matching takes precedence
// over aggregate.
// This is primarily me being lazy,
// because it's not worth a robust syntax for
// something that's rarely used
// (macro-wise, I mean;
// it's heavily utilized as a percentage of
// source file parsed since short-hand
// template applications are heavily used).
$(
(
st @ Attrs_(..),
XirfToken::Attr($attr_stream_binding),
) => Transition(st).ok($attr_stream_map),
// Override the aggregate attribute parser
// delegation by forcing the below match to
// become unreachable
// (xref anchor <>).
// Since we have already emitted the `$attrmap`
// object on `Open`,
// this yields an incomplete parse.
(Attrs_(meta, _), tok) => {
ele_parse!(@!ntref_delegate
stack,
$ntfirst(meta),
$ntfirst_st,
Transition($ntfirst_st::default())
.incomplete()
.with_lookahead(tok),
Transition($ntfirst(meta))
.incomplete()
.with_lookahead(tok)
)
}
)?
// This becomes unreachable when the `[attr]` special
// form is provided,
// which overrides this match directly above
// (xref <>).
#[allow(unreachable_patterns)]
(Attrs_(meta @ (qname, span, depth), sa), tok) => {
sa.delegate_until_obj::(
tok,
EmptyContext,
|sa| Transition(Attrs_(meta, sa)),
// If we enter a dead state then we have
// failed produce an attribute object,
// in which case we'll recover by
// ignoring the entire element.
|| Transition(RecoverEleIgnore_(qname, span, depth)),
|#[allow(unused_variables)] sa, attrs| {
let obj = match attrs {
// Attribute field bindings for `$attrmap`
[<$nt Attrs_>] {
$(
$field,
)*
} => {
// Optional `OpenSpan` binding
let _ = qname; // avoid unused warning
$(
use crate::xir::parse::attr::AttrParseState;
let $qname_matched = qname;
let $open_span = sa.element_span();
)?
$attrmap
},
};
// Lookahead is added by `delegate_until_obj`.
ele_parse!(@!ntref_delegate
stack,
$ntfirst(meta),
$ntfirst_st,
Transition(<$ntfirst_st>::default()).ok(obj),
Transition($ntfirst(meta)).ok(obj)
)
}
)
},
$(
// We're transitioning from `(ntprev) -> (ntnext)`.
// If we have a token that matches `ntprev`,
// we can transition _back_ to that state
// rather than transitioning forward.
// We can _only_ do this when we know we are
// transitioning away from this state,
// otherwise we could return to a previous state,
// which violates the semantics of the
// implied DFA.
(
$ntprev(meta),
XirfToken::Open(qname, span, depth)
) if $ntprev_st::matches(qname) => {
let tok = XirfToken::Open(qname, span, depth);
ele_parse!(@!ntref_delegate
stack,
$ntprev(meta),
$ntprev_st,
// This NT said it could process this token,
// so force it to either do so or error,
// to ensure that bugs don't cause
// infinite processing of lookahead.
Transition(<$ntprev_st>::NonPreemptableExpecting_)
.incomplete()
.with_lookahead(tok),
Transition($ntprev(meta)).incomplete().with_lookahead(tok)
)
},
($ntprev(meta), tok) => {
ele_parse!(@!ntref_delegate
stack,
$ntnext(meta),
$ntnext_st,
Transition(<$ntnext_st>::default())
.incomplete()
.with_lookahead(tok),
Transition($ntnext(meta)).incomplete().with_lookahead(tok)
)
},
// Since `ExpectClose_` does not have an
// `$ntprev` match,
// we have to handle transitioning back to
// the previous state as a special case.
// Further,
// we choose to transition back to this state
// _no matter what the element_,
// to force error recovery and diagnostics
// in that context,
// which will tell the user what elements
// were expected in the last NT rather
// than just telling them a closing tag
// was expected.
//
// To avoid a bunch of rework of this macro
// (which can hopefully be done in the future),
// this match is output for _every_ NT,
// but takes effect only for the final NT
// because of the `is_last_nt` predicate.
// _It is important that it only affect the
// final NT_,
// otherwise we'll transition back to _any_
// previous state at the close,
// which completely defeats the purpose of
// having ordered states.
(
ExpectClose_(meta),
XirfToken::Open(qname, span, depth)
) if $ntprev(meta).is_last_nt() => {
let tok = XirfToken::Open(qname, span, depth);
ele_parse!(@!ntref_delegate
stack,
$ntprev(meta),
$ntprev_st,
// If this NT cannot handle this element,
// it should error and enter recovery
// to ignore it.
Transition(<$ntprev_st>::NonPreemptableExpecting_)
.incomplete()
.with_lookahead(tok),
Transition(ExpectClose_(meta))
.incomplete()
.with_lookahead(tok)
)
},
)*
// XIRF ensures proper nesting,
// so we do not need to check the element name.
(
ExpectClose_((qname, _, depth))
| CloseRecoverIgnore_((qname, _, depth), _),
XirfToken::Close(_, span, tok_depth)
) if tok_depth == depth => {
$(
let $close_span = span;
)?
$closemap.transition(Closed_(Some(qname), span.tag_span()))
},
(ExpectClose_(meta @ (qname, otspan, _)), unexpected_tok) => {
use crate::parse::Token;
Transition(
CloseRecoverIgnore_(meta, unexpected_tok.span())
).err([<$nt Error_>]::CloseExpected(qname, otspan, unexpected_tok))
}
// We're still in recovery,
// so this token gets thrown out.
(st @ (RecoverEleIgnore_(..) | CloseRecoverIgnore_(..)), _) => {
Transition(st).incomplete()
},
// TODO: Use `is_accepting` guard if we do not utilize
// exhaustiveness check.
(
st @ (
Expecting_
| Closed_(..)
| RecoverEleIgnoreClosed_(..)
),
tok
) => {
Transition(st).dead(tok)
}
todo => todo!("{todo:?}"),
}
}
fn is_accepting(&self, _: &Self::Context) -> bool {
matches!(*self, Self::Closed_(..) | Self::RecoverEleIgnoreClosed_(..))
}
}
}
};
(@!ele_dfn_sum <$objty:ty> $vis:vis $super:ident
$(#[$nt_attr:meta])* $nt:ident [$($ntref:ident)*]
) => {
paste::paste! {
$(#[$nt_attr])*
///
#[doc=concat!(
"Parser expecting one of ",
$("[`", stringify!($ntref), "`], ",)*
"."
)]
#[derive(Debug, PartialEq, Eq, Default)]
$vis enum $nt {
#[default]
#[doc(hidden)]
Expecting_,
/// Non-preemptable [`Self::Expecting_`].
#[doc(hidden)]
#[allow(dead_code)] // used by superstate node preemption
NonPreemptableExpecting_,
/// Recovery state ignoring all remaining tokens for this
/// element.
#[doc(hidden)]
RecoverEleIgnore_(
crate::xir::QName,
crate::xir::OpenSpan,
crate::xir::flat::Depth,
),
}
impl $nt {
// Whether the given QName would be matched by any of the
// parsers associated with this type.
//
// This is short-circuiting and will return as soon as one
// parser is found,
// so it may be a good idea to order the sum type
// according to the most likely value to be encountered.
// At its worst,
// this may be equivalent to a linear search of the
// parsers.
// With that said,
// Rust/LLVM may optimize this in any number of ways,
// especially if each inner parser matches on a QName
// constant.
// Let a profiler and disassembly guide you.
#[allow(dead_code)] // used by superstate
fn matches(qname: crate::xir::QName) -> bool {
// If we used an array or a trait,
// then we'd need everything to be a similar type;
// this allows for _any_ type provided that it
// expands into something that contains a `matches`
// associated function of a compatible type.
false $(|| $ntref::matches(qname))*
}
// Number of
// [`NodeMatcher`](crate::xir::parse::NodeMatcher)s
// considered by this parser.
//
// This is the sum of the number of matches of each
// constituent NT.
const fn matches_n() -> usize {
// Count the number of NTs by adding the number of
// matches in each.
0 $(+ $ntref::matches_n())*
}
/// Format constituent NTs for display.
///
/// This function receives the number of values to be
/// formatted as `n` and the current 0-indexed offset
/// within that list as `i`.
/// This allows for zero-copy rendering of composable NTs.
///
/// See also [`SumNt::fmt_matches_top`] to initialize the
/// formatting process with the correct values.
///
/// [`SumNt::fmt_matches_top`]: crate::xir::parse::SumNt
fn fmt_matches(
n: usize,
i: &mut usize,
f: &mut std::fmt::Formatter
) -> std::fmt::Result {
$(
$ntref::fmt_matches(n, i, f)?;
)*
Ok(())
}
/// Whether the parser is in a state that can tolerate
/// superstate node preemption.
///
/// For more information,
/// see the superstate
#[doc=concat!(
" [`", stringify!($super), "::can_preempt_node`]."
)]
fn can_preempt_node(&self) -> bool {
use $nt::*;
match self {
// Preemption before the opening tag is safe,
// since we haven't started processing yet.
Expecting_ => true,
// The name says it all.
// Instantiated by the superstate.
NonPreemptableExpecting_ => false,
// Preemption during recovery would cause tokens to
// be parsed when they ought to be ignored,
// so we must process all tokens during recovery.
RecoverEleIgnore_(..) => false,
}
}
}
impl crate::xir::parse::SumNt for $nt {
/// Begin formatting using [`Self::fmt_matches`].
///
/// This provides the initial values for the function.
fn fmt_matches_top(f: &mut std::fmt::Formatter) -> std::fmt::Result {
Self::fmt_matches(Self::matches_n().saturating_sub(1), &mut 0, f)
}
}
impl std::fmt::Display for $nt {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
use crate::{
fmt::{DisplayWrapper, TtQuote},
xir::parse::SumNt
};
match self {
Self::Expecting_
| Self::NonPreemptableExpecting_ => {
write!(f, "expecting ")?;
::fmt_matches_top(f)
},
Self::RecoverEleIgnore_(name, _, _) => {
write!(
f,
"attempting to recover by ignoring element \
with unexpected name {given} \
(expected",
given = TtQuote::wrap(name),
)?;
::fmt_matches_top(f)?;
f.write_str(")")
}
}
}
}
// Used by superstate sum type.
#[doc(hidden)]
type [<$nt Error_>] = crate::xir::parse::SumNtError<$nt>;
impl crate::parse::ParseState for $nt {
type Token = crate::xir::flat::XirfToken<
crate::xir::flat::RefinedText
>;
type Object = $objty;
type Error = [<$nt Error_>];
type Context = crate::xir::parse::StateStackContext;
type Super = $super;
fn parse_token(
self,
tok: Self::Token,
stack: &mut Self::Context,
) -> crate::parse::TransitionResult {
use crate::{
parse::Transition,
xir::{
flat::XirfToken,
EleSpan,
},
};
use $nt::{
Expecting_, NonPreemptableExpecting_, RecoverEleIgnore_,
};
match (self, tok) {
$(
(
st @ (Expecting_ | NonPreemptableExpecting_),
XirfToken::Open(qname, span, depth)
) if $ntref::matches(qname) => {
ele_parse!(@!ntref_delegate
stack,
Expecting_,
$ntref,
Transition(
// Propagate non-preemption status,
// otherwise we'll provide a
// lookback of the original token
// and end up recursing until we
// hit the `stack` limit.
match st {
NonPreemptableExpecting_ => {
$ntref::NonPreemptableExpecting_
}
_ => {
$ntref::default()
}
}
).incomplete().with_lookahead(
XirfToken::Open(qname, span, depth)
),
unreachable!("TODO: remove me (ntref_delegate done)")
)
},
(
NonPreemptableExpecting_,
XirfToken::Open(qname, span, depth)
) if $ntref::matches(qname) => {
ele_parse!(@!ntref_delegate
stack,
Expecting_,
$ntref,
Transition(
$ntref::NonPreemptableExpecting_
).incomplete().with_lookahead(
XirfToken::Open(qname, span, depth)
),
unreachable!("TODO: remove me (ntref_delegate done)")
)
},
)*
// If we're non-preemptable,
// then we're expected to be able to process this
// token or fail trying.
(
NonPreemptableExpecting_,
XirfToken::Open(qname, span, depth)
) => {
Transition(RecoverEleIgnore_(qname, span, depth)).err(
// Use name span rather than full `OpenSpan`
// since it's specifically the name that
// was unexpected,
// not the fact that it's an element.
Self::Error::UnexpectedEle(
qname,
span.name_span(),
Default::default(),
)
)
},
// An unexpected token when repeating ends
// repetition and should not result in an error.
(
Expecting_ | NonPreemptableExpecting_,
tok
) => Transition(Expecting_).dead(tok),
// XIRF ensures that the closing tag matches the opening,
// so we need only check depth.
(
RecoverEleIgnore_(_, _, depth_open),
XirfToken::Close(_, _, depth_close)
) if depth_open == depth_close => {
Transition(Expecting_).incomplete()
},
(st @ RecoverEleIgnore_(..), _) => {
Transition(st).incomplete()
},
}
}
fn is_accepting(&self, _: &Self::Context) -> bool {
matches!(self, Self::Expecting_)
}
}
}
};
// Generate superstate sum type.
//
// This is really annoying because we cannot read the output of another
// macro,
// and so we have to do our best to re-parse the body of the
// original `ele_parse!` invocation without duplicating too much
// logic,
// and we have to do so in a way that we can aggregate all of
// those data.
(@!super_sum <$objty:ty> $(#[$super_attr:meta])* $vis:vis $super:ident
$(
[super] {
// Non-whitespace text nodes can be mapped into elements
// with the given QName as a preprocessing step,
// allowing them to reuse the existing element NT system.
$([text]($text:ident, $text_span:ident) => $text_map:expr,)?
// Optional _single_ NT to preempt arbitrary elements.
// Sum NTs can be used to preempt multiple elements.
$($pre_nt:ident)?
}
)?
$(
// NT definition is always followed by `:=`.
$(#[$_ident_attr:meta])*
$nt:ident :=
// Identifier if an element NT.
$($_i:ident)?
// Parenthesis for a sum NT,
// or possibly the span match for an element NT.
// So: `:= QN_IDENT(span)` or `:= (A | B | C)`.
$( ($($_p:tt)*) )?
// Braces for an element NT body.
$( {$($_b:tt)*} )?
// Element and sum NT both conclude with a semicolon,
// which we need to disambiguate the next `$nt`.
;
)*
) => {
paste::paste! {
$(#[$super_attr])*
///
/// Superstate representing the union of all related parsers.
///
/// This [`ParseState`] allows sub-parsers to independently
/// the states associated with their own subgraph,
/// and then yield a state transition directly to a state of
/// another parser.
/// This is conceptually like CPS (continuation passing style),
/// where this [`ParseState`] acts as a trampoline.
///
/// This [`ParseState`] is required for use with [`Parser`];
/// see [`ClosedParseState`] for more information.
///
/// [`Parser`]: crate::parse::Parser
/// [`ParseState`]: crate::parse::ParseState
/// [`ClosedParseState`]: crate::parse::ClosedParseState
#[derive(Debug, PartialEq, Eq)]
$vis enum $super {
$(
$nt($nt),
)*
}
// Default parser is the first NT,
// and is non-preemptable to force error handling if the root
// node is unexpected.
// Note that this also prevents preemption at the root,
// which is necessary for now anyway since we need to be able
// to statically resolve imports without template expansion in
// NIR
// (otherwise we have a chicken-and-egg problem).
impl Default for $super {
fn default() -> Self {
ele_parse!(@!ntfirst_init $super, $($nt)*)
}
}
$(
impl From<$nt> for $super {
fn from(st: $nt) -> Self {
$super::$nt(st)
}
}
)*
impl std::fmt::Display for $super {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self {
$(
Self::$nt(e) => std::fmt::Display::fmt(e, f),
)*
}
}
}
/// Superstate error object representing the union of all
/// related parsers' errors.
#[derive(Debug, PartialEq)]
$vis enum [<$super Error_>] {
$(
$nt([<$nt Error_>]),
)*
}
$(
impl From<[<$nt Error_>]> for [<$super Error_>] {
fn from(e: [<$nt Error_>]) -> Self {
[<$super Error_>]::$nt(e)
}
}
)*
impl std::error::Error for [<$super Error_>] {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
// TODO
None
}
}
impl std::fmt::Display for [<$super Error_>] {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self {
$(
Self::$nt(e) => std::fmt::Display::fmt(e, f),
)*
}
}
}
impl crate::diagnose::Diagnostic for [<$super Error_>] {
fn describe(&self) -> Vec {
match self {
$(
Self::$nt(e) => e.describe(),
)*
}
}
}
impl crate::parse::ParseState for $super {
type Token = crate::xir::flat::XirfToken<
crate::xir::flat::RefinedText
>;
type Object = $objty;
type Error = [<$super Error_>];
type Context = crate::xir::parse::StateStackContext;
fn parse_token(
self,
tok: Self::Token,
stack: &mut Self::Context,
) -> crate::parse::TransitionResult {
use crate::{
parse::Transition,
xir::flat::{XirfToken, RefinedText},
};
// Used only by _some_ expansions.
#[allow(unused_imports)]
use crate::xir::flat::Text;
match (self, tok) {
// [super] {
$(
// [text] preemption;
// see `Self::can_preempt_node`.
$(
(
st,
XirfToken::Text(
RefinedText::Unrefined(
Text($text, $text_span)
),
_,
)
) if st.can_preempt_node() => {
Transition(st).ok($text_map)
},
)?
// Preemption NT
$(
(
st,
XirfToken::Open(
qname,
ospan,
depth,
),
) if st.can_preempt_node() && $pre_nt::matches(qname) => {
stack.transfer_with_ret(
Transition(st),
Transition(
// Prevent recursing on this token.
$pre_nt::NonPreemptableExpecting_
)
.incomplete()
.with_lookahead(XirfToken::Open(
qname,
ospan,
depth,
)),
)
},
)?
)?
// }
// Depth check is unnecessary since _all_ xir::parse
// parsers
// (at least at the time of writing)
// ignore whitespace and comments,
// so may as well return early.
// TODO: I'm ignoring _all_ text for now to
// proceed with development; fix.
(
st,
XirfToken::Text(RefinedText::Whitespace(..), _)
| XirfToken::Comment(..)
) => {
Transition(st).incomplete()
}
$(
// Pass token directly to child until it reports
// a dead state,
// after which we return to the `ParseState`
// atop of the stack.
(Self::$nt(st), tok) => st.delegate_child(
tok,
stack,
|deadst, tok, stack| {
stack.ret_or_dead(tok, deadst)
},
),
)*
}
}
fn is_accepting(&self, stack: &Self::Context) -> bool {
// This is short-circuiting,
// starting at the _bottom_ of the stack and
// moving upward.
// The idea is that,
// is we're still in the middle of parsing,
// then it's almost certain that the [`ParseState`] on
// the bottom of the stack will not be in an
// accepting state,
// and so we can stop checking early.
// In most cases,
// if we haven't hit EOF early,
// the stack should be either empty or consist of only
// the root state.
//
// After having considered the stack,
// we can then consider the active `ParseState`.
stack.all(|st| st.is_inner_accepting(stack))
&& self.is_inner_accepting(stack)
}
}
impl $super {
/// Whether the inner (active child) [`ParseState`] is in an
/// accepting state.
///
/// [`ParseState`]: crate::parse::ParseState
fn is_inner_accepting(
&self,
ctx: &::Context
) -> bool {
use crate::parse::ParseState;
match self {
$(
Self::$nt(st) => st.is_accepting(ctx),
)*
}
}
/// Whether the inner parser is in a state that can tolerate
/// superstate node preemption.
///
/// Node preemption allows us (the superstate) to ask for
/// permission from the inner parser to parse some token
/// ourselves,
/// by asking whether the parser is in a state that
/// would cause semantic issues if we were to do so.
///
/// For example,
/// if we were to preempt text nodes while an inner parser
/// was still parsing attributes,
/// then we would emit an object associated with that
/// text before the inner parser had a chance to
/// conclude that attribute parsing has completed and
/// emit the opening object for that node;
/// the result would otherwise be an incorrect
/// `Text, Open` instead of the correct `Open, Text`,
/// which would effectively unparent the text.
/// Similarly,
/// if we were to parse our own tokens while an inner
/// parser was performing error recovery in such a way as
/// to ignore all child tokens,
/// then we would emit an object in an incorrect
/// context.
#[allow(dead_code)] // TODO: Remove when using for tpl apply
fn can_preempt_node(&self) -> bool {
match self {
$(
Self::$nt(st) => st.can_preempt_node(),
)*
}
}
}
}
};
(@!ntfirst_init $super:ident, $ntfirst:ident $($nt:ident)*) => {
$super::$ntfirst($ntfirst::NonPreemptableExpecting_)
}
}
/// Sum nonterminal.
///
/// This trait is used internally by the [`ele_parse!`] parser-generator.
pub trait SumNt: Debug {
fn fmt_matches_top(f: &mut std::fmt::Formatter) -> std::fmt::Result;
}
/// Error during parsing of a sum nonterminal.
#[derive(Debug, PartialEq)]
pub enum SumNtError {
UnexpectedEle(QName, Span, PhantomData),
}
impl Error for SumNtError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
None
}
}
impl Display for SumNtError {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
use crate::xir::fmt::TtOpenXmlEle;
match self {
Self::UnexpectedEle(qname, _, _) => {
write!(f, "unexpected {}", TtOpenXmlEle::wrap(qname))
}
}
}
}
impl Diagnostic for SumNtError {
fn describe(&self) -> Vec {
use crate::{diagnose::Annotate, fmt::DisplayFn};
// Note that we should place expected values in the help
// footnote rather than the span label because it can
// get rather long.
// Maybe in the future the diagnostic renderer can be
// smart about that based on the terminal width and
// automatically move into the footer.
match self {
Self::UnexpectedEle(qname, span, _) => span
.error(format!(
"element {name} cannot appear here",
name = TtQuote::wrap(qname),
))
.with_help(format!(
"expecting {}",
DisplayFn(NT::fmt_matches_top)
))
.into(),
}
}
}
#[cfg(test)]
mod test;