1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772
//! This is an NFA-based parser, which calls out to the main Rust parser for named non-terminals
//! (which it commits to fully when it hits one in a grammar). There's a set of current NFA threads
//! and a set of next ones. Instead of NTs, we have a special case for Kleene star. The big-O, in
//! pathological cases, is worse than traditional use of NFA or Earley parsing, but it's an easier
//! fit for Macro-by-Example-style rules.
//!
//! (In order to prevent the pathological case, we'd need to lazily construct the resulting
//! `NamedMatch`es at the very end. It'd be a pain, and require more memory to keep around old
//! matcher positions, but it would also save overhead)
//!
//! We don't say this parser uses the Earley algorithm, because it's unnecessarily inaccurate.
//! The macro parser restricts itself to the features of finite state automata. Earley parsers
//! can be described as an extension of NFAs with completion rules, prediction rules, and recursion.
//!
//! Quick intro to how the parser works:
//!
//! A "matcher position" (a.k.a. "position" or "mp") is a dot in the middle of a matcher, usually
//! written as a `·`. For example `· a $( a )* a b` is one, as is `a $( · a )* a b`.
//!
//! The parser walks through the input a token at a time, maintaining a list
//! of threads consistent with the current position in the input string: `cur_mps`.
//!
//! As it processes them, it fills up `eof_mps` with threads that would be valid if
//! the macro invocation is now over, `bb_mps` with threads that are waiting on
//! a Rust non-terminal like `$e:expr`, and `next_mps` with threads that are waiting
//! on a particular token. Most of the logic concerns moving the · through the
//! repetitions indicated by Kleene stars. The rules for moving the · without
//! consuming any input are called epsilon transitions. It only advances or calls
//! out to the real Rust parser when no `cur_mps` threads remain.
//!
//! Example:
//!
//! ```text, ignore
//! Start parsing a a a a b against [· a $( a )* a b].
//!
//! Remaining input: a a a a b
//! next: [· a $( a )* a b]
//!
//! - - - Advance over an a. - - -
//!
//! Remaining input: a a a b
//! cur: [a · $( a )* a b]
//! Descend/Skip (first position).
//! next: [a $( · a )* a b] [a $( a )* · a b].
//!
//! - - - Advance over an a. - - -
//!
//! Remaining input: a a b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first position)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over an a. - - - (this looks exactly like the last step)
//!
//! Remaining input: a b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first position)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over an a. - - - (this looks exactly like the last step)
//!
//! Remaining input: b
//! cur: [a $( a · )* a b] [a $( a )* a · b]
//! Follow epsilon transition: Finish/Repeat (first position)
//! next: [a $( a )* · a b] [a $( · a )* a b] [a $( a )* a · b]
//!
//! - - - Advance over a b. - - -
//!
//! Remaining input: ''
//! eof: [a $( a )* a b ·]
//! ```
pub(crate) use NamedMatch::*;
pub(crate) use ParseResult::*;
use crate::mbe::{macro_rules::Tracker, KleeneOp, TokenTree};
use rustc_ast::token::{self, DocComment, Nonterminal, NonterminalKind, Token};
use rustc_ast_pretty::pprust;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lrc;
use rustc_errors::ErrorGuaranteed;
use rustc_lint_defs::pluralize;
use rustc_parse::parser::{ParseNtResult, Parser};
use rustc_span::symbol::Ident;
use rustc_span::symbol::MacroRulesNormalizedIdent;
use rustc_span::Span;
use std::borrow::Cow;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use std::fmt::Display;
use std::rc::Rc;
/// A unit within a matcher that a `MatcherPos` can refer to. Similar to (and derived from)
/// `mbe::TokenTree`, but designed specifically for fast and easy traversal during matching.
/// Notable differences to `mbe::TokenTree`:
/// - It is non-recursive, i.e. there is no nesting.
/// - The end pieces of each sequence (the separator, if present, and the Kleene op) are
/// represented explicitly, as is the very end of the matcher.
///
/// This means a matcher can be represented by `&[MatcherLoc]`, and traversal mostly involves
/// simply incrementing the current matcher position index by one.
#[derive(Debug, PartialEq, Clone)]
pub(crate) enum MatcherLoc {
Token {
token: Token,
},
Delimited,
Sequence {
op: KleeneOp,
num_metavar_decls: usize,
idx_first_after: usize,
next_metavar: usize,
seq_depth: usize,
},
SequenceKleeneOpNoSep {
op: KleeneOp,
idx_first: usize,
},
SequenceSep {
separator: Token,
},
SequenceKleeneOpAfterSep {
idx_first: usize,
},
MetaVarDecl {
span: Span,
bind: Ident,
kind: Option<NonterminalKind>,
next_metavar: usize,
seq_depth: usize,
},
Eof,
}
impl MatcherLoc {
pub(super) fn span(&self) -> Option<Span> {
match self {
MatcherLoc::Token { token } => Some(token.span),
MatcherLoc::Delimited => None,
MatcherLoc::Sequence { .. } => None,
MatcherLoc::SequenceKleeneOpNoSep { .. } => None,
MatcherLoc::SequenceSep { .. } => None,
MatcherLoc::SequenceKleeneOpAfterSep { .. } => None,
MatcherLoc::MetaVarDecl { span, .. } => Some(*span),
MatcherLoc::Eof => None,
}
}
}
impl Display for MatcherLoc {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
MatcherLoc::Token { token } | MatcherLoc::SequenceSep { separator: token } => {
write!(f, "`{}`", pprust::token_to_string(token))
}
MatcherLoc::MetaVarDecl { bind, kind, .. } => {
write!(f, "meta-variable `${bind}")?;
if let Some(kind) = kind {
write!(f, ":{kind}")?;
}
write!(f, "`")?;
Ok(())
}
MatcherLoc::Eof => f.write_str("end of macro"),
// These are not printed in the diagnostic
MatcherLoc::Delimited => f.write_str("delimiter"),
MatcherLoc::Sequence { .. } => f.write_str("sequence start"),
MatcherLoc::SequenceKleeneOpNoSep { .. } => f.write_str("sequence end"),
MatcherLoc::SequenceKleeneOpAfterSep { .. } => f.write_str("sequence end"),
}
}
}
pub(super) fn compute_locs(matcher: &[TokenTree]) -> Vec<MatcherLoc> {
fn inner(
tts: &[TokenTree],
locs: &mut Vec<MatcherLoc>,
next_metavar: &mut usize,
seq_depth: usize,
) {
for tt in tts {
match tt {
TokenTree::Token(token) => {
locs.push(MatcherLoc::Token { token: token.clone() });
}
TokenTree::Delimited(span, delimited) => {
let open_token = Token::new(token::OpenDelim(delimited.delim), span.open);
let close_token = Token::new(token::CloseDelim(delimited.delim), span.close);
locs.push(MatcherLoc::Delimited);
locs.push(MatcherLoc::Token { token: open_token });
inner(&delimited.tts, locs, next_metavar, seq_depth);
locs.push(MatcherLoc::Token { token: close_token });
}
TokenTree::Sequence(_, seq) => {
// We can't determine `idx_first_after` and construct the final
// `MatcherLoc::Sequence` until after `inner()` is called and the sequence end
// pieces are processed. So we push a dummy value (`Eof` is cheapest to
// construct) now, and overwrite it with the proper value below.
let dummy = MatcherLoc::Eof;
locs.push(dummy);
let next_metavar_orig = *next_metavar;
let op = seq.kleene.op;
let idx_first = locs.len();
let idx_seq = idx_first - 1;
inner(&seq.tts, locs, next_metavar, seq_depth + 1);
if let Some(separator) = &seq.separator {
locs.push(MatcherLoc::SequenceSep { separator: separator.clone() });
locs.push(MatcherLoc::SequenceKleeneOpAfterSep { idx_first });
} else {
locs.push(MatcherLoc::SequenceKleeneOpNoSep { op, idx_first });
}
// Overwrite the dummy value pushed above with the proper value.
locs[idx_seq] = MatcherLoc::Sequence {
op,
num_metavar_decls: seq.num_captures,
idx_first_after: locs.len(),
next_metavar: next_metavar_orig,
seq_depth,
};
}
&TokenTree::MetaVarDecl(span, bind, kind) => {
locs.push(MatcherLoc::MetaVarDecl {
span,
bind,
kind,
next_metavar: *next_metavar,
seq_depth,
});
*next_metavar += 1;
}
TokenTree::MetaVar(..) | TokenTree::MetaVarExpr(..) => unreachable!(),
}
}
}
let mut locs = vec![];
let mut next_metavar = 0;
inner(matcher, &mut locs, &mut next_metavar, /* seq_depth */ 0);
// A final entry is needed for eof.
locs.push(MatcherLoc::Eof);
locs
}
/// A single matcher position, representing the state of matching.
#[derive(Debug)]
struct MatcherPos {
/// The index into `TtParser::locs`, which represents the "dot".
idx: usize,
/// The matches made against metavar decls so far. On a successful match, this vector ends up
/// with one element per metavar decl in the matcher. Each element records token trees matched
/// against the relevant metavar by the black box parser. An element will be a `MatchedSeq` if
/// the corresponding metavar decl is within a sequence.
///
/// It is critical to performance that this is an `Rc`, because it gets cloned frequently when
/// processing sequences. Mostly for sequence-ending possibilities that must be tried but end
/// up failing.
matches: Rc<Vec<NamedMatch>>,
}
// This type is used a lot. Make sure it doesn't unintentionally get bigger.
#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
rustc_data_structures::static_assert_size!(MatcherPos, 16);
impl MatcherPos {
/// Adds `m` as a named match for the `metavar_idx`-th metavar. There are only two call sites,
/// and both are hot enough to be always worth inlining.
#[inline(always)]
fn push_match(&mut self, metavar_idx: usize, seq_depth: usize, m: NamedMatch) {
let matches = Rc::make_mut(&mut self.matches);
match seq_depth {
0 => {
// We are not within a sequence. Just append `m`.
assert_eq!(metavar_idx, matches.len());
matches.push(m);
}
_ => {
// We are within a sequence. Find the final `MatchedSeq` at the appropriate depth
// and append `m` to its vector.
let mut curr = &mut matches[metavar_idx];
for _ in 0..seq_depth - 1 {
match curr {
MatchedSeq(seq) => curr = seq.last_mut().unwrap(),
_ => unreachable!(),
}
}
match curr {
MatchedSeq(seq) => seq.push(m),
_ => unreachable!(),
}
}
}
}
}
enum EofMatcherPositions {
None,
One(MatcherPos),
Multiple,
}
/// Represents the possible results of an attempted parse.
pub(crate) enum ParseResult<T, F> {
/// Parsed successfully.
Success(T),
/// Arm failed to match. If the second parameter is `token::Eof`, it indicates an unexpected
/// end of macro invocation. Otherwise, it indicates that no rules expected the given token.
/// The usize is the approximate position of the token in the input token stream.
Failure(F),
/// Fatal error (malformed macro?). Abort compilation.
Error(rustc_span::Span, String),
ErrorReported(ErrorGuaranteed),
}
/// A `ParseResult` where the `Success` variant contains a mapping of
/// `MacroRulesNormalizedIdent`s to `NamedMatch`es. This represents the mapping
/// of metavars to the token trees they bind to.
pub(crate) type NamedParseResult<F> = ParseResult<NamedMatches, F>;
/// Contains a mapping of `MacroRulesNormalizedIdent`s to `NamedMatch`es.
/// This represents the mapping of metavars to the token trees they bind to.
pub(crate) type NamedMatches = FxHashMap<MacroRulesNormalizedIdent, NamedMatch>;
/// Count how many metavars declarations are in `matcher`.
pub(super) fn count_metavar_decls(matcher: &[TokenTree]) -> usize {
matcher
.iter()
.map(|tt| match tt {
TokenTree::MetaVarDecl(..) => 1,
TokenTree::Sequence(_, seq) => seq.num_captures,
TokenTree::Delimited(_, delim) => count_metavar_decls(&delim.tts),
TokenTree::Token(..) => 0,
TokenTree::MetaVar(..) | TokenTree::MetaVarExpr(..) => unreachable!(),
})
.sum()
}
/// `NamedMatch` is a pattern-match result for a single metavar. All
/// `MatchedNonterminal`s in the `NamedMatch` have the same non-terminal type
/// (expr, item, etc).
///
/// The in-memory structure of a particular `NamedMatch` represents the match
/// that occurred when a particular subset of a matcher was applied to a
/// particular token tree.
///
/// The width of each `MatchedSeq` in the `NamedMatch`, and the identity of
/// the `MatchedNtNonTts`s, will depend on the token tree it was applied
/// to: each `MatchedSeq` corresponds to a single repetition in the originating
/// token tree. The depth of the `NamedMatch` structure will therefore depend
/// only on the nesting depth of repetitions in the originating token tree it
/// was derived from.
///
/// In layperson's terms: `NamedMatch` will form a tree representing nested matches of a particular
/// meta variable. For example, if we are matching the following macro against the following
/// invocation...
///
/// ```rust
/// macro_rules! foo {
/// ($($($x:ident),+);+) => {}
/// }
///
/// foo!(a, b, c, d; a, b, c, d, e);
/// ```
///
/// Then, the tree will have the following shape:
///
/// ```ignore (private-internal)
/// # use NamedMatch::*;
/// MatchedSeq([
/// MatchedSeq([
/// MatchedNonterminal(a),
/// MatchedNonterminal(b),
/// MatchedNonterminal(c),
/// MatchedNonterminal(d),
/// ]),
/// MatchedSeq([
/// MatchedNonterminal(a),
/// MatchedNonterminal(b),
/// MatchedNonterminal(c),
/// MatchedNonterminal(d),
/// MatchedNonterminal(e),
/// ])
/// ])
/// ```
#[derive(Debug, Clone)]
pub(crate) enum NamedMatch {
MatchedSeq(Vec<NamedMatch>),
// A metavar match of type `tt`.
MatchedTokenTree(rustc_ast::tokenstream::TokenTree),
// A metavar match of any type other than `tt`.
MatchedNonterminal(Lrc<Nonterminal>),
}
/// Performs a token equality check, ignoring syntax context (that is, an unhygienic comparison)
fn token_name_eq(t1: &Token, t2: &Token) -> bool {
if let (Some((ident1, is_raw1)), Some((ident2, is_raw2))) = (t1.ident(), t2.ident()) {
ident1.name == ident2.name && is_raw1 == is_raw2
} else if let (Some(ident1), Some(ident2)) = (t1.lifetime(), t2.lifetime()) {
ident1.name == ident2.name
} else {
t1.kind == t2.kind
}
}
// Note: the vectors could be created and dropped within `parse_tt`, but to avoid excess
// allocations we have a single vector for each kind that is cleared and reused repeatedly.
pub struct TtParser {
macro_name: Ident,
/// The set of current mps to be processed. This should be empty by the end of a successful
/// execution of `parse_tt_inner`.
cur_mps: Vec<MatcherPos>,
/// The set of newly generated mps. These are used to replenish `cur_mps` in the function
/// `parse_tt`.
next_mps: Vec<MatcherPos>,
/// The set of mps that are waiting for the black-box parser.
bb_mps: Vec<MatcherPos>,
/// Pre-allocate an empty match array, so it can be cloned cheaply for macros with many rules
/// that have no metavars.
empty_matches: Rc<Vec<NamedMatch>>,
}
impl TtParser {
pub(super) fn new(macro_name: Ident) -> TtParser {
TtParser {
macro_name,
cur_mps: vec![],
next_mps: vec![],
bb_mps: vec![],
empty_matches: Rc::new(vec![]),
}
}
pub(super) fn has_no_remaining_items_for_step(&self) -> bool {
self.cur_mps.is_empty()
}
/// Process the matcher positions of `cur_mps` until it is empty. In the process, this will
/// produce more mps in `next_mps` and `bb_mps`.
///
/// # Returns
///
/// `Some(result)` if everything is finished, `None` otherwise. Note that matches are kept
/// track of through the mps generated.
fn parse_tt_inner<'matcher, T: Tracker<'matcher>>(
&mut self,
matcher: &'matcher [MatcherLoc],
token: &Token,
approx_position: usize,
track: &mut T,
) -> Option<NamedParseResult<T::Failure>> {
// Matcher positions that would be valid if the macro invocation was over now. Only
// modified if `token == Eof`.
let mut eof_mps = EofMatcherPositions::None;
while let Some(mut mp) = self.cur_mps.pop() {
let matcher_loc = &matcher[mp.idx];
track.before_match_loc(self, matcher_loc);
match matcher_loc {
MatcherLoc::Token { token: t } => {
// If it's a doc comment, we just ignore it and move on to the next tt in the
// matcher. This is a bug, but #95267 showed that existing programs rely on
// this behaviour, and changing it would require some care and a transition
// period.
//
// If the token matches, we can just advance the parser.
//
// Otherwise, this match has failed, there is nothing to do, and hopefully
// another mp in `cur_mps` will match.
if matches!(t, Token { kind: DocComment(..), .. }) {
mp.idx += 1;
self.cur_mps.push(mp);
} else if token_name_eq(&t, token) {
mp.idx += 1;
self.next_mps.push(mp);
}
}
MatcherLoc::Delimited => {
// Entering the delimiter is trivial.
mp.idx += 1;
self.cur_mps.push(mp);
}
&MatcherLoc::Sequence {
op,
num_metavar_decls,
idx_first_after,
next_metavar,
seq_depth,
} => {
// Install an empty vec for each metavar within the sequence.
for metavar_idx in next_metavar..next_metavar + num_metavar_decls {
mp.push_match(metavar_idx, seq_depth, MatchedSeq(vec![]));
}
if matches!(op, KleeneOp::ZeroOrMore | KleeneOp::ZeroOrOne) {
// Try zero matches of this sequence, by skipping over it.
self.cur_mps.push(MatcherPos {
idx: idx_first_after,
matches: Rc::clone(&mp.matches),
});
}
// Try one or more matches of this sequence, by entering it.
mp.idx += 1;
self.cur_mps.push(mp);
}
&MatcherLoc::SequenceKleeneOpNoSep { op, idx_first } => {
// We are past the end of a sequence with no separator. Try ending the
// sequence. If that's not possible, `ending_mp` will fail quietly when it is
// processed next time around the loop.
let ending_mp = MatcherPos {
idx: mp.idx + 1, // +1 skips the Kleene op
matches: Rc::clone(&mp.matches),
};
self.cur_mps.push(ending_mp);
if op != KleeneOp::ZeroOrOne {
// Try another repetition.
mp.idx = idx_first;
self.cur_mps.push(mp);
}
}
MatcherLoc::SequenceSep { separator } => {
// We are past the end of a sequence with a separator but we haven't seen the
// separator yet. Try ending the sequence. If that's not possible, `ending_mp`
// will fail quietly when it is processed next time around the loop.
let ending_mp = MatcherPos {
idx: mp.idx + 2, // +2 skips the separator and the Kleene op
matches: Rc::clone(&mp.matches),
};
self.cur_mps.push(ending_mp);
if token_name_eq(token, separator) {
// The separator matches the current token. Advance past it.
mp.idx += 1;
self.next_mps.push(mp);
}
}
&MatcherLoc::SequenceKleeneOpAfterSep { idx_first } => {
// We are past the sequence separator. This can't be a `?` Kleene op, because
// they don't permit separators. Try another repetition.
mp.idx = idx_first;
self.cur_mps.push(mp);
}
&MatcherLoc::MetaVarDecl { span, kind, .. } => {
// Built-in nonterminals never start with these tokens, so we can eliminate
// them from consideration. We use the span of the metavariable declaration
// to determine any edition-specific matching behavior for non-terminals.
if let Some(kind) = kind {
if Parser::nonterminal_may_begin_with(kind, token) {
self.bb_mps.push(mp);
}
} else {
// E.g. `$e` instead of `$e:expr`, reported as a hard error if actually used.
// Both this check and the one in `nameize` are necessary, surprisingly.
return Some(Error(span, "missing fragment specifier".to_string()));
}
}
MatcherLoc::Eof => {
// We are past the matcher's end, and not in a sequence. Try to end things.
debug_assert_eq!(mp.idx, matcher.len() - 1);
if *token == token::Eof {
eof_mps = match eof_mps {
EofMatcherPositions::None => EofMatcherPositions::One(mp),
EofMatcherPositions::One(_) | EofMatcherPositions::Multiple => {
EofMatcherPositions::Multiple
}
}
}
}
}
}
// If we reached the end of input, check that there is EXACTLY ONE possible matcher.
// Otherwise, either the parse is ambiguous (which is an error) or there is a syntax error.
if *token == token::Eof {
Some(match eof_mps {
EofMatcherPositions::One(mut eof_mp) => {
// Need to take ownership of the matches from within the `Rc`.
Rc::make_mut(&mut eof_mp.matches);
let matches = Rc::try_unwrap(eof_mp.matches).unwrap().into_iter();
self.nameize(matcher, matches)
}
EofMatcherPositions::Multiple => {
Error(token.span, "ambiguity: multiple successful parses".to_string())
}
EofMatcherPositions::None => Failure(T::build_failure(
Token::new(
token::Eof,
if token.span.is_dummy() { token.span } else { token.span.shrink_to_hi() },
),
approx_position,
"missing tokens in macro arguments",
)),
})
} else {
None
}
}
/// Match the token stream from `parser` against `matcher`.
pub(super) fn parse_tt<'matcher, T: Tracker<'matcher>>(
&mut self,
parser: &mut Cow<'_, Parser<'_>>,
matcher: &'matcher [MatcherLoc],
track: &mut T,
) -> NamedParseResult<T::Failure> {
// A queue of possible matcher positions. We initialize it with the matcher position in
// which the "dot" is before the first token of the first token tree in `matcher`.
// `parse_tt_inner` then processes all of these possible matcher positions and produces
// possible next positions into `next_mps`. After some post-processing, the contents of
// `next_mps` replenish `cur_mps` and we start over again.
self.cur_mps.clear();
self.cur_mps.push(MatcherPos { idx: 0, matches: self.empty_matches.clone() });
loop {
self.next_mps.clear();
self.bb_mps.clear();
// Process `cur_mps` until either we have finished the input or we need to get some
// parsing from the black-box parser done.
let res = self.parse_tt_inner(
matcher,
&parser.token,
parser.approx_token_stream_pos(),
track,
);
if let Some(res) = res {
return res;
}
// `parse_tt_inner` handled all of `cur_mps`, so it's empty.
assert!(self.cur_mps.is_empty());
// Error messages here could be improved with links to original rules.
match (self.next_mps.len(), self.bb_mps.len()) {
(0, 0) => {
// There are no possible next positions AND we aren't waiting for the black-box
// parser: syntax error.
return Failure(T::build_failure(
parser.token.clone(),
parser.approx_token_stream_pos(),
"no rules expected this token in macro call",
));
}
(_, 0) => {
// Dump all possible `next_mps` into `cur_mps` for the next iteration. Then
// process the next token.
self.cur_mps.append(&mut self.next_mps);
parser.to_mut().bump();
}
(0, 1) => {
// We need to call the black-box parser to get some nonterminal.
let mut mp = self.bb_mps.pop().unwrap();
let loc = &matcher[mp.idx];
if let &MatcherLoc::MetaVarDecl {
span,
kind: Some(kind),
next_metavar,
seq_depth,
..
} = loc
{
// We use the span of the metavariable declaration to determine any
// edition-specific matching behavior for non-terminals.
let nt = match parser.to_mut().parse_nonterminal(kind) {
Err(mut err) => {
let guarantee = err.span_label(
span,
format!(
"while parsing argument for this `{kind}` macro fragment"
),
)
.emit();
return ErrorReported(guarantee);
}
Ok(nt) => nt,
};
let m = match nt {
ParseNtResult::Nt(nt) => MatchedNonterminal(Lrc::new(nt)),
ParseNtResult::Tt(tt) => MatchedTokenTree(tt),
};
mp.push_match(next_metavar, seq_depth, m);
mp.idx += 1;
} else {
unreachable!()
}
self.cur_mps.push(mp);
}
(_, _) => {
// Too many possibilities!
return self.ambiguity_error(matcher, parser.token.span);
}
}
assert!(!self.cur_mps.is_empty());
}
}
fn ambiguity_error<F>(
&self,
matcher: &[MatcherLoc],
token_span: rustc_span::Span,
) -> NamedParseResult<F> {
let nts = self
.bb_mps
.iter()
.map(|mp| match &matcher[mp.idx] {
MatcherLoc::MetaVarDecl { bind, kind: Some(kind), .. } => {
format!("{kind} ('{bind}')")
}
_ => unreachable!(),
})
.collect::<Vec<String>>()
.join(" or ");
Error(
token_span,
format!(
"local ambiguity when calling macro `{}`: multiple parsing options: {}",
self.macro_name,
match self.next_mps.len() {
0 => format!("built-in NTs {nts}."),
n => format!("built-in NTs {nts} or {n} other option{s}.", s = pluralize!(n)),
}
),
)
}
fn nameize<I: Iterator<Item = NamedMatch>, F>(
&self,
matcher: &[MatcherLoc],
mut res: I,
) -> NamedParseResult<F> {
// Make that each metavar has _exactly one_ binding. If so, insert the binding into the
// `NamedParseResult`. Otherwise, it's an error.
let mut ret_val = FxHashMap::default();
for loc in matcher {
if let &MatcherLoc::MetaVarDecl { span, bind, kind, .. } = loc {
if kind.is_some() {
match ret_val.entry(MacroRulesNormalizedIdent::new(bind)) {
Vacant(spot) => spot.insert(res.next().unwrap()),
Occupied(..) => {
return Error(span, format!("duplicated bind name: {bind}"));
}
};
} else {
// E.g. `$e` instead of `$e:expr`, reported as a hard error if actually used.
// Both this check and the one in `parse_tt_inner` are necessary, surprisingly.
return Error(span, "missing fragment specifier".to_string());
}
}
}
Success(ret_val)
}
}