1 use crate::base::{DummyResult, ExtCtxt, MacResult, TTMacroExpander};
2 use crate::base::{SyntaxExtension, SyntaxExtensionKind};
3 use crate::expand::{ensure_complete_parse, parse_ast_fragment, AstFragment, AstFragmentKind};
5 use crate::mbe::macro_check;
6 use crate::mbe::macro_parser::parse_tt;
7 use crate::mbe::macro_parser::{Error, ErrorReported, Failure, Success};
8 use crate::mbe::macro_parser::{MatchedNonterminal, MatchedSeq};
9 use crate::mbe::transcribe::transcribe;
12 use rustc_ast::token::{self, NonterminalKind, NtTT, Token, TokenKind::*};
13 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
14 use rustc_ast_pretty::pprust;
15 use rustc_attr::{self as attr, TransparencyError};
16 use rustc_data_structures::fx::FxHashMap;
17 use rustc_data_structures::sync::Lrc;
18 use rustc_errors::{Applicability, DiagnosticBuilder};
19 use rustc_feature::Features;
20 use rustc_parse::parser::Parser;
21 use rustc_session::parse::ParseSess;
22 use rustc_session::Session;
23 use rustc_span::edition::Edition;
24 use rustc_span::hygiene::Transparency;
25 use rustc_span::symbol::{kw, sym, Ident, MacroRulesNormalizedIdent};
29 use std::collections::hash_map::Entry;
30 use std::{mem, slice};
33 crate struct ParserAnyMacro<'a> {
36 /// Span of the expansion site of the macro this parser is for
38 /// The ident of the macro we're parsing
43 crate fn annotate_err_with_kind(
44 err: &mut DiagnosticBuilder<'_>,
45 kind: AstFragmentKind,
49 AstFragmentKind::Ty => {
50 err.span_label(span, "this macro call doesn't expand to a type");
52 AstFragmentKind::Pat => {
53 err.span_label(span, "this macro call doesn't expand to a pattern");
59 /// Instead of e.g. `vec![a, b, c]` in a pattern context, suggest `[a, b, c]`.
60 fn suggest_slice_pat(e: &mut DiagnosticBuilder<'_>, site_span: Span, parser: &Parser<'_>) {
61 let mut suggestion = None;
62 if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
63 if let Some(bang) = code.find('!') {
64 suggestion = Some(code[bang + 1..].to_string());
67 if let Some(suggestion) = suggestion {
70 "use a slice pattern here instead",
72 Applicability::MachineApplicable,
75 e.span_label(site_span, "use a slice pattern here instead");
78 "for more information, see https://doc.rust-lang.org/edition-guide/\
79 rust-2018/slice-patterns.html",
83 fn emit_frag_parse_err(
84 mut e: DiagnosticBuilder<'_>,
86 orig_parser: &mut Parser<'_>,
90 kind: AstFragmentKind,
92 if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
93 if !e.span.is_dummy() {
94 // early end of macro arm (#52866)
95 e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
97 let msg = &e.message[0];
100 "macro expansion ends with an incomplete expression: {}",
101 msg.0.replace(", found `<eof>`", ""),
106 if e.span.is_dummy() {
107 // Get around lack of span in error (#30128)
108 e.replace_span_with(site_span);
109 if !parser.sess.source_map().is_imported(arm_span) {
110 e.span_label(arm_span, "in this macro arm");
112 } else if parser.sess.source_map().is_imported(parser.token.span) {
113 e.span_label(site_span, "in this macro invocation");
116 AstFragmentKind::Pat if macro_ident.name == sym::vec => {
117 suggest_slice_pat(&mut e, site_span, parser);
119 // Try a statement if an expression is wanted but failed and suggest adding `;` to call.
120 AstFragmentKind::Expr => match parse_ast_fragment(orig_parser, AstFragmentKind::Stmts) {
121 Err(mut err) => err.cancel(),
124 "the macro call doesn't expand to an expression, but it can expand to a statement",
126 e.span_suggestion_verbose(
127 site_span.shrink_to_hi(),
128 "add `;` to interpret the expansion as a statement",
130 Applicability::MaybeIncorrect,
134 _ => annotate_err_with_kind(&mut e, kind, site_span),
139 impl<'a> ParserAnyMacro<'a> {
140 crate fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
141 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
142 let snapshot = &mut parser.clone();
143 let fragment = match parse_ast_fragment(parser, kind) {
146 emit_frag_parse_err(err, parser, snapshot, site_span, macro_ident, arm_span, kind);
147 return kind.dummy(site_span);
151 // We allow semicolons at the end of expressions -- e.g., the semicolon in
152 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
153 // but `m!()` is allowed in expression positions (cf. issue #34706).
154 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
158 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
159 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
160 ensure_complete_parse(parser, &path, kind.name(), site_span);
165 struct MacroRulesMacroExpander {
168 transparency: Transparency,
169 lhses: Vec<mbe::TokenTree>,
170 rhses: Vec<mbe::TokenTree>,
174 impl TTMacroExpander for MacroRulesMacroExpander {
177 cx: &'cx mut ExtCtxt<'_>,
180 ) -> Box<dyn MacResult + 'cx> {
182 return DummyResult::any(sp);
197 fn macro_rules_dummy_expander<'cx>(
198 _: &'cx mut ExtCtxt<'_>,
201 ) -> Box<dyn MacResult + 'cx> {
202 DummyResult::any(span)
205 fn trace_macros_note(cx_expansions: &mut FxHashMap<Span, Vec<String>>, sp: Span, message: String) {
206 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
207 cx_expansions.entry(sp).or_default().push(message);
210 /// Given `lhses` and `rhses`, this is the new macro we create
211 fn generic_extension<'cx>(
212 cx: &'cx mut ExtCtxt<'_>,
216 transparency: Transparency,
218 lhses: &[mbe::TokenTree],
219 rhses: &[mbe::TokenTree],
220 ) -> Box<dyn MacResult + 'cx> {
221 let sess = &cx.sess.parse_sess;
223 if cx.trace_macros() {
224 let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(&arg));
225 trace_macros_note(&mut cx.expansions, sp, msg);
228 // Which arm's failure should we report? (the one furthest along)
229 let mut best_failure: Option<(Token, &str)> = None;
231 // We create a base parser that can be used for the "black box" parts.
232 // Every iteration needs a fresh copy of that parser. However, the parser
233 // is not mutated on many of the iterations, particularly when dealing with
236 // macro_rules! foo {
240 // // ... etc. (maybe hundreds more)
243 // as seen in the `html5ever` benchmark. We use a `Cow` so that the base
244 // parser is only cloned when necessary (upon mutation). Furthermore, we
245 // reinitialize the `Cow` with the base parser at the start of every
246 // iteration, so that any mutated parsers are not reused. This is all quite
247 // hacky, but speeds up the `html5ever` benchmark significantly. (Issue
248 // 68836 suggests a more comprehensive but more complex change to deal with
250 let parser = parser_from_cx(sess, arg.clone());
252 for (i, lhs) in lhses.iter().enumerate() {
253 // try each arm's matchers
254 let lhs_tt = match *lhs {
255 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
256 _ => cx.span_bug(sp, "malformed macro lhs"),
259 // Take a snapshot of the state of pre-expansion gating at this point.
260 // This is used so that if a matcher is not `Success(..)`ful,
261 // then the spans which became gated when parsing the unsuccessful matcher
262 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
263 let mut gated_spans_snapshot = mem::take(&mut *sess.gated_spans.spans.borrow_mut());
265 match parse_tt(&mut Cow::Borrowed(&parser), lhs_tt) {
266 Success(named_matches) => {
267 // The matcher was `Success(..)`ful.
268 // Merge the gated spans from parsing the matcher with the pre-existing ones.
269 sess.gated_spans.merge(gated_spans_snapshot);
271 let rhs = match rhses[i] {
273 mbe::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
274 _ => cx.span_bug(sp, "malformed macro rhs"),
276 let arm_span = rhses[i].span();
278 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
279 // rhs has holes ( `$id` and `$(...)` that need filled)
280 let mut tts = match transcribe(cx, &named_matches, rhs, transparency) {
284 return DummyResult::any(arm_span);
288 // Replace all the tokens for the corresponding positions in the macro, to maintain
289 // proper positions in error reporting, while maintaining the macro_backtrace.
290 if rhs_spans.len() == tts.len() {
291 tts = tts.map_enumerated(|i, mut tt| {
292 let mut sp = rhs_spans[i];
293 sp = sp.with_ctxt(tt.span().ctxt());
299 if cx.trace_macros() {
300 let msg = format!("to `{}`", pprust::tts_to_string(&tts));
301 trace_macros_note(&mut cx.expansions, sp, msg);
304 let mut p = Parser::new(sess, tts, false, None);
305 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
307 // Let the context choose how to interpret the result.
308 // Weird, but useful for X-macros.
309 return Box::new(ParserAnyMacro {
312 // Pass along the original expansion site and the name of the macro
313 // so we can print a useful error message if the parse of the expanded
314 // macro leaves unparsed tokens.
320 Failure(token, msg) => match best_failure {
321 Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
322 _ => best_failure = Some((token, msg)),
324 Error(err_sp, ref msg) => {
325 let span = err_sp.substitute_dummy(sp);
326 cx.struct_span_err(span, &msg).emit();
327 return DummyResult::any(span);
329 ErrorReported => return DummyResult::any(sp),
332 // The matcher was not `Success(..)`ful.
333 // Restore to the state before snapshotting and maybe try again.
334 mem::swap(&mut gated_spans_snapshot, &mut sess.gated_spans.spans.borrow_mut());
338 let (token, label) = best_failure.expect("ran no matchers");
339 let span = token.span.substitute_dummy(sp);
340 let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
341 err.span_label(span, label);
342 if !def_span.is_dummy() && !cx.source_map().is_imported(def_span) {
343 err.span_label(cx.source_map().guess_head_span(def_span), "when calling this macro");
346 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
347 if let Some((arg, comma_span)) = arg.add_comma() {
349 // try each arm's matchers
350 let lhs_tt = match *lhs {
351 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
355 parse_tt(&mut Cow::Borrowed(&parser_from_cx(sess, arg.clone())), lhs_tt)
357 if comma_span.is_dummy() {
358 err.note("you might be missing a comma");
360 err.span_suggestion_short(
362 "missing comma here",
364 Applicability::MachineApplicable,
371 cx.trace_macros_diag();
375 // Note that macro-by-example's input is also matched against a token tree:
376 // $( $lhs:tt => $rhs:tt );+
378 // Holy self-referential!
380 /// Converts a macro item into a syntax extension.
381 pub fn compile_declarative_macro(
386 ) -> SyntaxExtension {
387 debug!("compile_declarative_macro: {:?}", def);
388 let mk_syn_ext = |expander| {
389 SyntaxExtension::new(
391 SyntaxExtensionKind::LegacyBang(expander),
400 let diag = &sess.parse_sess.span_diagnostic;
401 let lhs_nm = Ident::new(sym::lhs, def.span);
402 let rhs_nm = Ident::new(sym::rhs, def.span);
403 let tt_spec = Some(NonterminalKind::TT);
405 // Parse the macro_rules! invocation
406 let (macro_rules, body) = match &def.kind {
407 ast::ItemKind::MacroDef(def) => (def.macro_rules, def.body.inner_tokens()),
411 // The pattern that macro_rules matches.
412 // The grammar for macro_rules! is:
413 // $( $lhs:tt => $rhs:tt );+
414 // ...quasiquoting this would be nice.
415 // These spans won't matter, anyways
416 let argument_gram = vec![
417 mbe::TokenTree::Sequence(
419 Lrc::new(mbe::SequenceRepetition {
421 mbe::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
422 mbe::TokenTree::token(token::FatArrow, def.span),
423 mbe::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
425 separator: Some(Token::new(
426 if macro_rules { token::Semi } else { token::Comma },
429 kleene: mbe::KleeneToken::new(mbe::KleeneOp::OneOrMore, def.span),
433 // to phase into semicolon-termination instead of semicolon-separation
434 mbe::TokenTree::Sequence(
436 Lrc::new(mbe::SequenceRepetition {
437 tts: vec![mbe::TokenTree::token(
438 if macro_rules { token::Semi } else { token::Comma },
442 kleene: mbe::KleeneToken::new(mbe::KleeneOp::ZeroOrMore, def.span),
448 let parser = Parser::new(&sess.parse_sess, body, true, rustc_parse::MACRO_ARGUMENTS);
449 let argument_map = match parse_tt(&mut Cow::Borrowed(&parser), &argument_gram) {
451 Failure(token, msg) => {
452 let s = parse_failure_msg(&token);
453 let sp = token.span.substitute_dummy(def.span);
454 sess.parse_sess.span_diagnostic.struct_span_err(sp, &s).span_label(sp, msg).emit();
455 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
460 .struct_span_err(sp.substitute_dummy(def.span), &msg)
462 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
465 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
469 let mut valid = true;
471 // Extract the arguments:
472 let lhses = match argument_map[&MacroRulesNormalizedIdent::new(lhs_nm)] {
473 MatchedSeq(ref s) => s
476 if let MatchedNonterminal(ref nt) = *m {
477 if let NtTT(ref tt) = **nt {
479 mbe::quoted::parse(tt.clone().into(), true, &sess.parse_sess, def.id)
482 valid &= check_lhs_nt_follows(&sess.parse_sess, features, &def.attrs, &tt);
486 sess.parse_sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
488 .collect::<Vec<mbe::TokenTree>>(),
489 _ => sess.parse_sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
492 let rhses = match argument_map[&MacroRulesNormalizedIdent::new(rhs_nm)] {
493 MatchedSeq(ref s) => s
496 if let MatchedNonterminal(ref nt) = *m {
497 if let NtTT(ref tt) = **nt {
498 return mbe::quoted::parse(
508 sess.parse_sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
510 .collect::<Vec<mbe::TokenTree>>(),
511 _ => sess.parse_sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
515 valid &= check_rhs(&sess.parse_sess, rhs);
518 // don't abort iteration early, so that errors for multiple lhses can be reported
520 valid &= check_lhs_no_empty_seq(&sess.parse_sess, slice::from_ref(lhs));
523 valid &= macro_check::check_meta_variables(&sess.parse_sess, def.id, def.span, &lhses, &rhses);
525 let (transparency, transparency_error) = attr::find_transparency(sess, &def.attrs, macro_rules);
526 match transparency_error {
527 Some(TransparencyError::UnknownTransparency(value, span)) => {
528 diag.span_err(span, &format!("unknown macro transparency: `{}`", value))
530 Some(TransparencyError::MultipleTransparencyAttrs(old_span, new_span)) => {
531 diag.span_err(vec![old_span, new_span], "multiple macro transparency attributes")
536 mk_syn_ext(Box::new(MacroRulesMacroExpander {
546 fn check_lhs_nt_follows(
549 attrs: &[ast::Attribute],
550 lhs: &mbe::TokenTree,
552 // lhs is going to be like TokenTree::Delimited(...), where the
553 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
554 if let mbe::TokenTree::Delimited(_, ref tts) = *lhs {
555 check_matcher(sess, features, attrs, &tts.tts)
557 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
558 sess.span_diagnostic.span_err(lhs.span(), msg);
561 // we don't abort on errors on rejection, the driver will do that for us
562 // after parsing/expansion. we can report every error in every macro this way.
565 /// Checks that the lhs contains no repetition which could match an empty token
566 /// tree, because then the matcher would hang indefinitely.
567 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
571 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
572 TokenTree::Delimited(_, ref del) => {
573 if !check_lhs_no_empty_seq(sess, &del.tts) {
577 TokenTree::Sequence(span, ref seq) => {
578 if seq.separator.is_none()
579 && seq.tts.iter().all(|seq_tt| match *seq_tt {
580 TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)) => true,
581 TokenTree::Sequence(_, ref sub_seq) => {
582 sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
583 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
588 let sp = span.entire();
589 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
592 if !check_lhs_no_empty_seq(sess, &seq.tts) {
602 fn check_rhs(sess: &ParseSess, rhs: &mbe::TokenTree) -> bool {
604 mbe::TokenTree::Delimited(..) => return true,
605 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
613 attrs: &[ast::Attribute],
614 matcher: &[mbe::TokenTree],
616 let first_sets = FirstSets::new(matcher);
617 let empty_suffix = TokenSet::empty();
618 let err = sess.span_diagnostic.err_count();
619 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
620 err == sess.span_diagnostic.err_count()
623 // `The FirstSets` for a matcher is a mapping from subsequences in the
624 // matcher to the FIRST set for that subsequence.
626 // This mapping is partially precomputed via a backwards scan over the
627 // token trees of the matcher, which provides a mapping from each
628 // repetition sequence to its *first* set.
630 // (Hypothetically, sequences should be uniquely identifiable via their
631 // spans, though perhaps that is false, e.g., for macro-generated macros
632 // that do not try to inject artificial span information. My plan is
633 // to try to catch such cases ahead of time and not include them in
634 // the precomputed mapping.)
636 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
637 // span in the original matcher to the First set for the inner sequence `tt ...`.
639 // If two sequences have the same span in a matcher, then map that
640 // span to None (invalidating the mapping here and forcing the code to
642 first: FxHashMap<Span, Option<TokenSet>>,
646 fn new(tts: &[mbe::TokenTree]) -> FirstSets {
649 let mut sets = FirstSets { first: FxHashMap::default() };
650 build_recur(&mut sets, tts);
653 // walks backward over `tts`, returning the FIRST for `tts`
654 // and updating `sets` at the same time for all sequence
655 // substructure we find within `tts`.
656 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
657 let mut first = TokenSet::empty();
658 for tt in tts.iter().rev() {
660 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
661 first.replace_with(tt.clone());
663 TokenTree::Delimited(span, ref delimited) => {
664 build_recur(sets, &delimited.tts[..]);
665 first.replace_with(delimited.open_tt(span));
667 TokenTree::Sequence(sp, ref seq_rep) => {
668 let subfirst = build_recur(sets, &seq_rep.tts[..]);
670 match sets.first.entry(sp.entire()) {
671 Entry::Vacant(vac) => {
672 vac.insert(Some(subfirst.clone()));
674 Entry::Occupied(mut occ) => {
675 // if there is already an entry, then a span must have collided.
676 // This should not happen with typical macro_rules macros,
677 // but syntax extensions need not maintain distinct spans,
678 // so distinct syntax trees can be assigned the same span.
679 // In such a case, the map cannot be trusted; so mark this
680 // entry as unusable.
685 // If the sequence contents can be empty, then the first
686 // token could be the separator token itself.
688 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
689 first.add_one_maybe(TokenTree::Token(sep.clone()));
692 // Reverse scan: Sequence comes before `first`.
693 if subfirst.maybe_empty
694 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
695 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
697 // If sequence is potentially empty, then
698 // union them (preserving first emptiness).
699 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
701 // Otherwise, sequence guaranteed
702 // non-empty; replace first.
713 // walks forward over `tts` until all potential FIRST tokens are
715 fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
718 let mut first = TokenSet::empty();
719 for tt in tts.iter() {
720 assert!(first.maybe_empty);
722 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
723 first.add_one(tt.clone());
726 TokenTree::Delimited(span, ref delimited) => {
727 first.add_one(delimited.open_tt(span));
730 TokenTree::Sequence(sp, ref seq_rep) => {
732 let subfirst = match self.first.get(&sp.entire()) {
733 Some(&Some(ref subfirst)) => subfirst,
735 subfirst_owned = self.first(&seq_rep.tts[..]);
739 panic!("We missed a sequence during FirstSets construction");
743 // If the sequence contents can be empty, then the first
744 // token could be the separator token itself.
745 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
746 first.add_one_maybe(TokenTree::Token(sep.clone()));
749 assert!(first.maybe_empty);
750 first.add_all(subfirst);
751 if subfirst.maybe_empty
752 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
753 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
755 // Continue scanning for more first
756 // tokens, but also make sure we
757 // restore empty-tracking state.
758 first.maybe_empty = true;
767 // we only exit the loop if `tts` was empty or if every
768 // element of `tts` matches the empty sequence.
769 assert!(first.maybe_empty);
774 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
775 // (for macro-by-example syntactic variables). It also carries the
776 // `maybe_empty` flag; that is true if and only if the matcher can
777 // match an empty token sequence.
779 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
780 // which has corresponding FIRST = {$a:expr, c, d}.
781 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
783 // (Notably, we must allow for *-op to occur zero times.)
784 #[derive(Clone, Debug)]
786 tokens: Vec<mbe::TokenTree>,
791 // Returns a set for the empty sequence.
793 TokenSet { tokens: Vec::new(), maybe_empty: true }
796 // Returns the set `{ tok }` for the single-token (and thus
797 // non-empty) sequence [tok].
798 fn singleton(tok: mbe::TokenTree) -> Self {
799 TokenSet { tokens: vec![tok], maybe_empty: false }
802 // Changes self to be the set `{ tok }`.
803 // Since `tok` is always present, marks self as non-empty.
804 fn replace_with(&mut self, tok: mbe::TokenTree) {
806 self.tokens.push(tok);
807 self.maybe_empty = false;
810 // Changes self to be the empty set `{}`; meant for use when
811 // the particular token does not matter, but we want to
812 // record that it occurs.
813 fn replace_with_irrelevant(&mut self) {
815 self.maybe_empty = false;
818 // Adds `tok` to the set for `self`, marking sequence as non-empy.
819 fn add_one(&mut self, tok: mbe::TokenTree) {
820 if !self.tokens.contains(&tok) {
821 self.tokens.push(tok);
823 self.maybe_empty = false;
826 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
827 fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
828 if !self.tokens.contains(&tok) {
829 self.tokens.push(tok);
833 // Adds all elements of `other` to this.
835 // (Since this is a set, we filter out duplicates.)
837 // If `other` is potentially empty, then preserves the previous
838 // setting of the empty flag of `self`. If `other` is guaranteed
839 // non-empty, then `self` is marked non-empty.
840 fn add_all(&mut self, other: &Self) {
841 for tok in &other.tokens {
842 if !self.tokens.contains(tok) {
843 self.tokens.push(tok.clone());
846 if !other.maybe_empty {
847 self.maybe_empty = false;
852 // Checks that `matcher` is internally consistent and that it
853 // can legally be followed by a token `N`, for all `N` in `follow`.
854 // (If `follow` is empty, then it imposes no constraint on
857 // Returns the set of NT tokens that could possibly come last in
858 // `matcher`. (If `matcher` matches the empty sequence, then
859 // `maybe_empty` will be set to true.)
861 // Requires that `first_sets` is pre-computed for `matcher`;
862 // see `FirstSets::new`.
863 fn check_matcher_core(
866 attrs: &[ast::Attribute],
867 first_sets: &FirstSets,
868 matcher: &[mbe::TokenTree],
873 let mut last = TokenSet::empty();
875 // 2. For each token and suffix [T, SUFFIX] in M:
876 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
877 // then ensure T can also be followed by any element of FOLLOW.
878 'each_token: for i in 0..matcher.len() {
879 let token = &matcher[i];
880 let suffix = &matcher[i + 1..];
882 let build_suffix_first = || {
883 let mut s = first_sets.first(suffix);
890 // (we build `suffix_first` on demand below; you can tell
891 // which cases are supposed to fall through by looking for the
892 // initialization of this variable.)
895 // First, update `last` so that it corresponds to the set
896 // of NT tokens that might end the sequence `... token`.
898 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
899 if token_can_be_followed_by_any(token) {
900 // don't need to track tokens that work with any,
901 last.replace_with_irrelevant();
902 // ... and don't need to check tokens that can be
903 // followed by anything against SUFFIX.
904 continue 'each_token;
906 last.replace_with(token.clone());
907 suffix_first = build_suffix_first();
910 TokenTree::Delimited(span, ref d) => {
911 let my_suffix = TokenSet::singleton(d.close_tt(span));
912 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
913 // don't track non NT tokens
914 last.replace_with_irrelevant();
916 // also, we don't need to check delimited sequences
918 continue 'each_token;
920 TokenTree::Sequence(_, ref seq_rep) => {
921 suffix_first = build_suffix_first();
922 // The trick here: when we check the interior, we want
923 // to include the separator (if any) as a potential
924 // (but not guaranteed) element of FOLLOW. So in that
925 // case, we make a temp copy of suffix and stuff
926 // delimiter in there.
928 // FIXME: Should I first scan suffix_first to see if
929 // delimiter is already in it before I go through the
930 // work of cloning it? But then again, this way I may
931 // get a "tighter" span?
933 let my_suffix = if let Some(sep) = &seq_rep.separator {
934 new = suffix_first.clone();
935 new.add_one_maybe(TokenTree::Token(sep.clone()));
941 // At this point, `suffix_first` is built, and
942 // `my_suffix` is some TokenSet that we can use
943 // for checking the interior of `seq_rep`.
945 check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
946 if next.maybe_empty {
952 // the recursive call to check_matcher_core already ran the 'each_last
953 // check below, so we can just keep going forward here.
954 continue 'each_token;
958 // (`suffix_first` guaranteed initialized once reaching here.)
960 // Now `last` holds the complete set of NT tokens that could
961 // end the sequence before SUFFIX. Check that every one works with `suffix`.
962 for token in &last.tokens {
963 if let TokenTree::MetaVarDecl(_, name, Some(kind)) = *token {
964 for next_token in &suffix_first.tokens {
965 match is_in_follow(next_token, kind) {
966 IsInFollow::Yes => {}
967 IsInFollow::No(possible) => {
968 let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
975 let sp = next_token.span();
976 let mut err = sess.span_diagnostic.struct_span_err(
979 "`${name}:{frag}` {may_be} followed by `{next}`, which \
980 is not allowed for `{frag}` fragments",
983 next = quoted_tt_to_string(next_token),
987 err.span_label(sp, format!("not allowed after `{}` fragments", kind));
988 let msg = "allowed there are: ";
993 "only {} is allowed after `{}` fragments",
1004 .collect::<Vec<_>>()
1020 fn token_can_be_followed_by_any(tok: &mbe::TokenTree) -> bool {
1021 if let mbe::TokenTree::MetaVarDecl(_, _, Some(kind)) = *tok {
1022 frag_can_be_followed_by_any(kind)
1024 // (Non NT's can always be followed by anything in matchers.)
1029 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
1030 /// token. We use this (among other things) as a useful approximation
1031 /// for when `frag` can be followed by a repetition like `$(...)*` or
1032 /// `$(...)+`. In general, these can be a bit tricky to reason about,
1033 /// so we adopt a conservative position that says that any fragment
1034 /// specifier which consumes at most one token tree can be followed by
1035 /// a fragment specifier (indeed, these fragments can be followed by
1036 /// ANYTHING without fear of future compatibility hazards).
1037 fn frag_can_be_followed_by_any(kind: NonterminalKind) -> bool {
1039 NonterminalKind::Item // always terminated by `}` or `;`
1040 | NonterminalKind::Block // exactly one token tree
1041 | NonterminalKind::Ident // exactly one token tree
1042 | NonterminalKind::Literal // exactly one token tree
1043 | NonterminalKind::Meta // exactly one token tree
1044 | NonterminalKind::Lifetime // exactly one token tree
1045 | NonterminalKind::TT => true, // exactly one token tree
1053 No(&'static [&'static str]),
1056 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1057 /// fragments that can consume an unbounded number of tokens, `tok`
1058 /// must be within a well-defined follow set. This is intended to
1059 /// guarantee future compatibility: for example, without this rule, if
1060 /// we expanded `expr` to include a new binary operator, we might
1061 /// break macros that were relying on that binary operator as a
1063 // when changing this do not forget to update doc/book/macros.md!
1064 fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
1067 if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
1068 // closing a token tree can never be matched by any fragment;
1069 // iow, we always require that `(` and `)` match, etc.
1073 NonterminalKind::Item => {
1074 // since items *must* be followed by either a `;` or a `}`, we can
1075 // accept anything after them
1078 NonterminalKind::Block => {
1079 // anything can follow block, the braces provide an easy boundary to
1083 NonterminalKind::Stmt | NonterminalKind::Expr => {
1084 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
1086 TokenTree::Token(token) => match token.kind {
1087 FatArrow | Comma | Semi => IsInFollow::Yes,
1088 _ => IsInFollow::No(TOKENS),
1090 _ => IsInFollow::No(TOKENS),
1093 NonterminalKind::Pat => {
1094 const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1096 TokenTree::Token(token) => match token.kind {
1097 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
1098 Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
1099 _ => IsInFollow::No(TOKENS),
1101 _ => IsInFollow::No(TOKENS),
1104 NonterminalKind::Path | NonterminalKind::Ty => {
1105 const TOKENS: &[&str] = &[
1106 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1110 TokenTree::Token(token) => match token.kind {
1111 OpenDelim(token::DelimToken::Brace)
1112 | OpenDelim(token::DelimToken::Bracket)
1120 | BinOp(token::Or) => IsInFollow::Yes,
1121 Ident(name, false) if name == kw::As || name == kw::Where => {
1124 _ => IsInFollow::No(TOKENS),
1126 TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Block)) => IsInFollow::Yes,
1127 _ => IsInFollow::No(TOKENS),
1130 NonterminalKind::Ident | NonterminalKind::Lifetime => {
1131 // being a single token, idents and lifetimes are harmless
1134 NonterminalKind::Literal => {
1135 // literals may be of a single token, or two tokens (negative numbers)
1138 NonterminalKind::Meta | NonterminalKind::TT => {
1139 // being either a single token or a delimited sequence, tt is
1143 NonterminalKind::Vis => {
1144 // Explicitly disallow `priv`, on the off chance it comes back.
1145 const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
1147 TokenTree::Token(token) => match token.kind {
1148 Comma => IsInFollow::Yes,
1149 Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
1151 if token.can_begin_type() {
1154 IsInFollow::No(TOKENS)
1158 TokenTree::MetaVarDecl(
1161 Some(NonterminalKind::Ident | NonterminalKind::Ty | NonterminalKind::Path),
1162 ) => IsInFollow::Yes,
1163 _ => IsInFollow::No(TOKENS),
1170 fn quoted_tt_to_string(tt: &mbe::TokenTree) -> String {
1172 mbe::TokenTree::Token(ref token) => pprust::token_to_string(&token),
1173 mbe::TokenTree::MetaVar(_, name) => format!("${}", name),
1174 mbe::TokenTree::MetaVarDecl(_, name, Some(kind)) => format!("${}:{}", name, kind),
1175 mbe::TokenTree::MetaVarDecl(_, name, None) => format!("${}:", name),
1177 "unexpected mbe::TokenTree::{{Sequence or Delimited}} \
1178 in follow set checker"
1183 fn parser_from_cx(sess: &ParseSess, tts: TokenStream) -> Parser<'_> {
1184 Parser::new(sess, tts, true, rustc_parse::MACRO_ARGUMENTS)
1187 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
1188 /// other tokens, this is "unexpected token...".
1189 fn parse_failure_msg(tok: &Token) -> String {
1191 token::Eof => "unexpected end of macro invocation".to_string(),
1192 _ => format!("no rules expected the token `{}`", pprust::token_to_string(tok),),