1 use crate::base::{DummyResult, ExtCtxt, MacResult, TTMacroExpander};
2 use crate::base::{SyntaxExtension, SyntaxExtensionKind};
3 use crate::expand::{AstFragment, AstFragmentKind, ensure_complete_parse, parse_ast_fragment};
5 use crate::mbe::macro_check;
6 use crate::mbe::macro_parser::parse;
7 use crate::mbe::macro_parser::{Error, Failure, Success};
8 use crate::mbe::macro_parser::{MatchedNonterminal, MatchedSeq, NamedParseResult};
9 use crate::mbe::transcribe::transcribe;
11 use rustc_parse::parser::Parser;
12 use rustc_parse::Directory;
14 use syntax::attr::{self, TransparencyError};
15 use syntax::edition::Edition;
16 use syntax::feature_gate::Features;
17 use syntax::print::pprust;
18 use syntax::sess::ParseSess;
19 use syntax::symbol::{kw, sym, Symbol};
20 use syntax::token::{self, NtTT, Token, TokenKind::*};
21 use syntax::tokenstream::{DelimSpan, TokenStream};
22 use syntax_pos::hygiene::Transparency;
25 use errors::{DiagnosticBuilder, FatalError};
28 use rustc_data_structures::fx::FxHashMap;
29 use rustc_data_structures::sync::Lrc;
31 use std::collections::hash_map::Entry;
32 use std::{mem, slice};
34 use errors::Applicability;
36 const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
37 `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, \
38 `literal`, `path`, `meta`, `tt`, `item` and `vis`";
40 crate struct ParserAnyMacro<'a> {
43 /// Span of the expansion site of the macro this parser is for
45 /// The ident of the macro we're parsing
46 macro_ident: ast::Ident,
50 crate fn annotate_err_with_kind(
51 err: &mut DiagnosticBuilder<'_>,
52 kind: AstFragmentKind,
56 AstFragmentKind::Ty => {
57 err.span_label(span, "this macro call doesn't expand to a type");
59 AstFragmentKind::Pat => {
60 err.span_label(span, "this macro call doesn't expand to a pattern");
66 impl<'a> ParserAnyMacro<'a> {
67 crate fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
68 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
69 let fragment = panictry!(parse_ast_fragment(parser, kind, true).map_err(|mut e| {
70 if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
71 if !e.span.is_dummy() {
72 // early end of macro arm (#52866)
73 e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
75 let msg = &e.message[0];
78 "macro expansion ends with an incomplete expression: {}",
79 msg.0.replace(", found `<eof>`", ""),
84 if e.span.is_dummy() {
85 // Get around lack of span in error (#30128)
86 e.replace_span_with(site_span);
87 if parser.sess.source_map().span_to_filename(arm_span).is_real() {
88 e.span_label(arm_span, "in this macro arm");
90 } else if !parser.sess.source_map().span_to_filename(parser.token.span).is_real() {
91 e.span_label(site_span, "in this macro invocation");
94 AstFragmentKind::Pat if macro_ident.name == sym::vec => {
95 let mut suggestion = None;
96 if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
97 if let Some(bang) = code.find('!') {
98 suggestion = Some(code[bang + 1..].to_string());
101 if let Some(suggestion) = suggestion {
104 "use a slice pattern here instead",
106 Applicability::MachineApplicable,
111 "use a slice pattern here instead",
114 e.help("for more information, see https://doc.rust-lang.org/edition-guide/\
115 rust-2018/slice-patterns.html");
117 _ => annotate_err_with_kind(&mut e, kind, site_span),
122 // We allow semicolons at the end of expressions -- e.g., the semicolon in
123 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
124 // but `m!()` is allowed in expression positions (cf. issue #34706).
125 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
129 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
130 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
131 ensure_complete_parse(parser, &path, kind.name(), site_span);
136 struct MacroRulesMacroExpander {
139 transparency: Transparency,
140 lhses: Vec<mbe::TokenTree>,
141 rhses: Vec<mbe::TokenTree>,
145 impl TTMacroExpander for MacroRulesMacroExpander {
148 cx: &'cx mut ExtCtxt<'_>,
151 ) -> Box<dyn MacResult + 'cx> {
153 return DummyResult::any(sp);
156 cx, sp, self.span, self.name, self.transparency, input, &self.lhses, &self.rhses
161 fn trace_macros_note(cx: &mut ExtCtxt<'_>, sp: Span, message: String) {
162 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
163 cx.expansions.entry(sp).or_default().push(message);
166 /// Given `lhses` and `rhses`, this is the new macro we create
167 fn generic_extension<'cx>(
168 cx: &'cx mut ExtCtxt<'_>,
172 transparency: Transparency,
174 lhses: &[mbe::TokenTree],
175 rhses: &[mbe::TokenTree],
176 ) -> Box<dyn MacResult + 'cx> {
177 if cx.trace_macros() {
178 let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(arg.clone()));
179 trace_macros_note(cx, sp, msg);
182 // Which arm's failure should we report? (the one furthest along)
183 let mut best_failure: Option<(Token, &str)> = None;
184 for (i, lhs) in lhses.iter().enumerate() {
185 // try each arm's matchers
186 let lhs_tt = match *lhs {
187 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
188 _ => cx.span_bug(sp, "malformed macro lhs"),
191 // Take a snapshot of the state of pre-expansion gating at this point.
192 // This is used so that if a matcher is not `Success(..)`ful,
193 // then the spans which became gated when parsing the unsuccessful matcher
194 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
195 let mut gated_spans_snaphot = mem::take(&mut *cx.parse_sess.gated_spans.spans.borrow_mut());
197 match parse_tt(cx, lhs_tt, arg.clone()) {
198 Success(named_matches) => {
199 // The matcher was `Success(..)`ful.
200 // Merge the gated spans from parsing the matcher with the pre-existing ones.
201 cx.parse_sess.gated_spans.merge(gated_spans_snaphot);
203 let rhs = match rhses[i] {
205 mbe::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
206 _ => cx.span_bug(sp, "malformed macro rhs"),
208 let arm_span = rhses[i].span();
210 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
211 // rhs has holes ( `$id` and `$(...)` that need filled)
212 let mut tts = transcribe(cx, &named_matches, rhs, transparency);
214 // Replace all the tokens for the corresponding positions in the macro, to maintain
215 // proper positions in error reporting, while maintaining the macro_backtrace.
216 if rhs_spans.len() == tts.len() {
217 tts = tts.map_enumerated(|i, mut tt| {
218 let mut sp = rhs_spans[i];
219 sp = sp.with_ctxt(tt.span().ctxt());
225 if cx.trace_macros() {
226 let msg = format!("to `{}`", pprust::tts_to_string(tts.clone()));
227 trace_macros_note(cx, sp, msg);
230 let directory = Directory {
231 path: Cow::from(cx.current_expansion.module.directory.as_path()),
232 ownership: cx.current_expansion.directory_ownership,
234 let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false, None);
236 cx.current_expansion.module.mod_path.last().map(|id| id.to_string());
237 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
239 p.process_potential_macro_variable();
240 // Let the context choose how to interpret the result.
241 // Weird, but useful for X-macros.
242 return Box::new(ParserAnyMacro {
245 // Pass along the original expansion site and the name of the macro
246 // so we can print a useful error message if the parse of the expanded
247 // macro leaves unparsed tokens.
253 Failure(token, msg) => match best_failure {
254 Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
255 _ => best_failure = Some((token, msg)),
257 Error(err_sp, ref msg) => cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..]),
260 // The matcher was not `Success(..)`ful.
261 // Restore to the state before snapshotting and maybe try again.
262 mem::swap(&mut gated_spans_snaphot, &mut cx.parse_sess.gated_spans.spans.borrow_mut());
265 let (token, label) = best_failure.expect("ran no matchers");
266 let span = token.span.substitute_dummy(sp);
267 let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
268 err.span_label(span, label);
269 if !def_span.is_dummy() && cx.source_map().span_to_filename(def_span).is_real() {
270 err.span_label(cx.source_map().def_span(def_span), "when calling this macro");
273 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
274 if let Some((arg, comma_span)) = arg.add_comma() {
276 // try each arm's matchers
277 let lhs_tt = match *lhs {
278 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
281 match parse_tt(cx, lhs_tt, arg.clone()) {
283 if comma_span.is_dummy() {
284 err.note("you might be missing a comma");
286 err.span_suggestion_short(
288 "missing comma here",
290 Applicability::MachineApplicable,
299 cx.trace_macros_diag();
303 // Note that macro-by-example's input is also matched against a token tree:
304 // $( $lhs:tt => $rhs:tt );+
306 // Holy self-referential!
308 /// Converts a macro item into a syntax extension.
309 pub fn compile_declarative_macro(
314 ) -> SyntaxExtension {
315 let diag = &sess.span_diagnostic;
316 let lhs_nm = ast::Ident::new(sym::lhs, def.span);
317 let rhs_nm = ast::Ident::new(sym::rhs, def.span);
318 let tt_spec = ast::Ident::new(sym::tt, def.span);
320 // Parse the macro_rules! invocation
321 let body = match def.kind {
322 ast::ItemKind::MacroDef(ref body) => body,
326 // The pattern that macro_rules matches.
327 // The grammar for macro_rules! is:
328 // $( $lhs:tt => $rhs:tt );+
329 // ...quasiquoting this would be nice.
330 // These spans won't matter, anyways
331 let argument_gram = vec![
332 mbe::TokenTree::Sequence(
334 Lrc::new(mbe::SequenceRepetition {
336 mbe::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
337 mbe::TokenTree::token(token::FatArrow, def.span),
338 mbe::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
340 separator: Some(Token::new(
341 if body.legacy { token::Semi } else { token::Comma },
344 kleene: mbe::KleeneToken::new(mbe::KleeneOp::OneOrMore, def.span),
348 // to phase into semicolon-termination instead of semicolon-separation
349 mbe::TokenTree::Sequence(
351 Lrc::new(mbe::SequenceRepetition {
352 tts: vec![mbe::TokenTree::token(
353 if body.legacy { token::Semi } else { token::Comma },
357 kleene: mbe::KleeneToken::new(mbe::KleeneOp::ZeroOrMore, def.span),
363 let argument_map = match parse(sess, body.stream(), &argument_gram, None, true) {
365 Failure(token, msg) => {
366 let s = parse_failure_msg(&token);
367 let sp = token.span.substitute_dummy(def.span);
368 let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
369 err.span_label(sp, msg);
374 sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
378 let mut valid = true;
380 // Extract the arguments:
381 let lhses = match argument_map[&lhs_nm] {
382 MatchedSeq(ref s, _) => s
385 if let MatchedNonterminal(ref nt) = *m {
386 if let NtTT(ref tt) = **nt {
387 let tt = mbe::quoted::parse(
394 valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt);
398 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
400 .collect::<Vec<mbe::TokenTree>>(),
401 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
404 let rhses = match argument_map[&rhs_nm] {
405 MatchedSeq(ref s, _) => s
408 if let MatchedNonterminal(ref nt) = *m {
409 if let NtTT(ref tt) = **nt {
410 return mbe::quoted::parse(
419 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
421 .collect::<Vec<mbe::TokenTree>>(),
422 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
426 valid &= check_rhs(sess, rhs);
429 // don't abort iteration early, so that errors for multiple lhses can be reported
431 valid &= check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
434 // We use CRATE_NODE_ID instead of `def.id` otherwise we may emit buffered lints for a node id
435 // that is not lint-checked and trigger the "failed to process buffered lint here" bug.
436 valid &= macro_check::check_meta_variables(sess, ast::CRATE_NODE_ID, def.span, &lhses, &rhses);
438 let (transparency, transparency_error) = attr::find_transparency(&def.attrs, body.legacy);
439 match transparency_error {
440 Some(TransparencyError::UnknownTransparency(value, span)) =>
441 diag.span_err(span, &format!("unknown macro transparency: `{}`", value)),
442 Some(TransparencyError::MultipleTransparencyAttrs(old_span, new_span)) =>
443 diag.span_err(vec![old_span, new_span], "multiple macro transparency attributes"),
447 let expander: Box<_> = Box::new(MacroRulesMacroExpander {
448 name: def.ident, span: def.span, transparency, lhses, rhses, valid
451 SyntaxExtension::new(
453 SyntaxExtensionKind::LegacyBang(expander),
462 fn check_lhs_nt_follows(
465 attrs: &[ast::Attribute],
466 lhs: &mbe::TokenTree,
468 // lhs is going to be like TokenTree::Delimited(...), where the
469 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
470 if let mbe::TokenTree::Delimited(_, ref tts) = *lhs {
471 check_matcher(sess, features, attrs, &tts.tts)
473 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
474 sess.span_diagnostic.span_err(lhs.span(), msg);
477 // we don't abort on errors on rejection, the driver will do that for us
478 // after parsing/expansion. we can report every error in every macro this way.
481 /// Checks that the lhs contains no repetition which could match an empty token
482 /// tree, because then the matcher would hang indefinitely.
483 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
487 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
488 TokenTree::Delimited(_, ref del) => {
489 if !check_lhs_no_empty_seq(sess, &del.tts) {
493 TokenTree::Sequence(span, ref seq) => {
494 if seq.separator.is_none()
495 && seq.tts.iter().all(|seq_tt| match *seq_tt {
496 TokenTree::MetaVarDecl(_, _, id) => id.name == sym::vis,
497 TokenTree::Sequence(_, ref sub_seq) => {
498 sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
499 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
504 let sp = span.entire();
505 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
508 if !check_lhs_no_empty_seq(sess, &seq.tts) {
518 fn check_rhs(sess: &ParseSess, rhs: &mbe::TokenTree) -> bool {
520 mbe::TokenTree::Delimited(..) => return true,
521 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
529 attrs: &[ast::Attribute],
530 matcher: &[mbe::TokenTree],
532 let first_sets = FirstSets::new(matcher);
533 let empty_suffix = TokenSet::empty();
534 let err = sess.span_diagnostic.err_count();
535 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
536 err == sess.span_diagnostic.err_count()
539 // `The FirstSets` for a matcher is a mapping from subsequences in the
540 // matcher to the FIRST set for that subsequence.
542 // This mapping is partially precomputed via a backwards scan over the
543 // token trees of the matcher, which provides a mapping from each
544 // repetition sequence to its *first* set.
546 // (Hypothetically, sequences should be uniquely identifiable via their
547 // spans, though perhaps that is false, e.g., for macro-generated macros
548 // that do not try to inject artificial span information. My plan is
549 // to try to catch such cases ahead of time and not include them in
550 // the precomputed mapping.)
552 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
553 // span in the original matcher to the First set for the inner sequence `tt ...`.
555 // If two sequences have the same span in a matcher, then map that
556 // span to None (invalidating the mapping here and forcing the code to
558 first: FxHashMap<Span, Option<TokenSet>>,
562 fn new(tts: &[mbe::TokenTree]) -> FirstSets {
565 let mut sets = FirstSets { first: FxHashMap::default() };
566 build_recur(&mut sets, tts);
569 // walks backward over `tts`, returning the FIRST for `tts`
570 // and updating `sets` at the same time for all sequence
571 // substructure we find within `tts`.
572 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
573 let mut first = TokenSet::empty();
574 for tt in tts.iter().rev() {
576 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
577 first.replace_with(tt.clone());
579 TokenTree::Delimited(span, ref delimited) => {
580 build_recur(sets, &delimited.tts[..]);
581 first.replace_with(delimited.open_tt(span));
583 TokenTree::Sequence(sp, ref seq_rep) => {
584 let subfirst = build_recur(sets, &seq_rep.tts[..]);
586 match sets.first.entry(sp.entire()) {
587 Entry::Vacant(vac) => {
588 vac.insert(Some(subfirst.clone()));
590 Entry::Occupied(mut occ) => {
591 // if there is already an entry, then a span must have collided.
592 // This should not happen with typical macro_rules macros,
593 // but syntax extensions need not maintain distinct spans,
594 // so distinct syntax trees can be assigned the same span.
595 // In such a case, the map cannot be trusted; so mark this
596 // entry as unusable.
601 // If the sequence contents can be empty, then the first
602 // token could be the separator token itself.
604 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
605 first.add_one_maybe(TokenTree::Token(sep.clone()));
608 // Reverse scan: Sequence comes before `first`.
609 if subfirst.maybe_empty
610 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
611 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
613 // If sequence is potentially empty, then
614 // union them (preserving first emptiness).
615 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
617 // Otherwise, sequence guaranteed
618 // non-empty; replace first.
629 // walks forward over `tts` until all potential FIRST tokens are
631 fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
634 let mut first = TokenSet::empty();
635 for tt in tts.iter() {
636 assert!(first.maybe_empty);
638 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
639 first.add_one(tt.clone());
642 TokenTree::Delimited(span, ref delimited) => {
643 first.add_one(delimited.open_tt(span));
646 TokenTree::Sequence(sp, ref seq_rep) => {
648 let subfirst = match self.first.get(&sp.entire()) {
649 Some(&Some(ref subfirst)) => subfirst,
651 subfirst_owned = self.first(&seq_rep.tts[..]);
655 panic!("We missed a sequence during FirstSets construction");
659 // If the sequence contents can be empty, then the first
660 // token could be the separator token itself.
661 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
662 first.add_one_maybe(TokenTree::Token(sep.clone()));
665 assert!(first.maybe_empty);
666 first.add_all(subfirst);
667 if subfirst.maybe_empty
668 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
669 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
671 // Continue scanning for more first
672 // tokens, but also make sure we
673 // restore empty-tracking state.
674 first.maybe_empty = true;
683 // we only exit the loop if `tts` was empty or if every
684 // element of `tts` matches the empty sequence.
685 assert!(first.maybe_empty);
690 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
691 // (for macro-by-example syntactic variables). It also carries the
692 // `maybe_empty` flag; that is true if and only if the matcher can
693 // match an empty token sequence.
695 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
696 // which has corresponding FIRST = {$a:expr, c, d}.
697 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
699 // (Notably, we must allow for *-op to occur zero times.)
700 #[derive(Clone, Debug)]
702 tokens: Vec<mbe::TokenTree>,
707 // Returns a set for the empty sequence.
709 TokenSet { tokens: Vec::new(), maybe_empty: true }
712 // Returns the set `{ tok }` for the single-token (and thus
713 // non-empty) sequence [tok].
714 fn singleton(tok: mbe::TokenTree) -> Self {
715 TokenSet { tokens: vec![tok], maybe_empty: false }
718 // Changes self to be the set `{ tok }`.
719 // Since `tok` is always present, marks self as non-empty.
720 fn replace_with(&mut self, tok: mbe::TokenTree) {
722 self.tokens.push(tok);
723 self.maybe_empty = false;
726 // Changes self to be the empty set `{}`; meant for use when
727 // the particular token does not matter, but we want to
728 // record that it occurs.
729 fn replace_with_irrelevant(&mut self) {
731 self.maybe_empty = false;
734 // Adds `tok` to the set for `self`, marking sequence as non-empy.
735 fn add_one(&mut self, tok: mbe::TokenTree) {
736 if !self.tokens.contains(&tok) {
737 self.tokens.push(tok);
739 self.maybe_empty = false;
742 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
743 fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
744 if !self.tokens.contains(&tok) {
745 self.tokens.push(tok);
749 // Adds all elements of `other` to this.
751 // (Since this is a set, we filter out duplicates.)
753 // If `other` is potentially empty, then preserves the previous
754 // setting of the empty flag of `self`. If `other` is guaranteed
755 // non-empty, then `self` is marked non-empty.
756 fn add_all(&mut self, other: &Self) {
757 for tok in &other.tokens {
758 if !self.tokens.contains(tok) {
759 self.tokens.push(tok.clone());
762 if !other.maybe_empty {
763 self.maybe_empty = false;
768 // Checks that `matcher` is internally consistent and that it
769 // can legally be followed by a token `N`, for all `N` in `follow`.
770 // (If `follow` is empty, then it imposes no constraint on
773 // Returns the set of NT tokens that could possibly come last in
774 // `matcher`. (If `matcher` matches the empty sequence, then
775 // `maybe_empty` will be set to true.)
777 // Requires that `first_sets` is pre-computed for `matcher`;
778 // see `FirstSets::new`.
779 fn check_matcher_core(
782 attrs: &[ast::Attribute],
783 first_sets: &FirstSets,
784 matcher: &[mbe::TokenTree],
789 let mut last = TokenSet::empty();
791 // 2. For each token and suffix [T, SUFFIX] in M:
792 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
793 // then ensure T can also be followed by any element of FOLLOW.
794 'each_token: for i in 0..matcher.len() {
795 let token = &matcher[i];
796 let suffix = &matcher[i + 1..];
798 let build_suffix_first = || {
799 let mut s = first_sets.first(suffix);
806 // (we build `suffix_first` on demand below; you can tell
807 // which cases are supposed to fall through by looking for the
808 // initialization of this variable.)
811 // First, update `last` so that it corresponds to the set
812 // of NT tokens that might end the sequence `... token`.
814 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
815 let can_be_followed_by_any;
816 if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) {
817 let msg = format!("invalid fragment specifier `{}`", bad_frag);
819 .struct_span_err(token.span(), &msg)
820 .help(VALID_FRAGMENT_NAMES_MSG)
822 // (This eliminates false positives and duplicates
823 // from error messages.)
824 can_be_followed_by_any = true;
826 can_be_followed_by_any = token_can_be_followed_by_any(token);
829 if can_be_followed_by_any {
830 // don't need to track tokens that work with any,
831 last.replace_with_irrelevant();
832 // ... and don't need to check tokens that can be
833 // followed by anything against SUFFIX.
834 continue 'each_token;
836 last.replace_with(token.clone());
837 suffix_first = build_suffix_first();
840 TokenTree::Delimited(span, ref d) => {
841 let my_suffix = TokenSet::singleton(d.close_tt(span));
842 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
843 // don't track non NT tokens
844 last.replace_with_irrelevant();
846 // also, we don't need to check delimited sequences
848 continue 'each_token;
850 TokenTree::Sequence(_, ref seq_rep) => {
851 suffix_first = build_suffix_first();
852 // The trick here: when we check the interior, we want
853 // to include the separator (if any) as a potential
854 // (but not guaranteed) element of FOLLOW. So in that
855 // case, we make a temp copy of suffix and stuff
856 // delimiter in there.
858 // FIXME: Should I first scan suffix_first to see if
859 // delimiter is already in it before I go through the
860 // work of cloning it? But then again, this way I may
861 // get a "tighter" span?
863 let my_suffix = if let Some(sep) = &seq_rep.separator {
864 new = suffix_first.clone();
865 new.add_one_maybe(TokenTree::Token(sep.clone()));
871 // At this point, `suffix_first` is built, and
872 // `my_suffix` is some TokenSet that we can use
873 // for checking the interior of `seq_rep`.
875 check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
876 if next.maybe_empty {
882 // the recursive call to check_matcher_core already ran the 'each_last
883 // check below, so we can just keep going forward here.
884 continue 'each_token;
888 // (`suffix_first` guaranteed initialized once reaching here.)
890 // Now `last` holds the complete set of NT tokens that could
891 // end the sequence before SUFFIX. Check that every one works with `suffix`.
892 'each_last: for token in &last.tokens {
893 if let TokenTree::MetaVarDecl(_, name, frag_spec) = *token {
894 for next_token in &suffix_first.tokens {
895 match is_in_follow(next_token, frag_spec.name) {
896 IsInFollow::Invalid(msg, help) => {
898 .struct_span_err(next_token.span(), &msg)
901 // don't bother reporting every source of
902 // conflict for a particular element of `last`.
905 IsInFollow::Yes => {}
906 IsInFollow::No(possible) => {
907 let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
914 let sp = next_token.span();
915 let mut err = sess.span_diagnostic.struct_span_err(
918 "`${name}:{frag}` {may_be} followed by `{next}`, which \
919 is not allowed for `{frag}` fragments",
922 next = quoted_tt_to_string(next_token),
928 format!("not allowed after `{}` fragments", frag_spec),
930 let msg = "allowed there are: ";
935 "only {} is allowed after `{}` fragments",
962 fn token_can_be_followed_by_any(tok: &mbe::TokenTree) -> bool {
963 if let mbe::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok {
964 frag_can_be_followed_by_any(frag_spec.name)
966 // (Non NT's can always be followed by anthing in matchers.)
971 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
972 /// token. We use this (among other things) as a useful approximation
973 /// for when `frag` can be followed by a repetition like `$(...)*` or
974 /// `$(...)+`. In general, these can be a bit tricky to reason about,
975 /// so we adopt a conservative position that says that any fragment
976 /// specifier which consumes at most one token tree can be followed by
977 /// a fragment specifier (indeed, these fragments can be followed by
978 /// ANYTHING without fear of future compatibility hazards).
979 fn frag_can_be_followed_by_any(frag: Symbol) -> bool {
981 sym::item | // always terminated by `}` or `;`
982 sym::block | // exactly one token tree
983 sym::ident | // exactly one token tree
984 sym::literal | // exactly one token tree
985 sym::meta | // exactly one token tree
986 sym::lifetime | // exactly one token tree
987 sym::tt => // exactly one token tree
997 No(&'static [&'static str]),
998 Invalid(String, &'static str),
1001 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1002 /// fragments that can consume an unbounded number of tokens, `tok`
1003 /// must be within a well-defined follow set. This is intended to
1004 /// guarantee future compatibility: for example, without this rule, if
1005 /// we expanded `expr` to include a new binary operator, we might
1006 /// break macros that were relying on that binary operator as a
1008 // when changing this do not forget to update doc/book/macros.md!
1009 fn is_in_follow(tok: &mbe::TokenTree, frag: Symbol) -> IsInFollow {
1012 if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
1013 // closing a token tree can never be matched by any fragment;
1014 // iow, we always require that `(` and `)` match, etc.
1019 // since items *must* be followed by either a `;` or a `}`, we can
1020 // accept anything after them
1024 // anything can follow block, the braces provide an easy boundary to
1028 sym::stmt | sym::expr => {
1029 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
1031 TokenTree::Token(token) => match token.kind {
1032 FatArrow | Comma | Semi => IsInFollow::Yes,
1033 _ => IsInFollow::No(TOKENS),
1035 _ => IsInFollow::No(TOKENS),
1039 const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1041 TokenTree::Token(token) => match token.kind {
1042 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
1043 Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
1044 _ => IsInFollow::No(TOKENS),
1046 _ => IsInFollow::No(TOKENS),
1049 sym::path | sym::ty => {
1050 const TOKENS: &[&str] = &[
1051 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1055 TokenTree::Token(token) => match token.kind {
1056 OpenDelim(token::DelimToken::Brace)
1057 | OpenDelim(token::DelimToken::Bracket)
1065 | BinOp(token::Or) => IsInFollow::Yes,
1066 Ident(name, false) if name == kw::As || name == kw::Where => {
1069 _ => IsInFollow::No(TOKENS),
1071 TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block => {
1074 _ => IsInFollow::No(TOKENS),
1077 sym::ident | sym::lifetime => {
1078 // being a single token, idents and lifetimes are harmless
1082 // literals may be of a single token, or two tokens (negative numbers)
1085 sym::meta | sym::tt => {
1086 // being either a single token or a delimited sequence, tt is
1091 // Explicitly disallow `priv`, on the off chance it comes back.
1092 const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
1094 TokenTree::Token(token) => match token.kind {
1095 Comma => IsInFollow::Yes,
1096 Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
1098 if token.can_begin_type() {
1101 IsInFollow::No(TOKENS)
1105 TokenTree::MetaVarDecl(_, _, frag)
1106 if frag.name == sym::ident
1107 || frag.name == sym::ty
1108 || frag.name == sym::path =>
1112 _ => IsInFollow::No(TOKENS),
1115 kw::Invalid => IsInFollow::Yes,
1116 _ => IsInFollow::Invalid(
1117 format!("invalid fragment specifier `{}`", frag),
1118 VALID_FRAGMENT_NAMES_MSG,
1124 fn has_legal_fragment_specifier(
1126 features: &Features,
1127 attrs: &[ast::Attribute],
1128 tok: &mbe::TokenTree,
1129 ) -> Result<(), String> {
1130 debug!("has_legal_fragment_specifier({:?})", tok);
1131 if let mbe::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok {
1132 let frag_span = tok.span();
1133 if !is_legal_fragment_specifier(sess, features, attrs, frag_spec.name, frag_span) {
1134 return Err(frag_spec.to_string());
1140 fn is_legal_fragment_specifier(
1142 _features: &Features,
1143 _attrs: &[ast::Attribute],
1148 * If new fragment specifiers are invented in nightly, `_sess`,
1149 * `_features`, `_attrs`, and `_frag_span` will be useful here
1150 * for checking against feature gates. See past versions of
1167 | kw::Invalid => true,
1172 fn quoted_tt_to_string(tt: &mbe::TokenTree) -> String {
1174 mbe::TokenTree::Token(ref token) => pprust::token_to_string(&token),
1175 mbe::TokenTree::MetaVar(_, name) => format!("${}", name),
1176 mbe::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind),
1178 "unexpected mbe::TokenTree::{{Sequence or Delimited}} \
1179 in follow set checker"
1184 /// Use this token tree as a matcher to parse given tts.
1185 fn parse_tt(cx: &ExtCtxt<'_>, mtch: &[mbe::TokenTree], tts: TokenStream) -> NamedParseResult {
1186 // `None` is because we're not interpolating
1187 let directory = Directory {
1188 path: Cow::from(cx.current_expansion.module.directory.as_path()),
1189 ownership: cx.current_expansion.directory_ownership,
1191 parse(cx.parse_sess(), tts, mtch, Some(directory), true)
1194 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
1195 /// other tokens, this is "unexpected token...".
1196 fn parse_failure_msg(tok: &Token) -> String {
1198 token::Eof => "unexpected end of macro invocation".to_string(),
1200 "no rules expected the token `{}`",
1201 pprust::token_to_string(tok),