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_span::edition::Edition;
23 use rustc_span::hygiene::Transparency;
24 use rustc_span::symbol::{kw, sym, Ident, MacroRulesNormalizedIdent};
29 use std::collections::hash_map::Entry;
30 use std::{mem, slice};
32 crate struct ParserAnyMacro<'a> {
35 /// Span of the expansion site of the macro this parser is for
37 /// The ident of the macro we're parsing
42 crate fn annotate_err_with_kind(
43 err: &mut DiagnosticBuilder<'_>,
44 kind: AstFragmentKind,
48 AstFragmentKind::Ty => {
49 err.span_label(span, "this macro call doesn't expand to a type");
51 AstFragmentKind::Pat => {
52 err.span_label(span, "this macro call doesn't expand to a pattern");
58 /// Instead of e.g. `vec![a, b, c]` in a pattern context, suggest `[a, b, c]`.
59 fn suggest_slice_pat(e: &mut DiagnosticBuilder<'_>, site_span: Span, parser: &Parser<'_>) {
60 let mut suggestion = None;
61 if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
62 if let Some(bang) = code.find('!') {
63 suggestion = Some(code[bang + 1..].to_string());
66 if let Some(suggestion) = suggestion {
69 "use a slice pattern here instead",
71 Applicability::MachineApplicable,
74 e.span_label(site_span, "use a slice pattern here instead");
77 "for more information, see https://doc.rust-lang.org/edition-guide/\
78 rust-2018/slice-patterns.html",
82 fn emit_frag_parse_err(
83 mut e: DiagnosticBuilder<'_>,
85 orig_parser: &mut Parser<'_>,
89 kind: AstFragmentKind,
91 if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
92 if !e.span.is_dummy() {
93 // early end of macro arm (#52866)
94 e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
96 let msg = &e.message[0];
99 "macro expansion ends with an incomplete expression: {}",
100 msg.0.replace(", found `<eof>`", ""),
105 if e.span.is_dummy() {
106 // Get around lack of span in error (#30128)
107 e.replace_span_with(site_span);
108 if !parser.sess.source_map().is_imported(arm_span) {
109 e.span_label(arm_span, "in this macro arm");
111 } else if parser.sess.source_map().is_imported(parser.token.span) {
112 e.span_label(site_span, "in this macro invocation");
115 AstFragmentKind::Pat if macro_ident.name == sym::vec => {
116 suggest_slice_pat(&mut e, site_span, parser);
118 // Try a statement if an expression is wanted but failed and suggest adding `;` to call.
119 AstFragmentKind::Expr => match parse_ast_fragment(orig_parser, AstFragmentKind::Stmts) {
120 Err(mut err) => err.cancel(),
123 "the macro call doesn't expand to an expression, but it can expand to a statement",
125 e.span_suggestion_verbose(
126 site_span.shrink_to_hi(),
127 "add `;` to interpret the expansion as a statement",
129 Applicability::MaybeIncorrect,
133 _ => annotate_err_with_kind(&mut e, kind, site_span),
138 impl<'a> ParserAnyMacro<'a> {
139 crate fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
140 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
141 let snapshot = &mut parser.clone();
142 let fragment = match parse_ast_fragment(parser, kind) {
145 emit_frag_parse_err(err, parser, snapshot, site_span, macro_ident, arm_span, kind);
146 return kind.dummy(site_span);
150 // We allow semicolons at the end of expressions -- e.g., the semicolon in
151 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
152 // but `m!()` is allowed in expression positions (cf. issue #34706).
153 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
157 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
158 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
159 ensure_complete_parse(parser, &path, kind.name(), site_span);
164 struct MacroRulesMacroExpander {
167 transparency: Transparency,
168 lhses: Vec<mbe::TokenTree>,
169 rhses: Vec<mbe::TokenTree>,
173 impl TTMacroExpander for MacroRulesMacroExpander {
176 cx: &'cx mut ExtCtxt<'_>,
179 ) -> Box<dyn MacResult + 'cx> {
181 return DummyResult::any(sp);
196 fn macro_rules_dummy_expander<'cx>(
197 _: &'cx mut ExtCtxt<'_>,
200 ) -> Box<dyn MacResult + 'cx> {
201 DummyResult::any(span)
204 fn trace_macros_note(cx_expansions: &mut FxHashMap<Span, Vec<String>>, sp: Span, message: String) {
205 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
206 cx_expansions.entry(sp).or_default().push(message);
209 /// Given `lhses` and `rhses`, this is the new macro we create
210 fn generic_extension<'cx>(
211 cx: &'cx mut ExtCtxt<'_>,
215 transparency: Transparency,
217 lhses: &[mbe::TokenTree],
218 rhses: &[mbe::TokenTree],
219 ) -> Box<dyn MacResult + 'cx> {
220 let sess = cx.parse_sess;
222 if cx.trace_macros() {
223 let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(&arg));
224 trace_macros_note(&mut cx.expansions, sp, msg);
227 // Which arm's failure should we report? (the one furthest along)
228 let mut best_failure: Option<(Token, &str)> = None;
230 // We create a base parser that can be used for the "black box" parts.
231 // Every iteration needs a fresh copy of that parser. However, the parser
232 // is not mutated on many of the iterations, particularly when dealing with
235 // macro_rules! foo {
239 // // ... etc. (maybe hundreds more)
242 // as seen in the `html5ever` benchmark. We use a `Cow` so that the base
243 // parser is only cloned when necessary (upon mutation). Furthermore, we
244 // reinitialize the `Cow` with the base parser at the start of every
245 // iteration, so that any mutated parsers are not reused. This is all quite
246 // hacky, but speeds up the `html5ever` benchmark significantly. (Issue
247 // 68836 suggests a more comprehensive but more complex change to deal with
249 let parser = parser_from_cx(sess, arg.clone());
251 for (i, lhs) in lhses.iter().enumerate() {
252 // try each arm's matchers
253 let lhs_tt = match *lhs {
254 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
255 _ => cx.span_bug(sp, "malformed macro lhs"),
258 // Take a snapshot of the state of pre-expansion gating at this point.
259 // This is used so that if a matcher is not `Success(..)`ful,
260 // then the spans which became gated when parsing the unsuccessful matcher
261 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
262 let mut gated_spans_snapshot = mem::take(&mut *sess.gated_spans.spans.borrow_mut());
264 match parse_tt(&mut Cow::Borrowed(&parser), lhs_tt) {
265 Success(named_matches) => {
266 // The matcher was `Success(..)`ful.
267 // Merge the gated spans from parsing the matcher with the pre-existing ones.
268 sess.gated_spans.merge(gated_spans_snapshot);
270 let rhs = match rhses[i] {
272 mbe::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
273 _ => cx.span_bug(sp, "malformed macro rhs"),
275 let arm_span = rhses[i].span();
277 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
278 // rhs has holes ( `$id` and `$(...)` that need filled)
279 let mut tts = match transcribe(cx, &named_matches, rhs, transparency) {
283 return DummyResult::any(arm_span);
287 // Replace all the tokens for the corresponding positions in the macro, to maintain
288 // proper positions in error reporting, while maintaining the macro_backtrace.
289 if rhs_spans.len() == tts.len() {
290 tts = tts.map_enumerated(|i, mut tt| {
291 let mut sp = rhs_spans[i];
292 sp = sp.with_ctxt(tt.span().ctxt());
298 if cx.trace_macros() {
299 let msg = format!("to `{}`", pprust::tts_to_string(&tts));
300 trace_macros_note(&mut cx.expansions, sp, msg);
303 let mut p = Parser::new(sess, tts, false, None);
304 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
306 // Let the context choose how to interpret the result.
307 // Weird, but useful for X-macros.
308 return Box::new(ParserAnyMacro {
311 // Pass along the original expansion site and the name of the macro
312 // so we can print a useful error message if the parse of the expanded
313 // macro leaves unparsed tokens.
319 Failure(token, msg) => match best_failure {
320 Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
321 _ => best_failure = Some((token, msg)),
323 Error(err_sp, ref msg) => {
324 let span = err_sp.substitute_dummy(sp);
325 cx.struct_span_err(span, &msg).emit();
326 return DummyResult::any(span);
328 ErrorReported => return DummyResult::any(sp),
331 // The matcher was not `Success(..)`ful.
332 // Restore to the state before snapshotting and maybe try again.
333 mem::swap(&mut gated_spans_snapshot, &mut sess.gated_spans.spans.borrow_mut());
337 let (token, label) = best_failure.expect("ran no matchers");
338 let span = token.span.substitute_dummy(sp);
339 let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
340 err.span_label(span, label);
341 if !def_span.is_dummy() && !cx.source_map().is_imported(def_span) {
342 err.span_label(cx.source_map().guess_head_span(def_span), "when calling this macro");
345 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
346 if let Some((arg, comma_span)) = arg.add_comma() {
348 // try each arm's matchers
349 let lhs_tt = match *lhs {
350 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
354 parse_tt(&mut Cow::Borrowed(&parser_from_cx(sess, arg.clone())), lhs_tt)
356 if comma_span.is_dummy() {
357 err.note("you might be missing a comma");
359 err.span_suggestion_short(
361 "missing comma here",
363 Applicability::MachineApplicable,
370 cx.trace_macros_diag();
374 // Note that macro-by-example's input is also matched against a token tree:
375 // $( $lhs:tt => $rhs:tt );+
377 // Holy self-referential!
379 /// Converts a macro item into a syntax extension.
380 pub fn compile_declarative_macro(
385 ) -> SyntaxExtension {
386 debug!("compile_declarative_macro: {:?}", def);
387 let mk_syn_ext = |expander| {
388 SyntaxExtension::new(
390 SyntaxExtensionKind::LegacyBang(expander),
399 let diag = &sess.span_diagnostic;
400 let lhs_nm = Ident::new(sym::lhs, def.span);
401 let rhs_nm = Ident::new(sym::rhs, def.span);
402 let tt_spec = Some(NonterminalKind::TT);
404 // Parse the macro_rules! invocation
405 let (macro_rules, body) = match &def.kind {
406 ast::ItemKind::MacroDef(def) => (def.macro_rules, def.body.inner_tokens()),
410 // The pattern that macro_rules matches.
411 // The grammar for macro_rules! is:
412 // $( $lhs:tt => $rhs:tt );+
413 // ...quasiquoting this would be nice.
414 // These spans won't matter, anyways
415 let argument_gram = vec![
416 mbe::TokenTree::Sequence(
418 Lrc::new(mbe::SequenceRepetition {
420 mbe::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
421 mbe::TokenTree::token(token::FatArrow, def.span),
422 mbe::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
424 separator: Some(Token::new(
425 if macro_rules { token::Semi } else { token::Comma },
428 kleene: mbe::KleeneToken::new(mbe::KleeneOp::OneOrMore, def.span),
432 // to phase into semicolon-termination instead of semicolon-separation
433 mbe::TokenTree::Sequence(
435 Lrc::new(mbe::SequenceRepetition {
436 tts: vec![mbe::TokenTree::token(
437 if macro_rules { token::Semi } else { token::Comma },
441 kleene: mbe::KleeneToken::new(mbe::KleeneOp::ZeroOrMore, def.span),
447 let parser = Parser::new(sess, body, true, rustc_parse::MACRO_ARGUMENTS);
448 let argument_map = match parse_tt(&mut Cow::Borrowed(&parser), &argument_gram) {
450 Failure(token, msg) => {
451 let s = parse_failure_msg(&token);
452 let sp = token.span.substitute_dummy(def.span);
453 sess.span_diagnostic.struct_span_err(sp, &s).span_label(sp, msg).emit();
454 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
457 sess.span_diagnostic.struct_span_err(sp.substitute_dummy(def.span), &msg).emit();
458 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
461 return mk_syn_ext(Box::new(macro_rules_dummy_expander));
465 let mut valid = true;
467 // Extract the arguments:
468 let lhses = match argument_map[&MacroRulesNormalizedIdent::new(lhs_nm)] {
469 MatchedSeq(ref s) => s
472 if let MatchedNonterminal(ref nt) = *m {
473 if let NtTT(ref tt) = **nt {
474 let tt = mbe::quoted::parse(tt.clone().into(), true, sess, def.id)
477 valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt);
481 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
483 .collect::<Vec<mbe::TokenTree>>(),
484 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
487 let rhses = match argument_map[&MacroRulesNormalizedIdent::new(rhs_nm)] {
488 MatchedSeq(ref s) => s
491 if let MatchedNonterminal(ref nt) = *m {
492 if let NtTT(ref tt) = **nt {
493 return mbe::quoted::parse(tt.clone().into(), false, sess, def.id)
498 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
500 .collect::<Vec<mbe::TokenTree>>(),
501 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
505 valid &= check_rhs(sess, rhs);
508 // don't abort iteration early, so that errors for multiple lhses can be reported
510 valid &= check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
513 valid &= macro_check::check_meta_variables(sess, def.id, def.span, &lhses, &rhses);
515 let (transparency, transparency_error) = attr::find_transparency(&def.attrs, macro_rules);
516 match transparency_error {
517 Some(TransparencyError::UnknownTransparency(value, span)) => {
518 diag.span_err(span, &format!("unknown macro transparency: `{}`", value))
520 Some(TransparencyError::MultipleTransparencyAttrs(old_span, new_span)) => {
521 diag.span_err(vec![old_span, new_span], "multiple macro transparency attributes")
526 mk_syn_ext(Box::new(MacroRulesMacroExpander {
536 fn check_lhs_nt_follows(
539 attrs: &[ast::Attribute],
540 lhs: &mbe::TokenTree,
542 // lhs is going to be like TokenTree::Delimited(...), where the
543 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
544 if let mbe::TokenTree::Delimited(_, ref tts) = *lhs {
545 check_matcher(sess, features, attrs, &tts.tts)
547 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
548 sess.span_diagnostic.span_err(lhs.span(), msg);
551 // we don't abort on errors on rejection, the driver will do that for us
552 // after parsing/expansion. we can report every error in every macro this way.
555 /// Checks that the lhs contains no repetition which could match an empty token
556 /// tree, because then the matcher would hang indefinitely.
557 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
561 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
562 TokenTree::Delimited(_, ref del) => {
563 if !check_lhs_no_empty_seq(sess, &del.tts) {
567 TokenTree::Sequence(span, ref seq) => {
568 if seq.separator.is_none()
569 && seq.tts.iter().all(|seq_tt| match *seq_tt {
570 TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)) => true,
571 TokenTree::Sequence(_, ref sub_seq) => {
572 sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
573 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
578 let sp = span.entire();
579 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
582 if !check_lhs_no_empty_seq(sess, &seq.tts) {
592 fn check_rhs(sess: &ParseSess, rhs: &mbe::TokenTree) -> bool {
594 mbe::TokenTree::Delimited(..) => return true,
595 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
603 attrs: &[ast::Attribute],
604 matcher: &[mbe::TokenTree],
606 let first_sets = FirstSets::new(matcher);
607 let empty_suffix = TokenSet::empty();
608 let err = sess.span_diagnostic.err_count();
609 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
610 err == sess.span_diagnostic.err_count()
613 // `The FirstSets` for a matcher is a mapping from subsequences in the
614 // matcher to the FIRST set for that subsequence.
616 // This mapping is partially precomputed via a backwards scan over the
617 // token trees of the matcher, which provides a mapping from each
618 // repetition sequence to its *first* set.
620 // (Hypothetically, sequences should be uniquely identifiable via their
621 // spans, though perhaps that is false, e.g., for macro-generated macros
622 // that do not try to inject artificial span information. My plan is
623 // to try to catch such cases ahead of time and not include them in
624 // the precomputed mapping.)
626 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
627 // span in the original matcher to the First set for the inner sequence `tt ...`.
629 // If two sequences have the same span in a matcher, then map that
630 // span to None (invalidating the mapping here and forcing the code to
632 first: FxHashMap<Span, Option<TokenSet>>,
636 fn new(tts: &[mbe::TokenTree]) -> FirstSets {
639 let mut sets = FirstSets { first: FxHashMap::default() };
640 build_recur(&mut sets, tts);
643 // walks backward over `tts`, returning the FIRST for `tts`
644 // and updating `sets` at the same time for all sequence
645 // substructure we find within `tts`.
646 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
647 let mut first = TokenSet::empty();
648 for tt in tts.iter().rev() {
650 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
651 first.replace_with(tt.clone());
653 TokenTree::Delimited(span, ref delimited) => {
654 build_recur(sets, &delimited.tts[..]);
655 first.replace_with(delimited.open_tt(span));
657 TokenTree::Sequence(sp, ref seq_rep) => {
658 let subfirst = build_recur(sets, &seq_rep.tts[..]);
660 match sets.first.entry(sp.entire()) {
661 Entry::Vacant(vac) => {
662 vac.insert(Some(subfirst.clone()));
664 Entry::Occupied(mut occ) => {
665 // if there is already an entry, then a span must have collided.
666 // This should not happen with typical macro_rules macros,
667 // but syntax extensions need not maintain distinct spans,
668 // so distinct syntax trees can be assigned the same span.
669 // In such a case, the map cannot be trusted; so mark this
670 // entry as unusable.
675 // If the sequence contents can be empty, then the first
676 // token could be the separator token itself.
678 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
679 first.add_one_maybe(TokenTree::Token(sep.clone()));
682 // Reverse scan: Sequence comes before `first`.
683 if subfirst.maybe_empty
684 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
685 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
687 // If sequence is potentially empty, then
688 // union them (preserving first emptiness).
689 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
691 // Otherwise, sequence guaranteed
692 // non-empty; replace first.
703 // walks forward over `tts` until all potential FIRST tokens are
705 fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
708 let mut first = TokenSet::empty();
709 for tt in tts.iter() {
710 assert!(first.maybe_empty);
712 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
713 first.add_one(tt.clone());
716 TokenTree::Delimited(span, ref delimited) => {
717 first.add_one(delimited.open_tt(span));
720 TokenTree::Sequence(sp, ref seq_rep) => {
722 let subfirst = match self.first.get(&sp.entire()) {
723 Some(&Some(ref subfirst)) => subfirst,
725 subfirst_owned = self.first(&seq_rep.tts[..]);
729 panic!("We missed a sequence during FirstSets construction");
733 // If the sequence contents can be empty, then the first
734 // token could be the separator token itself.
735 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
736 first.add_one_maybe(TokenTree::Token(sep.clone()));
739 assert!(first.maybe_empty);
740 first.add_all(subfirst);
741 if subfirst.maybe_empty
742 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
743 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
745 // Continue scanning for more first
746 // tokens, but also make sure we
747 // restore empty-tracking state.
748 first.maybe_empty = true;
757 // we only exit the loop if `tts` was empty or if every
758 // element of `tts` matches the empty sequence.
759 assert!(first.maybe_empty);
764 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
765 // (for macro-by-example syntactic variables). It also carries the
766 // `maybe_empty` flag; that is true if and only if the matcher can
767 // match an empty token sequence.
769 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
770 // which has corresponding FIRST = {$a:expr, c, d}.
771 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
773 // (Notably, we must allow for *-op to occur zero times.)
774 #[derive(Clone, Debug)]
776 tokens: Vec<mbe::TokenTree>,
781 // Returns a set for the empty sequence.
783 TokenSet { tokens: Vec::new(), maybe_empty: true }
786 // Returns the set `{ tok }` for the single-token (and thus
787 // non-empty) sequence [tok].
788 fn singleton(tok: mbe::TokenTree) -> Self {
789 TokenSet { tokens: vec![tok], maybe_empty: false }
792 // Changes self to be the set `{ tok }`.
793 // Since `tok` is always present, marks self as non-empty.
794 fn replace_with(&mut self, tok: mbe::TokenTree) {
796 self.tokens.push(tok);
797 self.maybe_empty = false;
800 // Changes self to be the empty set `{}`; meant for use when
801 // the particular token does not matter, but we want to
802 // record that it occurs.
803 fn replace_with_irrelevant(&mut self) {
805 self.maybe_empty = false;
808 // Adds `tok` to the set for `self`, marking sequence as non-empy.
809 fn add_one(&mut self, tok: mbe::TokenTree) {
810 if !self.tokens.contains(&tok) {
811 self.tokens.push(tok);
813 self.maybe_empty = false;
816 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
817 fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
818 if !self.tokens.contains(&tok) {
819 self.tokens.push(tok);
823 // Adds all elements of `other` to this.
825 // (Since this is a set, we filter out duplicates.)
827 // If `other` is potentially empty, then preserves the previous
828 // setting of the empty flag of `self`. If `other` is guaranteed
829 // non-empty, then `self` is marked non-empty.
830 fn add_all(&mut self, other: &Self) {
831 for tok in &other.tokens {
832 if !self.tokens.contains(tok) {
833 self.tokens.push(tok.clone());
836 if !other.maybe_empty {
837 self.maybe_empty = false;
842 // Checks that `matcher` is internally consistent and that it
843 // can legally be followed by a token `N`, for all `N` in `follow`.
844 // (If `follow` is empty, then it imposes no constraint on
847 // Returns the set of NT tokens that could possibly come last in
848 // `matcher`. (If `matcher` matches the empty sequence, then
849 // `maybe_empty` will be set to true.)
851 // Requires that `first_sets` is pre-computed for `matcher`;
852 // see `FirstSets::new`.
853 fn check_matcher_core(
856 attrs: &[ast::Attribute],
857 first_sets: &FirstSets,
858 matcher: &[mbe::TokenTree],
863 let mut last = TokenSet::empty();
865 // 2. For each token and suffix [T, SUFFIX] in M:
866 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
867 // then ensure T can also be followed by any element of FOLLOW.
868 'each_token: for i in 0..matcher.len() {
869 let token = &matcher[i];
870 let suffix = &matcher[i + 1..];
872 let build_suffix_first = || {
873 let mut s = first_sets.first(suffix);
880 // (we build `suffix_first` on demand below; you can tell
881 // which cases are supposed to fall through by looking for the
882 // initialization of this variable.)
885 // First, update `last` so that it corresponds to the set
886 // of NT tokens that might end the sequence `... token`.
888 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
889 if token_can_be_followed_by_any(token) {
890 // don't need to track tokens that work with any,
891 last.replace_with_irrelevant();
892 // ... and don't need to check tokens that can be
893 // followed by anything against SUFFIX.
894 continue 'each_token;
896 last.replace_with(token.clone());
897 suffix_first = build_suffix_first();
900 TokenTree::Delimited(span, ref d) => {
901 let my_suffix = TokenSet::singleton(d.close_tt(span));
902 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
903 // don't track non NT tokens
904 last.replace_with_irrelevant();
906 // also, we don't need to check delimited sequences
908 continue 'each_token;
910 TokenTree::Sequence(_, ref seq_rep) => {
911 suffix_first = build_suffix_first();
912 // The trick here: when we check the interior, we want
913 // to include the separator (if any) as a potential
914 // (but not guaranteed) element of FOLLOW. So in that
915 // case, we make a temp copy of suffix and stuff
916 // delimiter in there.
918 // FIXME: Should I first scan suffix_first to see if
919 // delimiter is already in it before I go through the
920 // work of cloning it? But then again, this way I may
921 // get a "tighter" span?
923 let my_suffix = if let Some(sep) = &seq_rep.separator {
924 new = suffix_first.clone();
925 new.add_one_maybe(TokenTree::Token(sep.clone()));
931 // At this point, `suffix_first` is built, and
932 // `my_suffix` is some TokenSet that we can use
933 // for checking the interior of `seq_rep`.
935 check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
936 if next.maybe_empty {
942 // the recursive call to check_matcher_core already ran the 'each_last
943 // check below, so we can just keep going forward here.
944 continue 'each_token;
948 // (`suffix_first` guaranteed initialized once reaching here.)
950 // Now `last` holds the complete set of NT tokens that could
951 // end the sequence before SUFFIX. Check that every one works with `suffix`.
952 for token in &last.tokens {
953 if let TokenTree::MetaVarDecl(_, name, Some(kind)) = *token {
954 for next_token in &suffix_first.tokens {
955 match is_in_follow(next_token, kind) {
956 IsInFollow::Yes => {}
957 IsInFollow::No(possible) => {
958 let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
965 let sp = next_token.span();
966 let mut err = sess.span_diagnostic.struct_span_err(
969 "`${name}:{frag}` {may_be} followed by `{next}`, which \
970 is not allowed for `{frag}` fragments",
973 next = quoted_tt_to_string(next_token),
977 err.span_label(sp, format!("not allowed after `{}` fragments", kind));
978 let msg = "allowed there are: ";
983 "only {} is allowed after `{}` fragments",
1010 fn token_can_be_followed_by_any(tok: &mbe::TokenTree) -> bool {
1011 if let mbe::TokenTree::MetaVarDecl(_, _, Some(kind)) = *tok {
1012 frag_can_be_followed_by_any(kind)
1014 // (Non NT's can always be followed by anything in matchers.)
1019 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
1020 /// token. We use this (among other things) as a useful approximation
1021 /// for when `frag` can be followed by a repetition like `$(...)*` or
1022 /// `$(...)+`. In general, these can be a bit tricky to reason about,
1023 /// so we adopt a conservative position that says that any fragment
1024 /// specifier which consumes at most one token tree can be followed by
1025 /// a fragment specifier (indeed, these fragments can be followed by
1026 /// ANYTHING without fear of future compatibility hazards).
1027 fn frag_can_be_followed_by_any(kind: NonterminalKind) -> bool {
1029 NonterminalKind::Item // always terminated by `}` or `;`
1030 | NonterminalKind::Block // exactly one token tree
1031 | NonterminalKind::Ident // exactly one token tree
1032 | NonterminalKind::Literal // exactly one token tree
1033 | NonterminalKind::Meta // exactly one token tree
1034 | NonterminalKind::Lifetime // exactly one token tree
1035 | NonterminalKind::TT => true, // exactly one token tree
1043 No(&'static [&'static str]),
1046 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1047 /// fragments that can consume an unbounded number of tokens, `tok`
1048 /// must be within a well-defined follow set. This is intended to
1049 /// guarantee future compatibility: for example, without this rule, if
1050 /// we expanded `expr` to include a new binary operator, we might
1051 /// break macros that were relying on that binary operator as a
1053 // when changing this do not forget to update doc/book/macros.md!
1054 fn is_in_follow(tok: &mbe::TokenTree, kind: NonterminalKind) -> IsInFollow {
1057 if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
1058 // closing a token tree can never be matched by any fragment;
1059 // iow, we always require that `(` and `)` match, etc.
1063 NonterminalKind::Item => {
1064 // since items *must* be followed by either a `;` or a `}`, we can
1065 // accept anything after them
1068 NonterminalKind::Block => {
1069 // anything can follow block, the braces provide an easy boundary to
1073 NonterminalKind::Stmt | NonterminalKind::Expr => {
1074 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
1076 TokenTree::Token(token) => match token.kind {
1077 FatArrow | Comma | Semi => IsInFollow::Yes,
1078 _ => IsInFollow::No(TOKENS),
1080 _ => IsInFollow::No(TOKENS),
1083 NonterminalKind::Pat => {
1084 const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1086 TokenTree::Token(token) => match token.kind {
1087 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
1088 Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
1089 _ => IsInFollow::No(TOKENS),
1091 _ => IsInFollow::No(TOKENS),
1094 NonterminalKind::Path | NonterminalKind::Ty => {
1095 const TOKENS: &[&str] = &[
1096 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1100 TokenTree::Token(token) => match token.kind {
1101 OpenDelim(token::DelimToken::Brace)
1102 | OpenDelim(token::DelimToken::Bracket)
1110 | BinOp(token::Or) => IsInFollow::Yes,
1111 Ident(name, false) if name == kw::As || name == kw::Where => {
1114 _ => IsInFollow::No(TOKENS),
1116 TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Block)) => IsInFollow::Yes,
1117 _ => IsInFollow::No(TOKENS),
1120 NonterminalKind::Ident | NonterminalKind::Lifetime => {
1121 // being a single token, idents and lifetimes are harmless
1124 NonterminalKind::Literal => {
1125 // literals may be of a single token, or two tokens (negative numbers)
1128 NonterminalKind::Meta | NonterminalKind::TT => {
1129 // being either a single token or a delimited sequence, tt is
1133 NonterminalKind::Vis => {
1134 // Explicitly disallow `priv`, on the off chance it comes back.
1135 const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
1137 TokenTree::Token(token) => match token.kind {
1138 Comma => IsInFollow::Yes,
1139 Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
1141 if token.can_begin_type() {
1144 IsInFollow::No(TOKENS)
1148 TokenTree::MetaVarDecl(
1151 Some(NonterminalKind::Ident | NonterminalKind::Ty | NonterminalKind::Path),
1152 ) => IsInFollow::Yes,
1153 _ => IsInFollow::No(TOKENS),
1160 fn quoted_tt_to_string(tt: &mbe::TokenTree) -> String {
1162 mbe::TokenTree::Token(ref token) => pprust::token_to_string(&token),
1163 mbe::TokenTree::MetaVar(_, name) => format!("${}", name),
1164 mbe::TokenTree::MetaVarDecl(_, name, Some(kind)) => format!("${}:{}", name, kind),
1165 mbe::TokenTree::MetaVarDecl(_, name, None) => format!("${}:", name),
1167 "unexpected mbe::TokenTree::{{Sequence or Delimited}} \
1168 in follow set checker"
1173 fn parser_from_cx(sess: &ParseSess, tts: TokenStream) -> Parser<'_> {
1174 Parser::new(sess, tts, true, rustc_parse::MACRO_ARGUMENTS)
1177 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
1178 /// other tokens, this is "unexpected token...".
1179 fn parse_failure_msg(tok: &Token) -> String {
1181 token::Eof => "unexpected end of macro invocation".to_string(),
1182 _ => format!("no rules expected the token `{}`", pprust::token_to_string(tok),),