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;
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_data_structures::fx::FxHashMap;
12 use rustc_data_structures::sync::Lrc;
13 use rustc_errors::{Applicability, DiagnosticBuilder, FatalError};
14 use rustc_feature::Features;
15 use rustc_parse::parser::Parser;
16 use rustc_parse::Directory;
17 use rustc_span::edition::Edition;
18 use rustc_span::hygiene::Transparency;
19 use rustc_span::symbol::{kw, sym, Symbol};
22 use syntax::attr::{self, TransparencyError};
23 use syntax::print::pprust;
24 use syntax::sess::ParseSess;
25 use syntax::token::{self, NtTT, Token, TokenKind::*};
26 use syntax::tokenstream::{DelimSpan, TokenStream};
30 use std::collections::hash_map::Entry;
31 use std::{mem, slice};
33 const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
34 `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, \
35 `literal`, `path`, `meta`, `tt`, `item` and `vis`";
37 crate struct ParserAnyMacro<'a> {
40 /// Span of the expansion site of the macro this parser is for
42 /// The ident of the macro we're parsing
43 macro_ident: ast::Ident,
47 crate fn annotate_err_with_kind(
48 err: &mut DiagnosticBuilder<'_>,
49 kind: AstFragmentKind,
53 AstFragmentKind::Ty => {
54 err.span_label(span, "this macro call doesn't expand to a type");
56 AstFragmentKind::Pat => {
57 err.span_label(span, "this macro call doesn't expand to a pattern");
63 /// Instead of e.g. `vec![a, b, c]` in a pattern context, suggest `[a, b, c]`.
64 fn suggest_slice_pat(e: &mut DiagnosticBuilder<'_>, site_span: Span, parser: &Parser<'_>) {
65 let mut suggestion = None;
66 if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
67 if let Some(bang) = code.find('!') {
68 suggestion = Some(code[bang + 1..].to_string());
71 if let Some(suggestion) = suggestion {
74 "use a slice pattern here instead",
76 Applicability::MachineApplicable,
79 e.span_label(site_span, "use a slice pattern here instead");
82 "for more information, see https://doc.rust-lang.org/edition-guide/\
83 rust-2018/slice-patterns.html",
87 impl<'a> ParserAnyMacro<'a> {
88 crate fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
89 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
90 let fragment = panictry!(parse_ast_fragment(parser, kind, true).map_err(|mut e| {
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().span_to_filename(arm_span).is_real() {
109 e.span_label(arm_span, "in this macro arm");
111 } else if !parser.sess.source_map().span_to_filename(parser.token.span).is_real() {
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 _ => annotate_err_with_kind(&mut e, kind, site_span),
123 // We allow semicolons at the end of expressions -- e.g., the semicolon in
124 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
125 // but `m!()` is allowed in expression positions (cf. issue #34706).
126 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
130 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
131 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
132 ensure_complete_parse(parser, &path, kind.name(), site_span);
137 struct MacroRulesMacroExpander {
140 transparency: Transparency,
141 lhses: Vec<mbe::TokenTree>,
142 rhses: Vec<mbe::TokenTree>,
146 impl TTMacroExpander for MacroRulesMacroExpander {
149 cx: &'cx mut ExtCtxt<'_>,
152 ) -> Box<dyn MacResult + 'cx> {
154 return DummyResult::any(sp);
169 fn trace_macros_note(cx: &mut ExtCtxt<'_>, sp: Span, message: String) {
170 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
171 cx.expansions.entry(sp).or_default().push(message);
174 /// Given `lhses` and `rhses`, this is the new macro we create
175 fn generic_extension<'cx>(
176 cx: &'cx mut ExtCtxt<'_>,
180 transparency: Transparency,
182 lhses: &[mbe::TokenTree],
183 rhses: &[mbe::TokenTree],
184 ) -> Box<dyn MacResult + 'cx> {
185 if cx.trace_macros() {
186 let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(arg.clone()));
187 trace_macros_note(cx, sp, msg);
190 // Which arm's failure should we report? (the one furthest along)
191 let mut best_failure: Option<(Token, &str)> = None;
192 for (i, lhs) in lhses.iter().enumerate() {
193 // try each arm's matchers
194 let lhs_tt = match *lhs {
195 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
196 _ => cx.span_bug(sp, "malformed macro lhs"),
199 // Take a snapshot of the state of pre-expansion gating at this point.
200 // This is used so that if a matcher is not `Success(..)`ful,
201 // then the spans which became gated when parsing the unsuccessful matcher
202 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
203 let mut gated_spans_snaphot = mem::take(&mut *cx.parse_sess.gated_spans.spans.borrow_mut());
205 match parse_tt(cx, lhs_tt, arg.clone()) {
206 Success(named_matches) => {
207 // The matcher was `Success(..)`ful.
208 // Merge the gated spans from parsing the matcher with the pre-existing ones.
209 cx.parse_sess.gated_spans.merge(gated_spans_snaphot);
211 let rhs = match rhses[i] {
213 mbe::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
214 _ => cx.span_bug(sp, "malformed macro rhs"),
216 let arm_span = rhses[i].span();
218 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
219 // rhs has holes ( `$id` and `$(...)` that need filled)
220 let mut tts = transcribe(cx, &named_matches, rhs, transparency);
222 // Replace all the tokens for the corresponding positions in the macro, to maintain
223 // proper positions in error reporting, while maintaining the macro_backtrace.
224 if rhs_spans.len() == tts.len() {
225 tts = tts.map_enumerated(|i, mut tt| {
226 let mut sp = rhs_spans[i];
227 sp = sp.with_ctxt(tt.span().ctxt());
233 if cx.trace_macros() {
234 let msg = format!("to `{}`", pprust::tts_to_string(tts.clone()));
235 trace_macros_note(cx, sp, msg);
238 let directory = Directory {
239 path: Cow::from(cx.current_expansion.module.directory.as_path()),
240 ownership: cx.current_expansion.directory_ownership,
242 let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false, None);
244 cx.current_expansion.module.mod_path.last().map(|id| id.to_string());
245 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
247 p.process_potential_macro_variable();
248 // Let the context choose how to interpret the result.
249 // Weird, but useful for X-macros.
250 return Box::new(ParserAnyMacro {
253 // Pass along the original expansion site and the name of the macro
254 // so we can print a useful error message if the parse of the expanded
255 // macro leaves unparsed tokens.
261 Failure(token, msg) => match best_failure {
262 Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
263 _ => best_failure = Some((token, msg)),
265 Error(err_sp, ref msg) => cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..]),
268 // The matcher was not `Success(..)`ful.
269 // Restore to the state before snapshotting and maybe try again.
270 mem::swap(&mut gated_spans_snaphot, &mut cx.parse_sess.gated_spans.spans.borrow_mut());
273 let (token, label) = best_failure.expect("ran no matchers");
274 let span = token.span.substitute_dummy(sp);
275 let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
276 err.span_label(span, label);
277 if !def_span.is_dummy() && cx.source_map().span_to_filename(def_span).is_real() {
278 err.span_label(cx.source_map().def_span(def_span), "when calling this macro");
281 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
282 if let Some((arg, comma_span)) = arg.add_comma() {
284 // try each arm's matchers
285 let lhs_tt = match *lhs {
286 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
289 match parse_tt(cx, lhs_tt, arg.clone()) {
291 if comma_span.is_dummy() {
292 err.note("you might be missing a comma");
294 err.span_suggestion_short(
296 "missing comma here",
298 Applicability::MachineApplicable,
307 cx.trace_macros_diag();
311 // Note that macro-by-example's input is also matched against a token tree:
312 // $( $lhs:tt => $rhs:tt );+
314 // Holy self-referential!
316 /// Converts a macro item into a syntax extension.
317 pub fn compile_declarative_macro(
322 ) -> SyntaxExtension {
323 let diag = &sess.span_diagnostic;
324 let lhs_nm = ast::Ident::new(sym::lhs, def.span);
325 let rhs_nm = ast::Ident::new(sym::rhs, def.span);
326 let tt_spec = ast::Ident::new(sym::tt, def.span);
328 // Parse the macro_rules! invocation
329 let (is_legacy, body) = match &def.kind {
330 ast::ItemKind::MacroDef(macro_def) => (macro_def.legacy, macro_def.body.inner_tokens()),
334 // The pattern that macro_rules matches.
335 // The grammar for macro_rules! is:
336 // $( $lhs:tt => $rhs:tt );+
337 // ...quasiquoting this would be nice.
338 // These spans won't matter, anyways
339 let argument_gram = vec![
340 mbe::TokenTree::Sequence(
342 Lrc::new(mbe::SequenceRepetition {
344 mbe::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
345 mbe::TokenTree::token(token::FatArrow, def.span),
346 mbe::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
348 separator: Some(Token::new(
349 if is_legacy { token::Semi } else { token::Comma },
352 kleene: mbe::KleeneToken::new(mbe::KleeneOp::OneOrMore, def.span),
356 // to phase into semicolon-termination instead of semicolon-separation
357 mbe::TokenTree::Sequence(
359 Lrc::new(mbe::SequenceRepetition {
360 tts: vec![mbe::TokenTree::token(
361 if is_legacy { token::Semi } else { token::Comma },
365 kleene: mbe::KleeneToken::new(mbe::KleeneOp::ZeroOrMore, def.span),
371 let argument_map = match parse(sess, body, &argument_gram, None, true) {
373 Failure(token, msg) => {
374 let s = parse_failure_msg(&token);
375 let sp = token.span.substitute_dummy(def.span);
376 let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
377 err.span_label(sp, msg);
382 sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
386 let mut valid = true;
388 // Extract the arguments:
389 let lhses = match argument_map[&lhs_nm] {
390 MatchedSeq(ref s) => s
393 if let MatchedNonterminal(ref nt) = *m {
394 if let NtTT(ref tt) = **nt {
395 let tt = mbe::quoted::parse(tt.clone().into(), true, sess).pop().unwrap();
396 valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt);
400 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
402 .collect::<Vec<mbe::TokenTree>>(),
403 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
406 let rhses = match argument_map[&rhs_nm] {
407 MatchedSeq(ref s) => s
410 if let MatchedNonterminal(ref nt) = *m {
411 if let NtTT(ref tt) = **nt {
412 return mbe::quoted::parse(tt.clone().into(), false, sess).pop().unwrap();
415 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
417 .collect::<Vec<mbe::TokenTree>>(),
418 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
422 valid &= check_rhs(sess, rhs);
425 // don't abort iteration early, so that errors for multiple lhses can be reported
427 valid &= check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
430 // We use CRATE_NODE_ID instead of `def.id` otherwise we may emit buffered lints for a node id
431 // that is not lint-checked and trigger the "failed to process buffered lint here" bug.
432 valid &= macro_check::check_meta_variables(sess, ast::CRATE_NODE_ID, def.span, &lhses, &rhses);
434 let (transparency, transparency_error) = attr::find_transparency(&def.attrs, is_legacy);
435 match transparency_error {
436 Some(TransparencyError::UnknownTransparency(value, span)) => {
437 diag.span_err(span, &format!("unknown macro transparency: `{}`", value))
439 Some(TransparencyError::MultipleTransparencyAttrs(old_span, new_span)) => {
440 diag.span_err(vec![old_span, new_span], "multiple macro transparency attributes")
445 let expander: Box<_> = Box::new(MacroRulesMacroExpander {
454 SyntaxExtension::new(
456 SyntaxExtensionKind::LegacyBang(expander),
465 fn check_lhs_nt_follows(
468 attrs: &[ast::Attribute],
469 lhs: &mbe::TokenTree,
471 // lhs is going to be like TokenTree::Delimited(...), where the
472 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
473 if let mbe::TokenTree::Delimited(_, ref tts) = *lhs {
474 check_matcher(sess, features, attrs, &tts.tts)
476 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
477 sess.span_diagnostic.span_err(lhs.span(), msg);
480 // we don't abort on errors on rejection, the driver will do that for us
481 // after parsing/expansion. we can report every error in every macro this way.
484 /// Checks that the lhs contains no repetition which could match an empty token
485 /// tree, because then the matcher would hang indefinitely.
486 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
490 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
491 TokenTree::Delimited(_, ref del) => {
492 if !check_lhs_no_empty_seq(sess, &del.tts) {
496 TokenTree::Sequence(span, ref seq) => {
497 if seq.separator.is_none()
498 && seq.tts.iter().all(|seq_tt| match *seq_tt {
499 TokenTree::MetaVarDecl(_, _, id) => id.name == sym::vis,
500 TokenTree::Sequence(_, ref sub_seq) => {
501 sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
502 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
507 let sp = span.entire();
508 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
511 if !check_lhs_no_empty_seq(sess, &seq.tts) {
521 fn check_rhs(sess: &ParseSess, rhs: &mbe::TokenTree) -> bool {
523 mbe::TokenTree::Delimited(..) => return true,
524 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
532 attrs: &[ast::Attribute],
533 matcher: &[mbe::TokenTree],
535 let first_sets = FirstSets::new(matcher);
536 let empty_suffix = TokenSet::empty();
537 let err = sess.span_diagnostic.err_count();
538 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
539 err == sess.span_diagnostic.err_count()
542 // `The FirstSets` for a matcher is a mapping from subsequences in the
543 // matcher to the FIRST set for that subsequence.
545 // This mapping is partially precomputed via a backwards scan over the
546 // token trees of the matcher, which provides a mapping from each
547 // repetition sequence to its *first* set.
549 // (Hypothetically, sequences should be uniquely identifiable via their
550 // spans, though perhaps that is false, e.g., for macro-generated macros
551 // that do not try to inject artificial span information. My plan is
552 // to try to catch such cases ahead of time and not include them in
553 // the precomputed mapping.)
555 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
556 // span in the original matcher to the First set for the inner sequence `tt ...`.
558 // If two sequences have the same span in a matcher, then map that
559 // span to None (invalidating the mapping here and forcing the code to
561 first: FxHashMap<Span, Option<TokenSet>>,
565 fn new(tts: &[mbe::TokenTree]) -> FirstSets {
568 let mut sets = FirstSets { first: FxHashMap::default() };
569 build_recur(&mut sets, tts);
572 // walks backward over `tts`, returning the FIRST for `tts`
573 // and updating `sets` at the same time for all sequence
574 // substructure we find within `tts`.
575 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
576 let mut first = TokenSet::empty();
577 for tt in tts.iter().rev() {
579 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
580 first.replace_with(tt.clone());
582 TokenTree::Delimited(span, ref delimited) => {
583 build_recur(sets, &delimited.tts[..]);
584 first.replace_with(delimited.open_tt(span));
586 TokenTree::Sequence(sp, ref seq_rep) => {
587 let subfirst = build_recur(sets, &seq_rep.tts[..]);
589 match sets.first.entry(sp.entire()) {
590 Entry::Vacant(vac) => {
591 vac.insert(Some(subfirst.clone()));
593 Entry::Occupied(mut occ) => {
594 // if there is already an entry, then a span must have collided.
595 // This should not happen with typical macro_rules macros,
596 // but syntax extensions need not maintain distinct spans,
597 // so distinct syntax trees can be assigned the same span.
598 // In such a case, the map cannot be trusted; so mark this
599 // entry as unusable.
604 // If the sequence contents can be empty, then the first
605 // token could be the separator token itself.
607 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
608 first.add_one_maybe(TokenTree::Token(sep.clone()));
611 // Reverse scan: Sequence comes before `first`.
612 if subfirst.maybe_empty
613 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
614 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
616 // If sequence is potentially empty, then
617 // union them (preserving first emptiness).
618 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
620 // Otherwise, sequence guaranteed
621 // non-empty; replace first.
632 // walks forward over `tts` until all potential FIRST tokens are
634 fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
637 let mut first = TokenSet::empty();
638 for tt in tts.iter() {
639 assert!(first.maybe_empty);
641 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
642 first.add_one(tt.clone());
645 TokenTree::Delimited(span, ref delimited) => {
646 first.add_one(delimited.open_tt(span));
649 TokenTree::Sequence(sp, ref seq_rep) => {
651 let subfirst = match self.first.get(&sp.entire()) {
652 Some(&Some(ref subfirst)) => subfirst,
654 subfirst_owned = self.first(&seq_rep.tts[..]);
658 panic!("We missed a sequence during FirstSets construction");
662 // If the sequence contents can be empty, then the first
663 // token could be the separator token itself.
664 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
665 first.add_one_maybe(TokenTree::Token(sep.clone()));
668 assert!(first.maybe_empty);
669 first.add_all(subfirst);
670 if subfirst.maybe_empty
671 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
672 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
674 // Continue scanning for more first
675 // tokens, but also make sure we
676 // restore empty-tracking state.
677 first.maybe_empty = true;
686 // we only exit the loop if `tts` was empty or if every
687 // element of `tts` matches the empty sequence.
688 assert!(first.maybe_empty);
693 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
694 // (for macro-by-example syntactic variables). It also carries the
695 // `maybe_empty` flag; that is true if and only if the matcher can
696 // match an empty token sequence.
698 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
699 // which has corresponding FIRST = {$a:expr, c, d}.
700 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
702 // (Notably, we must allow for *-op to occur zero times.)
703 #[derive(Clone, Debug)]
705 tokens: Vec<mbe::TokenTree>,
710 // Returns a set for the empty sequence.
712 TokenSet { tokens: Vec::new(), maybe_empty: true }
715 // Returns the set `{ tok }` for the single-token (and thus
716 // non-empty) sequence [tok].
717 fn singleton(tok: mbe::TokenTree) -> Self {
718 TokenSet { tokens: vec![tok], maybe_empty: false }
721 // Changes self to be the set `{ tok }`.
722 // Since `tok` is always present, marks self as non-empty.
723 fn replace_with(&mut self, tok: mbe::TokenTree) {
725 self.tokens.push(tok);
726 self.maybe_empty = false;
729 // Changes self to be the empty set `{}`; meant for use when
730 // the particular token does not matter, but we want to
731 // record that it occurs.
732 fn replace_with_irrelevant(&mut self) {
734 self.maybe_empty = false;
737 // Adds `tok` to the set for `self`, marking sequence as non-empy.
738 fn add_one(&mut self, tok: mbe::TokenTree) {
739 if !self.tokens.contains(&tok) {
740 self.tokens.push(tok);
742 self.maybe_empty = false;
745 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
746 fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
747 if !self.tokens.contains(&tok) {
748 self.tokens.push(tok);
752 // Adds all elements of `other` to this.
754 // (Since this is a set, we filter out duplicates.)
756 // If `other` is potentially empty, then preserves the previous
757 // setting of the empty flag of `self`. If `other` is guaranteed
758 // non-empty, then `self` is marked non-empty.
759 fn add_all(&mut self, other: &Self) {
760 for tok in &other.tokens {
761 if !self.tokens.contains(tok) {
762 self.tokens.push(tok.clone());
765 if !other.maybe_empty {
766 self.maybe_empty = false;
771 // Checks that `matcher` is internally consistent and that it
772 // can legally be followed by a token `N`, for all `N` in `follow`.
773 // (If `follow` is empty, then it imposes no constraint on
776 // Returns the set of NT tokens that could possibly come last in
777 // `matcher`. (If `matcher` matches the empty sequence, then
778 // `maybe_empty` will be set to true.)
780 // Requires that `first_sets` is pre-computed for `matcher`;
781 // see `FirstSets::new`.
782 fn check_matcher_core(
785 attrs: &[ast::Attribute],
786 first_sets: &FirstSets,
787 matcher: &[mbe::TokenTree],
792 let mut last = TokenSet::empty();
794 // 2. For each token and suffix [T, SUFFIX] in M:
795 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
796 // then ensure T can also be followed by any element of FOLLOW.
797 'each_token: for i in 0..matcher.len() {
798 let token = &matcher[i];
799 let suffix = &matcher[i + 1..];
801 let build_suffix_first = || {
802 let mut s = first_sets.first(suffix);
809 // (we build `suffix_first` on demand below; you can tell
810 // which cases are supposed to fall through by looking for the
811 // initialization of this variable.)
814 // First, update `last` so that it corresponds to the set
815 // of NT tokens that might end the sequence `... token`.
817 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
818 let can_be_followed_by_any;
819 if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) {
820 let msg = format!("invalid fragment specifier `{}`", bad_frag);
822 .struct_span_err(token.span(), &msg)
823 .help(VALID_FRAGMENT_NAMES_MSG)
825 // (This eliminates false positives and duplicates
826 // from error messages.)
827 can_be_followed_by_any = true;
829 can_be_followed_by_any = token_can_be_followed_by_any(token);
832 if can_be_followed_by_any {
833 // don't need to track tokens that work with any,
834 last.replace_with_irrelevant();
835 // ... and don't need to check tokens that can be
836 // followed by anything against SUFFIX.
837 continue 'each_token;
839 last.replace_with(token.clone());
840 suffix_first = build_suffix_first();
843 TokenTree::Delimited(span, ref d) => {
844 let my_suffix = TokenSet::singleton(d.close_tt(span));
845 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
846 // don't track non NT tokens
847 last.replace_with_irrelevant();
849 // also, we don't need to check delimited sequences
851 continue 'each_token;
853 TokenTree::Sequence(_, ref seq_rep) => {
854 suffix_first = build_suffix_first();
855 // The trick here: when we check the interior, we want
856 // to include the separator (if any) as a potential
857 // (but not guaranteed) element of FOLLOW. So in that
858 // case, we make a temp copy of suffix and stuff
859 // delimiter in there.
861 // FIXME: Should I first scan suffix_first to see if
862 // delimiter is already in it before I go through the
863 // work of cloning it? But then again, this way I may
864 // get a "tighter" span?
866 let my_suffix = if let Some(sep) = &seq_rep.separator {
867 new = suffix_first.clone();
868 new.add_one_maybe(TokenTree::Token(sep.clone()));
874 // At this point, `suffix_first` is built, and
875 // `my_suffix` is some TokenSet that we can use
876 // for checking the interior of `seq_rep`.
878 check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
879 if next.maybe_empty {
885 // the recursive call to check_matcher_core already ran the 'each_last
886 // check below, so we can just keep going forward here.
887 continue 'each_token;
891 // (`suffix_first` guaranteed initialized once reaching here.)
893 // Now `last` holds the complete set of NT tokens that could
894 // end the sequence before SUFFIX. Check that every one works with `suffix`.
895 'each_last: for token in &last.tokens {
896 if let TokenTree::MetaVarDecl(_, name, frag_spec) = *token {
897 for next_token in &suffix_first.tokens {
898 match is_in_follow(next_token, frag_spec.name) {
899 IsInFollow::Invalid(msg, help) => {
901 .struct_span_err(next_token.span(), &msg)
904 // don't bother reporting every source of
905 // conflict for a particular element of `last`.
908 IsInFollow::Yes => {}
909 IsInFollow::No(possible) => {
910 let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
917 let sp = next_token.span();
918 let mut err = sess.span_diagnostic.struct_span_err(
921 "`${name}:{frag}` {may_be} followed by `{next}`, which \
922 is not allowed for `{frag}` fragments",
925 next = quoted_tt_to_string(next_token),
931 format!("not allowed after `{}` fragments", frag_spec),
933 let msg = "allowed there are: ";
938 "only {} is allowed after `{}` fragments",
965 fn token_can_be_followed_by_any(tok: &mbe::TokenTree) -> bool {
966 if let mbe::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok {
967 frag_can_be_followed_by_any(frag_spec.name)
969 // (Non NT's can always be followed by anthing in matchers.)
974 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
975 /// token. We use this (among other things) as a useful approximation
976 /// for when `frag` can be followed by a repetition like `$(...)*` or
977 /// `$(...)+`. In general, these can be a bit tricky to reason about,
978 /// so we adopt a conservative position that says that any fragment
979 /// specifier which consumes at most one token tree can be followed by
980 /// a fragment specifier (indeed, these fragments can be followed by
981 /// ANYTHING without fear of future compatibility hazards).
982 fn frag_can_be_followed_by_any(frag: Symbol) -> bool {
984 sym::item | // always terminated by `}` or `;`
985 sym::block | // exactly one token tree
986 sym::ident | // exactly one token tree
987 sym::literal | // exactly one token tree
988 sym::meta | // exactly one token tree
989 sym::lifetime | // exactly one token tree
990 sym::tt => // exactly one token tree
1000 No(&'static [&'static str]),
1001 Invalid(String, &'static str),
1004 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1005 /// fragments that can consume an unbounded number of tokens, `tok`
1006 /// must be within a well-defined follow set. This is intended to
1007 /// guarantee future compatibility: for example, without this rule, if
1008 /// we expanded `expr` to include a new binary operator, we might
1009 /// break macros that were relying on that binary operator as a
1011 // when changing this do not forget to update doc/book/macros.md!
1012 fn is_in_follow(tok: &mbe::TokenTree, frag: Symbol) -> IsInFollow {
1015 if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
1016 // closing a token tree can never be matched by any fragment;
1017 // iow, we always require that `(` and `)` match, etc.
1022 // since items *must* be followed by either a `;` or a `}`, we can
1023 // accept anything after them
1027 // anything can follow block, the braces provide an easy boundary to
1031 sym::stmt | sym::expr => {
1032 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
1034 TokenTree::Token(token) => match token.kind {
1035 FatArrow | Comma | Semi => IsInFollow::Yes,
1036 _ => IsInFollow::No(TOKENS),
1038 _ => IsInFollow::No(TOKENS),
1042 const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1044 TokenTree::Token(token) => match token.kind {
1045 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
1046 Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
1047 _ => IsInFollow::No(TOKENS),
1049 _ => IsInFollow::No(TOKENS),
1052 sym::path | sym::ty => {
1053 const TOKENS: &[&str] = &[
1054 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1058 TokenTree::Token(token) => match token.kind {
1059 OpenDelim(token::DelimToken::Brace)
1060 | OpenDelim(token::DelimToken::Bracket)
1068 | BinOp(token::Or) => IsInFollow::Yes,
1069 Ident(name, false) if name == kw::As || name == kw::Where => {
1072 _ => IsInFollow::No(TOKENS),
1074 TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block => {
1077 _ => IsInFollow::No(TOKENS),
1080 sym::ident | sym::lifetime => {
1081 // being a single token, idents and lifetimes are harmless
1085 // literals may be of a single token, or two tokens (negative numbers)
1088 sym::meta | sym::tt => {
1089 // being either a single token or a delimited sequence, tt is
1094 // Explicitly disallow `priv`, on the off chance it comes back.
1095 const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
1097 TokenTree::Token(token) => match token.kind {
1098 Comma => IsInFollow::Yes,
1099 Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
1101 if token.can_begin_type() {
1104 IsInFollow::No(TOKENS)
1108 TokenTree::MetaVarDecl(_, _, frag)
1109 if frag.name == sym::ident
1110 || frag.name == sym::ty
1111 || frag.name == sym::path =>
1115 _ => IsInFollow::No(TOKENS),
1118 kw::Invalid => IsInFollow::Yes,
1119 _ => IsInFollow::Invalid(
1120 format!("invalid fragment specifier `{}`", frag),
1121 VALID_FRAGMENT_NAMES_MSG,
1127 fn has_legal_fragment_specifier(
1129 features: &Features,
1130 attrs: &[ast::Attribute],
1131 tok: &mbe::TokenTree,
1132 ) -> Result<(), String> {
1133 debug!("has_legal_fragment_specifier({:?})", tok);
1134 if let mbe::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok {
1135 let frag_span = tok.span();
1136 if !is_legal_fragment_specifier(sess, features, attrs, frag_spec.name, frag_span) {
1137 return Err(frag_spec.to_string());
1143 fn is_legal_fragment_specifier(
1145 _features: &Features,
1146 _attrs: &[ast::Attribute],
1151 * If new fragment specifiers are invented in nightly, `_sess`,
1152 * `_features`, `_attrs`, and `_frag_span` will be useful here
1153 * for checking against feature gates. See past versions of
1170 | kw::Invalid => true,
1175 fn quoted_tt_to_string(tt: &mbe::TokenTree) -> String {
1177 mbe::TokenTree::Token(ref token) => pprust::token_to_string(&token),
1178 mbe::TokenTree::MetaVar(_, name) => format!("${}", name),
1179 mbe::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind),
1181 "unexpected mbe::TokenTree::{{Sequence or Delimited}} \
1182 in follow set checker"
1187 /// Use this token tree as a matcher to parse given tts.
1188 fn parse_tt(cx: &ExtCtxt<'_>, mtch: &[mbe::TokenTree], tts: TokenStream) -> NamedParseResult {
1189 // `None` is because we're not interpolating
1190 let directory = Directory {
1191 path: Cow::from(cx.current_expansion.module.directory.as_path()),
1192 ownership: cx.current_expansion.directory_ownership,
1194 parse(cx.parse_sess(), tts, mtch, Some(directory), true)
1197 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
1198 /// other tokens, this is "unexpected token...".
1199 fn parse_failure_msg(tok: &Token) -> String {
1201 token::Eof => "unexpected end of macro invocation".to_string(),
1202 _ => format!("no rules expected the token `{}`", pprust::token_to_string(tok),),