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_feature::Features;
12 use rustc_parse::parser::Parser;
13 use rustc_parse::Directory;
14 use rustc_span::edition::Edition;
15 use rustc_span::hygiene::Transparency;
16 use rustc_span::symbol::{kw, sym, Symbol};
19 use syntax::attr::{self, TransparencyError};
20 use syntax::print::pprust;
21 use syntax::sess::ParseSess;
22 use syntax::token::{self, NtTT, Token, TokenKind::*};
23 use syntax::tokenstream::{DelimSpan, TokenStream};
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 /// Instead of e.g. `vec![a, b, c]` in a pattern context, suggest `[a, b, c]`.
67 fn suggest_slice_pat(e: &mut DiagnosticBuilder<'_>, site_span: Span, parser: &Parser<'_>) {
68 let mut suggestion = None;
69 if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
70 if let Some(bang) = code.find('!') {
71 suggestion = Some(code[bang + 1..].to_string());
74 if let Some(suggestion) = suggestion {
77 "use a slice pattern here instead",
79 Applicability::MachineApplicable,
82 e.span_label(site_span, "use a slice pattern here instead");
85 "for more information, see https://doc.rust-lang.org/edition-guide/\
86 rust-2018/slice-patterns.html",
90 impl<'a> ParserAnyMacro<'a> {
91 crate fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
92 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
93 let fragment = panictry!(parse_ast_fragment(parser, kind, true).map_err(|mut e| {
94 if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
95 if !e.span.is_dummy() {
96 // early end of macro arm (#52866)
97 e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
99 let msg = &e.message[0];
102 "macro expansion ends with an incomplete expression: {}",
103 msg.0.replace(", found `<eof>`", ""),
108 if e.span.is_dummy() {
109 // Get around lack of span in error (#30128)
110 e.replace_span_with(site_span);
111 if parser.sess.source_map().span_to_filename(arm_span).is_real() {
112 e.span_label(arm_span, "in this macro arm");
114 } else if !parser.sess.source_map().span_to_filename(parser.token.span).is_real() {
115 e.span_label(site_span, "in this macro invocation");
118 AstFragmentKind::Pat if macro_ident.name == sym::vec => {
119 suggest_slice_pat(&mut e, site_span, parser);
121 _ => annotate_err_with_kind(&mut e, kind, site_span),
126 // We allow semicolons at the end of expressions -- e.g., the semicolon in
127 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
128 // but `m!()` is allowed in expression positions (cf. issue #34706).
129 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
133 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
134 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
135 ensure_complete_parse(parser, &path, kind.name(), site_span);
140 struct MacroRulesMacroExpander {
143 transparency: Transparency,
144 lhses: Vec<mbe::TokenTree>,
145 rhses: Vec<mbe::TokenTree>,
149 impl TTMacroExpander for MacroRulesMacroExpander {
152 cx: &'cx mut ExtCtxt<'_>,
155 ) -> Box<dyn MacResult + 'cx> {
157 return DummyResult::any(sp);
172 fn trace_macros_note(cx: &mut ExtCtxt<'_>, sp: Span, message: String) {
173 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
174 cx.expansions.entry(sp).or_default().push(message);
177 /// Given `lhses` and `rhses`, this is the new macro we create
178 fn generic_extension<'cx>(
179 cx: &'cx mut ExtCtxt<'_>,
183 transparency: Transparency,
185 lhses: &[mbe::TokenTree],
186 rhses: &[mbe::TokenTree],
187 ) -> Box<dyn MacResult + 'cx> {
188 if cx.trace_macros() {
189 let msg = format!("expanding `{}! {{ {} }}`", name, pprust::tts_to_string(arg.clone()));
190 trace_macros_note(cx, sp, msg);
193 // Which arm's failure should we report? (the one furthest along)
194 let mut best_failure: Option<(Token, &str)> = None;
195 for (i, lhs) in lhses.iter().enumerate() {
196 // try each arm's matchers
197 let lhs_tt = match *lhs {
198 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
199 _ => cx.span_bug(sp, "malformed macro lhs"),
202 // Take a snapshot of the state of pre-expansion gating at this point.
203 // This is used so that if a matcher is not `Success(..)`ful,
204 // then the spans which became gated when parsing the unsuccessful matcher
205 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
206 let mut gated_spans_snaphot = mem::take(&mut *cx.parse_sess.gated_spans.spans.borrow_mut());
208 match parse_tt(cx, lhs_tt, arg.clone()) {
209 Success(named_matches) => {
210 // The matcher was `Success(..)`ful.
211 // Merge the gated spans from parsing the matcher with the pre-existing ones.
212 cx.parse_sess.gated_spans.merge(gated_spans_snaphot);
214 let rhs = match rhses[i] {
216 mbe::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
217 _ => cx.span_bug(sp, "malformed macro rhs"),
219 let arm_span = rhses[i].span();
221 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
222 // rhs has holes ( `$id` and `$(...)` that need filled)
223 let mut tts = transcribe(cx, &named_matches, rhs, transparency);
225 // Replace all the tokens for the corresponding positions in the macro, to maintain
226 // proper positions in error reporting, while maintaining the macro_backtrace.
227 if rhs_spans.len() == tts.len() {
228 tts = tts.map_enumerated(|i, mut tt| {
229 let mut sp = rhs_spans[i];
230 sp = sp.with_ctxt(tt.span().ctxt());
236 if cx.trace_macros() {
237 let msg = format!("to `{}`", pprust::tts_to_string(tts.clone()));
238 trace_macros_note(cx, sp, msg);
241 let directory = Directory {
242 path: Cow::from(cx.current_expansion.module.directory.as_path()),
243 ownership: cx.current_expansion.directory_ownership,
245 let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false, None);
247 cx.current_expansion.module.mod_path.last().map(|id| id.to_string());
248 p.last_type_ascription = cx.current_expansion.prior_type_ascription;
250 p.process_potential_macro_variable();
251 // Let the context choose how to interpret the result.
252 // Weird, but useful for X-macros.
253 return Box::new(ParserAnyMacro {
256 // Pass along the original expansion site and the name of the macro
257 // so we can print a useful error message if the parse of the expanded
258 // macro leaves unparsed tokens.
264 Failure(token, msg) => match best_failure {
265 Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
266 _ => best_failure = Some((token, msg)),
268 Error(err_sp, ref msg) => cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..]),
271 // The matcher was not `Success(..)`ful.
272 // Restore to the state before snapshotting and maybe try again.
273 mem::swap(&mut gated_spans_snaphot, &mut cx.parse_sess.gated_spans.spans.borrow_mut());
276 let (token, label) = best_failure.expect("ran no matchers");
277 let span = token.span.substitute_dummy(sp);
278 let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
279 err.span_label(span, label);
280 if !def_span.is_dummy() && cx.source_map().span_to_filename(def_span).is_real() {
281 err.span_label(cx.source_map().def_span(def_span), "when calling this macro");
284 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
285 if let Some((arg, comma_span)) = arg.add_comma() {
287 // try each arm's matchers
288 let lhs_tt = match *lhs {
289 mbe::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
292 match parse_tt(cx, lhs_tt, arg.clone()) {
294 if comma_span.is_dummy() {
295 err.note("you might be missing a comma");
297 err.span_suggestion_short(
299 "missing comma here",
301 Applicability::MachineApplicable,
310 cx.trace_macros_diag();
314 // Note that macro-by-example's input is also matched against a token tree:
315 // $( $lhs:tt => $rhs:tt );+
317 // Holy self-referential!
319 /// Converts a macro item into a syntax extension.
320 pub fn compile_declarative_macro(
325 ) -> SyntaxExtension {
326 let diag = &sess.span_diagnostic;
327 let lhs_nm = ast::Ident::new(sym::lhs, def.span);
328 let rhs_nm = ast::Ident::new(sym::rhs, def.span);
329 let tt_spec = ast::Ident::new(sym::tt, def.span);
331 // Parse the macro_rules! invocation
332 let (is_legacy, body) = match &def.kind {
333 ast::ItemKind::MacroDef(macro_def) => (macro_def.legacy, macro_def.body.inner_tokens()),
337 // The pattern that macro_rules matches.
338 // The grammar for macro_rules! is:
339 // $( $lhs:tt => $rhs:tt );+
340 // ...quasiquoting this would be nice.
341 // These spans won't matter, anyways
342 let argument_gram = vec![
343 mbe::TokenTree::Sequence(
345 Lrc::new(mbe::SequenceRepetition {
347 mbe::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
348 mbe::TokenTree::token(token::FatArrow, def.span),
349 mbe::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
351 separator: Some(Token::new(
352 if is_legacy { token::Semi } else { token::Comma },
355 kleene: mbe::KleeneToken::new(mbe::KleeneOp::OneOrMore, def.span),
359 // to phase into semicolon-termination instead of semicolon-separation
360 mbe::TokenTree::Sequence(
362 Lrc::new(mbe::SequenceRepetition {
363 tts: vec![mbe::TokenTree::token(
364 if is_legacy { token::Semi } else { token::Comma },
368 kleene: mbe::KleeneToken::new(mbe::KleeneOp::ZeroOrMore, def.span),
374 let argument_map = match parse(sess, body, &argument_gram, None, true) {
376 Failure(token, msg) => {
377 let s = parse_failure_msg(&token);
378 let sp = token.span.substitute_dummy(def.span);
379 let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
380 err.span_label(sp, msg);
385 sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
389 let mut valid = true;
391 // Extract the arguments:
392 let lhses = match argument_map[&lhs_nm] {
393 MatchedSeq(ref s) => s
396 if let MatchedNonterminal(ref nt) = *m {
397 if let NtTT(ref tt) = **nt {
398 let tt = mbe::quoted::parse(tt.clone().into(), true, sess).pop().unwrap();
399 valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt);
403 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
405 .collect::<Vec<mbe::TokenTree>>(),
406 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
409 let rhses = match argument_map[&rhs_nm] {
410 MatchedSeq(ref s) => s
413 if let MatchedNonterminal(ref nt) = *m {
414 if let NtTT(ref tt) = **nt {
415 return mbe::quoted::parse(tt.clone().into(), false, sess).pop().unwrap();
418 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
420 .collect::<Vec<mbe::TokenTree>>(),
421 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
425 valid &= check_rhs(sess, rhs);
428 // don't abort iteration early, so that errors for multiple lhses can be reported
430 valid &= check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
433 // We use CRATE_NODE_ID instead of `def.id` otherwise we may emit buffered lints for a node id
434 // that is not lint-checked and trigger the "failed to process buffered lint here" bug.
435 valid &= macro_check::check_meta_variables(sess, ast::CRATE_NODE_ID, def.span, &lhses, &rhses);
437 let (transparency, transparency_error) = attr::find_transparency(&def.attrs, is_legacy);
438 match transparency_error {
439 Some(TransparencyError::UnknownTransparency(value, span)) => {
440 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")
448 let expander: Box<_> = Box::new(MacroRulesMacroExpander {
457 SyntaxExtension::new(
459 SyntaxExtensionKind::LegacyBang(expander),
468 fn check_lhs_nt_follows(
471 attrs: &[ast::Attribute],
472 lhs: &mbe::TokenTree,
474 // lhs is going to be like TokenTree::Delimited(...), where the
475 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
476 if let mbe::TokenTree::Delimited(_, ref tts) = *lhs {
477 check_matcher(sess, features, attrs, &tts.tts)
479 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
480 sess.span_diagnostic.span_err(lhs.span(), msg);
483 // we don't abort on errors on rejection, the driver will do that for us
484 // after parsing/expansion. we can report every error in every macro this way.
487 /// Checks that the lhs contains no repetition which could match an empty token
488 /// tree, because then the matcher would hang indefinitely.
489 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[mbe::TokenTree]) -> bool {
493 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
494 TokenTree::Delimited(_, ref del) => {
495 if !check_lhs_no_empty_seq(sess, &del.tts) {
499 TokenTree::Sequence(span, ref seq) => {
500 if seq.separator.is_none()
501 && seq.tts.iter().all(|seq_tt| match *seq_tt {
502 TokenTree::MetaVarDecl(_, _, id) => id.name == sym::vis,
503 TokenTree::Sequence(_, ref sub_seq) => {
504 sub_seq.kleene.op == mbe::KleeneOp::ZeroOrMore
505 || sub_seq.kleene.op == mbe::KleeneOp::ZeroOrOne
510 let sp = span.entire();
511 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
514 if !check_lhs_no_empty_seq(sess, &seq.tts) {
524 fn check_rhs(sess: &ParseSess, rhs: &mbe::TokenTree) -> bool {
526 mbe::TokenTree::Delimited(..) => return true,
527 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
535 attrs: &[ast::Attribute],
536 matcher: &[mbe::TokenTree],
538 let first_sets = FirstSets::new(matcher);
539 let empty_suffix = TokenSet::empty();
540 let err = sess.span_diagnostic.err_count();
541 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
542 err == sess.span_diagnostic.err_count()
545 // `The FirstSets` for a matcher is a mapping from subsequences in the
546 // matcher to the FIRST set for that subsequence.
548 // This mapping is partially precomputed via a backwards scan over the
549 // token trees of the matcher, which provides a mapping from each
550 // repetition sequence to its *first* set.
552 // (Hypothetically, sequences should be uniquely identifiable via their
553 // spans, though perhaps that is false, e.g., for macro-generated macros
554 // that do not try to inject artificial span information. My plan is
555 // to try to catch such cases ahead of time and not include them in
556 // the precomputed mapping.)
558 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
559 // span in the original matcher to the First set for the inner sequence `tt ...`.
561 // If two sequences have the same span in a matcher, then map that
562 // span to None (invalidating the mapping here and forcing the code to
564 first: FxHashMap<Span, Option<TokenSet>>,
568 fn new(tts: &[mbe::TokenTree]) -> FirstSets {
571 let mut sets = FirstSets { first: FxHashMap::default() };
572 build_recur(&mut sets, tts);
575 // walks backward over `tts`, returning the FIRST for `tts`
576 // and updating `sets` at the same time for all sequence
577 // substructure we find within `tts`.
578 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
579 let mut first = TokenSet::empty();
580 for tt in tts.iter().rev() {
582 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
583 first.replace_with(tt.clone());
585 TokenTree::Delimited(span, ref delimited) => {
586 build_recur(sets, &delimited.tts[..]);
587 first.replace_with(delimited.open_tt(span));
589 TokenTree::Sequence(sp, ref seq_rep) => {
590 let subfirst = build_recur(sets, &seq_rep.tts[..]);
592 match sets.first.entry(sp.entire()) {
593 Entry::Vacant(vac) => {
594 vac.insert(Some(subfirst.clone()));
596 Entry::Occupied(mut occ) => {
597 // if there is already an entry, then a span must have collided.
598 // This should not happen with typical macro_rules macros,
599 // but syntax extensions need not maintain distinct spans,
600 // so distinct syntax trees can be assigned the same span.
601 // In such a case, the map cannot be trusted; so mark this
602 // entry as unusable.
607 // If the sequence contents can be empty, then the first
608 // token could be the separator token itself.
610 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
611 first.add_one_maybe(TokenTree::Token(sep.clone()));
614 // Reverse scan: Sequence comes before `first`.
615 if subfirst.maybe_empty
616 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
617 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
619 // If sequence is potentially empty, then
620 // union them (preserving first emptiness).
621 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
623 // Otherwise, sequence guaranteed
624 // non-empty; replace first.
635 // walks forward over `tts` until all potential FIRST tokens are
637 fn first(&self, tts: &[mbe::TokenTree]) -> TokenSet {
640 let mut first = TokenSet::empty();
641 for tt in tts.iter() {
642 assert!(first.maybe_empty);
644 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
645 first.add_one(tt.clone());
648 TokenTree::Delimited(span, ref delimited) => {
649 first.add_one(delimited.open_tt(span));
652 TokenTree::Sequence(sp, ref seq_rep) => {
654 let subfirst = match self.first.get(&sp.entire()) {
655 Some(&Some(ref subfirst)) => subfirst,
657 subfirst_owned = self.first(&seq_rep.tts[..]);
661 panic!("We missed a sequence during FirstSets construction");
665 // If the sequence contents can be empty, then the first
666 // token could be the separator token itself.
667 if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
668 first.add_one_maybe(TokenTree::Token(sep.clone()));
671 assert!(first.maybe_empty);
672 first.add_all(subfirst);
673 if subfirst.maybe_empty
674 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrMore
675 || seq_rep.kleene.op == mbe::KleeneOp::ZeroOrOne
677 // Continue scanning for more first
678 // tokens, but also make sure we
679 // restore empty-tracking state.
680 first.maybe_empty = true;
689 // we only exit the loop if `tts` was empty or if every
690 // element of `tts` matches the empty sequence.
691 assert!(first.maybe_empty);
696 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
697 // (for macro-by-example syntactic variables). It also carries the
698 // `maybe_empty` flag; that is true if and only if the matcher can
699 // match an empty token sequence.
701 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
702 // which has corresponding FIRST = {$a:expr, c, d}.
703 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
705 // (Notably, we must allow for *-op to occur zero times.)
706 #[derive(Clone, Debug)]
708 tokens: Vec<mbe::TokenTree>,
713 // Returns a set for the empty sequence.
715 TokenSet { tokens: Vec::new(), maybe_empty: true }
718 // Returns the set `{ tok }` for the single-token (and thus
719 // non-empty) sequence [tok].
720 fn singleton(tok: mbe::TokenTree) -> Self {
721 TokenSet { tokens: vec![tok], maybe_empty: false }
724 // Changes self to be the set `{ tok }`.
725 // Since `tok` is always present, marks self as non-empty.
726 fn replace_with(&mut self, tok: mbe::TokenTree) {
728 self.tokens.push(tok);
729 self.maybe_empty = false;
732 // Changes self to be the empty set `{}`; meant for use when
733 // the particular token does not matter, but we want to
734 // record that it occurs.
735 fn replace_with_irrelevant(&mut self) {
737 self.maybe_empty = false;
740 // Adds `tok` to the set for `self`, marking sequence as non-empy.
741 fn add_one(&mut self, tok: mbe::TokenTree) {
742 if !self.tokens.contains(&tok) {
743 self.tokens.push(tok);
745 self.maybe_empty = false;
748 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
749 fn add_one_maybe(&mut self, tok: mbe::TokenTree) {
750 if !self.tokens.contains(&tok) {
751 self.tokens.push(tok);
755 // Adds all elements of `other` to this.
757 // (Since this is a set, we filter out duplicates.)
759 // If `other` is potentially empty, then preserves the previous
760 // setting of the empty flag of `self`. If `other` is guaranteed
761 // non-empty, then `self` is marked non-empty.
762 fn add_all(&mut self, other: &Self) {
763 for tok in &other.tokens {
764 if !self.tokens.contains(tok) {
765 self.tokens.push(tok.clone());
768 if !other.maybe_empty {
769 self.maybe_empty = false;
774 // Checks that `matcher` is internally consistent and that it
775 // can legally be followed by a token `N`, for all `N` in `follow`.
776 // (If `follow` is empty, then it imposes no constraint on
779 // Returns the set of NT tokens that could possibly come last in
780 // `matcher`. (If `matcher` matches the empty sequence, then
781 // `maybe_empty` will be set to true.)
783 // Requires that `first_sets` is pre-computed for `matcher`;
784 // see `FirstSets::new`.
785 fn check_matcher_core(
788 attrs: &[ast::Attribute],
789 first_sets: &FirstSets,
790 matcher: &[mbe::TokenTree],
795 let mut last = TokenSet::empty();
797 // 2. For each token and suffix [T, SUFFIX] in M:
798 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
799 // then ensure T can also be followed by any element of FOLLOW.
800 'each_token: for i in 0..matcher.len() {
801 let token = &matcher[i];
802 let suffix = &matcher[i + 1..];
804 let build_suffix_first = || {
805 let mut s = first_sets.first(suffix);
812 // (we build `suffix_first` on demand below; you can tell
813 // which cases are supposed to fall through by looking for the
814 // initialization of this variable.)
817 // First, update `last` so that it corresponds to the set
818 // of NT tokens that might end the sequence `... token`.
820 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
821 let can_be_followed_by_any;
822 if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) {
823 let msg = format!("invalid fragment specifier `{}`", bad_frag);
825 .struct_span_err(token.span(), &msg)
826 .help(VALID_FRAGMENT_NAMES_MSG)
828 // (This eliminates false positives and duplicates
829 // from error messages.)
830 can_be_followed_by_any = true;
832 can_be_followed_by_any = token_can_be_followed_by_any(token);
835 if can_be_followed_by_any {
836 // don't need to track tokens that work with any,
837 last.replace_with_irrelevant();
838 // ... and don't need to check tokens that can be
839 // followed by anything against SUFFIX.
840 continue 'each_token;
842 last.replace_with(token.clone());
843 suffix_first = build_suffix_first();
846 TokenTree::Delimited(span, ref d) => {
847 let my_suffix = TokenSet::singleton(d.close_tt(span));
848 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
849 // don't track non NT tokens
850 last.replace_with_irrelevant();
852 // also, we don't need to check delimited sequences
854 continue 'each_token;
856 TokenTree::Sequence(_, ref seq_rep) => {
857 suffix_first = build_suffix_first();
858 // The trick here: when we check the interior, we want
859 // to include the separator (if any) as a potential
860 // (but not guaranteed) element of FOLLOW. So in that
861 // case, we make a temp copy of suffix and stuff
862 // delimiter in there.
864 // FIXME: Should I first scan suffix_first to see if
865 // delimiter is already in it before I go through the
866 // work of cloning it? But then again, this way I may
867 // get a "tighter" span?
869 let my_suffix = if let Some(sep) = &seq_rep.separator {
870 new = suffix_first.clone();
871 new.add_one_maybe(TokenTree::Token(sep.clone()));
877 // At this point, `suffix_first` is built, and
878 // `my_suffix` is some TokenSet that we can use
879 // for checking the interior of `seq_rep`.
881 check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
882 if next.maybe_empty {
888 // the recursive call to check_matcher_core already ran the 'each_last
889 // check below, so we can just keep going forward here.
890 continue 'each_token;
894 // (`suffix_first` guaranteed initialized once reaching here.)
896 // Now `last` holds the complete set of NT tokens that could
897 // end the sequence before SUFFIX. Check that every one works with `suffix`.
898 'each_last: for token in &last.tokens {
899 if let TokenTree::MetaVarDecl(_, name, frag_spec) = *token {
900 for next_token in &suffix_first.tokens {
901 match is_in_follow(next_token, frag_spec.name) {
902 IsInFollow::Invalid(msg, help) => {
904 .struct_span_err(next_token.span(), &msg)
907 // don't bother reporting every source of
908 // conflict for a particular element of `last`.
911 IsInFollow::Yes => {}
912 IsInFollow::No(possible) => {
913 let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
920 let sp = next_token.span();
921 let mut err = sess.span_diagnostic.struct_span_err(
924 "`${name}:{frag}` {may_be} followed by `{next}`, which \
925 is not allowed for `{frag}` fragments",
928 next = quoted_tt_to_string(next_token),
934 format!("not allowed after `{}` fragments", frag_spec),
936 let msg = "allowed there are: ";
941 "only {} is allowed after `{}` fragments",
968 fn token_can_be_followed_by_any(tok: &mbe::TokenTree) -> bool {
969 if let mbe::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok {
970 frag_can_be_followed_by_any(frag_spec.name)
972 // (Non NT's can always be followed by anthing in matchers.)
977 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
978 /// token. We use this (among other things) as a useful approximation
979 /// for when `frag` can be followed by a repetition like `$(...)*` or
980 /// `$(...)+`. In general, these can be a bit tricky to reason about,
981 /// so we adopt a conservative position that says that any fragment
982 /// specifier which consumes at most one token tree can be followed by
983 /// a fragment specifier (indeed, these fragments can be followed by
984 /// ANYTHING without fear of future compatibility hazards).
985 fn frag_can_be_followed_by_any(frag: Symbol) -> bool {
987 sym::item | // always terminated by `}` or `;`
988 sym::block | // exactly one token tree
989 sym::ident | // exactly one token tree
990 sym::literal | // exactly one token tree
991 sym::meta | // exactly one token tree
992 sym::lifetime | // exactly one token tree
993 sym::tt => // exactly one token tree
1003 No(&'static [&'static str]),
1004 Invalid(String, &'static str),
1007 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1008 /// fragments that can consume an unbounded number of tokens, `tok`
1009 /// must be within a well-defined follow set. This is intended to
1010 /// guarantee future compatibility: for example, without this rule, if
1011 /// we expanded `expr` to include a new binary operator, we might
1012 /// break macros that were relying on that binary operator as a
1014 // when changing this do not forget to update doc/book/macros.md!
1015 fn is_in_follow(tok: &mbe::TokenTree, frag: Symbol) -> IsInFollow {
1018 if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
1019 // closing a token tree can never be matched by any fragment;
1020 // iow, we always require that `(` and `)` match, etc.
1025 // since items *must* be followed by either a `;` or a `}`, we can
1026 // accept anything after them
1030 // anything can follow block, the braces provide an easy boundary to
1034 sym::stmt | sym::expr => {
1035 const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
1037 TokenTree::Token(token) => match token.kind {
1038 FatArrow | Comma | Semi => IsInFollow::Yes,
1039 _ => IsInFollow::No(TOKENS),
1041 _ => IsInFollow::No(TOKENS),
1045 const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1047 TokenTree::Token(token) => match token.kind {
1048 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
1049 Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
1050 _ => IsInFollow::No(TOKENS),
1052 _ => IsInFollow::No(TOKENS),
1055 sym::path | sym::ty => {
1056 const TOKENS: &[&str] = &[
1057 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1061 TokenTree::Token(token) => match token.kind {
1062 OpenDelim(token::DelimToken::Brace)
1063 | OpenDelim(token::DelimToken::Bracket)
1071 | BinOp(token::Or) => IsInFollow::Yes,
1072 Ident(name, false) if name == kw::As || name == kw::Where => {
1075 _ => IsInFollow::No(TOKENS),
1077 TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block => {
1080 _ => IsInFollow::No(TOKENS),
1083 sym::ident | sym::lifetime => {
1084 // being a single token, idents and lifetimes are harmless
1088 // literals may be of a single token, or two tokens (negative numbers)
1091 sym::meta | sym::tt => {
1092 // being either a single token or a delimited sequence, tt is
1097 // Explicitly disallow `priv`, on the off chance it comes back.
1098 const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
1100 TokenTree::Token(token) => match token.kind {
1101 Comma => IsInFollow::Yes,
1102 Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
1104 if token.can_begin_type() {
1107 IsInFollow::No(TOKENS)
1111 TokenTree::MetaVarDecl(_, _, frag)
1112 if frag.name == sym::ident
1113 || frag.name == sym::ty
1114 || frag.name == sym::path =>
1118 _ => IsInFollow::No(TOKENS),
1121 kw::Invalid => IsInFollow::Yes,
1122 _ => IsInFollow::Invalid(
1123 format!("invalid fragment specifier `{}`", frag),
1124 VALID_FRAGMENT_NAMES_MSG,
1130 fn has_legal_fragment_specifier(
1132 features: &Features,
1133 attrs: &[ast::Attribute],
1134 tok: &mbe::TokenTree,
1135 ) -> Result<(), String> {
1136 debug!("has_legal_fragment_specifier({:?})", tok);
1137 if let mbe::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok {
1138 let frag_span = tok.span();
1139 if !is_legal_fragment_specifier(sess, features, attrs, frag_spec.name, frag_span) {
1140 return Err(frag_spec.to_string());
1146 fn is_legal_fragment_specifier(
1148 _features: &Features,
1149 _attrs: &[ast::Attribute],
1154 * If new fragment specifiers are invented in nightly, `_sess`,
1155 * `_features`, `_attrs`, and `_frag_span` will be useful here
1156 * for checking against feature gates. See past versions of
1173 | kw::Invalid => true,
1178 fn quoted_tt_to_string(tt: &mbe::TokenTree) -> String {
1180 mbe::TokenTree::Token(ref token) => pprust::token_to_string(&token),
1181 mbe::TokenTree::MetaVar(_, name) => format!("${}", name),
1182 mbe::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind),
1184 "unexpected mbe::TokenTree::{{Sequence or Delimited}} \
1185 in follow set checker"
1190 /// Use this token tree as a matcher to parse given tts.
1191 fn parse_tt(cx: &ExtCtxt<'_>, mtch: &[mbe::TokenTree], tts: TokenStream) -> NamedParseResult {
1192 // `None` is because we're not interpolating
1193 let directory = Directory {
1194 path: Cow::from(cx.current_expansion.module.directory.as_path()),
1195 ownership: cx.current_expansion.directory_ownership,
1197 parse(cx.parse_sess(), tts, mtch, Some(directory), true)
1200 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
1201 /// other tokens, this is "unexpected token...".
1202 fn parse_failure_msg(tok: &Token) -> String {
1204 token::Eof => "unexpected end of macro invocation".to_string(),
1205 _ => format!("no rules expected the token `{}`", pprust::token_to_string(tok),),