2 use syntax_pos::{Span, DUMMY_SP};
4 use errors::FatalError;
5 use ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension};
6 use ext::base::{NormalTT, TTMacroExpander};
7 use ext::expand::{AstFragment, AstFragmentKind};
8 use ext::tt::macro_parser::{Success, Error, Failure};
9 use ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal};
10 use ext::tt::macro_parser::{parse, parse_failure_msg};
12 use ext::tt::transcribe::transcribe;
13 use feature_gate::Features;
14 use parse::{Directory, ParseSess};
15 use parse::parser::Parser;
16 use parse::token::{self, NtTT};
17 use parse::token::Token::*;
19 use tokenstream::{DelimSpan, TokenStream, TokenTree};
21 use rustc_data_structures::fx::FxHashMap;
23 use std::collections::hash_map::Entry;
25 use rustc_data_structures::sync::Lrc;
26 use errors::Applicability;
28 const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
29 `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, \
30 `path`, `meta`, `tt`, `item` and `vis`";
32 pub 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
38 macro_ident: ast::Ident,
42 impl<'a> ParserAnyMacro<'a> {
43 pub fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
44 let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
45 let fragment = panictry!(parser.parse_ast_fragment(kind, true).map_err(|mut e| {
46 if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
47 if !e.span.is_dummy() { // early end of macro arm (#52866)
48 e.replace_span_with(parser.sess.source_map().next_point(parser.span));
50 let msg = &e.message[0];
53 "macro expansion ends with an incomplete expression: {}",
54 msg.0.replace(", found `<eof>`", ""),
59 if e.span.is_dummy() { // Get around lack of span in error (#30128)
60 e.replace_span_with(site_span);
61 if parser.sess.source_map().span_to_filename(arm_span).is_real() {
62 e.span_label(arm_span, "in this macro arm");
64 } else if !parser.sess.source_map().span_to_filename(parser.span).is_real() {
65 e.span_label(site_span, "in this macro invocation");
70 // We allow semicolons at the end of expressions -- e.g., the semicolon in
71 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
72 // but `m!()` is allowed in expression positions (cf. issue #34706).
73 if kind == AstFragmentKind::Expr && parser.token == token::Semi {
77 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
78 let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span));
79 parser.ensure_complete_parse(&path, kind.name(), site_span);
84 struct MacroRulesMacroExpander {
86 lhses: Vec<quoted::TokenTree>,
87 rhses: Vec<quoted::TokenTree>,
91 impl TTMacroExpander for MacroRulesMacroExpander {
97 def_span: Option<Span>,
98 ) -> Box<dyn MacResult+'cx> {
100 return DummyResult::any(sp);
102 generic_extension(cx,
112 fn trace_macros_note(cx: &mut ExtCtxt, sp: Span, message: String) {
113 let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
114 cx.expansions.entry(sp).or_default().push(message);
117 /// Given `lhses` and `rhses`, this is the new macro we create
118 fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
120 def_span: Option<Span>,
123 lhses: &[quoted::TokenTree],
124 rhses: &[quoted::TokenTree])
125 -> Box<dyn MacResult+'cx> {
126 if cx.trace_macros() {
127 trace_macros_note(cx, sp, format!("expanding `{}! {{ {} }}`", name, arg));
130 // Which arm's failure should we report? (the one furthest along)
131 let mut best_fail_spot = DUMMY_SP;
132 let mut best_fail_tok = None;
133 let mut best_fail_text = None;
135 for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers
136 let lhs_tt = match *lhs {
137 quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
138 _ => cx.span_bug(sp, "malformed macro lhs")
141 match TokenTree::parse(cx, lhs_tt, arg.clone()) {
142 Success(named_matches) => {
143 let rhs = match rhses[i] {
145 quoted::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(),
146 _ => cx.span_bug(sp, "malformed macro rhs"),
148 let arm_span = rhses[i].span();
150 let rhs_spans = rhs.iter().map(|t| t.span()).collect::<Vec<_>>();
151 // rhs has holes ( `$id` and `$(...)` that need filled)
152 let mut tts = transcribe(cx, Some(named_matches), rhs);
154 // Replace all the tokens for the corresponding positions in the macro, to maintain
155 // proper positions in error reporting, while maintaining the macro_backtrace.
156 if rhs_spans.len() == tts.len() {
157 tts = tts.map_enumerated(|i, mut tt| {
158 let mut sp = rhs_spans[i];
159 sp = sp.with_ctxt(tt.span().ctxt());
165 if cx.trace_macros() {
166 trace_macros_note(cx, sp, format!("to `{}`", tts));
169 let directory = Directory {
170 path: Cow::from(cx.current_expansion.module.directory.as_path()),
171 ownership: cx.current_expansion.directory_ownership,
173 let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false);
174 p.root_module_name = cx.current_expansion.module.mod_path.last()
175 .map(|id| id.as_str().to_string());
177 p.process_potential_macro_variable();
178 // Let the context choose how to interpret the result.
179 // Weird, but useful for X-macros.
180 return Box::new(ParserAnyMacro {
183 // Pass along the original expansion site and the name of the macro
184 // so we can print a useful error message if the parse of the expanded
185 // macro leaves unparsed tokens.
191 Failure(sp, tok, t) => if sp.lo() >= best_fail_spot.lo() {
193 best_fail_tok = Some(tok);
194 best_fail_text = Some(t);
196 Error(err_sp, ref msg) => {
197 cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..])
202 let best_fail_msg = parse_failure_msg(best_fail_tok.expect("ran no matchers"));
203 let span = best_fail_spot.substitute_dummy(sp);
204 let mut err = cx.struct_span_err(span, &best_fail_msg);
205 err.span_label(span, best_fail_text.unwrap_or(&best_fail_msg));
206 if let Some(sp) = def_span {
207 if cx.source_map().span_to_filename(sp).is_real() && !sp.is_dummy() {
208 err.span_label(cx.source_map().def_span(sp), "when calling this macro");
212 // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
213 if let Some((arg, comma_span)) = arg.add_comma() {
214 for lhs in lhses { // try each arm's matchers
215 let lhs_tt = match *lhs {
216 quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
219 match TokenTree::parse(cx, lhs_tt, arg.clone()) {
221 if comma_span.is_dummy() {
222 err.note("you might be missing a comma");
224 err.span_suggestion_short(
226 "missing comma here",
228 Applicability::MachineApplicable,
237 cx.trace_macros_diag();
241 // Note that macro-by-example's input is also matched against a token tree:
242 // $( $lhs:tt => $rhs:tt );+
244 // Holy self-referential!
246 /// Converts a `macro_rules!` invocation into a syntax extension.
247 pub fn compile(sess: &ParseSess, features: &Features, def: &ast::Item, edition: Edition)
249 let lhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("lhs"));
250 let rhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("rhs"));
252 // Parse the macro_rules! invocation
253 let body = match def.node {
254 ast::ItemKind::MacroDef(ref body) => body,
258 // The pattern that macro_rules matches.
259 // The grammar for macro_rules! is:
260 // $( $lhs:tt => $rhs:tt );+
261 // ...quasiquoting this would be nice.
262 // These spans won't matter, anyways
263 let argument_gram = vec![
264 quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition {
266 quoted::TokenTree::MetaVarDecl(DUMMY_SP, lhs_nm, ast::Ident::from_str("tt")),
267 quoted::TokenTree::Token(DUMMY_SP, token::FatArrow),
268 quoted::TokenTree::MetaVarDecl(DUMMY_SP, rhs_nm, ast::Ident::from_str("tt")),
270 separator: Some(if body.legacy { token::Semi } else { token::Comma }),
271 op: quoted::KleeneOp::OneOrMore,
274 // to phase into semicolon-termination instead of semicolon-separation
275 quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition {
276 tts: vec![quoted::TokenTree::Token(DUMMY_SP, token::Semi)],
278 op: quoted::KleeneOp::ZeroOrMore,
283 let argument_map = match parse(sess, body.stream(), &argument_gram, None, true) {
285 Failure(sp, tok, t) => {
286 let s = parse_failure_msg(tok);
287 let sp = sp.substitute_dummy(def.span);
288 let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
289 err.span_label(sp, t);
294 sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
298 let mut valid = true;
300 // Extract the arguments:
301 let lhses = match *argument_map[&lhs_nm] {
302 MatchedSeq(ref s, _) => {
304 if let MatchedNonterminal(ref nt) = *m {
305 if let NtTT(ref tt) = **nt {
306 let tt = quoted::parse(
317 valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt);
321 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
322 }).collect::<Vec<quoted::TokenTree>>()
324 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
327 let rhses = match *argument_map[&rhs_nm] {
328 MatchedSeq(ref s, _) => {
330 if let MatchedNonterminal(ref nt) = *m {
331 if let NtTT(ref tt) = **nt {
332 return quoted::parse(
344 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
345 }).collect::<Vec<quoted::TokenTree>>()
347 _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs")
351 valid &= check_rhs(sess, rhs);
354 // don't abort iteration early, so that errors for multiple lhses can be reported
356 valid &= check_lhs_no_empty_seq(sess, &[lhs.clone()])
359 let expander: Box<_> = Box::new(MacroRulesMacroExpander {
367 let allow_internal_unstable = attr::contains_name(&def.attrs, "allow_internal_unstable");
368 let allow_internal_unsafe = attr::contains_name(&def.attrs, "allow_internal_unsafe");
369 let mut local_inner_macros = false;
370 if let Some(macro_export) = attr::find_by_name(&def.attrs, "macro_export") {
371 if let Some(l) = macro_export.meta_item_list() {
372 local_inner_macros = attr::list_contains_name(&l, "local_inner_macros");
376 let unstable_feature = attr::find_stability(&sess,
377 &def.attrs, def.span).and_then(|stability| {
378 if let attr::StabilityLevel::Unstable { issue, .. } = stability.level {
379 Some((stability.feature, issue))
387 def_info: Some((def.id, def.span)),
388 allow_internal_unstable,
389 allow_internal_unsafe,
395 let is_transparent = attr::contains_name(&def.attrs, "rustc_transparent_macro");
397 SyntaxExtension::DeclMacro {
399 def_info: Some((def.id, def.span)),
406 fn check_lhs_nt_follows(sess: &ParseSess,
408 attrs: &[ast::Attribute],
409 lhs: "ed::TokenTree) -> bool {
410 // lhs is going to be like TokenTree::Delimited(...), where the
411 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
412 if let quoted::TokenTree::Delimited(_, ref tts) = *lhs {
413 check_matcher(sess, features, attrs, &tts.tts)
415 let msg = "invalid macro matcher; matchers must be contained in balanced delimiters";
416 sess.span_diagnostic.span_err(lhs.span(), msg);
419 // we don't abort on errors on rejection, the driver will do that for us
420 // after parsing/expansion. we can report every error in every macro this way.
423 /// Check that the lhs contains no repetition which could match an empty token
424 /// tree, because then the matcher would hang indefinitely.
425 fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[quoted::TokenTree]) -> bool {
426 use self::quoted::TokenTree;
429 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
430 TokenTree::Delimited(_, ref del) => if !check_lhs_no_empty_seq(sess, &del.tts) {
433 TokenTree::Sequence(span, ref seq) => {
434 if seq.separator.is_none() && seq.tts.iter().all(|seq_tt| {
436 TokenTree::MetaVarDecl(_, _, id) => id.name == "vis",
437 TokenTree::Sequence(_, ref sub_seq) =>
438 sub_seq.op == quoted::KleeneOp::ZeroOrMore
439 || sub_seq.op == quoted::KleeneOp::ZeroOrOne,
443 let sp = span.entire();
444 sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
447 if !check_lhs_no_empty_seq(sess, &seq.tts) {
457 fn check_rhs(sess: &ParseSess, rhs: "ed::TokenTree) -> bool {
459 quoted::TokenTree::Delimited(..) => return true,
460 _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited")
465 fn check_matcher(sess: &ParseSess,
467 attrs: &[ast::Attribute],
468 matcher: &[quoted::TokenTree]) -> bool {
469 let first_sets = FirstSets::new(matcher);
470 let empty_suffix = TokenSet::empty();
471 let err = sess.span_diagnostic.err_count();
472 check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix);
473 err == sess.span_diagnostic.err_count()
476 // `The FirstSets` for a matcher is a mapping from subsequences in the
477 // matcher to the FIRST set for that subsequence.
479 // This mapping is partially precomputed via a backwards scan over the
480 // token trees of the matcher, which provides a mapping from each
481 // repetition sequence to its *first* set.
483 // (Hypothetically, sequences should be uniquely identifiable via their
484 // spans, though perhaps that is false, e.g., for macro-generated macros
485 // that do not try to inject artificial span information. My plan is
486 // to try to catch such cases ahead of time and not include them in
487 // the precomputed mapping.)
489 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
490 // span in the original matcher to the First set for the inner sequence `tt ...`.
492 // If two sequences have the same span in a matcher, then map that
493 // span to None (invalidating the mapping here and forcing the code to
495 first: FxHashMap<Span, Option<TokenSet>>,
499 fn new(tts: &[quoted::TokenTree]) -> FirstSets {
500 use self::quoted::TokenTree;
502 let mut sets = FirstSets { first: FxHashMap::default() };
503 build_recur(&mut sets, tts);
506 // walks backward over `tts`, returning the FIRST for `tts`
507 // and updating `sets` at the same time for all sequence
508 // substructure we find within `tts`.
509 fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet {
510 let mut first = TokenSet::empty();
511 for tt in tts.iter().rev() {
513 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
514 first.replace_with(tt.clone());
516 TokenTree::Delimited(span, ref delimited) => {
517 build_recur(sets, &delimited.tts[..]);
518 first.replace_with(delimited.open_tt(span.open));
520 TokenTree::Sequence(sp, ref seq_rep) => {
521 let subfirst = build_recur(sets, &seq_rep.tts[..]);
523 match sets.first.entry(sp.entire()) {
524 Entry::Vacant(vac) => {
525 vac.insert(Some(subfirst.clone()));
527 Entry::Occupied(mut occ) => {
528 // if there is already an entry, then a span must have collided.
529 // This should not happen with typical macro_rules macros,
530 // but syntax extensions need not maintain distinct spans,
531 // so distinct syntax trees can be assigned the same span.
532 // In such a case, the map cannot be trusted; so mark this
533 // entry as unusable.
538 // If the sequence contents can be empty, then the first
539 // token could be the separator token itself.
541 if let (Some(ref sep), true) = (seq_rep.separator.clone(),
542 subfirst.maybe_empty) {
543 first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone()));
546 // Reverse scan: Sequence comes before `first`.
547 if subfirst.maybe_empty
548 || seq_rep.op == quoted::KleeneOp::ZeroOrMore
549 || seq_rep.op == quoted::KleeneOp::ZeroOrOne
551 // If sequence is potentially empty, then
552 // union them (preserving first emptiness).
553 first.add_all(&TokenSet { maybe_empty: true, ..subfirst });
555 // Otherwise, sequence guaranteed
556 // non-empty; replace first.
567 // walks forward over `tts` until all potential FIRST tokens are
569 fn first(&self, tts: &[quoted::TokenTree]) -> TokenSet {
570 use self::quoted::TokenTree;
572 let mut first = TokenSet::empty();
573 for tt in tts.iter() {
574 assert!(first.maybe_empty);
576 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
577 first.add_one(tt.clone());
580 TokenTree::Delimited(span, ref delimited) => {
581 first.add_one(delimited.open_tt(span.open));
584 TokenTree::Sequence(sp, ref seq_rep) => {
585 match self.first.get(&sp.entire()) {
586 Some(&Some(ref subfirst)) => {
588 // If the sequence contents can be empty, then the first
589 // token could be the separator token itself.
591 if let (Some(ref sep), true) = (seq_rep.separator.clone(),
592 subfirst.maybe_empty) {
593 first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone()));
596 assert!(first.maybe_empty);
597 first.add_all(subfirst);
598 if subfirst.maybe_empty
599 || seq_rep.op == quoted::KleeneOp::ZeroOrMore
600 || seq_rep.op == quoted::KleeneOp::ZeroOrOne
602 // continue scanning for more first
603 // tokens, but also make sure we
604 // restore empty-tracking state
605 first.maybe_empty = true;
613 panic!("assume all sequences have (unique) spans for now");
617 panic!("We missed a sequence during FirstSets construction");
624 // we only exit the loop if `tts` was empty or if every
625 // element of `tts` matches the empty sequence.
626 assert!(first.maybe_empty);
631 // A set of `quoted::TokenTree`s, which may include `TokenTree::Match`s
632 // (for macro-by-example syntactic variables). It also carries the
633 // `maybe_empty` flag; that is true if and only if the matcher can
634 // match an empty token sequence.
636 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
637 // which has corresponding FIRST = {$a:expr, c, d}.
638 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
640 // (Notably, we must allow for *-op to occur zero times.)
641 #[derive(Clone, Debug)]
643 tokens: Vec<quoted::TokenTree>,
648 // Returns a set for the empty sequence.
649 fn empty() -> Self { TokenSet { tokens: Vec::new(), maybe_empty: true } }
651 // Returns the set `{ tok }` for the single-token (and thus
652 // non-empty) sequence [tok].
653 fn singleton(tok: quoted::TokenTree) -> Self {
654 TokenSet { tokens: vec![tok], maybe_empty: false }
657 // Changes self to be the set `{ tok }`.
658 // Since `tok` is always present, marks self as non-empty.
659 fn replace_with(&mut self, tok: quoted::TokenTree) {
661 self.tokens.push(tok);
662 self.maybe_empty = false;
665 // Changes self to be the empty set `{}`; meant for use when
666 // the particular token does not matter, but we want to
667 // record that it occurs.
668 fn replace_with_irrelevant(&mut self) {
670 self.maybe_empty = false;
673 // Adds `tok` to the set for `self`, marking sequence as non-empy.
674 fn add_one(&mut self, tok: quoted::TokenTree) {
675 if !self.tokens.contains(&tok) {
676 self.tokens.push(tok);
678 self.maybe_empty = false;
681 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
682 fn add_one_maybe(&mut self, tok: quoted::TokenTree) {
683 if !self.tokens.contains(&tok) {
684 self.tokens.push(tok);
688 // Adds all elements of `other` to this.
690 // (Since this is a set, we filter out duplicates.)
692 // If `other` is potentially empty, then preserves the previous
693 // setting of the empty flag of `self`. If `other` is guaranteed
694 // non-empty, then `self` is marked non-empty.
695 fn add_all(&mut self, other: &Self) {
696 for tok in &other.tokens {
697 if !self.tokens.contains(tok) {
698 self.tokens.push(tok.clone());
701 if !other.maybe_empty {
702 self.maybe_empty = false;
707 // Checks that `matcher` is internally consistent and that it
708 // can legally by followed by a token N, for all N in `follow`.
709 // (If `follow` is empty, then it imposes no constraint on
712 // Returns the set of NT tokens that could possibly come last in
713 // `matcher`. (If `matcher` matches the empty sequence, then
714 // `maybe_empty` will be set to true.)
716 // Requires that `first_sets` is pre-computed for `matcher`;
717 // see `FirstSets::new`.
718 fn check_matcher_core(sess: &ParseSess,
720 attrs: &[ast::Attribute],
721 first_sets: &FirstSets,
722 matcher: &[quoted::TokenTree],
723 follow: &TokenSet) -> TokenSet {
724 use self::quoted::TokenTree;
726 let mut last = TokenSet::empty();
728 // 2. For each token and suffix [T, SUFFIX] in M:
729 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
730 // then ensure T can also be followed by any element of FOLLOW.
731 'each_token: for i in 0..matcher.len() {
732 let token = &matcher[i];
733 let suffix = &matcher[i+1..];
735 let build_suffix_first = || {
736 let mut s = first_sets.first(suffix);
737 if s.maybe_empty { s.add_all(follow); }
741 // (we build `suffix_first` on demand below; you can tell
742 // which cases are supposed to fall through by looking for the
743 // initialization of this variable.)
746 // First, update `last` so that it corresponds to the set
747 // of NT tokens that might end the sequence `... token`.
749 TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => {
750 let can_be_followed_by_any;
751 if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) {
752 let msg = format!("invalid fragment specifier `{}`", bad_frag);
753 sess.span_diagnostic.struct_span_err(token.span(), &msg)
754 .help(VALID_FRAGMENT_NAMES_MSG)
756 // (This eliminates false positives and duplicates
757 // from error messages.)
758 can_be_followed_by_any = true;
760 can_be_followed_by_any = token_can_be_followed_by_any(token);
763 if can_be_followed_by_any {
764 // don't need to track tokens that work with any,
765 last.replace_with_irrelevant();
766 // ... and don't need to check tokens that can be
767 // followed by anything against SUFFIX.
768 continue 'each_token;
770 last.replace_with(token.clone());
771 suffix_first = build_suffix_first();
774 TokenTree::Delimited(span, ref d) => {
775 let my_suffix = TokenSet::singleton(d.close_tt(span.close));
776 check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix);
777 // don't track non NT tokens
778 last.replace_with_irrelevant();
780 // also, we don't need to check delimited sequences
782 continue 'each_token;
784 TokenTree::Sequence(sp, ref seq_rep) => {
785 suffix_first = build_suffix_first();
786 // The trick here: when we check the interior, we want
787 // to include the separator (if any) as a potential
788 // (but not guaranteed) element of FOLLOW. So in that
789 // case, we make a temp copy of suffix and stuff
790 // delimiter in there.
792 // FIXME: Should I first scan suffix_first to see if
793 // delimiter is already in it before I go through the
794 // work of cloning it? But then again, this way I may
795 // get a "tighter" span?
797 let my_suffix = if let Some(ref u) = seq_rep.separator {
798 new = suffix_first.clone();
799 new.add_one_maybe(TokenTree::Token(sp.entire(), u.clone()));
805 // At this point, `suffix_first` is built, and
806 // `my_suffix` is some TokenSet that we can use
807 // for checking the interior of `seq_rep`.
808 let next = check_matcher_core(sess,
814 if next.maybe_empty {
820 // the recursive call to check_matcher_core already ran the 'each_last
821 // check below, so we can just keep going forward here.
822 continue 'each_token;
826 // (`suffix_first` guaranteed initialized once reaching here.)
828 // Now `last` holds the complete set of NT tokens that could
829 // end the sequence before SUFFIX. Check that every one works with `suffix`.
830 'each_last: for token in &last.tokens {
831 if let TokenTree::MetaVarDecl(_, ref name, ref frag_spec) = *token {
832 for next_token in &suffix_first.tokens {
833 match is_in_follow(next_token, &frag_spec.as_str()) {
834 IsInFollow::Invalid(msg, help) => {
835 sess.span_diagnostic.struct_span_err(next_token.span(), &msg)
837 // don't bother reporting every source of
838 // conflict for a particular element of `last`.
841 IsInFollow::Yes => {}
842 IsInFollow::No(ref possible) => {
843 let may_be = if last.tokens.len() == 1 &&
844 suffix_first.tokens.len() == 1
851 let sp = next_token.span();
852 let mut err = sess.span_diagnostic.struct_span_err(
854 &format!("`${name}:{frag}` {may_be} followed by `{next}`, which \
855 is not allowed for `{frag}` fragments",
858 next=quoted_tt_to_string(next_token),
863 format!("not allowed after `{}` fragments", frag_spec),
865 let msg = "allowed there are: ";
866 match &possible[..] {
870 "only {} is allowed after `{}` fragments",
879 ts[..ts.len() - 1].iter().map(|s| *s)
880 .collect::<Vec<_>>().join(", "),
895 fn token_can_be_followed_by_any(tok: "ed::TokenTree) -> bool {
896 if let quoted::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok {
897 frag_can_be_followed_by_any(&frag_spec.as_str())
899 // (Non NT's can always be followed by anthing in matchers.)
904 /// True if a fragment of type `frag` can be followed by any sort of
905 /// token. We use this (among other things) as a useful approximation
906 /// for when `frag` can be followed by a repetition like `$(...)*` or
907 /// `$(...)+`. In general, these can be a bit tricky to reason about,
908 /// so we adopt a conservative position that says that any fragment
909 /// specifier which consumes at most one token tree can be followed by
910 /// a fragment specifier (indeed, these fragments can be followed by
911 /// ANYTHING without fear of future compatibility hazards).
912 fn frag_can_be_followed_by_any(frag: &str) -> bool {
914 "item" | // always terminated by `}` or `;`
915 "block" | // exactly one token tree
916 "ident" | // exactly one token tree
917 "literal" | // exactly one token tree
918 "meta" | // exactly one token tree
919 "lifetime" | // exactly one token tree
920 "tt" => // exactly one token tree
930 No(Vec<&'static str>),
931 Invalid(String, &'static str),
934 /// True if `frag` can legally be followed by the token `tok`. For
935 /// fragments that can consume an unbounded number of tokens, `tok`
936 /// must be within a well-defined follow set. This is intended to
937 /// guarantee future compatibility: for example, without this rule, if
938 /// we expanded `expr` to include a new binary operator, we might
939 /// break macros that were relying on that binary operator as a
941 // when changing this do not forget to update doc/book/macros.md!
942 fn is_in_follow(tok: "ed::TokenTree, frag: &str) -> IsInFollow {
943 use self::quoted::TokenTree;
945 if let TokenTree::Token(_, token::CloseDelim(_)) = *tok {
946 // closing a token tree can never be matched by any fragment;
947 // iow, we always require that `(` and `)` match, etc.
952 // since items *must* be followed by either a `;` or a `}`, we can
953 // accept anything after them
957 // anything can follow block, the braces provide an easy boundary to
962 let tokens = vec!["`=>`", "`,`", "`;`"];
964 TokenTree::Token(_, ref tok) => match *tok {
965 FatArrow | Comma | Semi => IsInFollow::Yes,
966 _ => IsInFollow::No(tokens),
968 _ => IsInFollow::No(tokens),
972 let tokens = vec!["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
974 TokenTree::Token(_, ref tok) => match *tok {
975 FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
976 Ident(i, false) if i.name == "if" || i.name == "in" => IsInFollow::Yes,
977 _ => IsInFollow::No(tokens),
979 _ => IsInFollow::No(tokens),
984 "`{`", "`[`", "`=>`", "`,`", "`>`","`=`", "`:`", "`;`", "`|`", "`as`",
988 TokenTree::Token(_, ref tok) => match *tok {
989 OpenDelim(token::DelimToken::Brace) |
990 OpenDelim(token::DelimToken::Bracket) |
991 Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi |
992 BinOp(token::Or) => IsInFollow::Yes,
993 Ident(i, false) if i.name == "as" || i.name == "where" => IsInFollow::Yes,
994 _ => IsInFollow::No(tokens),
996 TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => IsInFollow::Yes,
997 _ => IsInFollow::No(tokens),
1000 "ident" | "lifetime" => {
1001 // being a single token, idents and lifetimes are harmless
1005 // literals may be of a single token, or two tokens (negative numbers)
1009 // being either a single token or a delimited sequence, tt is
1014 // Explicitly disallow `priv`, on the off chance it comes back.
1015 let tokens = vec!["`,`", "an ident", "a type"];
1017 TokenTree::Token(_, ref tok) => match *tok {
1018 Comma => IsInFollow::Yes,
1019 Ident(i, is_raw) if is_raw || i.name != "priv" => IsInFollow::Yes,
1020 ref tok => if tok.can_begin_type() {
1023 IsInFollow::No(tokens)
1026 TokenTree::MetaVarDecl(_, _, frag) if frag.name == "ident"
1027 || frag.name == "ty"
1028 || frag.name == "path" => IsInFollow::Yes,
1029 _ => IsInFollow::No(tokens),
1032 "" => IsInFollow::Yes, // keywords::Invalid
1033 _ => IsInFollow::Invalid(format!("invalid fragment specifier `{}`", frag),
1034 VALID_FRAGMENT_NAMES_MSG),
1039 fn has_legal_fragment_specifier(sess: &ParseSess,
1040 features: &Features,
1041 attrs: &[ast::Attribute],
1042 tok: "ed::TokenTree) -> Result<(), String> {
1043 debug!("has_legal_fragment_specifier({:?})", tok);
1044 if let quoted::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok {
1045 let frag_name = frag_spec.as_str();
1046 let frag_span = tok.span();
1047 if !is_legal_fragment_specifier(sess, features, attrs, &frag_name, frag_span) {
1048 return Err(frag_name.to_string());
1054 fn is_legal_fragment_specifier(_sess: &ParseSess,
1055 _features: &Features,
1056 _attrs: &[ast::Attribute],
1058 _frag_span: Span) -> bool {
1060 * If new fragment specifiers are invented in nightly, `_sess`,
1061 * `_features`, `_attrs`, and `_frag_span` will be useful here
1062 * for checking against feature gates. See past versions of
1066 "item" | "block" | "stmt" | "expr" | "pat" | "lifetime" |
1067 "path" | "ty" | "ident" | "meta" | "tt" | "vis" | "literal" |
1073 fn quoted_tt_to_string(tt: "ed::TokenTree) -> String {
1075 quoted::TokenTree::Token(_, ref tok) => ::print::pprust::token_to_string(tok),
1076 quoted::TokenTree::MetaVar(_, name) => format!("${}", name),
1077 quoted::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind),
1078 _ => panic!("unexpected quoted::TokenTree::{{Sequence or Delimited}} \
1079 in follow set checker"),