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
::diagnostics
::{annotate_doc_comment, parse_failure_msg}
;
6 use crate::mbe
::macro_check
;
7 use crate::mbe
::macro_parser
::{Error, ErrorReported, Failure, Success, TtParser}
;
8 use crate::mbe
::macro_parser
::{MatchedSeq, MatchedTokenTree, MatcherLoc}
;
9 use crate::mbe
::transcribe
::transcribe
;
12 use rustc_ast
::token
::{self, Delimiter, NonterminalKind, Token, TokenKind, TokenKind::*}
;
13 use rustc_ast
::tokenstream
::{DelimSpan, TokenStream}
;
14 use rustc_ast
::{NodeId, DUMMY_NODE_ID}
;
15 use rustc_ast_pretty
::pprust
;
16 use rustc_attr
::{self as attr, TransparencyError}
;
17 use rustc_data_structures
::fx
::{FxHashMap, FxIndexMap}
;
18 use rustc_errors
::{Applicability, ErrorGuaranteed}
;
19 use rustc_feature
::Features
;
20 use rustc_lint_defs
::builtin
::{
21 RUST_2021_INCOMPATIBLE_OR_PATTERNS
, SEMICOLON_IN_EXPRESSIONS_FROM_MACROS
,
23 use rustc_lint_defs
::BuiltinLintDiagnostics
;
24 use rustc_parse
::parser
::{Parser, Recovery}
;
25 use rustc_session
::parse
::ParseSess
;
26 use rustc_session
::Session
;
27 use rustc_span
::edition
::Edition
;
28 use rustc_span
::hygiene
::Transparency
;
29 use rustc_span
::symbol
::{kw, sym, Ident, MacroRulesNormalizedIdent}
;
33 use std
::collections
::hash_map
::Entry
;
34 use std
::{mem, slice}
;
36 use super::diagnostics
;
37 use super::macro_parser
::{NamedMatches, NamedParseResult}
;
39 pub(crate) struct ParserAnyMacro
<'a
> {
42 /// Span of the expansion site of the macro this parser is for
44 /// The ident of the macro we're parsing
47 is_trailing_mac
: bool
,
49 /// Whether or not this macro is defined in the current crate
53 impl<'a
> ParserAnyMacro
<'a
> {
54 pub(crate) fn make(mut self: Box
<ParserAnyMacro
<'a
>>, kind
: AstFragmentKind
) -> AstFragment
{
64 let snapshot
= &mut parser
.create_snapshot_for_diagnostic();
65 let fragment
= match parse_ast_fragment(parser
, kind
) {
68 diagnostics
::emit_frag_parse_err(err
, parser
, snapshot
, site_span
, arm_span
, kind
);
69 return kind
.dummy(site_span
);
73 // We allow semicolons at the end of expressions -- e.g., the semicolon in
74 // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
75 // but `m!()` is allowed in expression positions (cf. issue #34706).
76 if kind
== AstFragmentKind
::Expr
&& parser
.token
== token
::Semi
{
78 parser
.sess
.buffer_lint_with_diagnostic(
79 SEMICOLON_IN_EXPRESSIONS_FROM_MACROS
,
82 "trailing semicolon in macro used in expression position",
83 BuiltinLintDiagnostics
::TrailingMacro(is_trailing_mac
, macro_ident
),
89 // Make sure we don't have any tokens left to parse so we don't silently drop anything.
90 let path
= ast
::Path
::from_ident(macro_ident
.with_span_pos(site_span
));
91 ensure_complete_parse(parser
, &path
, kind
.name(), site_span
);
96 struct MacroRulesMacroExpander
{
100 transparency
: Transparency
,
101 lhses
: Vec
<Vec
<MatcherLoc
>>,
102 rhses
: Vec
<mbe
::TokenTree
>,
106 impl TTMacroExpander
for MacroRulesMacroExpander
{
109 cx
: &'cx
mut ExtCtxt
<'_
>,
112 ) -> Box
<dyn MacResult
+ 'cx
> {
114 return DummyResult
::any(sp
);
130 fn macro_rules_dummy_expander
<'cx
>(
131 _
: &'cx
mut ExtCtxt
<'_
>,
134 ) -> Box
<dyn MacResult
+ 'cx
> {
135 DummyResult
::any(span
)
138 fn trace_macros_note(cx_expansions
: &mut FxIndexMap
<Span
, Vec
<String
>>, sp
: Span
, message
: String
) {
139 let sp
= sp
.macro_backtrace().last().map_or(sp
, |trace
| trace
.call_site
);
140 cx_expansions
.entry(sp
).or_default().push(message
);
143 pub(super) trait Tracker
<'matcher
> {
144 /// This is called before trying to match next MatcherLoc on the current token.
145 fn before_match_loc(&mut self, parser
: &TtParser
, matcher
: &'matcher MatcherLoc
);
147 /// This is called after an arm has been parsed, either successfully or unsuccessfully. When this is called,
148 /// `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
149 fn after_arm(&mut self, result
: &NamedParseResult
);
152 fn description() -> &'
static str;
154 fn recovery() -> Recovery
;
157 /// A noop tracker that is used in the hot path of the expansion, has zero overhead thanks to monomorphization.
158 pub(super) struct NoopTracker
;
160 impl<'matcher
> Tracker
<'matcher
> for NoopTracker
{
161 fn before_match_loc(&mut self, _
: &TtParser
, _
: &'matcher MatcherLoc
) {}
162 fn after_arm(&mut self, _
: &NamedParseResult
) {}
163 fn description() -> &'
static str {
166 fn recovery() -> Recovery
{
171 /// Expands the rules based macro defined by `lhses` and `rhses` for a given
173 #[instrument(skip(cx, transparency, arg, lhses, rhses))]
174 fn expand_macro
<'cx
>(
175 cx
: &'cx
mut ExtCtxt
<'_
>,
180 transparency
: Transparency
,
182 lhses
: &[Vec
<MatcherLoc
>],
183 rhses
: &[mbe
::TokenTree
],
184 ) -> Box
<dyn MacResult
+ 'cx
> {
185 let sess
= &cx
.sess
.parse_sess
;
186 // Macros defined in the current crate have a real node id,
187 // whereas macros from an external crate have a dummy id.
188 let is_local
= node_id
!= DUMMY_NODE_ID
;
190 if cx
.trace_macros() {
191 let msg
= format
!("expanding `{}! {{ {} }}`", name
, pprust
::tts_to_string(&arg
));
192 trace_macros_note(&mut cx
.expansions
, sp
, msg
);
195 // Track nothing for the best performance.
196 let try_success_result
= try_match_macro(sess
, name
, &arg
, lhses
, &mut NoopTracker
);
198 match try_success_result
{
199 Ok((i
, named_matches
)) => {
200 let (rhs
, rhs_span
): (&mbe
::Delimited
, DelimSpan
) = match &rhses
[i
] {
201 mbe
::TokenTree
::Delimited(span
, delimited
) => (&delimited
, *span
),
202 _
=> cx
.span_bug(sp
, "malformed macro rhs"),
204 let arm_span
= rhses
[i
].span();
206 let rhs_spans
= rhs
.tts
.iter().map(|t
| t
.span()).collect
::<Vec
<_
>>();
207 // rhs has holes ( `$id` and `$(...)` that need filled)
208 let mut tts
= match transcribe(cx
, &named_matches
, &rhs
, rhs_span
, transparency
) {
212 return DummyResult
::any(arm_span
);
216 // Replace all the tokens for the corresponding positions in the macro, to maintain
217 // proper positions in error reporting, while maintaining the macro_backtrace.
218 if rhs_spans
.len() == tts
.len() {
219 tts
= tts
.map_enumerated(|i
, tt
| {
220 let mut tt
= tt
.clone();
221 let mut sp
= rhs_spans
[i
];
222 sp
= sp
.with_ctxt(tt
.span().ctxt());
228 if cx
.trace_macros() {
229 let msg
= format
!("to `{}`", pprust
::tts_to_string(&tts
));
230 trace_macros_note(&mut cx
.expansions
, sp
, msg
);
233 let mut p
= Parser
::new(sess
, tts
, false, None
);
234 p
.last_type_ascription
= cx
.current_expansion
.prior_type_ascription
;
237 cx
.resolver
.record_macro_rule_usage(node_id
, i
);
240 // Let the context choose how to interpret the result.
241 // Weird, but useful for X-macros.
242 return Box
::new(ParserAnyMacro
{
245 // Pass along the original expansion site and the name of the macro
246 // so we can print a useful error message if the parse of the expanded
247 // macro leaves unparsed tokens.
250 lint_node_id
: cx
.current_expansion
.lint_node_id
,
251 is_trailing_mac
: cx
.current_expansion
.is_trailing_mac
,
256 Err(CanRetry
::No(_
)) => {
257 debug
!("Will not retry matching as an error was emitted already");
258 return DummyResult
::any(sp
);
260 Err(CanRetry
::Yes
) => {
261 // Retry and emit a better error below.
265 diagnostics
::failed_to_match_macro(cx
, sp
, def_span
, name
, arg
, lhses
)
268 pub(super) enum CanRetry
{
270 /// We are not allowed to retry macro expansion as a fatal error has been emitted already.
274 /// Try expanding the macro. Returns the index of the successful arm and its named_matches if it was successful,
275 /// and nothing if it failed. On failure, it's the callers job to use `track` accordingly to record all errors
277 #[instrument(level = "debug", skip(sess, arg, lhses, track), fields(tracking = %T::description()))]
278 pub(super) fn try_match_macro
<'matcher
, T
: Tracker
<'matcher
>>(
282 lhses
: &'matcher
[Vec
<MatcherLoc
>],
284 ) -> Result
<(usize, NamedMatches
), CanRetry
> {
285 // We create a base parser that can be used for the "black box" parts.
286 // Every iteration needs a fresh copy of that parser. However, the parser
287 // is not mutated on many of the iterations, particularly when dealing with
290 // macro_rules! foo {
294 // // ... etc. (maybe hundreds more)
297 // as seen in the `html5ever` benchmark. We use a `Cow` so that the base
298 // parser is only cloned when necessary (upon mutation). Furthermore, we
299 // reinitialize the `Cow` with the base parser at the start of every
300 // iteration, so that any mutated parsers are not reused. This is all quite
301 // hacky, but speeds up the `html5ever` benchmark significantly. (Issue
302 // 68836 suggests a more comprehensive but more complex change to deal with
304 let parser
= parser_from_cx(sess
, arg
.clone(), T
::recovery());
305 // Try each arm's matchers.
306 let mut tt_parser
= TtParser
::new(name
);
307 for (i
, lhs
) in lhses
.iter().enumerate() {
308 let _tracing_span
= trace_span
!("Matching arm", %i
);
310 // Take a snapshot of the state of pre-expansion gating at this point.
311 // This is used so that if a matcher is not `Success(..)`ful,
312 // then the spans which became gated when parsing the unsuccessful matcher
313 // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
314 let mut gated_spans_snapshot
= mem
::take(&mut *sess
.gated_spans
.spans
.borrow_mut());
316 let result
= tt_parser
.parse_tt(&mut Cow
::Borrowed(&parser
), lhs
, track
);
318 track
.after_arm(&result
);
321 Success(named_matches
) => {
322 debug
!("Parsed arm successfully");
323 // The matcher was `Success(..)`ful.
324 // Merge the gated spans from parsing the matcher with the pre-existing ones.
325 sess
.gated_spans
.merge(gated_spans_snapshot
);
327 return Ok((i
, named_matches
));
330 trace
!("Failed to match arm, trying the next one");
334 debug
!("Fatal error occurred during matching");
335 // We haven't emitted an error yet, so we can retry.
336 return Err(CanRetry
::Yes
);
338 ErrorReported(guarantee
) => {
339 debug
!("Fatal error occurred and was reported during matching");
340 // An error has been reported already, we cannot retry as that would cause duplicate errors.
341 return Err(CanRetry
::No(guarantee
));
345 // The matcher was not `Success(..)`ful.
346 // Restore to the state before snapshotting and maybe try again.
347 mem
::swap(&mut gated_spans_snapshot
, &mut sess
.gated_spans
.spans
.borrow_mut());
353 // Note that macro-by-example's input is also matched against a token tree:
354 // $( $lhs:tt => $rhs:tt );+
356 // Holy self-referential!
358 /// Converts a macro item into a syntax extension.
359 pub fn compile_declarative_macro(
364 ) -> (SyntaxExtension
, Vec
<(usize, Span
)>) {
365 debug
!("compile_declarative_macro: {:?}", def
);
366 let mk_syn_ext
= |expander
| {
367 SyntaxExtension
::new(
369 SyntaxExtensionKind
::LegacyBang(expander
),
377 let dummy_syn_ext
= || (mk_syn_ext(Box
::new(macro_rules_dummy_expander
)), Vec
::new());
379 let diag
= &sess
.parse_sess
.span_diagnostic
;
380 let lhs_nm
= Ident
::new(sym
::lhs
, def
.span
);
381 let rhs_nm
= Ident
::new(sym
::rhs
, def
.span
);
382 let tt_spec
= Some(NonterminalKind
::TT
);
384 // Parse the macro_rules! invocation
385 let (macro_rules
, body
) = match &def
.kind
{
386 ast
::ItemKind
::MacroDef(def
) => (def
.macro_rules
, def
.body
.tokens
.clone()),
390 // The pattern that macro_rules matches.
391 // The grammar for macro_rules! is:
392 // $( $lhs:tt => $rhs:tt );+
393 // ...quasiquoting this would be nice.
394 // These spans won't matter, anyways
395 let argument_gram
= vec
![
396 mbe
::TokenTree
::Sequence(
398 mbe
::SequenceRepetition
{
400 mbe
::TokenTree
::MetaVarDecl(def
.span
, lhs_nm
, tt_spec
),
401 mbe
::TokenTree
::token(token
::FatArrow
, def
.span
),
402 mbe
::TokenTree
::MetaVarDecl(def
.span
, rhs_nm
, tt_spec
),
404 separator
: Some(Token
::new(
405 if macro_rules { token::Semi }
else { token::Comma }
,
408 kleene
: mbe
::KleeneToken
::new(mbe
::KleeneOp
::OneOrMore
, def
.span
),
412 // to phase into semicolon-termination instead of semicolon-separation
413 mbe
::TokenTree
::Sequence(
415 mbe
::SequenceRepetition
{
416 tts
: vec
![mbe
::TokenTree
::token(
417 if macro_rules { token::Semi }
else { token::Comma }
,
421 kleene
: mbe
::KleeneToken
::new(mbe
::KleeneOp
::ZeroOrMore
, def
.span
),
426 // Convert it into `MatcherLoc` form.
427 let argument_gram
= mbe
::macro_parser
::compute_locs(&argument_gram
);
429 let parser
= Parser
::new(&sess
.parse_sess
, body
, true, rustc_parse
::MACRO_ARGUMENTS
);
431 TtParser
::new(Ident
::with_dummy_span(if macro_rules { kw::MacroRules }
else { kw::Macro }
));
433 match tt_parser
.parse_tt(&mut Cow
::Owned(parser
), &argument_gram
, &mut NoopTracker
) {
435 Failure(token
, msg
) => {
436 let s
= parse_failure_msg(&token
);
437 let sp
= token
.span
.substitute_dummy(def
.span
);
438 let mut err
= sess
.parse_sess
.span_diagnostic
.struct_span_err(sp
, &s
);
439 err
.span_label(sp
, msg
);
440 annotate_doc_comment(&mut err
, sess
.source_map(), sp
);
442 return dummy_syn_ext();
447 .struct_span_err(sp
.substitute_dummy(def
.span
), &msg
)
449 return dummy_syn_ext();
451 ErrorReported(_
) => {
452 return dummy_syn_ext();
456 let mut valid
= true;
458 // Extract the arguments:
459 let lhses
= match argument_map
[&MacroRulesNormalizedIdent
::new(lhs_nm
)] {
460 MatchedSeq(ref s
) => s
463 if let MatchedTokenTree(ref tt
) = *m
{
464 let tt
= mbe
::quoted
::parse(
465 TokenStream
::new(vec
![tt
.clone()]),
474 valid
&= check_lhs_nt_follows(&sess
.parse_sess
, &def
, &tt
);
477 sess
.parse_sess
.span_diagnostic
.span_bug(def
.span
, "wrong-structured lhs")
479 .collect
::<Vec
<mbe
::TokenTree
>>(),
480 _
=> sess
.parse_sess
.span_diagnostic
.span_bug(def
.span
, "wrong-structured lhs"),
483 let rhses
= match argument_map
[&MacroRulesNormalizedIdent
::new(rhs_nm
)] {
484 MatchedSeq(ref s
) => s
487 if let MatchedTokenTree(ref tt
) = *m
{
488 return mbe
::quoted
::parse(
489 TokenStream
::new(vec
![tt
.clone()]),
499 sess
.parse_sess
.span_diagnostic
.span_bug(def
.span
, "wrong-structured lhs")
501 .collect
::<Vec
<mbe
::TokenTree
>>(),
502 _
=> sess
.parse_sess
.span_diagnostic
.span_bug(def
.span
, "wrong-structured rhs"),
506 valid
&= check_rhs(&sess
.parse_sess
, rhs
);
509 // don't abort iteration early, so that errors for multiple lhses can be reported
511 valid
&= check_lhs_no_empty_seq(&sess
.parse_sess
, slice
::from_ref(lhs
));
514 valid
&= macro_check
::check_meta_variables(&sess
.parse_sess
, def
.id
, def
.span
, &lhses
, &rhses
);
516 let (transparency
, transparency_error
) = attr
::find_transparency(&def
.attrs
, macro_rules
);
517 match transparency_error
{
518 Some(TransparencyError
::UnknownTransparency(value
, span
)) => {
519 diag
.span_err(span
, &format
!("unknown macro transparency: `{}`", value
));
521 Some(TransparencyError
::MultipleTransparencyAttrs(old_span
, new_span
)) => {
522 diag
.span_err(vec
![old_span
, new_span
], "multiple macro transparency attributes");
527 // Compute the spans of the macro rules for unused rule linting.
528 // To avoid warning noise, only consider the rules of this
529 // macro for the lint, if all rules are valid.
530 // Also, we are only interested in non-foreign macros.
531 let rule_spans
= if valid
&& def
.id
!= DUMMY_NODE_ID
{
536 // If the rhs contains an invocation like compile_error!,
537 // don't consider the rule for the unused rule lint.
538 .filter(|(_idx
, (_lhs
, rhs
))| !has_compile_error_macro(rhs
))
539 // We only take the span of the lhs here,
540 // so that the spans of created warnings are smaller.
541 .map(|(idx
, (lhs
, _rhs
))| (idx
, lhs
.span()))
547 // Convert the lhses into `MatcherLoc` form, which is better for doing the
548 // actual matching. Unless the matcher is invalid.
549 let lhses
= if valid
{
553 // Ignore the delimiters around the matcher.
555 mbe
::TokenTree
::Delimited(_
, delimited
) => {
556 mbe
::macro_parser
::compute_locs(&delimited
.tts
)
558 _
=> sess
.parse_sess
.span_diagnostic
.span_bug(def
.span
, "malformed macro lhs"),
566 let expander
= Box
::new(MacroRulesMacroExpander
{
575 (mk_syn_ext(expander
), rule_spans
)
578 fn check_lhs_nt_follows(sess
: &ParseSess
, def
: &ast
::Item
, lhs
: &mbe
::TokenTree
) -> bool
{
579 // lhs is going to be like TokenTree::Delimited(...), where the
580 // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
581 if let mbe
::TokenTree
::Delimited(_
, delimited
) = lhs
{
582 check_matcher(sess
, def
, &delimited
.tts
)
584 let msg
= "invalid macro matcher; matchers must be contained in balanced delimiters";
585 sess
.span_diagnostic
.span_err(lhs
.span(), msg
);
588 // we don't abort on errors on rejection, the driver will do that for us
589 // after parsing/expansion. we can report every error in every macro this way.
592 /// Checks that the lhs contains no repetition which could match an empty token
593 /// tree, because then the matcher would hang indefinitely.
594 fn check_lhs_no_empty_seq(sess
: &ParseSess
, tts
: &[mbe
::TokenTree
]) -> bool
{
599 | TokenTree
::MetaVar(..)
600 | TokenTree
::MetaVarDecl(..)
601 | TokenTree
::MetaVarExpr(..) => (),
602 TokenTree
::Delimited(_
, ref del
) => {
603 if !check_lhs_no_empty_seq(sess
, &del
.tts
) {
607 TokenTree
::Sequence(span
, ref seq
) => {
608 if seq
.separator
.is_none()
609 && seq
.tts
.iter().all(|seq_tt
| match *seq_tt
{
610 TokenTree
::MetaVarDecl(_
, _
, Some(NonterminalKind
::Vis
)) => true,
611 TokenTree
::Sequence(_
, ref sub_seq
) => {
612 sub_seq
.kleene
.op
== mbe
::KleeneOp
::ZeroOrMore
613 || sub_seq
.kleene
.op
== mbe
::KleeneOp
::ZeroOrOne
618 let sp
= span
.entire();
619 sess
.span_diagnostic
.span_err(sp
, "repetition matches empty token tree");
622 if !check_lhs_no_empty_seq(sess
, &seq
.tts
) {
632 fn check_rhs(sess
: &ParseSess
, rhs
: &mbe
::TokenTree
) -> bool
{
634 mbe
::TokenTree
::Delimited(..) => return true,
636 sess
.span_diagnostic
.span_err(rhs
.span(), "macro rhs must be delimited");
642 fn check_matcher(sess
: &ParseSess
, def
: &ast
::Item
, matcher
: &[mbe
::TokenTree
]) -> bool
{
643 let first_sets
= FirstSets
::new(matcher
);
644 let empty_suffix
= TokenSet
::empty();
645 let err
= sess
.span_diagnostic
.err_count();
646 check_matcher_core(sess
, def
, &first_sets
, matcher
, &empty_suffix
);
647 err
== sess
.span_diagnostic
.err_count()
650 fn has_compile_error_macro(rhs
: &mbe
::TokenTree
) -> bool
{
652 mbe
::TokenTree
::Delimited(_sp
, d
) => {
653 let has_compile_error
= d
.tts
.array_windows
::<3>().any(|[ident
, bang
, args
]| {
654 if let mbe
::TokenTree
::Token(ident
) = ident
&&
655 let TokenKind
::Ident(ident
, _
) = ident
.kind
&&
656 ident
== sym
::compile_error
&&
657 let mbe
::TokenTree
::Token(bang
) = bang
&&
658 let TokenKind
::Not
= bang
.kind
&&
659 let mbe
::TokenTree
::Delimited(_
, del
) = args
&&
660 del
.delim
!= Delimiter
::Invisible
667 if has_compile_error { true }
else { d.tts.iter().any(has_compile_error_macro) }
673 // `The FirstSets` for a matcher is a mapping from subsequences in the
674 // matcher to the FIRST set for that subsequence.
676 // This mapping is partially precomputed via a backwards scan over the
677 // token trees of the matcher, which provides a mapping from each
678 // repetition sequence to its *first* set.
680 // (Hypothetically, sequences should be uniquely identifiable via their
681 // spans, though perhaps that is false, e.g., for macro-generated macros
682 // that do not try to inject artificial span information. My plan is
683 // to try to catch such cases ahead of time and not include them in
684 // the precomputed mapping.)
685 struct FirstSets
<'tt
> {
686 // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its
687 // span in the original matcher to the First set for the inner sequence `tt ...`.
689 // If two sequences have the same span in a matcher, then map that
690 // span to None (invalidating the mapping here and forcing the code to
692 first
: FxHashMap
<Span
, Option
<TokenSet
<'tt
>>>,
695 impl<'tt
> FirstSets
<'tt
> {
696 fn new(tts
: &'tt
[mbe
::TokenTree
]) -> FirstSets
<'tt
> {
699 let mut sets
= FirstSets { first: FxHashMap::default() }
;
700 build_recur(&mut sets
, tts
);
703 // walks backward over `tts`, returning the FIRST for `tts`
704 // and updating `sets` at the same time for all sequence
705 // substructure we find within `tts`.
706 fn build_recur
<'tt
>(sets
: &mut FirstSets
<'tt
>, tts
: &'tt
[TokenTree
]) -> TokenSet
<'tt
> {
707 let mut first
= TokenSet
::empty();
708 for tt
in tts
.iter().rev() {
711 | TokenTree
::MetaVar(..)
712 | TokenTree
::MetaVarDecl(..)
713 | TokenTree
::MetaVarExpr(..) => {
714 first
.replace_with(TtHandle
::TtRef(tt
));
716 TokenTree
::Delimited(span
, ref delimited
) => {
717 build_recur(sets
, &delimited
.tts
);
718 first
.replace_with(TtHandle
::from_token_kind(
719 token
::OpenDelim(delimited
.delim
),
723 TokenTree
::Sequence(sp
, ref seq_rep
) => {
724 let subfirst
= build_recur(sets
, &seq_rep
.tts
);
726 match sets
.first
.entry(sp
.entire()) {
727 Entry
::Vacant(vac
) => {
728 vac
.insert(Some(subfirst
.clone()));
730 Entry
::Occupied(mut occ
) => {
731 // if there is already an entry, then a span must have collided.
732 // This should not happen with typical macro_rules macros,
733 // but syntax extensions need not maintain distinct spans,
734 // so distinct syntax trees can be assigned the same span.
735 // In such a case, the map cannot be trusted; so mark this
736 // entry as unusable.
741 // If the sequence contents can be empty, then the first
742 // token could be the separator token itself.
744 if let (Some(sep
), true) = (&seq_rep
.separator
, subfirst
.maybe_empty
) {
745 first
.add_one_maybe(TtHandle
::from_token(sep
.clone()));
748 // Reverse scan: Sequence comes before `first`.
749 if subfirst
.maybe_empty
750 || seq_rep
.kleene
.op
== mbe
::KleeneOp
::ZeroOrMore
751 || seq_rep
.kleene
.op
== mbe
::KleeneOp
::ZeroOrOne
753 // If sequence is potentially empty, then
754 // union them (preserving first emptiness).
755 first
.add_all(&TokenSet { maybe_empty: true, ..subfirst }
);
757 // Otherwise, sequence guaranteed
758 // non-empty; replace first.
769 // walks forward over `tts` until all potential FIRST tokens are
771 fn first(&self, tts
: &'tt
[mbe
::TokenTree
]) -> TokenSet
<'tt
> {
774 let mut first
= TokenSet
::empty();
775 for tt
in tts
.iter() {
776 assert
!(first
.maybe_empty
);
779 | TokenTree
::MetaVar(..)
780 | TokenTree
::MetaVarDecl(..)
781 | TokenTree
::MetaVarExpr(..) => {
782 first
.add_one(TtHandle
::TtRef(tt
));
785 TokenTree
::Delimited(span
, ref delimited
) => {
786 first
.add_one(TtHandle
::from_token_kind(
787 token
::OpenDelim(delimited
.delim
),
792 TokenTree
::Sequence(sp
, ref seq_rep
) => {
794 let subfirst
= match self.first
.get(&sp
.entire()) {
795 Some(&Some(ref subfirst
)) => subfirst
,
797 subfirst_owned
= self.first(&seq_rep
.tts
);
801 panic
!("We missed a sequence during FirstSets construction");
805 // If the sequence contents can be empty, then the first
806 // token could be the separator token itself.
807 if let (Some(sep
), true) = (&seq_rep
.separator
, subfirst
.maybe_empty
) {
808 first
.add_one_maybe(TtHandle
::from_token(sep
.clone()));
811 assert
!(first
.maybe_empty
);
812 first
.add_all(subfirst
);
813 if subfirst
.maybe_empty
814 || seq_rep
.kleene
.op
== mbe
::KleeneOp
::ZeroOrMore
815 || seq_rep
.kleene
.op
== mbe
::KleeneOp
::ZeroOrOne
817 // Continue scanning for more first
818 // tokens, but also make sure we
819 // restore empty-tracking state.
820 first
.maybe_empty
= true;
829 // we only exit the loop if `tts` was empty or if every
830 // element of `tts` matches the empty sequence.
831 assert
!(first
.maybe_empty
);
836 // Most `mbe::TokenTree`s are pre-existing in the matcher, but some are defined
837 // implicitly, such as opening/closing delimiters and sequence repetition ops.
838 // This type encapsulates both kinds. It implements `Clone` while avoiding the
839 // need for `mbe::TokenTree` to implement `Clone`.
842 /// This is used in most cases.
843 TtRef(&'tt mbe
::TokenTree
),
845 /// This is only used for implicit token trees. The `mbe::TokenTree` *must*
846 /// be `mbe::TokenTree::Token`. No other variants are allowed. We store an
847 /// `mbe::TokenTree` rather than a `Token` so that `get()` can return a
848 /// `&mbe::TokenTree`.
849 Token(mbe
::TokenTree
),
852 impl<'tt
> TtHandle
<'tt
> {
853 fn from_token(tok
: Token
) -> Self {
854 TtHandle
::Token(mbe
::TokenTree
::Token(tok
))
857 fn from_token_kind(kind
: TokenKind
, span
: Span
) -> Self {
858 TtHandle
::from_token(Token
::new(kind
, span
))
861 // Get a reference to a token tree.
862 fn get(&'tt
self) -> &'tt mbe
::TokenTree
{
864 TtHandle
::TtRef(tt
) => tt
,
865 TtHandle
::Token(token_tt
) => &token_tt
,
870 impl<'tt
> PartialEq
for TtHandle
<'tt
> {
871 fn eq(&self, other
: &TtHandle
<'tt
>) -> bool
{
872 self.get() == other
.get()
876 impl<'tt
> Clone
for TtHandle
<'tt
> {
877 fn clone(&self) -> Self {
879 TtHandle
::TtRef(tt
) => TtHandle
::TtRef(tt
),
881 // This variant *must* contain a `mbe::TokenTree::Token`, and not
882 // any other variant of `mbe::TokenTree`.
883 TtHandle
::Token(mbe
::TokenTree
::Token(tok
)) => {
884 TtHandle
::Token(mbe
::TokenTree
::Token(tok
.clone()))
892 // A set of `mbe::TokenTree`s, which may include `TokenTree::Match`s
893 // (for macro-by-example syntactic variables). It also carries the
894 // `maybe_empty` flag; that is true if and only if the matcher can
895 // match an empty token sequence.
897 // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`,
898 // which has corresponding FIRST = {$a:expr, c, d}.
899 // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}.
901 // (Notably, we must allow for *-op to occur zero times.)
902 #[derive(Clone, Debug)]
903 struct TokenSet
<'tt
> {
904 tokens
: Vec
<TtHandle
<'tt
>>,
908 impl<'tt
> TokenSet
<'tt
> {
909 // Returns a set for the empty sequence.
911 TokenSet { tokens: Vec::new(), maybe_empty: true }
914 // Returns the set `{ tok }` for the single-token (and thus
915 // non-empty) sequence [tok].
916 fn singleton(tt
: TtHandle
<'tt
>) -> Self {
917 TokenSet { tokens: vec![tt], maybe_empty: false }
920 // Changes self to be the set `{ tok }`.
921 // Since `tok` is always present, marks self as non-empty.
922 fn replace_with(&mut self, tt
: TtHandle
<'tt
>) {
924 self.tokens
.push(tt
);
925 self.maybe_empty
= false;
928 // Changes self to be the empty set `{}`; meant for use when
929 // the particular token does not matter, but we want to
930 // record that it occurs.
931 fn replace_with_irrelevant(&mut self) {
933 self.maybe_empty
= false;
936 // Adds `tok` to the set for `self`, marking sequence as non-empty.
937 fn add_one(&mut self, tt
: TtHandle
<'tt
>) {
938 if !self.tokens
.contains(&tt
) {
939 self.tokens
.push(tt
);
941 self.maybe_empty
= false;
944 // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.)
945 fn add_one_maybe(&mut self, tt
: TtHandle
<'tt
>) {
946 if !self.tokens
.contains(&tt
) {
947 self.tokens
.push(tt
);
951 // Adds all elements of `other` to this.
953 // (Since this is a set, we filter out duplicates.)
955 // If `other` is potentially empty, then preserves the previous
956 // setting of the empty flag of `self`. If `other` is guaranteed
957 // non-empty, then `self` is marked non-empty.
958 fn add_all(&mut self, other
: &Self) {
959 for tt
in &other
.tokens
{
960 if !self.tokens
.contains(tt
) {
961 self.tokens
.push(tt
.clone());
964 if !other
.maybe_empty
{
965 self.maybe_empty
= false;
970 // Checks that `matcher` is internally consistent and that it
971 // can legally be followed by a token `N`, for all `N` in `follow`.
972 // (If `follow` is empty, then it imposes no constraint on
975 // Returns the set of NT tokens that could possibly come last in
976 // `matcher`. (If `matcher` matches the empty sequence, then
977 // `maybe_empty` will be set to true.)
979 // Requires that `first_sets` is pre-computed for `matcher`;
980 // see `FirstSets::new`.
981 fn check_matcher_core
<'tt
>(
984 first_sets
: &FirstSets
<'tt
>,
985 matcher
: &'tt
[mbe
::TokenTree
],
986 follow
: &TokenSet
<'tt
>,
990 let mut last
= TokenSet
::empty();
992 // 2. For each token and suffix [T, SUFFIX] in M:
993 // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty,
994 // then ensure T can also be followed by any element of FOLLOW.
995 'each_token
: for i
in 0..matcher
.len() {
996 let token
= &matcher
[i
];
997 let suffix
= &matcher
[i
+ 1..];
999 let build_suffix_first
= || {
1000 let mut s
= first_sets
.first(suffix
);
1007 // (we build `suffix_first` on demand below; you can tell
1008 // which cases are supposed to fall through by looking for the
1009 // initialization of this variable.)
1012 // First, update `last` so that it corresponds to the set
1013 // of NT tokens that might end the sequence `... token`.
1015 TokenTree
::Token(..)
1016 | TokenTree
::MetaVar(..)
1017 | TokenTree
::MetaVarDecl(..)
1018 | TokenTree
::MetaVarExpr(..) => {
1019 if token_can_be_followed_by_any(token
) {
1020 // don't need to track tokens that work with any,
1021 last
.replace_with_irrelevant();
1022 // ... and don't need to check tokens that can be
1023 // followed by anything against SUFFIX.
1024 continue 'each_token
;
1026 last
.replace_with(TtHandle
::TtRef(token
));
1027 suffix_first
= build_suffix_first();
1030 TokenTree
::Delimited(span
, ref d
) => {
1031 let my_suffix
= TokenSet
::singleton(TtHandle
::from_token_kind(
1032 token
::CloseDelim(d
.delim
),
1035 check_matcher_core(sess
, def
, first_sets
, &d
.tts
, &my_suffix
);
1036 // don't track non NT tokens
1037 last
.replace_with_irrelevant();
1039 // also, we don't need to check delimited sequences
1041 continue 'each_token
;
1043 TokenTree
::Sequence(_
, ref seq_rep
) => {
1044 suffix_first
= build_suffix_first();
1045 // The trick here: when we check the interior, we want
1046 // to include the separator (if any) as a potential
1047 // (but not guaranteed) element of FOLLOW. So in that
1048 // case, we make a temp copy of suffix and stuff
1049 // delimiter in there.
1051 // FIXME: Should I first scan suffix_first to see if
1052 // delimiter is already in it before I go through the
1053 // work of cloning it? But then again, this way I may
1054 // get a "tighter" span?
1056 let my_suffix
= if let Some(sep
) = &seq_rep
.separator
{
1057 new
= suffix_first
.clone();
1058 new
.add_one_maybe(TtHandle
::from_token(sep
.clone()));
1064 // At this point, `suffix_first` is built, and
1065 // `my_suffix` is some TokenSet that we can use
1066 // for checking the interior of `seq_rep`.
1067 let next
= check_matcher_core(sess
, def
, first_sets
, &seq_rep
.tts
, my_suffix
);
1068 if next
.maybe_empty
{
1069 last
.add_all(&next
);
1074 // the recursive call to check_matcher_core already ran the 'each_last
1075 // check below, so we can just keep going forward here.
1076 continue 'each_token
;
1080 // (`suffix_first` guaranteed initialized once reaching here.)
1082 // Now `last` holds the complete set of NT tokens that could
1083 // end the sequence before SUFFIX. Check that every one works with `suffix`.
1084 for tt
in &last
.tokens
{
1085 if let &TokenTree
::MetaVarDecl(span
, name
, Some(kind
)) = tt
.get() {
1086 for next_token
in &suffix_first
.tokens
{
1087 let next_token
= next_token
.get();
1089 // Check if the old pat is used and the next token is `|`
1090 // to warn about incompatibility with Rust 2021.
1091 // We only emit this lint if we're parsing the original
1092 // definition of this macro_rules, not while (re)parsing
1093 // the macro when compiling another crate that is using the
1094 // macro. (See #86567.)
1095 // Macros defined in the current crate have a real node id,
1096 // whereas macros from an external crate have a dummy id.
1097 if def
.id
!= DUMMY_NODE_ID
1098 && matches
!(kind
, NonterminalKind
::PatParam { inferred: true }
)
1099 && matches
!(next_token
, TokenTree
::Token(token
) if token
.kind
== BinOp(token
::BinOpToken
::Or
))
1101 // It is suggestion to use pat_param, for example: $x:pat -> $x:pat_param.
1102 let suggestion
= quoted_tt_to_string(&TokenTree
::MetaVarDecl(
1105 Some(NonterminalKind
::PatParam { inferred: false }
),
1107 sess
.buffer_lint_with_diagnostic(
1108 &RUST_2021_INCOMPATIBLE_OR_PATTERNS
,
1111 "the meaning of the `pat` fragment specifier is changing in Rust 2021, which may affect this macro",
1112 BuiltinLintDiagnostics
::OrPatternsBackCompat(span
, suggestion
),
1115 match is_in_follow(next_token
, kind
) {
1116 IsInFollow
::Yes
=> {}
1117 IsInFollow
::No(possible
) => {
1118 let may_be
= if last
.tokens
.len() == 1 && suffix_first
.tokens
.len() == 1
1125 let sp
= next_token
.span();
1126 let mut err
= sess
.span_diagnostic
.struct_span_err(
1129 "`${name}:{frag}` {may_be} followed by `{next}`, which \
1130 is not allowed for `{frag}` fragments",
1133 next
= quoted_tt_to_string(next_token
),
1137 err
.span_label(sp
, format
!("not allowed after `{}` fragments", kind
));
1139 if kind
== NonterminalKind
::PatWithOr
1140 && sess
.edition
.rust_2021()
1141 && next_token
.is_token(&BinOp(token
::BinOpToken
::Or
))
1143 let suggestion
= quoted_tt_to_string(&TokenTree
::MetaVarDecl(
1146 Some(NonterminalKind
::PatParam { inferred: false }
),
1148 err
.span_suggestion(
1150 "try a `pat_param` fragment specifier instead",
1152 Applicability
::MaybeIncorrect
,
1156 let msg
= "allowed there are: ";
1161 "only {} is allowed after `{}` fragments",
1172 .collect
::<Vec
<_
>>()
1188 fn token_can_be_followed_by_any(tok
: &mbe
::TokenTree
) -> bool
{
1189 if let mbe
::TokenTree
::MetaVarDecl(_
, _
, Some(kind
)) = *tok
{
1190 frag_can_be_followed_by_any(kind
)
1192 // (Non NT's can always be followed by anything in matchers.)
1197 /// Returns `true` if a fragment of type `frag` can be followed by any sort of
1198 /// token. We use this (among other things) as a useful approximation
1199 /// for when `frag` can be followed by a repetition like `$(...)*` or
1200 /// `$(...)+`. In general, these can be a bit tricky to reason about,
1201 /// so we adopt a conservative position that says that any fragment
1202 /// specifier which consumes at most one token tree can be followed by
1203 /// a fragment specifier (indeed, these fragments can be followed by
1204 /// ANYTHING without fear of future compatibility hazards).
1205 fn frag_can_be_followed_by_any(kind
: NonterminalKind
) -> bool
{
1208 NonterminalKind
::Item
// always terminated by `}` or `;`
1209 | NonterminalKind
::Block
// exactly one token tree
1210 | NonterminalKind
::Ident
// exactly one token tree
1211 | NonterminalKind
::Literal
// exactly one token tree
1212 | NonterminalKind
::Meta
// exactly one token tree
1213 | NonterminalKind
::Lifetime
// exactly one token tree
1214 | NonterminalKind
::TT
// exactly one token tree
1220 No(&'
static [&'
static str]),
1223 /// Returns `true` if `frag` can legally be followed by the token `tok`. For
1224 /// fragments that can consume an unbounded number of tokens, `tok`
1225 /// must be within a well-defined follow set. This is intended to
1226 /// guarantee future compatibility: for example, without this rule, if
1227 /// we expanded `expr` to include a new binary operator, we might
1228 /// break macros that were relying on that binary operator as a
1230 // when changing this do not forget to update doc/book/macros.md!
1231 fn is_in_follow(tok
: &mbe
::TokenTree
, kind
: NonterminalKind
) -> IsInFollow
{
1234 if let TokenTree
::Token(Token { kind: token::CloseDelim(_), .. }
) = *tok
{
1235 // closing a token tree can never be matched by any fragment;
1236 // iow, we always require that `(` and `)` match, etc.
1240 NonterminalKind
::Item
=> {
1241 // since items *must* be followed by either a `;` or a `}`, we can
1242 // accept anything after them
1245 NonterminalKind
::Block
=> {
1246 // anything can follow block, the braces provide an easy boundary to
1250 NonterminalKind
::Stmt
| NonterminalKind
::Expr
=> {
1251 const TOKENS
: &[&str] = &["`=>`", "`,`", "`;`"];
1253 TokenTree
::Token(token
) => match token
.kind
{
1254 FatArrow
| Comma
| Semi
=> IsInFollow
::Yes
,
1255 _
=> IsInFollow
::No(TOKENS
),
1257 _
=> IsInFollow
::No(TOKENS
),
1260 NonterminalKind
::PatParam { .. }
=> {
1261 const TOKENS
: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
1263 TokenTree
::Token(token
) => match token
.kind
{
1264 FatArrow
| Comma
| Eq
| BinOp(token
::Or
) => IsInFollow
::Yes
,
1265 Ident(name
, false) if name
== kw
::If
|| name
== kw
::In
=> IsInFollow
::Yes
,
1266 _
=> IsInFollow
::No(TOKENS
),
1268 _
=> IsInFollow
::No(TOKENS
),
1271 NonterminalKind
::PatWithOr { .. }
=> {
1272 const TOKENS
: &[&str] = &["`=>`", "`,`", "`=`", "`if`", "`in`"];
1274 TokenTree
::Token(token
) => match token
.kind
{
1275 FatArrow
| Comma
| Eq
=> IsInFollow
::Yes
,
1276 Ident(name
, false) if name
== kw
::If
|| name
== kw
::In
=> IsInFollow
::Yes
,
1277 _
=> IsInFollow
::No(TOKENS
),
1279 _
=> IsInFollow
::No(TOKENS
),
1282 NonterminalKind
::Path
| NonterminalKind
::Ty
=> {
1283 const TOKENS
: &[&str] = &[
1284 "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
1288 TokenTree
::Token(token
) => match token
.kind
{
1289 OpenDelim(Delimiter
::Brace
)
1290 | OpenDelim(Delimiter
::Bracket
)
1298 | BinOp(token
::Or
) => IsInFollow
::Yes
,
1299 Ident(name
, false) if name
== kw
::As
|| name
== kw
::Where
=> {
1302 _
=> IsInFollow
::No(TOKENS
),
1304 TokenTree
::MetaVarDecl(_
, _
, Some(NonterminalKind
::Block
)) => IsInFollow
::Yes
,
1305 _
=> IsInFollow
::No(TOKENS
),
1308 NonterminalKind
::Ident
| NonterminalKind
::Lifetime
=> {
1309 // being a single token, idents and lifetimes are harmless
1312 NonterminalKind
::Literal
=> {
1313 // literals may be of a single token, or two tokens (negative numbers)
1316 NonterminalKind
::Meta
| NonterminalKind
::TT
=> {
1317 // being either a single token or a delimited sequence, tt is
1321 NonterminalKind
::Vis
=> {
1322 // Explicitly disallow `priv`, on the off chance it comes back.
1323 const TOKENS
: &[&str] = &["`,`", "an ident", "a type"];
1325 TokenTree
::Token(token
) => match token
.kind
{
1326 Comma
=> IsInFollow
::Yes
,
1327 Ident(name
, is_raw
) if is_raw
|| name
!= kw
::Priv
=> IsInFollow
::Yes
,
1329 if token
.can_begin_type() {
1332 IsInFollow
::No(TOKENS
)
1336 TokenTree
::MetaVarDecl(
1339 Some(NonterminalKind
::Ident
| NonterminalKind
::Ty
| NonterminalKind
::Path
),
1340 ) => IsInFollow
::Yes
,
1341 _
=> IsInFollow
::No(TOKENS
),
1348 fn quoted_tt_to_string(tt
: &mbe
::TokenTree
) -> String
{
1350 mbe
::TokenTree
::Token(ref token
) => pprust
::token_to_string(&token
).into(),
1351 mbe
::TokenTree
::MetaVar(_
, name
) => format
!("${}", name
),
1352 mbe
::TokenTree
::MetaVarDecl(_
, name
, Some(kind
)) => format
!("${}:{}", name
, kind
),
1353 mbe
::TokenTree
::MetaVarDecl(_
, name
, None
) => format
!("${}:", name
),
1356 "unexpected mbe::TokenTree::{Sequence or Delimited} \
1357 in follow set checker"
1362 pub(super) fn parser_from_cx(sess
: &ParseSess
, tts
: TokenStream
, recovery
: Recovery
) -> Parser
<'_
> {
1363 Parser
::new(sess
, tts
, true, rustc_parse
::MACRO_ARGUMENTS
).recovery(recovery
)