1 use super::{Parser, PathStyle};
2 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
3 use rustc_ast::ast::{self, AttrVec, Attribute, FieldPat, MacCall, Pat, PatKind, RangeEnd};
4 use rustc_ast::ast::{BindingMode, Expr, ExprKind, Ident, Mutability, Path, QSelf, RangeSyntax};
5 use rustc_ast::mut_visit::{noop_visit_mac, noop_visit_pat, MutVisitor};
8 use rustc_ast_pretty::pprust;
9 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, PResult};
10 use rustc_span::source_map::{respan, Span, Spanned};
11 use rustc_span::symbol::{kw, sym};
13 type Expected = Option<&'static str>;
15 /// `Expected` for function and lambda parameter patterns.
16 pub(super) const PARAM_EXPECTED: Expected = Some("parameter name");
18 const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here";
20 /// Whether or not an or-pattern should be gated when occurring in the current context.
22 pub(super) enum GateOr {
27 /// Whether or not to recover a `,` when parsing or-patterns.
28 #[derive(PartialEq, Copy, Clone)]
37 /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
38 /// at the top level. Used when parsing the parameters of lambda expressions,
39 /// functions, function pointers, and `pat` macro fragments.
40 pub fn parse_pat(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
41 self.parse_pat_with_range_pat(true, expected)
44 /// Entry point to the main pattern parser.
45 /// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
46 pub(super) fn parse_top_pat(&mut self, gate_or: GateOr) -> PResult<'a, P<Pat>> {
47 // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
48 let gated_leading_vert = self.eat_or_separator(None) && gate_or == GateOr::Yes;
49 let leading_vert_span = self.prev_token.span;
51 // Parse the possibly-or-pattern.
52 let pat = self.parse_pat_with_or(None, gate_or, RecoverComma::Yes)?;
54 // If we parsed a leading `|` which should be gated,
55 // and no other gated or-pattern has been parsed thus far,
56 // then we should really gate the leading `|`.
57 // This complicated procedure is done purely for diagnostics UX.
58 if gated_leading_vert && self.sess.gated_spans.is_ungated(sym::or_patterns) {
59 self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
65 /// Parse the pattern for a function or function pointer parameter.
66 /// Special recovery is provided for or-patterns and leading `|`.
67 pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
68 self.recover_leading_vert(None, "not allowed in a parameter pattern");
69 let pat = self.parse_pat_with_or(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
71 if let PatKind::Or(..) = &pat.kind {
72 self.ban_illegal_fn_param_or_pat(&pat);
78 /// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
79 fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
80 let msg = "wrap the pattern in parenthesis";
81 let fix = format!("({})", pprust::pat_to_string(pat));
82 self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parenthesis")
83 .span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
87 /// Parses a pattern, that may be a or-pattern (e.g. `Foo | Bar` in `Some(Foo | Bar)`).
88 /// Corresponds to `pat<allow_top_alt>` in RFC 2535.
94 ) -> PResult<'a, P<Pat>> {
95 // Parse the first pattern (`p_0`).
96 let first_pat = self.parse_pat(expected)?;
97 self.maybe_recover_unexpected_comma(first_pat.span, rc)?;
99 // If the next token is not a `|`,
100 // this is not an or-pattern and we should exit here.
101 if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
102 return Ok(first_pat);
105 // Parse the patterns `p_1 | ... | p_n` where `n > 0`.
106 let lo = first_pat.span;
107 let mut pats = vec![first_pat];
108 while self.eat_or_separator(Some(lo)) {
109 let pat = self.parse_pat(expected).map_err(|mut err| {
110 err.span_label(lo, WHILE_PARSING_OR_MSG);
113 self.maybe_recover_unexpected_comma(pat.span, rc)?;
116 let or_pattern_span = lo.to(self.prev_token.span);
118 // Feature gate the or-pattern if instructed:
119 if gate_or == GateOr::Yes {
120 self.sess.gated_spans.gate(sym::or_patterns, or_pattern_span);
123 Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
126 /// Eat the or-pattern `|` separator.
127 /// If instead a `||` token is encountered, recover and pretend we parsed `|`.
128 fn eat_or_separator(&mut self, lo: Option<Span>) -> bool {
129 if self.recover_trailing_vert(lo) {
133 match self.token.kind {
135 // Found `||`; Recover and pretend we parsed `|`.
136 self.ban_unexpected_or_or(lo);
140 _ => self.eat(&token::BinOp(token::Or)),
144 /// Recover if `|` or `||` is the current token and we have one of the
145 /// tokens `=>`, `if`, `=`, `:`, `;`, `,`, `]`, `)`, or `}` ahead of us.
147 /// These tokens all indicate that we reached the end of the or-pattern
148 /// list and can now reliably say that the `|` was an illegal trailing vert.
149 /// Note that there are more tokens such as `@` for which we know that the `|`
150 /// is an illegal parse. However, the user's intent is less clear in that case.
151 fn recover_trailing_vert(&mut self, lo: Option<Span>) -> bool {
152 let is_end_ahead = self.look_ahead(1, |token| match &token.uninterpolate().kind {
153 token::FatArrow // e.g. `a | => 0,`.
154 | token::Ident(kw::If, false) // e.g. `a | if expr`.
155 | token::Eq // e.g. `let a | = 0`.
156 | token::Semi // e.g. `let a |;`.
157 | token::Colon // e.g. `let a | :`.
158 | token::Comma // e.g. `let (a |,)`.
159 | token::CloseDelim(token::Bracket) // e.g. `let [a | ]`.
160 | token::CloseDelim(token::Paren) // e.g. `let (a | )`.
161 | token::CloseDelim(token::Brace) => true, // e.g. `let A { f: a | }`.
164 match (is_end_ahead, &self.token.kind) {
165 (true, token::BinOp(token::Or)) | (true, token::OrOr) => {
166 self.ban_illegal_vert(lo, "trailing", "not allowed in an or-pattern");
174 /// We have parsed `||` instead of `|`. Error and suggest `|` instead.
175 fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
176 let mut err = self.struct_span_err(self.token.span, "unexpected token `||` after pattern");
179 "use a single `|` to separate multiple alternative patterns",
181 Applicability::MachineApplicable,
183 if let Some(lo) = lo {
184 err.span_label(lo, WHILE_PARSING_OR_MSG);
189 /// Some special error handling for the "top-level" patterns in a match arm,
190 /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
191 fn maybe_recover_unexpected_comma(&mut self, lo: Span, rc: RecoverComma) -> PResult<'a, ()> {
192 if rc == RecoverComma::No || self.token != token::Comma {
196 // An unexpected comma after a top-level pattern is a clue that the
197 // user (perhaps more accustomed to some other language) forgot the
198 // parentheses in what should have been a tuple pattern; return a
199 // suggestion-enhanced error here rather than choking on the comma later.
200 let comma_span = self.token.span;
202 if let Err(mut err) = self.skip_pat_list() {
203 // We didn't expect this to work anyway; we just wanted to advance to the
204 // end of the comma-sequence so we know the span to suggest parenthesizing.
207 let seq_span = lo.to(self.prev_token.span);
208 let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
209 if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
212 "try adding parentheses to match on a tuple...",
213 format!("({})", seq_snippet),
214 Applicability::MachineApplicable,
218 "...or a vertical bar to match on multiple alternatives",
219 seq_snippet.replace(",", " |"),
220 Applicability::MachineApplicable,
226 /// Parse and throw away a parentesized comma separated
227 /// sequence of patterns until `)` is reached.
228 fn skip_pat_list(&mut self) -> PResult<'a, ()> {
229 while !self.check(&token::CloseDelim(token::Paren)) {
230 self.parse_pat(None)?;
231 if !self.eat(&token::Comma) {
238 /// Recursive possibly-or-pattern parser with recovery for an erroneous leading `|`.
239 /// See `parse_pat_with_or` for details on parsing or-patterns.
240 fn parse_pat_with_or_inner(&mut self) -> PResult<'a, P<Pat>> {
241 self.recover_leading_vert(None, "only allowed in a top-level pattern");
242 self.parse_pat_with_or(None, GateOr::Yes, RecoverComma::No)
245 /// Recover if `|` or `||` is here.
246 /// The user is thinking that a leading `|` is allowed in this position.
247 fn recover_leading_vert(&mut self, lo: Option<Span>, ctx: &str) {
248 if let token::BinOp(token::Or) | token::OrOr = self.token.kind {
249 self.ban_illegal_vert(lo, "leading", ctx);
254 /// A `|` or possibly `||` token shouldn't be here. Ban it.
255 fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
256 let span = self.token.span;
257 let mut err = self.struct_span_err(span, &format!("a {} `|` is {}", pos, ctx));
260 &format!("remove the `{}`", pprust::token_to_string(&self.token)),
262 Applicability::MachineApplicable,
264 if let Some(lo) = lo {
265 err.span_label(lo, WHILE_PARSING_OR_MSG);
267 if let token::OrOr = self.token.kind {
268 err.note("alternatives in or-patterns are separated with `|`, not `||`");
273 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
275 fn parse_pat_with_range_pat(
277 allow_range_pat: bool,
279 ) -> PResult<'a, P<Pat>> {
280 maybe_recover_from_interpolated_ty_qpath!(self, true);
281 maybe_whole!(self, NtPat, |x| x);
283 let lo = self.token.span;
285 let pat = if self.check(&token::BinOp(token::And)) || self.token.kind == token::AndAnd {
286 self.parse_pat_deref(expected)?
287 } else if self.check(&token::OpenDelim(token::Paren)) {
288 self.parse_pat_tuple_or_parens()?
289 } else if self.check(&token::OpenDelim(token::Bracket)) {
290 // Parse `[pat, pat,...]` as a slice pattern.
292 self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat_with_or_inner())?;
294 } else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
295 // A rest pattern `..`.
298 } else if let Some(form) = self.parse_range_end() {
299 self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
300 } else if self.eat_keyword(kw::Underscore) {
303 } else if self.eat_keyword(kw::Mut) {
304 self.parse_pat_ident_mut()?
305 } else if self.eat_keyword(kw::Ref) {
306 // Parse ref ident @ pat / ref mut ident @ pat
307 let mutbl = self.parse_mutability();
308 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
309 } else if self.eat_keyword(kw::Box) {
311 let pat = self.parse_pat_with_range_pat(false, None)?;
312 self.sess.gated_spans.gate(sym::box_patterns, lo.to(self.prev_token.span));
314 } else if self.can_be_ident_pat() {
315 // Parse `ident @ pat`
316 // This can give false positives and parse nullary enums,
317 // they are dealt with later in resolve.
318 self.parse_pat_ident(BindingMode::ByValue(Mutability::Not))?
319 } else if self.is_start_of_pat_with_path() {
320 // Parse pattern starting with a path
321 let (qself, path) = if self.eat_lt() {
322 // Parse a qualified path
323 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
326 // Parse an unqualified path
327 (None, self.parse_path(PathStyle::Expr)?)
329 let span = lo.to(self.prev_token.span);
331 if qself.is_none() && self.check(&token::Not) {
332 self.parse_pat_mac_invoc(path)?
333 } else if let Some(form) = self.parse_range_end() {
334 let begin = self.mk_expr(span, ExprKind::Path(qself, path), AttrVec::new());
335 self.parse_pat_range_begin_with(begin, form)?
336 } else if self.check(&token::OpenDelim(token::Brace)) {
337 self.parse_pat_struct(qself, path)?
338 } else if self.check(&token::OpenDelim(token::Paren)) {
339 self.parse_pat_tuple_struct(qself, path)?
341 PatKind::Path(qself, path)
344 // Try to parse everything else as literal with optional minus
345 match self.parse_literal_maybe_minus() {
346 Ok(begin) => match self.parse_range_end() {
347 Some(form) => self.parse_pat_range_begin_with(begin, form)?,
348 None => PatKind::Lit(begin),
350 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
354 let pat = self.mk_pat(lo.to(self.prev_token.span), pat);
355 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
356 let pat = self.recover_intersection_pat(pat)?;
358 if !allow_range_pat {
359 self.ban_pat_range_if_ambiguous(&pat)
365 /// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
367 /// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
368 /// should already have been parsed by now at this point,
369 /// if the next token is `@` then we can try to parse the more general form.
371 /// Consult `parse_pat_ident` for the `binding` grammar.
373 /// The notion of intersection patterns are found in
374 /// e.g. [F#][and] where they are called AND-patterns.
376 /// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
377 fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
378 if self.token.kind != token::At {
379 // Next token is not `@` so it's not going to be an intersection pattern.
383 // At this point we attempt to parse `@ $pat_rhs` and emit an error.
385 let mut rhs = self.parse_pat(None)?;
386 let sp = lhs.span.to(rhs.span);
388 if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
389 // The user inverted the order, so help them fix that.
390 let mut applicability = Applicability::MachineApplicable;
391 // FIXME(bindings_after_at): Remove this code when stabilizing the feature.
392 lhs.walk(&mut |p| match p.kind {
393 // `check_match` is unhappy if the subpattern has a binding anywhere.
394 PatKind::Ident(..) => {
395 applicability = Applicability::MaybeIncorrect;
396 false // Short-circuit.
401 let lhs_span = lhs.span;
402 // Move the LHS into the RHS as a subpattern.
403 // The RHS is now the full pattern.
406 self.struct_span_err(sp, "pattern on wrong side of `@`")
407 .span_label(lhs_span, "pattern on the left, should be on the right")
408 .span_label(rhs.span, "binding on the right, should be on the left")
409 .span_suggestion(sp, "switch the order", pprust::pat_to_string(&rhs), applicability)
412 // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
413 rhs.kind = PatKind::Wild;
414 self.struct_span_err(sp, "left-hand side of `@` must be a binding")
415 .span_label(lhs.span, "interpreted as a pattern, not a binding")
416 .span_label(rhs.span, "also a pattern")
417 .note("bindings are `x`, `mut x`, `ref x`, and `ref mut x`")
425 /// Ban a range pattern if it has an ambiguous interpretation.
426 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) {
430 Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. },
432 PatKind::Range(..) => {}
436 self.struct_span_err(pat.span, "the range pattern here has ambiguous interpretation")
439 "add parentheses to clarify the precedence",
440 format!("({})", pprust::pat_to_string(&pat)),
441 // "ambiguous interpretation" implies that we have to be guessing
442 Applicability::MaybeIncorrect,
447 /// Parse `&pat` / `&mut pat`.
448 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
450 self.recover_lifetime_in_deref_pat();
451 let mutbl = self.parse_mutability();
452 let subpat = self.parse_pat_with_range_pat(false, expected)?;
453 Ok(PatKind::Ref(subpat, mutbl))
456 fn recover_lifetime_in_deref_pat(&mut self) {
457 if let token::Lifetime(name) = self.token.kind {
460 let span = self.prev_token.span;
461 self.struct_span_err(span, &format!("unexpected lifetime `{}` in pattern", name))
464 "remove the lifetime",
466 Applicability::MachineApplicable,
472 /// Parse a tuple or parenthesis pattern.
473 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
474 let (fields, trailing_comma) =
475 self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
477 // Here, `(pat,)` is a tuple pattern.
478 // For backward compatibility, `(..)` is a tuple pattern as well.
479 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
480 PatKind::Paren(fields.into_iter().next().unwrap())
482 PatKind::Tuple(fields)
486 /// Parse a mutable binding with the `mut` token already eaten.
487 fn parse_pat_ident_mut(&mut self) -> PResult<'a, PatKind> {
488 let mut_span = self.prev_token.span;
490 if self.eat_keyword(kw::Ref) {
491 return self.recover_mut_ref_ident(mut_span);
494 self.recover_additional_muts();
496 // Make sure we don't allow e.g. `let mut $p;` where `$p:pat`.
497 if let token::Interpolated(ref nt) = self.token.kind {
498 if let token::NtPat(_) = **nt {
499 self.expected_ident_found().emit();
503 // Parse the pattern we hope to be an identifier.
504 let mut pat = self.parse_pat(Some("identifier"))?;
506 // If we don't have `mut $ident (@ pat)?`, error.
507 if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind {
508 // Don't recurse into the subpattern.
509 // `mut` on the outer binding doesn't affect the inner bindings.
510 *m = Mutability::Mut;
512 // Add `mut` to any binding in the parsed pattern.
513 let changed_any_binding = Self::make_all_value_bindings_mutable(&mut pat);
514 self.ban_mut_general_pat(mut_span, &pat, changed_any_binding);
517 Ok(pat.into_inner().kind)
520 /// Recover on `mut ref? ident @ pat` and suggest
521 /// that the order of `mut` and `ref` is incorrect.
522 fn recover_mut_ref_ident(&mut self, lo: Span) -> PResult<'a, PatKind> {
523 let mutref_span = lo.to(self.prev_token.span);
524 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
527 "try switching the order",
529 Applicability::MachineApplicable,
533 self.parse_pat_ident(BindingMode::ByRef(Mutability::Mut))
536 /// Turn all by-value immutable bindings in a pattern into mutable bindings.
537 /// Returns `true` if any change was made.
538 fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
540 impl MutVisitor for AddMut {
541 fn visit_mac(&mut self, mac: &mut MacCall) {
542 noop_visit_mac(mac, self);
545 fn visit_pat(&mut self, pat: &mut P<Pat>) {
546 if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind
549 *m = Mutability::Mut;
551 noop_visit_pat(pat, self);
555 let mut add_mut = AddMut(false);
556 add_mut.visit_pat(pat);
560 /// Error on `mut $pat` where `$pat` is not an ident.
561 fn ban_mut_general_pat(&self, lo: Span, pat: &Pat, changed_any_binding: bool) {
562 let span = lo.to(pat.span);
563 let fix = pprust::pat_to_string(&pat);
564 let (problem, suggestion) = if changed_any_binding {
565 ("`mut` must be attached to each individual binding", "add `mut` to each binding")
567 ("`mut` must be followed by a named binding", "remove the `mut` prefix")
569 self.struct_span_err(span, problem)
570 .span_suggestion(span, suggestion, fix, Applicability::MachineApplicable)
571 .note("`mut` may be followed by `variable` and `variable @ pattern`")
575 /// Eat any extraneous `mut`s and error + recover if we ate any.
576 fn recover_additional_muts(&mut self) {
577 let lo = self.token.span;
578 while self.eat_keyword(kw::Mut) {}
579 if lo == self.token.span {
583 let span = lo.to(self.prev_token.span);
584 self.struct_span_err(span, "`mut` on a binding may not be repeated")
587 "remove the additional `mut`s",
589 Applicability::MachineApplicable,
594 /// Parse macro invocation
595 fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
597 let args = self.parse_mac_args()?;
598 let mac = MacCall { path, args, prior_type_ascription: self.last_type_ascription };
599 Ok(PatKind::MacCall(mac))
602 fn fatal_unexpected_non_pat(
604 mut err: DiagnosticBuilder<'a>,
606 ) -> PResult<'a, P<Pat>> {
609 let expected = expected.unwrap_or("pattern");
610 let msg = format!("expected {}, found {}", expected, super::token_descr(&self.token));
612 let mut err = self.struct_span_err(self.token.span, &msg);
613 err.span_label(self.token.span, format!("expected {}", expected));
615 let sp = self.sess.source_map().start_point(self.token.span);
616 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
617 self.sess.expr_parentheses_needed(&mut err, *sp, None);
623 /// Parses the range pattern end form `".." | "..." | "..=" ;`.
624 fn parse_range_end(&mut self) -> Option<Spanned<RangeEnd>> {
625 let re = if self.eat(&token::DotDotDot) {
626 RangeEnd::Included(RangeSyntax::DotDotDot)
627 } else if self.eat(&token::DotDotEq) {
628 RangeEnd::Included(RangeSyntax::DotDotEq)
629 } else if self.eat(&token::DotDot) {
630 self.sess.gated_spans.gate(sym::exclusive_range_pattern, self.prev_token.span);
635 Some(respan(self.prev_token.span, re))
638 /// Parse a range pattern `$begin $form $end?` where `$form = ".." | "..." | "..=" ;`.
639 /// `$begin $form` has already been parsed.
640 fn parse_pat_range_begin_with(
643 re: Spanned<RangeEnd>,
644 ) -> PResult<'a, PatKind> {
645 let end = if self.is_pat_range_end_start(0) {
646 // Parsing e.g. `X..=Y`.
647 Some(self.parse_pat_range_end()?)
649 // Parsing e.g. `X..`.
650 self.sess.gated_spans.gate(sym::half_open_range_patterns, begin.span.to(re.span));
651 if let RangeEnd::Included(_) = re.node {
652 // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
653 // Possibly also do this for `X..=` in *expression* contexts.
654 self.error_inclusive_range_with_no_end(re.span);
658 Ok(PatKind::Range(Some(begin), end, re))
661 pub(super) fn error_inclusive_range_with_no_end(&self, span: Span) {
662 struct_span_err!(self.sess.span_diagnostic, span, E0586, "inclusive range with no end")
663 .span_suggestion_short(
667 Applicability::MachineApplicable,
669 .note("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
673 /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
675 /// The form `...X` is prohibited to reduce confusion with the potential
676 /// expression syntax `...expr` for splatting in expressions.
677 fn parse_pat_range_to(&mut self, mut re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
678 let end = self.parse_pat_range_end()?;
679 self.sess.gated_spans.gate(sym::half_open_range_patterns, re.span.to(self.prev_token.span));
680 if let RangeEnd::Included(ref mut syn @ RangeSyntax::DotDotDot) = &mut re.node {
681 *syn = RangeSyntax::DotDotEq;
682 self.struct_span_err(re.span, "range-to patterns with `...` are not allowed")
683 .span_suggestion_short(
687 Applicability::MachineApplicable,
691 Ok(PatKind::Range(None, Some(end), re))
694 /// Is the token `dist` away from the current suitable as the start of a range patterns end?
695 fn is_pat_range_end_start(&self, dist: usize) -> bool {
696 self.look_ahead(dist, |t| {
697 t.is_path_start() // e.g. `MY_CONST`;
698 || t.kind == token::Dot // e.g. `.5` for recovery;
699 || t.can_begin_literal_or_bool() // e.g. `42`.
704 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
705 if self.check_path() {
706 let lo = self.token.span;
707 let (qself, path) = if self.eat_lt() {
708 // Parse a qualified path
709 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
712 // Parse an unqualified path
713 (None, self.parse_path(PathStyle::Expr)?)
715 let hi = self.prev_token.span;
716 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), AttrVec::new()))
718 self.parse_literal_maybe_minus()
722 /// Is this the start of a pattern beginning with a path?
723 fn is_start_of_pat_with_path(&mut self) -> bool {
725 // Just for recovery (see `can_be_ident`).
726 || self.token.is_ident() && !self.token.is_bool_lit() && !self.token.is_keyword(kw::In)
729 /// Would `parse_pat_ident` be appropriate here?
730 fn can_be_ident_pat(&mut self) -> bool {
732 && !self.token.is_bool_lit() // Avoid `true` or `false` as a binding as it is a literal.
733 && !self.token.is_path_segment_keyword() // Avoid e.g. `Self` as it is a path.
734 // Avoid `in`. Due to recovery in the list parser this messes with `for ( $pat in $expr )`.
735 && !self.token.is_keyword(kw::In)
736 && self.look_ahead(1, |t| match t.kind { // Try to do something more complex?
737 token::OpenDelim(token::Paren) // A tuple struct pattern.
738 | token::OpenDelim(token::Brace) // A struct pattern.
739 | token::DotDotDot | token::DotDotEq | token::DotDot // A range pattern.
740 | token::ModSep // A tuple / struct variant pattern.
741 | token::Not => false, // A macro expanding to a pattern.
746 /// Parses `ident` or `ident @ pat`.
747 /// Used by the copy foo and ref foo patterns to give a good
748 /// error message when parsing mistakes like `ref foo(a, b)`.
749 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
750 let ident = self.parse_ident()?;
751 let sub = if self.eat(&token::At) {
752 Some(self.parse_pat(Some("binding pattern"))?)
757 // Just to be friendly, if they write something like `ref Some(i)`,
758 // we end up here with `(` as the current token.
759 // This shortly leads to a parse error. Note that if there is no explicit
760 // binding mode then we do not end up here, because the lookahead
761 // will direct us over to `parse_enum_variant()`.
762 if self.token == token::OpenDelim(token::Paren) {
764 .struct_span_err(self.prev_token.span, "expected identifier, found enum pattern"));
767 Ok(PatKind::Ident(binding_mode, ident, sub))
770 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
771 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
773 return self.error_qpath_before_pat(&path, "{");
776 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
782 Ok(PatKind::Struct(path, fields, etc))
785 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
786 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
788 return self.error_qpath_before_pat(&path, "(");
790 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
791 Ok(PatKind::TupleStruct(path, fields))
794 /// Error when there's a qualified path, e.g. `<Foo as Bar>::Baz`
795 /// as the path of e.g., a tuple or record struct pattern.
796 fn error_qpath_before_pat(&mut self, path: &Path, token: &str) -> PResult<'a, PatKind> {
797 let msg = &format!("unexpected `{}` after qualified path", token);
798 let mut err = self.struct_span_err(self.token.span, msg);
799 err.span_label(self.token.span, msg);
800 err.span_label(path.span, "the qualified path");
804 /// Parses the fields of a struct-like pattern.
805 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
806 let mut fields = Vec::new();
808 let mut ate_comma = true;
809 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
810 let mut etc_span = None;
812 while self.token != token::CloseDelim(token::Brace) {
813 let attrs = match self.parse_outer_attributes() {
816 if let Some(mut delayed) = delayed_err {
822 let lo = self.token.span;
824 // check that a comma comes after every field
826 let err = self.struct_span_err(self.prev_token.span, "expected `,`");
827 if let Some(mut delayed) = delayed_err {
834 if self.check(&token::DotDot) || self.token == token::DotDotDot {
836 let mut etc_sp = self.token.span;
838 self.recover_one_fewer_dotdot();
839 self.bump(); // `..` || `...`
841 if self.token == token::CloseDelim(token::Brace) {
842 etc_span = Some(etc_sp);
845 let token_str = super::token_descr(&self.token);
846 let msg = &format!("expected `}}`, found {}", token_str);
847 let mut err = self.struct_span_err(self.token.span, msg);
849 err.span_label(self.token.span, "expected `}`");
850 let mut comma_sp = None;
851 if self.token == token::Comma {
853 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
854 etc_sp = etc_sp.to(nw_span);
857 "`..` must be at the end and cannot have a trailing comma",
859 comma_sp = Some(self.token.span);
864 etc_span = Some(etc_sp.until(self.token.span));
865 if self.token == token::CloseDelim(token::Brace) {
866 // If the struct looks otherwise well formed, recover and continue.
867 if let Some(sp) = comma_sp {
868 err.span_suggestion_short(
872 Applicability::MachineApplicable,
877 } else if self.token.is_ident() && ate_comma {
878 // Accept fields coming after `..,`.
879 // This way we avoid "pattern missing fields" errors afterwards.
880 // We delay this error until the end in order to have a span for a
882 if let Some(mut delayed_err) = delayed_err {
886 delayed_err = Some(err);
889 if let Some(mut err) = delayed_err {
896 fields.push(match self.parse_pat_field(lo, attrs) {
899 if let Some(mut delayed_err) = delayed_err {
905 ate_comma = self.eat(&token::Comma);
908 if let Some(mut err) = delayed_err {
909 if let Some(etc_span) = etc_span {
910 err.multipart_suggestion(
911 "move the `..` to the end of the field list",
913 (etc_span, String::new()),
914 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
916 Applicability::MachineApplicable,
921 return Ok((fields, etc));
924 /// Recover on `...` as if it were `..` to avoid further errors.
925 /// See issue #46718.
926 fn recover_one_fewer_dotdot(&self) {
927 if self.token != token::DotDotDot {
931 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
934 "to omit remaining fields, use one fewer `.`",
936 Applicability::MachineApplicable,
941 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
942 // Check if a colon exists one ahead. This means we're parsing a fieldname.
944 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
945 // Parsing a pattern of the form `fieldname: pat`.
946 let fieldname = self.parse_field_name()?;
948 let pat = self.parse_pat_with_or_inner()?;
950 (pat, fieldname, false)
952 // Parsing a pattern of the form `(box) (ref) (mut) fieldname`.
953 let is_box = self.eat_keyword(kw::Box);
954 let boxed_span = self.token.span;
955 let is_ref = self.eat_keyword(kw::Ref);
956 let is_mut = self.eat_keyword(kw::Mut);
957 let fieldname = self.parse_ident()?;
958 hi = self.prev_token.span;
960 let bind_type = match (is_ref, is_mut) {
961 (true, true) => BindingMode::ByRef(Mutability::Mut),
962 (true, false) => BindingMode::ByRef(Mutability::Not),
963 (false, true) => BindingMode::ByValue(Mutability::Mut),
964 (false, false) => BindingMode::ByValue(Mutability::Not),
967 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
969 if is_box { self.mk_pat(lo.to(hi), PatKind::Box(fieldpat)) } else { fieldpat };
970 (subpat, fieldname, true)
978 id: ast::DUMMY_NODE_ID,
980 is_placeholder: false,
984 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
985 self.mk_pat(span, PatKind::Ident(bm, ident, None))
988 fn mk_pat(&self, span: Span, kind: PatKind) -> P<Pat> {
989 P(Pat { kind, span, id: ast::DUMMY_NODE_ID })