1 use super::{Parser, PathStyle};
2 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
4 self, AttrVec, Attribute, FieldPat, Mac, Pat, PatKind, RangeEnd, RangeSyntax,
6 use rustc_ast::ast::{BindingMode, Expr, ExprKind, Ident, Mutability, Path, QSelf};
7 use rustc_ast::mut_visit::{noop_visit_mac, noop_visit_pat, MutVisitor};
10 use rustc_ast_pretty::pprust;
11 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, PResult};
12 use rustc_span::source_map::{respan, Span, Spanned};
13 use rustc_span::symbol::{kw, sym};
15 type Expected = Option<&'static str>;
17 /// `Expected` for function and lambda parameter patterns.
18 pub(super) const PARAM_EXPECTED: Expected = Some("parameter name");
20 const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here";
22 /// Whether or not an or-pattern should be gated when occurring in the current context.
24 pub(super) enum GateOr {
29 /// Whether or not to recover a `,` when parsing or-patterns.
30 #[derive(PartialEq, Copy, Clone)]
39 /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
40 /// at the top level. Used when parsing the parameters of lambda expressions,
41 /// functions, function pointers, and `pat` macro fragments.
42 pub fn parse_pat(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
43 self.parse_pat_with_range_pat(true, expected)
46 /// Entry point to the main pattern parser.
47 /// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
48 pub(super) fn parse_top_pat(&mut self, gate_or: GateOr) -> PResult<'a, P<Pat>> {
49 // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
50 let gated_leading_vert = self.eat_or_separator(None) && gate_or == GateOr::Yes;
51 let leading_vert_span = self.prev_span;
53 // Parse the possibly-or-pattern.
54 let pat = self.parse_pat_with_or(None, gate_or, RecoverComma::Yes)?;
56 // If we parsed a leading `|` which should be gated,
57 // and no other gated or-pattern has been parsed thus far,
58 // then we should really gate the leading `|`.
59 // This complicated procedure is done purely for diagnostics UX.
60 if gated_leading_vert && self.sess.gated_spans.is_ungated(sym::or_patterns) {
61 self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
67 /// Parse the pattern for a function or function pointer parameter.
68 /// Special recovery is provided for or-patterns and leading `|`.
69 pub(super) fn parse_fn_param_pat(&mut self) -> PResult<'a, P<Pat>> {
70 self.recover_leading_vert(None, "not allowed in a parameter pattern");
71 let pat = self.parse_pat_with_or(PARAM_EXPECTED, GateOr::No, RecoverComma::No)?;
73 if let PatKind::Or(..) = &pat.kind {
74 self.ban_illegal_fn_param_or_pat(&pat);
80 /// Ban `A | B` immediately in a parameter pattern and suggest wrapping in parens.
81 fn ban_illegal_fn_param_or_pat(&self, pat: &Pat) {
82 let msg = "wrap the pattern in parenthesis";
83 let fix = format!("({})", pprust::pat_to_string(pat));
84 self.struct_span_err(pat.span, "an or-pattern parameter must be wrapped in parenthesis")
85 .span_suggestion(pat.span, msg, fix, Applicability::MachineApplicable)
89 /// Parses a pattern, that may be a or-pattern (e.g. `Foo | Bar` in `Some(Foo | Bar)`).
90 /// Corresponds to `pat<allow_top_alt>` in RFC 2535.
96 ) -> PResult<'a, P<Pat>> {
97 // Parse the first pattern (`p_0`).
98 let first_pat = self.parse_pat(expected)?;
99 self.maybe_recover_unexpected_comma(first_pat.span, rc)?;
101 // If the next token is not a `|`,
102 // this is not an or-pattern and we should exit here.
103 if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
104 return Ok(first_pat);
107 // Parse the patterns `p_1 | ... | p_n` where `n > 0`.
108 let lo = first_pat.span;
109 let mut pats = vec![first_pat];
110 while self.eat_or_separator(Some(lo)) {
111 let pat = self.parse_pat(expected).map_err(|mut err| {
112 err.span_label(lo, WHILE_PARSING_OR_MSG);
115 self.maybe_recover_unexpected_comma(pat.span, rc)?;
118 let or_pattern_span = lo.to(self.prev_span);
120 // Feature gate the or-pattern if instructed:
121 if gate_or == GateOr::Yes {
122 self.sess.gated_spans.gate(sym::or_patterns, or_pattern_span);
125 Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
128 /// Eat the or-pattern `|` separator.
129 /// If instead a `||` token is encountered, recover and pretend we parsed `|`.
130 fn eat_or_separator(&mut self, lo: Option<Span>) -> bool {
131 if self.recover_trailing_vert(lo) {
135 match self.token.kind {
137 // Found `||`; Recover and pretend we parsed `|`.
138 self.ban_unexpected_or_or(lo);
142 _ => self.eat(&token::BinOp(token::Or)),
146 /// Recover if `|` or `||` is the current token and we have one of the
147 /// tokens `=>`, `if`, `=`, `:`, `;`, `,`, `]`, `)`, or `}` ahead of us.
149 /// These tokens all indicate that we reached the end of the or-pattern
150 /// list and can now reliably say that the `|` was an illegal trailing vert.
151 /// Note that there are more tokens such as `@` for which we know that the `|`
152 /// is an illegal parse. However, the user's intent is less clear in that case.
153 fn recover_trailing_vert(&mut self, lo: Option<Span>) -> bool {
154 let is_end_ahead = self.look_ahead(1, |token| match &token.kind {
155 token::FatArrow // e.g. `a | => 0,`.
156 | token::Ident(kw::If, false) // e.g. `a | if expr`.
157 | token::Eq // e.g. `let a | = 0`.
158 | token::Semi // e.g. `let a |;`.
159 | token::Colon // e.g. `let a | :`.
160 | token::Comma // e.g. `let (a |,)`.
161 | token::CloseDelim(token::Bracket) // e.g. `let [a | ]`.
162 | token::CloseDelim(token::Paren) // e.g. `let (a | )`.
163 | token::CloseDelim(token::Brace) => true, // e.g. `let A { f: a | }`.
166 match (is_end_ahead, &self.token.kind) {
167 (true, token::BinOp(token::Or)) | (true, token::OrOr) => {
168 self.ban_illegal_vert(lo, "trailing", "not allowed in an or-pattern");
176 /// We have parsed `||` instead of `|`. Error and suggest `|` instead.
177 fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
178 let mut err = self.struct_span_err(self.token.span, "unexpected token `||` after pattern");
181 "use a single `|` to separate multiple alternative patterns",
183 Applicability::MachineApplicable,
185 if let Some(lo) = lo {
186 err.span_label(lo, WHILE_PARSING_OR_MSG);
191 /// Some special error handling for the "top-level" patterns in a match arm,
192 /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
193 fn maybe_recover_unexpected_comma(&mut self, lo: Span, rc: RecoverComma) -> PResult<'a, ()> {
194 if rc == RecoverComma::No || self.token != token::Comma {
198 // An unexpected comma after a top-level pattern is a clue that the
199 // user (perhaps more accustomed to some other language) forgot the
200 // parentheses in what should have been a tuple pattern; return a
201 // suggestion-enhanced error here rather than choking on the comma later.
202 let comma_span = self.token.span;
204 if let Err(mut err) = self.skip_pat_list() {
205 // We didn't expect this to work anyway; we just wanted to advance to the
206 // end of the comma-sequence so we know the span to suggest parenthesizing.
209 let seq_span = lo.to(self.prev_span);
210 let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
211 if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
214 "try adding parentheses to match on a tuple...",
215 format!("({})", seq_snippet),
216 Applicability::MachineApplicable,
220 "...or a vertical bar to match on multiple alternatives",
221 seq_snippet.replace(",", " |"),
222 Applicability::MachineApplicable,
228 /// Parse and throw away a parentesized comma separated
229 /// sequence of patterns until `)` is reached.
230 fn skip_pat_list(&mut self) -> PResult<'a, ()> {
231 while !self.check(&token::CloseDelim(token::Paren)) {
232 self.parse_pat(None)?;
233 if !self.eat(&token::Comma) {
240 /// Recursive possibly-or-pattern parser with recovery for an erroneous leading `|`.
241 /// See `parse_pat_with_or` for details on parsing or-patterns.
242 fn parse_pat_with_or_inner(&mut self) -> PResult<'a, P<Pat>> {
243 self.recover_leading_vert(None, "only allowed in a top-level pattern");
244 self.parse_pat_with_or(None, GateOr::Yes, RecoverComma::No)
247 /// Recover if `|` or `||` is here.
248 /// The user is thinking that a leading `|` is allowed in this position.
249 fn recover_leading_vert(&mut self, lo: Option<Span>, ctx: &str) {
250 if let token::BinOp(token::Or) | token::OrOr = self.token.kind {
251 self.ban_illegal_vert(lo, "leading", ctx);
256 /// A `|` or possibly `||` token shouldn't be here. Ban it.
257 fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
258 let span = self.token.span;
259 let mut err = self.struct_span_err(span, &format!("a {} `|` is {}", pos, ctx));
262 &format!("remove the `{}`", pprust::token_to_string(&self.token)),
264 Applicability::MachineApplicable,
266 if let Some(lo) = lo {
267 err.span_label(lo, WHILE_PARSING_OR_MSG);
269 if let token::OrOr = self.token.kind {
270 err.note("alternatives in or-patterns are separated with `|`, not `||`");
275 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
277 fn parse_pat_with_range_pat(
279 allow_range_pat: bool,
281 ) -> PResult<'a, P<Pat>> {
282 maybe_recover_from_interpolated_ty_qpath!(self, true);
283 maybe_whole!(self, NtPat, |x| x);
285 let lo = self.token.span;
287 let pat = if self.check(&token::BinOp(token::And)) || self.token.kind == token::AndAnd {
288 self.parse_pat_deref(expected)?
289 } else if self.check(&token::OpenDelim(token::Paren)) {
290 self.parse_pat_tuple_or_parens()?
291 } else if self.check(&token::OpenDelim(token::Bracket)) {
292 // Parse `[pat, pat,...]` as a slice pattern.
294 self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat_with_or_inner())?;
296 } else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
297 // A rest pattern `..`.
300 } else if let Some(form) = self.parse_range_end() {
301 self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
302 } else if self.eat_keyword(kw::Underscore) {
305 } else if self.eat_keyword(kw::Mut) {
306 self.parse_pat_ident_mut()?
307 } else if self.eat_keyword(kw::Ref) {
308 // Parse ref ident @ pat / ref mut ident @ pat
309 let mutbl = self.parse_mutability();
310 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
311 } else if self.eat_keyword(kw::Box) {
313 let pat = self.parse_pat_with_range_pat(false, None)?;
314 self.sess.gated_spans.gate(sym::box_patterns, lo.to(self.prev_span));
316 } else if self.can_be_ident_pat() {
317 // Parse `ident @ pat`
318 // This can give false positives and parse nullary enums,
319 // they are dealt with later in resolve.
320 self.parse_pat_ident(BindingMode::ByValue(Mutability::Not))?
321 } else if self.is_start_of_pat_with_path() {
322 // Parse pattern starting with a path
323 let (qself, path) = if self.eat_lt() {
324 // Parse a qualified path
325 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
328 // Parse an unqualified path
329 (None, self.parse_path(PathStyle::Expr)?)
331 let span = lo.to(self.prev_span);
333 if qself.is_none() && self.check(&token::Not) {
334 self.parse_pat_mac_invoc(path)?
335 } else if let Some(form) = self.parse_range_end() {
336 let begin = self.mk_expr(span, ExprKind::Path(qself, path), AttrVec::new());
337 self.parse_pat_range_begin_with(begin, form)?
338 } else if self.check(&token::OpenDelim(token::Brace)) {
339 self.parse_pat_struct(qself, path)?
340 } else if self.check(&token::OpenDelim(token::Paren)) {
341 self.parse_pat_tuple_struct(qself, path)?
343 PatKind::Path(qself, path)
346 // Try to parse everything else as literal with optional minus
347 match self.parse_literal_maybe_minus() {
348 Ok(begin) => match self.parse_range_end() {
349 Some(form) => self.parse_pat_range_begin_with(begin, form)?,
350 None => PatKind::Lit(begin),
352 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
356 let pat = self.mk_pat(lo.to(self.prev_span), pat);
357 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
358 let pat = self.recover_intersection_pat(pat)?;
360 if !allow_range_pat {
361 self.ban_pat_range_if_ambiguous(&pat)
367 /// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
369 /// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
370 /// should already have been parsed by now at this point,
371 /// if the next token is `@` then we can try to parse the more general form.
373 /// Consult `parse_pat_ident` for the `binding` grammar.
375 /// The notion of intersection patterns are found in
376 /// e.g. [F#][and] where they are called AND-patterns.
378 /// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
379 fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
380 if self.token.kind != token::At {
381 // Next token is not `@` so it's not going to be an intersection pattern.
385 // At this point we attempt to parse `@ $pat_rhs` and emit an error.
387 let mut rhs = self.parse_pat(None)?;
388 let sp = lhs.span.to(rhs.span);
390 if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
391 // The user inverted the order, so help them fix that.
392 let mut applicability = Applicability::MachineApplicable;
393 // FIXME(bindings_after_at): Remove this code when stabilizing the feature.
394 lhs.walk(&mut |p| match p.kind {
395 // `check_match` is unhappy if the subpattern has a binding anywhere.
396 PatKind::Ident(..) => {
397 applicability = Applicability::MaybeIncorrect;
398 false // Short-circuit.
403 let lhs_span = lhs.span;
404 // Move the LHS into the RHS as a subpattern.
405 // The RHS is now the full pattern.
408 self.struct_span_err(sp, "pattern on wrong side of `@`")
409 .span_label(lhs_span, "pattern on the left, should be on the right")
410 .span_label(rhs.span, "binding on the right, should be on the left")
411 .span_suggestion(sp, "switch the order", pprust::pat_to_string(&rhs), applicability)
414 // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
415 rhs.kind = PatKind::Wild;
416 self.struct_span_err(sp, "left-hand side of `@` must be a binding")
417 .span_label(lhs.span, "interpreted as a pattern, not a binding")
418 .span_label(rhs.span, "also a pattern")
419 .note("bindings are `x`, `mut x`, `ref x`, and `ref mut x`")
427 /// Ban a range pattern if it has an ambiguous interpretation.
428 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) {
432 Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. },
434 PatKind::Range(..) => {}
438 self.struct_span_err(pat.span, "the range pattern here has ambiguous interpretation")
441 "add parentheses to clarify the precedence",
442 format!("({})", pprust::pat_to_string(&pat)),
443 // "ambiguous interpretation" implies that we have to be guessing
444 Applicability::MaybeIncorrect,
449 /// Parse `&pat` / `&mut pat`.
450 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
452 self.recover_lifetime_in_deref_pat();
453 let mutbl = self.parse_mutability();
454 let subpat = self.parse_pat_with_range_pat(false, expected)?;
455 Ok(PatKind::Ref(subpat, mutbl))
458 fn recover_lifetime_in_deref_pat(&mut self) {
459 if let token::Lifetime(name) = self.token.kind {
462 let span = self.prev_span;
463 self.struct_span_err(span, &format!("unexpected lifetime `{}` in pattern", name))
466 "remove the lifetime",
468 Applicability::MachineApplicable,
474 /// Parse a tuple or parenthesis pattern.
475 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
476 let (fields, trailing_comma) =
477 self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
479 // Here, `(pat,)` is a tuple pattern.
480 // For backward compatibility, `(..)` is a tuple pattern as well.
481 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
482 PatKind::Paren(fields.into_iter().nth(0).unwrap())
484 PatKind::Tuple(fields)
488 /// Parse a mutable binding with the `mut` token already eaten.
489 fn parse_pat_ident_mut(&mut self) -> PResult<'a, PatKind> {
490 let mut_span = self.prev_span;
492 if self.eat_keyword(kw::Ref) {
493 return self.recover_mut_ref_ident(mut_span);
496 self.recover_additional_muts();
498 // Make sure we don't allow e.g. `let mut $p;` where `$p:pat`.
499 if let token::Interpolated(ref nt) = self.token.kind {
500 if let token::NtPat(_) = **nt {
501 self.expected_ident_found().emit();
505 // Parse the pattern we hope to be an identifier.
506 let mut pat = self.parse_pat(Some("identifier"))?;
508 // If we don't have `mut $ident (@ pat)?`, error.
509 if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind {
510 // Don't recurse into the subpattern.
511 // `mut` on the outer binding doesn't affect the inner bindings.
512 *m = Mutability::Mut;
514 // Add `mut` to any binding in the parsed pattern.
515 let changed_any_binding = Self::make_all_value_bindings_mutable(&mut pat);
516 self.ban_mut_general_pat(mut_span, &pat, changed_any_binding);
519 Ok(pat.into_inner().kind)
522 /// Recover on `mut ref? ident @ pat` and suggest
523 /// that the order of `mut` and `ref` is incorrect.
524 fn recover_mut_ref_ident(&mut self, lo: Span) -> PResult<'a, PatKind> {
525 let mutref_span = lo.to(self.prev_span);
526 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
529 "try switching the order",
531 Applicability::MachineApplicable,
535 self.parse_pat_ident(BindingMode::ByRef(Mutability::Mut))
538 /// Turn all by-value immutable bindings in a pattern into mutable bindings.
539 /// Returns `true` if any change was made.
540 fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
542 impl MutVisitor for AddMut {
543 fn visit_mac(&mut self, mac: &mut Mac) {
544 noop_visit_mac(mac, self);
547 fn visit_pat(&mut self, pat: &mut P<Pat>) {
548 if let PatKind::Ident(BindingMode::ByValue(m @ Mutability::Not), ..) = &mut pat.kind
551 *m = Mutability::Mut;
553 noop_visit_pat(pat, self);
557 let mut add_mut = AddMut(false);
558 add_mut.visit_pat(pat);
562 /// Error on `mut $pat` where `$pat` is not an ident.
563 fn ban_mut_general_pat(&self, lo: Span, pat: &Pat, changed_any_binding: bool) {
564 let span = lo.to(pat.span);
565 let fix = pprust::pat_to_string(&pat);
566 let (problem, suggestion) = if changed_any_binding {
567 ("`mut` must be attached to each individual binding", "add `mut` to each binding")
569 ("`mut` must be followed by a named binding", "remove the `mut` prefix")
571 self.struct_span_err(span, problem)
572 .span_suggestion(span, suggestion, fix, Applicability::MachineApplicable)
573 .note("`mut` may be followed by `variable` and `variable @ pattern`")
577 /// Eat any extraneous `mut`s and error + recover if we ate any.
578 fn recover_additional_muts(&mut self) {
579 let lo = self.token.span;
580 while self.eat_keyword(kw::Mut) {}
581 if lo == self.token.span {
585 let span = lo.to(self.prev_span);
586 self.struct_span_err(span, "`mut` on a binding may not be repeated")
589 "remove the additional `mut`s",
591 Applicability::MachineApplicable,
596 /// Parse macro invocation
597 fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
599 let args = self.parse_mac_args()?;
600 let mac = Mac { path, args, prior_type_ascription: self.last_type_ascription };
601 Ok(PatKind::Mac(mac))
604 fn fatal_unexpected_non_pat(
606 mut err: DiagnosticBuilder<'a>,
608 ) -> PResult<'a, P<Pat>> {
611 let expected = expected.unwrap_or("pattern");
612 let msg = format!("expected {}, found {}", expected, super::token_descr(&self.token));
614 let mut err = self.struct_span_err(self.token.span, &msg);
615 err.span_label(self.token.span, format!("expected {}", expected));
617 let sp = self.sess.source_map().start_point(self.token.span);
618 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
619 self.sess.expr_parentheses_needed(&mut err, *sp, None);
625 /// Parses the range pattern end form `".." | "..." | "..=" ;`.
626 fn parse_range_end(&mut self) -> Option<Spanned<RangeEnd>> {
627 let re = if self.eat(&token::DotDotDot) {
628 RangeEnd::Included(RangeSyntax::DotDotDot)
629 } else if self.eat(&token::DotDotEq) {
630 RangeEnd::Included(RangeSyntax::DotDotEq)
631 } else if self.eat(&token::DotDot) {
632 self.sess.gated_spans.gate(sym::exclusive_range_pattern, self.prev_span);
637 Some(respan(self.prev_span, re))
640 /// Parse a range pattern `$begin $form $end?` where `$form = ".." | "..." | "..=" ;`.
641 /// `$begin $form` has already been parsed.
642 fn parse_pat_range_begin_with(
645 re: Spanned<RangeEnd>,
646 ) -> PResult<'a, PatKind> {
647 let end = if self.is_pat_range_end_start(0) {
648 // Parsing e.g. `X..=Y`.
649 Some(self.parse_pat_range_end()?)
651 // Parsing e.g. `X..`.
652 self.sess.gated_spans.gate(sym::half_open_range_patterns, begin.span.to(re.span));
653 if let RangeEnd::Included(_) = re.node {
654 // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
655 // Possibly also do this for `X..=` in *expression* contexts.
656 self.error_inclusive_range_with_no_end(re.span);
660 Ok(PatKind::Range(Some(begin), end, re))
663 pub(super) fn error_inclusive_range_with_no_end(&self, span: Span) {
664 struct_span_err!(self.sess.span_diagnostic, span, E0586, "inclusive range with no end")
665 .span_suggestion_short(
669 Applicability::MachineApplicable,
671 .note("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
675 /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
677 /// The form `...X` is prohibited to reduce confusion with the potential
678 /// expression syntax `...expr` for splatting in expressions.
679 fn parse_pat_range_to(&mut self, mut re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
680 let end = self.parse_pat_range_end()?;
681 self.sess.gated_spans.gate(sym::half_open_range_patterns, re.span.to(self.prev_span));
682 if let RangeEnd::Included(ref mut syn @ RangeSyntax::DotDotDot) = &mut re.node {
683 *syn = RangeSyntax::DotDotEq;
684 self.struct_span_err(re.span, "range-to patterns with `...` are not allowed")
685 .span_suggestion_short(
689 Applicability::MachineApplicable,
693 Ok(PatKind::Range(None, Some(end), re))
696 /// Is the token `dist` away from the current suitable as the start of a range patterns end?
697 fn is_pat_range_end_start(&self, dist: usize) -> bool {
698 self.look_ahead(dist, |t| {
699 t.is_path_start() // e.g. `MY_CONST`;
700 || t.kind == token::Dot // e.g. `.5` for recovery;
701 || t.can_begin_literal_or_bool() // e.g. `42`.
706 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
707 if self.token.is_path_start() {
708 let lo = self.token.span;
709 let (qself, path) = if self.eat_lt() {
710 // Parse a qualified path
711 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
714 // Parse an unqualified path
715 (None, self.parse_path(PathStyle::Expr)?)
717 let hi = self.prev_span;
718 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), AttrVec::new()))
720 self.parse_literal_maybe_minus()
724 /// Is this the start of a pattern beginning with a path?
725 fn is_start_of_pat_with_path(&mut self) -> bool {
727 // Just for recovery (see `can_be_ident`).
728 || self.token.is_ident() && !self.token.is_bool_lit() && !self.token.is_keyword(kw::In)
731 /// Would `parse_pat_ident` be appropriate here?
732 fn can_be_ident_pat(&mut self) -> bool {
734 && !self.token.is_bool_lit() // Avoid `true` or `false` as a binding as it is a literal.
735 && !self.token.is_path_segment_keyword() // Avoid e.g. `Self` as it is a path.
736 // Avoid `in`. Due to recovery in the list parser this messes with `for ( $pat in $expr )`.
737 && !self.token.is_keyword(kw::In)
738 && self.look_ahead(1, |t| match t.kind { // Try to do something more complex?
739 token::OpenDelim(token::Paren) // A tuple struct pattern.
740 | token::OpenDelim(token::Brace) // A struct pattern.
741 | token::DotDotDot | token::DotDotEq | token::DotDot // A range pattern.
742 | token::ModSep // A tuple / struct variant pattern.
743 | token::Not => false, // A macro expanding to a pattern.
748 /// Parses `ident` or `ident @ pat`.
749 /// Used by the copy foo and ref foo patterns to give a good
750 /// error message when parsing mistakes like `ref foo(a, b)`.
751 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
752 let ident = self.parse_ident()?;
753 let sub = if self.eat(&token::At) {
754 Some(self.parse_pat(Some("binding pattern"))?)
759 // Just to be friendly, if they write something like `ref Some(i)`,
760 // we end up here with `(` as the current token.
761 // This shortly leads to a parse error. Note that if there is no explicit
762 // binding mode then we do not end up here, because the lookahead
763 // will direct us over to `parse_enum_variant()`.
764 if self.token == token::OpenDelim(token::Paren) {
766 self.struct_span_err(self.prev_span, "expected identifier, found enum pattern")
770 Ok(PatKind::Ident(binding_mode, ident, sub))
773 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
774 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
776 return self.error_qpath_before_pat(&path, "{");
779 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
785 Ok(PatKind::Struct(path, fields, etc))
788 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
789 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
791 return self.error_qpath_before_pat(&path, "(");
793 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or_inner())?;
794 Ok(PatKind::TupleStruct(path, fields))
797 /// Error when there's a qualified path, e.g. `<Foo as Bar>::Baz`
798 /// as the path of e.g., a tuple or record struct pattern.
799 fn error_qpath_before_pat(&mut self, path: &Path, token: &str) -> PResult<'a, PatKind> {
800 let msg = &format!("unexpected `{}` after qualified path", token);
801 let mut err = self.struct_span_err(self.token.span, msg);
802 err.span_label(self.token.span, msg);
803 err.span_label(path.span, "the qualified path");
807 /// Parses the fields of a struct-like pattern.
808 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
809 let mut fields = Vec::new();
811 let mut ate_comma = true;
812 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
813 let mut etc_span = None;
815 while self.token != token::CloseDelim(token::Brace) {
816 let attrs = match self.parse_outer_attributes() {
819 if let Some(mut delayed) = delayed_err {
825 let lo = self.token.span;
827 // check that a comma comes after every field
829 let err = self.struct_span_err(self.prev_span, "expected `,`");
830 if let Some(mut delayed) = delayed_err {
837 if self.check(&token::DotDot) || self.token == token::DotDotDot {
839 let mut etc_sp = self.token.span;
841 self.recover_one_fewer_dotdot();
842 self.bump(); // `..` || `...`
844 if self.token == token::CloseDelim(token::Brace) {
845 etc_span = Some(etc_sp);
848 let token_str = super::token_descr(&self.token);
849 let msg = &format!("expected `}}`, found {}", token_str);
850 let mut err = self.struct_span_err(self.token.span, msg);
852 err.span_label(self.token.span, "expected `}`");
853 let mut comma_sp = None;
854 if self.token == token::Comma {
856 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
857 etc_sp = etc_sp.to(nw_span);
860 "`..` must be at the end and cannot have a trailing comma",
862 comma_sp = Some(self.token.span);
867 etc_span = Some(etc_sp.until(self.token.span));
868 if self.token == token::CloseDelim(token::Brace) {
869 // If the struct looks otherwise well formed, recover and continue.
870 if let Some(sp) = comma_sp {
871 err.span_suggestion_short(
875 Applicability::MachineApplicable,
880 } else if self.token.is_ident() && ate_comma {
881 // Accept fields coming after `..,`.
882 // This way we avoid "pattern missing fields" errors afterwards.
883 // We delay this error until the end in order to have a span for a
885 if let Some(mut delayed_err) = delayed_err {
889 delayed_err = Some(err);
892 if let Some(mut err) = delayed_err {
899 fields.push(match self.parse_pat_field(lo, attrs) {
902 if let Some(mut delayed_err) = delayed_err {
908 ate_comma = self.eat(&token::Comma);
911 if let Some(mut err) = delayed_err {
912 if let Some(etc_span) = etc_span {
913 err.multipart_suggestion(
914 "move the `..` to the end of the field list",
916 (etc_span, String::new()),
917 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
919 Applicability::MachineApplicable,
924 return Ok((fields, etc));
927 /// Recover on `...` as if it were `..` to avoid further errors.
928 /// See issue #46718.
929 fn recover_one_fewer_dotdot(&self) {
930 if self.token != token::DotDotDot {
934 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
937 "to omit remaining fields, use one fewer `.`",
939 Applicability::MachineApplicable,
944 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
945 // Check if a colon exists one ahead. This means we're parsing a fieldname.
947 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
948 // Parsing a pattern of the form `fieldname: pat`.
949 let fieldname = self.parse_field_name()?;
951 let pat = self.parse_pat_with_or_inner()?;
953 (pat, fieldname, false)
955 // Parsing a pattern of the form `(box) (ref) (mut) fieldname`.
956 let is_box = self.eat_keyword(kw::Box);
957 let boxed_span = self.token.span;
958 let is_ref = self.eat_keyword(kw::Ref);
959 let is_mut = self.eat_keyword(kw::Mut);
960 let fieldname = self.parse_ident()?;
963 let bind_type = match (is_ref, is_mut) {
964 (true, true) => BindingMode::ByRef(Mutability::Mut),
965 (true, false) => BindingMode::ByRef(Mutability::Not),
966 (false, true) => BindingMode::ByValue(Mutability::Mut),
967 (false, false) => BindingMode::ByValue(Mutability::Not),
970 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
972 if is_box { self.mk_pat(lo.to(hi), PatKind::Box(fieldpat)) } else { fieldpat };
973 (subpat, fieldname, true)
981 id: ast::DUMMY_NODE_ID,
983 is_placeholder: false,
987 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
988 self.mk_pat(span, PatKind::Ident(bm, ident, None))
991 fn mk_pat(&self, span: Span, kind: PatKind) -> P<Pat> {
992 P(Pat { kind, span, id: ast::DUMMY_NODE_ID })