1 use super::{Parser, PResult, PathStyle};
3 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
5 use crate::ast::{self, Attribute, Pat, PatKind, FieldPat, RangeEnd, RangeSyntax, Mac};
6 use crate::ast::{BindingMode, Ident, Mutability, Path, QSelf, Expr, ExprKind};
7 use crate::parse::token::{self};
8 use crate::print::pprust;
9 use crate::source_map::{respan, Span, Spanned};
10 use crate::symbol::kw;
13 use errors::{Applicability, DiagnosticBuilder};
15 type Expected = Option<&'static str>;
19 pub fn parse_pat(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
20 self.parse_pat_with_range_pat(true, expected)
23 /// Parses patterns, separated by '|' s.
24 pub(super) fn parse_pats(&mut self) -> PResult<'a, Vec<P<Pat>>> {
25 // Allow a '|' before the pats (RFC 1925 + RFC 2530)
26 self.eat(&token::BinOp(token::Or));
28 let mut pats = Vec::new();
30 pats.push(self.parse_top_level_pat()?);
32 if !self.eat_or_separator() {
38 /// A wrapper around `parse_pat` with some special error handling for the
39 /// "top-level" patterns in a match arm, `for` loop, `let`, &c. (in contrast
40 /// to subpatterns within such).
41 pub(super) fn parse_top_level_pat(&mut self) -> PResult<'a, P<Pat>> {
42 let pat = self.parse_pat(None)?;
43 self.maybe_recover_unexpected_comma(pat.span, true)?;
47 fn maybe_recover_unexpected_comma(&mut self, lo: Span, top_level: bool) -> PResult<'a, ()> {
48 if !top_level || self.token != token::Comma {
52 // An unexpected comma after a top-level pattern is a clue that the
53 // user (perhaps more accustomed to some other language) forgot the
54 // parentheses in what should have been a tuple pattern; return a
55 // suggestion-enhanced error here rather than choking on the comma later.
56 let comma_span = self.token.span;
58 if let Err(mut err) = self.skip_pat_list() {
59 // We didn't expect this to work anyway; we just wanted to advance to the
60 // end of the comma-sequence so we know the span to suggest parenthesizing.
63 let seq_span = lo.to(self.prev_span);
64 let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
65 if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
68 "try adding parentheses to match on a tuple..",
69 format!("({})", seq_snippet),
70 Applicability::MachineApplicable
74 "..or a vertical bar to match on multiple alternatives",
75 format!("{}", seq_snippet.replace(",", " |")),
76 Applicability::MachineApplicable
82 /// Parse and throw away a parentesized comma separated
83 /// sequence of patterns until `)` is reached.
84 fn skip_pat_list(&mut self) -> PResult<'a, ()> {
85 while !self.check(&token::CloseDelim(token::Paren)) {
86 self.parse_pat(None)?;
87 if !self.eat(&token::Comma) {
94 /// Parses a pattern, that may be a or-pattern (e.g. `Some(Foo | Bar)`).
100 ) -> PResult<'a, P<Pat>> {
101 // Parse the first pattern.
102 let first_pat = self.parse_pat(expected)?;
103 self.maybe_recover_unexpected_comma(first_pat.span, top_level)?;
105 // If the next token is not a `|`,
106 // this is not an or-pattern and we should exit here.
107 if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
111 let lo = first_pat.span;
112 let mut pats = vec![first_pat];
113 while self.eat_or_separator() {
114 let pat = self.parse_pat(expected)?;
115 self.maybe_recover_unexpected_comma(pat.span, top_level)?;
118 let or_pattern_span = lo.to(self.prev_span);
120 // Feature gate the or-pattern if instructed:
122 self.sess.gated_spans.or_patterns.borrow_mut().push(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) -> bool {
131 match self.token.kind {
133 // Found `||`; Recover and pretend we parsed `|`.
134 self.ban_unexpected_or_or();
138 _ => self.eat(&token::BinOp(token::Or)),
142 fn ban_unexpected_or_or(&mut self) {
143 self.struct_span_err(self.token.span, "unexpected token `||` after pattern")
146 "use a single `|` to specify multiple patterns",
148 Applicability::MachineApplicable
153 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
155 fn parse_pat_with_range_pat(
157 allow_range_pat: bool,
159 ) -> PResult<'a, P<Pat>> {
160 maybe_recover_from_interpolated_ty_qpath!(self, true);
161 maybe_whole!(self, NtPat, |x| x);
163 let lo = self.token.span;
164 let pat = match self.token.kind {
165 token::BinOp(token::And) | token::AndAnd => self.parse_pat_deref(expected)?,
166 token::OpenDelim(token::Paren) => self.parse_pat_tuple_or_parens()?,
167 token::OpenDelim(token::Bracket) => {
168 // Parse `[pat, pat,...]` as a slice pattern.
169 let (pats, _) = self.parse_delim_comma_seq(
171 |p| p.parse_pat_with_or(None, true, false),
177 if self.is_pat_range_end_start() {
178 // Parse `..42` for recovery.
179 self.parse_pat_range_to(RangeEnd::Excluded, "..")?
181 // A rest pattern `..`.
186 // Parse `..=42` for recovery.
188 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotEq), "..=")?
190 token::DotDotDot => {
191 // Parse `...42` for recovery.
193 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotDot), "...")?
195 // At this point, token != &, &&, (, [
196 _ => if self.eat_keyword(kw::Underscore) {
199 } else if self.eat_keyword(kw::Mut) {
200 self.recover_pat_ident_mut_first()?
201 } else if self.eat_keyword(kw::Ref) {
202 // Parse ref ident @ pat / ref mut ident @ pat
203 let mutbl = self.parse_mutability();
204 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
205 } else if self.eat_keyword(kw::Box) {
207 PatKind::Box(self.parse_pat_with_range_pat(false, None)?)
208 } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
209 self.parse_as_ident() {
210 // Parse `ident @ pat`
211 // This can give false positives and parse nullary enums,
212 // they are dealt with later in resolve.
213 self.parse_pat_ident(BindingMode::ByValue(Mutability::Immutable))?
214 } else if self.token.is_path_start() {
215 // Parse pattern starting with a path
216 let (qself, path) = if self.eat_lt() {
217 // Parse a qualified path
218 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
221 // Parse an unqualified path
222 (None, self.parse_path(PathStyle::Expr)?)
224 match self.token.kind {
225 token::Not if qself.is_none() => self.parse_pat_mac_invoc(lo, path)?,
226 token::DotDotDot | token::DotDotEq | token::DotDot => {
227 self.parse_pat_range_starting_with_path(lo, qself, path)?
229 token::OpenDelim(token::Brace) => self.parse_pat_struct(qself, path)?,
230 token::OpenDelim(token::Paren) => self.parse_pat_tuple_struct(qself, path)?,
231 _ => PatKind::Path(qself, path),
234 // Try to parse everything else as literal with optional minus
235 match self.parse_literal_maybe_minus() {
237 if self.check(&token::DotDot)
238 || self.check(&token::DotDotEq)
239 || self.check(&token::DotDotDot) =>
241 self.parse_pat_range_starting_with_lit(begin)?
243 Ok(begin) => PatKind::Lit(begin),
244 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
249 let pat = self.mk_pat(lo.to(self.prev_span), pat);
250 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
252 if !allow_range_pat {
253 self.ban_pat_range_if_ambiguous(&pat)?
259 /// Ban a range pattern if it has an ambiguous interpretation.
260 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
263 .., Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
265 PatKind::Range(..) => {}
269 let mut err = self.struct_span_err(
271 "the range pattern here has ambiguous interpretation",
275 "add parentheses to clarify the precedence",
276 format!("({})", pprust::pat_to_string(&pat)),
277 // "ambiguous interpretation" implies that we have to be guessing
278 Applicability::MaybeIncorrect
283 /// Parse `&pat` / `&mut pat`.
284 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
286 let mutbl = self.parse_mutability();
288 if let token::Lifetime(name) = self.token.kind {
289 let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
290 err.span_label(self.token.span, "unexpected lifetime");
294 let subpat = self.parse_pat_with_range_pat(false, expected)?;
295 Ok(PatKind::Ref(subpat, mutbl))
298 /// Parse a tuple or parenthesis pattern.
299 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
300 let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
301 p.parse_pat_with_or(None, true, false)
304 // Here, `(pat,)` is a tuple pattern.
305 // For backward compatibility, `(..)` is a tuple pattern as well.
306 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
307 PatKind::Paren(fields.into_iter().nth(0).unwrap())
309 PatKind::Tuple(fields)
313 /// Recover on `mut ref? ident @ pat` and suggest
314 /// that the order of `mut` and `ref` is incorrect.
315 fn recover_pat_ident_mut_first(&mut self) -> PResult<'a, PatKind> {
316 let mutref_span = self.prev_span.to(self.token.span);
317 let binding_mode = if self.eat_keyword(kw::Ref) {
318 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
321 "try switching the order",
323 Applicability::MachineApplicable
326 BindingMode::ByRef(Mutability::Mutable)
328 BindingMode::ByValue(Mutability::Mutable)
330 self.parse_pat_ident(binding_mode)
333 /// Parse macro invocation
334 fn parse_pat_mac_invoc(&mut self, lo: Span, path: Path) -> PResult<'a, PatKind> {
336 let (delim, tts) = self.expect_delimited_token_tree()?;
341 span: lo.to(self.prev_span),
342 prior_type_ascription: self.last_type_ascription,
344 Ok(PatKind::Mac(mac))
347 /// Parse a range pattern `$path $form $end?` where `$form = ".." | "..." | "..=" ;`.
348 /// The `$path` has already been parsed and the next token is the `$form`.
349 fn parse_pat_range_starting_with_path(
352 qself: Option<QSelf>,
354 ) -> PResult<'a, PatKind> {
355 let (end_kind, form) = match self.token.kind {
356 token::DotDot => (RangeEnd::Excluded, ".."),
357 token::DotDotDot => (RangeEnd::Included(RangeSyntax::DotDotDot), "..."),
358 token::DotDotEq => (RangeEnd::Included(RangeSyntax::DotDotEq), "..="),
359 _ => panic!("can only parse `..`/`...`/`..=` for ranges (checked above)"),
361 let op_span = self.token.span;
363 let span = lo.to(self.prev_span);
364 let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
366 let end = self.parse_pat_range_end_opt(&begin, form)?;
367 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
370 /// Parse a range pattern `$literal $form $end?` where `$form = ".." | "..." | "..=" ;`.
371 /// The `$path` has already been parsed and the next token is the `$form`.
372 fn parse_pat_range_starting_with_lit(&mut self, begin: P<Expr>) -> PResult<'a, PatKind> {
373 let op_span = self.token.span;
374 let (end_kind, form) = if self.eat(&token::DotDotDot) {
375 (RangeEnd::Included(RangeSyntax::DotDotDot), "...")
376 } else if self.eat(&token::DotDotEq) {
377 (RangeEnd::Included(RangeSyntax::DotDotEq), "..=")
378 } else if self.eat(&token::DotDot) {
379 (RangeEnd::Excluded, "..")
381 panic!("impossible case: we already matched on a range-operator token")
383 let end = self.parse_pat_range_end_opt(&begin, form)?;
384 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
387 fn fatal_unexpected_non_pat(
389 mut err: DiagnosticBuilder<'a>,
391 ) -> PResult<'a, P<Pat>> {
392 self.cancel(&mut err);
394 let expected = expected.unwrap_or("pattern");
395 let msg = format!("expected {}, found {}", expected, self.this_token_descr());
397 let mut err = self.fatal(&msg);
398 err.span_label(self.token.span, format!("expected {}", expected));
400 let sp = self.sess.source_map().start_point(self.token.span);
401 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
402 self.sess.expr_parentheses_needed(&mut err, *sp, None);
408 // Helper function to decide whether to parse as ident binding
409 // or to try to do something more complex like range patterns.
410 fn parse_as_ident(&mut self) -> bool {
411 self.look_ahead(1, |t| match t.kind {
412 token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
413 token::DotDotDot | token::DotDotEq | token::DotDot |
414 token::ModSep | token::Not => false,
419 /// Is the current token suitable as the start of a range patterns end?
420 fn is_pat_range_end_start(&self) -> bool {
421 self.token.is_path_start() // e.g. `MY_CONST`;
422 || self.token == token::Dot // e.g. `.5` for recovery;
423 || self.token.can_begin_literal_or_bool() // e.g. `42`.
424 || self.token.is_whole_expr()
427 /// Parse a range-to pattern, e.g. `..X` and `..=X` for recovery.
428 fn parse_pat_range_to(&mut self, re: RangeEnd, form: &str) -> PResult<'a, PatKind> {
429 let lo = self.prev_span;
430 let end = self.parse_pat_range_end()?;
431 let range_span = lo.to(end.span);
432 let begin = self.mk_expr(range_span, ExprKind::Err, ThinVec::new());
435 .struct_span_err(range_span, &format!("`{}X` range patterns are not supported", form))
438 "try using the minimum value for the type",
439 format!("MIN{}{}", form, pprust::expr_to_string(&end)),
440 Applicability::HasPlaceholders,
444 Ok(PatKind::Range(begin, end, respan(lo, re)))
447 /// Parse the end of a `X..Y`, `X..=Y`, or `X...Y` range pattern or recover
448 /// if that end is missing treating it as `X..`, `X..=`, or `X...` respectively.
449 fn parse_pat_range_end_opt(&mut self, begin: &Expr, form: &str) -> PResult<'a, P<Expr>> {
450 if self.is_pat_range_end_start() {
451 // Parsing e.g. `X..=Y`.
452 self.parse_pat_range_end()
454 // Parsing e.g. `X..`.
455 let range_span = begin.span.to(self.prev_span);
460 &format!("`X{}` range patterns are not supported", form),
464 "try using the maximum value for the type",
465 format!("{}{}MAX", pprust::expr_to_string(&begin), form),
466 Applicability::HasPlaceholders,
470 Ok(self.mk_expr(range_span, ExprKind::Err, ThinVec::new()))
474 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
475 if self.token.is_path_start() {
476 let lo = self.token.span;
477 let (qself, path) = if self.eat_lt() {
478 // Parse a qualified path
479 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
482 // Parse an unqualified path
483 (None, self.parse_path(PathStyle::Expr)?)
485 let hi = self.prev_span;
486 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
488 self.parse_literal_maybe_minus()
492 /// Parses `ident` or `ident @ pat`.
493 /// Used by the copy foo and ref foo patterns to give a good
494 /// error message when parsing mistakes like `ref foo(a, b)`.
495 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
496 let ident = self.parse_ident()?;
497 let sub = if self.eat(&token::At) {
498 Some(self.parse_pat(Some("binding pattern"))?)
503 // Just to be friendly, if they write something like `ref Some(i)`,
504 // we end up here with `(` as the current token.
505 // This shortly leads to a parse error. Note that if there is no explicit
506 // binding mode then we do not end up here, because the lookahead
507 // will direct us over to `parse_enum_variant()`.
508 if self.token == token::OpenDelim(token::Paren) {
509 return Err(self.span_fatal(
511 "expected identifier, found enum pattern",
515 Ok(PatKind::Ident(binding_mode, ident, sub))
518 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
519 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
521 let msg = "unexpected `{` after qualified path";
522 let mut err = self.fatal(msg);
523 err.span_label(self.token.span, msg);
528 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
534 Ok(PatKind::Struct(path, fields, etc))
537 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
538 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
540 let msg = "unexpected `(` after qualified path";
541 let mut err = self.fatal(msg);
542 err.span_label(self.token.span, msg);
545 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or(None, true, false))?;
546 Ok(PatKind::TupleStruct(path, fields))
549 /// Parses the fields of a struct-like pattern.
550 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
551 let mut fields = Vec::new();
553 let mut ate_comma = true;
554 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
555 let mut etc_span = None;
557 while self.token != token::CloseDelim(token::Brace) {
558 let attrs = match self.parse_outer_attributes() {
561 if let Some(mut delayed) = delayed_err {
567 let lo = self.token.span;
569 // check that a comma comes after every field
571 let err = self.struct_span_err(self.prev_span, "expected `,`");
572 if let Some(mut delayed) = delayed_err {
579 if self.check(&token::DotDot) || self.token == token::DotDotDot {
581 let mut etc_sp = self.token.span;
583 self.recover_one_fewer_dotdot();
584 self.bump(); // `..` || `...`
586 if self.token == token::CloseDelim(token::Brace) {
587 etc_span = Some(etc_sp);
590 let token_str = self.this_token_descr();
591 let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
593 err.span_label(self.token.span, "expected `}`");
594 let mut comma_sp = None;
595 if self.token == token::Comma { // Issue #49257
596 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
597 etc_sp = etc_sp.to(nw_span);
598 err.span_label(etc_sp,
599 "`..` must be at the end and cannot have a trailing comma");
600 comma_sp = Some(self.token.span);
605 etc_span = Some(etc_sp.until(self.token.span));
606 if self.token == token::CloseDelim(token::Brace) {
607 // If the struct looks otherwise well formed, recover and continue.
608 if let Some(sp) = comma_sp {
609 err.span_suggestion_short(
613 Applicability::MachineApplicable,
618 } else if self.token.is_ident() && ate_comma {
619 // Accept fields coming after `..,`.
620 // This way we avoid "pattern missing fields" errors afterwards.
621 // We delay this error until the end in order to have a span for a
623 if let Some(mut delayed_err) = delayed_err {
627 delayed_err = Some(err);
630 if let Some(mut err) = delayed_err {
637 fields.push(match self.parse_pat_field(lo, attrs) {
640 if let Some(mut delayed_err) = delayed_err {
646 ate_comma = self.eat(&token::Comma);
649 if let Some(mut err) = delayed_err {
650 if let Some(etc_span) = etc_span {
651 err.multipart_suggestion(
652 "move the `..` to the end of the field list",
654 (etc_span, String::new()),
655 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
657 Applicability::MachineApplicable,
662 return Ok((fields, etc));
665 /// Recover on `...` as if it were `..` to avoid further errors.
666 /// See issue #46718.
667 fn recover_one_fewer_dotdot(&self) {
668 if self.token != token::DotDotDot {
672 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
675 "to omit remaining fields, use one fewer `.`",
677 Applicability::MachineApplicable
682 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
683 // Check if a colon exists one ahead. This means we're parsing a fieldname.
685 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
686 // Parsing a pattern of the form "fieldname: pat"
687 let fieldname = self.parse_field_name()?;
689 let pat = self.parse_pat_with_or(None, true, false)?;
691 (pat, fieldname, false)
693 // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
694 let is_box = self.eat_keyword(kw::Box);
695 let boxed_span = self.token.span;
696 let is_ref = self.eat_keyword(kw::Ref);
697 let is_mut = self.eat_keyword(kw::Mut);
698 let fieldname = self.parse_ident()?;
701 let bind_type = match (is_ref, is_mut) {
702 (true, true) => BindingMode::ByRef(Mutability::Mutable),
703 (true, false) => BindingMode::ByRef(Mutability::Immutable),
704 (false, true) => BindingMode::ByValue(Mutability::Mutable),
705 (false, false) => BindingMode::ByValue(Mutability::Immutable),
708 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
709 let subpat = if is_box {
710 self.mk_pat(lo.to(hi), PatKind::Box(fieldpat))
714 (subpat, fieldname, true)
722 id: ast::DUMMY_NODE_ID,
727 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
728 self.mk_pat(span, PatKind::Ident(bm, ident, None))
731 fn mk_pat(&self, span: Span, node: PatKind) -> P<Pat> {
732 P(Pat { node, span, id: ast::DUMMY_NODE_ID })