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.token == token::OrOr {
33 self.ban_unexpected_or_or();
35 } else if self.eat(&token::BinOp(token::Or)) {
36 // This is a No-op. Continue the loop to parse the next
44 fn ban_unexpected_or_or(&mut self) {
45 self.struct_span_err(self.token.span, "unexpected token `||` after pattern")
48 "use a single `|` to specify multiple patterns",
50 Applicability::MachineApplicable
55 /// A wrapper around `parse_pat` with some special error handling for the
56 /// "top-level" patterns in a match arm, `for` loop, `let`, &c. (in contrast
57 /// to subpatterns within such).
58 pub(super) fn parse_top_level_pat(&mut self) -> PResult<'a, P<Pat>> {
59 let pat = self.parse_pat(None)?;
60 self.maybe_recover_unexpected_comma(pat.span)?;
64 fn maybe_recover_unexpected_comma(&mut self, lo: Span) -> PResult<'a, ()> {
65 if self.token != token::Comma {
69 // An unexpected comma after a top-level pattern is a clue that the
70 // user (perhaps more accustomed to some other language) forgot the
71 // parentheses in what should have been a tuple pattern; return a
72 // suggestion-enhanced error here rather than choking on the comma later.
73 let comma_span = self.token.span;
75 if let Err(mut err) = self.skip_pat_list() {
76 // We didn't expect this to work anyway; we just wanted to advance to the
77 // end of the comma-sequence so we know the span to suggest parenthesizing.
80 let seq_span = lo.to(self.prev_span);
81 let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
82 if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
85 "try adding parentheses to match on a tuple..",
86 format!("({})", seq_snippet),
87 Applicability::MachineApplicable
91 "..or a vertical bar to match on multiple alternatives",
92 format!("{}", seq_snippet.replace(",", " |")),
93 Applicability::MachineApplicable
99 /// Parse and throw away a parentesized comma separated
100 /// sequence of patterns until `)` is reached.
101 fn skip_pat_list(&mut self) -> PResult<'a, ()> {
102 while !self.check(&token::CloseDelim(token::Paren)) {
103 self.parse_pat(None)?;
104 if !self.eat(&token::Comma) {
111 /// Parses a pattern, that may be a or-pattern (e.g. `Some(Foo | Bar)`).
112 fn parse_pat_with_or(&mut self, expected: Expected, gate_or: bool) -> PResult<'a, P<Pat>> {
113 // Parse the first pattern.
114 let first_pat = self.parse_pat(expected)?;
116 // If the next token is not a `|`,
117 // this is not an or-pattern and we should exit here.
118 if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
122 let lo = first_pat.span;
123 let mut pats = vec![first_pat];
125 if self.token == token::OrOr {
126 // Found `||`; Recover and pretend we parsed `|`.
127 self.ban_unexpected_or_or();
129 } else if self.eat(&token::BinOp(token::Or)) {
130 // Found `|`. Working towards a proper or-pattern.
135 pats.push(self.parse_pat(expected)?);
137 let or_pattern_span = lo.to(self.prev_span);
139 // Feature gate the or-pattern if instructed:
141 self.sess.gated_spans.or_patterns.borrow_mut().push(or_pattern_span);
144 Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
147 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
149 fn parse_pat_with_range_pat(
151 allow_range_pat: bool,
153 ) -> PResult<'a, P<Pat>> {
154 maybe_recover_from_interpolated_ty_qpath!(self, true);
155 maybe_whole!(self, NtPat, |x| x);
157 let lo = self.token.span;
158 let pat = match self.token.kind {
159 token::BinOp(token::And) | token::AndAnd => self.parse_pat_deref(expected)?,
160 token::OpenDelim(token::Paren) => self.parse_pat_tuple_or_parens()?,
161 token::OpenDelim(token::Bracket) => {
162 // Parse `[pat, pat,...]` as a slice pattern.
163 let (pats, _) = self.parse_delim_comma_seq(
165 |p| p.parse_pat_with_or(None, true),
171 if self.is_pat_range_end_start() {
172 // Parse `..42` for recovery.
173 self.parse_pat_range_to(RangeEnd::Excluded, "..")?
175 // A rest pattern `..`.
180 // Parse `..=42` for recovery.
182 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotEq), "..=")?
184 token::DotDotDot => {
185 // Parse `...42` for recovery.
187 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotDot), "...")?
189 // At this point, token != &, &&, (, [
190 _ => if self.eat_keyword(kw::Underscore) {
193 } else if self.eat_keyword(kw::Mut) {
194 self.recover_pat_ident_mut_first()?
195 } else if self.eat_keyword(kw::Ref) {
196 // Parse ref ident @ pat / ref mut ident @ pat
197 let mutbl = self.parse_mutability();
198 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
199 } else if self.eat_keyword(kw::Box) {
201 PatKind::Box(self.parse_pat_with_range_pat(false, None)?)
202 } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
203 self.parse_as_ident() {
204 // Parse `ident @ pat`
205 // This can give false positives and parse nullary enums,
206 // they are dealt with later in resolve.
207 self.parse_pat_ident(BindingMode::ByValue(Mutability::Immutable))?
208 } else if self.token.is_path_start() {
209 // Parse pattern starting with a path
210 let (qself, path) = if self.eat_lt() {
211 // Parse a qualified path
212 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
215 // Parse an unqualified path
216 (None, self.parse_path(PathStyle::Expr)?)
218 match self.token.kind {
219 token::Not if qself.is_none() => self.parse_pat_mac_invoc(lo, path)?,
220 token::DotDotDot | token::DotDotEq | token::DotDot => {
221 self.parse_pat_range_starting_with_path(lo, qself, path)?
223 token::OpenDelim(token::Brace) => self.parse_pat_struct(qself, path)?,
224 token::OpenDelim(token::Paren) => self.parse_pat_tuple_struct(qself, path)?,
225 _ => PatKind::Path(qself, path),
228 // Try to parse everything else as literal with optional minus
229 match self.parse_literal_maybe_minus() {
231 if self.check(&token::DotDot)
232 || self.check(&token::DotDotEq)
233 || self.check(&token::DotDotDot) =>
235 self.parse_pat_range_starting_with_lit(begin)?
237 Ok(begin) => PatKind::Lit(begin),
238 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
243 let pat = self.mk_pat(lo.to(self.prev_span), pat);
244 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
246 if !allow_range_pat {
247 self.ban_pat_range_if_ambiguous(&pat)?
253 /// Ban a range pattern if it has an ambiguous interpretation.
254 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
257 .., Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
259 PatKind::Range(..) => {}
263 let mut err = self.struct_span_err(
265 "the range pattern here has ambiguous interpretation",
269 "add parentheses to clarify the precedence",
270 format!("({})", pprust::pat_to_string(&pat)),
271 // "ambiguous interpretation" implies that we have to be guessing
272 Applicability::MaybeIncorrect
277 /// Parse `&pat` / `&mut pat`.
278 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
280 let mutbl = self.parse_mutability();
282 if let token::Lifetime(name) = self.token.kind {
283 let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
284 err.span_label(self.token.span, "unexpected lifetime");
288 let subpat = self.parse_pat_with_range_pat(false, expected)?;
289 Ok(PatKind::Ref(subpat, mutbl))
292 /// Parse a tuple or parenthesis pattern.
293 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
294 let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
295 p.parse_pat_with_or(None, true)
298 // Here, `(pat,)` is a tuple pattern.
299 // For backward compatibility, `(..)` is a tuple pattern as well.
300 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
301 PatKind::Paren(fields.into_iter().nth(0).unwrap())
303 PatKind::Tuple(fields)
307 /// Recover on `mut ref? ident @ pat` and suggest
308 /// that the order of `mut` and `ref` is incorrect.
309 fn recover_pat_ident_mut_first(&mut self) -> PResult<'a, PatKind> {
310 let mutref_span = self.prev_span.to(self.token.span);
311 let binding_mode = if self.eat_keyword(kw::Ref) {
312 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
315 "try switching the order",
317 Applicability::MachineApplicable
320 BindingMode::ByRef(Mutability::Mutable)
322 BindingMode::ByValue(Mutability::Mutable)
324 self.parse_pat_ident(binding_mode)
327 /// Parse macro invocation
328 fn parse_pat_mac_invoc(&mut self, lo: Span, path: Path) -> PResult<'a, PatKind> {
330 let (delim, tts) = self.expect_delimited_token_tree()?;
335 span: lo.to(self.prev_span),
336 prior_type_ascription: self.last_type_ascription,
338 Ok(PatKind::Mac(mac))
341 /// Parse a range pattern `$path $form $end?` where `$form = ".." | "..." | "..=" ;`.
342 /// The `$path` has already been parsed and the next token is the `$form`.
343 fn parse_pat_range_starting_with_path(
346 qself: Option<QSelf>,
348 ) -> PResult<'a, PatKind> {
349 let (end_kind, form) = match self.token.kind {
350 token::DotDot => (RangeEnd::Excluded, ".."),
351 token::DotDotDot => (RangeEnd::Included(RangeSyntax::DotDotDot), "..."),
352 token::DotDotEq => (RangeEnd::Included(RangeSyntax::DotDotEq), "..="),
353 _ => panic!("can only parse `..`/`...`/`..=` for ranges (checked above)"),
355 let op_span = self.token.span;
357 let span = lo.to(self.prev_span);
358 let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
360 let end = self.parse_pat_range_end_opt(&begin, form)?;
361 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
364 /// Parse a range pattern `$literal $form $end?` where `$form = ".." | "..." | "..=" ;`.
365 /// The `$path` has already been parsed and the next token is the `$form`.
366 fn parse_pat_range_starting_with_lit(&mut self, begin: P<Expr>) -> PResult<'a, PatKind> {
367 let op_span = self.token.span;
368 let (end_kind, form) = if self.eat(&token::DotDotDot) {
369 (RangeEnd::Included(RangeSyntax::DotDotDot), "...")
370 } else if self.eat(&token::DotDotEq) {
371 (RangeEnd::Included(RangeSyntax::DotDotEq), "..=")
372 } else if self.eat(&token::DotDot) {
373 (RangeEnd::Excluded, "..")
375 panic!("impossible case: we already matched on a range-operator token")
377 let end = self.parse_pat_range_end_opt(&begin, form)?;
378 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
381 fn fatal_unexpected_non_pat(
383 mut err: DiagnosticBuilder<'a>,
385 ) -> PResult<'a, P<Pat>> {
386 self.cancel(&mut err);
388 let expected = expected.unwrap_or("pattern");
389 let msg = format!("expected {}, found {}", expected, self.this_token_descr());
391 let mut err = self.fatal(&msg);
392 err.span_label(self.token.span, format!("expected {}", expected));
394 let sp = self.sess.source_map().start_point(self.token.span);
395 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
396 self.sess.expr_parentheses_needed(&mut err, *sp, None);
402 // Helper function to decide whether to parse as ident binding
403 // or to try to do something more complex like range patterns.
404 fn parse_as_ident(&mut self) -> bool {
405 self.look_ahead(1, |t| match t.kind {
406 token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
407 token::DotDotDot | token::DotDotEq | token::DotDot |
408 token::ModSep | token::Not => false,
413 /// Is the current token suitable as the start of a range patterns end?
414 fn is_pat_range_end_start(&self) -> bool {
415 self.token.is_path_start() // e.g. `MY_CONST`;
416 || self.token == token::Dot // e.g. `.5` for recovery;
417 || self.token.can_begin_literal_or_bool() // e.g. `42`.
418 || self.token.is_whole_expr()
421 /// Parse a range-to pattern, e.g. `..X` and `..=X` for recovery.
422 fn parse_pat_range_to(&mut self, re: RangeEnd, form: &str) -> PResult<'a, PatKind> {
423 let lo = self.prev_span;
424 let end = self.parse_pat_range_end()?;
425 let range_span = lo.to(end.span);
426 let begin = self.mk_expr(range_span, ExprKind::Err, ThinVec::new());
429 .struct_span_err(range_span, &format!("`{}X` range patterns are not supported", form))
432 "try using the minimum value for the type",
433 format!("MIN{}{}", form, pprust::expr_to_string(&end)),
434 Applicability::HasPlaceholders,
438 Ok(PatKind::Range(begin, end, respan(lo, re)))
441 /// Parse the end of a `X..Y`, `X..=Y`, or `X...Y` range pattern or recover
442 /// if that end is missing treating it as `X..`, `X..=`, or `X...` respectively.
443 fn parse_pat_range_end_opt(&mut self, begin: &Expr, form: &str) -> PResult<'a, P<Expr>> {
444 if self.is_pat_range_end_start() {
445 // Parsing e.g. `X..=Y`.
446 self.parse_pat_range_end()
448 // Parsing e.g. `X..`.
449 let range_span = begin.span.to(self.prev_span);
454 &format!("`X{}` range patterns are not supported", form),
458 "try using the maximum value for the type",
459 format!("{}{}MAX", pprust::expr_to_string(&begin), form),
460 Applicability::HasPlaceholders,
464 Ok(self.mk_expr(range_span, ExprKind::Err, ThinVec::new()))
468 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
469 if self.token.is_path_start() {
470 let lo = self.token.span;
471 let (qself, path) = if self.eat_lt() {
472 // Parse a qualified path
473 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
476 // Parse an unqualified path
477 (None, self.parse_path(PathStyle::Expr)?)
479 let hi = self.prev_span;
480 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
482 self.parse_literal_maybe_minus()
486 /// Parses `ident` or `ident @ pat`.
487 /// Used by the copy foo and ref foo patterns to give a good
488 /// error message when parsing mistakes like `ref foo(a, b)`.
489 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
490 let ident = self.parse_ident()?;
491 let sub = if self.eat(&token::At) {
492 Some(self.parse_pat(Some("binding pattern"))?)
497 // Just to be friendly, if they write something like `ref Some(i)`,
498 // we end up here with `(` as the current token.
499 // This shortly leads to a parse error. Note that if there is no explicit
500 // binding mode then we do not end up here, because the lookahead
501 // will direct us over to `parse_enum_variant()`.
502 if self.token == token::OpenDelim(token::Paren) {
503 return Err(self.span_fatal(
505 "expected identifier, found enum pattern",
509 Ok(PatKind::Ident(binding_mode, ident, sub))
512 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
513 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
515 let msg = "unexpected `{` after qualified path";
516 let mut err = self.fatal(msg);
517 err.span_label(self.token.span, msg);
522 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
528 Ok(PatKind::Struct(path, fields, etc))
531 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
532 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
534 let msg = "unexpected `(` after qualified path";
535 let mut err = self.fatal(msg);
536 err.span_label(self.token.span, msg);
539 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or(None, true))?;
540 Ok(PatKind::TupleStruct(path, fields))
543 /// Parses the fields of a struct-like pattern.
544 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
545 let mut fields = Vec::new();
547 let mut ate_comma = true;
548 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
549 let mut etc_span = None;
551 while self.token != token::CloseDelim(token::Brace) {
552 let attrs = match self.parse_outer_attributes() {
555 if let Some(mut delayed) = delayed_err {
561 let lo = self.token.span;
563 // check that a comma comes after every field
565 let err = self.struct_span_err(self.prev_span, "expected `,`");
566 if let Some(mut delayed) = delayed_err {
573 if self.check(&token::DotDot) || self.token == token::DotDotDot {
575 let mut etc_sp = self.token.span;
577 self.recover_one_fewer_dotdot();
578 self.bump(); // `..` || `...`
580 if self.token == token::CloseDelim(token::Brace) {
581 etc_span = Some(etc_sp);
584 let token_str = self.this_token_descr();
585 let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
587 err.span_label(self.token.span, "expected `}`");
588 let mut comma_sp = None;
589 if self.token == token::Comma { // Issue #49257
590 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
591 etc_sp = etc_sp.to(nw_span);
592 err.span_label(etc_sp,
593 "`..` must be at the end and cannot have a trailing comma");
594 comma_sp = Some(self.token.span);
599 etc_span = Some(etc_sp.until(self.token.span));
600 if self.token == token::CloseDelim(token::Brace) {
601 // If the struct looks otherwise well formed, recover and continue.
602 if let Some(sp) = comma_sp {
603 err.span_suggestion_short(
607 Applicability::MachineApplicable,
612 } else if self.token.is_ident() && ate_comma {
613 // Accept fields coming after `..,`.
614 // This way we avoid "pattern missing fields" errors afterwards.
615 // We delay this error until the end in order to have a span for a
617 if let Some(mut delayed_err) = delayed_err {
621 delayed_err = Some(err);
624 if let Some(mut err) = delayed_err {
631 fields.push(match self.parse_pat_field(lo, attrs) {
634 if let Some(mut delayed_err) = delayed_err {
640 ate_comma = self.eat(&token::Comma);
643 if let Some(mut err) = delayed_err {
644 if let Some(etc_span) = etc_span {
645 err.multipart_suggestion(
646 "move the `..` to the end of the field list",
648 (etc_span, String::new()),
649 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
651 Applicability::MachineApplicable,
656 return Ok((fields, etc));
659 /// Recover on `...` as if it were `..` to avoid further errors.
660 /// See issue #46718.
661 fn recover_one_fewer_dotdot(&self) {
662 if self.token != token::DotDotDot {
666 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
669 "to omit remaining fields, use one fewer `.`",
671 Applicability::MachineApplicable
676 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
677 // Check if a colon exists one ahead. This means we're parsing a fieldname.
679 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
680 // Parsing a pattern of the form "fieldname: pat"
681 let fieldname = self.parse_field_name()?;
683 let pat = self.parse_pat_with_or(None, true)?;
685 (pat, fieldname, false)
687 // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
688 let is_box = self.eat_keyword(kw::Box);
689 let boxed_span = self.token.span;
690 let is_ref = self.eat_keyword(kw::Ref);
691 let is_mut = self.eat_keyword(kw::Mut);
692 let fieldname = self.parse_ident()?;
695 let bind_type = match (is_ref, is_mut) {
696 (true, true) => BindingMode::ByRef(Mutability::Mutable),
697 (true, false) => BindingMode::ByRef(Mutability::Immutable),
698 (false, true) => BindingMode::ByValue(Mutability::Mutable),
699 (false, false) => BindingMode::ByValue(Mutability::Immutable),
702 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
703 let subpat = if is_box {
704 self.mk_pat(lo.to(hi), PatKind::Box(fieldpat))
708 (subpat, fieldname, true)
716 id: ast::DUMMY_NODE_ID,
721 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
722 self.mk_pat(span, PatKind::Ident(bm, ident, None))
725 fn mk_pat(&self, span: Span, node: PatKind) -> P<Pat> {
726 P(Pat { node, span, id: ast::DUMMY_NODE_ID })