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 if self.token == token::Comma {
61 // An unexpected comma after a top-level pattern is a clue that the
62 // user (perhaps more accustomed to some other language) forgot the
63 // parentheses in what should have been a tuple pattern; return a
64 // suggestion-enhanced error here rather than choking on the comma
66 let comma_span = self.token.span;
68 if let Err(mut err) = self.skip_pat_list() {
69 // We didn't expect this to work anyway; we just wanted
70 // to advance to the end of the comma-sequence so we know
71 // the span to suggest parenthesizing
74 let seq_span = pat.span.to(self.prev_span);
75 let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
76 if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
79 "try adding parentheses to match on a tuple..",
80 format!("({})", seq_snippet),
81 Applicability::MachineApplicable
84 "..or a vertical bar to match on multiple alternatives",
85 format!("{}", seq_snippet.replace(",", " |")),
86 Applicability::MachineApplicable
94 /// Parse and throw away a parentesized comma separated
95 /// sequence of patterns until `)` is reached.
96 fn skip_pat_list(&mut self) -> PResult<'a, ()> {
97 while !self.check(&token::CloseDelim(token::Paren)) {
98 self.parse_pat(None)?;
99 if !self.eat(&token::Comma) {
106 /// Parses a pattern, that may be a or-pattern (e.g. `Some(Foo | Bar)`).
107 fn parse_pat_with_or(&mut self, expected: Expected, gate_or: bool) -> PResult<'a, P<Pat>> {
108 // Parse the first pattern.
109 let first_pat = self.parse_pat(expected)?;
111 // If the next token is not a `|`,
112 // this is not an or-pattern and we should exit here.
113 if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
117 let lo = first_pat.span;
118 let mut pats = vec![first_pat];
120 if self.token == token::OrOr {
121 // Found `||`; Recover and pretend we parsed `|`.
122 self.ban_unexpected_or_or();
124 } else if self.eat(&token::BinOp(token::Or)) {
125 // Found `|`. Working towards a proper or-pattern.
130 pats.push(self.parse_pat(expected)?);
132 let or_pattern_span = lo.to(self.prev_span);
134 // Feature gate the or-pattern if instructed:
136 self.sess.gated_spans.or_patterns.borrow_mut().push(or_pattern_span);
139 Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
142 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
144 fn parse_pat_with_range_pat(
146 allow_range_pat: bool,
148 ) -> PResult<'a, P<Pat>> {
149 maybe_recover_from_interpolated_ty_qpath!(self, true);
150 maybe_whole!(self, NtPat, |x| x);
152 let lo = self.token.span;
153 let pat = match self.token.kind {
154 token::BinOp(token::And) | token::AndAnd => self.parse_pat_deref(expected)?,
155 token::OpenDelim(token::Paren) => self.parse_pat_tuple_or_parens()?,
156 token::OpenDelim(token::Bracket) => {
157 // Parse `[pat, pat,...]` as a slice pattern.
158 let (pats, _) = self.parse_delim_comma_seq(
160 |p| p.parse_pat_with_or(None, true),
166 if self.is_pat_range_end_start() {
167 // Parse `..42` for recovery.
168 self.parse_pat_range_to(RangeEnd::Excluded, "..")?
170 // A rest pattern `..`.
175 // Parse `..=42` for recovery.
177 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotEq), "..=")?
179 token::DotDotDot => {
180 // Parse `...42` for recovery.
182 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotDot), "...")?
184 // At this point, token != &, &&, (, [
185 _ => if self.eat_keyword(kw::Underscore) {
188 } else if self.eat_keyword(kw::Mut) {
189 self.recover_pat_ident_mut_first()?
190 } else if self.eat_keyword(kw::Ref) {
191 // Parse ref ident @ pat / ref mut ident @ pat
192 let mutbl = self.parse_mutability();
193 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
194 } else if self.eat_keyword(kw::Box) {
196 PatKind::Box(self.parse_pat_with_range_pat(false, None)?)
197 } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
198 self.parse_as_ident() {
199 // Parse `ident @ pat`
200 // This can give false positives and parse nullary enums,
201 // they are dealt with later in resolve.
202 self.parse_pat_ident(BindingMode::ByValue(Mutability::Immutable))?
203 } else if self.token.is_path_start() {
204 // Parse pattern starting with a path
205 let (qself, path) = if self.eat_lt() {
206 // Parse a qualified path
207 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
210 // Parse an unqualified path
211 (None, self.parse_path(PathStyle::Expr)?)
213 match self.token.kind {
214 token::Not if qself.is_none() => self.parse_pat_mac_invoc(lo, path)?,
215 token::DotDotDot | token::DotDotEq | token::DotDot => {
216 self.parse_pat_range_starting_with_path(lo, qself, path)?
218 token::OpenDelim(token::Brace) => self.parse_pat_struct(qself, path)?,
219 token::OpenDelim(token::Paren) => self.parse_pat_tuple_struct(qself, path)?,
220 _ => PatKind::Path(qself, path),
223 // Try to parse everything else as literal with optional minus
224 match self.parse_literal_maybe_minus() {
226 if self.check(&token::DotDot)
227 || self.check(&token::DotDotEq)
228 || self.check(&token::DotDotDot) =>
230 self.parse_pat_range_starting_with_lit(begin)?
232 Ok(begin) => PatKind::Lit(begin),
233 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
238 let pat = self.mk_pat(lo.to(self.prev_span), pat);
239 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
241 if !allow_range_pat {
242 self.ban_pat_range_if_ambiguous(&pat)?
248 /// Ban a range pattern if it has an ambiguous interpretation.
249 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
252 .., Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
254 PatKind::Range(..) => {}
258 let mut err = self.struct_span_err(
260 "the range pattern here has ambiguous interpretation",
264 "add parentheses to clarify the precedence",
265 format!("({})", pprust::pat_to_string(&pat)),
266 // "ambiguous interpretation" implies that we have to be guessing
267 Applicability::MaybeIncorrect
272 /// Parse `&pat` / `&mut pat`.
273 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
275 let mutbl = self.parse_mutability();
277 if let token::Lifetime(name) = self.token.kind {
278 let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
279 err.span_label(self.token.span, "unexpected lifetime");
283 let subpat = self.parse_pat_with_range_pat(false, expected)?;
284 Ok(PatKind::Ref(subpat, mutbl))
287 /// Parse a tuple or parenthesis pattern.
288 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
289 let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
290 p.parse_pat_with_or(None, true)
293 // Here, `(pat,)` is a tuple pattern.
294 // For backward compatibility, `(..)` is a tuple pattern as well.
295 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
296 PatKind::Paren(fields.into_iter().nth(0).unwrap())
298 PatKind::Tuple(fields)
302 /// Recover on `mut ref? ident @ pat` and suggest
303 /// that the order of `mut` and `ref` is incorrect.
304 fn recover_pat_ident_mut_first(&mut self) -> PResult<'a, PatKind> {
305 let mutref_span = self.prev_span.to(self.token.span);
306 let binding_mode = if self.eat_keyword(kw::Ref) {
307 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
310 "try switching the order",
312 Applicability::MachineApplicable
315 BindingMode::ByRef(Mutability::Mutable)
317 BindingMode::ByValue(Mutability::Mutable)
319 self.parse_pat_ident(binding_mode)
322 /// Parse macro invocation
323 fn parse_pat_mac_invoc(&mut self, lo: Span, path: Path) -> PResult<'a, PatKind> {
325 let (delim, tts) = self.expect_delimited_token_tree()?;
330 span: lo.to(self.prev_span),
331 prior_type_ascription: self.last_type_ascription,
333 Ok(PatKind::Mac(mac))
336 /// Parse a range pattern `$path $form $end?` where `$form = ".." | "..." | "..=" ;`.
337 /// The `$path` has already been parsed and the next token is the `$form`.
338 fn parse_pat_range_starting_with_path(
341 qself: Option<QSelf>,
343 ) -> PResult<'a, PatKind> {
344 let (end_kind, form) = match self.token.kind {
345 token::DotDot => (RangeEnd::Excluded, ".."),
346 token::DotDotDot => (RangeEnd::Included(RangeSyntax::DotDotDot), "..."),
347 token::DotDotEq => (RangeEnd::Included(RangeSyntax::DotDotEq), "..="),
348 _ => panic!("can only parse `..`/`...`/`..=` for ranges (checked above)"),
350 let op_span = self.token.span;
352 let span = lo.to(self.prev_span);
353 let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
355 let end = self.parse_pat_range_end_opt(&begin, form)?;
356 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
359 /// Parse a range pattern `$literal $form $end?` where `$form = ".." | "..." | "..=" ;`.
360 /// The `$path` has already been parsed and the next token is the `$form`.
361 fn parse_pat_range_starting_with_lit(&mut self, begin: P<Expr>) -> PResult<'a, PatKind> {
362 let op_span = self.token.span;
363 let (end_kind, form) = if self.eat(&token::DotDotDot) {
364 (RangeEnd::Included(RangeSyntax::DotDotDot), "...")
365 } else if self.eat(&token::DotDotEq) {
366 (RangeEnd::Included(RangeSyntax::DotDotEq), "..=")
367 } else if self.eat(&token::DotDot) {
368 (RangeEnd::Excluded, "..")
370 panic!("impossible case: we already matched on a range-operator token")
372 let end = self.parse_pat_range_end_opt(&begin, form)?;
373 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
376 fn fatal_unexpected_non_pat(
378 mut err: DiagnosticBuilder<'a>,
380 ) -> PResult<'a, P<Pat>> {
381 self.cancel(&mut err);
383 let expected = expected.unwrap_or("pattern");
384 let msg = format!("expected {}, found {}", expected, self.this_token_descr());
386 let mut err = self.fatal(&msg);
387 err.span_label(self.token.span, format!("expected {}", expected));
389 let sp = self.sess.source_map().start_point(self.token.span);
390 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
391 self.sess.expr_parentheses_needed(&mut err, *sp, None);
397 // Helper function to decide whether to parse as ident binding
398 // or to try to do something more complex like range patterns.
399 fn parse_as_ident(&mut self) -> bool {
400 self.look_ahead(1, |t| match t.kind {
401 token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
402 token::DotDotDot | token::DotDotEq | token::DotDot |
403 token::ModSep | token::Not => false,
408 /// Is the current token suitable as the start of a range patterns end?
409 fn is_pat_range_end_start(&self) -> bool {
410 self.token.is_path_start() // e.g. `MY_CONST`;
411 || self.token == token::Dot // e.g. `.5` for recovery;
412 || self.token.can_begin_literal_or_bool() // e.g. `42`.
413 || self.token.is_whole_expr()
416 /// Parse a range-to pattern, e.g. `..X` and `..=X` for recovery.
417 fn parse_pat_range_to(&mut self, re: RangeEnd, form: &str) -> PResult<'a, PatKind> {
418 let lo = self.prev_span;
419 let end = self.parse_pat_range_end()?;
420 let range_span = lo.to(end.span);
421 let begin = self.mk_expr(range_span, ExprKind::Err, ThinVec::new());
424 .struct_span_err(range_span, &format!("`{}X` range patterns are not supported", form))
427 "try using the minimum value for the type",
428 format!("MIN{}{}", form, pprust::expr_to_string(&end)),
429 Applicability::HasPlaceholders,
433 Ok(PatKind::Range(begin, end, respan(lo, re)))
436 /// Parse the end of a `X..Y`, `X..=Y`, or `X...Y` range pattern or recover
437 /// if that end is missing treating it as `X..`, `X..=`, or `X...` respectively.
438 fn parse_pat_range_end_opt(&mut self, begin: &Expr, form: &str) -> PResult<'a, P<Expr>> {
439 if self.is_pat_range_end_start() {
440 // Parsing e.g. `X..=Y`.
441 self.parse_pat_range_end()
443 // Parsing e.g. `X..`.
444 let range_span = begin.span.to(self.prev_span);
449 &format!("`X{}` range patterns are not supported", form),
453 "try using the maximum value for the type",
454 format!("{}{}MAX", pprust::expr_to_string(&begin), form),
455 Applicability::HasPlaceholders,
459 Ok(self.mk_expr(range_span, ExprKind::Err, ThinVec::new()))
463 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
464 if self.token.is_path_start() {
465 let lo = self.token.span;
466 let (qself, path) = if self.eat_lt() {
467 // Parse a qualified path
468 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
471 // Parse an unqualified path
472 (None, self.parse_path(PathStyle::Expr)?)
474 let hi = self.prev_span;
475 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
477 self.parse_literal_maybe_minus()
481 /// Parses `ident` or `ident @ pat`.
482 /// Used by the copy foo and ref foo patterns to give a good
483 /// error message when parsing mistakes like `ref foo(a, b)`.
484 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
485 let ident = self.parse_ident()?;
486 let sub = if self.eat(&token::At) {
487 Some(self.parse_pat(Some("binding pattern"))?)
492 // Just to be friendly, if they write something like `ref Some(i)`,
493 // we end up here with `(` as the current token.
494 // This shortly leads to a parse error. Note that if there is no explicit
495 // binding mode then we do not end up here, because the lookahead
496 // will direct us over to `parse_enum_variant()`.
497 if self.token == token::OpenDelim(token::Paren) {
498 return Err(self.span_fatal(
500 "expected identifier, found enum pattern",
504 Ok(PatKind::Ident(binding_mode, ident, sub))
507 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
508 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
510 let msg = "unexpected `{` after qualified path";
511 let mut err = self.fatal(msg);
512 err.span_label(self.token.span, msg);
517 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
523 Ok(PatKind::Struct(path, fields, etc))
526 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
527 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
529 let msg = "unexpected `(` after qualified path";
530 let mut err = self.fatal(msg);
531 err.span_label(self.token.span, msg);
534 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or(None, true))?;
535 Ok(PatKind::TupleStruct(path, fields))
538 /// Parses the fields of a struct-like pattern.
539 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
540 let mut fields = Vec::new();
542 let mut ate_comma = true;
543 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
544 let mut etc_span = None;
546 while self.token != token::CloseDelim(token::Brace) {
547 let attrs = match self.parse_outer_attributes() {
550 if let Some(mut delayed) = delayed_err {
556 let lo = self.token.span;
558 // check that a comma comes after every field
560 let err = self.struct_span_err(self.prev_span, "expected `,`");
561 if let Some(mut delayed) = delayed_err {
568 if self.check(&token::DotDot) || self.token == token::DotDotDot {
570 let mut etc_sp = self.token.span;
572 self.recover_one_fewer_dotdot();
573 self.bump(); // `..` || `...`
575 if self.token == token::CloseDelim(token::Brace) {
576 etc_span = Some(etc_sp);
579 let token_str = self.this_token_descr();
580 let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
582 err.span_label(self.token.span, "expected `}`");
583 let mut comma_sp = None;
584 if self.token == token::Comma { // Issue #49257
585 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
586 etc_sp = etc_sp.to(nw_span);
587 err.span_label(etc_sp,
588 "`..` must be at the end and cannot have a trailing comma");
589 comma_sp = Some(self.token.span);
594 etc_span = Some(etc_sp.until(self.token.span));
595 if self.token == token::CloseDelim(token::Brace) {
596 // If the struct looks otherwise well formed, recover and continue.
597 if let Some(sp) = comma_sp {
598 err.span_suggestion_short(
602 Applicability::MachineApplicable,
607 } else if self.token.is_ident() && ate_comma {
608 // Accept fields coming after `..,`.
609 // This way we avoid "pattern missing fields" errors afterwards.
610 // We delay this error until the end in order to have a span for a
612 if let Some(mut delayed_err) = delayed_err {
616 delayed_err = Some(err);
619 if let Some(mut err) = delayed_err {
626 fields.push(match self.parse_pat_field(lo, attrs) {
629 if let Some(mut delayed_err) = delayed_err {
635 ate_comma = self.eat(&token::Comma);
638 if let Some(mut err) = delayed_err {
639 if let Some(etc_span) = etc_span {
640 err.multipart_suggestion(
641 "move the `..` to the end of the field list",
643 (etc_span, String::new()),
644 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
646 Applicability::MachineApplicable,
651 return Ok((fields, etc));
654 /// Recover on `...` as if it were `..` to avoid further errors.
655 /// See issue #46718.
656 fn recover_one_fewer_dotdot(&self) {
657 if self.token != token::DotDotDot {
661 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
664 "to omit remaining fields, use one fewer `.`",
666 Applicability::MachineApplicable
671 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
672 // Check if a colon exists one ahead. This means we're parsing a fieldname.
674 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
675 // Parsing a pattern of the form "fieldname: pat"
676 let fieldname = self.parse_field_name()?;
678 let pat = self.parse_pat_with_or(None, true)?;
680 (pat, fieldname, false)
682 // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
683 let is_box = self.eat_keyword(kw::Box);
684 let boxed_span = self.token.span;
685 let is_ref = self.eat_keyword(kw::Ref);
686 let is_mut = self.eat_keyword(kw::Mut);
687 let fieldname = self.parse_ident()?;
690 let bind_type = match (is_ref, is_mut) {
691 (true, true) => BindingMode::ByRef(Mutability::Mutable),
692 (true, false) => BindingMode::ByRef(Mutability::Immutable),
693 (false, true) => BindingMode::ByValue(Mutability::Mutable),
694 (false, false) => BindingMode::ByValue(Mutability::Immutable),
697 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
698 let subpat = if is_box {
699 self.mk_pat(lo.to(hi), PatKind::Box(fieldpat))
703 (subpat, fieldname, true)
711 id: ast::DUMMY_NODE_ID,
716 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
717 self.mk_pat(span, PatKind::Ident(bm, ident, None))
720 fn mk_pat(&self, span: Span, node: PatKind) -> P<Pat> {
721 P(Pat { node, span, id: ast::DUMMY_NODE_ID })