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)) {
117 let lo = first_pat.span;
119 let mut pats = vec![first_pat];
121 while self.eat(&token::BinOp(token::Or)) {
122 pats.push(self.parse_pat_with_range_pat(true, expected)?);
125 let or_pattern_span = lo.to(self.prev_span);
127 // Feature gate the or-pattern if instructed:
129 self.sess.gated_spans.or_patterns.borrow_mut().push(or_pattern_span);
132 Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
135 /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
137 fn parse_pat_with_range_pat(
139 allow_range_pat: bool,
141 ) -> PResult<'a, P<Pat>> {
142 maybe_recover_from_interpolated_ty_qpath!(self, true);
143 maybe_whole!(self, NtPat, |x| x);
145 let lo = self.token.span;
146 let pat = match self.token.kind {
147 token::BinOp(token::And) | token::AndAnd => self.parse_pat_deref(expected)?,
148 token::OpenDelim(token::Paren) => self.parse_pat_tuple_or_parens()?,
149 token::OpenDelim(token::Bracket) => {
150 // Parse `[pat, pat,...]` as a slice pattern.
151 let (pats, _) = self.parse_delim_comma_seq(
153 |p| p.parse_pat_with_or(None, true),
159 if self.is_pat_range_end_start() {
160 // Parse `..42` for recovery.
161 self.parse_pat_range_to(RangeEnd::Excluded, "..")?
163 // A rest pattern `..`.
168 // Parse `..=42` for recovery.
170 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotEq), "..=")?
172 token::DotDotDot => {
173 // Parse `...42` for recovery.
175 self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotDot), "...")?
177 // At this point, token != &, &&, (, [
178 _ => if self.eat_keyword(kw::Underscore) {
181 } else if self.eat_keyword(kw::Mut) {
182 self.recover_pat_ident_mut_first()?
183 } else if self.eat_keyword(kw::Ref) {
184 // Parse ref ident @ pat / ref mut ident @ pat
185 let mutbl = self.parse_mutability();
186 self.parse_pat_ident(BindingMode::ByRef(mutbl))?
187 } else if self.eat_keyword(kw::Box) {
189 PatKind::Box(self.parse_pat_with_range_pat(false, None)?)
190 } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
191 self.parse_as_ident() {
192 // Parse `ident @ pat`
193 // This can give false positives and parse nullary enums,
194 // they are dealt with later in resolve.
195 self.parse_pat_ident(BindingMode::ByValue(Mutability::Immutable))?
196 } else if self.token.is_path_start() {
197 // Parse pattern starting with a path
198 let (qself, path) = if self.eat_lt() {
199 // Parse a qualified path
200 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
203 // Parse an unqualified path
204 (None, self.parse_path(PathStyle::Expr)?)
206 match self.token.kind {
207 token::Not if qself.is_none() => self.parse_pat_mac_invoc(lo, path)?,
208 token::DotDotDot | token::DotDotEq | token::DotDot => {
209 self.parse_pat_range_starting_with_path(lo, qself, path)?
211 token::OpenDelim(token::Brace) => self.parse_pat_struct(qself, path)?,
212 token::OpenDelim(token::Paren) => self.parse_pat_tuple_struct(qself, path)?,
213 _ => PatKind::Path(qself, path),
216 // Try to parse everything else as literal with optional minus
217 match self.parse_literal_maybe_minus() {
219 if self.check(&token::DotDot)
220 || self.check(&token::DotDotEq)
221 || self.check(&token::DotDotDot) =>
223 self.parse_pat_range_starting_with_lit(begin)?
225 Ok(begin) => PatKind::Lit(begin),
226 Err(err) => return self.fatal_unexpected_non_pat(err, expected),
231 let pat = self.mk_pat(lo.to(self.prev_span), pat);
232 let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
234 if !allow_range_pat {
235 self.ban_pat_range_if_ambiguous(&pat)?
241 /// Ban a range pattern if it has an ambiguous interpretation.
242 fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
245 .., Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
247 PatKind::Range(..) => {}
251 let mut err = self.struct_span_err(
253 "the range pattern here has ambiguous interpretation",
257 "add parentheses to clarify the precedence",
258 format!("({})", pprust::pat_to_string(&pat)),
259 // "ambiguous interpretation" implies that we have to be guessing
260 Applicability::MaybeIncorrect
265 /// Parse `&pat` / `&mut pat`.
266 fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
268 let mutbl = self.parse_mutability();
270 if let token::Lifetime(name) = self.token.kind {
271 let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
272 err.span_label(self.token.span, "unexpected lifetime");
276 let subpat = self.parse_pat_with_range_pat(false, expected)?;
277 Ok(PatKind::Ref(subpat, mutbl))
280 /// Parse a tuple or parenthesis pattern.
281 fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
282 let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
283 p.parse_pat_with_or(None, true)
286 // Here, `(pat,)` is a tuple pattern.
287 // For backward compatibility, `(..)` is a tuple pattern as well.
288 Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
289 PatKind::Paren(fields.into_iter().nth(0).unwrap())
291 PatKind::Tuple(fields)
295 /// Recover on `mut ref? ident @ pat` and suggest
296 /// that the order of `mut` and `ref` is incorrect.
297 fn recover_pat_ident_mut_first(&mut self) -> PResult<'a, PatKind> {
298 let mutref_span = self.prev_span.to(self.token.span);
299 let binding_mode = if self.eat_keyword(kw::Ref) {
300 self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
303 "try switching the order",
305 Applicability::MachineApplicable
308 BindingMode::ByRef(Mutability::Mutable)
310 BindingMode::ByValue(Mutability::Mutable)
312 self.parse_pat_ident(binding_mode)
315 /// Parse macro invocation
316 fn parse_pat_mac_invoc(&mut self, lo: Span, path: Path) -> PResult<'a, PatKind> {
318 let (delim, tts) = self.expect_delimited_token_tree()?;
323 span: lo.to(self.prev_span),
324 prior_type_ascription: self.last_type_ascription,
326 Ok(PatKind::Mac(mac))
329 /// Parse a range pattern `$path $form $end?` where `$form = ".." | "..." | "..=" ;`.
330 /// The `$path` has already been parsed and the next token is the `$form`.
331 fn parse_pat_range_starting_with_path(
334 qself: Option<QSelf>,
336 ) -> PResult<'a, PatKind> {
337 let (end_kind, form) = match self.token.kind {
338 token::DotDot => (RangeEnd::Excluded, ".."),
339 token::DotDotDot => (RangeEnd::Included(RangeSyntax::DotDotDot), "..."),
340 token::DotDotEq => (RangeEnd::Included(RangeSyntax::DotDotEq), "..="),
341 _ => panic!("can only parse `..`/`...`/`..=` for ranges (checked above)"),
343 let op_span = self.token.span;
345 let span = lo.to(self.prev_span);
346 let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
348 let end = self.parse_pat_range_end_opt(&begin, form)?;
349 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
352 /// Parse a range pattern `$literal $form $end?` where `$form = ".." | "..." | "..=" ;`.
353 /// The `$path` has already been parsed and the next token is the `$form`.
354 fn parse_pat_range_starting_with_lit(&mut self, begin: P<Expr>) -> PResult<'a, PatKind> {
355 let op_span = self.token.span;
356 let (end_kind, form) = if self.eat(&token::DotDotDot) {
357 (RangeEnd::Included(RangeSyntax::DotDotDot), "...")
358 } else if self.eat(&token::DotDotEq) {
359 (RangeEnd::Included(RangeSyntax::DotDotEq), "..=")
360 } else if self.eat(&token::DotDot) {
361 (RangeEnd::Excluded, "..")
363 panic!("impossible case: we already matched on a range-operator token")
365 let end = self.parse_pat_range_end_opt(&begin, form)?;
366 Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
369 fn fatal_unexpected_non_pat(
371 mut err: DiagnosticBuilder<'a>,
373 ) -> PResult<'a, P<Pat>> {
374 self.cancel(&mut err);
376 let expected = expected.unwrap_or("pattern");
377 let msg = format!("expected {}, found {}", expected, self.this_token_descr());
379 let mut err = self.fatal(&msg);
380 err.span_label(self.token.span, format!("expected {}", expected));
382 let sp = self.sess.source_map().start_point(self.token.span);
383 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
384 self.sess.expr_parentheses_needed(&mut err, *sp, None);
390 // Helper function to decide whether to parse as ident binding
391 // or to try to do something more complex like range patterns.
392 fn parse_as_ident(&mut self) -> bool {
393 self.look_ahead(1, |t| match t.kind {
394 token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
395 token::DotDotDot | token::DotDotEq | token::DotDot |
396 token::ModSep | token::Not => false,
401 /// Is the current token suitable as the start of a range patterns end?
402 fn is_pat_range_end_start(&self) -> bool {
403 self.token.is_path_start() // e.g. `MY_CONST`;
404 || self.token == token::Dot // e.g. `.5` for recovery;
405 || self.token.can_begin_literal_or_bool() // e.g. `42`.
406 || self.token.is_whole_expr()
409 /// Parse a range-to pattern, e.g. `..X` and `..=X` for recovery.
410 fn parse_pat_range_to(&mut self, re: RangeEnd, form: &str) -> PResult<'a, PatKind> {
411 let lo = self.prev_span;
412 let end = self.parse_pat_range_end()?;
413 let range_span = lo.to(end.span);
414 let begin = self.mk_expr(range_span, ExprKind::Err, ThinVec::new());
417 .struct_span_err(range_span, &format!("`{}X` range patterns are not supported", form))
420 "try using the minimum value for the type",
421 format!("MIN{}{}", form, pprust::expr_to_string(&end)),
422 Applicability::HasPlaceholders,
426 Ok(PatKind::Range(begin, end, respan(lo, re)))
429 /// Parse the end of a `X..Y`, `X..=Y`, or `X...Y` range pattern or recover
430 /// if that end is missing treating it as `X..`, `X..=`, or `X...` respectively.
431 fn parse_pat_range_end_opt(&mut self, begin: &Expr, form: &str) -> PResult<'a, P<Expr>> {
432 if self.is_pat_range_end_start() {
433 // Parsing e.g. `X..=Y`.
434 self.parse_pat_range_end()
436 // Parsing e.g. `X..`.
437 let range_span = begin.span.to(self.prev_span);
442 &format!("`X{}` range patterns are not supported", form),
446 "try using the maximum value for the type",
447 format!("{}{}MAX", pprust::expr_to_string(&begin), form),
448 Applicability::HasPlaceholders,
452 Ok(self.mk_expr(range_span, ExprKind::Err, ThinVec::new()))
456 fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
457 if self.token.is_path_start() {
458 let lo = self.token.span;
459 let (qself, path) = if self.eat_lt() {
460 // Parse a qualified path
461 let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
464 // Parse an unqualified path
465 (None, self.parse_path(PathStyle::Expr)?)
467 let hi = self.prev_span;
468 Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
470 self.parse_literal_maybe_minus()
474 /// Parses `ident` or `ident @ pat`.
475 /// Used by the copy foo and ref foo patterns to give a good
476 /// error message when parsing mistakes like `ref foo(a, b)`.
477 fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
478 let ident = self.parse_ident()?;
479 let sub = if self.eat(&token::At) {
480 Some(self.parse_pat(Some("binding pattern"))?)
485 // Just to be friendly, if they write something like `ref Some(i)`,
486 // we end up here with `(` as the current token.
487 // This shortly leads to a parse error. Note that if there is no explicit
488 // binding mode then we do not end up here, because the lookahead
489 // will direct us over to `parse_enum_variant()`.
490 if self.token == token::OpenDelim(token::Paren) {
491 return Err(self.span_fatal(
493 "expected identifier, found enum pattern",
497 Ok(PatKind::Ident(binding_mode, ident, sub))
500 /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
501 fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
503 let msg = "unexpected `{` after qualified path";
504 let mut err = self.fatal(msg);
505 err.span_label(self.token.span, msg);
510 let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
516 Ok(PatKind::Struct(path, fields, etc))
519 /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
520 fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
522 let msg = "unexpected `(` after qualified path";
523 let mut err = self.fatal(msg);
524 err.span_label(self.token.span, msg);
527 let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or(None, true))?;
528 Ok(PatKind::TupleStruct(path, fields))
531 /// Parses the fields of a struct-like pattern.
532 fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
533 let mut fields = Vec::new();
535 let mut ate_comma = true;
536 let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
537 let mut etc_span = None;
539 while self.token != token::CloseDelim(token::Brace) {
540 let attrs = match self.parse_outer_attributes() {
543 if let Some(mut delayed) = delayed_err {
549 let lo = self.token.span;
551 // check that a comma comes after every field
553 let err = self.struct_span_err(self.prev_span, "expected `,`");
554 if let Some(mut delayed) = delayed_err {
561 if self.check(&token::DotDot) || self.token == token::DotDotDot {
563 let mut etc_sp = self.token.span;
565 self.recover_one_fewer_dotdot();
566 self.bump(); // `..` || `...`
568 if self.token == token::CloseDelim(token::Brace) {
569 etc_span = Some(etc_sp);
572 let token_str = self.this_token_descr();
573 let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
575 err.span_label(self.token.span, "expected `}`");
576 let mut comma_sp = None;
577 if self.token == token::Comma { // Issue #49257
578 let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
579 etc_sp = etc_sp.to(nw_span);
580 err.span_label(etc_sp,
581 "`..` must be at the end and cannot have a trailing comma");
582 comma_sp = Some(self.token.span);
587 etc_span = Some(etc_sp.until(self.token.span));
588 if self.token == token::CloseDelim(token::Brace) {
589 // If the struct looks otherwise well formed, recover and continue.
590 if let Some(sp) = comma_sp {
591 err.span_suggestion_short(
595 Applicability::MachineApplicable,
600 } else if self.token.is_ident() && ate_comma {
601 // Accept fields coming after `..,`.
602 // This way we avoid "pattern missing fields" errors afterwards.
603 // We delay this error until the end in order to have a span for a
605 if let Some(mut delayed_err) = delayed_err {
609 delayed_err = Some(err);
612 if let Some(mut err) = delayed_err {
619 fields.push(match self.parse_pat_field(lo, attrs) {
622 if let Some(mut delayed_err) = delayed_err {
628 ate_comma = self.eat(&token::Comma);
631 if let Some(mut err) = delayed_err {
632 if let Some(etc_span) = etc_span {
633 err.multipart_suggestion(
634 "move the `..` to the end of the field list",
636 (etc_span, String::new()),
637 (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
639 Applicability::MachineApplicable,
644 return Ok((fields, etc));
647 /// Recover on `...` as if it were `..` to avoid further errors.
648 /// See issue #46718.
649 fn recover_one_fewer_dotdot(&self) {
650 if self.token != token::DotDotDot {
654 self.struct_span_err(self.token.span, "expected field pattern, found `...`")
657 "to omit remaining fields, use one fewer `.`",
659 Applicability::MachineApplicable
664 fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
665 // Check if a colon exists one ahead. This means we're parsing a fieldname.
667 let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
668 // Parsing a pattern of the form "fieldname: pat"
669 let fieldname = self.parse_field_name()?;
671 let pat = self.parse_pat_with_or(None, true)?;
673 (pat, fieldname, false)
675 // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
676 let is_box = self.eat_keyword(kw::Box);
677 let boxed_span = self.token.span;
678 let is_ref = self.eat_keyword(kw::Ref);
679 let is_mut = self.eat_keyword(kw::Mut);
680 let fieldname = self.parse_ident()?;
683 let bind_type = match (is_ref, is_mut) {
684 (true, true) => BindingMode::ByRef(Mutability::Mutable),
685 (true, false) => BindingMode::ByRef(Mutability::Immutable),
686 (false, true) => BindingMode::ByValue(Mutability::Mutable),
687 (false, false) => BindingMode::ByValue(Mutability::Immutable),
690 let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
691 let subpat = if is_box {
692 self.mk_pat(lo.to(hi), PatKind::Box(fieldpat))
696 (subpat, fieldname, true)
704 id: ast::DUMMY_NODE_ID,
709 pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
710 self.mk_pat(span, PatKind::Ident(bm, ident, None))
713 fn mk_pat(&self, span: Span, node: PatKind) -> P<Pat> {
714 P(Pat { node, span, id: ast::DUMMY_NODE_ID })