1 use super::ty
::{AllowPlus, RecoverQPath, RecoverReturnSign}
;
2 use super::{Parser, TokenType}
;
3 use crate::maybe_whole
;
5 use rustc_ast
::token
::{self, Token}
;
6 use rustc_ast
::{self as ast, AngleBracketedArg, AngleBracketedArgs, ParenthesizedArgs}
;
7 use rustc_ast
::{AnonConst, AssocTyConstraint, AssocTyConstraintKind, BlockCheckMode}
;
8 use rustc_ast
::{GenericArg, GenericArgs}
;
9 use rustc_ast
::{Path, PathSegment, QSelf}
;
10 use rustc_errors
::{pluralize, Applicability, PResult}
;
11 use rustc_span
::source_map
::{BytePos, Span}
;
12 use rustc_span
::symbol
::{kw, sym, Ident}
;
17 /// Specifies how to parse a path.
18 #[derive(Copy, Clone, PartialEq)]
20 /// In some contexts, notably in expressions, paths with generic arguments are ambiguous
21 /// with something else. For example, in expressions `segment < ....` can be interpreted
22 /// as a comparison and `segment ( ....` can be interpreted as a function call.
23 /// In all such contexts the non-path interpretation is preferred by default for practical
24 /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g.
25 /// `x<y>` - comparisons, `x::<y>` - unambiguously a path.
27 /// In other contexts, notably in types, no ambiguity exists and paths can be written
28 /// without the disambiguator, e.g., `x<y>` - unambiguously a path.
29 /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too.
31 /// A path with generic arguments disallowed, e.g., `foo::bar::Baz`, used in imports,
32 /// visibilities or attributes.
33 /// Technically, this variant is unnecessary and e.g., `Expr` can be used instead
34 /// (paths in "mod" contexts have to be checked later for absence of generic arguments
35 /// anyway, due to macros), but it is used to avoid weird suggestions about expected
36 /// tokens when something goes wrong.
41 /// Parses a qualified path.
42 /// Assumes that the leading `<` has been parsed already.
44 /// `qualified_path = <type [as trait_ref]>::path`
49 /// `<T as U>::F::a<S>` (without disambiguator)
50 /// `<T as U>::F::a::<S>` (with disambiguator)
51 pub(super) fn parse_qpath(&mut self, style
: PathStyle
) -> PResult
<'a
, (QSelf
, Path
)> {
52 let lo
= self.prev_token
.span
;
53 let ty
= self.parse_ty()?
;
55 // `path` will contain the prefix of the path up to the `>`,
56 // if any (e.g., `U` in the `<T as U>::*` examples
57 // above). `path_span` has the span of that path, or an empty
58 // span in the case of something like `<T>::Bar`.
59 let (mut path
, path_span
);
60 if self.eat_keyword(kw
::As
) {
61 let path_lo
= self.token
.span
;
62 path
= self.parse_path(PathStyle
::Type
)?
;
63 path_span
= path_lo
.to(self.prev_token
.span
);
65 path_span
= self.token
.span
.to(self.token
.span
);
66 path
= ast
::Path { segments: Vec::new(), span: path_span, tokens: None }
;
69 // See doc comment for `unmatched_angle_bracket_count`.
70 self.expect(&token
::Gt
)?
;
71 if self.unmatched_angle_bracket_count
> 0 {
72 self.unmatched_angle_bracket_count
-= 1;
73 debug
!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count
);
76 if !self.recover_colon_before_qpath_proj() {
77 self.expect(&token
::ModSep
)?
;
80 let qself
= QSelf { ty, path_span, position: path.segments.len() }
;
81 self.parse_path_segments(&mut path
.segments
, style
)?
;
85 Path { segments: path.segments, span: lo.to(self.prev_token.span), tokens: None }
,
89 /// Recover from an invalid single colon, when the user likely meant a qualified path.
90 /// We avoid emitting this if not followed by an identifier, as our assumption that the user
91 /// intended this to be a qualified path may not be correct.
93 /// ```ignore (diagnostics)
94 /// <Bar as Baz<T>>:Qux
95 /// ^ help: use double colon
97 fn recover_colon_before_qpath_proj(&mut self) -> bool
{
98 if self.token
.kind
!= token
::Colon
99 || self.look_ahead(1, |t
| !t
.is_ident() || t
.is_reserved_ident())
104 self.bump(); // colon
108 self.prev_token
.span
,
109 "found single colon before projection in qualified path",
112 self.prev_token
.span
,
115 Applicability
::MachineApplicable
,
122 /// Parses simple paths.
124 /// `path = [::] segment+`
125 /// `segment = ident | ident[::]<args> | ident[::](args) [-> type]`
128 /// `a::b::C<D>` (without disambiguator)
129 /// `a::b::C::<D>` (with disambiguator)
130 /// `Fn(Args)` (without disambiguator)
131 /// `Fn::(Args)` (with disambiguator)
132 pub(super) fn parse_path(&mut self, style
: PathStyle
) -> PResult
<'a
, Path
> {
133 maybe_whole
!(self, NtPath
, |path
| {
134 if style
== PathStyle
::Mod
&& path
.segments
.iter().any(|segment
| segment
.args
.is_some())
136 self.struct_span_err(
139 .filter_map(|segment
| segment
.args
.as_ref())
140 .map(|arg
| arg
.span())
141 .collect
::<Vec
<_
>>(),
142 "unexpected generic arguments in path",
149 let lo
= self.token
.span
;
150 let mut segments
= Vec
::new();
151 let mod_sep_ctxt
= self.token
.span
.ctxt();
152 if self.eat(&token
::ModSep
) {
153 segments
.push(PathSegment
::path_root(lo
.shrink_to_lo().with_ctxt(mod_sep_ctxt
)));
155 self.parse_path_segments(&mut segments
, style
)?
;
157 Ok(Path { segments, span: lo.to(self.prev_token.span), tokens: None }
)
160 pub(super) fn parse_path_segments(
162 segments
: &mut Vec
<PathSegment
>,
164 ) -> PResult
<'a
, ()> {
166 let segment
= self.parse_path_segment(style
)?
;
167 if style
== PathStyle
::Expr
{
168 // In order to check for trailing angle brackets, we must have finished
169 // recursing (`parse_path_segment` can indirectly call this function),
170 // that is, the next token must be the highlighted part of the below example:
172 // `Foo::<Bar as Baz<T>>::Qux`
175 // As opposed to the below highlight (if we had only finished the first
178 // `Foo::<Bar as Baz<T>>::Qux`
181 // `PathStyle::Expr` is only provided at the root invocation and never in
182 // `parse_path_segment` to recurse and therefore can be checked to maintain
184 self.check_trailing_angle_brackets(&segment
, &[&token
::ModSep
]);
186 segments
.push(segment
);
188 if self.is_import_coupler() || !self.eat(&token
::ModSep
) {
194 pub(super) fn parse_path_segment(&mut self, style
: PathStyle
) -> PResult
<'a
, PathSegment
> {
195 let ident
= self.parse_path_segment_ident()?
;
196 let is_args_start
= |token
: &Token
| {
200 | token
::BinOp(token
::Shl
)
201 | token
::OpenDelim(token
::Paren
)
205 let check_args_start
= |this
: &mut Self| {
206 this
.expected_tokens
.extend_from_slice(&[
207 TokenType
::Token(token
::Lt
),
208 TokenType
::Token(token
::OpenDelim(token
::Paren
)),
210 is_args_start(&this
.token
)
214 if style
== PathStyle
::Type
&& check_args_start(self)
215 || style
!= PathStyle
::Mod
216 && self.check(&token
::ModSep
)
217 && self.look_ahead(1, |t
| is_args_start(t
))
219 // We use `style == PathStyle::Expr` to check if this is in a recursion or not. If
220 // it isn't, then we reset the unmatched angle bracket count as we're about to start
221 // parsing a new path.
222 if style
== PathStyle
::Expr
{
223 self.unmatched_angle_bracket_count
= 0;
224 self.max_angle_bracket_count
= 0;
227 // Generic arguments are found - `<`, `(`, `::<` or `::(`.
228 self.eat(&token
::ModSep
);
229 let lo
= self.token
.span
;
230 let args
= if self.eat_lt() {
233 self.parse_angle_args_with_leading_angle_bracket_recovery(style
, lo
)?
;
235 let span
= lo
.to(self.prev_token
.span
);
236 AngleBracketedArgs { args, span }
.into()
239 let (inputs
, _
) = self.parse_paren_comma_seq(|p
| p
.parse_ty())?
;
240 let inputs_span
= lo
.to(self.prev_token
.span
);
241 let span
= ident
.span
.to(self.prev_token
.span
);
243 self.parse_ret_ty(AllowPlus
::No
, RecoverQPath
::No
, RecoverReturnSign
::No
)?
;
244 ParenthesizedArgs { span, inputs, inputs_span, output }
.into()
247 PathSegment { ident, args, id: ast::DUMMY_NODE_ID }
249 // Generic arguments are not found.
250 PathSegment
::from_ident(ident
)
255 pub(super) fn parse_path_segment_ident(&mut self) -> PResult
<'a
, Ident
> {
256 match self.token
.ident() {
257 Some((ident
, false)) if ident
.is_path_segment_keyword() => {
261 _
=> self.parse_ident(),
265 /// Parses generic args (within a path segment) with recovery for extra leading angle brackets.
266 /// For the purposes of understanding the parsing logic of generic arguments, this function
267 /// can be thought of being the same as just calling `self.parse_angle_args()` if the source
268 /// had the correct amount of leading angle brackets.
270 /// ```ignore (diagnostics)
271 /// bar::<<<<T as Foo>::Output>();
272 /// ^^ help: remove extra angle brackets
274 fn parse_angle_args_with_leading_angle_bracket_recovery(
278 ) -> PResult
<'a
, Vec
<AngleBracketedArg
>> {
279 // We need to detect whether there are extra leading left angle brackets and produce an
280 // appropriate error and suggestion. This cannot be implemented by looking ahead at
281 // upcoming tokens for a matching `>` character - if there are unmatched `<` tokens
282 // then there won't be matching `>` tokens to find.
284 // To explain how this detection works, consider the following example:
286 // ```ignore (diagnostics)
287 // bar::<<<<T as Foo>::Output>();
288 // ^^ help: remove extra angle brackets
291 // Parsing of the left angle brackets starts in this function. We start by parsing the
292 // `<` token (incrementing the counter of unmatched angle brackets on `Parser` via
295 // *Upcoming tokens:* `<<<<T as Foo>::Output>;`
296 // *Unmatched count:* 1
297 // *`parse_path_segment` calls deep:* 0
299 // This has the effect of recursing as this function is called if a `<` character
300 // is found within the expected generic arguments:
302 // *Upcoming tokens:* `<<<T as Foo>::Output>;`
303 // *Unmatched count:* 2
304 // *`parse_path_segment` calls deep:* 1
306 // Eventually we will have recursed until having consumed all of the `<` tokens and
307 // this will be reflected in the count:
309 // *Upcoming tokens:* `T as Foo>::Output>;`
310 // *Unmatched count:* 4
311 // `parse_path_segment` calls deep:* 3
313 // The parser will continue until reaching the first `>` - this will decrement the
314 // unmatched angle bracket count and return to the parent invocation of this function
315 // having succeeded in parsing:
317 // *Upcoming tokens:* `::Output>;`
318 // *Unmatched count:* 3
319 // *`parse_path_segment` calls deep:* 2
321 // This will continue until the next `>` character which will also return successfully
322 // to the parent invocation of this function and decrement the count:
324 // *Upcoming tokens:* `;`
325 // *Unmatched count:* 2
326 // *`parse_path_segment` calls deep:* 1
328 // At this point, this function will expect to find another matching `>` character but
329 // won't be able to and will return an error. This will continue all the way up the
330 // call stack until the first invocation:
332 // *Upcoming tokens:* `;`
333 // *Unmatched count:* 2
334 // *`parse_path_segment` calls deep:* 0
336 // In doing this, we have managed to work out how many unmatched leading left angle
337 // brackets there are, but we cannot recover as the unmatched angle brackets have
338 // already been consumed. To remedy this, we keep a snapshot of the parser state
339 // before we do the above. We can then inspect whether we ended up with a parsing error
340 // and unmatched left angle brackets and if so, restore the parser state before we
341 // consumed any `<` characters to emit an error and consume the erroneous tokens to
342 // recover by attempting to parse again.
344 // In practice, the recursion of this function is indirect and there will be other
345 // locations that consume some `<` characters - as long as we update the count when
346 // this happens, it isn't an issue.
348 let is_first_invocation
= style
== PathStyle
::Expr
;
349 // Take a snapshot before attempting to parse - we can restore this later.
350 let snapshot
= if is_first_invocation { Some(self.clone()) }
else { None }
;
352 debug
!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
353 match self.parse_angle_args() {
354 Ok(args
) => Ok(args
),
355 Err(ref mut e
) if is_first_invocation
&& self.unmatched_angle_bracket_count
> 0 => {
356 // Cancel error from being unable to find `>`. We know the error
357 // must have been this due to a non-zero unmatched angle bracket
361 // Swap `self` with our backup of the parser state before attempting to parse
362 // generic arguments.
363 let snapshot
= mem
::replace(self, snapshot
.unwrap());
366 "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \
367 snapshot.count={:?}",
368 snapshot
.unmatched_angle_bracket_count
,
371 // Eat the unmatched angle brackets.
372 for _
in 0..snapshot
.unmatched_angle_bracket_count
{
376 // Make a span over ${unmatched angle bracket count} characters.
377 let span
= lo
.with_hi(lo
.lo() + BytePos(snapshot
.unmatched_angle_bracket_count
));
378 self.struct_span_err(
381 "unmatched angle bracket{}",
382 pluralize
!(snapshot
.unmatched_angle_bracket_count
)
388 "remove extra angle bracket{}",
389 pluralize
!(snapshot
.unmatched_angle_bracket_count
)
392 Applicability
::MachineApplicable
,
396 // Try again without unmatched angle bracket characters.
397 self.parse_angle_args()
403 /// Parses (possibly empty) list of generic arguments / associated item constraints,
404 /// possibly including trailing comma.
405 pub(super) fn parse_angle_args(&mut self) -> PResult
<'a
, Vec
<AngleBracketedArg
>> {
406 let mut args
= Vec
::new();
407 while let Some(arg
) = self.parse_angle_arg()?
{
409 if !self.eat(&token
::Comma
) {
410 if !self.token
.kind
.should_end_const_arg() {
411 if self.handle_ambiguous_unbraced_const_arg(&mut args
)?
{
412 // We've managed to (partially) recover, so continue trying to parse
423 /// Parses a single argument in the angle arguments `<...>` of a path segment.
424 fn parse_angle_arg(&mut self) -> PResult
<'a
, Option
<AngleBracketedArg
>> {
425 let lo
= self.token
.span
;
426 let arg
= self.parse_generic_arg()?
;
429 if self.check(&token
::Colon
) | self.check(&token
::Eq
) {
430 let (ident
, gen_args
) = match self.get_ident_from_generic_arg(arg
) {
431 Ok(ident_gen_args
) => ident_gen_args
,
432 Err(arg
) => return Ok(Some(AngleBracketedArg
::Arg(arg
))),
434 let kind
= if self.eat(&token
::Colon
) {
435 // Parse associated type constraint bound.
437 let bounds
= self.parse_generic_bounds(Some(self.prev_token
.span
))?
;
438 AssocTyConstraintKind
::Bound { bounds }
439 } else if self.eat(&token
::Eq
) {
440 // Parse associated type equality constraint
442 let ty
= self.parse_assoc_equality_term(ident
, self.prev_token
.span
)?
;
443 AssocTyConstraintKind
::Equality { ty }
448 let span
= lo
.to(self.prev_token
.span
);
450 // Gate associated type bounds, e.g., `Iterator<Item: Ord>`.
451 if let AssocTyConstraintKind
::Bound { .. }
= kind
{
452 self.sess
.gated_spans
.gate(sym
::associated_type_bounds
, span
);
455 AssocTyConstraint { id: ast::DUMMY_NODE_ID, ident, gen_args, kind, span }
;
456 Ok(Some(AngleBracketedArg
::Constraint(constraint
)))
458 Ok(Some(AngleBracketedArg
::Arg(arg
)))
465 /// Parse the term to the right of an associated item equality constraint.
466 /// That is, parse `<term>` in `Item = <term>`.
467 /// Right now, this only admits types in `<term>`.
468 fn parse_assoc_equality_term(&mut self, ident
: Ident
, eq
: Span
) -> PResult
<'a
, P
<ast
::Ty
>> {
469 let arg
= self.parse_generic_arg()?
;
470 let span
= ident
.span
.to(self.prev_token
.span
);
472 Some(GenericArg
::Type(ty
)) => return Ok(ty
),
473 Some(GenericArg
::Const(expr
)) => {
474 self.struct_span_err(span
, "cannot constrain an associated constant to a value")
475 .span_label(ident
.span
, "this associated constant...")
476 .span_label(expr
.value
.span
, "...cannot be constrained to this value")
479 Some(GenericArg
::Lifetime(lt
)) => {
480 self.struct_span_err(span
, "associated lifetimes are not supported")
481 .span_label(lt
.ident
.span
, "the lifetime is given here")
482 .help("if you meant to specify a trait object, write `dyn Trait + 'lifetime`")
486 let after_eq
= eq
.shrink_to_hi();
487 let before_next
= self.token
.span
.shrink_to_lo();
488 self.struct_span_err(after_eq
.to(before_next
), "missing type to the right of `=`")
490 self.sess
.source_map().next_point(eq
).to(before_next
),
491 "to constrain the associated type, add a type after `=`",
492 " TheType".to_string(),
493 Applicability
::HasPlaceholders
,
497 &format
!("remove the `=` if `{}` is a type", ident
),
499 Applicability
::MaybeIncorrect
,
504 Ok(self.mk_ty(span
, ast
::TyKind
::Err
))
507 /// We do not permit arbitrary expressions as const arguments. They must be one of:
508 /// - An expression surrounded in `{}`.
510 /// - A numeric literal prefixed by `-`.
511 /// - A single-segment path.
512 pub(super) fn expr_is_valid_const_arg(&self, expr
: &P
<rustc_ast
::Expr
>) -> bool
{
514 ast
::ExprKind
::Block(_
, _
) | ast
::ExprKind
::Lit(_
) => true,
515 ast
::ExprKind
::Unary(ast
::UnOp
::Neg
, expr
) => {
516 matches
!(expr
.kind
, ast
::ExprKind
::Lit(_
))
518 // We can only resolve single-segment paths at the moment, because multi-segment paths
519 // require type-checking: see `visit_generic_arg` in `src/librustc_resolve/late.rs`.
520 ast
::ExprKind
::Path(None
, path
)
521 if path
.segments
.len() == 1 && path
.segments
[0].args
.is_none() =>
529 /// Parse a const argument, e.g. `<3>`. It is assumed the angle brackets will be parsed by
531 pub(super) fn parse_const_arg(&mut self) -> PResult
<'a
, AnonConst
> {
532 // Parse const argument.
533 let value
= if let token
::OpenDelim(token
::Brace
) = self.token
.kind
{
534 self.parse_block_expr(
537 BlockCheckMode
::Default
,
541 self.handle_unambiguous_unbraced_const_arg()?
543 Ok(AnonConst { id: ast::DUMMY_NODE_ID, value }
)
546 /// Parse a generic argument in a path segment.
547 /// This does not include constraints, e.g., `Item = u8`, which is handled in `parse_angle_arg`.
548 fn parse_generic_arg(&mut self) -> PResult
<'a
, Option
<GenericArg
>> {
549 let start
= self.token
.span
;
550 let arg
= if self.check_lifetime() && self.look_ahead(1, |t
| !t
.is_like_plus()) {
551 // Parse lifetime argument.
552 GenericArg
::Lifetime(self.expect_lifetime())
553 } else if self.check_const_arg() {
554 // Parse const argument.
555 GenericArg
::Const(self.parse_const_arg()?
)
556 } else if self.check_type() {
557 // Parse type argument.
558 match self.parse_ty() {
559 Ok(ty
) => GenericArg
::Type(ty
),
561 // Try to recover from possible `const` arg without braces.
562 return self.recover_const_arg(start
, err
).map(Some
);
571 fn get_ident_from_generic_arg(
574 ) -> Result
<(Ident
, Option
<GenericArgs
>), GenericArg
> {
575 if let GenericArg
::Type(ty
) = &gen_arg
{
576 if let ast
::TyKind
::Path(qself
, path
) = &ty
.kind
{
577 if qself
.is_none() && path
.segments
.len() == 1 {
578 let seg
= &path
.segments
[0];
579 return Ok((seg
.ident
, seg
.args
.as_deref().cloned()));