src/librustc_parse/parser/ty.rs

   1 use super::{Parser, PathStyle, PrevTokenKind, TokenType};
   2 use super::item::ParamCfg;
   3
   4 use crate::{maybe_whole, maybe_recover_from_interpolated_ty_qpath};
   5
   6 use rustc_errors::{PResult, Applicability, pluralize};
   7 use rustc_error_codes::*;
   8 use syntax::ptr::P;
   9 use syntax::ast::{self, Ty, TyKind, MutTy, BareFnTy, FunctionRetTy, GenericParam, Lifetime, Ident};
  10 use syntax::ast::{TraitBoundModifier, TraitObjectSyntax, GenericBound, GenericBounds, PolyTraitRef};
  11 use syntax::ast::{Mutability, AnonConst, Mac};
  12 use syntax::token::{self, Token};
  13 use syntax::struct_span_err;
  14 use syntax_pos::source_map::Span;
  15 use syntax_pos::symbol::kw;
  16
  17 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
  18 /// `IDENT<<u8 as Trait>::AssocTy>`.
  19 ///
  20 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
  21 /// that `IDENT` is not the ident of a fn trait.
  22 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
  23     t == &token::ModSep || t == &token::Lt ||
  24     t == &token::BinOp(token::Shl)
  25 }
  26
  27 impl<'a> Parser<'a> {
  28     /// Parses a type.
  29     pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
  30         self.parse_ty_common(true, true, false)
  31     }
  32
  33     /// Parse a type suitable for a function or function pointer parameter.
  34     /// The difference from `parse_ty` is that this version allows `...`
  35     /// (`CVarArgs`) at the top level of the the type.
  36     pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
  37         self.parse_ty_common(true, true, true)
  38     }
  39
  40     /// Parses a type in restricted contexts where `+` is not permitted.
  41     ///
  42     /// Example 1: `&'a TYPE`
  43     ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
  44     /// Example 2: `value1 as TYPE + value2`
  45     ///     `+` is prohibited to avoid interactions with expression grammar.
  46     pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
  47         self.parse_ty_common(false, true, false)
  48     }
  49
  50     /// Parses an optional return type `[ -> TY ]` in a function declaration.
  51     pub(super) fn parse_ret_ty(
  52         &mut self,
  53         allow_plus: bool,
  54         allow_qpath_recovery: bool,
  55     ) -> PResult<'a, FunctionRetTy> {
  56         Ok(if self.eat(&token::RArrow) {
  57             // FIXME(Centril): Can we unconditionally `allow_plus`?
  58             FunctionRetTy::Ty(self.parse_ty_common(allow_plus, allow_qpath_recovery, false)?)
  59         } else {
  60             FunctionRetTy::Default(self.token.span.shrink_to_lo())
  61         })
  62     }
  63
  64     fn parse_ty_common(
  65         &mut self,
  66         allow_plus: bool,
  67         allow_qpath_recovery: bool,
  68         // Is `...` (`CVarArgs`) legal in the immediate top level call?
  69         allow_c_variadic: bool,
  70     ) -> PResult<'a, P<Ty>> {
  71         maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
  72         maybe_whole!(self, NtTy, |x| x);
  73
  74         let lo = self.token.span;
  75         let mut impl_dyn_multi = false;
  76         let kind = if self.check(&token::OpenDelim(token::Paren)) {
  77             self.parse_ty_tuple_or_parens(lo, allow_plus)?
  78         } else if self.eat(&token::Not) {
  79             // Never type `!`
  80             TyKind::Never
  81         } else if self.eat(&token::BinOp(token::Star)) {
  82             // Raw pointer
  83             TyKind::Ptr(self.parse_ptr()?)
  84         } else if self.eat(&token::OpenDelim(token::Bracket)) {
  85             // Array or slice
  86             let t = self.parse_ty()?;
  87             // Parse optional `; EXPR` in `[TYPE; EXPR]`
  88             let t = match self.maybe_parse_fixed_length_of_vec()? {
  89                 None => TyKind::Slice(t),
  90                 Some(length) => TyKind::Array(t, AnonConst {
  91                     id: ast::DUMMY_NODE_ID,
  92                     value: length,
  93                 }),
  94             };
  95             self.expect(&token::CloseDelim(token::Bracket))?;
  96             t
  97         } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
  98             // Reference
  99             self.expect_and()?;
 100             self.parse_borrowed_pointee()?
 101         } else if self.eat_keyword_noexpect(kw::Typeof) {
 102             // `typeof(EXPR)`
 103             // In order to not be ambiguous, the type must be surrounded by parens.
 104             self.expect(&token::OpenDelim(token::Paren))?;
 105             let e = AnonConst {
 106                 id: ast::DUMMY_NODE_ID,
 107                 value: self.parse_expr()?,
 108             };
 109             self.expect(&token::CloseDelim(token::Paren))?;
 110             TyKind::Typeof(e)
 111         } else if self.eat_keyword(kw::Underscore) {
 112             // A type to be inferred `_`
 113             TyKind::Infer
 114         } else if self.token_is_bare_fn_keyword() {
 115             // Function pointer type
 116             self.parse_ty_bare_fn(Vec::new())?
 117         } else if self.check_keyword(kw::For) {
 118             // Function pointer type or bound list (trait object type) starting with a poly-trait.
 119             //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
 120             //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
 121             let lo = self.token.span;
 122             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 123             if self.token_is_bare_fn_keyword() {
 124                 self.parse_ty_bare_fn(lifetime_defs)?
 125             } else {
 126                 let path = self.parse_path(PathStyle::Type)?;
 127                 let parse_plus = allow_plus && self.check_plus();
 128                 self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
 129             }
 130         } else if self.eat_keyword(kw::Impl) {
 131             // Always parse bounds greedily for better error recovery.
 132             let bounds = self.parse_generic_bounds(None)?;
 133             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
 134             TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
 135         } else if self.check_keyword(kw::Dyn) &&
 136                   (self.token.span.rust_2018() ||
 137                    self.look_ahead(1, |t| t.can_begin_bound() &&
 138                                           !can_continue_type_after_non_fn_ident(t))) {
 139             self.bump(); // `dyn`
 140             // Always parse bounds greedily for better error recovery.
 141             let bounds = self.parse_generic_bounds(None)?;
 142             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
 143             TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
 144         } else if self.check(&token::Question) ||
 145                   self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
 146             // Bound list (trait object type)
 147             TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
 148                                 TraitObjectSyntax::None)
 149         } else if self.eat_lt() {
 150             // Qualified path
 151             let (qself, path) = self.parse_qpath(PathStyle::Type)?;
 152             TyKind::Path(Some(qself), path)
 153         } else if self.token.is_path_start() {
 154             // Simple path
 155             let path = self.parse_path(PathStyle::Type)?;
 156             if self.eat(&token::Not) {
 157                 // Macro invocation in type position
 158                 let args = self.parse_mac_args()?;
 159                 let mac = Mac {
 160                     path,
 161                     args,
 162                     prior_type_ascription: self.last_type_ascription,
 163                 };
 164                 TyKind::Mac(mac)
 165             } else {
 166                 // Just a type path or bound list (trait object type) starting with a trait.
 167                 //   `Type`
 168                 //   `Trait1 + Trait2 + 'a`
 169                 if allow_plus && self.check_plus() {
 170                     self.parse_remaining_bounds(Vec::new(), path, lo, true)?
 171                 } else {
 172                     TyKind::Path(None, path)
 173                 }
 174             }
 175         } else if self.eat(&token::DotDotDot) {
 176             if allow_c_variadic {
 177                 TyKind::CVarArgs
 178             } else {
 179                 // FIXME(Centril): Should we just allow `...` syntactically
 180                 // anywhere in a type and use semantic restrictions instead?
 181                 struct_span_err!(
 182                     self.sess.span_diagnostic,
 183                     lo.to(self.prev_span),
 184                     E0743,
 185                     "C-variadic type `...` may not be nested inside another type",
 186                 )
 187                 .emit();
 188
 189                 TyKind::Err
 190             }
 191         } else {
 192             let msg = format!("expected type, found {}", self.this_token_descr());
 193             let mut err = self.fatal(&msg);
 194             err.span_label(self.token.span, "expected type");
 195             self.maybe_annotate_with_ascription(&mut err, true);
 196             return Err(err);
 197         };
 198
 199         let span = lo.to(self.prev_span);
 200         let ty = self.mk_ty(span, kind);
 201
 202         // Try to recover from use of `+` with incorrect priority.
 203         self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
 204         self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
 205         self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
 206     }
 207
 208     /// Parses either:
 209     /// - `(TYPE)`, a parenthesized type.
 210     /// - `(TYPE,)`, a tuple with a single field of type TYPE.
 211     fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: bool) -> PResult<'a, TyKind> {
 212         let mut trailing_plus = false;
 213         let (ts, trailing) = self.parse_paren_comma_seq(|p| {
 214             let ty = p.parse_ty()?;
 215             trailing_plus = p.prev_token_kind == PrevTokenKind::Plus;
 216             Ok(ty)
 217         })?;
 218
 219         if ts.len() == 1 && !trailing {
 220             let ty = ts.into_iter().nth(0).unwrap().into_inner();
 221             let maybe_bounds = allow_plus && self.token.is_like_plus();
 222             match ty.kind {
 223                 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
 224                 TyKind::Path(None, path) if maybe_bounds => {
 225                     self.parse_remaining_bounds(Vec::new(), path, lo, true)
 226                 }
 227                 TyKind::TraitObject(mut bounds, TraitObjectSyntax::None)
 228                 if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
 229                     let path = match bounds.remove(0) {
 230                         GenericBound::Trait(pt, ..) => pt.trait_ref.path,
 231                         GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
 232                     };
 233                     self.parse_remaining_bounds(Vec::new(), path, lo, true)
 234                 }
 235                 // `(TYPE)`
 236                 _ => Ok(TyKind::Paren(P(ty)))
 237             }
 238         } else {
 239             Ok(TyKind::Tup(ts))
 240         }
 241     }
 242
 243     fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
 244                               lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
 245         let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
 246         let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
 247         if parse_plus {
 248             self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
 249             bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
 250         }
 251         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
 252     }
 253
 254     fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
 255         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
 256             let span = self.prev_span;
 257             let msg = "expected mut or const in raw pointer type";
 258             self.struct_span_err(span, msg)
 259                 .span_label(span, msg)
 260                 .help("use `*mut T` or `*const T` as appropriate")
 261                 .emit();
 262             Mutability::Immutable
 263         });
 264         let t = self.parse_ty_no_plus()?;
 265         Ok(MutTy { ty: t, mutbl })
 266     }
 267
 268     fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
 269         if self.eat(&token::Semi) {
 270             Ok(Some(self.parse_expr()?))
 271         } else {
 272             Ok(None)
 273         }
 274     }
 275
 276     fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
 277         let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
 278         let mutbl = self.parse_mutability();
 279         let ty = self.parse_ty_no_plus()?;
 280         return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }));
 281     }
 282
 283     /// Is the current token one of the keywords that signals a bare function type?
 284     fn token_is_bare_fn_keyword(&mut self) -> bool {
 285         self.check_keyword(kw::Fn) ||
 286             self.check_keyword(kw::Unsafe) ||
 287             self.check_keyword(kw::Extern)
 288     }
 289
 290     /// Parses a `TyKind::BareFn` type.
 291     fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
 292         /*
 293
 294         [unsafe] [extern "ABI"] fn (S) -> T
 295          ^~~~^           ^~~~^     ^~^    ^
 296            |               |        |     |
 297            |               |        |   Return type
 298            |               |      Argument types
 299            |               |
 300            |              ABI
 301         Function Style
 302         */
 303
 304         let unsafety = self.parse_unsafety();
 305         let ext = self.parse_extern()?;
 306         self.expect_keyword(kw::Fn)?;
 307         let cfg = ParamCfg {
 308             is_self_allowed: false,
 309             is_name_required: |_| false,
 310         };
 311         let decl = self.parse_fn_decl(cfg, false)?;
 312         Ok(TyKind::BareFn(P(BareFnTy {
 313             ext,
 314             unsafety,
 315             generic_params,
 316             decl,
 317         })))
 318     }
 319
 320     pub(super) fn parse_generic_bounds(&mut self,
 321                                   colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
 322         self.parse_generic_bounds_common(true, colon_span)
 323     }
 324
 325     /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
 326     ///
 327     /// ```
 328     /// BOUND = TY_BOUND | LT_BOUND
 329     /// LT_BOUND = LIFETIME (e.g., `'a`)
 330     /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
 331     /// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
 332     /// ```
 333     fn parse_generic_bounds_common(&mut self,
 334                                    allow_plus: bool,
 335                                    colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
 336         let mut bounds = Vec::new();
 337         let mut negative_bounds = Vec::new();
 338         let mut last_plus_span = None;
 339         let mut was_negative = false;
 340         loop {
 341             // This needs to be synchronized with `TokenKind::can_begin_bound`.
 342             let is_bound_start = self.check_path() || self.check_lifetime() ||
 343                                  self.check(&token::Not) || // used for error reporting only
 344                                  self.check(&token::Question) ||
 345                                  self.check_keyword(kw::For) ||
 346                                  self.check(&token::OpenDelim(token::Paren));
 347             if is_bound_start {
 348                 let lo = self.token.span;
 349                 let has_parens = self.eat(&token::OpenDelim(token::Paren));
 350                 let inner_lo = self.token.span;
 351                 let is_negative = self.eat(&token::Not);
 352                 let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
 353                 if self.token.is_lifetime() {
 354                     if let Some(question_span) = question {
 355                         self.span_err(question_span,
 356                                       "`?` may only modify trait bounds, not lifetime bounds");
 357                     }
 358                     bounds.push(GenericBound::Outlives(self.expect_lifetime()));
 359                     if has_parens {
 360                         let inner_span = inner_lo.to(self.prev_span);
 361                         self.expect(&token::CloseDelim(token::Paren))?;
 362                         let mut err = self.struct_span_err(
 363                             lo.to(self.prev_span),
 364                             "parenthesized lifetime bounds are not supported"
 365                         );
 366                         if let Ok(snippet) = self.span_to_snippet(inner_span) {
 367                             err.span_suggestion_short(
 368                                 lo.to(self.prev_span),
 369                                 "remove the parentheses",
 370                                 snippet.to_owned(),
 371                                 Applicability::MachineApplicable
 372                             );
 373                         }
 374                         err.emit();
 375                     }
 376                 } else {
 377                     let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 378                     let path = self.parse_path(PathStyle::Type)?;
 379                     if has_parens {
 380                         self.expect(&token::CloseDelim(token::Paren))?;
 381                     }
 382                     let poly_span = lo.to(self.prev_span);
 383                     if is_negative {
 384                         was_negative = true;
 385                         if let Some(sp) = last_plus_span.or(colon_span) {
 386                             negative_bounds.push(sp.to(poly_span));
 387                         }
 388                     } else {
 389                         let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
 390                         let modifier = if question.is_some() {
 391                             TraitBoundModifier::Maybe
 392                         } else {
 393                             TraitBoundModifier::None
 394                         };
 395                         bounds.push(GenericBound::Trait(poly_trait, modifier));
 396                     }
 397                 }
 398             } else {
 399                 break
 400             }
 401
 402             if !allow_plus || !self.eat_plus() {
 403                 break
 404             } else {
 405                 last_plus_span = Some(self.prev_span);
 406             }
 407         }
 408
 409         if !negative_bounds.is_empty() || was_negative {
 410             let negative_bounds_len = negative_bounds.len();
 411             let last_span = negative_bounds.last().map(|sp| *sp);
 412             let mut err = self.struct_span_err(
 413                 negative_bounds,
 414                 "negative trait bounds are not supported",
 415             );
 416             if let Some(sp) = last_span {
 417                 err.span_label(sp, "negative trait bounds are not supported");
 418             }
 419             if let Some(bound_list) = colon_span {
 420                 let bound_list = bound_list.to(self.prev_span);
 421                 let mut new_bound_list = String::new();
 422                 if !bounds.is_empty() {
 423                     let mut snippets = bounds.iter().map(|bound| bound.span())
 424                         .map(|span| self.span_to_snippet(span));
 425                     while let Some(Ok(snippet)) = snippets.next() {
 426                         new_bound_list.push_str(" + ");
 427                         new_bound_list.push_str(&snippet);
 428                     }
 429                     new_bound_list = new_bound_list.replacen(" +", ":", 1);
 430                 }
 431                 err.span_suggestion_hidden(
 432                     bound_list,
 433                     &format!("remove the trait bound{}", pluralize!(negative_bounds_len)),
 434                     new_bound_list,
 435                     Applicability::MachineApplicable,
 436                 );
 437             }
 438             err.emit();
 439         }
 440
 441         return Ok(bounds);
 442     }
 443
 444     pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
 445         if self.eat_keyword(kw::For) {
 446             self.expect_lt()?;
 447             let params = self.parse_generic_params()?;
 448             self.expect_gt()?;
 449             // We rely on AST validation to rule out invalid cases: There must not be type
 450             // parameters, and the lifetime parameters must not have bounds.
 451             Ok(params)
 452         } else {
 453             Ok(Vec::new())
 454         }
 455     }
 456
 457     pub fn check_lifetime(&mut self) -> bool {
 458         self.expected_tokens.push(TokenType::Lifetime);
 459         self.token.is_lifetime()
 460     }
 461
 462     /// Parses a single lifetime `'a` or panics.
 463     pub fn expect_lifetime(&mut self) -> Lifetime {
 464         if let Some(ident) = self.token.lifetime() {
 465             let span = self.token.span;
 466             self.bump();
 467             Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
 468         } else {
 469             self.span_bug(self.token.span, "not a lifetime")
 470         }
 471     }
 472
 473     pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
 474         P(Ty { kind, span, id: ast::DUMMY_NODE_ID })
 475     }
 476 }