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.eat(&token::OpenDelim(token::Paren)) {
  77             // `(TYPE)` is a parenthesized type.
  78             // `(TYPE,)` is a tuple with a single field of type TYPE.
  79             let mut ts = vec![];
  80             let mut last_comma = false;
  81             while self.token != token::CloseDelim(token::Paren) {
  82                 ts.push(self.parse_ty()?);
  83                 if self.eat(&token::Comma) {
  84                     last_comma = true;
  85                 } else {
  86                     last_comma = false;
  87                     break;
  88                 }
  89             }
  90             let trailing_plus = self.prev_token_kind == PrevTokenKind::Plus;
  91             self.expect(&token::CloseDelim(token::Paren))?;
  92
  93             if ts.len() == 1 && !last_comma {
  94                 let ty = ts.into_iter().nth(0).unwrap().into_inner();
  95                 let maybe_bounds = allow_plus && self.token.is_like_plus();
  96                 match ty.kind {
  97                     // `(TY_BOUND_NOPAREN) + BOUND + ...`.
  98                     TyKind::Path(None, ref path) if maybe_bounds => {
  99                         self.parse_remaining_bounds(Vec::new(), path.clone(), lo, true)?
 100                     }
 101                     TyKind::TraitObject(ref bounds, TraitObjectSyntax::None)
 102                             if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
 103                         let path = match bounds[0] {
 104                             GenericBound::Trait(ref pt, ..) => pt.trait_ref.path.clone(),
 105                             GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
 106                         };
 107                         self.parse_remaining_bounds(Vec::new(), path, lo, true)?
 108                     }
 109                     // `(TYPE)`
 110                     _ => TyKind::Paren(P(ty))
 111                 }
 112             } else {
 113                 TyKind::Tup(ts)
 114             }
 115         } else if self.eat(&token::Not) {
 116             // Never type `!`
 117             TyKind::Never
 118         } else if self.eat(&token::BinOp(token::Star)) {
 119             // Raw pointer
 120             TyKind::Ptr(self.parse_ptr()?)
 121         } else if self.eat(&token::OpenDelim(token::Bracket)) {
 122             // Array or slice
 123             let t = self.parse_ty()?;
 124             // Parse optional `; EXPR` in `[TYPE; EXPR]`
 125             let t = match self.maybe_parse_fixed_length_of_vec()? {
 126                 None => TyKind::Slice(t),
 127                 Some(length) => TyKind::Array(t, AnonConst {
 128                     id: ast::DUMMY_NODE_ID,
 129                     value: length,
 130                 }),
 131             };
 132             self.expect(&token::CloseDelim(token::Bracket))?;
 133             t
 134         } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
 135             // Reference
 136             self.expect_and()?;
 137             self.parse_borrowed_pointee()?
 138         } else if self.eat_keyword_noexpect(kw::Typeof) {
 139             // `typeof(EXPR)`
 140             // In order to not be ambiguous, the type must be surrounded by parens.
 141             self.expect(&token::OpenDelim(token::Paren))?;
 142             let e = AnonConst {
 143                 id: ast::DUMMY_NODE_ID,
 144                 value: self.parse_expr()?,
 145             };
 146             self.expect(&token::CloseDelim(token::Paren))?;
 147             TyKind::Typeof(e)
 148         } else if self.eat_keyword(kw::Underscore) {
 149             // A type to be inferred `_`
 150             TyKind::Infer
 151         } else if self.token_is_bare_fn_keyword() {
 152             // Function pointer type
 153             self.parse_ty_bare_fn(Vec::new())?
 154         } else if self.check_keyword(kw::For) {
 155             // Function pointer type or bound list (trait object type) starting with a poly-trait.
 156             //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
 157             //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
 158             let lo = self.token.span;
 159             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 160             if self.token_is_bare_fn_keyword() {
 161                 self.parse_ty_bare_fn(lifetime_defs)?
 162             } else {
 163                 let path = self.parse_path(PathStyle::Type)?;
 164                 let parse_plus = allow_plus && self.check_plus();
 165                 self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
 166             }
 167         } else if self.eat_keyword(kw::Impl) {
 168             // Always parse bounds greedily for better error recovery.
 169             let bounds = self.parse_generic_bounds(None)?;
 170             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
 171             TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
 172         } else if self.check_keyword(kw::Dyn) &&
 173                   (self.token.span.rust_2018() ||
 174                    self.look_ahead(1, |t| t.can_begin_bound() &&
 175                                           !can_continue_type_after_non_fn_ident(t))) {
 176             self.bump(); // `dyn`
 177             // Always parse bounds greedily for better error recovery.
 178             let bounds = self.parse_generic_bounds(None)?;
 179             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
 180             TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
 181         } else if self.check(&token::Question) ||
 182                   self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
 183             // Bound list (trait object type)
 184             TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
 185                                 TraitObjectSyntax::None)
 186         } else if self.eat_lt() {
 187             // Qualified path
 188             let (qself, path) = self.parse_qpath(PathStyle::Type)?;
 189             TyKind::Path(Some(qself), path)
 190         } else if self.token.is_path_start() {
 191             // Simple path
 192             let path = self.parse_path(PathStyle::Type)?;
 193             if self.eat(&token::Not) {
 194                 // Macro invocation in type position
 195                 let args = self.parse_mac_args()?;
 196                 let mac = Mac {
 197                     path,
 198                     args,
 199                     prior_type_ascription: self.last_type_ascription,
 200                 };
 201                 TyKind::Mac(mac)
 202             } else {
 203                 // Just a type path or bound list (trait object type) starting with a trait.
 204                 //   `Type`
 205                 //   `Trait1 + Trait2 + 'a`
 206                 if allow_plus && self.check_plus() {
 207                     self.parse_remaining_bounds(Vec::new(), path, lo, true)?
 208                 } else {
 209                     TyKind::Path(None, path)
 210                 }
 211             }
 212         } else if self.eat(&token::DotDotDot) {
 213             if allow_c_variadic {
 214                 TyKind::CVarArgs
 215             } else {
 216                 // FIXME(Centril): Should we just allow `...` syntactically
 217                 // anywhere in a type and use semantic restrictions instead?
 218                 struct_span_err!(
 219                     self.sess.span_diagnostic,
 220                     lo.to(self.prev_span),
 221                     E0743,
 222                     "C-variadic type `...` may not be nested inside another type",
 223                 )
 224                 .emit();
 225
 226                 TyKind::Err
 227             }
 228         } else {
 229             let msg = format!("expected type, found {}", self.this_token_descr());
 230             let mut err = self.fatal(&msg);
 231             err.span_label(self.token.span, "expected type");
 232             self.maybe_annotate_with_ascription(&mut err, true);
 233             return Err(err);
 234         };
 235
 236         let span = lo.to(self.prev_span);
 237         let ty = self.mk_ty(span, kind);
 238
 239         // Try to recover from use of `+` with incorrect priority.
 240         self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
 241         self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
 242         self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
 243     }
 244
 245     fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
 246                               lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
 247         let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
 248         let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
 249         if parse_plus {
 250             self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
 251             bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
 252         }
 253         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
 254     }
 255
 256     fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
 257         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
 258             let span = self.prev_span;
 259             let msg = "expected mut or const in raw pointer type";
 260             self.struct_span_err(span, msg)
 261                 .span_label(span, msg)
 262                 .help("use `*mut T` or `*const T` as appropriate")
 263                 .emit();
 264             Mutability::Immutable
 265         });
 266         let t = self.parse_ty_no_plus()?;
 267         Ok(MutTy { ty: t, mutbl })
 268     }
 269
 270     fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
 271         if self.eat(&token::Semi) {
 272             Ok(Some(self.parse_expr()?))
 273         } else {
 274             Ok(None)
 275         }
 276     }
 277
 278     fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
 279         let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
 280         let mutbl = self.parse_mutability();
 281         let ty = self.parse_ty_no_plus()?;
 282         return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }));
 283     }
 284
 285     /// Is the current token one of the keywords that signals a bare function type?
 286     fn token_is_bare_fn_keyword(&mut self) -> bool {
 287         self.check_keyword(kw::Fn) ||
 288             self.check_keyword(kw::Unsafe) ||
 289             self.check_keyword(kw::Extern)
 290     }
 291
 292     /// Parses a `TyKind::BareFn` type.
 293     fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
 294         /*
 295
 296         [unsafe] [extern "ABI"] fn (S) -> T
 297          ^~~~^           ^~~~^     ^~^    ^
 298            |               |        |     |
 299            |               |        |   Return type
 300            |               |      Argument types
 301            |               |
 302            |              ABI
 303         Function Style
 304         */
 305
 306         let unsafety = self.parse_unsafety();
 307         let ext = self.parse_extern()?;
 308         self.expect_keyword(kw::Fn)?;
 309         let cfg = ParamCfg {
 310             is_self_allowed: false,
 311             is_name_required: |_| false,
 312         };
 313         let decl = self.parse_fn_decl(cfg, false)?;
 314         Ok(TyKind::BareFn(P(BareFnTy {
 315             ext,
 316             unsafety,
 317             generic_params,
 318             decl,
 319         })))
 320     }
 321
 322     pub(super) fn parse_generic_bounds(&mut self,
 323                                   colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
 324         self.parse_generic_bounds_common(true, colon_span)
 325     }
 326
 327     /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
 328     ///
 329     /// ```
 330     /// BOUND = TY_BOUND | LT_BOUND
 331     /// LT_BOUND = LIFETIME (e.g., `'a`)
 332     /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
 333     /// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
 334     /// ```
 335     fn parse_generic_bounds_common(&mut self,
 336                                    allow_plus: bool,
 337                                    colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
 338         let mut bounds = Vec::new();
 339         let mut negative_bounds = Vec::new();
 340         let mut last_plus_span = None;
 341         let mut was_negative = false;
 342         loop {
 343             // This needs to be synchronized with `TokenKind::can_begin_bound`.
 344             let is_bound_start = self.check_path() || self.check_lifetime() ||
 345                                  self.check(&token::Not) || // used for error reporting only
 346                                  self.check(&token::Question) ||
 347                                  self.check_keyword(kw::For) ||
 348                                  self.check(&token::OpenDelim(token::Paren));
 349             if is_bound_start {
 350                 let lo = self.token.span;
 351                 let has_parens = self.eat(&token::OpenDelim(token::Paren));
 352                 let inner_lo = self.token.span;
 353                 let is_negative = self.eat(&token::Not);
 354                 let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
 355                 if self.token.is_lifetime() {
 356                     if let Some(question_span) = question {
 357                         self.span_err(question_span,
 358                                       "`?` may only modify trait bounds, not lifetime bounds");
 359                     }
 360                     bounds.push(GenericBound::Outlives(self.expect_lifetime()));
 361                     if has_parens {
 362                         let inner_span = inner_lo.to(self.prev_span);
 363                         self.expect(&token::CloseDelim(token::Paren))?;
 364                         let mut err = self.struct_span_err(
 365                             lo.to(self.prev_span),
 366                             "parenthesized lifetime bounds are not supported"
 367                         );
 368                         if let Ok(snippet) = self.span_to_snippet(inner_span) {
 369                             err.span_suggestion_short(
 370                                 lo.to(self.prev_span),
 371                                 "remove the parentheses",
 372                                 snippet.to_owned(),
 373                                 Applicability::MachineApplicable
 374                             );
 375                         }
 376                         err.emit();
 377                     }
 378                 } else {
 379                     let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 380                     let path = self.parse_path(PathStyle::Type)?;
 381                     if has_parens {
 382                         self.expect(&token::CloseDelim(token::Paren))?;
 383                     }
 384                     let poly_span = lo.to(self.prev_span);
 385                     if is_negative {
 386                         was_negative = true;
 387                         if let Some(sp) = last_plus_span.or(colon_span) {
 388                             negative_bounds.push(sp.to(poly_span));
 389                         }
 390                     } else {
 391                         let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
 392                         let modifier = if question.is_some() {
 393                             TraitBoundModifier::Maybe
 394                         } else {
 395                             TraitBoundModifier::None
 396                         };
 397                         bounds.push(GenericBound::Trait(poly_trait, modifier));
 398                     }
 399                 }
 400             } else {
 401                 break
 402             }
 403
 404             if !allow_plus || !self.eat_plus() {
 405                 break
 406             } else {
 407                 last_plus_span = Some(self.prev_span);
 408             }
 409         }
 410
 411         if !negative_bounds.is_empty() || was_negative {
 412             let negative_bounds_len = negative_bounds.len();
 413             let last_span = negative_bounds.last().map(|sp| *sp);
 414             let mut err = self.struct_span_err(
 415                 negative_bounds,
 416                 "negative trait bounds are not supported",
 417             );
 418             if let Some(sp) = last_span {
 419                 err.span_label(sp, "negative trait bounds are not supported");
 420             }
 421             if let Some(bound_list) = colon_span {
 422                 let bound_list = bound_list.to(self.prev_span);
 423                 let mut new_bound_list = String::new();
 424                 if !bounds.is_empty() {
 425                     let mut snippets = bounds.iter().map(|bound| bound.span())
 426                         .map(|span| self.span_to_snippet(span));
 427                     while let Some(Ok(snippet)) = snippets.next() {
 428                         new_bound_list.push_str(" + ");
 429                         new_bound_list.push_str(&snippet);
 430                     }
 431                     new_bound_list = new_bound_list.replacen(" +", ":", 1);
 432                 }
 433                 err.span_suggestion_hidden(
 434                     bound_list,
 435                     &format!("remove the trait bound{}", pluralize!(negative_bounds_len)),
 436                     new_bound_list,
 437                     Applicability::MachineApplicable,
 438                 );
 439             }
 440             err.emit();
 441         }
 442
 443         return Ok(bounds);
 444     }
 445
 446     pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
 447         if self.eat_keyword(kw::For) {
 448             self.expect_lt()?;
 449             let params = self.parse_generic_params()?;
 450             self.expect_gt()?;
 451             // We rely on AST validation to rule out invalid cases: There must not be type
 452             // parameters, and the lifetime parameters must not have bounds.
 453             Ok(params)
 454         } else {
 455             Ok(Vec::new())
 456         }
 457     }
 458
 459     pub fn check_lifetime(&mut self) -> bool {
 460         self.expected_tokens.push(TokenType::Lifetime);
 461         self.token.is_lifetime()
 462     }
 463
 464     /// Parses a single lifetime `'a` or panics.
 465     pub fn expect_lifetime(&mut self) -> Lifetime {
 466         if let Some(ident) = self.token.lifetime() {
 467             let span = self.token.span;
 468             self.bump();
 469             Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
 470         } else {
 471             self.span_bug(self.token.span, "not a lifetime")
 472         }
 473     }
 474
 475     pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
 476         P(Ty { kind, span, id: ast::DUMMY_NODE_ID })
 477     }
 478 }