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