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