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