src/librustc_parse/parser/ty.rs - third_party/rust - Git at Google

 use super::{Parser, PathStyle, PrevTokenKind, TokenType};
 use super::item::ParamCfg;

 use crate::{maybe_whole, maybe_recover_from_interpolated_ty_qpath};

 use syntax::ptr::P;
 use syntax::ast::{self, Ty, TyKind, MutTy, BareFnTy, FunctionRetTy, GenericParam, Lifetime, Ident};
 use syntax::ast::{TraitBoundModifier, TraitObjectSyntax, GenericBound, GenericBounds, PolyTraitRef};
 use syntax::ast::{Mutability, AnonConst, Mac};
 use syntax::token::{self, Token};
 use syntax::source_map::Span;
 use syntax::struct_span_fatal;
 use syntax_pos::symbol::kw;

 use errors::{PResult, Applicability, pluralize};

 use rustc_error_codes::*;

 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
 /// `IDENT<<u8 as Trait>::AssocTy>`.
 ///
 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
 /// that `IDENT` is not the ident of a fn trait.
 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
     t == &token::ModSep || t == &token::Lt ||
     t == &token::BinOp(token::Shl)
 }

 impl<'a> Parser<'a> {
     /// Parses a type.
     pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
         self.parse_ty_common(true, true, false)
     }

     /// Parses a type in restricted contexts where `+` is not permitted.
     ///
     /// Example 1: `&'a TYPE`
     ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
     /// Example 2: `value1 as TYPE + value2`
     ///     `+` is prohibited to avoid interactions with expression grammar.
     pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
         self.parse_ty_common(false, true, false)
     }

     /// Parses an optional return type `[ -> TY ]` in a function declaration.
     pub(super) fn parse_ret_ty(&mut self, allow_plus: bool) -> PResult<'a, FunctionRetTy> {
         if self.eat(&token::RArrow) {
             Ok(FunctionRetTy::Ty(self.parse_ty_common(allow_plus, true, false)?))
         } else {
             Ok(FunctionRetTy::Default(self.token.span.shrink_to_lo()))
         }
     }

     pub(super) fn parse_ty_common(&mut self, allow_plus: bool, allow_qpath_recovery: bool,
                        allow_c_variadic: bool) -> PResult<'a, P<Ty>> {
         maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
         maybe_whole!(self, NtTy, |x| x);

         let lo = self.token.span;
         let mut impl_dyn_multi = false;
         let kind = if self.eat(&token::OpenDelim(token::Paren)) {
             // `(TYPE)` is a parenthesized type.
             // `(TYPE,)` is a tuple with a single field of type TYPE.
             let mut ts = vec![];
             let mut last_comma = false;
             while self.token != token::CloseDelim(token::Paren) {
                 ts.push(self.parse_ty()?);
                 if self.eat(&token::Comma) {
                     last_comma = true;
                 } else {
                     last_comma = false;
                     break;
                 }
             }
             let trailing_plus = self.prev_token_kind == PrevTokenKind::Plus;
             self.expect(&token::CloseDelim(token::Paren))?;

             if ts.len() == 1 && !last_comma {
                 let ty = ts.into_iter().nth(0).unwrap().into_inner();
                 let maybe_bounds = allow_plus && self.token.is_like_plus();
                 match ty.kind {
                     // `(TY_BOUND_NOPAREN) + BOUND + ...`.
                     TyKind::Path(None, ref path) if maybe_bounds => {
                         self.parse_remaining_bounds(Vec::new(), path.clone(), lo, true)?
                     }
                     TyKind::TraitObject(ref bounds, TraitObjectSyntax::None)
                             if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
                         let path = match bounds[0] {
                             GenericBound::Trait(ref pt, ..) => pt.trait_ref.path.clone(),
                             GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
                         };
                         self.parse_remaining_bounds(Vec::new(), path, lo, true)?
                     }
                     // `(TYPE)`
                     _ => TyKind::Paren(P(ty))
                 }
             } else {
                 TyKind::Tup(ts)
             }
         } else if self.eat(&token::Not) {
             // Never type `!`
             TyKind::Never
         } else if self.eat(&token::BinOp(token::Star)) {
             // Raw pointer
             TyKind::Ptr(self.parse_ptr()?)
         } else if self.eat(&token::OpenDelim(token::Bracket)) {
             // Array or slice
             let t = self.parse_ty()?;
             // Parse optional `; EXPR` in `[TYPE; EXPR]`
             let t = match self.maybe_parse_fixed_length_of_vec()? {
                 None => TyKind::Slice(t),
                 Some(length) => TyKind::Array(t, AnonConst {
                     id: ast::DUMMY_NODE_ID,
                     value: length,
                 }),
             };
             self.expect(&token::CloseDelim(token::Bracket))?;
             t
         } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
             // Reference
             self.expect_and()?;
             self.parse_borrowed_pointee()?
         } else if self.eat_keyword_noexpect(kw::Typeof) {
             // `typeof(EXPR)`
             // In order to not be ambiguous, the type must be surrounded by parens.
             self.expect(&token::OpenDelim(token::Paren))?;
             let e = AnonConst {
                 id: ast::DUMMY_NODE_ID,
                 value: self.parse_expr()?,
             };
             self.expect(&token::CloseDelim(token::Paren))?;
             TyKind::Typeof(e)
         } else if self.eat_keyword(kw::Underscore) {
             // A type to be inferred `_`
             TyKind::Infer
         } else if self.token_is_bare_fn_keyword() {
             // Function pointer type
             self.parse_ty_bare_fn(Vec::new())?
         } else if self.check_keyword(kw::For) {
             // Function pointer type or bound list (trait object type) starting with a poly-trait.
             //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
             //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
             let lo = self.token.span;
             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
             if self.token_is_bare_fn_keyword() {
                 self.parse_ty_bare_fn(lifetime_defs)?
             } else {
                 let path = self.parse_path(PathStyle::Type)?;
                 let parse_plus = allow_plus && self.check_plus();
                 self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
             }
         } else if self.eat_keyword(kw::Impl) {
             // Always parse bounds greedily for better error recovery.
             let bounds = self.parse_generic_bounds(None)?;
             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
             TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
         } else if self.check_keyword(kw::Dyn) &&
                   (self.token.span.rust_2018() ||
                    self.look_ahead(1, |t| t.can_begin_bound() &&
                                           !can_continue_type_after_non_fn_ident(t))) {
             self.bump(); // `dyn`
             // Always parse bounds greedily for better error recovery.
             let bounds = self.parse_generic_bounds(None)?;
             impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
             TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
         } else if self.check(&token::Question) ||
                   self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
             // Bound list (trait object type)
             TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
                                 TraitObjectSyntax::None)
         } else if self.eat_lt() {
             // Qualified path
             let (qself, path) = self.parse_qpath(PathStyle::Type)?;
             TyKind::Path(Some(qself), path)
         } else if self.token.is_path_start() {
             // Simple path
             let path = self.parse_path(PathStyle::Type)?;
             if self.eat(&token::Not) {
                 // Macro invocation in type position
                 let args = self.parse_mac_args()?;
                 let mac = Mac {
                     path,
                     args,
                     prior_type_ascription: self.last_type_ascription,
                 };
                 TyKind::Mac(mac)
             } else {
                 // Just a type path or bound list (trait object type) starting with a trait.
                 //   `Type`
                 //   `Trait1 + Trait2 + 'a`
                 if allow_plus && self.check_plus() {
                     self.parse_remaining_bounds(Vec::new(), path, lo, true)?
                 } else {
                     TyKind::Path(None, path)
                 }
             }
         } else if self.check(&token::DotDotDot) {
             if allow_c_variadic {
                 self.eat(&token::DotDotDot);
                 TyKind::CVarArgs
             } else {
                 return Err(struct_span_fatal!(
                     self.sess.span_diagnostic,
                     self.token.span,
                     E0743,
                     "only foreign functions are allowed to be C-variadic",
                 ));
             }
         } else {
             let msg = format!("expected type, found {}", self.this_token_descr());
             let mut err = self.fatal(&msg);
             err.span_label(self.token.span, "expected type");
             self.maybe_annotate_with_ascription(&mut err, true);
             return Err(err);
         };

         let span = lo.to(self.prev_span);
         let ty = self.mk_ty(span, kind);

         // Try to recover from use of `+` with incorrect priority.
         self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
         self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
         self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
     }

     fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
                               lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
         let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
         let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
         if parse_plus {
             self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
             bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
         }
         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
     }

     fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
             let span = self.prev_span;
             let msg = "expected mut or const in raw pointer type";
             self.struct_span_err(span, msg)
                 .span_label(span, msg)
                 .help("use `*mut T` or `*const T` as appropriate")
                 .emit();
             Mutability::Immutable
         });
         let t = self.parse_ty_no_plus()?;
         Ok(MutTy { ty: t, mutbl })
     }

     fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
         if self.eat(&token::Semi) {
             Ok(Some(self.parse_expr()?))
         } else {
             Ok(None)
         }
     }

     fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
         let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
         let mutbl = self.parse_mutability();
         let ty = self.parse_ty_no_plus()?;
         return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }));
     }

     /// Is the current token one of the keywords that signals a bare function type?
     fn token_is_bare_fn_keyword(&mut self) -> bool {
         self.check_keyword(kw::Fn) ||
             self.check_keyword(kw::Unsafe) ||
             self.check_keyword(kw::Extern)
     }

     /// Parses a `TyKind::BareFn` type.
     fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
         /*

         [unsafe] [extern "ABI"] fn (S) -> T
          ^~~~^           ^~~~^     ^~^    ^
            |               |        |     |
            |               |        |   Return type
            |               |      Argument types
            |               |
            |              ABI
         Function Style
         */

         let unsafety = self.parse_unsafety();
         let ext = self.parse_extern()?;
         self.expect_keyword(kw::Fn)?;
         let cfg = ParamCfg {
             is_self_allowed: false,
             allow_c_variadic: true,
             is_name_required: |_| false,
         };
         let decl = self.parse_fn_decl(cfg, false)?;
         Ok(TyKind::BareFn(P(BareFnTy {
             ext,
             unsafety,
             generic_params,
             decl,
         })))
     }

     pub(super) fn parse_generic_bounds(&mut self,
                                   colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
         self.parse_generic_bounds_common(true, colon_span)
     }

     /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
     ///
     /// ```
     /// BOUND = TY_BOUND | LT_BOUND
     /// LT_BOUND = LIFETIME (e.g., `'a`)
     /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
     /// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
     /// ```
     fn parse_generic_bounds_common(&mut self,
                                    allow_plus: bool,
                                    colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
         let mut bounds = Vec::new();
         let mut negative_bounds = Vec::new();
         let mut last_plus_span = None;
         let mut was_negative = false;
         loop {
             // This needs to be synchronized with `TokenKind::can_begin_bound`.
             let is_bound_start = self.check_path() || self.check_lifetime() ||
                                  self.check(&token::Not) || // used for error reporting only
                                  self.check(&token::Question) ||
                                  self.check_keyword(kw::For) ||
                                  self.check(&token::OpenDelim(token::Paren));
             if is_bound_start {
                 let lo = self.token.span;
                 let has_parens = self.eat(&token::OpenDelim(token::Paren));
                 let inner_lo = self.token.span;
                 let is_negative = self.eat(&token::Not);
                 let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
                 if self.token.is_lifetime() {
                     if let Some(question_span) = question {
                         self.span_err(question_span,
                                       "`?` may only modify trait bounds, not lifetime bounds");
                     }
                     bounds.push(GenericBound::Outlives(self.expect_lifetime()));
                     if has_parens {
                         let inner_span = inner_lo.to(self.prev_span);
                         self.expect(&token::CloseDelim(token::Paren))?;
                         let mut err = self.struct_span_err(
                             lo.to(self.prev_span),
                             "parenthesized lifetime bounds are not supported"
                         );
                         if let Ok(snippet) = self.span_to_snippet(inner_span) {
                             err.span_suggestion_short(
                                 lo.to(self.prev_span),
                                 "remove the parentheses",
                                 snippet.to_owned(),
                                 Applicability::MachineApplicable
                             );
                         }
                         err.emit();
                     }
                 } else {
                     let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
                     let path = self.parse_path(PathStyle::Type)?;
                     if has_parens {
                         self.expect(&token::CloseDelim(token::Paren))?;
                     }
                     let poly_span = lo.to(self.prev_span);
                     if is_negative {
                         was_negative = true;
                         if let Some(sp) = last_plus_span.or(colon_span) {
                             negative_bounds.push(sp.to(poly_span));
                         }
                     } else {
                         let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
                         let modifier = if question.is_some() {
                             TraitBoundModifier::Maybe
                         } else {
                             TraitBoundModifier::None
                         };
                         bounds.push(GenericBound::Trait(poly_trait, modifier));
                     }
                 }
             } else {
                 break
             }

             if !allow_plus || !self.eat_plus() {
                 break
             } else {
                 last_plus_span = Some(self.prev_span);
             }
         }

         if !negative_bounds.is_empty() || was_negative {
             let negative_bounds_len = negative_bounds.len();
             let last_span = negative_bounds.last().map(|sp| *sp);
             let mut err = self.struct_span_err(
                 negative_bounds,
                 "negative trait bounds are not supported",
             );
             if let Some(sp) = last_span {
                 err.span_label(sp, "negative trait bounds are not supported");
             }
             if let Some(bound_list) = colon_span {
                 let bound_list = bound_list.to(self.prev_span);
                 let mut new_bound_list = String::new();
                 if !bounds.is_empty() {
                     let mut snippets = bounds.iter().map(|bound| bound.span())
                         .map(|span| self.span_to_snippet(span));
                     while let Some(Ok(snippet)) = snippets.next() {
                         new_bound_list.push_str(" + ");
                         new_bound_list.push_str(&snippet);
                     }
                     new_bound_list = new_bound_list.replacen(" +", ":", 1);
                 }
                 err.span_suggestion_hidden(
                     bound_list,
                     &format!("remove the trait bound{}", pluralize!(negative_bounds_len)),
                     new_bound_list,
                     Applicability::MachineApplicable,
                 );
             }
             err.emit();
         }

         return Ok(bounds);
     }

     pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
         if self.eat_keyword(kw::For) {
             self.expect_lt()?;
             let params = self.parse_generic_params()?;
             self.expect_gt()?;
             // We rely on AST validation to rule out invalid cases: There must not be type
             // parameters, and the lifetime parameters must not have bounds.
             Ok(params)
         } else {
             Ok(Vec::new())
         }
     }

     pub fn check_lifetime(&mut self) -> bool {
         self.expected_tokens.push(TokenType::Lifetime);
         self.token.is_lifetime()
     }

     /// Parses a single lifetime `'a` or panics.
     pub fn expect_lifetime(&mut self) -> Lifetime {
         if let Some(ident) = self.token.lifetime() {
             let span = self.token.span;
             self.bump();
             Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
         } else {
             self.span_bug(self.token.span, "not a lifetime")
         }
     }

     pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
         P(Ty { kind, span, id: ast::DUMMY_NODE_ID })
     }
 }
	use super::{Parser, PathStyle, PrevTokenKind, TokenType};
	use super::item::ParamCfg;

	use crate::{maybe_whole, maybe_recover_from_interpolated_ty_qpath};

	use syntax::ptr::P;
	use syntax::ast::{self, Ty, TyKind, MutTy, BareFnTy, FunctionRetTy, GenericParam, Lifetime, Ident};
	use syntax::ast::{TraitBoundModifier, TraitObjectSyntax, GenericBound, GenericBounds, PolyTraitRef};
	use syntax::ast::{Mutability, AnonConst, Mac};
	use syntax::token::{self, Token};
	use syntax::source_map::Span;
	use syntax::struct_span_fatal;
	use syntax_pos::symbol::kw;

	use errors::{PResult, Applicability, pluralize};

	use rustc_error_codes::*;

	/// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
	/// `IDENT<<u8 as Trait>::AssocTy>`.
	///
	/// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
	/// that `IDENT` is not the ident of a fn trait.
	fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
	t == &token::ModSep \|\| t == &token::Lt \|\|
	t == &token::BinOp(token::Shl)
	}

	impl<'a> Parser<'a> {
	/// Parses a type.
	pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
	self.parse_ty_common(true, true, false)
	}

	/// Parses a type in restricted contexts where `+` is not permitted.
	///
	/// Example 1: `&'a TYPE`
	/// `+` is prohibited to maintain operator priority (P(+) < P(&)).
	/// Example 2: `value1 as TYPE + value2`
	/// `+` is prohibited to avoid interactions with expression grammar.
	pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
	self.parse_ty_common(false, true, false)
	}

	/// Parses an optional return type `[ -> TY ]` in a function declaration.
	pub(super) fn parse_ret_ty(&mut self, allow_plus: bool) -> PResult<'a, FunctionRetTy> {
	if self.eat(&token::RArrow) {
	Ok(FunctionRetTy::Ty(self.parse_ty_common(allow_plus, true, false)?))
	} else {
	Ok(FunctionRetTy::Default(self.token.span.shrink_to_lo()))
	}
	}

	pub(super) fn parse_ty_common(&mut self, allow_plus: bool, allow_qpath_recovery: bool,
	allow_c_variadic: bool) -> PResult<'a, P<Ty>> {
	maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
	maybe_whole!(self, NtTy, \|x\| x);

	let lo = self.token.span;
	let mut impl_dyn_multi = false;
	let kind = if self.eat(&token::OpenDelim(token::Paren)) {
	// `(TYPE)` is a parenthesized type.
	// `(TYPE,)` is a tuple with a single field of type TYPE.
	let mut ts = vec![];
	let mut last_comma = false;
	while self.token != token::CloseDelim(token::Paren) {
	ts.push(self.parse_ty()?);
	if self.eat(&token::Comma) {
	last_comma = true;
	} else {
	last_comma = false;
	break;
	}
	}
	let trailing_plus = self.prev_token_kind == PrevTokenKind::Plus;
	self.expect(&token::CloseDelim(token::Paren))?;

	if ts.len() == 1 && !last_comma {
	let ty = ts.into_iter().nth(0).unwrap().into_inner();
	let maybe_bounds = allow_plus && self.token.is_like_plus();
	match ty.kind {
	// `(TY_BOUND_NOPAREN) + BOUND + ...`.
	TyKind::Path(None, ref path) if maybe_bounds => {
	self.parse_remaining_bounds(Vec::new(), path.clone(), lo, true)?
	}
	TyKind::TraitObject(ref bounds, TraitObjectSyntax::None)
	if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
	let path = match bounds[0] {
	GenericBound::Trait(ref pt, ..) => pt.trait_ref.path.clone(),
	GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
	};
	self.parse_remaining_bounds(Vec::new(), path, lo, true)?
	}
	// `(TYPE)`
	_ => TyKind::Paren(P(ty))
	}
	} else {
	TyKind::Tup(ts)
	}
	} else if self.eat(&token::Not) {
	// Never type `!`
	TyKind::Never
	} else if self.eat(&token::BinOp(token::Star)) {
	// Raw pointer
	TyKind::Ptr(self.parse_ptr()?)
	} else if self.eat(&token::OpenDelim(token::Bracket)) {
	// Array or slice
	let t = self.parse_ty()?;
	// Parse optional `; EXPR` in `[TYPE; EXPR]`
	let t = match self.maybe_parse_fixed_length_of_vec()? {
	None => TyKind::Slice(t),
	Some(length) => TyKind::Array(t, AnonConst {
	id: ast::DUMMY_NODE_ID,
	value: length,
	}),
	};
	self.expect(&token::CloseDelim(token::Bracket))?;
	t
	} else if self.check(&token::BinOp(token::And)) \|\| self.check(&token::AndAnd) {
	// Reference
	self.expect_and()?;
	self.parse_borrowed_pointee()?
	} else if self.eat_keyword_noexpect(kw::Typeof) {
	// `typeof(EXPR)`
	// In order to not be ambiguous, the type must be surrounded by parens.
	self.expect(&token::OpenDelim(token::Paren))?;
	let e = AnonConst {
	id: ast::DUMMY_NODE_ID,
	value: self.parse_expr()?,
	};
	self.expect(&token::CloseDelim(token::Paren))?;
	TyKind::Typeof(e)
	} else if self.eat_keyword(kw::Underscore) {
	// A type to be inferred `_`
	TyKind::Infer
	} else if self.token_is_bare_fn_keyword() {
	// Function pointer type
	self.parse_ty_bare_fn(Vec::new())?
	} else if self.check_keyword(kw::For) {
	// Function pointer type or bound list (trait object type) starting with a poly-trait.
	// `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
	// `for<'lt> Trait1<'lt> + Trait2 + 'a`
	let lo = self.token.span;
	let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
	if self.token_is_bare_fn_keyword() {
	self.parse_ty_bare_fn(lifetime_defs)?
	} else {
	let path = self.parse_path(PathStyle::Type)?;
	let parse_plus = allow_plus && self.check_plus();
	self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
	}
	} else if self.eat_keyword(kw::Impl) {
	// Always parse bounds greedily for better error recovery.
	let bounds = self.parse_generic_bounds(None)?;
	impl_dyn_multi = bounds.len() > 1 \|\| self.prev_token_kind == PrevTokenKind::Plus;
	TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
	} else if self.check_keyword(kw::Dyn) &&
	(self.token.span.rust_2018() \|\|
	self.look_ahead(1, \|t\| t.can_begin_bound() &&
	!can_continue_type_after_non_fn_ident(t))) {
	self.bump(); // `dyn`
	// Always parse bounds greedily for better error recovery.
	let bounds = self.parse_generic_bounds(None)?;
	impl_dyn_multi = bounds.len() > 1 \|\| self.prev_token_kind == PrevTokenKind::Plus;
	TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
	} else if self.check(&token::Question) \|\|
	self.check_lifetime() && self.look_ahead(1, \|t\| t.is_like_plus()) {
	// Bound list (trait object type)
	TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
	TraitObjectSyntax::None)
	} else if self.eat_lt() {
	// Qualified path
	let (qself, path) = self.parse_qpath(PathStyle::Type)?;
	TyKind::Path(Some(qself), path)
	} else if self.token.is_path_start() {
	// Simple path
	let path = self.parse_path(PathStyle::Type)?;
	if self.eat(&token::Not) {
	// Macro invocation in type position
	let args = self.parse_mac_args()?;
	let mac = Mac {
	path,
	args,
	prior_type_ascription: self.last_type_ascription,
	};
	TyKind::Mac(mac)
	} else {
	// Just a type path or bound list (trait object type) starting with a trait.
	// `Type`
	// `Trait1 + Trait2 + 'a`
	if allow_plus && self.check_plus() {
	self.parse_remaining_bounds(Vec::new(), path, lo, true)?
	} else {
	TyKind::Path(None, path)
	}
	}
	} else if self.check(&token::DotDotDot) {
	if allow_c_variadic {
	self.eat(&token::DotDotDot);
	TyKind::CVarArgs
	} else {
	return Err(struct_span_fatal!(
	self.sess.span_diagnostic,
	self.token.span,
	E0743,
	"only foreign functions are allowed to be C-variadic",
	));
	}
	} else {
	let msg = format!("expected type, found {}", self.this_token_descr());
	let mut err = self.fatal(&msg);
	err.span_label(self.token.span, "expected type");
	self.maybe_annotate_with_ascription(&mut err, true);
	return Err(err);
	};

	let span = lo.to(self.prev_span);
	let ty = self.mk_ty(span, kind);

	// Try to recover from use of `+` with incorrect priority.
	self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
	self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
	self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
	}

	fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
	lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
	let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
	let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
	if parse_plus {
	self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
	bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
	}
	Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
	}

	fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
	let mutbl = self.parse_const_or_mut().unwrap_or_else(\|\| {
	let span = self.prev_span;
	let msg = "expected mut or const in raw pointer type";
	self.struct_span_err(span, msg)
	.span_label(span, msg)
	.help("use `mut T` or `const T` as appropriate")
	.emit();
	Mutability::Immutable
	});
	let t = self.parse_ty_no_plus()?;
	Ok(MutTy { ty: t, mutbl })
	}

	fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
	if self.eat(&token::Semi) {
	Ok(Some(self.parse_expr()?))
	} else {
	Ok(None)
	}
	}

	fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
	let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
	let mutbl = self.parse_mutability();
	let ty = self.parse_ty_no_plus()?;
	return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }));
	}

	/// Is the current token one of the keywords that signals a bare function type?
	fn token_is_bare_fn_keyword(&mut self) -> bool {
	self.check_keyword(kw::Fn) \|\|
	self.check_keyword(kw::Unsafe) \|\|
	self.check_keyword(kw::Extern)
	}

	/// Parses a `TyKind::BareFn` type.
	fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
	/*

	[unsafe] [extern "ABI"] fn (S) -> T
	^~~~^ ^~~~^ ^~^ ^
	\| \| \| \|
	\| \| \| Return type
	\| \| Argument types
	\| \|
	\| ABI
	Function Style
	*/

	let unsafety = self.parse_unsafety();
	let ext = self.parse_extern()?;
	self.expect_keyword(kw::Fn)?;
	let cfg = ParamCfg {
	is_self_allowed: false,
	allow_c_variadic: true,
	is_name_required: \|_\| false,
	};
	let decl = self.parse_fn_decl(cfg, false)?;
	Ok(TyKind::BareFn(P(BareFnTy {
	ext,
	unsafety,
	generic_params,
	decl,
	})))
	}

	pub(super) fn parse_generic_bounds(&mut self,
	colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
	self.parse_generic_bounds_common(true, colon_span)
	}

	/// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
	///
	/// ```
	/// BOUND = TY_BOUND \| LT_BOUND
	/// LT_BOUND = LIFETIME (e.g., `'a`)
	/// TY_BOUND = TY_BOUND_NOPAREN \| (TY_BOUND_NOPAREN)
	/// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
	/// ```
	fn parse_generic_bounds_common(&mut self,
	allow_plus: bool,
	colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
	let mut bounds = Vec::new();
	let mut negative_bounds = Vec::new();
	let mut last_plus_span = None;
	let mut was_negative = false;
	loop {
	// This needs to be synchronized with `TokenKind::can_begin_bound`.
	let is_bound_start = self.check_path() \|\| self.check_lifetime() \|\|
	self.check(&token::Not) \|\| // used for error reporting only
	self.check(&token::Question) \|\|
	self.check_keyword(kw::For) \|\|
	self.check(&token::OpenDelim(token::Paren));
	if is_bound_start {
	let lo = self.token.span;
	let has_parens = self.eat(&token::OpenDelim(token::Paren));
	let inner_lo = self.token.span;
	let is_negative = self.eat(&token::Not);
	let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
	if self.token.is_lifetime() {
	if let Some(question_span) = question {
	self.span_err(question_span,
	"`?` may only modify trait bounds, not lifetime bounds");
	}
	bounds.push(GenericBound::Outlives(self.expect_lifetime()));
	if has_parens {
	let inner_span = inner_lo.to(self.prev_span);
	self.expect(&token::CloseDelim(token::Paren))?;
	let mut err = self.struct_span_err(
	lo.to(self.prev_span),
	"parenthesized lifetime bounds are not supported"
	);
	if let Ok(snippet) = self.span_to_snippet(inner_span) {
	err.span_suggestion_short(
	lo.to(self.prev_span),
	"remove the parentheses",
	snippet.to_owned(),
	Applicability::MachineApplicable
	);
	}
	err.emit();
	}
	} else {
	let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
	let path = self.parse_path(PathStyle::Type)?;
	if has_parens {
	self.expect(&token::CloseDelim(token::Paren))?;
	}
	let poly_span = lo.to(self.prev_span);
	if is_negative {
	was_negative = true;
	if let Some(sp) = last_plus_span.or(colon_span) {
	negative_bounds.push(sp.to(poly_span));
	}
	} else {
	let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
	let modifier = if question.is_some() {
	TraitBoundModifier::Maybe
	} else {
	TraitBoundModifier::None
	};
	bounds.push(GenericBound::Trait(poly_trait, modifier));
	}
	}
	} else {
	break
	}

	if !allow_plus \|\| !self.eat_plus() {
	break
	} else {
	last_plus_span = Some(self.prev_span);
	}
	}

	if !negative_bounds.is_empty() \|\| was_negative {
	let negative_bounds_len = negative_bounds.len();
	let last_span = negative_bounds.last().map(\|sp\| *sp);
	let mut err = self.struct_span_err(
	negative_bounds,
	"negative trait bounds are not supported",
	);
	if let Some(sp) = last_span {
	err.span_label(sp, "negative trait bounds are not supported");
	}
	if let Some(bound_list) = colon_span {
	let bound_list = bound_list.to(self.prev_span);
	let mut new_bound_list = String::new();
	if !bounds.is_empty() {
	let mut snippets = bounds.iter().map(\|bound\| bound.span())
	.map(\|span\| self.span_to_snippet(span));
	while let Some(Ok(snippet)) = snippets.next() {
	new_bound_list.push_str(" + ");
	new_bound_list.push_str(&snippet);
	}
	new_bound_list = new_bound_list.replacen(" +", ":", 1);
	}
	err.span_suggestion_hidden(
	bound_list,
	&format!("remove the trait bound{}", pluralize!(negative_bounds_len)),
	new_bound_list,
	Applicability::MachineApplicable,
	);
	}
	err.emit();
	}

	return Ok(bounds);
	}

	pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
	if self.eat_keyword(kw::For) {
	self.expect_lt()?;
	let params = self.parse_generic_params()?;
	self.expect_gt()?;
	// We rely on AST validation to rule out invalid cases: There must not be type
	// parameters, and the lifetime parameters must not have bounds.
	Ok(params)
	} else {
	Ok(Vec::new())
	}
	}

	pub fn check_lifetime(&mut self) -> bool {
	self.expected_tokens.push(TokenType::Lifetime);
	self.token.is_lifetime()
	}

	/// Parses a single lifetime `'a` or panics.
	pub fn expect_lifetime(&mut self) -> Lifetime {
	if let Some(ident) = self.token.lifetime() {
	let span = self.token.span;
	self.bump();
	Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
	} else {
	self.span_bug(self.token.span, "not a lifetime")
	}
	}

	pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
	P(Ty { kind, span, id: ast::DUMMY_NODE_ID })
	}
	}