src/libsyntax/parse/parser/expr.rs

   1 use super::{
   2     Parser, PResult, Restrictions, PrevTokenKind, TokenType, PathStyle, BlockMode, SemiColonMode,
   3     SeqSep, TokenExpectType,
   4 };
   5 use super::pat::{GateOr, PARAM_EXPECTED};
   6
   7 use crate::ast::{
   8     self, DUMMY_NODE_ID, Attribute, AttrStyle, Ident, CaptureBy, BlockCheckMode,
   9     Expr, ExprKind, RangeLimits, Label, Movability, IsAsync, Arm, Ty, TyKind,
  10     FunctionRetTy, Param, FnDecl, BinOpKind, BinOp, UnOp, Mac, AnonConst, Field,
  11 };
  12 use crate::maybe_recover_from_interpolated_ty_qpath;
  13 use crate::parse::classify;
  14 use crate::parse::token::{self, Token};
  15 use crate::parse::diagnostics::Error;
  16 use crate::print::pprust;
  17 use crate::ptr::P;
  18 use crate::source_map::{self, Span};
  19 use crate::symbol::{kw, sym};
  20 use crate::util::parser::{AssocOp, Fixity, prec_let_scrutinee_needs_par};
  21
  22 use errors::Applicability;
  23 use std::mem;
  24 use rustc_data_structures::thin_vec::ThinVec;
  25
  26 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  27 /// dropped into the token stream, which happens while parsing the result of
  28 /// macro expansion). Placement of these is not as complex as I feared it would
  29 /// be. The important thing is to make sure that lookahead doesn't balk at
  30 /// `token::Interpolated` tokens.
  31 macro_rules! maybe_whole_expr {
  32     ($p:expr) => {
  33         if let token::Interpolated(nt) = &$p.token.kind {
  34             match &**nt {
  35                 token::NtExpr(e) | token::NtLiteral(e) => {
  36                     let e = e.clone();
  37                     $p.bump();
  38                     return Ok(e);
  39                 }
  40                 token::NtPath(path) => {
  41                     let path = path.clone();
  42                     $p.bump();
  43                     return Ok($p.mk_expr(
  44                         $p.token.span, ExprKind::Path(None, path), ThinVec::new()
  45                     ));
  46                 }
  47                 token::NtBlock(block) => {
  48                     let block = block.clone();
  49                     $p.bump();
  50                     return Ok($p.mk_expr(
  51                         $p.token.span, ExprKind::Block(block, None), ThinVec::new()
  52                     ));
  53                 }
  54                 // N.B., `NtIdent(ident)` is normalized to `Ident` in `fn bump`.
  55                 _ => {},
  56             };
  57         }
  58     }
  59 }
  60
  61 #[derive(Debug)]
  62 pub(super) enum LhsExpr {
  63     NotYetParsed,
  64     AttributesParsed(ThinVec<Attribute>),
  65     AlreadyParsed(P<Expr>),
  66 }
  67
  68 impl From<Option<ThinVec<Attribute>>> for LhsExpr {
  69     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  70     /// and `None` into `LhsExpr::NotYetParsed`.
  71     ///
  72     /// This conversion does not allocate.
  73     fn from(o: Option<ThinVec<Attribute>>) -> Self {
  74         if let Some(attrs) = o {
  75             LhsExpr::AttributesParsed(attrs)
  76         } else {
  77             LhsExpr::NotYetParsed
  78         }
  79     }
  80 }
  81
  82 impl From<P<Expr>> for LhsExpr {
  83     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
  84     ///
  85     /// This conversion does not allocate.
  86     fn from(expr: P<Expr>) -> Self {
  87         LhsExpr::AlreadyParsed(expr)
  88     }
  89 }
  90
  91 impl<'a> Parser<'a> {
  92     /// Parses an expression.
  93     #[inline]
  94     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
  95         self.parse_expr_res(Restrictions::empty(), None)
  96     }
  97
  98     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
  99         self.parse_paren_comma_seq(|p| {
 100             match p.parse_expr() {
 101                 Ok(expr) => Ok(expr),
 102                 Err(mut err) => match p.token.kind {
 103                     token::Ident(name, false)
 104                     if name == kw::Underscore && p.look_ahead(1, |t| {
 105                         t == &token::Comma
 106                     }) => {
 107                         // Special-case handling of `foo(_, _, _)`
 108                         err.emit();
 109                         let sp = p.token.span;
 110                         p.bump();
 111                         Ok(p.mk_expr(sp, ExprKind::Err, ThinVec::new()))
 112                     }
 113                     _ => Err(err),
 114                 },
 115             }
 116         }).map(|(r, _)| r)
 117     }
 118
 119     /// Parses an expression, subject to the given restrictions.
 120     #[inline]
 121     pub(super) fn parse_expr_res(
 122         &mut self,
 123         r: Restrictions,
 124         already_parsed_attrs: Option<ThinVec<Attribute>>
 125     ) -> PResult<'a, P<Expr>> {
 126         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 127     }
 128
 129     /// Parses an associative expression.
 130     ///
 131     /// This parses an expression accounting for associativity and precedence of the operators in
 132     /// the expression.
 133     #[inline]
 134     fn parse_assoc_expr(
 135         &mut self,
 136         already_parsed_attrs: Option<ThinVec<Attribute>>,
 137     ) -> PResult<'a, P<Expr>> {
 138         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 139     }
 140
 141     /// Parses an associative expression with operators of at least `min_prec` precedence.
 142     pub(super) fn parse_assoc_expr_with(
 143         &mut self,
 144         min_prec: usize,
 145         lhs: LhsExpr,
 146     ) -> PResult<'a, P<Expr>> {
 147         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 148             expr
 149         } else {
 150             let attrs = match lhs {
 151                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 152                 _ => None,
 153             };
 154             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 155                 return self.parse_prefix_range_expr(attrs);
 156             } else {
 157                 self.parse_prefix_expr(attrs)?
 158             }
 159         };
 160         let last_type_ascription_set = self.last_type_ascription.is_some();
 161
 162         match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) {
 163             (true, None) => {
 164                 self.last_type_ascription = None;
 165                 // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071
 166                 return Ok(lhs);
 167             }
 168             (false, _) => {} // continue parsing the expression
 169             // An exhaustive check is done in the following block, but these are checked first
 170             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 171             // want to keep their span info to improve diagnostics in these cases in a later stage.
 172             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 173             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 174             (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
 175             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 176             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 177             // `if x { a } else { b } && if y { c } else { d }`
 178             if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
 179                 self.last_type_ascription = None;
 180                 // These cases are ambiguous and can't be identified in the parser alone
 181                 let sp = self.sess.source_map().start_point(self.token.span);
 182                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 183                 return Ok(lhs);
 184             }
 185             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => {
 186                 self.last_type_ascription = None;
 187                 return Ok(lhs);
 188             }
 189             (true, Some(_)) => {
 190                 // We've found an expression that would be parsed as a statement, but the next
 191                 // token implies this should be parsed as an expression.
 192                 // For example: `if let Some(x) = x { x } else { 0 } / 2`
 193                 let mut err = self.struct_span_err(self.token.span, &format!(
 194                     "expected expression, found `{}`",
 195                     pprust::token_to_string(&self.token),
 196                 ));
 197                 err.span_label(self.token.span, "expected expression");
 198                 self.sess.expr_parentheses_needed(
 199                     &mut err,
 200                     lhs.span,
 201                     Some(pprust::expr_to_string(&lhs),
 202                 ));
 203                 err.emit();
 204             }
 205         }
 206         self.expected_tokens.push(TokenType::Operator);
 207         while let Some(op) = AssocOp::from_token(&self.token) {
 208
 209             // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
 210             // it refers to. Interpolated identifiers are unwrapped early and never show up here
 211             // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
 212             // it as "interpolated", it doesn't change the answer for non-interpolated idents.
 213             let lhs_span = match (self.prev_token_kind, &lhs.kind) {
 214                 (PrevTokenKind::Interpolated, _) => self.prev_span,
 215                 (PrevTokenKind::Ident, &ExprKind::Path(None, ref path))
 216                     if path.segments.len() == 1 => self.prev_span,
 217                 _ => lhs.span,
 218             };
 219
 220             let cur_op_span = self.token.span;
 221             let restrictions = if op.is_assign_like() {
 222                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 223             } else {
 224                 self.restrictions
 225             };
 226             let prec = op.precedence();
 227             if prec < min_prec {
 228                 break;
 229             }
 230             // Check for deprecated `...` syntax
 231             if self.token == token::DotDotDot && op == AssocOp::DotDotEq {
 232                 self.err_dotdotdot_syntax(self.token.span);
 233             }
 234
 235             if self.token == token::LArrow {
 236                 self.err_larrow_operator(self.token.span);
 237             }
 238
 239             self.bump();
 240             if op.is_comparison() {
 241                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 242                     return Ok(expr);
 243                 }
 244             }
 245             // Special cases:
 246             if op == AssocOp::As {
 247                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 248                 continue
 249             } else if op == AssocOp::Colon {
 250                 let maybe_path = self.could_ascription_be_path(&lhs.kind);
 251                 self.last_type_ascription = Some((self.prev_span, maybe_path));
 252
 253                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 254                 continue
 255             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 256                 // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
 257                 // generalise it to the Fixity::None code.
 258                 //
 259                 // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
 260                 // two variants are handled with `parse_prefix_range_expr` call above.
 261                 let rhs = if self.is_at_start_of_range_notation_rhs() {
 262                     Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 263                 } else {
 264                     None
 265                 };
 266                 let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
 267                     x.span
 268                 } else {
 269                     cur_op_span
 270                 });
 271                 let limits = if op == AssocOp::DotDot {
 272                     RangeLimits::HalfOpen
 273                 } else {
 274                     RangeLimits::Closed
 275                 };
 276
 277                 let r = self.mk_range(Some(lhs), rhs, limits)?;
 278                 lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
 279                 break
 280             }
 281
 282             let fixity = op.fixity();
 283             let prec_adjustment = match fixity {
 284                 Fixity::Right => 0,
 285                 Fixity::Left => 1,
 286                 // We currently have no non-associative operators that are not handled above by
 287                 // the special cases. The code is here only for future convenience.
 288                 Fixity::None => 1,
 289             };
 290             let rhs = self.with_res(
 291                 restrictions - Restrictions::STMT_EXPR,
 292                 |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 293             )?;
 294
 295             // Make sure that the span of the parent node is larger than the span of lhs and rhs,
 296             // including the attributes.
 297             let lhs_span = lhs
 298                 .attrs
 299                 .iter()
 300                 .filter(|a| a.style == AttrStyle::Outer)
 301                 .next()
 302                 .map_or(lhs_span, |a| a.span);
 303             let span = lhs_span.to(rhs.span);
 304             lhs = match op {
 305                 AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
 306                 AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
 307                 AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
 308                 AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
 309                 AssocOp::Greater | AssocOp::GreaterEqual => {
 310                     let ast_op = op.to_ast_binop().unwrap();
 311                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 312                     self.mk_expr(span, binary, ThinVec::new())
 313                 }
 314                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
 315                 AssocOp::AssignOp(k) => {
 316                     let aop = match k {
 317                         token::Plus =>    BinOpKind::Add,
 318                         token::Minus =>   BinOpKind::Sub,
 319                         token::Star =>    BinOpKind::Mul,
 320                         token::Slash =>   BinOpKind::Div,
 321                         token::Percent => BinOpKind::Rem,
 322                         token::Caret =>   BinOpKind::BitXor,
 323                         token::And =>     BinOpKind::BitAnd,
 324                         token::Or =>      BinOpKind::BitOr,
 325                         token::Shl =>     BinOpKind::Shl,
 326                         token::Shr =>     BinOpKind::Shr,
 327                     };
 328                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 329                     self.mk_expr(span, aopexpr, ThinVec::new())
 330                 }
 331                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 332                     self.bug("AssocOp should have been handled by special case")
 333                 }
 334             };
 335
 336             if let Fixity::None = fixity { break }
 337         }
 338         if last_type_ascription_set {
 339             self.last_type_ascription = None;
 340         }
 341         Ok(lhs)
 342     }
 343
 344     /// Checks if this expression is a successfully parsed statement.
 345     fn expr_is_complete(&self, e: &Expr) -> bool {
 346         self.restrictions.contains(Restrictions::STMT_EXPR) &&
 347             !classify::expr_requires_semi_to_be_stmt(e)
 348     }
 349
 350     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 351         if self.token.can_begin_expr() {
 352             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 353             if self.token == token::OpenDelim(token::Brace) {
 354                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 355             }
 356             true
 357         } else {
 358             false
 359         }
 360     }
 361
 362     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 363     fn parse_prefix_range_expr(
 364         &mut self,
 365         already_parsed_attrs: Option<ThinVec<Attribute>>
 366     ) -> PResult<'a, P<Expr>> {
 367         // Check for deprecated `...` syntax.
 368         if self.token == token::DotDotDot {
 369             self.err_dotdotdot_syntax(self.token.span);
 370         }
 371
 372         debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 373                       "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 374                       self.token);
 375         let tok = self.token.clone();
 376         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 377         let lo = self.token.span;
 378         let mut hi = self.token.span;
 379         self.bump();
 380         let opt_end = if self.is_at_start_of_range_notation_rhs() {
 381             // RHS must be parsed with more associativity than the dots.
 382             let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
 383             Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed)
 384                 .map(|x| {
 385                     hi = x.span;
 386                     x
 387                 })?)
 388         } else {
 389             None
 390         };
 391         let limits = if tok == token::DotDot {
 392             RangeLimits::HalfOpen
 393         } else {
 394             RangeLimits::Closed
 395         };
 396
 397         let r = self.mk_range(None, opt_end, limits)?;
 398         Ok(self.mk_expr(lo.to(hi), r, attrs))
 399     }
 400
 401     /// Parses a prefix-unary-operator expr.
 402     fn parse_prefix_expr(
 403         &mut self,
 404         already_parsed_attrs: Option<ThinVec<Attribute>>
 405     ) -> PResult<'a, P<Expr>> {
 406         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 407         let lo = self.token.span;
 408         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 409         let (hi, ex) = match self.token.kind {
 410             token::Not => {
 411                 self.bump();
 412                 let e = self.parse_prefix_expr(None);
 413                 let (span, e) = self.interpolated_or_expr_span(e)?;
 414                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 415             }
 416             // Suggest `!` for bitwise negation when encountering a `~`
 417             token::Tilde => {
 418                 self.bump();
 419                 let e = self.parse_prefix_expr(None);
 420                 let (span, e) = self.interpolated_or_expr_span(e)?;
 421                 let span_of_tilde = lo;
 422                 self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator")
 423                     .span_suggestion_short(
 424                         span_of_tilde,
 425                         "use `!` to perform bitwise negation",
 426                         "!".to_owned(),
 427                         Applicability::MachineApplicable
 428                     )
 429                     .emit();
 430                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 431             }
 432             token::BinOp(token::Minus) => {
 433                 self.bump();
 434                 let e = self.parse_prefix_expr(None);
 435                 let (span, e) = self.interpolated_or_expr_span(e)?;
 436                 (lo.to(span), self.mk_unary(UnOp::Neg, e))
 437             }
 438             token::BinOp(token::Star) => {
 439                 self.bump();
 440                 let e = self.parse_prefix_expr(None);
 441                 let (span, e) = self.interpolated_or_expr_span(e)?;
 442                 (lo.to(span), self.mk_unary(UnOp::Deref, e))
 443             }
 444             token::BinOp(token::And) | token::AndAnd => {
 445                 self.expect_and()?;
 446                 let m = self.parse_mutability();
 447                 let e = self.parse_prefix_expr(None);
 448                 let (span, e) = self.interpolated_or_expr_span(e)?;
 449                 (lo.to(span), ExprKind::AddrOf(m, e))
 450             }
 451             token::Ident(..) if self.token.is_keyword(kw::Box) => {
 452                 self.bump();
 453                 let e = self.parse_prefix_expr(None);
 454                 let (span, e) = self.interpolated_or_expr_span(e)?;
 455                 (lo.to(span), ExprKind::Box(e))
 456             }
 457             token::Ident(..) if self.token.is_ident_named(sym::not) => {
 458                 // `not` is just an ordinary identifier in Rust-the-language,
 459                 // but as `rustc`-the-compiler, we can issue clever diagnostics
 460                 // for confused users who really want to say `!`
 461                 let token_cannot_continue_expr = |t: &Token| match t.kind {
 462                     // These tokens can start an expression after `!`, but
 463                     // can't continue an expression after an ident
 464                     token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 465                     token::Literal(..) | token::Pound => true,
 466                     _ => t.is_whole_expr(),
 467                 };
 468                 let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
 469                 if cannot_continue_expr {
 470                     self.bump();
 471                     // Emit the error ...
 472                     self.struct_span_err(
 473                         self.token.span,
 474                         &format!("unexpected {} after identifier",self.this_token_descr())
 475                     )
 476                     .span_suggestion_short(
 477                         // Span the `not` plus trailing whitespace to avoid
 478                         // trailing whitespace after the `!` in our suggestion
 479                         self.sess.source_map()
 480                             .span_until_non_whitespace(lo.to(self.token.span)),
 481                         "use `!` to perform logical negation",
 482                         "!".to_owned(),
 483                         Applicability::MachineApplicable
 484                     )
 485                     .emit();
 486                     // —and recover! (just as if we were in the block
 487                     // for the `token::Not` arm)
 488                     let e = self.parse_prefix_expr(None);
 489                     let (span, e) = self.interpolated_or_expr_span(e)?;
 490                     (lo.to(span), self.mk_unary(UnOp::Not, e))
 491                 } else {
 492                     return self.parse_dot_or_call_expr(Some(attrs));
 493                 }
 494             }
 495             _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
 496         };
 497         return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 498     }
 499
 500     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 501     fn interpolated_or_expr_span(
 502         &self,
 503         expr: PResult<'a, P<Expr>>,
 504     ) -> PResult<'a, (Span, P<Expr>)> {
 505         expr.map(|e| {
 506             if self.prev_token_kind == PrevTokenKind::Interpolated {
 507                 (self.prev_span, e)
 508             } else {
 509                 (e.span, e)
 510             }
 511         })
 512     }
 513
 514     fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
 515                            expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
 516                            -> PResult<'a, P<Expr>> {
 517         let mk_expr = |this: &mut Self, rhs: P<Ty>| {
 518             this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
 519         };
 520
 521         // Save the state of the parser before parsing type normally, in case there is a
 522         // LessThan comparison after this cast.
 523         let parser_snapshot_before_type = self.clone();
 524         match self.parse_ty_no_plus() {
 525             Ok(rhs) => {
 526                 Ok(mk_expr(self, rhs))
 527             }
 528             Err(mut type_err) => {
 529                 // Rewind to before attempting to parse the type with generics, to recover
 530                 // from situations like `x as usize < y` in which we first tried to parse
 531                 // `usize < y` as a type with generic arguments.
 532                 let parser_snapshot_after_type = self.clone();
 533                 mem::replace(self, parser_snapshot_before_type);
 534
 535                 match self.parse_path(PathStyle::Expr) {
 536                     Ok(path) => {
 537                         let (op_noun, op_verb) = match self.token.kind {
 538                             token::Lt => ("comparison", "comparing"),
 539                             token::BinOp(token::Shl) => ("shift", "shifting"),
 540                             _ => {
 541                                 // We can end up here even without `<` being the next token, for
 542                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 543                                 // but `parse_path` returns `Ok` on them due to error recovery.
 544                                 // Return original error and parser state.
 545                                 mem::replace(self, parser_snapshot_after_type);
 546                                 return Err(type_err);
 547                             }
 548                         };
 549
 550                         // Successfully parsed the type path leaving a `<` yet to parse.
 551                         type_err.cancel();
 552
 553                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 554                         // in AST and continue parsing.
 555                         let msg = format!("`<` is interpreted as a start of generic \
 556                                            arguments for `{}`, not a {}", path, op_noun);
 557                         let span_after_type = parser_snapshot_after_type.token.span;
 558                         let expr = mk_expr(self, P(Ty {
 559                             span: path.span,
 560                             kind: TyKind::Path(None, path),
 561                             id: DUMMY_NODE_ID,
 562                         }));
 563
 564                         let expr_str = self.span_to_snippet(expr.span)
 565                             .unwrap_or_else(|_| pprust::expr_to_string(&expr));
 566
 567                         self.struct_span_err(self.token.span, &msg)
 568                             .span_label(
 569                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 570                                 "interpreted as generic arguments"
 571                             )
 572                             .span_label(self.token.span, format!("not interpreted as {}", op_noun))
 573                             .span_suggestion(
 574                                 expr.span,
 575                                 &format!("try {} the cast value", op_verb),
 576                                 format!("({})", expr_str),
 577                                 Applicability::MachineApplicable,
 578                             )
 579                             .emit();
 580
 581                         Ok(expr)
 582                     }
 583                     Err(mut path_err) => {
 584                         // Couldn't parse as a path, return original error and parser state.
 585                         path_err.cancel();
 586                         mem::replace(self, parser_snapshot_after_type);
 587                         Err(type_err)
 588                     }
 589                 }
 590             }
 591         }
 592     }
 593
 594     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 595     fn parse_dot_or_call_expr(
 596         &mut self,
 597         already_parsed_attrs: Option<ThinVec<Attribute>>,
 598     ) -> PResult<'a, P<Expr>> {
 599         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 600
 601         let b = self.parse_bottom_expr();
 602         let (span, b) = self.interpolated_or_expr_span(b)?;
 603         self.parse_dot_or_call_expr_with(b, span, attrs)
 604     }
 605
 606     pub(super) fn parse_dot_or_call_expr_with(
 607         &mut self,
 608         e0: P<Expr>,
 609         lo: Span,
 610         mut attrs: ThinVec<Attribute>,
 611     ) -> PResult<'a, P<Expr>> {
 612         // Stitch the list of outer attributes onto the return value.
 613         // A little bit ugly, but the best way given the current code
 614         // structure
 615         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr|
 616             expr.map(|mut expr| {
 617                 attrs.extend::<Vec<_>>(expr.attrs.into());
 618                 expr.attrs = attrs;
 619                 match expr.kind {
 620                     ExprKind::If(..) if !expr.attrs.is_empty() => {
 621                         // Just point to the first attribute in there...
 622                         let span = expr.attrs[0].span;
 623                         self.span_err(span, "attributes are not yet allowed on `if` expressions");
 624                     }
 625                     _ => {}
 626                 }
 627                 expr
 628             })
 629         )
 630     }
 631
 632     fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 633         let mut e = e0;
 634         let mut hi;
 635         loop {
 636             // expr?
 637             while self.eat(&token::Question) {
 638                 let hi = self.prev_span;
 639                 e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
 640             }
 641
 642             // expr.f
 643             if self.eat(&token::Dot) {
 644                 match self.token.kind {
 645                     token::Ident(..) => {
 646                         e = self.parse_dot_suffix(e, lo)?;
 647                     }
 648                     token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 649                         let span = self.token.span;
 650                         self.bump();
 651                         let field = ExprKind::Field(e, Ident::new(symbol, span));
 652                         e = self.mk_expr(lo.to(span), field, ThinVec::new());
 653
 654                         self.expect_no_suffix(span, "a tuple index", suffix);
 655                     }
 656                     token::Literal(token::Lit { kind: token::Float, symbol, .. }) => {
 657                       self.bump();
 658                       let fstr = symbol.as_str();
 659                       let msg = format!("unexpected token: `{}`", symbol);
 660                       let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg);
 661                       err.span_label(self.prev_span, "unexpected token");
 662                       if fstr.chars().all(|x| "0123456789.".contains(x)) {
 663                           let float = match fstr.parse::<f64>().ok() {
 664                               Some(f) => f,
 665                               None => continue,
 666                           };
 667                           let sugg = pprust::to_string(|s| {
 668                               s.popen();
 669                               s.print_expr(&e);
 670                               s.s.word( ".");
 671                               s.print_usize(float.trunc() as usize);
 672                               s.pclose();
 673                               s.s.word(".");
 674                               s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
 675                           });
 676                           err.span_suggestion(
 677                               lo.to(self.prev_span),
 678                               "try parenthesizing the first index",
 679                               sugg,
 680                               Applicability::MachineApplicable
 681                           );
 682                       }
 683                       return Err(err);
 684
 685                     }
 686                     _ => {
 687                         // FIXME Could factor this out into non_fatal_unexpected or something.
 688                         let actual = self.this_token_to_string();
 689                         self.span_err(self.token.span, &format!("unexpected token: `{}`", actual));
 690                     }
 691                 }
 692                 continue;
 693             }
 694             if self.expr_is_complete(&e) { break; }
 695             match self.token.kind {
 696                 // expr(...)
 697                 token::OpenDelim(token::Paren) => {
 698                     let seq = self.parse_paren_expr_seq().map(|es| {
 699                         let nd = self.mk_call(e, es);
 700                         let hi = self.prev_span;
 701                         self.mk_expr(lo.to(hi), nd, ThinVec::new())
 702                     });
 703                     e = self.recover_seq_parse_error(token::Paren, lo, seq);
 704                 }
 705
 706                 // expr[...]
 707                 // Could be either an index expression or a slicing expression.
 708                 token::OpenDelim(token::Bracket) => {
 709                     self.bump();
 710                     let ix = self.parse_expr()?;
 711                     hi = self.token.span;
 712                     self.expect(&token::CloseDelim(token::Bracket))?;
 713                     let index = self.mk_index(e, ix);
 714                     e = self.mk_expr(lo.to(hi), index, ThinVec::new())
 715                 }
 716                 _ => return Ok(e)
 717             }
 718         }
 719         return Ok(e);
 720     }
 721
 722     /// Assuming we have just parsed `.`, continue parsing into an expression.
 723     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 724         if self.token.span.rust_2018() && self.eat_keyword(kw::Await) {
 725             return self.mk_await_expr(self_arg, lo);
 726         }
 727
 728         let segment = self.parse_path_segment(PathStyle::Expr)?;
 729         self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
 730
 731         Ok(match self.token.kind {
 732             token::OpenDelim(token::Paren) => {
 733                 // Method call `expr.f()`
 734                 let mut args = self.parse_paren_expr_seq()?;
 735                 args.insert(0, self_arg);
 736
 737                 let span = lo.to(self.prev_span);
 738                 self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
 739             }
 740             _ => {
 741                 // Field access `expr.f`
 742                 if let Some(args) = segment.args {
 743                     self.span_err(args.span(),
 744                                   "field expressions may not have generic arguments");
 745                 }
 746
 747                 let span = lo.to(self.prev_span);
 748                 self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
 749             }
 750         })
 751     }
 752
 753     /// At the bottom (top?) of the precedence hierarchy,
 754     /// Parses things like parenthesized exprs, macros, `return`, etc.
 755     ///
 756     /// N.B., this does not parse outer attributes, and is private because it only works
 757     /// correctly if called from `parse_dot_or_call_expr()`.
 758     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
 759         maybe_recover_from_interpolated_ty_qpath!(self, true);
 760         maybe_whole_expr!(self);
 761
 762         // Outer attributes are already parsed and will be
 763         // added to the return value after the fact.
 764         //
 765         // Therefore, prevent sub-parser from parsing
 766         // attributes by giving them a empty "already-parsed" list.
 767         let mut attrs = ThinVec::new();
 768
 769         let lo = self.token.span;
 770         let mut hi = self.token.span;
 771
 772         let ex: ExprKind;
 773
 774         macro_rules! parse_lit {
 775             () => {
 776                 match self.parse_lit() {
 777                     Ok(literal) => {
 778                         hi = self.prev_span;
 779                         ex = ExprKind::Lit(literal);
 780                     }
 781                     Err(mut err) => {
 782                         err.cancel();
 783                         return Err(self.expected_expression_found());
 784                     }
 785                 }
 786             }
 787         }
 788
 789         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
 790         match self.token.kind {
 791             // This match arm is a special-case of the `_` match arm below and
 792             // could be removed without changing functionality, but it's faster
 793             // to have it here, especially for programs with large constants.
 794             token::Literal(_) => {
 795                 parse_lit!()
 796             }
 797             token::OpenDelim(token::Paren) => {
 798                 self.bump();
 799
 800                 attrs.extend(self.parse_inner_attributes()?);
 801
 802                 // `(e)` is parenthesized `e`.
 803                 // `(e,)` is a tuple with only one field, `e`.
 804                 let mut es = vec![];
 805                 let mut trailing_comma = false;
 806                 let mut recovered = false;
 807                 while self.token != token::CloseDelim(token::Paren) {
 808                     es.push(match self.parse_expr() {
 809                         Ok(es) => es,
 810                         Err(mut err) => {
 811                             // Recover from parse error in tuple list.
 812                             match self.token.kind {
 813                                 token::Ident(name, false)
 814                                 if name == kw::Underscore && self.look_ahead(1, |t| {
 815                                     t == &token::Comma
 816                                 }) => {
 817                                     // Special-case handling of `Foo<(_, _, _)>`
 818                                     err.emit();
 819                                     let sp = self.token.span;
 820                                     self.bump();
 821                                     self.mk_expr(sp, ExprKind::Err, ThinVec::new())
 822                                 }
 823                                 _ => return Ok(
 824                                     self.recover_seq_parse_error(token::Paren, lo, Err(err)),
 825                                 ),
 826                             }
 827                         }
 828                     });
 829                     recovered = self.expect_one_of(
 830                         &[],
 831                         &[token::Comma, token::CloseDelim(token::Paren)],
 832                     )?;
 833                     if self.eat(&token::Comma) {
 834                         trailing_comma = true;
 835                     } else {
 836                         trailing_comma = false;
 837                         break;
 838                     }
 839                 }
 840                 if !recovered {
 841                     self.bump();
 842                 }
 843
 844                 hi = self.prev_span;
 845                 ex = if es.len() == 1 && !trailing_comma {
 846                     ExprKind::Paren(es.into_iter().nth(0).unwrap())
 847                 } else {
 848                     ExprKind::Tup(es)
 849                 };
 850             }
 851             token::OpenDelim(token::Brace) => {
 852                 return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
 853             }
 854             token::BinOp(token::Or) | token::OrOr => {
 855                 return self.parse_closure_expr(attrs);
 856             }
 857             token::OpenDelim(token::Bracket) => {
 858                 self.bump();
 859
 860                 attrs.extend(self.parse_inner_attributes()?);
 861
 862                 if self.eat(&token::CloseDelim(token::Bracket)) {
 863                     // Empty vector
 864                     ex = ExprKind::Array(Vec::new());
 865                 } else {
 866                     // Non-empty vector
 867                     let first_expr = self.parse_expr()?;
 868                     if self.eat(&token::Semi) {
 869                         // Repeating array syntax: `[ 0; 512 ]`
 870                         let count = AnonConst {
 871                             id: DUMMY_NODE_ID,
 872                             value: self.parse_expr()?,
 873                         };
 874                         self.expect(&token::CloseDelim(token::Bracket))?;
 875                         ex = ExprKind::Repeat(first_expr, count);
 876                     } else if self.eat(&token::Comma) {
 877                         // Vector with two or more elements
 878                         let remaining_exprs = self.parse_seq_to_end(
 879                             &token::CloseDelim(token::Bracket),
 880                             SeqSep::trailing_allowed(token::Comma),
 881                             |p| Ok(p.parse_expr()?)
 882                         )?;
 883                         let mut exprs = vec![first_expr];
 884                         exprs.extend(remaining_exprs);
 885                         ex = ExprKind::Array(exprs);
 886                     } else {
 887                         // Vector with one element
 888                         self.expect(&token::CloseDelim(token::Bracket))?;
 889                         ex = ExprKind::Array(vec![first_expr]);
 890                     }
 891                 }
 892                 hi = self.prev_span;
 893             }
 894             _ => {
 895                 if self.eat_lt() {
 896                     let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
 897                     hi = path.span;
 898                     return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
 899                 }
 900                 if self.token.is_path_start() {
 901                     let path = self.parse_path(PathStyle::Expr)?;
 902
 903                     // `!`, as an operator, is prefix, so we know this isn't that.
 904                     if self.eat(&token::Not) {
 905                         // MACRO INVOCATION expression
 906                         let (delim, tts) = self.expect_delimited_token_tree()?;
 907                         hi = self.prev_span;
 908                         ex = ExprKind::Mac(Mac {
 909                             path,
 910                             tts,
 911                             delim,
 912                             span: lo.to(hi),
 913                             prior_type_ascription: self.last_type_ascription,
 914                         });
 915                     } else if self.check(&token::OpenDelim(token::Brace)) {
 916                         if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
 917                             return expr;
 918                         } else {
 919                             hi = path.span;
 920                             ex = ExprKind::Path(None, path);
 921                         }
 922                     } else {
 923                         hi = path.span;
 924                         ex = ExprKind::Path(None, path);
 925                     }
 926
 927                     let expr = self.mk_expr(lo.to(hi), ex, attrs);
 928                     return self.maybe_recover_from_bad_qpath(expr, true);
 929                 }
 930                 if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
 931                     return self.parse_closure_expr(attrs);
 932                 }
 933                 if self.eat_keyword(kw::If) {
 934                     return self.parse_if_expr(attrs);
 935                 }
 936                 if self.eat_keyword(kw::For) {
 937                     let lo = self.prev_span;
 938                     return self.parse_for_expr(None, lo, attrs);
 939                 }
 940                 if self.eat_keyword(kw::While) {
 941                     let lo = self.prev_span;
 942                     return self.parse_while_expr(None, lo, attrs);
 943                 }
 944                 if let Some(label) = self.eat_label() {
 945                     let lo = label.ident.span;
 946                     self.expect(&token::Colon)?;
 947                     if self.eat_keyword(kw::While) {
 948                         return self.parse_while_expr(Some(label), lo, attrs)
 949                     }
 950                     if self.eat_keyword(kw::For) {
 951                         return self.parse_for_expr(Some(label), lo, attrs)
 952                     }
 953                     if self.eat_keyword(kw::Loop) {
 954                         return self.parse_loop_expr(Some(label), lo, attrs)
 955                     }
 956                     if self.token == token::OpenDelim(token::Brace) {
 957                         return self.parse_block_expr(Some(label),
 958                                                      lo,
 959                                                      BlockCheckMode::Default,
 960                                                      attrs);
 961                     }
 962                     let msg = "expected `while`, `for`, `loop` or `{` after a label";
 963                     let mut err = self.fatal(msg);
 964                     err.span_label(self.token.span, msg);
 965                     return Err(err);
 966                 }
 967                 if self.eat_keyword(kw::Loop) {
 968                     let lo = self.prev_span;
 969                     return self.parse_loop_expr(None, lo, attrs);
 970                 }
 971                 if self.eat_keyword(kw::Continue) {
 972                     let label = self.eat_label();
 973                     let ex = ExprKind::Continue(label);
 974                     let hi = self.prev_span;
 975                     return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 976                 }
 977                 if self.eat_keyword(kw::Match) {
 978                     let match_sp = self.prev_span;
 979                     return self.parse_match_expr(attrs).map_err(|mut err| {
 980                         err.span_label(match_sp, "while parsing this match expression");
 981                         err
 982                     });
 983                 }
 984                 if self.eat_keyword(kw::Unsafe) {
 985                     return self.parse_block_expr(
 986                         None,
 987                         lo,
 988                         BlockCheckMode::Unsafe(ast::UserProvided),
 989                         attrs);
 990                 }
 991                 if self.is_do_catch_block() {
 992                     let mut db = self.fatal("found removed `do catch` syntax");
 993                     db.help("following RFC #2388, the new non-placeholder syntax is `try`");
 994                     return Err(db);
 995                 }
 996                 if self.is_try_block() {
 997                     let lo = self.token.span;
 998                     assert!(self.eat_keyword(kw::Try));
 999                     return self.parse_try_block(lo, attrs);
1000                 }
1001
1002                 // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1003                 let is_span_rust_2018 = self.token.span.rust_2018();
1004                 if is_span_rust_2018 && self.check_keyword(kw::Async) {
1005                     return if self.is_async_block() { // Check for `async {` and `async move {`.
1006                         self.parse_async_block(attrs)
1007                     } else {
1008                         self.parse_closure_expr(attrs)
1009                     };
1010                 }
1011                 if self.eat_keyword(kw::Return) {
1012                     if self.token.can_begin_expr() {
1013                         let e = self.parse_expr()?;
1014                         hi = e.span;
1015                         ex = ExprKind::Ret(Some(e));
1016                     } else {
1017                         ex = ExprKind::Ret(None);
1018                     }
1019                 } else if self.eat_keyword(kw::Break) {
1020                     let label = self.eat_label();
1021                     let e = if self.token.can_begin_expr()
1022                                && !(self.token == token::OpenDelim(token::Brace)
1023                                     && self.restrictions.contains(
1024                                            Restrictions::NO_STRUCT_LITERAL)) {
1025                         Some(self.parse_expr()?)
1026                     } else {
1027                         None
1028                     };
1029                     ex = ExprKind::Break(label, e);
1030                     hi = self.prev_span;
1031                 } else if self.eat_keyword(kw::Yield) {
1032                     if self.token.can_begin_expr() {
1033                         let e = self.parse_expr()?;
1034                         hi = e.span;
1035                         ex = ExprKind::Yield(Some(e));
1036                     } else {
1037                         ex = ExprKind::Yield(None);
1038                     }
1039
1040                     let span = lo.to(hi);
1041                     self.sess.gated_spans.yields.borrow_mut().push(span);
1042                 } else if self.eat_keyword(kw::Let) {
1043                     return self.parse_let_expr(attrs);
1044                 } else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
1045                     let (await_hi, e_kind) = self.parse_incorrect_await_syntax(lo, self.prev_span)?;
1046                     hi = await_hi;
1047                     ex = e_kind;
1048                 } else {
1049                     if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1050                         // Don't complain about bare semicolons after unclosed braces
1051                         // recovery in order to keep the error count down. Fixing the
1052                         // delimiters will possibly also fix the bare semicolon found in
1053                         // expression context. For example, silence the following error:
1054                         //
1055                         //     error: expected expression, found `;`
1056                         //      --> file.rs:2:13
1057                         //       |
1058                         //     2 |     foo(bar(;
1059                         //       |             ^ expected expression
1060                         self.bump();
1061                         return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()));
1062                     }
1063                     parse_lit!()
1064                 }
1065             }
1066         }
1067
1068         let expr = self.mk_expr(lo.to(hi), ex, attrs);
1069         self.maybe_recover_from_bad_qpath(expr, true)
1070     }
1071
1072     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1073     crate fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1074         maybe_whole_expr!(self);
1075
1076         let minus_lo = self.token.span;
1077         let minus_present = self.eat(&token::BinOp(token::Minus));
1078         let lo = self.token.span;
1079         let literal = self.parse_lit()?;
1080         let hi = self.prev_span;
1081         let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
1082
1083         if minus_present {
1084             let minus_hi = self.prev_span;
1085             let unary = self.mk_unary(UnOp::Neg, expr);
1086             Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
1087         } else {
1088             Ok(expr)
1089         }
1090     }
1091
1092     /// Parses a block or unsafe block.
1093     crate fn parse_block_expr(
1094         &mut self,
1095         opt_label: Option<Label>,
1096         lo: Span,
1097         blk_mode: BlockCheckMode,
1098         outer_attrs: ThinVec<Attribute>,
1099     ) -> PResult<'a, P<Expr>> {
1100         self.expect(&token::OpenDelim(token::Brace))?;
1101
1102         let mut attrs = outer_attrs;
1103         attrs.extend(self.parse_inner_attributes()?);
1104
1105         let blk = self.parse_block_tail(lo, blk_mode)?;
1106         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1107     }
1108
1109     /// Parses a closure expression (e.g., `move |args| expr`).
1110     fn parse_closure_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1111         let lo = self.token.span;
1112
1113         let movability = if self.eat_keyword(kw::Static) {
1114             Movability::Static
1115         } else {
1116             Movability::Movable
1117         };
1118
1119         let asyncness = if self.token.span.rust_2018() {
1120             self.parse_asyncness()
1121         } else {
1122             IsAsync::NotAsync
1123         };
1124         if asyncness.is_async() {
1125             // Feature-gate `async ||` closures.
1126             self.sess.gated_spans.async_closure.borrow_mut().push(self.prev_span);
1127         }
1128
1129         let capture_clause = self.parse_capture_clause();
1130         let decl = self.parse_fn_block_decl()?;
1131         let decl_hi = self.prev_span;
1132         let body = match decl.output {
1133             FunctionRetTy::Default(_) => {
1134                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1135                 self.parse_expr_res(restrictions, None)?
1136             },
1137             _ => {
1138                 // If an explicit return type is given, require a block to appear (RFC 968).
1139                 let body_lo = self.token.span;
1140                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
1141             }
1142         };
1143
1144         Ok(self.mk_expr(
1145             lo.to(body.span),
1146             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
1147             attrs))
1148     }
1149
1150     /// Parses an optional `move` prefix to a closure lke construct.
1151     fn parse_capture_clause(&mut self) -> CaptureBy {
1152         if self.eat_keyword(kw::Move) {
1153             CaptureBy::Value
1154         } else {
1155             CaptureBy::Ref
1156         }
1157     }
1158
1159     /// Parses the `|arg, arg|` header of a closure.
1160     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
1161         let inputs_captures = {
1162             if self.eat(&token::OrOr) {
1163                 Vec::new()
1164             } else {
1165                 self.expect(&token::BinOp(token::Or))?;
1166                 let args = self.parse_seq_to_before_tokens(
1167                     &[&token::BinOp(token::Or), &token::OrOr],
1168                     SeqSep::trailing_allowed(token::Comma),
1169                     TokenExpectType::NoExpect,
1170                     |p| p.parse_fn_block_param()
1171                 )?.0;
1172                 self.expect_or()?;
1173                 args
1174             }
1175         };
1176         let output = self.parse_ret_ty(true)?;
1177
1178         Ok(P(FnDecl {
1179             inputs: inputs_captures,
1180             output,
1181         }))
1182     }
1183
1184     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
1185     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
1186         let lo = self.token.span;
1187         let attrs = self.parse_outer_attributes()?;
1188         let pat = self.parse_pat(PARAM_EXPECTED)?;
1189         let t = if self.eat(&token::Colon) {
1190             self.parse_ty()?
1191         } else {
1192             P(Ty {
1193                 id: DUMMY_NODE_ID,
1194                 kind: TyKind::Infer,
1195                 span: self.prev_span,
1196             })
1197         };
1198         let span = lo.to(self.token.span);
1199         Ok(Param {
1200             attrs: attrs.into(),
1201             ty: t,
1202             pat,
1203             span,
1204             id: DUMMY_NODE_ID,
1205             is_placeholder: false,
1206         })
1207     }
1208
1209     /// Parses an `if` expression (`if` token already eaten).
1210     fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1211         let lo = self.prev_span;
1212         let cond = self.parse_cond_expr()?;
1213
1214         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
1215         // verify that the last statement is either an implicit return (no `;`) or an explicit
1216         // return. This won't catch blocks with an explicit `return`, but that would be caught by
1217         // the dead code lint.
1218         if self.eat_keyword(kw::Else) || !cond.returns() {
1219             let sp = self.sess.source_map().next_point(lo);
1220             let mut err = self.diagnostic()
1221                 .struct_span_err(sp, "missing condition for `if` expression");
1222             err.span_label(sp, "expected if condition here");
1223             return Err(err)
1224         }
1225         let not_block = self.token != token::OpenDelim(token::Brace);
1226         let thn = self.parse_block().map_err(|mut err| {
1227             if not_block {
1228                 err.span_label(lo, "this `if` statement has a condition, but no block");
1229             }
1230             err
1231         })?;
1232         let mut els: Option<P<Expr>> = None;
1233         let mut hi = thn.span;
1234         if self.eat_keyword(kw::Else) {
1235             let elexpr = self.parse_else_expr()?;
1236             hi = elexpr.span;
1237             els = Some(elexpr);
1238         }
1239         Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
1240     }
1241
1242     /// Parses the condition of a `if` or `while` expression.
1243     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
1244         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1245
1246         if let ExprKind::Let(..) = cond.kind {
1247             // Remove the last feature gating of a `let` expression since it's stable.
1248             let last = self.sess.gated_spans.let_chains.borrow_mut().pop();
1249             debug_assert_eq!(cond.span, last.unwrap());
1250         }
1251
1252         Ok(cond)
1253     }
1254
1255     /// Parses a `let $pat = $expr` pseudo-expression.
1256     /// The `let` token has already been eaten.
1257     fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1258         let lo = self.prev_span;
1259         let pat = self.parse_top_pat(GateOr::No)?;
1260         self.expect(&token::Eq)?;
1261         let expr = self.with_res(
1262             Restrictions::NO_STRUCT_LITERAL,
1263             |this| this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
1264         )?;
1265         let span = lo.to(expr.span);
1266         self.sess.gated_spans.let_chains.borrow_mut().push(span);
1267         Ok(self.mk_expr(span, ExprKind::Let(pat, expr), attrs))
1268     }
1269
1270     /// Parses an `else { ... }` expression (`else` token already eaten).
1271     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
1272         if self.eat_keyword(kw::If) {
1273             return self.parse_if_expr(ThinVec::new());
1274         } else {
1275             let blk = self.parse_block()?;
1276             return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
1277         }
1278     }
1279
1280     /// Parses a `for ... in` expression (`for` token already eaten).
1281     fn parse_for_expr(
1282         &mut self,
1283         opt_label: Option<Label>,
1284         span_lo: Span,
1285         mut attrs: ThinVec<Attribute>
1286     ) -> PResult<'a, P<Expr>> {
1287         // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
1288
1289         // Record whether we are about to parse `for (`.
1290         // This is used below for recovery in case of `for ( $stuff ) $block`
1291         // in which case we will suggest `for $stuff $block`.
1292         let begin_paren = match self.token.kind {
1293             token::OpenDelim(token::Paren) => Some(self.token.span),
1294             _ => None,
1295         };
1296
1297         let pat = self.parse_top_pat(GateOr::Yes)?;
1298         if !self.eat_keyword(kw::In) {
1299             let in_span = self.prev_span.between(self.token.span);
1300             self.struct_span_err(in_span, "missing `in` in `for` loop")
1301                 .span_suggestion_short(
1302                     in_span,
1303                     "try adding `in` here", " in ".into(),
1304                     // has been misleading, at least in the past (closed Issue #48492)
1305                     Applicability::MaybeIncorrect
1306                 )
1307                 .emit();
1308         }
1309         let in_span = self.prev_span;
1310         self.check_for_for_in_in_typo(in_span);
1311         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1312
1313         let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
1314
1315         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
1316         attrs.extend(iattrs);
1317
1318         let hi = self.prev_span;
1319         Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
1320     }
1321
1322     /// Parses a `while` or `while let` expression (`while` token already eaten).
1323     fn parse_while_expr(
1324         &mut self,
1325         opt_label: Option<Label>,
1326         span_lo: Span,
1327         mut attrs: ThinVec<Attribute>
1328     ) -> PResult<'a, P<Expr>> {
1329         let cond = self.parse_cond_expr()?;
1330         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1331         attrs.extend(iattrs);
1332         let span = span_lo.to(body.span);
1333         Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs))
1334     }
1335
1336     /// Parses `loop { ... }` (`loop` token already eaten).
1337     fn parse_loop_expr(
1338         &mut self,
1339         opt_label: Option<Label>,
1340         span_lo: Span,
1341         mut attrs: ThinVec<Attribute>
1342     ) -> PResult<'a, P<Expr>> {
1343         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1344         attrs.extend(iattrs);
1345         let span = span_lo.to(body.span);
1346         Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
1347     }
1348
1349     fn eat_label(&mut self) -> Option<Label> {
1350         if let Some(ident) = self.token.lifetime() {
1351             let span = self.token.span;
1352             self.bump();
1353             Some(Label { ident: Ident::new(ident.name, span) })
1354         } else {
1355             None
1356         }
1357     }
1358
1359     /// Parses a `match ... { ... }` expression (`match` token already eaten).
1360     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1361         let match_span = self.prev_span;
1362         let lo = self.prev_span;
1363         let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1364         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
1365             if self.token == token::Semi {
1366                 e.span_suggestion_short(
1367                     match_span,
1368                     "try removing this `match`",
1369                     String::new(),
1370                     Applicability::MaybeIncorrect // speculative
1371                 );
1372             }
1373             return Err(e)
1374         }
1375         attrs.extend(self.parse_inner_attributes()?);
1376
1377         let mut arms: Vec<Arm> = Vec::new();
1378         while self.token != token::CloseDelim(token::Brace) {
1379             match self.parse_arm() {
1380                 Ok(arm) => arms.push(arm),
1381                 Err(mut e) => {
1382                     // Recover by skipping to the end of the block.
1383                     e.emit();
1384                     self.recover_stmt();
1385                     let span = lo.to(self.token.span);
1386                     if self.token == token::CloseDelim(token::Brace) {
1387                         self.bump();
1388                     }
1389                     return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
1390                 }
1391             }
1392         }
1393         let hi = self.token.span;
1394         self.bump();
1395         return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
1396     }
1397
1398     crate fn parse_arm(&mut self) -> PResult<'a, Arm> {
1399         let attrs = self.parse_outer_attributes()?;
1400         let lo = self.token.span;
1401         let pat = self.parse_top_pat(GateOr::No)?;
1402         let guard = if self.eat_keyword(kw::If) {
1403             Some(self.parse_expr()?)
1404         } else {
1405             None
1406         };
1407         let arrow_span = self.token.span;
1408         self.expect(&token::FatArrow)?;
1409         let arm_start_span = self.token.span;
1410
1411         let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
1412             .map_err(|mut err| {
1413                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
1414                 err
1415             })?;
1416
1417         let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
1418             && self.token != token::CloseDelim(token::Brace);
1419
1420         let hi = self.token.span;
1421
1422         if require_comma {
1423             let cm = self.sess.source_map();
1424             self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
1425                 .map_err(|mut err| {
1426                     match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
1427                         (Ok(ref expr_lines), Ok(ref arm_start_lines))
1428                         if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
1429                             && expr_lines.lines.len() == 2
1430                             && self.token == token::FatArrow => {
1431                             // We check whether there's any trailing code in the parse span,
1432                             // if there isn't, we very likely have the following:
1433                             //
1434                             // X |     &Y => "y"
1435                             //   |        --    - missing comma
1436                             //   |        |
1437                             //   |        arrow_span
1438                             // X |     &X => "x"
1439                             //   |      - ^^ self.token.span
1440                             //   |      |
1441                             //   |      parsed until here as `"y" & X`
1442                             err.span_suggestion_short(
1443                                 cm.next_point(arm_start_span),
1444                                 "missing a comma here to end this `match` arm",
1445                                 ",".to_owned(),
1446                                 Applicability::MachineApplicable
1447                             );
1448                         }
1449                         _ => {
1450                             err.span_label(arrow_span,
1451                                            "while parsing the `match` arm starting here");
1452                         }
1453                     }
1454                     err
1455                 })?;
1456         } else {
1457             self.eat(&token::Comma);
1458         }
1459
1460         Ok(ast::Arm {
1461             attrs,
1462             pat,
1463             guard,
1464             body: expr,
1465             span: lo.to(hi),
1466             id: DUMMY_NODE_ID,
1467             is_placeholder: false,
1468         })
1469     }
1470
1471     /// Parses a `try {...}` expression (`try` token already eaten).
1472     fn parse_try_block(
1473         &mut self,
1474         span_lo: Span,
1475         mut attrs: ThinVec<Attribute>
1476     ) -> PResult<'a, P<Expr>> {
1477         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1478         attrs.extend(iattrs);
1479         if self.eat_keyword(kw::Catch) {
1480             let mut error = self.struct_span_err(self.prev_span,
1481                                                  "keyword `catch` cannot follow a `try` block");
1482             error.help("try using `match` on the result of the `try` block instead");
1483             error.emit();
1484             Err(error)
1485         } else {
1486             Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
1487         }
1488     }
1489
1490     fn is_do_catch_block(&self) -> bool {
1491         self.token.is_keyword(kw::Do) &&
1492         self.is_keyword_ahead(1, &[kw::Catch]) &&
1493         self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
1494         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1495     }
1496
1497     fn is_try_block(&self) -> bool {
1498         self.token.is_keyword(kw::Try) &&
1499         self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
1500         self.token.span.rust_2018() &&
1501         // Prevent `while try {} {}`, `if try {} {} else {}`, etc.
1502         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1503     }
1504
1505     /// Parses an `async move? {...}` expression.
1506     pub fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1507         let span_lo = self.token.span;
1508         self.expect_keyword(kw::Async)?;
1509         let capture_clause = self.parse_capture_clause();
1510         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1511         attrs.extend(iattrs);
1512         Ok(self.mk_expr(
1513             span_lo.to(body.span),
1514             ExprKind::Async(capture_clause, DUMMY_NODE_ID, body), attrs))
1515     }
1516
1517     fn is_async_block(&self) -> bool {
1518         self.token.is_keyword(kw::Async) &&
1519         (
1520             ( // `async move {`
1521                 self.is_keyword_ahead(1, &[kw::Move]) &&
1522                 self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
1523             ) || ( // `async {`
1524                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
1525             )
1526         )
1527     }
1528
1529     fn maybe_parse_struct_expr(
1530         &mut self,
1531         lo: Span,
1532         path: &ast::Path,
1533         attrs: &ThinVec<Attribute>,
1534     ) -> Option<PResult<'a, P<Expr>>> {
1535         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
1536         let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
1537             // `{ ident, ` cannot start a block.
1538             self.look_ahead(2, |t| t == &token::Comma) ||
1539             self.look_ahead(2, |t| t == &token::Colon) && (
1540                 // `{ ident: token, ` cannot start a block.
1541                 self.look_ahead(4, |t| t == &token::Comma) ||
1542                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
1543                 self.look_ahead(3, |t| !t.can_begin_type())
1544             )
1545         );
1546
1547         if struct_allowed || certainly_not_a_block() {
1548             // This is a struct literal, but we don't can't accept them here.
1549             let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
1550             if let (Ok(expr), false) = (&expr, struct_allowed) {
1551                 self.struct_span_err(
1552                     expr.span,
1553                     "struct literals are not allowed here",
1554                 )
1555                 .multipart_suggestion(
1556                     "surround the struct literal with parentheses",
1557                     vec![
1558                         (lo.shrink_to_lo(), "(".to_string()),
1559                         (expr.span.shrink_to_hi(), ")".to_string()),
1560                     ],
1561                     Applicability::MachineApplicable,
1562                 )
1563                 .emit();
1564             }
1565             return Some(expr);
1566         }
1567         None
1568     }
1569
1570     pub(super) fn parse_struct_expr(
1571         &mut self,
1572         lo: Span,
1573         pth: ast::Path,
1574         mut attrs: ThinVec<Attribute>
1575     ) -> PResult<'a, P<Expr>> {
1576         let struct_sp = lo.to(self.prev_span);
1577         self.bump();
1578         let mut fields = Vec::new();
1579         let mut base = None;
1580
1581         attrs.extend(self.parse_inner_attributes()?);
1582
1583         while self.token != token::CloseDelim(token::Brace) {
1584             if self.eat(&token::DotDot) {
1585                 let exp_span = self.prev_span;
1586                 match self.parse_expr() {
1587                     Ok(e) => {
1588                         base = Some(e);
1589                     }
1590                     Err(mut e) => {
1591                         e.emit();
1592                         self.recover_stmt();
1593                     }
1594                 }
1595                 if self.token == token::Comma {
1596                     self.struct_span_err(
1597                         exp_span.to(self.prev_span),
1598                         "cannot use a comma after the base struct",
1599                     )
1600                     .span_suggestion_short(
1601                         self.token.span,
1602                         "remove this comma",
1603                         String::new(),
1604                         Applicability::MachineApplicable
1605                     )
1606                     .note("the base struct must always be the last field")
1607                     .emit();
1608                     self.recover_stmt();
1609                 }
1610                 break;
1611             }
1612
1613             let mut recovery_field = None;
1614             if let token::Ident(name, _) = self.token.kind {
1615                 if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
1616                     // Use in case of error after field-looking code: `S { foo: () with a }`.
1617                     recovery_field = Some(ast::Field {
1618                         ident: Ident::new(name, self.token.span),
1619                         span: self.token.span,
1620                         expr: self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()),
1621                         is_shorthand: false,
1622                         attrs: ThinVec::new(),
1623                         id: DUMMY_NODE_ID,
1624                         is_placeholder: false,
1625                     });
1626                 }
1627             }
1628             let mut parsed_field = None;
1629             match self.parse_field() {
1630                 Ok(f) => parsed_field = Some(f),
1631                 Err(mut e) => {
1632                     e.span_label(struct_sp, "while parsing this struct");
1633                     e.emit();
1634
1635                     // If the next token is a comma, then try to parse
1636                     // what comes next as additional fields, rather than
1637                     // bailing out until next `}`.
1638                     if self.token != token::Comma {
1639                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1640                         if self.token != token::Comma {
1641                             break;
1642                         }
1643                     }
1644                 }
1645             }
1646
1647             match self.expect_one_of(&[token::Comma],
1648                                      &[token::CloseDelim(token::Brace)]) {
1649                 Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
1650                     // Only include the field if there's no parse error for the field name.
1651                     fields.push(f);
1652                 }
1653                 Err(mut e) => {
1654                     if let Some(f) = recovery_field {
1655                         fields.push(f);
1656                     }
1657                     e.span_label(struct_sp, "while parsing this struct");
1658                     e.emit();
1659                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1660                     self.eat(&token::Comma);
1661                 }
1662             }
1663         }
1664
1665         let span = lo.to(self.token.span);
1666         self.expect(&token::CloseDelim(token::Brace))?;
1667         return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
1668     }
1669
1670     /// Parses `ident (COLON expr)?`.
1671     fn parse_field(&mut self) -> PResult<'a, Field> {
1672         let attrs = self.parse_outer_attributes()?;
1673         let lo = self.token.span;
1674
1675         // Check if a colon exists one ahead. This means we're parsing a fieldname.
1676         let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
1677             t == &token::Colon || t == &token::Eq
1678         }) {
1679             let fieldname = self.parse_field_name()?;
1680
1681             // Check for an equals token. This means the source incorrectly attempts to
1682             // initialize a field with an eq rather than a colon.
1683             if self.token == token::Eq {
1684                 self.diagnostic()
1685                     .struct_span_err(self.token.span, "expected `:`, found `=`")
1686                     .span_suggestion(
1687                         fieldname.span.shrink_to_hi().to(self.token.span),
1688                         "replace equals symbol with a colon",
1689                         ":".to_string(),
1690                         Applicability::MachineApplicable,
1691                     )
1692                     .emit();
1693             }
1694             self.bump(); // `:`
1695             (fieldname, self.parse_expr()?, false)
1696         } else {
1697             let fieldname = self.parse_ident_common(false)?;
1698
1699             // Mimic `x: x` for the `x` field shorthand.
1700             let path = ast::Path::from_ident(fieldname);
1701             let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
1702             (fieldname, expr, true)
1703         };
1704         Ok(ast::Field {
1705             ident: fieldname,
1706             span: lo.to(expr.span),
1707             expr,
1708             is_shorthand,
1709             attrs: attrs.into(),
1710             id: DUMMY_NODE_ID,
1711             is_placeholder: false,
1712         })
1713     }
1714
1715     fn err_dotdotdot_syntax(&self, span: Span) {
1716         self.struct_span_err(span, "unexpected token: `...`")
1717             .span_suggestion(
1718                 span,
1719                 "use `..` for an exclusive range", "..".to_owned(),
1720                 Applicability::MaybeIncorrect
1721             )
1722             .span_suggestion(
1723                 span,
1724                 "or `..=` for an inclusive range", "..=".to_owned(),
1725                 Applicability::MaybeIncorrect
1726             )
1727             .emit();
1728     }
1729
1730     fn err_larrow_operator(&self, span: Span) {
1731         self.struct_span_err(
1732             span,
1733             "unexpected token: `<-`"
1734         ).span_suggestion(
1735             span,
1736             "if you meant to write a comparison against a negative value, add a \
1737              space in between `<` and `-`",
1738             "< -".to_string(),
1739             Applicability::MaybeIncorrect
1740         ).emit();
1741     }
1742
1743     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1744         ExprKind::AssignOp(binop, lhs, rhs)
1745     }
1746
1747     fn mk_range(
1748         &self,
1749         start: Option<P<Expr>>,
1750         end: Option<P<Expr>>,
1751         limits: RangeLimits
1752     ) -> PResult<'a, ExprKind> {
1753         if end.is_none() && limits == RangeLimits::Closed {
1754             Err(self.span_fatal_err(self.token.span, Error::InclusiveRangeWithNoEnd))
1755         } else {
1756             Ok(ExprKind::Range(start, end, limits))
1757         }
1758     }
1759
1760     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
1761         ExprKind::Unary(unop, expr)
1762     }
1763
1764     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1765         ExprKind::Binary(binop, lhs, rhs)
1766     }
1767
1768     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
1769         ExprKind::Index(expr, idx)
1770     }
1771
1772     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
1773         ExprKind::Call(f, args)
1774     }
1775
1776     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1777         let span = lo.to(self.prev_span);
1778         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), ThinVec::new());
1779         self.recover_from_await_method_call();
1780         Ok(await_expr)
1781     }
1782
1783     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
1784         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID })
1785     }
1786 }