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