src/libsyntax/parse/parser/expr.rs

   1 use super::{Parser, PResult, Restrictions, PrevTokenKind, TokenType, PathStyle, BlockMode};
   2 use super::{SemiColonMode, SeqSep, TokenExpectType};
   3 use super::pat::{GateOr, PARAM_EXPECTED};
   4 use super::diagnostics::Error;
   5
   6 use crate::parse::literal::LitError;
   7
   8 use crate::ast::{
   9     self, DUMMY_NODE_ID, Attribute, AttrStyle, Ident, CaptureBy, BlockCheckMode,
  10     Expr, ExprKind, RangeLimits, Label, Movability, IsAsync, Arm, Ty, TyKind,
  11     FunctionRetTy, Param, FnDecl, BinOpKind, BinOp, UnOp, Mac, AnonConst, Field, Lit,
  12 };
  13 use crate::maybe_recover_from_interpolated_ty_qpath;
  14 use crate::parse::classify;
  15 use crate::parse::token::{self, Token, TokenKind};
  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 syntax_pos::Symbol;
  24 use std::mem;
  25 use rustc_data_structures::thin_vec::ThinVec;
  26
  27 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  28 /// dropped into the token stream, which happens while parsing the result of
  29 /// macro expansion). Placement of these is not as complex as I feared it would
  30 /// be. The important thing is to make sure that lookahead doesn't balk at
  31 /// `token::Interpolated` tokens.
  32 macro_rules! maybe_whole_expr {
  33     ($p:expr) => {
  34         if let token::Interpolated(nt) = &$p.token.kind {
  35             match &**nt {
  36                 token::NtExpr(e) | token::NtLiteral(e) => {
  37                     let e = e.clone();
  38                     $p.bump();
  39                     return Ok(e);
  40                 }
  41                 token::NtPath(path) => {
  42                     let path = path.clone();
  43                     $p.bump();
  44                     return Ok($p.mk_expr(
  45                         $p.token.span, ExprKind::Path(None, path), ThinVec::new()
  46                     ));
  47                 }
  48                 token::NtBlock(block) => {
  49                     let block = block.clone();
  50                     $p.bump();
  51                     return Ok($p.mk_expr(
  52                         $p.token.span, ExprKind::Block(block, None), ThinVec::new()
  53                     ));
  54                 }
  55                 // N.B., `NtIdent(ident)` is normalized to `Ident` in `fn bump`.
  56                 _ => {},
  57             };
  58         }
  59     }
  60 }
  61
  62 #[derive(Debug)]
  63 pub(super) enum LhsExpr {
  64     NotYetParsed,
  65     AttributesParsed(ThinVec<Attribute>),
  66     AlreadyParsed(P<Expr>),
  67 }
  68
  69 impl From<Option<ThinVec<Attribute>>> for LhsExpr {
  70     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  71     /// and `None` into `LhsExpr::NotYetParsed`.
  72     ///
  73     /// This conversion does not allocate.
  74     fn from(o: Option<ThinVec<Attribute>>) -> Self {
  75         if let Some(attrs) = o {
  76             LhsExpr::AttributesParsed(attrs)
  77         } else {
  78             LhsExpr::NotYetParsed
  79         }
  80     }
  81 }
  82
  83 impl From<P<Expr>> for LhsExpr {
  84     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
  85     ///
  86     /// This conversion does not allocate.
  87     fn from(expr: P<Expr>) -> Self {
  88         LhsExpr::AlreadyParsed(expr)
  89     }
  90 }
  91
  92 impl<'a> Parser<'a> {
  93     /// Parses an expression.
  94     #[inline]
  95     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
  96         self.parse_expr_res(Restrictions::empty(), None)
  97     }
  98
  99     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 100         self.parse_paren_comma_seq(|p| {
 101             match p.parse_expr() {
 102                 Ok(expr) => Ok(expr),
 103                 Err(mut err) => match p.token.kind {
 104                     token::Ident(name, false)
 105                     if name == kw::Underscore && p.look_ahead(1, |t| {
 106                         t == &token::Comma
 107                     }) => {
 108                         // Special-case handling of `foo(_, _, _)`
 109                         err.emit();
 110                         let sp = p.token.span;
 111                         p.bump();
 112                         Ok(p.mk_expr(sp, ExprKind::Err, ThinVec::new()))
 113                     }
 114                     _ => Err(err),
 115                 },
 116             }
 117         }).map(|(r, _)| r)
 118     }
 119
 120     /// Parses an expression, subject to the given restrictions.
 121     #[inline]
 122     pub(super) fn parse_expr_res(
 123         &mut self,
 124         r: Restrictions,
 125         already_parsed_attrs: Option<ThinVec<Attribute>>
 126     ) -> PResult<'a, P<Expr>> {
 127         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 128     }
 129
 130     /// Parses an associative expression.
 131     ///
 132     /// This parses an expression accounting for associativity and precedence of the operators in
 133     /// the expression.
 134     #[inline]
 135     fn parse_assoc_expr(
 136         &mut self,
 137         already_parsed_attrs: Option<ThinVec<Attribute>>,
 138     ) -> PResult<'a, P<Expr>> {
 139         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 140     }
 141
 142     /// Parses an associative expression with operators of at least `min_prec` precedence.
 143     pub(super) fn parse_assoc_expr_with(
 144         &mut self,
 145         min_prec: usize,
 146         lhs: LhsExpr,
 147     ) -> PResult<'a, P<Expr>> {
 148         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 149             expr
 150         } else {
 151             let attrs = match lhs {
 152                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 153                 _ => None,
 154             };
 155             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 156                 return self.parse_prefix_range_expr(attrs);
 157             } else {
 158                 self.parse_prefix_expr(attrs)?
 159             }
 160         };
 161         let last_type_ascription_set = self.last_type_ascription.is_some();
 162
 163         match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) {
 164             (true, None) => {
 165                 self.last_type_ascription = None;
 166                 // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071
 167                 return Ok(lhs);
 168             }
 169             (false, _) => {} // continue parsing the expression
 170             // An exhaustive check is done in the following block, but these are checked first
 171             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 172             // want to keep their span info to improve diagnostics in these cases in a later stage.
 173             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 174             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 175             (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
 176             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 177             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 178             // `if x { a } else { b } && if y { c } else { d }`
 179             if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
 180                 self.last_type_ascription = None;
 181                 // These cases are ambiguous and can't be identified in the parser alone
 182                 let sp = self.sess.source_map().start_point(self.token.span);
 183                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 184                 return Ok(lhs);
 185             }
 186             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => {
 187                 self.last_type_ascription = None;
 188                 return Ok(lhs);
 189             }
 190             (true, Some(_)) => {
 191                 // We've found an expression that would be parsed as a statement, but the next
 192                 // token implies this should be parsed as an expression.
 193                 // For example: `if let Some(x) = x { x } else { 0 } / 2`
 194                 let mut err = self.struct_span_err(self.token.span, &format!(
 195                     "expected expression, found `{}`",
 196                     pprust::token_to_string(&self.token),
 197                 ));
 198                 err.span_label(self.token.span, "expected expression");
 199                 self.sess.expr_parentheses_needed(
 200                     &mut err,
 201                     lhs.span,
 202                     Some(pprust::expr_to_string(&lhs),
 203                 ));
 204                 err.emit();
 205             }
 206         }
 207         self.expected_tokens.push(TokenType::Operator);
 208         while let Some(op) = AssocOp::from_token(&self.token) {
 209
 210             // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
 211             // it refers to. Interpolated identifiers are unwrapped early and never show up here
 212             // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
 213             // it as "interpolated", it doesn't change the answer for non-interpolated idents.
 214             let lhs_span = match (self.prev_token_kind, &lhs.kind) {
 215                 (PrevTokenKind::Interpolated, _) => self.prev_span,
 216                 (PrevTokenKind::Ident, &ExprKind::Path(None, ref path))
 217                     if path.segments.len() == 1 => self.prev_span,
 218                 _ => lhs.span,
 219             };
 220
 221             let cur_op_span = self.token.span;
 222             let restrictions = if op.is_assign_like() {
 223                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 224             } else {
 225                 self.restrictions
 226             };
 227             let prec = op.precedence();
 228             if prec < min_prec {
 229                 break;
 230             }
 231             // Check for deprecated `...` syntax
 232             if self.token == token::DotDotDot && op == AssocOp::DotDotEq {
 233                 self.err_dotdotdot_syntax(self.token.span);
 234             }
 235
 236             if self.token == token::LArrow {
 237                 self.err_larrow_operator(self.token.span);
 238             }
 239
 240             self.bump();
 241             if op.is_comparison() {
 242                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 243                     return Ok(expr);
 244                 }
 245             }
 246             // Special cases:
 247             if op == AssocOp::As {
 248                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 249                 continue
 250             } else if op == AssocOp::Colon {
 251                 let maybe_path = self.could_ascription_be_path(&lhs.kind);
 252                 self.last_type_ascription = Some((self.prev_span, maybe_path));
 253
 254                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 255                 continue
 256             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 257                 // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
 258                 // generalise it to the Fixity::None code.
 259                 //
 260                 // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
 261                 // two variants are handled with `parse_prefix_range_expr` call above.
 262                 let rhs = if self.is_at_start_of_range_notation_rhs() {
 263                     Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 264                 } else {
 265                     None
 266                 };
 267                 let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
 268                     x.span
 269                 } else {
 270                     cur_op_span
 271                 });
 272                 let limits = if op == AssocOp::DotDot {
 273                     RangeLimits::HalfOpen
 274                 } else {
 275                     RangeLimits::Closed
 276                 };
 277
 278                 let r = self.mk_range(Some(lhs), rhs, limits)?;
 279                 lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
 280                 break
 281             }
 282
 283             let fixity = op.fixity();
 284             let prec_adjustment = match fixity {
 285                 Fixity::Right => 0,
 286                 Fixity::Left => 1,
 287                 // We currently have no non-associative operators that are not handled above by
 288                 // the special cases. The code is here only for future convenience.
 289                 Fixity::None => 1,
 290             };
 291             let rhs = self.with_res(
 292                 restrictions - Restrictions::STMT_EXPR,
 293                 |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 294             )?;
 295
 296             // Make sure that the span of the parent node is larger than the span of lhs and rhs,
 297             // including the attributes.
 298             let lhs_span = lhs
 299                 .attrs
 300                 .iter()
 301                 .filter(|a| a.style == AttrStyle::Outer)
 302                 .next()
 303                 .map_or(lhs_span, |a| a.span);
 304             let span = lhs_span.to(rhs.span);
 305             lhs = match op {
 306                 AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
 307                 AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
 308                 AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
 309                 AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
 310                 AssocOp::Greater | AssocOp::GreaterEqual => {
 311                     let ast_op = op.to_ast_binop().unwrap();
 312                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 313                     self.mk_expr(span, binary, ThinVec::new())
 314                 }
 315                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
 316                 AssocOp::AssignOp(k) => {
 317                     let aop = match k {
 318                         token::Plus =>    BinOpKind::Add,
 319                         token::Minus =>   BinOpKind::Sub,
 320                         token::Star =>    BinOpKind::Mul,
 321                         token::Slash =>   BinOpKind::Div,
 322                         token::Percent => BinOpKind::Rem,
 323                         token::Caret =>   BinOpKind::BitXor,
 324                         token::And =>     BinOpKind::BitAnd,
 325                         token::Or =>      BinOpKind::BitOr,
 326                         token::Shl =>     BinOpKind::Shl,
 327                         token::Shr =>     BinOpKind::Shr,
 328                     };
 329                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 330                     self.mk_expr(span, aopexpr, ThinVec::new())
 331                 }
 332                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 333                     self.bug("AssocOp should have been handled by special case")
 334                 }
 335             };
 336
 337             if let Fixity::None = fixity { break }
 338         }
 339         if last_type_ascription_set {
 340             self.last_type_ascription = None;
 341         }
 342         Ok(lhs)
 343     }
 344
 345     /// Checks if this expression is a successfully parsed statement.
 346     fn expr_is_complete(&self, e: &Expr) -> bool {
 347         self.restrictions.contains(Restrictions::STMT_EXPR) &&
 348             !classify::expr_requires_semi_to_be_stmt(e)
 349     }
 350
 351     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 352         if self.token.can_begin_expr() {
 353             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 354             if self.token == token::OpenDelim(token::Brace) {
 355                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 356             }
 357             true
 358         } else {
 359             false
 360         }
 361     }
 362
 363     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 364     fn parse_prefix_range_expr(
 365         &mut self,
 366         already_parsed_attrs: Option<ThinVec<Attribute>>
 367     ) -> PResult<'a, P<Expr>> {
 368         // Check for deprecated `...` syntax.
 369         if self.token == token::DotDotDot {
 370             self.err_dotdotdot_syntax(self.token.span);
 371         }
 372
 373         debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 374                       "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 375                       self.token);
 376         let tok = self.token.clone();
 377         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 378         let lo = self.token.span;
 379         let mut hi = self.token.span;
 380         self.bump();
 381         let opt_end = if self.is_at_start_of_range_notation_rhs() {
 382             // RHS must be parsed with more associativity than the dots.
 383             let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
 384             Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed)
 385                 .map(|x| {
 386                     hi = x.span;
 387                     x
 388                 })?)
 389         } else {
 390             None
 391         };
 392         let limits = if tok == token::DotDot {
 393             RangeLimits::HalfOpen
 394         } else {
 395             RangeLimits::Closed
 396         };
 397
 398         let r = self.mk_range(None, opt_end, limits)?;
 399         Ok(self.mk_expr(lo.to(hi), r, attrs))
 400     }
 401
 402     /// Parses a prefix-unary-operator expr.
 403     fn parse_prefix_expr(
 404         &mut self,
 405         already_parsed_attrs: Option<ThinVec<Attribute>>
 406     ) -> PResult<'a, P<Expr>> {
 407         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 408         let lo = self.token.span;
 409         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 410         let (hi, ex) = match self.token.kind {
 411             token::Not => {
 412                 self.bump();
 413                 let e = self.parse_prefix_expr(None);
 414                 let (span, e) = self.interpolated_or_expr_span(e)?;
 415                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 416             }
 417             // Suggest `!` for bitwise negation when encountering a `~`
 418             token::Tilde => {
 419                 self.bump();
 420                 let e = self.parse_prefix_expr(None);
 421                 let (span, e) = self.interpolated_or_expr_span(e)?;
 422                 let span_of_tilde = lo;
 423                 self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator")
 424                     .span_suggestion_short(
 425                         span_of_tilde,
 426                         "use `!` to perform bitwise negation",
 427                         "!".to_owned(),
 428                         Applicability::MachineApplicable
 429                     )
 430                     .emit();
 431                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 432             }
 433             token::BinOp(token::Minus) => {
 434                 self.bump();
 435                 let e = self.parse_prefix_expr(None);
 436                 let (span, e) = self.interpolated_or_expr_span(e)?;
 437                 (lo.to(span), self.mk_unary(UnOp::Neg, e))
 438             }
 439             token::BinOp(token::Star) => {
 440                 self.bump();
 441                 let e = self.parse_prefix_expr(None);
 442                 let (span, e) = self.interpolated_or_expr_span(e)?;
 443                 (lo.to(span), self.mk_unary(UnOp::Deref, e))
 444             }
 445             token::BinOp(token::And) | token::AndAnd => {
 446                 self.expect_and()?;
 447                 let m = self.parse_mutability();
 448                 let e = self.parse_prefix_expr(None);
 449                 let (span, e) = self.interpolated_or_expr_span(e)?;
 450                 (lo.to(span), ExprKind::AddrOf(m, e))
 451             }
 452             token::Ident(..) if self.token.is_keyword(kw::Box) => {
 453                 self.bump();
 454                 let e = self.parse_prefix_expr(None);
 455                 let (span, e) = self.interpolated_or_expr_span(e)?;
 456                 (lo.to(span), ExprKind::Box(e))
 457             }
 458             token::Ident(..) if self.token.is_ident_named(sym::not) => {
 459                 // `not` is just an ordinary identifier in Rust-the-language,
 460                 // but as `rustc`-the-compiler, we can issue clever diagnostics
 461                 // for confused users who really want to say `!`
 462                 let token_cannot_continue_expr = |t: &Token| match t.kind {
 463                     // These tokens can start an expression after `!`, but
 464                     // can't continue an expression after an ident
 465                     token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 466                     token::Literal(..) | token::Pound => true,
 467                     _ => t.is_whole_expr(),
 468                 };
 469                 let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
 470                 if cannot_continue_expr {
 471                     self.bump();
 472                     // Emit the error ...
 473                     self.struct_span_err(
 474                         self.token.span,
 475                         &format!("unexpected {} after identifier",self.this_token_descr())
 476                     )
 477                     .span_suggestion_short(
 478                         // Span the `not` plus trailing whitespace to avoid
 479                         // trailing whitespace after the `!` in our suggestion
 480                         self.sess.source_map()
 481                             .span_until_non_whitespace(lo.to(self.token.span)),
 482                         "use `!` to perform logical negation",
 483                         "!".to_owned(),
 484                         Applicability::MachineApplicable
 485                     )
 486                     .emit();
 487                     // —and recover! (just as if we were in the block
 488                     // for the `token::Not` arm)
 489                     let e = self.parse_prefix_expr(None);
 490                     let (span, e) = self.interpolated_or_expr_span(e)?;
 491                     (lo.to(span), self.mk_unary(UnOp::Not, e))
 492                 } else {
 493                     return self.parse_dot_or_call_expr(Some(attrs));
 494                 }
 495             }
 496             _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
 497         };
 498         return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 499     }
 500
 501     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 502     fn interpolated_or_expr_span(
 503         &self,
 504         expr: PResult<'a, P<Expr>>,
 505     ) -> PResult<'a, (Span, P<Expr>)> {
 506         expr.map(|e| {
 507             if self.prev_token_kind == PrevTokenKind::Interpolated {
 508                 (self.prev_span, e)
 509             } else {
 510                 (e.span, e)
 511             }
 512         })
 513     }
 514
 515     fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
 516                            expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
 517                            -> PResult<'a, P<Expr>> {
 518         let mk_expr = |this: &mut Self, rhs: P<Ty>| {
 519             this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
 520         };
 521
 522         // Save the state of the parser before parsing type normally, in case there is a
 523         // LessThan comparison after this cast.
 524         let parser_snapshot_before_type = self.clone();
 525         match self.parse_ty_no_plus() {
 526             Ok(rhs) => {
 527                 Ok(mk_expr(self, rhs))
 528             }
 529             Err(mut type_err) => {
 530                 // Rewind to before attempting to parse the type with generics, to recover
 531                 // from situations like `x as usize < y` in which we first tried to parse
 532                 // `usize < y` as a type with generic arguments.
 533                 let parser_snapshot_after_type = self.clone();
 534                 mem::replace(self, parser_snapshot_before_type);
 535
 536                 match self.parse_path(PathStyle::Expr) {
 537                     Ok(path) => {
 538                         let (op_noun, op_verb) = match self.token.kind {
 539                             token::Lt => ("comparison", "comparing"),
 540                             token::BinOp(token::Shl) => ("shift", "shifting"),
 541                             _ => {
 542                                 // We can end up here even without `<` being the next token, for
 543                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 544                                 // but `parse_path` returns `Ok` on them due to error recovery.
 545                                 // Return original error and parser state.
 546                                 mem::replace(self, parser_snapshot_after_type);
 547                                 return Err(type_err);
 548                             }
 549                         };
 550
 551                         // Successfully parsed the type path leaving a `<` yet to parse.
 552                         type_err.cancel();
 553
 554                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 555                         // in AST and continue parsing.
 556                         let msg = format!(
 557                             "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
 558                             pprust::path_to_string(&path),
 559                             op_noun,
 560                         );
 561                         let span_after_type = parser_snapshot_after_type.token.span;
 562                         let expr = mk_expr(self, P(Ty {
 563                             span: path.span,
 564                             kind: TyKind::Path(None, path),
 565                             id: DUMMY_NODE_ID,
 566                         }));
 567
 568                         let expr_str = self.span_to_snippet(expr.span)
 569                             .unwrap_or_else(|_| pprust::expr_to_string(&expr));
 570
 571                         self.struct_span_err(self.token.span, &msg)
 572                             .span_label(
 573                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 574                                 "interpreted as generic arguments"
 575                             )
 576                             .span_label(self.token.span, format!("not interpreted as {}", op_noun))
 577                             .span_suggestion(
 578                                 expr.span,
 579                                 &format!("try {} the cast value", op_verb),
 580                                 format!("({})", expr_str),
 581                                 Applicability::MachineApplicable,
 582                             )
 583                             .emit();
 584
 585                         Ok(expr)
 586                     }
 587                     Err(mut path_err) => {
 588                         // Couldn't parse as a path, return original error and parser state.
 589                         path_err.cancel();
 590                         mem::replace(self, parser_snapshot_after_type);
 591                         Err(type_err)
 592                     }
 593                 }
 594             }
 595         }
 596     }
 597
 598     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 599     fn parse_dot_or_call_expr(
 600         &mut self,
 601         already_parsed_attrs: Option<ThinVec<Attribute>>,
 602     ) -> PResult<'a, P<Expr>> {
 603         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 604
 605         let b = self.parse_bottom_expr();
 606         let (span, b) = self.interpolated_or_expr_span(b)?;
 607         self.parse_dot_or_call_expr_with(b, span, attrs)
 608     }
 609
 610     pub(super) fn parse_dot_or_call_expr_with(
 611         &mut self,
 612         e0: P<Expr>,
 613         lo: Span,
 614         mut attrs: ThinVec<Attribute>,
 615     ) -> PResult<'a, P<Expr>> {
 616         // Stitch the list of outer attributes onto the return value.
 617         // A little bit ugly, but the best way given the current code
 618         // structure
 619         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr|
 620             expr.map(|mut expr| {
 621                 attrs.extend::<Vec<_>>(expr.attrs.into());
 622                 expr.attrs = attrs;
 623                 match expr.kind {
 624                     ExprKind::If(..) if !expr.attrs.is_empty() => {
 625                         // Just point to the first attribute in there...
 626                         let span = expr.attrs[0].span;
 627                         self.span_err(span, "attributes are not yet allowed on `if` expressions");
 628                     }
 629                     _ => {}
 630                 }
 631                 expr
 632             })
 633         )
 634     }
 635
 636     fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 637         let mut e = e0;
 638         let mut hi;
 639         loop {
 640             // expr?
 641             while self.eat(&token::Question) {
 642                 let hi = self.prev_span;
 643                 e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
 644             }
 645
 646             // expr.f
 647             if self.eat(&token::Dot) {
 648                 match self.token.kind {
 649                     token::Ident(..) => {
 650                         e = self.parse_dot_suffix(e, lo)?;
 651                     }
 652                     token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 653                         let span = self.token.span;
 654                         self.bump();
 655                         let field = ExprKind::Field(e, Ident::new(symbol, span));
 656                         e = self.mk_expr(lo.to(span), field, ThinVec::new());
 657
 658                         self.expect_no_suffix(span, "a tuple index", suffix);
 659                     }
 660                     token::Literal(token::Lit { kind: token::Float, symbol, .. }) => {
 661                       self.bump();
 662                       let fstr = symbol.as_str();
 663                       let msg = format!("unexpected token: `{}`", symbol);
 664                       let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg);
 665                       err.span_label(self.prev_span, "unexpected token");
 666                       if fstr.chars().all(|x| "0123456789.".contains(x)) {
 667                           let float = match fstr.parse::<f64>().ok() {
 668                               Some(f) => f,
 669                               None => continue,
 670                           };
 671                           let sugg = pprust::to_string(|s| {
 672                               s.popen();
 673                               s.print_expr(&e);
 674                               s.s.word( ".");
 675                               s.print_usize(float.trunc() as usize);
 676                               s.pclose();
 677                               s.s.word(".");
 678                               s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
 679                           });
 680                           err.span_suggestion(
 681                               lo.to(self.prev_span),
 682                               "try parenthesizing the first index",
 683                               sugg,
 684                               Applicability::MachineApplicable
 685                           );
 686                       }
 687                       return Err(err);
 688
 689                     }
 690                     _ => {
 691                         // FIXME Could factor this out into non_fatal_unexpected or something.
 692                         let actual = self.this_token_to_string();
 693                         self.span_err(self.token.span, &format!("unexpected token: `{}`", actual));
 694                     }
 695                 }
 696                 continue;
 697             }
 698             if self.expr_is_complete(&e) { break; }
 699             match self.token.kind {
 700                 // expr(...)
 701                 token::OpenDelim(token::Paren) => {
 702                     let seq = self.parse_paren_expr_seq().map(|es| {
 703                         let nd = self.mk_call(e, es);
 704                         let hi = self.prev_span;
 705                         self.mk_expr(lo.to(hi), nd, ThinVec::new())
 706                     });
 707                     e = self.recover_seq_parse_error(token::Paren, lo, seq);
 708                 }
 709
 710                 // expr[...]
 711                 // Could be either an index expression or a slicing expression.
 712                 token::OpenDelim(token::Bracket) => {
 713                     self.bump();
 714                     let ix = self.parse_expr()?;
 715                     hi = self.token.span;
 716                     self.expect(&token::CloseDelim(token::Bracket))?;
 717                     let index = self.mk_index(e, ix);
 718                     e = self.mk_expr(lo.to(hi), index, ThinVec::new())
 719                 }
 720                 _ => return Ok(e)
 721             }
 722         }
 723         return Ok(e);
 724     }
 725
 726     /// Assuming we have just parsed `.`, continue parsing into an expression.
 727     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 728         if self.token.span.rust_2018() && self.eat_keyword(kw::Await) {
 729             return self.mk_await_expr(self_arg, lo);
 730         }
 731
 732         let segment = self.parse_path_segment(PathStyle::Expr)?;
 733         self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
 734
 735         Ok(match self.token.kind {
 736             token::OpenDelim(token::Paren) => {
 737                 // Method call `expr.f()`
 738                 let mut args = self.parse_paren_expr_seq()?;
 739                 args.insert(0, self_arg);
 740
 741                 let span = lo.to(self.prev_span);
 742                 self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
 743             }
 744             _ => {
 745                 // Field access `expr.f`
 746                 if let Some(args) = segment.args {
 747                     self.span_err(args.span(),
 748                                   "field expressions may not have generic arguments");
 749                 }
 750
 751                 let span = lo.to(self.prev_span);
 752                 self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
 753             }
 754         })
 755     }
 756
 757     /// At the bottom (top?) of the precedence hierarchy,
 758     /// Parses things like parenthesized exprs, macros, `return`, etc.
 759     ///
 760     /// N.B., this does not parse outer attributes, and is private because it only works
 761     /// correctly if called from `parse_dot_or_call_expr()`.
 762     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
 763         maybe_recover_from_interpolated_ty_qpath!(self, true);
 764         maybe_whole_expr!(self);
 765
 766         // Outer attributes are already parsed and will be
 767         // added to the return value after the fact.
 768         //
 769         // Therefore, prevent sub-parser from parsing
 770         // attributes by giving them a empty "already-parsed" list.
 771         let mut attrs = ThinVec::new();
 772
 773         let lo = self.token.span;
 774         let mut hi = self.token.span;
 775
 776         let ex: ExprKind;
 777
 778         macro_rules! parse_lit {
 779             () => {
 780                 match self.parse_lit() {
 781                     Ok(literal) => {
 782                         hi = self.prev_span;
 783                         ex = ExprKind::Lit(literal);
 784                     }
 785                     Err(mut err) => {
 786                         err.cancel();
 787                         return Err(self.expected_expression_found());
 788                     }
 789                 }
 790             }
 791         }
 792
 793         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
 794         match self.token.kind {
 795             // This match arm is a special-case of the `_` match arm below and
 796             // could be removed without changing functionality, but it's faster
 797             // to have it here, especially for programs with large constants.
 798             token::Literal(_) => {
 799                 parse_lit!()
 800             }
 801             token::OpenDelim(token::Paren) => {
 802                 self.bump();
 803
 804                 attrs.extend(self.parse_inner_attributes()?);
 805
 806                 // `(e)` is parenthesized `e`.
 807                 // `(e,)` is a tuple with only one field, `e`.
 808                 let mut es = vec![];
 809                 let mut trailing_comma = false;
 810                 let mut recovered = false;
 811                 while self.token != token::CloseDelim(token::Paren) {
 812                     es.push(match self.parse_expr() {
 813                         Ok(es) => es,
 814                         Err(mut err) => {
 815                             // Recover from parse error in tuple list.
 816                             match self.token.kind {
 817                                 token::Ident(name, false)
 818                                 if name == kw::Underscore && self.look_ahead(1, |t| {
 819                                     t == &token::Comma
 820                                 }) => {
 821                                     // Special-case handling of `Foo<(_, _, _)>`
 822                                     err.emit();
 823                                     let sp = self.token.span;
 824                                     self.bump();
 825                                     self.mk_expr(sp, ExprKind::Err, ThinVec::new())
 826                                 }
 827                                 _ => return Ok(
 828                                     self.recover_seq_parse_error(token::Paren, lo, Err(err)),
 829                                 ),
 830                             }
 831                         }
 832                     });
 833                     recovered = self.expect_one_of(
 834                         &[],
 835                         &[token::Comma, token::CloseDelim(token::Paren)],
 836                     )?;
 837                     if self.eat(&token::Comma) {
 838                         trailing_comma = true;
 839                     } else {
 840                         trailing_comma = false;
 841                         break;
 842                     }
 843                 }
 844                 if !recovered {
 845                     self.bump();
 846                 }
 847
 848                 hi = self.prev_span;
 849                 ex = if es.len() == 1 && !trailing_comma {
 850                     ExprKind::Paren(es.into_iter().nth(0).unwrap())
 851                 } else {
 852                     ExprKind::Tup(es)
 853                 };
 854             }
 855             token::OpenDelim(token::Brace) => {
 856                 return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
 857             }
 858             token::BinOp(token::Or) | token::OrOr => {
 859                 return self.parse_closure_expr(attrs);
 860             }
 861             token::OpenDelim(token::Bracket) => {
 862                 self.bump();
 863
 864                 attrs.extend(self.parse_inner_attributes()?);
 865
 866                 if self.eat(&token::CloseDelim(token::Bracket)) {
 867                     // Empty vector
 868                     ex = ExprKind::Array(Vec::new());
 869                 } else {
 870                     // Non-empty vector
 871                     let first_expr = self.parse_expr()?;
 872                     if self.eat(&token::Semi) {
 873                         // Repeating array syntax: `[ 0; 512 ]`
 874                         let count = AnonConst {
 875                             id: DUMMY_NODE_ID,
 876                             value: self.parse_expr()?,
 877                         };
 878                         self.expect(&token::CloseDelim(token::Bracket))?;
 879                         ex = ExprKind::Repeat(first_expr, count);
 880                     } else if self.eat(&token::Comma) {
 881                         // Vector with two or more elements
 882                         let remaining_exprs = self.parse_seq_to_end(
 883                             &token::CloseDelim(token::Bracket),
 884                             SeqSep::trailing_allowed(token::Comma),
 885                             |p| Ok(p.parse_expr()?)
 886                         )?;
 887                         let mut exprs = vec![first_expr];
 888                         exprs.extend(remaining_exprs);
 889                         ex = ExprKind::Array(exprs);
 890                     } else {
 891                         // Vector with one element
 892                         self.expect(&token::CloseDelim(token::Bracket))?;
 893                         ex = ExprKind::Array(vec![first_expr]);
 894                     }
 895                 }
 896                 hi = self.prev_span;
 897             }
 898             _ => {
 899                 if self.eat_lt() {
 900                     let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
 901                     hi = path.span;
 902                     return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
 903                 }
 904                 if self.token.is_path_start() {
 905                     let path = self.parse_path(PathStyle::Expr)?;
 906
 907                     // `!`, as an operator, is prefix, so we know this isn't that.
 908                     if self.eat(&token::Not) {
 909                         // MACRO INVOCATION expression
 910                         let (delim, tts) = self.expect_delimited_token_tree()?;
 911                         hi = self.prev_span;
 912                         ex = ExprKind::Mac(Mac {
 913                             path,
 914                             tts,
 915                             delim,
 916                             span: lo.to(hi),
 917                             prior_type_ascription: self.last_type_ascription,
 918                         });
 919                     } else if self.check(&token::OpenDelim(token::Brace)) {
 920                         if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
 921                             return expr;
 922                         } else {
 923                             hi = path.span;
 924                             ex = ExprKind::Path(None, path);
 925                         }
 926                     } else {
 927                         hi = path.span;
 928                         ex = ExprKind::Path(None, path);
 929                     }
 930
 931                     let expr = self.mk_expr(lo.to(hi), ex, attrs);
 932                     return self.maybe_recover_from_bad_qpath(expr, true);
 933                 }
 934                 if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
 935                     return self.parse_closure_expr(attrs);
 936                 }
 937                 if self.eat_keyword(kw::If) {
 938                     return self.parse_if_expr(attrs);
 939                 }
 940                 if self.eat_keyword(kw::For) {
 941                     let lo = self.prev_span;
 942                     return self.parse_for_expr(None, lo, attrs);
 943                 }
 944                 if self.eat_keyword(kw::While) {
 945                     let lo = self.prev_span;
 946                     return self.parse_while_expr(None, lo, attrs);
 947                 }
 948                 if let Some(label) = self.eat_label() {
 949                     let lo = label.ident.span;
 950                     self.expect(&token::Colon)?;
 951                     if self.eat_keyword(kw::While) {
 952                         return self.parse_while_expr(Some(label), lo, attrs)
 953                     }
 954                     if self.eat_keyword(kw::For) {
 955                         return self.parse_for_expr(Some(label), lo, attrs)
 956                     }
 957                     if self.eat_keyword(kw::Loop) {
 958                         return self.parse_loop_expr(Some(label), lo, attrs)
 959                     }
 960                     if self.token == token::OpenDelim(token::Brace) {
 961                         return self.parse_block_expr(Some(label),
 962                                                      lo,
 963                                                      BlockCheckMode::Default,
 964                                                      attrs);
 965                     }
 966                     let msg = "expected `while`, `for`, `loop` or `{` after a label";
 967                     let mut err = self.fatal(msg);
 968                     err.span_label(self.token.span, msg);
 969                     return Err(err);
 970                 }
 971                 if self.eat_keyword(kw::Loop) {
 972                     let lo = self.prev_span;
 973                     return self.parse_loop_expr(None, lo, attrs);
 974                 }
 975                 if self.eat_keyword(kw::Continue) {
 976                     let label = self.eat_label();
 977                     let ex = ExprKind::Continue(label);
 978                     let hi = self.prev_span;
 979                     return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 980                 }
 981                 if self.eat_keyword(kw::Match) {
 982                     let match_sp = self.prev_span;
 983                     return self.parse_match_expr(attrs).map_err(|mut err| {
 984                         err.span_label(match_sp, "while parsing this match expression");
 985                         err
 986                     });
 987                 }
 988                 if self.eat_keyword(kw::Unsafe) {
 989                     return self.parse_block_expr(
 990                         None,
 991                         lo,
 992                         BlockCheckMode::Unsafe(ast::UserProvided),
 993                         attrs);
 994                 }
 995                 if self.is_do_catch_block() {
 996                     let mut db = self.fatal("found removed `do catch` syntax");
 997                     db.help("following RFC #2388, the new non-placeholder syntax is `try`");
 998                     return Err(db);
 999                 }
1000                 if self.is_try_block() {
1001                     let lo = self.token.span;
1002                     assert!(self.eat_keyword(kw::Try));
1003                     return self.parse_try_block(lo, attrs);
1004                 }
1005
1006                 // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1007                 let is_span_rust_2018 = self.token.span.rust_2018();
1008                 if is_span_rust_2018 && self.check_keyword(kw::Async) {
1009                     return if self.is_async_block() { // Check for `async {` and `async move {`.
1010                         self.parse_async_block(attrs)
1011                     } else {
1012                         self.parse_closure_expr(attrs)
1013                     };
1014                 }
1015                 if self.eat_keyword(kw::Return) {
1016                     if self.token.can_begin_expr() {
1017                         let e = self.parse_expr()?;
1018                         hi = e.span;
1019                         ex = ExprKind::Ret(Some(e));
1020                     } else {
1021                         ex = ExprKind::Ret(None);
1022                     }
1023                 } else if self.eat_keyword(kw::Break) {
1024                     let label = self.eat_label();
1025                     let e = if self.token.can_begin_expr()
1026                                && !(self.token == token::OpenDelim(token::Brace)
1027                                     && self.restrictions.contains(
1028                                            Restrictions::NO_STRUCT_LITERAL)) {
1029                         Some(self.parse_expr()?)
1030                     } else {
1031                         None
1032                     };
1033                     ex = ExprKind::Break(label, e);
1034                     hi = self.prev_span;
1035                 } else if self.eat_keyword(kw::Yield) {
1036                     if self.token.can_begin_expr() {
1037                         let e = self.parse_expr()?;
1038                         hi = e.span;
1039                         ex = ExprKind::Yield(Some(e));
1040                     } else {
1041                         ex = ExprKind::Yield(None);
1042                     }
1043
1044                     let span = lo.to(hi);
1045                     self.sess.gated_spans.yields.borrow_mut().push(span);
1046                 } else if self.eat_keyword(kw::Let) {
1047                     return self.parse_let_expr(attrs);
1048                 } else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
1049                     let (await_hi, e_kind) = self.parse_incorrect_await_syntax(lo, self.prev_span)?;
1050                     hi = await_hi;
1051                     ex = e_kind;
1052                 } else {
1053                     if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1054                         // Don't complain about bare semicolons after unclosed braces
1055                         // recovery in order to keep the error count down. Fixing the
1056                         // delimiters will possibly also fix the bare semicolon found in
1057                         // expression context. For example, silence the following error:
1058                         //
1059                         //     error: expected expression, found `;`
1060                         //      --> file.rs:2:13
1061                         //       |
1062                         //     2 |     foo(bar(;
1063                         //       |             ^ expected expression
1064                         self.bump();
1065                         return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()));
1066                     }
1067                     parse_lit!()
1068                 }
1069             }
1070         }
1071
1072         let expr = self.mk_expr(lo.to(hi), ex, attrs);
1073         self.maybe_recover_from_bad_qpath(expr, true)
1074     }
1075
1076     /// Matches `lit = true | false | token_lit`.
1077     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1078         let mut recovered = None;
1079         if self.token == token::Dot {
1080             // Attempt to recover `.4` as `0.4`.
1081             recovered = self.look_ahead(1, |next_token| {
1082                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
1083                         = next_token.kind {
1084                     if self.token.span.hi() == next_token.span.lo() {
1085                         let s = String::from("0.") + &symbol.as_str();
1086                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1087                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1088                     }
1089                 }
1090                 None
1091             });
1092             if let Some(token) = &recovered {
1093                 self.bump();
1094                 self.struct_span_err(token.span, "float literals must have an integer part")
1095                     .span_suggestion(
1096                         token.span,
1097                         "must have an integer part",
1098                         pprust::token_to_string(token),
1099                         Applicability::MachineApplicable,
1100                     )
1101                     .emit();
1102             }
1103         }
1104
1105         let token = recovered.as_ref().unwrap_or(&self.token);
1106         match Lit::from_token(token) {
1107             Ok(lit) => {
1108                 self.bump();
1109                 Ok(lit)
1110             }
1111             Err(LitError::NotLiteral) => {
1112                 let msg = format!("unexpected token: {}", self.this_token_descr());
1113                 Err(self.span_fatal(token.span, &msg))
1114             }
1115             Err(err) => {
1116                 let (lit, span) = (token.expect_lit(), token.span);
1117                 self.bump();
1118                 self.error_literal_from_token(err, lit, span);
1119                 // Pack possible quotes and prefixes from the original literal into
1120                 // the error literal's symbol so they can be pretty-printed faithfully.
1121                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1122                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1123                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1124                 Lit::from_lit_token(lit, span).map_err(|_| unreachable!())
1125             }
1126         }
1127     }
1128
1129     fn error_literal_from_token(&self, err: LitError, lit: token::Lit, span: Span) {
1130         // Checks if `s` looks like i32 or u1234 etc.
1131         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1132             s.len() > 1
1133             && s.starts_with(first_chars)
1134             && s[1..].chars().all(|c| c.is_ascii_digit())
1135         }
1136
1137         let token::Lit { kind, suffix, .. } = lit;
1138         match err {
1139             // `NotLiteral` is not an error by itself, so we don't report
1140             // it and give the parser opportunity to try something else.
1141             LitError::NotLiteral => {}
1142             // `LexerError` *is* an error, but it was already reported
1143             // by lexer, so here we don't report it the second time.
1144             LitError::LexerError => {}
1145             LitError::InvalidSuffix => {
1146                 self.expect_no_suffix(
1147                     span,
1148                     &format!("{} {} literal", kind.article(), kind.descr()),
1149                     suffix,
1150                 );
1151             }
1152             LitError::InvalidIntSuffix => {
1153                 let suf = suffix.expect("suffix error with no suffix").as_str();
1154                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1155                     // If it looks like a width, try to be helpful.
1156                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1157                     self.struct_span_err(span, &msg)
1158                         .help("valid widths are 8, 16, 32, 64 and 128")
1159                         .emit();
1160                 } else {
1161                     let msg = format!("invalid suffix `{}` for integer literal", suf);
1162                     self.struct_span_err(span, &msg)
1163                         .span_label(span, format!("invalid suffix `{}`", suf))
1164                         .help("the suffix must be one of the integral types (`u32`, `isize`, etc)")
1165                         .emit();
1166                 }
1167             }
1168             LitError::InvalidFloatSuffix => {
1169                 let suf = suffix.expect("suffix error with no suffix").as_str();
1170                 if looks_like_width_suffix(&['f'], &suf) {
1171                     // If it looks like a width, try to be helpful.
1172                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1173                     self.struct_span_err(span, &msg)
1174                         .help("valid widths are 32 and 64")
1175                         .emit();
1176                 } else {
1177                     let msg = format!("invalid suffix `{}` for float literal", suf);
1178                     self.struct_span_err(span, &msg)
1179                         .span_label(span, format!("invalid suffix `{}`", suf))
1180                         .help("valid suffixes are `f32` and `f64`")
1181                         .emit();
1182                 }
1183             }
1184             LitError::NonDecimalFloat(base) => {
1185                 let descr = match base {
1186                     16 => "hexadecimal",
1187                     8 => "octal",
1188                     2 => "binary",
1189                     _ => unreachable!(),
1190                 };
1191                 self.struct_span_err(span, &format!("{} float literal is not supported", descr))
1192                     .span_label(span, "not supported")
1193                     .emit();
1194             }
1195             LitError::IntTooLarge => {
1196                 self.struct_span_err(span, "integer literal is too large")
1197                     .emit();
1198             }
1199         }
1200     }
1201
1202     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1203         if let Some(suf) = suffix {
1204             let mut err = if kind == "a tuple index"
1205                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1206             {
1207                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1208                 // through the ecosystem when people fix their macros
1209                 let mut err = self.sess.span_diagnostic.struct_span_warn(
1210                     sp,
1211                     &format!("suffixes on {} are invalid", kind),
1212                 );
1213                 err.note(&format!(
1214                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1215                         incorrectly accepted on stable for a few releases",
1216                     suf,
1217                 ));
1218                 err.help(
1219                     "on proc macros, you'll want to use `syn::Index::from` or \
1220                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1221                         to tuple field access",
1222                 );
1223                 err.note(
1224                     "for more context, see https://github.com/rust-lang/rust/issues/60210",
1225                 );
1226                 err
1227             } else {
1228                 self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
1229             };
1230             err.span_label(sp, format!("invalid suffix `{}`", suf));
1231             err.emit();
1232         }
1233     }
1234
1235     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1236     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1237         maybe_whole_expr!(self);
1238
1239         let minus_lo = self.token.span;
1240         let minus_present = self.eat(&token::BinOp(token::Minus));
1241         let lo = self.token.span;
1242         let literal = self.parse_lit()?;
1243         let hi = self.prev_span;
1244         let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
1245
1246         if minus_present {
1247             let minus_hi = self.prev_span;
1248             let unary = self.mk_unary(UnOp::Neg, expr);
1249             Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
1250         } else {
1251             Ok(expr)
1252         }
1253     }
1254
1255     /// Parses a block or unsafe block.
1256     pub(super) fn parse_block_expr(
1257         &mut self,
1258         opt_label: Option<Label>,
1259         lo: Span,
1260         blk_mode: BlockCheckMode,
1261         outer_attrs: ThinVec<Attribute>,
1262     ) -> PResult<'a, P<Expr>> {
1263         self.expect(&token::OpenDelim(token::Brace))?;
1264
1265         let mut attrs = outer_attrs;
1266         attrs.extend(self.parse_inner_attributes()?);
1267
1268         let blk = self.parse_block_tail(lo, blk_mode)?;
1269         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1270     }
1271
1272     /// Parses a closure expression (e.g., `move |args| expr`).
1273     fn parse_closure_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1274         let lo = self.token.span;
1275
1276         let movability = if self.eat_keyword(kw::Static) {
1277             Movability::Static
1278         } else {
1279             Movability::Movable
1280         };
1281
1282         let asyncness = if self.token.span.rust_2018() {
1283             self.parse_asyncness()
1284         } else {
1285             IsAsync::NotAsync
1286         };
1287         if asyncness.is_async() {
1288             // Feature-gate `async ||` closures.
1289             self.sess.gated_spans.async_closure.borrow_mut().push(self.prev_span);
1290         }
1291
1292         let capture_clause = self.parse_capture_clause();
1293         let decl = self.parse_fn_block_decl()?;
1294         let decl_hi = self.prev_span;
1295         let body = match decl.output {
1296             FunctionRetTy::Default(_) => {
1297                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1298                 self.parse_expr_res(restrictions, None)?
1299             },
1300             _ => {
1301                 // If an explicit return type is given, require a block to appear (RFC 968).
1302                 let body_lo = self.token.span;
1303                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
1304             }
1305         };
1306
1307         Ok(self.mk_expr(
1308             lo.to(body.span),
1309             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
1310             attrs))
1311     }
1312
1313     /// Parses an optional `move` prefix to a closure lke construct.
1314     fn parse_capture_clause(&mut self) -> CaptureBy {
1315         if self.eat_keyword(kw::Move) {
1316             CaptureBy::Value
1317         } else {
1318             CaptureBy::Ref
1319         }
1320     }
1321
1322     /// Parses the `|arg, arg|` header of a closure.
1323     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
1324         let inputs_captures = {
1325             if self.eat(&token::OrOr) {
1326                 Vec::new()
1327             } else {
1328                 self.expect(&token::BinOp(token::Or))?;
1329                 let args = self.parse_seq_to_before_tokens(
1330                     &[&token::BinOp(token::Or), &token::OrOr],
1331                     SeqSep::trailing_allowed(token::Comma),
1332                     TokenExpectType::NoExpect,
1333                     |p| p.parse_fn_block_param()
1334                 )?.0;
1335                 self.expect_or()?;
1336                 args
1337             }
1338         };
1339         let output = self.parse_ret_ty(true)?;
1340
1341         Ok(P(FnDecl {
1342             inputs: inputs_captures,
1343             output,
1344         }))
1345     }
1346
1347     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
1348     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
1349         let lo = self.token.span;
1350         let attrs = self.parse_outer_attributes()?;
1351         let pat = self.parse_pat(PARAM_EXPECTED)?;
1352         let t = if self.eat(&token::Colon) {
1353             self.parse_ty()?
1354         } else {
1355             P(Ty {
1356                 id: DUMMY_NODE_ID,
1357                 kind: TyKind::Infer,
1358                 span: self.prev_span,
1359             })
1360         };
1361         let span = lo.to(self.token.span);
1362         Ok(Param {
1363             attrs: attrs.into(),
1364             ty: t,
1365             pat,
1366             span,
1367             id: DUMMY_NODE_ID,
1368             is_placeholder: false,
1369         })
1370     }
1371
1372     /// Parses an `if` expression (`if` token already eaten).
1373     fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1374         let lo = self.prev_span;
1375         let cond = self.parse_cond_expr()?;
1376
1377         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
1378         // verify that the last statement is either an implicit return (no `;`) or an explicit
1379         // return. This won't catch blocks with an explicit `return`, but that would be caught by
1380         // the dead code lint.
1381         if self.eat_keyword(kw::Else) || !cond.returns() {
1382             let sp = self.sess.source_map().next_point(lo);
1383             let mut err = self.diagnostic()
1384                 .struct_span_err(sp, "missing condition for `if` expression");
1385             err.span_label(sp, "expected if condition here");
1386             return Err(err)
1387         }
1388         let not_block = self.token != token::OpenDelim(token::Brace);
1389         let thn = self.parse_block().map_err(|mut err| {
1390             if not_block {
1391                 err.span_label(lo, "this `if` statement has a condition, but no block");
1392             }
1393             err
1394         })?;
1395         let mut els: Option<P<Expr>> = None;
1396         let mut hi = thn.span;
1397         if self.eat_keyword(kw::Else) {
1398             let elexpr = self.parse_else_expr()?;
1399             hi = elexpr.span;
1400             els = Some(elexpr);
1401         }
1402         Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
1403     }
1404
1405     /// Parses the condition of a `if` or `while` expression.
1406     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
1407         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1408
1409         if let ExprKind::Let(..) = cond.kind {
1410             // Remove the last feature gating of a `let` expression since it's stable.
1411             let last = self.sess.gated_spans.let_chains.borrow_mut().pop();
1412             debug_assert_eq!(cond.span, last.unwrap());
1413         }
1414
1415         Ok(cond)
1416     }
1417
1418     /// Parses a `let $pat = $expr` pseudo-expression.
1419     /// The `let` token has already been eaten.
1420     fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1421         let lo = self.prev_span;
1422         let pat = self.parse_top_pat(GateOr::No)?;
1423         self.expect(&token::Eq)?;
1424         let expr = self.with_res(
1425             Restrictions::NO_STRUCT_LITERAL,
1426             |this| this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
1427         )?;
1428         let span = lo.to(expr.span);
1429         self.sess.gated_spans.let_chains.borrow_mut().push(span);
1430         Ok(self.mk_expr(span, ExprKind::Let(pat, expr), attrs))
1431     }
1432
1433     /// Parses an `else { ... }` expression (`else` token already eaten).
1434     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
1435         if self.eat_keyword(kw::If) {
1436             return self.parse_if_expr(ThinVec::new());
1437         } else {
1438             let blk = self.parse_block()?;
1439             return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
1440         }
1441     }
1442
1443     /// Parses a `for ... in` expression (`for` token already eaten).
1444     fn parse_for_expr(
1445         &mut self,
1446         opt_label: Option<Label>,
1447         span_lo: Span,
1448         mut attrs: ThinVec<Attribute>
1449     ) -> PResult<'a, P<Expr>> {
1450         // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
1451
1452         // Record whether we are about to parse `for (`.
1453         // This is used below for recovery in case of `for ( $stuff ) $block`
1454         // in which case we will suggest `for $stuff $block`.
1455         let begin_paren = match self.token.kind {
1456             token::OpenDelim(token::Paren) => Some(self.token.span),
1457             _ => None,
1458         };
1459
1460         let pat = self.parse_top_pat(GateOr::Yes)?;
1461         if !self.eat_keyword(kw::In) {
1462             let in_span = self.prev_span.between(self.token.span);
1463             self.struct_span_err(in_span, "missing `in` in `for` loop")
1464                 .span_suggestion_short(
1465                     in_span,
1466                     "try adding `in` here", " in ".into(),
1467                     // has been misleading, at least in the past (closed Issue #48492)
1468                     Applicability::MaybeIncorrect
1469                 )
1470                 .emit();
1471         }
1472         let in_span = self.prev_span;
1473         self.check_for_for_in_in_typo(in_span);
1474         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1475
1476         let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
1477
1478         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
1479         attrs.extend(iattrs);
1480
1481         let hi = self.prev_span;
1482         Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
1483     }
1484
1485     /// Parses a `while` or `while let` expression (`while` token already eaten).
1486     fn parse_while_expr(
1487         &mut self,
1488         opt_label: Option<Label>,
1489         span_lo: Span,
1490         mut attrs: ThinVec<Attribute>
1491     ) -> PResult<'a, P<Expr>> {
1492         let cond = self.parse_cond_expr()?;
1493         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1494         attrs.extend(iattrs);
1495         let span = span_lo.to(body.span);
1496         Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs))
1497     }
1498
1499     /// Parses `loop { ... }` (`loop` token already eaten).
1500     fn parse_loop_expr(
1501         &mut self,
1502         opt_label: Option<Label>,
1503         span_lo: Span,
1504         mut attrs: ThinVec<Attribute>
1505     ) -> PResult<'a, P<Expr>> {
1506         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1507         attrs.extend(iattrs);
1508         let span = span_lo.to(body.span);
1509         Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
1510     }
1511
1512     fn eat_label(&mut self) -> Option<Label> {
1513         if let Some(ident) = self.token.lifetime() {
1514             let span = self.token.span;
1515             self.bump();
1516             Some(Label { ident: Ident::new(ident.name, span) })
1517         } else {
1518             None
1519         }
1520     }
1521
1522     /// Parses a `match ... { ... }` expression (`match` token already eaten).
1523     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1524         let match_span = self.prev_span;
1525         let lo = self.prev_span;
1526         let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1527         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
1528             if self.token == token::Semi {
1529                 e.span_suggestion_short(
1530                     match_span,
1531                     "try removing this `match`",
1532                     String::new(),
1533                     Applicability::MaybeIncorrect // speculative
1534                 );
1535             }
1536             return Err(e)
1537         }
1538         attrs.extend(self.parse_inner_attributes()?);
1539
1540         let mut arms: Vec<Arm> = Vec::new();
1541         while self.token != token::CloseDelim(token::Brace) {
1542             match self.parse_arm() {
1543                 Ok(arm) => arms.push(arm),
1544                 Err(mut e) => {
1545                     // Recover by skipping to the end of the block.
1546                     e.emit();
1547                     self.recover_stmt();
1548                     let span = lo.to(self.token.span);
1549                     if self.token == token::CloseDelim(token::Brace) {
1550                         self.bump();
1551                     }
1552                     return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
1553                 }
1554             }
1555         }
1556         let hi = self.token.span;
1557         self.bump();
1558         return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
1559     }
1560
1561     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
1562         let attrs = self.parse_outer_attributes()?;
1563         let lo = self.token.span;
1564         let pat = self.parse_top_pat(GateOr::No)?;
1565         let guard = if self.eat_keyword(kw::If) {
1566             Some(self.parse_expr()?)
1567         } else {
1568             None
1569         };
1570         let arrow_span = self.token.span;
1571         self.expect(&token::FatArrow)?;
1572         let arm_start_span = self.token.span;
1573
1574         let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
1575             .map_err(|mut err| {
1576                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
1577                 err
1578             })?;
1579
1580         let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
1581             && self.token != token::CloseDelim(token::Brace);
1582
1583         let hi = self.token.span;
1584
1585         if require_comma {
1586             let cm = self.sess.source_map();
1587             self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
1588                 .map_err(|mut err| {
1589                     match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
1590                         (Ok(ref expr_lines), Ok(ref arm_start_lines))
1591                         if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
1592                             && expr_lines.lines.len() == 2
1593                             && self.token == token::FatArrow => {
1594                             // We check whether there's any trailing code in the parse span,
1595                             // if there isn't, we very likely have the following:
1596                             //
1597                             // X |     &Y => "y"
1598                             //   |        --    - missing comma
1599                             //   |        |
1600                             //   |        arrow_span
1601                             // X |     &X => "x"
1602                             //   |      - ^^ self.token.span
1603                             //   |      |
1604                             //   |      parsed until here as `"y" & X`
1605                             err.span_suggestion_short(
1606                                 cm.next_point(arm_start_span),
1607                                 "missing a comma here to end this `match` arm",
1608                                 ",".to_owned(),
1609                                 Applicability::MachineApplicable
1610                             );
1611                         }
1612                         _ => {
1613                             err.span_label(arrow_span,
1614                                            "while parsing the `match` arm starting here");
1615                         }
1616                     }
1617                     err
1618                 })?;
1619         } else {
1620             self.eat(&token::Comma);
1621         }
1622
1623         Ok(ast::Arm {
1624             attrs,
1625             pat,
1626             guard,
1627             body: expr,
1628             span: lo.to(hi),
1629             id: DUMMY_NODE_ID,
1630             is_placeholder: false,
1631         })
1632     }
1633
1634     /// Parses a `try {...}` expression (`try` token already eaten).
1635     fn parse_try_block(
1636         &mut self,
1637         span_lo: Span,
1638         mut attrs: ThinVec<Attribute>
1639     ) -> PResult<'a, P<Expr>> {
1640         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1641         attrs.extend(iattrs);
1642         if self.eat_keyword(kw::Catch) {
1643             let mut error = self.struct_span_err(self.prev_span,
1644                                                  "keyword `catch` cannot follow a `try` block");
1645             error.help("try using `match` on the result of the `try` block instead");
1646             error.emit();
1647             Err(error)
1648         } else {
1649             Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
1650         }
1651     }
1652
1653     fn is_do_catch_block(&self) -> bool {
1654         self.token.is_keyword(kw::Do) &&
1655         self.is_keyword_ahead(1, &[kw::Catch]) &&
1656         self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
1657         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1658     }
1659
1660     fn is_try_block(&self) -> bool {
1661         self.token.is_keyword(kw::Try) &&
1662         self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
1663         self.token.span.rust_2018() &&
1664         // Prevent `while try {} {}`, `if try {} {} else {}`, etc.
1665         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1666     }
1667
1668     /// Parses an `async move? {...}` expression.
1669     fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1670         let span_lo = self.token.span;
1671         self.expect_keyword(kw::Async)?;
1672         let capture_clause = self.parse_capture_clause();
1673         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1674         attrs.extend(iattrs);
1675         Ok(self.mk_expr(
1676             span_lo.to(body.span),
1677             ExprKind::Async(capture_clause, DUMMY_NODE_ID, body), attrs))
1678     }
1679
1680     fn is_async_block(&self) -> bool {
1681         self.token.is_keyword(kw::Async) &&
1682         (
1683             ( // `async move {`
1684                 self.is_keyword_ahead(1, &[kw::Move]) &&
1685                 self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
1686             ) || ( // `async {`
1687                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
1688             )
1689         )
1690     }
1691
1692     fn maybe_parse_struct_expr(
1693         &mut self,
1694         lo: Span,
1695         path: &ast::Path,
1696         attrs: &ThinVec<Attribute>,
1697     ) -> Option<PResult<'a, P<Expr>>> {
1698         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
1699         let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
1700             // `{ ident, ` cannot start a block.
1701             self.look_ahead(2, |t| t == &token::Comma) ||
1702             self.look_ahead(2, |t| t == &token::Colon) && (
1703                 // `{ ident: token, ` cannot start a block.
1704                 self.look_ahead(4, |t| t == &token::Comma) ||
1705                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
1706                 self.look_ahead(3, |t| !t.can_begin_type())
1707             )
1708         );
1709
1710         if struct_allowed || certainly_not_a_block() {
1711             // This is a struct literal, but we don't can't accept them here.
1712             let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
1713             if let (Ok(expr), false) = (&expr, struct_allowed) {
1714                 self.struct_span_err(
1715                     expr.span,
1716                     "struct literals are not allowed here",
1717                 )
1718                 .multipart_suggestion(
1719                     "surround the struct literal with parentheses",
1720                     vec![
1721                         (lo.shrink_to_lo(), "(".to_string()),
1722                         (expr.span.shrink_to_hi(), ")".to_string()),
1723                     ],
1724                     Applicability::MachineApplicable,
1725                 )
1726                 .emit();
1727             }
1728             return Some(expr);
1729         }
1730         None
1731     }
1732
1733     pub(super) fn parse_struct_expr(
1734         &mut self,
1735         lo: Span,
1736         pth: ast::Path,
1737         mut attrs: ThinVec<Attribute>
1738     ) -> PResult<'a, P<Expr>> {
1739         let struct_sp = lo.to(self.prev_span);
1740         self.bump();
1741         let mut fields = Vec::new();
1742         let mut base = None;
1743
1744         attrs.extend(self.parse_inner_attributes()?);
1745
1746         while self.token != token::CloseDelim(token::Brace) {
1747             if self.eat(&token::DotDot) {
1748                 let exp_span = self.prev_span;
1749                 match self.parse_expr() {
1750                     Ok(e) => {
1751                         base = Some(e);
1752                     }
1753                     Err(mut e) => {
1754                         e.emit();
1755                         self.recover_stmt();
1756                     }
1757                 }
1758                 if self.token == token::Comma {
1759                     self.struct_span_err(
1760                         exp_span.to(self.prev_span),
1761                         "cannot use a comma after the base struct",
1762                     )
1763                     .span_suggestion_short(
1764                         self.token.span,
1765                         "remove this comma",
1766                         String::new(),
1767                         Applicability::MachineApplicable
1768                     )
1769                     .note("the base struct must always be the last field")
1770                     .emit();
1771                     self.recover_stmt();
1772                 }
1773                 break;
1774             }
1775
1776             let mut recovery_field = None;
1777             if let token::Ident(name, _) = self.token.kind {
1778                 if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
1779                     // Use in case of error after field-looking code: `S { foo: () with a }`.
1780                     recovery_field = Some(ast::Field {
1781                         ident: Ident::new(name, self.token.span),
1782                         span: self.token.span,
1783                         expr: self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()),
1784                         is_shorthand: false,
1785                         attrs: ThinVec::new(),
1786                         id: DUMMY_NODE_ID,
1787                         is_placeholder: false,
1788                     });
1789                 }
1790             }
1791             let mut parsed_field = None;
1792             match self.parse_field() {
1793                 Ok(f) => parsed_field = Some(f),
1794                 Err(mut e) => {
1795                     e.span_label(struct_sp, "while parsing this struct");
1796                     e.emit();
1797
1798                     // If the next token is a comma, then try to parse
1799                     // what comes next as additional fields, rather than
1800                     // bailing out until next `}`.
1801                     if self.token != token::Comma {
1802                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1803                         if self.token != token::Comma {
1804                             break;
1805                         }
1806                     }
1807                 }
1808             }
1809
1810             match self.expect_one_of(&[token::Comma],
1811                                      &[token::CloseDelim(token::Brace)]) {
1812                 Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
1813                     // Only include the field if there's no parse error for the field name.
1814                     fields.push(f);
1815                 }
1816                 Err(mut e) => {
1817                     if let Some(f) = recovery_field {
1818                         fields.push(f);
1819                     }
1820                     e.span_label(struct_sp, "while parsing this struct");
1821                     e.emit();
1822                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1823                     self.eat(&token::Comma);
1824                 }
1825             }
1826         }
1827
1828         let span = lo.to(self.token.span);
1829         self.expect(&token::CloseDelim(token::Brace))?;
1830         return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
1831     }
1832
1833     /// Parses `ident (COLON expr)?`.
1834     fn parse_field(&mut self) -> PResult<'a, Field> {
1835         let attrs = self.parse_outer_attributes()?;
1836         let lo = self.token.span;
1837
1838         // Check if a colon exists one ahead. This means we're parsing a fieldname.
1839         let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
1840             t == &token::Colon || t == &token::Eq
1841         }) {
1842             let fieldname = self.parse_field_name()?;
1843
1844             // Check for an equals token. This means the source incorrectly attempts to
1845             // initialize a field with an eq rather than a colon.
1846             if self.token == token::Eq {
1847                 self.diagnostic()
1848                     .struct_span_err(self.token.span, "expected `:`, found `=`")
1849                     .span_suggestion(
1850                         fieldname.span.shrink_to_hi().to(self.token.span),
1851                         "replace equals symbol with a colon",
1852                         ":".to_string(),
1853                         Applicability::MachineApplicable,
1854                     )
1855                     .emit();
1856             }
1857             self.bump(); // `:`
1858             (fieldname, self.parse_expr()?, false)
1859         } else {
1860             let fieldname = self.parse_ident_common(false)?;
1861
1862             // Mimic `x: x` for the `x` field shorthand.
1863             let path = ast::Path::from_ident(fieldname);
1864             let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
1865             (fieldname, expr, true)
1866         };
1867         Ok(ast::Field {
1868             ident: fieldname,
1869             span: lo.to(expr.span),
1870             expr,
1871             is_shorthand,
1872             attrs: attrs.into(),
1873             id: DUMMY_NODE_ID,
1874             is_placeholder: false,
1875         })
1876     }
1877
1878     fn err_dotdotdot_syntax(&self, span: Span) {
1879         self.struct_span_err(span, "unexpected token: `...`")
1880             .span_suggestion(
1881                 span,
1882                 "use `..` for an exclusive range", "..".to_owned(),
1883                 Applicability::MaybeIncorrect
1884             )
1885             .span_suggestion(
1886                 span,
1887                 "or `..=` for an inclusive range", "..=".to_owned(),
1888                 Applicability::MaybeIncorrect
1889             )
1890             .emit();
1891     }
1892
1893     fn err_larrow_operator(&self, span: Span) {
1894         self.struct_span_err(
1895             span,
1896             "unexpected token: `<-`"
1897         ).span_suggestion(
1898             span,
1899             "if you meant to write a comparison against a negative value, add a \
1900              space in between `<` and `-`",
1901             "< -".to_string(),
1902             Applicability::MaybeIncorrect
1903         ).emit();
1904     }
1905
1906     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1907         ExprKind::AssignOp(binop, lhs, rhs)
1908     }
1909
1910     fn mk_range(
1911         &self,
1912         start: Option<P<Expr>>,
1913         end: Option<P<Expr>>,
1914         limits: RangeLimits
1915     ) -> PResult<'a, ExprKind> {
1916         if end.is_none() && limits == RangeLimits::Closed {
1917             Err(self.span_fatal_err(self.token.span, Error::InclusiveRangeWithNoEnd))
1918         } else {
1919             Ok(ExprKind::Range(start, end, limits))
1920         }
1921     }
1922
1923     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
1924         ExprKind::Unary(unop, expr)
1925     }
1926
1927     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1928         ExprKind::Binary(binop, lhs, rhs)
1929     }
1930
1931     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
1932         ExprKind::Index(expr, idx)
1933     }
1934
1935     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
1936         ExprKind::Call(f, args)
1937     }
1938
1939     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1940         let span = lo.to(self.prev_span);
1941         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), ThinVec::new());
1942         self.recover_from_await_method_call();
1943         Ok(await_expr)
1944     }
1945
1946     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
1947         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID })
1948     }
1949
1950     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
1951         self.mk_expr(span, ExprKind::Err, ThinVec::new())
1952     }
1953 }