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                 self.sess.gated_spans.type_ascription.borrow_mut().push(lhs.span);
 256                 continue
 257             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 258                 // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
 259                 // generalise it to the Fixity::None code.
 260                 //
 261                 // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
 262                 // two variants are handled with `parse_prefix_range_expr` call above.
 263                 let rhs = if self.is_at_start_of_range_notation_rhs() {
 264                     Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 265                 } else {
 266                     None
 267                 };
 268                 let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
 269                     x.span
 270                 } else {
 271                     cur_op_span
 272                 });
 273                 let limits = if op == AssocOp::DotDot {
 274                     RangeLimits::HalfOpen
 275                 } else {
 276                     RangeLimits::Closed
 277                 };
 278
 279                 let r = self.mk_range(Some(lhs), rhs, limits)?;
 280                 lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
 281                 break
 282             }
 283
 284             let fixity = op.fixity();
 285             let prec_adjustment = match fixity {
 286                 Fixity::Right => 0,
 287                 Fixity::Left => 1,
 288                 // We currently have no non-associative operators that are not handled above by
 289                 // the special cases. The code is here only for future convenience.
 290                 Fixity::None => 1,
 291             };
 292             let rhs = self.with_res(
 293                 restrictions - Restrictions::STMT_EXPR,
 294                 |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 295             )?;
 296
 297             // Make sure that the span of the parent node is larger than the span of lhs and rhs,
 298             // including the attributes.
 299             let lhs_span = lhs
 300                 .attrs
 301                 .iter()
 302                 .filter(|a| a.style == AttrStyle::Outer)
 303                 .next()
 304                 .map_or(lhs_span, |a| a.span);
 305             let span = lhs_span.to(rhs.span);
 306             lhs = match op {
 307                 AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
 308                 AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
 309                 AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
 310                 AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
 311                 AssocOp::Greater | AssocOp::GreaterEqual => {
 312                     let ast_op = op.to_ast_binop().unwrap();
 313                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 314                     self.mk_expr(span, binary, ThinVec::new())
 315                 }
 316                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
 317                 AssocOp::AssignOp(k) => {
 318                     let aop = match k {
 319                         token::Plus =>    BinOpKind::Add,
 320                         token::Minus =>   BinOpKind::Sub,
 321                         token::Star =>    BinOpKind::Mul,
 322                         token::Slash =>   BinOpKind::Div,
 323                         token::Percent => BinOpKind::Rem,
 324                         token::Caret =>   BinOpKind::BitXor,
 325                         token::And =>     BinOpKind::BitAnd,
 326                         token::Or =>      BinOpKind::BitOr,
 327                         token::Shl =>     BinOpKind::Shl,
 328                         token::Shr =>     BinOpKind::Shr,
 329                     };
 330                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 331                     self.mk_expr(span, aopexpr, ThinVec::new())
 332                 }
 333                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 334                     self.bug("AssocOp should have been handled by special case")
 335                 }
 336             };
 337
 338             if let Fixity::None = fixity { break }
 339         }
 340         if last_type_ascription_set {
 341             self.last_type_ascription = None;
 342         }
 343         Ok(lhs)
 344     }
 345
 346     /// Checks if this expression is a successfully parsed statement.
 347     fn expr_is_complete(&self, e: &Expr) -> bool {
 348         self.restrictions.contains(Restrictions::STMT_EXPR) &&
 349             !classify::expr_requires_semi_to_be_stmt(e)
 350     }
 351
 352     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 353         if self.token.can_begin_expr() {
 354             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 355             if self.token == token::OpenDelim(token::Brace) {
 356                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 357             }
 358             true
 359         } else {
 360             false
 361         }
 362     }
 363
 364     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 365     fn parse_prefix_range_expr(
 366         &mut self,
 367         already_parsed_attrs: Option<ThinVec<Attribute>>
 368     ) -> PResult<'a, P<Expr>> {
 369         // Check for deprecated `...` syntax.
 370         if self.token == token::DotDotDot {
 371             self.err_dotdotdot_syntax(self.token.span);
 372         }
 373
 374         debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 375                       "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 376                       self.token);
 377         let tok = self.token.clone();
 378         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 379         let lo = self.token.span;
 380         let mut hi = self.token.span;
 381         self.bump();
 382         let opt_end = if self.is_at_start_of_range_notation_rhs() {
 383             // RHS must be parsed with more associativity than the dots.
 384             let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
 385             Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed)
 386                 .map(|x| {
 387                     hi = x.span;
 388                     x
 389                 })?)
 390         } else {
 391             None
 392         };
 393         let limits = if tok == token::DotDot {
 394             RangeLimits::HalfOpen
 395         } else {
 396             RangeLimits::Closed
 397         };
 398
 399         let r = self.mk_range(None, opt_end, limits)?;
 400         Ok(self.mk_expr(lo.to(hi), r, attrs))
 401     }
 402
 403     /// Parses a prefix-unary-operator expr.
 404     fn parse_prefix_expr(
 405         &mut self,
 406         already_parsed_attrs: Option<ThinVec<Attribute>>
 407     ) -> PResult<'a, P<Expr>> {
 408         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 409         let lo = self.token.span;
 410         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 411         let (hi, ex) = match self.token.kind {
 412             token::Not => {
 413                 self.bump();
 414                 let e = self.parse_prefix_expr(None);
 415                 let (span, e) = self.interpolated_or_expr_span(e)?;
 416                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 417             }
 418             // Suggest `!` for bitwise negation when encountering a `~`
 419             token::Tilde => {
 420                 self.bump();
 421                 let e = self.parse_prefix_expr(None);
 422                 let (span, e) = self.interpolated_or_expr_span(e)?;
 423                 let span_of_tilde = lo;
 424                 self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator")
 425                     .span_suggestion_short(
 426                         span_of_tilde,
 427                         "use `!` to perform bitwise not",
 428                         "!".to_owned(),
 429                         Applicability::MachineApplicable
 430                     )
 431                     .emit();
 432                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 433             }
 434             token::BinOp(token::Minus) => {
 435                 self.bump();
 436                 let e = self.parse_prefix_expr(None);
 437                 let (span, e) = self.interpolated_or_expr_span(e)?;
 438                 (lo.to(span), self.mk_unary(UnOp::Neg, e))
 439             }
 440             token::BinOp(token::Star) => {
 441                 self.bump();
 442                 let e = self.parse_prefix_expr(None);
 443                 let (span, e) = self.interpolated_or_expr_span(e)?;
 444                 (lo.to(span), self.mk_unary(UnOp::Deref, e))
 445             }
 446             token::BinOp(token::And) | token::AndAnd => {
 447                 self.expect_and()?;
 448                 let m = self.parse_mutability();
 449                 let e = self.parse_prefix_expr(None);
 450                 let (span, e) = self.interpolated_or_expr_span(e)?;
 451                 (lo.to(span), ExprKind::AddrOf(m, e))
 452             }
 453             token::Ident(..) if self.token.is_keyword(kw::Box) => {
 454                 self.bump();
 455                 let e = self.parse_prefix_expr(None);
 456                 let (span, e) = self.interpolated_or_expr_span(e)?;
 457                 let span = lo.to(span);
 458                 self.sess.gated_spans.box_syntax.borrow_mut().push(span);
 459                 (span, ExprKind::Box(e))
 460             }
 461             token::Ident(..) if self.token.is_ident_named(sym::not) => {
 462                 // `not` is just an ordinary identifier in Rust-the-language,
 463                 // but as `rustc`-the-compiler, we can issue clever diagnostics
 464                 // for confused users who really want to say `!`
 465                 let token_cannot_continue_expr = |t: &Token| match t.kind {
 466                     // These tokens can start an expression after `!`, but
 467                     // can't continue an expression after an ident
 468                     token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 469                     token::Literal(..) | token::Pound => true,
 470                     _ => t.is_whole_expr(),
 471                 };
 472                 let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
 473                 if cannot_continue_expr {
 474                     self.bump();
 475                     // Emit the error ...
 476                     self.struct_span_err(
 477                         self.token.span,
 478                         &format!("unexpected {} after identifier",self.this_token_descr())
 479                     )
 480                     .span_suggestion_short(
 481                         // Span the `not` plus trailing whitespace to avoid
 482                         // trailing whitespace after the `!` in our suggestion
 483                         self.sess.source_map()
 484                             .span_until_non_whitespace(lo.to(self.token.span)),
 485                         "use `!` to perform logical negation",
 486                         "!".to_owned(),
 487                         Applicability::MachineApplicable
 488                     )
 489                     .emit();
 490                     // —and recover! (just as if we were in the block
 491                     // for the `token::Not` arm)
 492                     let e = self.parse_prefix_expr(None);
 493                     let (span, e) = self.interpolated_or_expr_span(e)?;
 494                     (lo.to(span), self.mk_unary(UnOp::Not, e))
 495                 } else {
 496                     return self.parse_dot_or_call_expr(Some(attrs));
 497                 }
 498             }
 499             _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
 500         };
 501         return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 502     }
 503
 504     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 505     fn interpolated_or_expr_span(
 506         &self,
 507         expr: PResult<'a, P<Expr>>,
 508     ) -> PResult<'a, (Span, P<Expr>)> {
 509         expr.map(|e| {
 510             if self.prev_token_kind == PrevTokenKind::Interpolated {
 511                 (self.prev_span, e)
 512             } else {
 513                 (e.span, e)
 514             }
 515         })
 516     }
 517
 518     fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
 519                            expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
 520                            -> PResult<'a, P<Expr>> {
 521         let mk_expr = |this: &mut Self, rhs: P<Ty>| {
 522             this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
 523         };
 524
 525         // Save the state of the parser before parsing type normally, in case there is a
 526         // LessThan comparison after this cast.
 527         let parser_snapshot_before_type = self.clone();
 528         match self.parse_ty_no_plus() {
 529             Ok(rhs) => {
 530                 Ok(mk_expr(self, rhs))
 531             }
 532             Err(mut type_err) => {
 533                 // Rewind to before attempting to parse the type with generics, to recover
 534                 // from situations like `x as usize < y` in which we first tried to parse
 535                 // `usize < y` as a type with generic arguments.
 536                 let parser_snapshot_after_type = self.clone();
 537                 mem::replace(self, parser_snapshot_before_type);
 538
 539                 match self.parse_path(PathStyle::Expr) {
 540                     Ok(path) => {
 541                         let (op_noun, op_verb) = match self.token.kind {
 542                             token::Lt => ("comparison", "comparing"),
 543                             token::BinOp(token::Shl) => ("shift", "shifting"),
 544                             _ => {
 545                                 // We can end up here even without `<` being the next token, for
 546                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 547                                 // but `parse_path` returns `Ok` on them due to error recovery.
 548                                 // Return original error and parser state.
 549                                 mem::replace(self, parser_snapshot_after_type);
 550                                 return Err(type_err);
 551                             }
 552                         };
 553
 554                         // Successfully parsed the type path leaving a `<` yet to parse.
 555                         type_err.cancel();
 556
 557                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 558                         // in AST and continue parsing.
 559                         let msg = format!(
 560                             "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
 561                             pprust::path_to_string(&path),
 562                             op_noun,
 563                         );
 564                         let span_after_type = parser_snapshot_after_type.token.span;
 565                         let expr = mk_expr(self, P(Ty {
 566                             span: path.span,
 567                             kind: TyKind::Path(None, path),
 568                             id: DUMMY_NODE_ID,
 569                         }));
 570
 571                         let expr_str = self.span_to_snippet(expr.span)
 572                             .unwrap_or_else(|_| pprust::expr_to_string(&expr));
 573
 574                         self.struct_span_err(self.token.span, &msg)
 575                             .span_label(
 576                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 577                                 "interpreted as generic arguments"
 578                             )
 579                             .span_label(self.token.span, format!("not interpreted as {}", op_noun))
 580                             .span_suggestion(
 581                                 expr.span,
 582                                 &format!("try {} the cast value", op_verb),
 583                                 format!("({})", expr_str),
 584                                 Applicability::MachineApplicable,
 585                             )
 586                             .emit();
 587
 588                         Ok(expr)
 589                     }
 590                     Err(mut path_err) => {
 591                         // Couldn't parse as a path, return original error and parser state.
 592                         path_err.cancel();
 593                         mem::replace(self, parser_snapshot_after_type);
 594                         Err(type_err)
 595                     }
 596                 }
 597             }
 598         }
 599     }
 600
 601     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 602     fn parse_dot_or_call_expr(
 603         &mut self,
 604         already_parsed_attrs: Option<ThinVec<Attribute>>,
 605     ) -> PResult<'a, P<Expr>> {
 606         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 607
 608         let b = self.parse_bottom_expr();
 609         let (span, b) = self.interpolated_or_expr_span(b)?;
 610         self.parse_dot_or_call_expr_with(b, span, attrs)
 611     }
 612
 613     pub(super) fn parse_dot_or_call_expr_with(
 614         &mut self,
 615         e0: P<Expr>,
 616         lo: Span,
 617         mut attrs: ThinVec<Attribute>,
 618     ) -> PResult<'a, P<Expr>> {
 619         // Stitch the list of outer attributes onto the return value.
 620         // A little bit ugly, but the best way given the current code
 621         // structure
 622         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr|
 623             expr.map(|mut expr| {
 624                 attrs.extend::<Vec<_>>(expr.attrs.into());
 625                 expr.attrs = attrs;
 626                 match expr.kind {
 627                     ExprKind::If(..) if !expr.attrs.is_empty() => {
 628                         // Just point to the first attribute in there...
 629                         let span = expr.attrs[0].span;
 630                         self.span_err(span, "attributes are not yet allowed on `if` expressions");
 631                     }
 632                     _ => {}
 633                 }
 634                 expr
 635             })
 636         )
 637     }
 638
 639     fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 640         let mut e = e0;
 641         let mut hi;
 642         loop {
 643             // expr?
 644             while self.eat(&token::Question) {
 645                 let hi = self.prev_span;
 646                 e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
 647             }
 648
 649             // expr.f
 650             if self.eat(&token::Dot) {
 651                 match self.token.kind {
 652                     token::Ident(..) => {
 653                         e = self.parse_dot_suffix(e, lo)?;
 654                     }
 655                     token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 656                         let span = self.token.span;
 657                         self.bump();
 658                         let field = ExprKind::Field(e, Ident::new(symbol, span));
 659                         e = self.mk_expr(lo.to(span), field, ThinVec::new());
 660
 661                         self.expect_no_suffix(span, "a tuple index", suffix);
 662                     }
 663                     token::Literal(token::Lit { kind: token::Float, symbol, .. }) => {
 664                       self.bump();
 665                       let fstr = symbol.as_str();
 666                       let msg = format!("unexpected token: `{}`", symbol);
 667                       let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg);
 668                       err.span_label(self.prev_span, "unexpected token");
 669                       if fstr.chars().all(|x| "0123456789.".contains(x)) {
 670                           let float = match fstr.parse::<f64>().ok() {
 671                               Some(f) => f,
 672                               None => continue,
 673                           };
 674                           let sugg = pprust::to_string(|s| {
 675                               s.popen();
 676                               s.print_expr(&e);
 677                               s.s.word( ".");
 678                               s.print_usize(float.trunc() as usize);
 679                               s.pclose();
 680                               s.s.word(".");
 681                               s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
 682                           });
 683                           err.span_suggestion(
 684                               lo.to(self.prev_span),
 685                               "try parenthesizing the first index",
 686                               sugg,
 687                               Applicability::MachineApplicable
 688                           );
 689                       }
 690                       return Err(err);
 691
 692                     }
 693                     _ => {
 694                         // FIXME Could factor this out into non_fatal_unexpected or something.
 695                         let actual = self.this_token_to_string();
 696                         self.span_err(self.token.span, &format!("unexpected token: `{}`", actual));
 697                     }
 698                 }
 699                 continue;
 700             }
 701             if self.expr_is_complete(&e) { break; }
 702             match self.token.kind {
 703                 // expr(...)
 704                 token::OpenDelim(token::Paren) => {
 705                     let seq = self.parse_paren_expr_seq().map(|es| {
 706                         let nd = self.mk_call(e, es);
 707                         let hi = self.prev_span;
 708                         self.mk_expr(lo.to(hi), nd, ThinVec::new())
 709                     });
 710                     e = self.recover_seq_parse_error(token::Paren, lo, seq);
 711                 }
 712
 713                 // expr[...]
 714                 // Could be either an index expression or a slicing expression.
 715                 token::OpenDelim(token::Bracket) => {
 716                     self.bump();
 717                     let ix = self.parse_expr()?;
 718                     hi = self.token.span;
 719                     self.expect(&token::CloseDelim(token::Bracket))?;
 720                     let index = self.mk_index(e, ix);
 721                     e = self.mk_expr(lo.to(hi), index, ThinVec::new())
 722                 }
 723                 _ => return Ok(e)
 724             }
 725         }
 726         return Ok(e);
 727     }
 728
 729     /// Assuming we have just parsed `.`, continue parsing into an expression.
 730     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 731         if self.token.span.rust_2018() && self.eat_keyword(kw::Await) {
 732             return self.mk_await_expr(self_arg, lo);
 733         }
 734
 735         let segment = self.parse_path_segment(PathStyle::Expr)?;
 736         self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
 737
 738         Ok(match self.token.kind {
 739             token::OpenDelim(token::Paren) => {
 740                 // Method call `expr.f()`
 741                 let mut args = self.parse_paren_expr_seq()?;
 742                 args.insert(0, self_arg);
 743
 744                 let span = lo.to(self.prev_span);
 745                 self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
 746             }
 747             _ => {
 748                 // Field access `expr.f`
 749                 if let Some(args) = segment.args {
 750                     self.span_err(args.span(),
 751                                   "field expressions may not have generic arguments");
 752                 }
 753
 754                 let span = lo.to(self.prev_span);
 755                 self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
 756             }
 757         })
 758     }
 759
 760     /// At the bottom (top?) of the precedence hierarchy,
 761     /// Parses things like parenthesized exprs, macros, `return`, etc.
 762     ///
 763     /// N.B., this does not parse outer attributes, and is private because it only works
 764     /// correctly if called from `parse_dot_or_call_expr()`.
 765     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
 766         maybe_recover_from_interpolated_ty_qpath!(self, true);
 767         maybe_whole_expr!(self);
 768
 769         // Outer attributes are already parsed and will be
 770         // added to the return value after the fact.
 771         //
 772         // Therefore, prevent sub-parser from parsing
 773         // attributes by giving them a empty "already-parsed" list.
 774         let mut attrs = ThinVec::new();
 775
 776         let lo = self.token.span;
 777         let mut hi = self.token.span;
 778
 779         let ex: ExprKind;
 780
 781         macro_rules! parse_lit {
 782             () => {
 783                 match self.parse_lit() {
 784                     Ok(literal) => {
 785                         hi = self.prev_span;
 786                         ex = ExprKind::Lit(literal);
 787                     }
 788                     Err(mut err) => {
 789                         err.cancel();
 790                         return Err(self.expected_expression_found());
 791                     }
 792                 }
 793             }
 794         }
 795
 796         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
 797         match self.token.kind {
 798             // This match arm is a special-case of the `_` match arm below and
 799             // could be removed without changing functionality, but it's faster
 800             // to have it here, especially for programs with large constants.
 801             token::Literal(_) => {
 802                 parse_lit!()
 803             }
 804             token::OpenDelim(token::Paren) => {
 805                 self.bump();
 806
 807                 attrs.extend(self.parse_inner_attributes()?);
 808
 809                 // `(e)` is parenthesized `e`.
 810                 // `(e,)` is a tuple with only one field, `e`.
 811                 let mut es = vec![];
 812                 let mut trailing_comma = false;
 813                 let mut recovered = false;
 814                 while self.token != token::CloseDelim(token::Paren) {
 815                     es.push(match self.parse_expr() {
 816                         Ok(es) => es,
 817                         Err(mut err) => {
 818                             // Recover from parse error in tuple list.
 819                             match self.token.kind {
 820                                 token::Ident(name, false)
 821                                 if name == kw::Underscore && self.look_ahead(1, |t| {
 822                                     t == &token::Comma
 823                                 }) => {
 824                                     // Special-case handling of `Foo<(_, _, _)>`
 825                                     err.emit();
 826                                     let sp = self.token.span;
 827                                     self.bump();
 828                                     self.mk_expr(sp, ExprKind::Err, ThinVec::new())
 829                                 }
 830                                 _ => return Ok(
 831                                     self.recover_seq_parse_error(token::Paren, lo, Err(err)),
 832                                 ),
 833                             }
 834                         }
 835                     });
 836                     recovered = self.expect_one_of(
 837                         &[],
 838                         &[token::Comma, token::CloseDelim(token::Paren)],
 839                     )?;
 840                     if self.eat(&token::Comma) {
 841                         trailing_comma = true;
 842                     } else {
 843                         trailing_comma = false;
 844                         break;
 845                     }
 846                 }
 847                 if !recovered {
 848                     self.bump();
 849                 }
 850
 851                 hi = self.prev_span;
 852                 ex = if es.len() == 1 && !trailing_comma {
 853                     ExprKind::Paren(es.into_iter().nth(0).unwrap())
 854                 } else {
 855                     ExprKind::Tup(es)
 856                 };
 857             }
 858             token::OpenDelim(token::Brace) => {
 859                 return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
 860             }
 861             token::BinOp(token::Or) | token::OrOr => {
 862                 return self.parse_closure_expr(attrs);
 863             }
 864             token::OpenDelim(token::Bracket) => {
 865                 self.bump();
 866
 867                 attrs.extend(self.parse_inner_attributes()?);
 868
 869                 if self.eat(&token::CloseDelim(token::Bracket)) {
 870                     // Empty vector
 871                     ex = ExprKind::Array(Vec::new());
 872                 } else {
 873                     // Non-empty vector
 874                     let first_expr = self.parse_expr()?;
 875                     if self.eat(&token::Semi) {
 876                         // Repeating array syntax: `[ 0; 512 ]`
 877                         let count = AnonConst {
 878                             id: DUMMY_NODE_ID,
 879                             value: self.parse_expr()?,
 880                         };
 881                         self.expect(&token::CloseDelim(token::Bracket))?;
 882                         ex = ExprKind::Repeat(first_expr, count);
 883                     } else if self.eat(&token::Comma) {
 884                         // Vector with two or more elements
 885                         let remaining_exprs = self.parse_seq_to_end(
 886                             &token::CloseDelim(token::Bracket),
 887                             SeqSep::trailing_allowed(token::Comma),
 888                             |p| Ok(p.parse_expr()?)
 889                         )?;
 890                         let mut exprs = vec![first_expr];
 891                         exprs.extend(remaining_exprs);
 892                         ex = ExprKind::Array(exprs);
 893                     } else {
 894                         // Vector with one element
 895                         self.expect(&token::CloseDelim(token::Bracket))?;
 896                         ex = ExprKind::Array(vec![first_expr]);
 897                     }
 898                 }
 899                 hi = self.prev_span;
 900             }
 901             _ => {
 902                 if self.eat_lt() {
 903                     let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
 904                     hi = path.span;
 905                     return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
 906                 }
 907                 if self.token.is_path_start() {
 908                     let path = self.parse_path(PathStyle::Expr)?;
 909
 910                     // `!`, as an operator, is prefix, so we know this isn't that.
 911                     if self.eat(&token::Not) {
 912                         // MACRO INVOCATION expression
 913                         let (delim, tts) = self.expect_delimited_token_tree()?;
 914                         hi = self.prev_span;
 915                         ex = ExprKind::Mac(Mac {
 916                             path,
 917                             tts,
 918                             delim,
 919                             span: lo.to(hi),
 920                             prior_type_ascription: self.last_type_ascription,
 921                         });
 922                     } else if self.check(&token::OpenDelim(token::Brace)) {
 923                         if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
 924                             return expr;
 925                         } else {
 926                             hi = path.span;
 927                             ex = ExprKind::Path(None, path);
 928                         }
 929                     } else {
 930                         hi = path.span;
 931                         ex = ExprKind::Path(None, path);
 932                     }
 933
 934                     let expr = self.mk_expr(lo.to(hi), ex, attrs);
 935                     return self.maybe_recover_from_bad_qpath(expr, true);
 936                 }
 937                 if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
 938                     return self.parse_closure_expr(attrs);
 939                 }
 940                 if self.eat_keyword(kw::If) {
 941                     return self.parse_if_expr(attrs);
 942                 }
 943                 if self.eat_keyword(kw::For) {
 944                     let lo = self.prev_span;
 945                     return self.parse_for_expr(None, lo, attrs);
 946                 }
 947                 if self.eat_keyword(kw::While) {
 948                     let lo = self.prev_span;
 949                     return self.parse_while_expr(None, lo, attrs);
 950                 }
 951                 if let Some(label) = self.eat_label() {
 952                     let lo = label.ident.span;
 953                     self.expect(&token::Colon)?;
 954                     if self.eat_keyword(kw::While) {
 955                         return self.parse_while_expr(Some(label), lo, attrs)
 956                     }
 957                     if self.eat_keyword(kw::For) {
 958                         return self.parse_for_expr(Some(label), lo, attrs)
 959                     }
 960                     if self.eat_keyword(kw::Loop) {
 961                         return self.parse_loop_expr(Some(label), lo, attrs)
 962                     }
 963                     if self.token == token::OpenDelim(token::Brace) {
 964                         return self.parse_block_expr(Some(label),
 965                                                      lo,
 966                                                      BlockCheckMode::Default,
 967                                                      attrs);
 968                     }
 969                     let msg = "expected `while`, `for`, `loop` or `{` after a label";
 970                     let mut err = self.fatal(msg);
 971                     err.span_label(self.token.span, msg);
 972                     return Err(err);
 973                 }
 974                 if self.eat_keyword(kw::Loop) {
 975                     let lo = self.prev_span;
 976                     return self.parse_loop_expr(None, lo, attrs);
 977                 }
 978                 if self.eat_keyword(kw::Continue) {
 979                     let label = self.eat_label();
 980                     let ex = ExprKind::Continue(label);
 981                     let hi = self.prev_span;
 982                     return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 983                 }
 984                 if self.eat_keyword(kw::Match) {
 985                     let match_sp = self.prev_span;
 986                     return self.parse_match_expr(attrs).map_err(|mut err| {
 987                         err.span_label(match_sp, "while parsing this match expression");
 988                         err
 989                     });
 990                 }
 991                 if self.eat_keyword(kw::Unsafe) {
 992                     return self.parse_block_expr(
 993                         None,
 994                         lo,
 995                         BlockCheckMode::Unsafe(ast::UserProvided),
 996                         attrs);
 997                 }
 998                 if self.is_do_catch_block() {
 999                     let mut db = self.fatal("found removed `do catch` syntax");
1000                     db.help("following RFC #2388, the new non-placeholder syntax is `try`");
1001                     return Err(db);
1002                 }
1003                 if self.is_try_block() {
1004                     let lo = self.token.span;
1005                     assert!(self.eat_keyword(kw::Try));
1006                     return self.parse_try_block(lo, attrs);
1007                 }
1008
1009                 // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1010                 let is_span_rust_2018 = self.token.span.rust_2018();
1011                 if is_span_rust_2018 && self.check_keyword(kw::Async) {
1012                     return if self.is_async_block() { // Check for `async {` and `async move {`.
1013                         self.parse_async_block(attrs)
1014                     } else {
1015                         self.parse_closure_expr(attrs)
1016                     };
1017                 }
1018                 if self.eat_keyword(kw::Return) {
1019                     if self.token.can_begin_expr() {
1020                         let e = self.parse_expr()?;
1021                         hi = e.span;
1022                         ex = ExprKind::Ret(Some(e));
1023                     } else {
1024                         ex = ExprKind::Ret(None);
1025                     }
1026                 } else if self.eat_keyword(kw::Break) {
1027                     let label = self.eat_label();
1028                     let e = if self.token.can_begin_expr()
1029                                && !(self.token == token::OpenDelim(token::Brace)
1030                                     && self.restrictions.contains(
1031                                            Restrictions::NO_STRUCT_LITERAL)) {
1032                         Some(self.parse_expr()?)
1033                     } else {
1034                         None
1035                     };
1036                     ex = ExprKind::Break(label, e);
1037                     hi = self.prev_span;
1038                 } else if self.eat_keyword(kw::Yield) {
1039                     if self.token.can_begin_expr() {
1040                         let e = self.parse_expr()?;
1041                         hi = e.span;
1042                         ex = ExprKind::Yield(Some(e));
1043                     } else {
1044                         ex = ExprKind::Yield(None);
1045                     }
1046
1047                     let span = lo.to(hi);
1048                     self.sess.gated_spans.yields.borrow_mut().push(span);
1049                 } else if self.eat_keyword(kw::Let) {
1050                     return self.parse_let_expr(attrs);
1051                 } else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
1052                     let (await_hi, e_kind) = self.parse_incorrect_await_syntax(lo, self.prev_span)?;
1053                     hi = await_hi;
1054                     ex = e_kind;
1055                 } else {
1056                     if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1057                         // Don't complain about bare semicolons after unclosed braces
1058                         // recovery in order to keep the error count down. Fixing the
1059                         // delimiters will possibly also fix the bare semicolon found in
1060                         // expression context. For example, silence the following error:
1061                         //
1062                         //     error: expected expression, found `;`
1063                         //      --> file.rs:2:13
1064                         //       |
1065                         //     2 |     foo(bar(;
1066                         //       |             ^ expected expression
1067                         self.bump();
1068                         return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()));
1069                     }
1070                     parse_lit!()
1071                 }
1072             }
1073         }
1074
1075         let expr = self.mk_expr(lo.to(hi), ex, attrs);
1076         self.maybe_recover_from_bad_qpath(expr, true)
1077     }
1078
1079     /// Matches `lit = true | false | token_lit`.
1080     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1081         let mut recovered = None;
1082         if self.token == token::Dot {
1083             // Attempt to recover `.4` as `0.4`.
1084             recovered = self.look_ahead(1, |next_token| {
1085                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
1086                         = next_token.kind {
1087                     if self.token.span.hi() == next_token.span.lo() {
1088                         let s = String::from("0.") + &symbol.as_str();
1089                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1090                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1091                     }
1092                 }
1093                 None
1094             });
1095             if let Some(token) = &recovered {
1096                 self.bump();
1097                 self.struct_span_err(token.span, "float literals must have an integer part")
1098                     .span_suggestion(
1099                         token.span,
1100                         "must have an integer part",
1101                         pprust::token_to_string(token),
1102                         Applicability::MachineApplicable,
1103                     )
1104                     .emit();
1105             }
1106         }
1107
1108         let token = recovered.as_ref().unwrap_or(&self.token);
1109         match Lit::from_token(token) {
1110             Ok(lit) => {
1111                 self.bump();
1112                 Ok(lit)
1113             }
1114             Err(LitError::NotLiteral) => {
1115                 let msg = format!("unexpected token: {}", self.this_token_descr());
1116                 Err(self.span_fatal(token.span, &msg))
1117             }
1118             Err(err) => {
1119                 let (lit, span) = (token.expect_lit(), token.span);
1120                 self.bump();
1121                 self.error_literal_from_token(err, lit, span);
1122                 // Pack possible quotes and prefixes from the original literal into
1123                 // the error literal's symbol so they can be pretty-printed faithfully.
1124                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1125                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1126                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1127                 Lit::from_lit_token(lit, span).map_err(|_| unreachable!())
1128             }
1129         }
1130     }
1131
1132     fn error_literal_from_token(&self, err: LitError, lit: token::Lit, span: Span) {
1133         // Checks if `s` looks like i32 or u1234 etc.
1134         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1135             s.len() > 1
1136             && s.starts_with(first_chars)
1137             && s[1..].chars().all(|c| c.is_ascii_digit())
1138         }
1139
1140         let token::Lit { kind, suffix, .. } = lit;
1141         match err {
1142             // `NotLiteral` is not an error by itself, so we don't report
1143             // it and give the parser opportunity to try something else.
1144             LitError::NotLiteral => {}
1145             // `LexerError` *is* an error, but it was already reported
1146             // by lexer, so here we don't report it the second time.
1147             LitError::LexerError => {}
1148             LitError::InvalidSuffix => {
1149                 self.expect_no_suffix(
1150                     span,
1151                     &format!("{} {} literal", kind.article(), kind.descr()),
1152                     suffix,
1153                 );
1154             }
1155             LitError::InvalidIntSuffix => {
1156                 let suf = suffix.expect("suffix error with no suffix").as_str();
1157                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1158                     // If it looks like a width, try to be helpful.
1159                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1160                     self.struct_span_err(span, &msg)
1161                         .help("valid widths are 8, 16, 32, 64 and 128")
1162                         .emit();
1163                 } else {
1164                     let msg = format!("invalid suffix `{}` for integer literal", suf);
1165                     self.struct_span_err(span, &msg)
1166                         .span_label(span, format!("invalid suffix `{}`", suf))
1167                         .help("the suffix must be one of the integral types (`u32`, `isize`, etc)")
1168                         .emit();
1169                 }
1170             }
1171             LitError::InvalidFloatSuffix => {
1172                 let suf = suffix.expect("suffix error with no suffix").as_str();
1173                 if looks_like_width_suffix(&['f'], &suf) {
1174                     // If it looks like a width, try to be helpful.
1175                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1176                     self.struct_span_err(span, &msg)
1177                         .help("valid widths are 32 and 64")
1178                         .emit();
1179                 } else {
1180                     let msg = format!("invalid suffix `{}` for float literal", suf);
1181                     self.struct_span_err(span, &msg)
1182                         .span_label(span, format!("invalid suffix `{}`", suf))
1183                         .help("valid suffixes are `f32` and `f64`")
1184                         .emit();
1185                 }
1186             }
1187             LitError::NonDecimalFloat(base) => {
1188                 let descr = match base {
1189                     16 => "hexadecimal",
1190                     8 => "octal",
1191                     2 => "binary",
1192                     _ => unreachable!(),
1193                 };
1194                 self.struct_span_err(span, &format!("{} float literal is not supported", descr))
1195                     .span_label(span, "not supported")
1196                     .emit();
1197             }
1198             LitError::IntTooLarge => {
1199                 self.struct_span_err(span, "integer literal is too large")
1200                     .emit();
1201             }
1202         }
1203     }
1204
1205     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1206         if let Some(suf) = suffix {
1207             let mut err = if kind == "a tuple index"
1208                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1209             {
1210                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1211                 // through the ecosystem when people fix their macros
1212                 let mut err = self.sess.span_diagnostic.struct_span_warn(
1213                     sp,
1214                     &format!("suffixes on {} are invalid", kind),
1215                 );
1216                 err.note(&format!(
1217                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1218                         incorrectly accepted on stable for a few releases",
1219                     suf,
1220                 ));
1221                 err.help(
1222                     "on proc macros, you'll want to use `syn::Index::from` or \
1223                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1224                         to tuple field access",
1225                 );
1226                 err.note(
1227                     "for more context, see https://github.com/rust-lang/rust/issues/60210",
1228                 );
1229                 err
1230             } else {
1231                 self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
1232             };
1233             err.span_label(sp, format!("invalid suffix `{}`", suf));
1234             err.emit();
1235         }
1236     }
1237
1238     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1239     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1240         maybe_whole_expr!(self);
1241
1242         let minus_lo = self.token.span;
1243         let minus_present = self.eat(&token::BinOp(token::Minus));
1244         let lo = self.token.span;
1245         let literal = self.parse_lit()?;
1246         let hi = self.prev_span;
1247         let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
1248
1249         if minus_present {
1250             let minus_hi = self.prev_span;
1251             let unary = self.mk_unary(UnOp::Neg, expr);
1252             Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
1253         } else {
1254             Ok(expr)
1255         }
1256     }
1257
1258     /// Parses a block or unsafe block.
1259     pub(super) fn parse_block_expr(
1260         &mut self,
1261         opt_label: Option<Label>,
1262         lo: Span,
1263         blk_mode: BlockCheckMode,
1264         outer_attrs: ThinVec<Attribute>,
1265     ) -> PResult<'a, P<Expr>> {
1266         if let Some(label) = opt_label {
1267             self.sess.gated_spans.label_break_value.borrow_mut().push(label.ident.span);
1268         }
1269
1270         self.expect(&token::OpenDelim(token::Brace))?;
1271
1272         let mut attrs = outer_attrs;
1273         attrs.extend(self.parse_inner_attributes()?);
1274
1275         let blk = self.parse_block_tail(lo, blk_mode)?;
1276         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1277     }
1278
1279     /// Parses a closure expression (e.g., `move |args| expr`).
1280     fn parse_closure_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1281         let lo = self.token.span;
1282
1283         let movability = if self.eat_keyword(kw::Static) {
1284             Movability::Static
1285         } else {
1286             Movability::Movable
1287         };
1288
1289         let asyncness = if self.token.span.rust_2018() {
1290             self.parse_asyncness()
1291         } else {
1292             IsAsync::NotAsync
1293         };
1294         if asyncness.is_async() {
1295             // Feature-gate `async ||` closures.
1296             self.sess.gated_spans.async_closure.borrow_mut().push(self.prev_span);
1297         }
1298
1299         let capture_clause = self.parse_capture_clause();
1300         let decl = self.parse_fn_block_decl()?;
1301         let decl_hi = self.prev_span;
1302         let body = match decl.output {
1303             FunctionRetTy::Default(_) => {
1304                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1305                 self.parse_expr_res(restrictions, None)?
1306             },
1307             _ => {
1308                 // If an explicit return type is given, require a block to appear (RFC 968).
1309                 let body_lo = self.token.span;
1310                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
1311             }
1312         };
1313
1314         Ok(self.mk_expr(
1315             lo.to(body.span),
1316             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
1317             attrs))
1318     }
1319
1320     /// Parses an optional `move` prefix to a closure lke construct.
1321     fn parse_capture_clause(&mut self) -> CaptureBy {
1322         if self.eat_keyword(kw::Move) {
1323             CaptureBy::Value
1324         } else {
1325             CaptureBy::Ref
1326         }
1327     }
1328
1329     /// Parses the `|arg, arg|` header of a closure.
1330     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
1331         let inputs_captures = {
1332             if self.eat(&token::OrOr) {
1333                 Vec::new()
1334             } else {
1335                 self.expect(&token::BinOp(token::Or))?;
1336                 let args = self.parse_seq_to_before_tokens(
1337                     &[&token::BinOp(token::Or), &token::OrOr],
1338                     SeqSep::trailing_allowed(token::Comma),
1339                     TokenExpectType::NoExpect,
1340                     |p| p.parse_fn_block_param()
1341                 )?.0;
1342                 self.expect_or()?;
1343                 args
1344             }
1345         };
1346         let output = self.parse_ret_ty(true)?;
1347
1348         Ok(P(FnDecl {
1349             inputs: inputs_captures,
1350             output,
1351         }))
1352     }
1353
1354     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
1355     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
1356         let lo = self.token.span;
1357         let attrs = self.parse_outer_attributes()?;
1358         let pat = self.parse_pat(PARAM_EXPECTED)?;
1359         let t = if self.eat(&token::Colon) {
1360             self.parse_ty()?
1361         } else {
1362             P(Ty {
1363                 id: DUMMY_NODE_ID,
1364                 kind: TyKind::Infer,
1365                 span: self.prev_span,
1366             })
1367         };
1368         let span = lo.to(self.token.span);
1369         Ok(Param {
1370             attrs: attrs.into(),
1371             ty: t,
1372             pat,
1373             span,
1374             id: DUMMY_NODE_ID,
1375             is_placeholder: false,
1376         })
1377     }
1378
1379     /// Parses an `if` expression (`if` token already eaten).
1380     fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1381         let lo = self.prev_span;
1382         let cond = self.parse_cond_expr()?;
1383
1384         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
1385         // verify that the last statement is either an implicit return (no `;`) or an explicit
1386         // return. This won't catch blocks with an explicit `return`, but that would be caught by
1387         // the dead code lint.
1388         if self.eat_keyword(kw::Else) || !cond.returns() {
1389             let sp = self.sess.source_map().next_point(lo);
1390             let mut err = self.diagnostic()
1391                 .struct_span_err(sp, "missing condition for `if` expression");
1392             err.span_label(sp, "expected if condition here");
1393             return Err(err)
1394         }
1395         let not_block = self.token != token::OpenDelim(token::Brace);
1396         let thn = self.parse_block().map_err(|mut err| {
1397             if not_block {
1398                 err.span_label(lo, "this `if` statement has a condition, but no block");
1399             }
1400             err
1401         })?;
1402         let mut els: Option<P<Expr>> = None;
1403         let mut hi = thn.span;
1404         if self.eat_keyword(kw::Else) {
1405             let elexpr = self.parse_else_expr()?;
1406             hi = elexpr.span;
1407             els = Some(elexpr);
1408         }
1409         Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
1410     }
1411
1412     /// Parses the condition of a `if` or `while` expression.
1413     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
1414         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1415
1416         if let ExprKind::Let(..) = cond.kind {
1417             // Remove the last feature gating of a `let` expression since it's stable.
1418             let last = self.sess.gated_spans.let_chains.borrow_mut().pop();
1419             debug_assert_eq!(cond.span, last.unwrap());
1420         }
1421
1422         Ok(cond)
1423     }
1424
1425     /// Parses a `let $pat = $expr` pseudo-expression.
1426     /// The `let` token has already been eaten.
1427     fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1428         let lo = self.prev_span;
1429         let pat = self.parse_top_pat(GateOr::No)?;
1430         self.expect(&token::Eq)?;
1431         let expr = self.with_res(
1432             Restrictions::NO_STRUCT_LITERAL,
1433             |this| this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
1434         )?;
1435         let span = lo.to(expr.span);
1436         self.sess.gated_spans.let_chains.borrow_mut().push(span);
1437         Ok(self.mk_expr(span, ExprKind::Let(pat, expr), attrs))
1438     }
1439
1440     /// Parses an `else { ... }` expression (`else` token already eaten).
1441     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
1442         if self.eat_keyword(kw::If) {
1443             return self.parse_if_expr(ThinVec::new());
1444         } else {
1445             let blk = self.parse_block()?;
1446             return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
1447         }
1448     }
1449
1450     /// Parses a `for ... in` expression (`for` token already eaten).
1451     fn parse_for_expr(
1452         &mut self,
1453         opt_label: Option<Label>,
1454         span_lo: Span,
1455         mut attrs: ThinVec<Attribute>
1456     ) -> PResult<'a, P<Expr>> {
1457         // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
1458
1459         // Record whether we are about to parse `for (`.
1460         // This is used below for recovery in case of `for ( $stuff ) $block`
1461         // in which case we will suggest `for $stuff $block`.
1462         let begin_paren = match self.token.kind {
1463             token::OpenDelim(token::Paren) => Some(self.token.span),
1464             _ => None,
1465         };
1466
1467         let pat = self.parse_top_pat(GateOr::Yes)?;
1468         if !self.eat_keyword(kw::In) {
1469             let in_span = self.prev_span.between(self.token.span);
1470             self.struct_span_err(in_span, "missing `in` in `for` loop")
1471                 .span_suggestion_short(
1472                     in_span,
1473                     "try adding `in` here", " in ".into(),
1474                     // has been misleading, at least in the past (closed Issue #48492)
1475                     Applicability::MaybeIncorrect
1476                 )
1477                 .emit();
1478         }
1479         let in_span = self.prev_span;
1480         self.check_for_for_in_in_typo(in_span);
1481         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1482
1483         let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
1484
1485         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
1486         attrs.extend(iattrs);
1487
1488         let hi = self.prev_span;
1489         Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
1490     }
1491
1492     /// Parses a `while` or `while let` expression (`while` token already eaten).
1493     fn parse_while_expr(
1494         &mut self,
1495         opt_label: Option<Label>,
1496         span_lo: Span,
1497         mut attrs: ThinVec<Attribute>
1498     ) -> PResult<'a, P<Expr>> {
1499         let cond = self.parse_cond_expr()?;
1500         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1501         attrs.extend(iattrs);
1502         let span = span_lo.to(body.span);
1503         Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs))
1504     }
1505
1506     /// Parses `loop { ... }` (`loop` token already eaten).
1507     fn parse_loop_expr(
1508         &mut self,
1509         opt_label: Option<Label>,
1510         span_lo: Span,
1511         mut attrs: ThinVec<Attribute>
1512     ) -> PResult<'a, P<Expr>> {
1513         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1514         attrs.extend(iattrs);
1515         let span = span_lo.to(body.span);
1516         Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
1517     }
1518
1519     fn eat_label(&mut self) -> Option<Label> {
1520         if let Some(ident) = self.token.lifetime() {
1521             let span = self.token.span;
1522             self.bump();
1523             Some(Label { ident: Ident::new(ident.name, span) })
1524         } else {
1525             None
1526         }
1527     }
1528
1529     /// Parses a `match ... { ... }` expression (`match` token already eaten).
1530     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1531         let match_span = self.prev_span;
1532         let lo = self.prev_span;
1533         let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1534         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
1535             if self.token == token::Semi {
1536                 e.span_suggestion_short(
1537                     match_span,
1538                     "try removing this `match`",
1539                     String::new(),
1540                     Applicability::MaybeIncorrect // speculative
1541                 );
1542             }
1543             return Err(e)
1544         }
1545         attrs.extend(self.parse_inner_attributes()?);
1546
1547         let mut arms: Vec<Arm> = Vec::new();
1548         while self.token != token::CloseDelim(token::Brace) {
1549             match self.parse_arm() {
1550                 Ok(arm) => arms.push(arm),
1551                 Err(mut e) => {
1552                     // Recover by skipping to the end of the block.
1553                     e.emit();
1554                     self.recover_stmt();
1555                     let span = lo.to(self.token.span);
1556                     if self.token == token::CloseDelim(token::Brace) {
1557                         self.bump();
1558                     }
1559                     return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
1560                 }
1561             }
1562         }
1563         let hi = self.token.span;
1564         self.bump();
1565         return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
1566     }
1567
1568     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
1569         let attrs = self.parse_outer_attributes()?;
1570         let lo = self.token.span;
1571         let pat = self.parse_top_pat(GateOr::No)?;
1572         let guard = if self.eat_keyword(kw::If) {
1573             Some(self.parse_expr()?)
1574         } else {
1575             None
1576         };
1577         let arrow_span = self.token.span;
1578         self.expect(&token::FatArrow)?;
1579         let arm_start_span = self.token.span;
1580
1581         let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
1582             .map_err(|mut err| {
1583                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
1584                 err
1585             })?;
1586
1587         let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
1588             && self.token != token::CloseDelim(token::Brace);
1589
1590         let hi = self.token.span;
1591
1592         if require_comma {
1593             let cm = self.sess.source_map();
1594             self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
1595                 .map_err(|mut err| {
1596                     match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
1597                         (Ok(ref expr_lines), Ok(ref arm_start_lines))
1598                         if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
1599                             && expr_lines.lines.len() == 2
1600                             && self.token == token::FatArrow => {
1601                             // We check whether there's any trailing code in the parse span,
1602                             // if there isn't, we very likely have the following:
1603                             //
1604                             // X |     &Y => "y"
1605                             //   |        --    - missing comma
1606                             //   |        |
1607                             //   |        arrow_span
1608                             // X |     &X => "x"
1609                             //   |      - ^^ self.token.span
1610                             //   |      |
1611                             //   |      parsed until here as `"y" & X`
1612                             err.span_suggestion_short(
1613                                 cm.next_point(arm_start_span),
1614                                 "missing a comma here to end this `match` arm",
1615                                 ",".to_owned(),
1616                                 Applicability::MachineApplicable
1617                             );
1618                         }
1619                         _ => {
1620                             err.span_label(arrow_span,
1621                                            "while parsing the `match` arm starting here");
1622                         }
1623                     }
1624                     err
1625                 })?;
1626         } else {
1627             self.eat(&token::Comma);
1628         }
1629
1630         Ok(ast::Arm {
1631             attrs,
1632             pat,
1633             guard,
1634             body: expr,
1635             span: lo.to(hi),
1636             id: DUMMY_NODE_ID,
1637             is_placeholder: false,
1638         })
1639     }
1640
1641     /// Parses a `try {...}` expression (`try` token already eaten).
1642     fn parse_try_block(
1643         &mut self,
1644         span_lo: Span,
1645         mut attrs: ThinVec<Attribute>
1646     ) -> PResult<'a, P<Expr>> {
1647         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1648         attrs.extend(iattrs);
1649         if self.eat_keyword(kw::Catch) {
1650             let mut error = self.struct_span_err(self.prev_span,
1651                                                  "keyword `catch` cannot follow a `try` block");
1652             error.help("try using `match` on the result of the `try` block instead");
1653             error.emit();
1654             Err(error)
1655         } else {
1656             let span = span_lo.to(body.span);
1657             self.sess.gated_spans.try_blocks.borrow_mut().push(span);
1658             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
1659         }
1660     }
1661
1662     fn is_do_catch_block(&self) -> bool {
1663         self.token.is_keyword(kw::Do) &&
1664         self.is_keyword_ahead(1, &[kw::Catch]) &&
1665         self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
1666         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1667     }
1668
1669     fn is_try_block(&self) -> bool {
1670         self.token.is_keyword(kw::Try) &&
1671         self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
1672         self.token.span.rust_2018() &&
1673         // Prevent `while try {} {}`, `if try {} {} else {}`, etc.
1674         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1675     }
1676
1677     /// Parses an `async move? {...}` expression.
1678     fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1679         let span_lo = self.token.span;
1680         self.expect_keyword(kw::Async)?;
1681         let capture_clause = self.parse_capture_clause();
1682         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1683         attrs.extend(iattrs);
1684         Ok(self.mk_expr(
1685             span_lo.to(body.span),
1686             ExprKind::Async(capture_clause, DUMMY_NODE_ID, body), attrs))
1687     }
1688
1689     fn is_async_block(&self) -> bool {
1690         self.token.is_keyword(kw::Async) &&
1691         (
1692             ( // `async move {`
1693                 self.is_keyword_ahead(1, &[kw::Move]) &&
1694                 self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
1695             ) || ( // `async {`
1696                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
1697             )
1698         )
1699     }
1700
1701     fn maybe_parse_struct_expr(
1702         &mut self,
1703         lo: Span,
1704         path: &ast::Path,
1705         attrs: &ThinVec<Attribute>,
1706     ) -> Option<PResult<'a, P<Expr>>> {
1707         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
1708         let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
1709             // `{ ident, ` cannot start a block.
1710             self.look_ahead(2, |t| t == &token::Comma) ||
1711             self.look_ahead(2, |t| t == &token::Colon) && (
1712                 // `{ ident: token, ` cannot start a block.
1713                 self.look_ahead(4, |t| t == &token::Comma) ||
1714                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
1715                 self.look_ahead(3, |t| !t.can_begin_type())
1716             )
1717         );
1718
1719         if struct_allowed || certainly_not_a_block() {
1720             // This is a struct literal, but we don't can't accept them here.
1721             let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
1722             if let (Ok(expr), false) = (&expr, struct_allowed) {
1723                 self.struct_span_err(
1724                     expr.span,
1725                     "struct literals are not allowed here",
1726                 )
1727                 .multipart_suggestion(
1728                     "surround the struct literal with parentheses",
1729                     vec![
1730                         (lo.shrink_to_lo(), "(".to_string()),
1731                         (expr.span.shrink_to_hi(), ")".to_string()),
1732                     ],
1733                     Applicability::MachineApplicable,
1734                 )
1735                 .emit();
1736             }
1737             return Some(expr);
1738         }
1739         None
1740     }
1741
1742     pub(super) fn parse_struct_expr(
1743         &mut self,
1744         lo: Span,
1745         pth: ast::Path,
1746         mut attrs: ThinVec<Attribute>
1747     ) -> PResult<'a, P<Expr>> {
1748         let struct_sp = lo.to(self.prev_span);
1749         self.bump();
1750         let mut fields = Vec::new();
1751         let mut base = None;
1752
1753         attrs.extend(self.parse_inner_attributes()?);
1754
1755         while self.token != token::CloseDelim(token::Brace) {
1756             if self.eat(&token::DotDot) {
1757                 let exp_span = self.prev_span;
1758                 match self.parse_expr() {
1759                     Ok(e) => {
1760                         base = Some(e);
1761                     }
1762                     Err(mut e) => {
1763                         e.emit();
1764                         self.recover_stmt();
1765                     }
1766                 }
1767                 if self.token == token::Comma {
1768                     self.struct_span_err(
1769                         exp_span.to(self.prev_span),
1770                         "cannot use a comma after the base struct",
1771                     )
1772                     .span_suggestion_short(
1773                         self.token.span,
1774                         "remove this comma",
1775                         String::new(),
1776                         Applicability::MachineApplicable
1777                     )
1778                     .note("the base struct must always be the last field")
1779                     .emit();
1780                     self.recover_stmt();
1781                 }
1782                 break;
1783             }
1784
1785             let mut recovery_field = None;
1786             if let token::Ident(name, _) = self.token.kind {
1787                 if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
1788                     // Use in case of error after field-looking code: `S { foo: () with a }`.
1789                     recovery_field = Some(ast::Field {
1790                         ident: Ident::new(name, self.token.span),
1791                         span: self.token.span,
1792                         expr: self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()),
1793                         is_shorthand: false,
1794                         attrs: ThinVec::new(),
1795                         id: DUMMY_NODE_ID,
1796                         is_placeholder: false,
1797                     });
1798                 }
1799             }
1800             let mut parsed_field = None;
1801             match self.parse_field() {
1802                 Ok(f) => parsed_field = Some(f),
1803                 Err(mut e) => {
1804                     e.span_label(struct_sp, "while parsing this struct");
1805                     e.emit();
1806
1807                     // If the next token is a comma, then try to parse
1808                     // what comes next as additional fields, rather than
1809                     // bailing out until next `}`.
1810                     if self.token != token::Comma {
1811                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1812                         if self.token != token::Comma {
1813                             break;
1814                         }
1815                     }
1816                 }
1817             }
1818
1819             match self.expect_one_of(&[token::Comma],
1820                                      &[token::CloseDelim(token::Brace)]) {
1821                 Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
1822                     // Only include the field if there's no parse error for the field name.
1823                     fields.push(f);
1824                 }
1825                 Err(mut e) => {
1826                     if let Some(f) = recovery_field {
1827                         fields.push(f);
1828                     }
1829                     e.span_label(struct_sp, "while parsing this struct");
1830                     e.emit();
1831                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1832                     self.eat(&token::Comma);
1833                 }
1834             }
1835         }
1836
1837         let span = lo.to(self.token.span);
1838         self.expect(&token::CloseDelim(token::Brace))?;
1839         return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
1840     }
1841
1842     /// Parses `ident (COLON expr)?`.
1843     fn parse_field(&mut self) -> PResult<'a, Field> {
1844         let attrs = self.parse_outer_attributes()?;
1845         let lo = self.token.span;
1846
1847         // Check if a colon exists one ahead. This means we're parsing a fieldname.
1848         let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
1849             t == &token::Colon || t == &token::Eq
1850         }) {
1851             let fieldname = self.parse_field_name()?;
1852
1853             // Check for an equals token. This means the source incorrectly attempts to
1854             // initialize a field with an eq rather than a colon.
1855             if self.token == token::Eq {
1856                 self.diagnostic()
1857                     .struct_span_err(self.token.span, "expected `:`, found `=`")
1858                     .span_suggestion(
1859                         fieldname.span.shrink_to_hi().to(self.token.span),
1860                         "replace equals symbol with a colon",
1861                         ":".to_string(),
1862                         Applicability::MachineApplicable,
1863                     )
1864                     .emit();
1865             }
1866             self.bump(); // `:`
1867             (fieldname, self.parse_expr()?, false)
1868         } else {
1869             let fieldname = self.parse_ident_common(false)?;
1870
1871             // Mimic `x: x` for the `x` field shorthand.
1872             let path = ast::Path::from_ident(fieldname);
1873             let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
1874             (fieldname, expr, true)
1875         };
1876         Ok(ast::Field {
1877             ident: fieldname,
1878             span: lo.to(expr.span),
1879             expr,
1880             is_shorthand,
1881             attrs: attrs.into(),
1882             id: DUMMY_NODE_ID,
1883             is_placeholder: false,
1884         })
1885     }
1886
1887     fn err_dotdotdot_syntax(&self, span: Span) {
1888         self.struct_span_err(span, "unexpected token: `...`")
1889             .span_suggestion(
1890                 span,
1891                 "use `..` for an exclusive range", "..".to_owned(),
1892                 Applicability::MaybeIncorrect
1893             )
1894             .span_suggestion(
1895                 span,
1896                 "or `..=` for an inclusive range", "..=".to_owned(),
1897                 Applicability::MaybeIncorrect
1898             )
1899             .emit();
1900     }
1901
1902     fn err_larrow_operator(&self, span: Span) {
1903         self.struct_span_err(
1904             span,
1905             "unexpected token: `<-`"
1906         ).span_suggestion(
1907             span,
1908             "if you meant to write a comparison against a negative value, add a \
1909              space in between `<` and `-`",
1910             "< -".to_string(),
1911             Applicability::MaybeIncorrect
1912         ).emit();
1913     }
1914
1915     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1916         ExprKind::AssignOp(binop, lhs, rhs)
1917     }
1918
1919     fn mk_range(
1920         &self,
1921         start: Option<P<Expr>>,
1922         end: Option<P<Expr>>,
1923         limits: RangeLimits
1924     ) -> PResult<'a, ExprKind> {
1925         if end.is_none() && limits == RangeLimits::Closed {
1926             Err(self.span_fatal_err(self.token.span, Error::InclusiveRangeWithNoEnd))
1927         } else {
1928             Ok(ExprKind::Range(start, end, limits))
1929         }
1930     }
1931
1932     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
1933         ExprKind::Unary(unop, expr)
1934     }
1935
1936     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1937         ExprKind::Binary(binop, lhs, rhs)
1938     }
1939
1940     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
1941         ExprKind::Index(expr, idx)
1942     }
1943
1944     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
1945         ExprKind::Call(f, args)
1946     }
1947
1948     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1949         let span = lo.to(self.prev_span);
1950         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), ThinVec::new());
1951         self.recover_from_await_method_call();
1952         Ok(await_expr)
1953     }
1954
1955     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
1956         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID })
1957     }
1958
1959     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
1960         self.mk_expr(span, ExprKind::Err, ThinVec::new())
1961     }
1962 }