src/librustc_parse/parser/expr.rs

   1 use super::{Parser, Restrictions, PrevTokenKind, TokenType, PathStyle, BlockMode};
   2 use super::{SemiColonMode, SeqSep, TokenExpectType};
   3 use super::pat::{GateOr, PARAM_EXPECTED};
   4 use super::diagnostics::Error;
   5 use crate::maybe_recover_from_interpolated_ty_qpath;
   6
   7 use rustc_data_structures::thin_vec::ThinVec;
   8 use rustc_errors::{PResult, Applicability};
   9 use syntax::ast::{self, DUMMY_NODE_ID, Attribute, AttrStyle, Ident, CaptureBy, BlockCheckMode};
  10 use syntax::ast::{Expr, ExprKind, RangeLimits, Label, Movability, IsAsync, Arm, Ty, TyKind};
  11 use syntax::ast::{FunctionRetTy, Param, FnDecl, BinOpKind, BinOp, UnOp, Mac, AnonConst, Field, Lit};
  12 use syntax::token::{self, Token, TokenKind};
  13 use syntax::print::pprust;
  14 use syntax::ptr::P;
  15 use syntax::util::classify;
  16 use syntax::util::literal::LitError;
  17 use syntax::util::parser::{AssocOp, Fixity, prec_let_scrutinee_needs_par};
  18 use syntax_pos::source_map::{self, Span};
  19 use syntax_pos::symbol::{kw, sym, Symbol};
  20 use std::mem;
  21
  22 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  23 /// dropped into the token stream, which happens while parsing the result of
  24 /// macro expansion). Placement of these is not as complex as I feared it would
  25 /// be. The important thing is to make sure that lookahead doesn't balk at
  26 /// `token::Interpolated` tokens.
  27 macro_rules! maybe_whole_expr {
  28     ($p:expr) => {
  29         if let token::Interpolated(nt) = &$p.token.kind {
  30             match &**nt {
  31                 token::NtExpr(e) | token::NtLiteral(e) => {
  32                     let e = e.clone();
  33                     $p.bump();
  34                     return Ok(e);
  35                 }
  36                 token::NtPath(path) => {
  37                     let path = path.clone();
  38                     $p.bump();
  39                     return Ok($p.mk_expr(
  40                         $p.token.span, ExprKind::Path(None, path), ThinVec::new()
  41                     ));
  42                 }
  43                 token::NtBlock(block) => {
  44                     let block = block.clone();
  45                     $p.bump();
  46                     return Ok($p.mk_expr(
  47                         $p.token.span, ExprKind::Block(block, None), ThinVec::new()
  48                     ));
  49                 }
  50                 // N.B., `NtIdent(ident)` is normalized to `Ident` in `fn bump`.
  51                 _ => {},
  52             };
  53         }
  54     }
  55 }
  56
  57 #[derive(Debug)]
  58 pub(super) enum LhsExpr {
  59     NotYetParsed,
  60     AttributesParsed(ThinVec<Attribute>),
  61     AlreadyParsed(P<Expr>),
  62 }
  63
  64 impl From<Option<ThinVec<Attribute>>> for LhsExpr {
  65     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  66     /// and `None` into `LhsExpr::NotYetParsed`.
  67     ///
  68     /// This conversion does not allocate.
  69     fn from(o: Option<ThinVec<Attribute>>) -> Self {
  70         if let Some(attrs) = o {
  71             LhsExpr::AttributesParsed(attrs)
  72         } else {
  73             LhsExpr::NotYetParsed
  74         }
  75     }
  76 }
  77
  78 impl From<P<Expr>> for LhsExpr {
  79     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
  80     ///
  81     /// This conversion does not allocate.
  82     fn from(expr: P<Expr>) -> Self {
  83         LhsExpr::AlreadyParsed(expr)
  84     }
  85 }
  86
  87 impl<'a> Parser<'a> {
  88     /// Parses an expression.
  89     #[inline]
  90     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
  91         self.parse_expr_res(Restrictions::empty(), None)
  92     }
  93
  94     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
  95         match self.parse_expr() {
  96             Ok(expr) => Ok(expr),
  97             Err(mut err) => match self.token.kind {
  98                 token::Ident(name, false)
  99                 if name == kw::Underscore && self.look_ahead(1, |t| {
 100                     t == &token::Comma
 101                 }) => {
 102                     // Special-case handling of `foo(_, _, _)`
 103                     err.emit();
 104                     let sp = self.token.span;
 105                     self.bump();
 106                     Ok(self.mk_expr(sp, ExprKind::Err, ThinVec::new()))
 107                 }
 108                 _ => Err(err),
 109             },
 110         }
 111     }
 112
 113     /// Parses a sequence of expressions bounded by parentheses.
 114     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 115         self.parse_paren_comma_seq(|p| {
 116             p.parse_expr_catch_underscore()
 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         if !self.should_continue_as_assoc_expr(&lhs) {
 164             self.last_type_ascription = None;
 165             return Ok(lhs);
 166         }
 167
 168         self.expected_tokens.push(TokenType::Operator);
 169         while let Some(op) = self.check_assoc_op() {
 170             // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
 171             // it refers to. Interpolated identifiers are unwrapped early and never show up here
 172             // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
 173             // it as "interpolated", it doesn't change the answer for non-interpolated idents.
 174             let lhs_span = match (self.prev_token_kind, &lhs.kind) {
 175                 (PrevTokenKind::Interpolated, _) => self.prev_span,
 176                 (PrevTokenKind::Ident, &ExprKind::Path(None, ref path))
 177                     if path.segments.len() == 1 => self.prev_span,
 178                 _ => lhs.span,
 179             };
 180
 181             let cur_op_span = self.token.span;
 182             let restrictions = if op.is_assign_like() {
 183                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 184             } else {
 185                 self.restrictions
 186             };
 187             let prec = op.precedence();
 188             if prec < min_prec {
 189                 break;
 190             }
 191             // Check for deprecated `...` syntax
 192             if self.token == token::DotDotDot && op == AssocOp::DotDotEq {
 193                 self.err_dotdotdot_syntax(self.token.span);
 194             }
 195
 196             if self.token == token::LArrow {
 197                 self.err_larrow_operator(self.token.span);
 198             }
 199
 200             self.bump();
 201             if op.is_comparison() {
 202                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 203                     return Ok(expr);
 204                 }
 205             }
 206             // Special cases:
 207             if op == AssocOp::As {
 208                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 209                 continue
 210             } else if op == AssocOp::Colon {
 211                 let maybe_path = self.could_ascription_be_path(&lhs.kind);
 212                 self.last_type_ascription = Some((self.prev_span, maybe_path));
 213
 214                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 215                 self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 216                 continue
 217             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 218                 // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
 219                 // generalise it to the Fixity::None code.
 220                 //
 221                 // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
 222                 // two variants are handled with `parse_prefix_range_expr` call above.
 223                 let rhs = if self.is_at_start_of_range_notation_rhs() {
 224                     Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 225                 } else {
 226                     None
 227                 };
 228                 let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
 229                     x.span
 230                 } else {
 231                     cur_op_span
 232                 });
 233                 let limits = if op == AssocOp::DotDot {
 234                     RangeLimits::HalfOpen
 235                 } else {
 236                     RangeLimits::Closed
 237                 };
 238
 239                 let r = self.mk_range(Some(lhs), rhs, limits)?;
 240                 lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
 241                 break
 242             }
 243
 244             let fixity = op.fixity();
 245             let prec_adjustment = match fixity {
 246                 Fixity::Right => 0,
 247                 Fixity::Left => 1,
 248                 // We currently have no non-associative operators that are not handled above by
 249                 // the special cases. The code is here only for future convenience.
 250                 Fixity::None => 1,
 251             };
 252             let rhs = self.with_res(
 253                 restrictions - Restrictions::STMT_EXPR,
 254                 |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 255             )?;
 256
 257             // Make sure that the span of the parent node is larger than the span of lhs and rhs,
 258             // including the attributes.
 259             let lhs_span = lhs
 260                 .attrs
 261                 .iter()
 262                 .filter(|a| a.style == AttrStyle::Outer)
 263                 .next()
 264                 .map_or(lhs_span, |a| a.span);
 265             let span = lhs_span.to(rhs.span);
 266             lhs = match op {
 267                 AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
 268                 AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
 269                 AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
 270                 AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
 271                 AssocOp::Greater | AssocOp::GreaterEqual => {
 272                     let ast_op = op.to_ast_binop().unwrap();
 273                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 274                     self.mk_expr(span, binary, ThinVec::new())
 275                 }
 276                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
 277                 AssocOp::AssignOp(k) => {
 278                     let aop = match k {
 279                         token::Plus =>    BinOpKind::Add,
 280                         token::Minus =>   BinOpKind::Sub,
 281                         token::Star =>    BinOpKind::Mul,
 282                         token::Slash =>   BinOpKind::Div,
 283                         token::Percent => BinOpKind::Rem,
 284                         token::Caret =>   BinOpKind::BitXor,
 285                         token::And =>     BinOpKind::BitAnd,
 286                         token::Or =>      BinOpKind::BitOr,
 287                         token::Shl =>     BinOpKind::Shl,
 288                         token::Shr =>     BinOpKind::Shr,
 289                     };
 290                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 291                     self.mk_expr(span, aopexpr, ThinVec::new())
 292                 }
 293                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 294                     self.bug("AssocOp should have been handled by special case")
 295                 }
 296             };
 297
 298             if let Fixity::None = fixity { break }
 299         }
 300         if last_type_ascription_set {
 301             self.last_type_ascription = None;
 302         }
 303         Ok(lhs)
 304     }
 305
 306     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 307         match (self.expr_is_complete(lhs), self.check_assoc_op()) {
 308             // Semi-statement forms are odd:
 309             // See https://github.com/rust-lang/rust/issues/29071
 310             (true, None) => false,
 311             (false, _) => true, // Continue parsing the expression.
 312             // An exhaustive check is done in the following block, but these are checked first
 313             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 314             // want to keep their span info to improve diagnostics in these cases in a later stage.
 315             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 316             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 317             (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
 318             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 319             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 320             // `if x { a } else { b } && if y { c } else { d }`
 321             if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
 322                 // These cases are ambiguous and can't be identified in the parser alone.
 323                 let sp = self.sess.source_map().start_point(self.token.span);
 324                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 325                 false
 326             }
 327             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 328             (true, Some(_)) => {
 329                 self.error_found_expr_would_be_stmt(lhs);
 330                 true
 331             }
 332         }
 333     }
 334
 335     /// We've found an expression that would be parsed as a statement,
 336     /// but the next token implies this should be parsed as an expression.
 337     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 338     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 339         let mut err = self.struct_span_err(self.token.span, &format!(
 340             "expected expression, found `{}`",
 341             pprust::token_to_string(&self.token),
 342         ));
 343         err.span_label(self.token.span, "expected expression");
 344         self.sess.expr_parentheses_needed(&mut err, lhs.span, Some(pprust::expr_to_string(&lhs)));
 345         err.emit();
 346     }
 347
 348     /// Possibly translate the current token to an associative operator.
 349     /// The method does not advance the current token.
 350     ///
 351     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 352     fn check_assoc_op(&self) -> Option<AssocOp> {
 353         match (AssocOp::from_token(&self.token), &self.token.kind) {
 354             (op @ Some(_), _) => op,
 355             (None, token::Ident(sym::and, false)) => {
 356                 self.error_bad_logical_op("and", "&&", "conjunction");
 357                 Some(AssocOp::LAnd)
 358             }
 359             (None, token::Ident(sym::or, false)) => {
 360                 self.error_bad_logical_op("or", "||", "disjunction");
 361                 Some(AssocOp::LOr)
 362             }
 363             _ => None,
 364         }
 365     }
 366
 367     /// Error on `and` and `or` suggesting `&&` and `||` respectively.
 368     fn error_bad_logical_op(&self, bad: &str, good: &str, english: &str) {
 369         self.struct_span_err(self.token.span, &format!("`{}` is not a logical operator", bad))
 370             .span_suggestion(
 371                 self.token.span,
 372                 &format!("instead of `{}`, use `{}` to perform logical {}", bad, good, english),
 373                 good.to_string(),
 374                 Applicability::MachineApplicable,
 375             )
 376             .note("unlike in e.g., python and PHP, `&&` and `||` are used for logical operators")
 377             .emit();
 378     }
 379
 380     /// Checks if this expression is a successfully parsed statement.
 381     fn expr_is_complete(&self, e: &Expr) -> bool {
 382         self.restrictions.contains(Restrictions::STMT_EXPR) &&
 383             !classify::expr_requires_semi_to_be_stmt(e)
 384     }
 385
 386     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 387         if self.token.can_begin_expr() {
 388             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 389             if self.token == token::OpenDelim(token::Brace) {
 390                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 391             }
 392             true
 393         } else {
 394             false
 395         }
 396     }
 397
 398     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 399     fn parse_prefix_range_expr(
 400         &mut self,
 401         already_parsed_attrs: Option<ThinVec<Attribute>>
 402     ) -> PResult<'a, P<Expr>> {
 403         // Check for deprecated `...` syntax.
 404         if self.token == token::DotDotDot {
 405             self.err_dotdotdot_syntax(self.token.span);
 406         }
 407
 408         debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 409                       "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 410                       self.token);
 411         let tok = self.token.clone();
 412         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 413         let lo = self.token.span;
 414         let mut hi = self.token.span;
 415         self.bump();
 416         let opt_end = if self.is_at_start_of_range_notation_rhs() {
 417             // RHS must be parsed with more associativity than the dots.
 418             let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
 419             Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed)
 420                 .map(|x| {
 421                     hi = x.span;
 422                     x
 423                 })?)
 424         } else {
 425             None
 426         };
 427         let limits = if tok == token::DotDot {
 428             RangeLimits::HalfOpen
 429         } else {
 430             RangeLimits::Closed
 431         };
 432
 433         let r = self.mk_range(None, opt_end, limits)?;
 434         Ok(self.mk_expr(lo.to(hi), r, attrs))
 435     }
 436
 437     /// Parses a prefix-unary-operator expr.
 438     fn parse_prefix_expr(
 439         &mut self,
 440         already_parsed_attrs: Option<ThinVec<Attribute>>
 441     ) -> PResult<'a, P<Expr>> {
 442         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 443         let lo = self.token.span;
 444         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 445         let (hi, ex) = match self.token.kind {
 446             token::Not => {
 447                 self.bump();
 448                 let e = self.parse_prefix_expr(None);
 449                 let (span, e) = self.interpolated_or_expr_span(e)?;
 450                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 451             }
 452             // Suggest `!` for bitwise negation when encountering a `~`
 453             token::Tilde => {
 454                 self.bump();
 455                 let e = self.parse_prefix_expr(None);
 456                 let (span, e) = self.interpolated_or_expr_span(e)?;
 457                 let span_of_tilde = lo;
 458                 self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator")
 459                     .span_suggestion_short(
 460                         span_of_tilde,
 461                         "use `!` to perform bitwise not",
 462                         "!".to_owned(),
 463                         Applicability::MachineApplicable
 464                     )
 465                     .emit();
 466                 (lo.to(span), self.mk_unary(UnOp::Not, e))
 467             }
 468             token::BinOp(token::Minus) => {
 469                 self.bump();
 470                 let e = self.parse_prefix_expr(None);
 471                 let (span, e) = self.interpolated_or_expr_span(e)?;
 472                 (lo.to(span), self.mk_unary(UnOp::Neg, e))
 473             }
 474             token::BinOp(token::Star) => {
 475                 self.bump();
 476                 let e = self.parse_prefix_expr(None);
 477                 let (span, e) = self.interpolated_or_expr_span(e)?;
 478                 (lo.to(span), self.mk_unary(UnOp::Deref, e))
 479             }
 480             token::BinOp(token::And) | token::AndAnd => {
 481                 self.parse_address_of(lo)?
 482             }
 483             token::Ident(..) if self.token.is_keyword(kw::Box) => {
 484                 self.bump();
 485                 let e = self.parse_prefix_expr(None);
 486                 let (span, e) = self.interpolated_or_expr_span(e)?;
 487                 let span = lo.to(span);
 488                 self.sess.gated_spans.gate(sym::box_syntax, span);
 489                 (span, ExprKind::Box(e))
 490             }
 491             token::Ident(..) if self.token.is_ident_named(sym::not) => {
 492                 // `not` is just an ordinary identifier in Rust-the-language,
 493                 // but as `rustc`-the-compiler, we can issue clever diagnostics
 494                 // for confused users who really want to say `!`
 495                 let token_cannot_continue_expr = |t: &Token| match t.kind {
 496                     // These tokens can start an expression after `!`, but
 497                     // can't continue an expression after an ident
 498                     token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 499                     token::Literal(..) | token::Pound => true,
 500                     _ => t.is_whole_expr(),
 501                 };
 502                 let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
 503                 if cannot_continue_expr {
 504                     self.bump();
 505                     // Emit the error ...
 506                     self.struct_span_err(
 507                         self.token.span,
 508                         &format!("unexpected {} after identifier",self.this_token_descr())
 509                     )
 510                     .span_suggestion_short(
 511                         // Span the `not` plus trailing whitespace to avoid
 512                         // trailing whitespace after the `!` in our suggestion
 513                         self.sess.source_map()
 514                             .span_until_non_whitespace(lo.to(self.token.span)),
 515                         "use `!` to perform logical negation",
 516                         "!".to_owned(),
 517                         Applicability::MachineApplicable
 518                     )
 519                     .emit();
 520                     // —and recover! (just as if we were in the block
 521                     // for the `token::Not` arm)
 522                     let e = self.parse_prefix_expr(None);
 523                     let (span, e) = self.interpolated_or_expr_span(e)?;
 524                     (lo.to(span), self.mk_unary(UnOp::Not, e))
 525                 } else {
 526                     return self.parse_dot_or_call_expr(Some(attrs));
 527                 }
 528             }
 529             _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
 530         };
 531         return Ok(self.mk_expr(lo.to(hi), ex, attrs));
 532     }
 533
 534     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 535     fn interpolated_or_expr_span(
 536         &self,
 537         expr: PResult<'a, P<Expr>>,
 538     ) -> PResult<'a, (Span, P<Expr>)> {
 539         expr.map(|e| {
 540             if self.prev_token_kind == PrevTokenKind::Interpolated {
 541                 (self.prev_span, e)
 542             } else {
 543                 (e.span, e)
 544             }
 545         })
 546     }
 547
 548     fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
 549                            expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
 550                            -> PResult<'a, P<Expr>> {
 551         let mk_expr = |this: &mut Self, rhs: P<Ty>| {
 552             this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
 553         };
 554
 555         // Save the state of the parser before parsing type normally, in case there is a
 556         // LessThan comparison after this cast.
 557         let parser_snapshot_before_type = self.clone();
 558         match self.parse_ty_no_plus() {
 559             Ok(rhs) => {
 560                 Ok(mk_expr(self, rhs))
 561             }
 562             Err(mut type_err) => {
 563                 // Rewind to before attempting to parse the type with generics, to recover
 564                 // from situations like `x as usize < y` in which we first tried to parse
 565                 // `usize < y` as a type with generic arguments.
 566                 let parser_snapshot_after_type = self.clone();
 567                 mem::replace(self, parser_snapshot_before_type);
 568
 569                 match self.parse_path(PathStyle::Expr) {
 570                     Ok(path) => {
 571                         let (op_noun, op_verb) = match self.token.kind {
 572                             token::Lt => ("comparison", "comparing"),
 573                             token::BinOp(token::Shl) => ("shift", "shifting"),
 574                             _ => {
 575                                 // We can end up here even without `<` being the next token, for
 576                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 577                                 // but `parse_path` returns `Ok` on them due to error recovery.
 578                                 // Return original error and parser state.
 579                                 mem::replace(self, parser_snapshot_after_type);
 580                                 return Err(type_err);
 581                             }
 582                         };
 583
 584                         // Successfully parsed the type path leaving a `<` yet to parse.
 585                         type_err.cancel();
 586
 587                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 588                         // in AST and continue parsing.
 589                         let msg = format!(
 590                             "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
 591                             pprust::path_to_string(&path),
 592                             op_noun,
 593                         );
 594                         let span_after_type = parser_snapshot_after_type.token.span;
 595                         let expr = mk_expr(self, P(Ty {
 596                             span: path.span,
 597                             kind: TyKind::Path(None, path),
 598                             id: DUMMY_NODE_ID,
 599                         }));
 600
 601                         let expr_str = self.span_to_snippet(expr.span)
 602                             .unwrap_or_else(|_| pprust::expr_to_string(&expr));
 603
 604                         self.struct_span_err(self.token.span, &msg)
 605                             .span_label(
 606                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 607                                 "interpreted as generic arguments"
 608                             )
 609                             .span_label(self.token.span, format!("not interpreted as {}", op_noun))
 610                             .span_suggestion(
 611                                 expr.span,
 612                                 &format!("try {} the cast value", op_verb),
 613                                 format!("({})", expr_str),
 614                                 Applicability::MachineApplicable,
 615                             )
 616                             .emit();
 617
 618                         Ok(expr)
 619                     }
 620                     Err(mut path_err) => {
 621                         // Couldn't parse as a path, return original error and parser state.
 622                         path_err.cancel();
 623                         mem::replace(self, parser_snapshot_after_type);
 624                         Err(type_err)
 625                     }
 626                 }
 627             }
 628         }
 629     }
 630
 631     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 632     fn parse_address_of(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 633         self.expect_and()?;
 634         let (k, m) = if self.check_keyword(kw::Raw)
 635             && self.look_ahead(1, Token::is_mutability)
 636         {
 637             let found_raw = self.eat_keyword(kw::Raw);
 638             assert!(found_raw);
 639             let mutability = self.parse_const_or_mut().unwrap();
 640             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_span));
 641             (ast::BorrowKind::Raw, mutability)
 642         } else {
 643             (ast::BorrowKind::Ref, self.parse_mutability())
 644         };
 645         let e = self.parse_prefix_expr(None);
 646         let (span, e) = self.interpolated_or_expr_span(e)?;
 647         Ok((lo.to(span), ExprKind::AddrOf(k, m, e)))
 648     }
 649
 650     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 651     fn parse_dot_or_call_expr(
 652         &mut self,
 653         already_parsed_attrs: Option<ThinVec<Attribute>>,
 654     ) -> PResult<'a, P<Expr>> {
 655         let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
 656
 657         let b = self.parse_bottom_expr();
 658         let (span, b) = self.interpolated_or_expr_span(b)?;
 659         self.parse_dot_or_call_expr_with(b, span, attrs)
 660     }
 661
 662     pub(super) fn parse_dot_or_call_expr_with(
 663         &mut self,
 664         e0: P<Expr>,
 665         lo: Span,
 666         mut attrs: ThinVec<Attribute>,
 667     ) -> PResult<'a, P<Expr>> {
 668         // Stitch the list of outer attributes onto the return value.
 669         // A little bit ugly, but the best way given the current code
 670         // structure
 671         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr|
 672             expr.map(|mut expr| {
 673                 attrs.extend::<Vec<_>>(expr.attrs.into());
 674                 expr.attrs = attrs;
 675                 match expr.kind {
 676                     ExprKind::If(..) if !expr.attrs.is_empty() => {
 677                         // Just point to the first attribute in there...
 678                         let span = expr.attrs[0].span;
 679                         self.span_err(span, "attributes are not yet allowed on `if` expressions");
 680                     }
 681                     _ => {}
 682                 }
 683                 expr
 684             })
 685         )
 686     }
 687
 688     fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 689         let mut e = e0;
 690         let mut hi;
 691         loop {
 692             // expr?
 693             while self.eat(&token::Question) {
 694                 let hi = self.prev_span;
 695                 e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
 696             }
 697
 698             // expr.f
 699             if self.eat(&token::Dot) {
 700                 match self.token.kind {
 701                     token::Ident(..) => {
 702                         e = self.parse_dot_suffix(e, lo)?;
 703                     }
 704                     token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 705                         let span = self.token.span;
 706                         self.bump();
 707                         let field = ExprKind::Field(e, Ident::new(symbol, span));
 708                         e = self.mk_expr(lo.to(span), field, ThinVec::new());
 709
 710                         self.expect_no_suffix(span, "a tuple index", suffix);
 711                     }
 712                     token::Literal(token::Lit { kind: token::Float, symbol, .. }) => {
 713                       self.bump();
 714                       let fstr = symbol.as_str();
 715                       let msg = format!("unexpected token: `{}`", symbol);
 716                       let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg);
 717                       err.span_label(self.prev_span, "unexpected token");
 718                       if fstr.chars().all(|x| "0123456789.".contains(x)) {
 719                           let float = match fstr.parse::<f64>().ok() {
 720                               Some(f) => f,
 721                               None => continue,
 722                           };
 723                           let sugg = pprust::to_string(|s| {
 724                               s.popen();
 725                               s.print_expr(&e);
 726                               s.s.word( ".");
 727                               s.print_usize(float.trunc() as usize);
 728                               s.pclose();
 729                               s.s.word(".");
 730                               s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
 731                           });
 732                           err.span_suggestion(
 733                               lo.to(self.prev_span),
 734                               "try parenthesizing the first index",
 735                               sugg,
 736                               Applicability::MachineApplicable
 737                           );
 738                       }
 739                       return Err(err);
 740
 741                     }
 742                     _ => {
 743                         // FIXME Could factor this out into non_fatal_unexpected or something.
 744                         let actual = self.this_token_to_string();
 745                         self.span_err(self.token.span, &format!("unexpected token: `{}`", actual));
 746                     }
 747                 }
 748                 continue;
 749             }
 750             if self.expr_is_complete(&e) { break; }
 751             match self.token.kind {
 752                 // expr(...)
 753                 token::OpenDelim(token::Paren) => {
 754                     let seq = self.parse_paren_expr_seq().map(|es| {
 755                         let nd = self.mk_call(e, es);
 756                         let hi = self.prev_span;
 757                         self.mk_expr(lo.to(hi), nd, ThinVec::new())
 758                     });
 759                     e = self.recover_seq_parse_error(token::Paren, lo, seq);
 760                 }
 761
 762                 // expr[...]
 763                 // Could be either an index expression or a slicing expression.
 764                 token::OpenDelim(token::Bracket) => {
 765                     self.bump();
 766                     let ix = self.parse_expr()?;
 767                     hi = self.token.span;
 768                     self.expect(&token::CloseDelim(token::Bracket))?;
 769                     let index = self.mk_index(e, ix);
 770                     e = self.mk_expr(lo.to(hi), index, ThinVec::new())
 771                 }
 772                 _ => return Ok(e)
 773             }
 774         }
 775         return Ok(e);
 776     }
 777
 778     /// Assuming we have just parsed `.`, continue parsing into an expression.
 779     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 780         if self.token.span.rust_2018() && self.eat_keyword(kw::Await) {
 781             return self.mk_await_expr(self_arg, lo);
 782         }
 783
 784         let segment = self.parse_path_segment(PathStyle::Expr)?;
 785         self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
 786
 787         Ok(match self.token.kind {
 788             token::OpenDelim(token::Paren) => {
 789                 // Method call `expr.f()`
 790                 let mut args = self.parse_paren_expr_seq()?;
 791                 args.insert(0, self_arg);
 792
 793                 let span = lo.to(self.prev_span);
 794                 self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
 795             }
 796             _ => {
 797                 // Field access `expr.f`
 798                 if let Some(args) = segment.args {
 799                     self.span_err(args.span(),
 800                                   "field expressions may not have generic arguments");
 801                 }
 802
 803                 let span = lo.to(self.prev_span);
 804                 self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
 805             }
 806         })
 807     }
 808
 809     /// At the bottom (top?) of the precedence hierarchy,
 810     /// Parses things like parenthesized exprs, macros, `return`, etc.
 811     ///
 812     /// N.B., this does not parse outer attributes, and is private because it only works
 813     /// correctly if called from `parse_dot_or_call_expr()`.
 814     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
 815         maybe_recover_from_interpolated_ty_qpath!(self, true);
 816         maybe_whole_expr!(self);
 817
 818         // Outer attributes are already parsed and will be
 819         // added to the return value after the fact.
 820         //
 821         // Therefore, prevent sub-parser from parsing
 822         // attributes by giving them a empty "already-parsed" list.
 823         let attrs = ThinVec::new();
 824
 825         let lo = self.token.span;
 826
 827         macro_rules! parse_lit {
 828             () => {
 829                 match self.parse_opt_lit() {
 830                     Some(literal) => (self.prev_span, ExprKind::Lit(literal)),
 831                     None => return Err(self.expected_expression_found()),
 832                 }
 833             }
 834         }
 835
 836         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
 837         let (hi, ex) = match self.token.kind {
 838             // This match arm is a special-case of the `_` match arm below and
 839             // could be removed without changing functionality, but it's faster
 840             // to have it here, especially for programs with large constants.
 841             token::Literal(_) => parse_lit!(),
 842             token::OpenDelim(token::Paren) => return self.parse_tuple_parens_expr(attrs),
 843             token::OpenDelim(token::Brace) => {
 844                 return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
 845             }
 846             token::BinOp(token::Or) | token::OrOr => return self.parse_closure_expr(attrs),
 847             token::OpenDelim(token::Bracket) => return self.parse_array_or_repeat_expr(attrs),
 848             _ => {
 849                 if self.eat_lt() {
 850                     let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
 851                     let hi = path.span;
 852                     return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
 853                 }
 854                 if self.token.is_path_start() {
 855                     return self.parse_path_start_expr(attrs);
 856                 }
 857                 if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
 858                     return self.parse_closure_expr(attrs);
 859                 }
 860                 if self.eat_keyword(kw::If) {
 861                     return self.parse_if_expr(attrs);
 862                 }
 863                 if self.eat_keyword(kw::For) {
 864                     return self.parse_for_expr(None, self.prev_span, attrs);
 865                 }
 866                 if self.eat_keyword(kw::While) {
 867                     return self.parse_while_expr(None, self.prev_span, attrs);
 868                 }
 869                 if let Some(label) = self.eat_label() {
 870                     return self.parse_labeled_expr(label, attrs);
 871                 }
 872                 if self.eat_keyword(kw::Loop) {
 873                     return self.parse_loop_expr(None, self.prev_span, attrs);
 874                 }
 875                 if self.eat_keyword(kw::Continue) {
 876                     let kind = ExprKind::Continue(self.eat_label());
 877                     return Ok(self.mk_expr(lo.to(self.prev_span), kind, attrs));
 878                 }
 879                 if self.eat_keyword(kw::Match) {
 880                     let match_sp = self.prev_span;
 881                     return self.parse_match_expr(attrs).map_err(|mut err| {
 882                         err.span_label(match_sp, "while parsing this match expression");
 883                         err
 884                     });
 885                 }
 886                 if self.eat_keyword(kw::Unsafe) {
 887                     let mode = BlockCheckMode::Unsafe(ast::UserProvided);
 888                     return self.parse_block_expr(None, lo, mode, attrs);
 889                 }
 890                 if self.is_do_catch_block() {
 891                     return self.recover_do_catch(attrs);
 892                 }
 893                 if self.is_try_block() {
 894                     self.expect_keyword(kw::Try)?;
 895                     return self.parse_try_block(lo, attrs);
 896                 }
 897
 898                 // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
 899                 let is_span_rust_2018 = self.token.span.rust_2018();
 900                 if is_span_rust_2018 && self.check_keyword(kw::Async) {
 901                     return if self.is_async_block() { // Check for `async {` and `async move {`.
 902                         self.parse_async_block(attrs)
 903                     } else {
 904                         self.parse_closure_expr(attrs)
 905                     };
 906                 }
 907                 if self.eat_keyword(kw::Return) {
 908                     return self.parse_return_expr(attrs);
 909                 } else if self.eat_keyword(kw::Break) {
 910                     let label = self.eat_label();
 911                     let e = if self.token.can_begin_expr()
 912                                && !(self.token == token::OpenDelim(token::Brace)
 913                                     && self.restrictions.contains(
 914                                            Restrictions::NO_STRUCT_LITERAL)) {
 915                         Some(self.parse_expr()?)
 916                     } else {
 917                         None
 918                     };
 919                     (self.prev_span, ExprKind::Break(label, e))
 920                 } else if self.eat_keyword(kw::Yield) {
 921                     return self.parse_yield_expr(attrs);
 922                 } else if self.eat_keyword(kw::Let) {
 923                     return self.parse_let_expr(attrs);
 924                 } else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
 925                     self.parse_incorrect_await_syntax(lo, self.prev_span)?
 926                 } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
 927                     // Don't complain about bare semicolons after unclosed braces
 928                     // recovery in order to keep the error count down. Fixing the
 929                     // delimiters will possibly also fix the bare semicolon found in
 930                     // expression context. For example, silence the following error:
 931                     //
 932                     //     error: expected expression, found `;`
 933                     //      --> file.rs:2:13
 934                     //       |
 935                     //     2 |     foo(bar(;
 936                     //       |             ^ expected expression
 937                     self.bump();
 938                     return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()));
 939                 } else {
 940                     parse_lit!()
 941                 }
 942             }
 943         };
 944
 945         let expr = self.mk_expr(lo.to(hi), ex, attrs);
 946         self.maybe_recover_from_bad_qpath(expr, true)
 947     }
 948
 949     fn parse_tuple_parens_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
 950         let lo = self.token.span;
 951         let mut first = true;
 952         let parse_leading_attr_expr = |p: &mut Self| {
 953             if first {
 954                 // `(#![foo] a, b, ...)` is OK...
 955                 attrs.extend(p.parse_inner_attributes()?);
 956                 // ...but not `(a, #![foo] b, ...)`.
 957                 first = false;
 958             }
 959             p.parse_expr_catch_underscore()
 960         };
 961         let (es, trailing_comma) = match self.parse_paren_comma_seq(parse_leading_attr_expr) {
 962             Ok(x) => x,
 963             Err(err) => return Ok(self.recover_seq_parse_error(token::Paren, lo, Err(err))),
 964         };
 965         let kind = if es.len() == 1 && !trailing_comma {
 966             // `(e)` is parenthesized `e`.
 967             ExprKind::Paren(es.into_iter().nth(0).unwrap())
 968         } else {
 969             // `(e,)` is a tuple with only one field, `e`.
 970             ExprKind::Tup(es)
 971         };
 972         let expr = self.mk_expr(lo.to(self.prev_span), kind, attrs);
 973         self.maybe_recover_from_bad_qpath(expr, true)
 974     }
 975
 976     fn parse_array_or_repeat_expr(
 977         &mut self,
 978         mut attrs: ThinVec<Attribute>,
 979     ) -> PResult<'a, P<Expr>> {
 980         let lo = self.token.span;
 981         self.bump(); // `[`
 982
 983         attrs.extend(self.parse_inner_attributes()?);
 984
 985         let kind = if self.eat(&token::CloseDelim(token::Bracket)) {
 986             // Empty vector
 987             ExprKind::Array(Vec::new())
 988         } else {
 989             // Non-empty vector
 990             let first_expr = self.parse_expr()?;
 991             if self.eat(&token::Semi) {
 992                 // Repeating array syntax: `[ 0; 512 ]`
 993                 let count = AnonConst {
 994                     id: DUMMY_NODE_ID,
 995                     value: self.parse_expr()?,
 996                 };
 997                 self.expect(&token::CloseDelim(token::Bracket))?;
 998                 ExprKind::Repeat(first_expr, count)
 999             } else if self.eat(&token::Comma) {
1000                 // Vector with two or more elements.
1001                 let remaining_exprs = self.parse_seq_to_end(
1002                     &token::CloseDelim(token::Bracket),
1003                     SeqSep::trailing_allowed(token::Comma),
1004                     |p| Ok(p.parse_expr()?)
1005                 )?;
1006                 let mut exprs = vec![first_expr];
1007                 exprs.extend(remaining_exprs);
1008                 ExprKind::Array(exprs)
1009             } else {
1010                 // Vector with one element
1011                 self.expect(&token::CloseDelim(token::Bracket))?;
1012                 ExprKind::Array(vec![first_expr])
1013             }
1014         };
1015         let expr = self.mk_expr(lo.to(self.prev_span), kind, attrs);
1016         self.maybe_recover_from_bad_qpath(expr, true)
1017     }
1018
1019     fn parse_path_start_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1020         let lo = self.token.span;
1021         let path = self.parse_path(PathStyle::Expr)?;
1022
1023         // `!`, as an operator, is prefix, so we know this isn't that.
1024         let (hi, kind) = if self.eat(&token::Not) {
1025             // MACRO INVOCATION expression
1026             let mac = Mac {
1027                 path,
1028                 args: self.parse_mac_args()?,
1029                 prior_type_ascription: self.last_type_ascription,
1030             };
1031             (self.prev_span, ExprKind::Mac(mac))
1032         } else if self.check(&token::OpenDelim(token::Brace)) {
1033             if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
1034                 return expr;
1035             } else {
1036                 (path.span, ExprKind::Path(None, path))
1037             }
1038         } else {
1039             (path.span, ExprKind::Path(None, path))
1040         };
1041
1042         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1043         self.maybe_recover_from_bad_qpath(expr, true)
1044     }
1045
1046     fn parse_labeled_expr(
1047         &mut self,
1048         label: Label,
1049         attrs: ThinVec<Attribute>,
1050     ) -> PResult<'a, P<Expr>> {
1051         let lo = label.ident.span;
1052         self.expect(&token::Colon)?;
1053         if self.eat_keyword(kw::While) {
1054             return self.parse_while_expr(Some(label), lo, attrs)
1055         }
1056         if self.eat_keyword(kw::For) {
1057             return self.parse_for_expr(Some(label), lo, attrs)
1058         }
1059         if self.eat_keyword(kw::Loop) {
1060             return self.parse_loop_expr(Some(label), lo, attrs)
1061         }
1062         if self.token == token::OpenDelim(token::Brace) {
1063             return self.parse_block_expr(Some(label), lo, BlockCheckMode::Default, attrs);
1064         }
1065
1066         let msg = "expected `while`, `for`, `loop` or `{` after a label";
1067         self.struct_span_err(self.token.span, msg)
1068             .span_label(self.token.span, msg)
1069             .emit();
1070         // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1071         self.parse_expr()
1072     }
1073
1074     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1075     fn recover_do_catch(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1076         let lo = self.token.span;
1077
1078         self.bump(); // `do`
1079         self.bump(); // `catch`
1080
1081         let span_dc = lo.to(self.prev_span);
1082         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1083             .span_suggestion(
1084                 span_dc,
1085                 "replace with the new syntax",
1086                 "try".to_string(),
1087                 Applicability::MachineApplicable,
1088             )
1089             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1090             .emit();
1091
1092         self.parse_try_block(lo, attrs)
1093     }
1094
1095     /// Parse an expression if the token can begin one.
1096     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1097         Ok(if self.token.can_begin_expr() {
1098             Some(self.parse_expr()?)
1099         } else {
1100             None
1101         })
1102     }
1103
1104     /// Parse `"return" expr?`.
1105     fn parse_return_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1106         let lo = self.prev_span;
1107         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1108         let expr = self.mk_expr(lo.to(self.prev_span), kind, attrs);
1109         self.maybe_recover_from_bad_qpath(expr, true)
1110     }
1111
1112     /// Parse `"yield" expr?`.
1113     fn parse_yield_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1114         let lo = self.prev_span;
1115         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1116         let span = lo.to(self.prev_span);
1117         self.sess.gated_spans.gate(sym::generators, span);
1118         let expr = self.mk_expr(span, kind, attrs);
1119         self.maybe_recover_from_bad_qpath(expr, true)
1120     }
1121
1122     /// Returns a string literal if the next token is a string literal.
1123     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1124     /// and returns `None` if the next token is not literal at all.
1125     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1126         match self.parse_opt_lit() {
1127             Some(lit) => match lit.kind {
1128                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1129                     style,
1130                     symbol: lit.token.symbol,
1131                     suffix: lit.token.suffix,
1132                     span: lit.span,
1133                     symbol_unescaped,
1134                 }),
1135                 _ => Err(Some(lit)),
1136             }
1137             None => Err(None),
1138         }
1139     }
1140
1141     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1142         self.parse_opt_lit().ok_or_else(|| {
1143             let msg = format!("unexpected token: {}", self.this_token_descr());
1144             self.span_fatal(self.token.span, &msg)
1145         })
1146     }
1147
1148     /// Matches `lit = true | false | token_lit`.
1149     /// Returns `None` if the next token is not a literal.
1150     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1151         let mut recovered = None;
1152         if self.token == token::Dot {
1153             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1154             // dot would follow an optional literal, so we do this unconditionally.
1155             recovered = self.look_ahead(1, |next_token| {
1156                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
1157                         = next_token.kind {
1158                     if self.token.span.hi() == next_token.span.lo() {
1159                         let s = String::from("0.") + &symbol.as_str();
1160                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1161                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1162                     }
1163                 }
1164                 None
1165             });
1166             if let Some(token) = &recovered {
1167                 self.bump();
1168                 self.struct_span_err(token.span, "float literals must have an integer part")
1169                     .span_suggestion(
1170                         token.span,
1171                         "must have an integer part",
1172                         pprust::token_to_string(token),
1173                         Applicability::MachineApplicable,
1174                     )
1175                     .emit();
1176             }
1177         }
1178
1179         let token = recovered.as_ref().unwrap_or(&self.token);
1180         match Lit::from_token(token) {
1181             Ok(lit) => {
1182                 self.bump();
1183                 Some(lit)
1184             }
1185             Err(LitError::NotLiteral) => {
1186                 None
1187             }
1188             Err(err) => {
1189                 let span = token.span;
1190                 let lit = match token.kind {
1191                     token::Literal(lit) => lit,
1192                     _ => unreachable!(),
1193                 };
1194                 self.bump();
1195                 self.report_lit_error(err, lit, span);
1196                 // Pack possible quotes and prefixes from the original literal into
1197                 // the error literal's symbol so they can be pretty-printed faithfully.
1198                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1199                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1200                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1201                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1202             }
1203         }
1204     }
1205
1206     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1207         // Checks if `s` looks like i32 or u1234 etc.
1208         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1209             s.len() > 1
1210             && s.starts_with(first_chars)
1211             && s[1..].chars().all(|c| c.is_ascii_digit())
1212         }
1213
1214         let token::Lit { kind, suffix, .. } = lit;
1215         match err {
1216             // `NotLiteral` is not an error by itself, so we don't report
1217             // it and give the parser opportunity to try something else.
1218             LitError::NotLiteral => {}
1219             // `LexerError` *is* an error, but it was already reported
1220             // by lexer, so here we don't report it the second time.
1221             LitError::LexerError => {}
1222             LitError::InvalidSuffix => {
1223                 self.expect_no_suffix(
1224                     span,
1225                     &format!("{} {} literal", kind.article(), kind.descr()),
1226                     suffix,
1227                 );
1228             }
1229             LitError::InvalidIntSuffix => {
1230                 let suf = suffix.expect("suffix error with no suffix").as_str();
1231                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1232                     // If it looks like a width, try to be helpful.
1233                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1234                     self.struct_span_err(span, &msg)
1235                         .help("valid widths are 8, 16, 32, 64 and 128")
1236                         .emit();
1237                 } else {
1238                     let msg = format!("invalid suffix `{}` for integer literal", suf);
1239                     self.struct_span_err(span, &msg)
1240                         .span_label(span, format!("invalid suffix `{}`", suf))
1241                         .help("the suffix must be one of the integral types (`u32`, `isize`, etc)")
1242                         .emit();
1243                 }
1244             }
1245             LitError::InvalidFloatSuffix => {
1246                 let suf = suffix.expect("suffix error with no suffix").as_str();
1247                 if looks_like_width_suffix(&['f'], &suf) {
1248                     // If it looks like a width, try to be helpful.
1249                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1250                     self.struct_span_err(span, &msg)
1251                         .help("valid widths are 32 and 64")
1252                         .emit();
1253                 } else {
1254                     let msg = format!("invalid suffix `{}` for float literal", suf);
1255                     self.struct_span_err(span, &msg)
1256                         .span_label(span, format!("invalid suffix `{}`", suf))
1257                         .help("valid suffixes are `f32` and `f64`")
1258                         .emit();
1259                 }
1260             }
1261             LitError::NonDecimalFloat(base) => {
1262                 let descr = match base {
1263                     16 => "hexadecimal",
1264                     8 => "octal",
1265                     2 => "binary",
1266                     _ => unreachable!(),
1267                 };
1268                 self.struct_span_err(span, &format!("{} float literal is not supported", descr))
1269                     .span_label(span, "not supported")
1270                     .emit();
1271             }
1272             LitError::IntTooLarge => {
1273                 self.struct_span_err(span, "integer literal is too large")
1274                     .emit();
1275             }
1276         }
1277     }
1278
1279     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1280         if let Some(suf) = suffix {
1281             let mut err = if kind == "a tuple index"
1282                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1283             {
1284                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1285                 // through the ecosystem when people fix their macros
1286                 let mut err = self.sess.span_diagnostic.struct_span_warn(
1287                     sp,
1288                     &format!("suffixes on {} are invalid", kind),
1289                 );
1290                 err.note(&format!(
1291                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1292                         incorrectly accepted on stable for a few releases",
1293                     suf,
1294                 ));
1295                 err.help(
1296                     "on proc macros, you'll want to use `syn::Index::from` or \
1297                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1298                         to tuple field access",
1299                 );
1300                 err.note(
1301                     "for more context, see https://github.com/rust-lang/rust/issues/60210",
1302                 );
1303                 err
1304             } else {
1305                 self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
1306             };
1307             err.span_label(sp, format!("invalid suffix `{}`", suf));
1308             err.emit();
1309         }
1310     }
1311
1312     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1313     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1314         maybe_whole_expr!(self);
1315
1316         let minus_lo = self.token.span;
1317         let minus_present = self.eat(&token::BinOp(token::Minus));
1318         let lo = self.token.span;
1319         let literal = self.parse_lit()?;
1320         let hi = self.prev_span;
1321         let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
1322
1323         if minus_present {
1324             let minus_hi = self.prev_span;
1325             let unary = self.mk_unary(UnOp::Neg, expr);
1326             Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
1327         } else {
1328             Ok(expr)
1329         }
1330     }
1331
1332     /// Parses a block or unsafe block.
1333     pub(super) fn parse_block_expr(
1334         &mut self,
1335         opt_label: Option<Label>,
1336         lo: Span,
1337         blk_mode: BlockCheckMode,
1338         outer_attrs: ThinVec<Attribute>,
1339     ) -> PResult<'a, P<Expr>> {
1340         if let Some(label) = opt_label {
1341             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
1342         }
1343
1344         self.expect(&token::OpenDelim(token::Brace))?;
1345
1346         let mut attrs = outer_attrs;
1347         attrs.extend(self.parse_inner_attributes()?);
1348
1349         let blk = self.parse_block_tail(lo, blk_mode)?;
1350         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1351     }
1352
1353     /// Parses a closure expression (e.g., `move |args| expr`).
1354     fn parse_closure_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1355         let lo = self.token.span;
1356
1357         let movability = if self.eat_keyword(kw::Static) {
1358             Movability::Static
1359         } else {
1360             Movability::Movable
1361         };
1362
1363         let asyncness = if self.token.span.rust_2018() {
1364             self.parse_asyncness()
1365         } else {
1366             IsAsync::NotAsync
1367         };
1368         if asyncness.is_async() {
1369             // Feature-gate `async ||` closures.
1370             self.sess.gated_spans.gate(sym::async_closure, self.prev_span);
1371         }
1372
1373         let capture_clause = self.parse_capture_clause();
1374         let decl = self.parse_fn_block_decl()?;
1375         let decl_hi = self.prev_span;
1376         let body = match decl.output {
1377             FunctionRetTy::Default(_) => {
1378                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1379                 self.parse_expr_res(restrictions, None)?
1380             },
1381             _ => {
1382                 // If an explicit return type is given, require a block to appear (RFC 968).
1383                 let body_lo = self.token.span;
1384                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
1385             }
1386         };
1387
1388         Ok(self.mk_expr(
1389             lo.to(body.span),
1390             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
1391             attrs))
1392     }
1393
1394     /// Parses an optional `move` prefix to a closure lke construct.
1395     fn parse_capture_clause(&mut self) -> CaptureBy {
1396         if self.eat_keyword(kw::Move) {
1397             CaptureBy::Value
1398         } else {
1399             CaptureBy::Ref
1400         }
1401     }
1402
1403     /// Parses the `|arg, arg|` header of a closure.
1404     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
1405         let inputs_captures = {
1406             if self.eat(&token::OrOr) {
1407                 Vec::new()
1408             } else {
1409                 self.expect(&token::BinOp(token::Or))?;
1410                 let args = self.parse_seq_to_before_tokens(
1411                     &[&token::BinOp(token::Or), &token::OrOr],
1412                     SeqSep::trailing_allowed(token::Comma),
1413                     TokenExpectType::NoExpect,
1414                     |p| p.parse_fn_block_param()
1415                 )?.0;
1416                 self.expect_or()?;
1417                 args
1418             }
1419         };
1420         let output = self.parse_ret_ty(true, true)?;
1421
1422         Ok(P(FnDecl {
1423             inputs: inputs_captures,
1424             output,
1425         }))
1426     }
1427
1428     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
1429     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
1430         let lo = self.token.span;
1431         let attrs = self.parse_outer_attributes()?;
1432         let pat = self.parse_pat(PARAM_EXPECTED)?;
1433         let t = if self.eat(&token::Colon) {
1434             self.parse_ty()?
1435         } else {
1436             P(Ty {
1437                 id: DUMMY_NODE_ID,
1438                 kind: TyKind::Infer,
1439                 span: self.prev_span,
1440             })
1441         };
1442         let span = lo.to(self.token.span);
1443         Ok(Param {
1444             attrs: attrs.into(),
1445             ty: t,
1446             pat,
1447             span,
1448             id: DUMMY_NODE_ID,
1449             is_placeholder: false,
1450         })
1451     }
1452
1453     /// Parses an `if` expression (`if` token already eaten).
1454     fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1455         let lo = self.prev_span;
1456         let cond = self.parse_cond_expr()?;
1457
1458         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
1459         // verify that the last statement is either an implicit return (no `;`) or an explicit
1460         // return. This won't catch blocks with an explicit `return`, but that would be caught by
1461         // the dead code lint.
1462         if self.eat_keyword(kw::Else) || !cond.returns() {
1463             let sp = self.sess.source_map().next_point(lo);
1464             let mut err = self.diagnostic()
1465                 .struct_span_err(sp, "missing condition for `if` expression");
1466             err.span_label(sp, "expected if condition here");
1467             return Err(err)
1468         }
1469         let not_block = self.token != token::OpenDelim(token::Brace);
1470         let thn = self.parse_block().map_err(|mut err| {
1471             if not_block {
1472                 err.span_label(lo, "this `if` statement has a condition, but no block");
1473             }
1474             err
1475         })?;
1476         let mut els: Option<P<Expr>> = None;
1477         let mut hi = thn.span;
1478         if self.eat_keyword(kw::Else) {
1479             let elexpr = self.parse_else_expr()?;
1480             hi = elexpr.span;
1481             els = Some(elexpr);
1482         }
1483         Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
1484     }
1485
1486     /// Parses the condition of a `if` or `while` expression.
1487     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
1488         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1489
1490         if let ExprKind::Let(..) = cond.kind {
1491             // Remove the last feature gating of a `let` expression since it's stable.
1492             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
1493         }
1494
1495         Ok(cond)
1496     }
1497
1498     /// Parses a `let $pat = $expr` pseudo-expression.
1499     /// The `let` token has already been eaten.
1500     fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1501         let lo = self.prev_span;
1502         let pat = self.parse_top_pat(GateOr::No)?;
1503         self.expect(&token::Eq)?;
1504         let expr = self.with_res(
1505             Restrictions::NO_STRUCT_LITERAL,
1506             |this| this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
1507         )?;
1508         let span = lo.to(expr.span);
1509         self.sess.gated_spans.gate(sym::let_chains, span);
1510         Ok(self.mk_expr(span, ExprKind::Let(pat, expr), attrs))
1511     }
1512
1513     /// Parses an `else { ... }` expression (`else` token already eaten).
1514     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
1515         if self.eat_keyword(kw::If) {
1516             return self.parse_if_expr(ThinVec::new());
1517         } else {
1518             let blk = self.parse_block()?;
1519             return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
1520         }
1521     }
1522
1523     /// Parses a `for ... in` expression (`for` token already eaten).
1524     fn parse_for_expr(
1525         &mut self,
1526         opt_label: Option<Label>,
1527         span_lo: Span,
1528         mut attrs: ThinVec<Attribute>
1529     ) -> PResult<'a, P<Expr>> {
1530         // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
1531
1532         // Record whether we are about to parse `for (`.
1533         // This is used below for recovery in case of `for ( $stuff ) $block`
1534         // in which case we will suggest `for $stuff $block`.
1535         let begin_paren = match self.token.kind {
1536             token::OpenDelim(token::Paren) => Some(self.token.span),
1537             _ => None,
1538         };
1539
1540         let pat = self.parse_top_pat(GateOr::Yes)?;
1541         if !self.eat_keyword(kw::In) {
1542             let in_span = self.prev_span.between(self.token.span);
1543             self.struct_span_err(in_span, "missing `in` in `for` loop")
1544                 .span_suggestion_short(
1545                     in_span,
1546                     "try adding `in` here", " in ".into(),
1547                     // has been misleading, at least in the past (closed Issue #48492)
1548                     Applicability::MaybeIncorrect
1549                 )
1550                 .emit();
1551         }
1552         let in_span = self.prev_span;
1553         self.check_for_for_in_in_typo(in_span);
1554         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1555
1556         let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
1557
1558         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
1559         attrs.extend(iattrs);
1560
1561         let hi = self.prev_span;
1562         Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
1563     }
1564
1565     /// Parses a `while` or `while let` expression (`while` token already eaten).
1566     fn parse_while_expr(
1567         &mut self,
1568         opt_label: Option<Label>,
1569         span_lo: Span,
1570         mut attrs: ThinVec<Attribute>
1571     ) -> PResult<'a, P<Expr>> {
1572         let cond = self.parse_cond_expr()?;
1573         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1574         attrs.extend(iattrs);
1575         let span = span_lo.to(body.span);
1576         Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs))
1577     }
1578
1579     /// Parses `loop { ... }` (`loop` token already eaten).
1580     fn parse_loop_expr(
1581         &mut self,
1582         opt_label: Option<Label>,
1583         span_lo: Span,
1584         mut attrs: ThinVec<Attribute>
1585     ) -> PResult<'a, P<Expr>> {
1586         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1587         attrs.extend(iattrs);
1588         let span = span_lo.to(body.span);
1589         Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
1590     }
1591
1592     fn eat_label(&mut self) -> Option<Label> {
1593         if let Some(ident) = self.token.lifetime() {
1594             let span = self.token.span;
1595             self.bump();
1596             Some(Label { ident: Ident::new(ident.name, span) })
1597         } else {
1598             None
1599         }
1600     }
1601
1602     /// Parses a `match ... { ... }` expression (`match` token already eaten).
1603     fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1604         let match_span = self.prev_span;
1605         let lo = self.prev_span;
1606         let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1607         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
1608             if self.token == token::Semi {
1609                 e.span_suggestion_short(
1610                     match_span,
1611                     "try removing this `match`",
1612                     String::new(),
1613                     Applicability::MaybeIncorrect // speculative
1614                 );
1615             }
1616             return Err(e)
1617         }
1618         attrs.extend(self.parse_inner_attributes()?);
1619
1620         let mut arms: Vec<Arm> = Vec::new();
1621         while self.token != token::CloseDelim(token::Brace) {
1622             match self.parse_arm() {
1623                 Ok(arm) => arms.push(arm),
1624                 Err(mut e) => {
1625                     // Recover by skipping to the end of the block.
1626                     e.emit();
1627                     self.recover_stmt();
1628                     let span = lo.to(self.token.span);
1629                     if self.token == token::CloseDelim(token::Brace) {
1630                         self.bump();
1631                     }
1632                     return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
1633                 }
1634             }
1635         }
1636         let hi = self.token.span;
1637         self.bump();
1638         return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
1639     }
1640
1641     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
1642         let attrs = self.parse_outer_attributes()?;
1643         let lo = self.token.span;
1644         let pat = self.parse_top_pat(GateOr::No)?;
1645         let guard = if self.eat_keyword(kw::If) {
1646             Some(self.parse_expr()?)
1647         } else {
1648             None
1649         };
1650         let arrow_span = self.token.span;
1651         self.expect(&token::FatArrow)?;
1652         let arm_start_span = self.token.span;
1653
1654         let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
1655             .map_err(|mut err| {
1656                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
1657                 err
1658             })?;
1659
1660         let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
1661             && self.token != token::CloseDelim(token::Brace);
1662
1663         let hi = self.token.span;
1664
1665         if require_comma {
1666             let cm = self.sess.source_map();
1667             self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
1668                 .map_err(|mut err| {
1669                     match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
1670                         (Ok(ref expr_lines), Ok(ref arm_start_lines))
1671                         if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
1672                             && expr_lines.lines.len() == 2
1673                             && self.token == token::FatArrow => {
1674                             // We check whether there's any trailing code in the parse span,
1675                             // if there isn't, we very likely have the following:
1676                             //
1677                             // X |     &Y => "y"
1678                             //   |        --    - missing comma
1679                             //   |        |
1680                             //   |        arrow_span
1681                             // X |     &X => "x"
1682                             //   |      - ^^ self.token.span
1683                             //   |      |
1684                             //   |      parsed until here as `"y" & X`
1685                             err.span_suggestion_short(
1686                                 cm.next_point(arm_start_span),
1687                                 "missing a comma here to end this `match` arm",
1688                                 ",".to_owned(),
1689                                 Applicability::MachineApplicable
1690                             );
1691                         }
1692                         _ => {
1693                             err.span_label(arrow_span,
1694                                            "while parsing the `match` arm starting here");
1695                         }
1696                     }
1697                     err
1698                 })?;
1699         } else {
1700             self.eat(&token::Comma);
1701         }
1702
1703         Ok(ast::Arm {
1704             attrs,
1705             pat,
1706             guard,
1707             body: expr,
1708             span: lo.to(hi),
1709             id: DUMMY_NODE_ID,
1710             is_placeholder: false,
1711         })
1712     }
1713
1714     /// Parses a `try {...}` expression (`try` token already eaten).
1715     fn parse_try_block(
1716         &mut self,
1717         span_lo: Span,
1718         mut attrs: ThinVec<Attribute>
1719     ) -> PResult<'a, P<Expr>> {
1720         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1721         attrs.extend(iattrs);
1722         if self.eat_keyword(kw::Catch) {
1723             let mut error = self.struct_span_err(self.prev_span,
1724                                                  "keyword `catch` cannot follow a `try` block");
1725             error.help("try using `match` on the result of the `try` block instead");
1726             error.emit();
1727             Err(error)
1728         } else {
1729             let span = span_lo.to(body.span);
1730             self.sess.gated_spans.gate(sym::try_blocks, span);
1731             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
1732         }
1733     }
1734
1735     fn is_do_catch_block(&self) -> bool {
1736         self.token.is_keyword(kw::Do) &&
1737         self.is_keyword_ahead(1, &[kw::Catch]) &&
1738         self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
1739         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1740     }
1741
1742     fn is_try_block(&self) -> bool {
1743         self.token.is_keyword(kw::Try) &&
1744         self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
1745         self.token.span.rust_2018() &&
1746         // Prevent `while try {} {}`, `if try {} {} else {}`, etc.
1747         !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1748     }
1749
1750     /// Parses an `async move? {...}` expression.
1751     fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
1752         let span_lo = self.token.span;
1753         self.expect_keyword(kw::Async)?;
1754         let capture_clause = self.parse_capture_clause();
1755         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
1756         attrs.extend(iattrs);
1757         Ok(self.mk_expr(
1758             span_lo.to(body.span),
1759             ExprKind::Async(capture_clause, DUMMY_NODE_ID, body), attrs))
1760     }
1761
1762     fn is_async_block(&self) -> bool {
1763         self.token.is_keyword(kw::Async) &&
1764         (
1765             ( // `async move {`
1766                 self.is_keyword_ahead(1, &[kw::Move]) &&
1767                 self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
1768             ) || ( // `async {`
1769                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
1770             )
1771         )
1772     }
1773
1774     fn maybe_parse_struct_expr(
1775         &mut self,
1776         lo: Span,
1777         path: &ast::Path,
1778         attrs: &ThinVec<Attribute>,
1779     ) -> Option<PResult<'a, P<Expr>>> {
1780         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
1781         let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
1782             // `{ ident, ` cannot start a block.
1783             self.look_ahead(2, |t| t == &token::Comma) ||
1784             self.look_ahead(2, |t| t == &token::Colon) && (
1785                 // `{ ident: token, ` cannot start a block.
1786                 self.look_ahead(4, |t| t == &token::Comma) ||
1787                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
1788                 self.look_ahead(3, |t| !t.can_begin_type())
1789             )
1790         );
1791
1792         if struct_allowed || certainly_not_a_block() {
1793             // This is a struct literal, but we don't can't accept them here.
1794             let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
1795             if let (Ok(expr), false) = (&expr, struct_allowed) {
1796                 self.struct_span_err(
1797                     expr.span,
1798                     "struct literals are not allowed here",
1799                 )
1800                 .multipart_suggestion(
1801                     "surround the struct literal with parentheses",
1802                     vec![
1803                         (lo.shrink_to_lo(), "(".to_string()),
1804                         (expr.span.shrink_to_hi(), ")".to_string()),
1805                     ],
1806                     Applicability::MachineApplicable,
1807                 )
1808                 .emit();
1809             }
1810             return Some(expr);
1811         }
1812         None
1813     }
1814
1815     pub(super) fn parse_struct_expr(
1816         &mut self,
1817         lo: Span,
1818         pth: ast::Path,
1819         mut attrs: ThinVec<Attribute>
1820     ) -> PResult<'a, P<Expr>> {
1821         let struct_sp = lo.to(self.prev_span);
1822         self.bump();
1823         let mut fields = Vec::new();
1824         let mut base = None;
1825
1826         attrs.extend(self.parse_inner_attributes()?);
1827
1828         while self.token != token::CloseDelim(token::Brace) {
1829             if self.eat(&token::DotDot) {
1830                 let exp_span = self.prev_span;
1831                 match self.parse_expr() {
1832                     Ok(e) => {
1833                         base = Some(e);
1834                     }
1835                     Err(mut e) => {
1836                         e.emit();
1837                         self.recover_stmt();
1838                     }
1839                 }
1840                 if self.token == token::Comma {
1841                     self.struct_span_err(
1842                         exp_span.to(self.prev_span),
1843                         "cannot use a comma after the base struct",
1844                     )
1845                     .span_suggestion_short(
1846                         self.token.span,
1847                         "remove this comma",
1848                         String::new(),
1849                         Applicability::MachineApplicable
1850                     )
1851                     .note("the base struct must always be the last field")
1852                     .emit();
1853                     self.recover_stmt();
1854                 }
1855                 break;
1856             }
1857
1858             let mut recovery_field = None;
1859             if let token::Ident(name, _) = self.token.kind {
1860                 if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
1861                     // Use in case of error after field-looking code: `S { foo: () with a }`.
1862                     recovery_field = Some(ast::Field {
1863                         ident: Ident::new(name, self.token.span),
1864                         span: self.token.span,
1865                         expr: self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()),
1866                         is_shorthand: false,
1867                         attrs: ThinVec::new(),
1868                         id: DUMMY_NODE_ID,
1869                         is_placeholder: false,
1870                     });
1871                 }
1872             }
1873             let mut parsed_field = None;
1874             match self.parse_field() {
1875                 Ok(f) => parsed_field = Some(f),
1876                 Err(mut e) => {
1877                     e.span_label(struct_sp, "while parsing this struct");
1878                     e.emit();
1879
1880                     // If the next token is a comma, then try to parse
1881                     // what comes next as additional fields, rather than
1882                     // bailing out until next `}`.
1883                     if self.token != token::Comma {
1884                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1885                         if self.token != token::Comma {
1886                             break;
1887                         }
1888                     }
1889                 }
1890             }
1891
1892             match self.expect_one_of(&[token::Comma],
1893                                      &[token::CloseDelim(token::Brace)]) {
1894                 Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
1895                     // Only include the field if there's no parse error for the field name.
1896                     fields.push(f);
1897                 }
1898                 Err(mut e) => {
1899                     if let Some(f) = recovery_field {
1900                         fields.push(f);
1901                     }
1902                     e.span_label(struct_sp, "while parsing this struct");
1903                     e.emit();
1904                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
1905                     self.eat(&token::Comma);
1906                 }
1907             }
1908         }
1909
1910         let span = lo.to(self.token.span);
1911         self.expect(&token::CloseDelim(token::Brace))?;
1912         return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
1913     }
1914
1915     /// Parses `ident (COLON expr)?`.
1916     fn parse_field(&mut self) -> PResult<'a, Field> {
1917         let attrs = self.parse_outer_attributes()?;
1918         let lo = self.token.span;
1919
1920         // Check if a colon exists one ahead. This means we're parsing a fieldname.
1921         let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
1922             t == &token::Colon || t == &token::Eq
1923         }) {
1924             let fieldname = self.parse_field_name()?;
1925
1926             // Check for an equals token. This means the source incorrectly attempts to
1927             // initialize a field with an eq rather than a colon.
1928             if self.token == token::Eq {
1929                 self.diagnostic()
1930                     .struct_span_err(self.token.span, "expected `:`, found `=`")
1931                     .span_suggestion(
1932                         fieldname.span.shrink_to_hi().to(self.token.span),
1933                         "replace equals symbol with a colon",
1934                         ":".to_string(),
1935                         Applicability::MachineApplicable,
1936                     )
1937                     .emit();
1938             }
1939             self.bump(); // `:`
1940             (fieldname, self.parse_expr()?, false)
1941         } else {
1942             let fieldname = self.parse_ident_common(false)?;
1943
1944             // Mimic `x: x` for the `x` field shorthand.
1945             let path = ast::Path::from_ident(fieldname);
1946             let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
1947             (fieldname, expr, true)
1948         };
1949         Ok(ast::Field {
1950             ident: fieldname,
1951             span: lo.to(expr.span),
1952             expr,
1953             is_shorthand,
1954             attrs: attrs.into(),
1955             id: DUMMY_NODE_ID,
1956             is_placeholder: false,
1957         })
1958     }
1959
1960     fn err_dotdotdot_syntax(&self, span: Span) {
1961         self.struct_span_err(span, "unexpected token: `...`")
1962             .span_suggestion(
1963                 span,
1964                 "use `..` for an exclusive range", "..".to_owned(),
1965                 Applicability::MaybeIncorrect
1966             )
1967             .span_suggestion(
1968                 span,
1969                 "or `..=` for an inclusive range", "..=".to_owned(),
1970                 Applicability::MaybeIncorrect
1971             )
1972             .emit();
1973     }
1974
1975     fn err_larrow_operator(&self, span: Span) {
1976         self.struct_span_err(
1977             span,
1978             "unexpected token: `<-`"
1979         ).span_suggestion(
1980             span,
1981             "if you meant to write a comparison against a negative value, add a \
1982              space in between `<` and `-`",
1983             "< -".to_string(),
1984             Applicability::MaybeIncorrect
1985         ).emit();
1986     }
1987
1988     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
1989         ExprKind::AssignOp(binop, lhs, rhs)
1990     }
1991
1992     fn mk_range(
1993         &self,
1994         start: Option<P<Expr>>,
1995         end: Option<P<Expr>>,
1996         limits: RangeLimits
1997     ) -> PResult<'a, ExprKind> {
1998         if end.is_none() && limits == RangeLimits::Closed {
1999             Err(self.span_fatal_err(self.token.span, Error::InclusiveRangeWithNoEnd))
2000         } else {
2001             Ok(ExprKind::Range(start, end, limits))
2002         }
2003     }
2004
2005     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
2006         ExprKind::Unary(unop, expr)
2007     }
2008
2009     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2010         ExprKind::Binary(binop, lhs, rhs)
2011     }
2012
2013     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
2014         ExprKind::Index(expr, idx)
2015     }
2016
2017     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
2018         ExprKind::Call(f, args)
2019     }
2020
2021     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
2022         let span = lo.to(self.prev_span);
2023         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), ThinVec::new());
2024         self.recover_from_await_method_call();
2025         Ok(await_expr)
2026     }
2027
2028     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
2029         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID })
2030     }
2031
2032     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
2033         self.mk_expr(span, ExprKind::Err, ThinVec::new())
2034     }
2035 }