compiler/rustc_parse/src/parser/expr.rs

   1 use super::pat::{RecoverColon, RecoverComma, PARAM_EXPECTED};
   2 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   3 use super::{
   4     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions, TokenType,
   5 };
   6 use super::{SemiColonMode, SeqSep, TokenExpectType, TrailingToken};
   7 use crate::maybe_recover_from_interpolated_ty_qpath;
   8
   9 use ast::token::DelimToken;
  10 use rustc_ast::ptr::P;
  11 use rustc_ast::token::{self, Token, TokenKind};
  12 use rustc_ast::tokenstream::Spacing;
  13 use rustc_ast::util::classify;
  14 use rustc_ast::util::literal::LitError;
  15 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  16 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  17 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  18 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  19 use rustc_ast_pretty::pprust;
  20 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorReported, PResult};
  21 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  22 use rustc_session::lint::BuiltinLintDiagnostics;
  23 use rustc_span::edition::LATEST_STABLE_EDITION;
  24 use rustc_span::source_map::{self, Span, Spanned};
  25 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  26 use rustc_span::{BytePos, Pos};
  27 use std::mem;
  28
  29 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  30 /// dropped into the token stream, which happens while parsing the result of
  31 /// macro expansion). Placement of these is not as complex as I feared it would
  32 /// be. The important thing is to make sure that lookahead doesn't balk at
  33 /// `token::Interpolated` tokens.
  34 macro_rules! maybe_whole_expr {
  35     ($p:expr) => {
  36         if let token::Interpolated(nt) = &$p.token.kind {
  37             match &**nt {
  38                 token::NtExpr(e) | token::NtLiteral(e) => {
  39                     let e = e.clone();
  40                     $p.bump();
  41                     return Ok(e);
  42                 }
  43                 token::NtPath(path) => {
  44                     let path = path.clone();
  45                     $p.bump();
  46                     return Ok($p.mk_expr(
  47                         $p.prev_token.span,
  48                         ExprKind::Path(None, path),
  49                         AttrVec::new(),
  50                     ));
  51                 }
  52                 token::NtBlock(block) => {
  53                     let block = block.clone();
  54                     $p.bump();
  55                     return Ok($p.mk_expr(
  56                         $p.prev_token.span,
  57                         ExprKind::Block(block, None),
  58                         AttrVec::new(),
  59                     ));
  60                 }
  61                 _ => {}
  62             };
  63         }
  64     };
  65 }
  66
  67 #[derive(Debug)]
  68 pub(super) enum LhsExpr {
  69     NotYetParsed,
  70     AttributesParsed(AttrWrapper),
  71     AlreadyParsed(P<Expr>),
  72 }
  73
  74 impl From<Option<AttrWrapper>> for LhsExpr {
  75     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  76     /// and `None` into `LhsExpr::NotYetParsed`.
  77     ///
  78     /// This conversion does not allocate.
  79     fn from(o: Option<AttrWrapper>) -> Self {
  80         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
  81     }
  82 }
  83
  84 impl From<P<Expr>> for LhsExpr {
  85     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
  86     ///
  87     /// This conversion does not allocate.
  88     fn from(expr: P<Expr>) -> Self {
  89         LhsExpr::AlreadyParsed(expr)
  90     }
  91 }
  92
  93 impl<'a> Parser<'a> {
  94     /// Parses an expression.
  95     #[inline]
  96     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
  97         self.current_closure.take();
  98
  99         self.parse_expr_res(Restrictions::empty(), None)
 100     }
 101
 102     /// Parses an expression, forcing tokens to be collected
 103     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 104         self.collect_tokens_no_attrs(|this| this.parse_expr())
 105     }
 106
 107     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 108         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 109     }
 110
 111     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 112         match self.parse_expr() {
 113             Ok(expr) => Ok(expr),
 114             Err(mut err) => match self.token.ident() {
 115                 Some((Ident { name: kw::Underscore, .. }, false))
 116                     if self.look_ahead(1, |t| t == &token::Comma) =>
 117                 {
 118                     // Special-case handling of `foo(_, _, _)`
 119                     err.emit();
 120                     self.bump();
 121                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err, AttrVec::new()))
 122                 }
 123                 _ => Err(err),
 124             },
 125         }
 126     }
 127
 128     /// Parses a sequence of expressions delimited by parentheses.
 129     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 130         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 131     }
 132
 133     /// Parses an expression, subject to the given restrictions.
 134     #[inline]
 135     pub(super) fn parse_expr_res(
 136         &mut self,
 137         r: Restrictions,
 138         already_parsed_attrs: Option<AttrWrapper>,
 139     ) -> PResult<'a, P<Expr>> {
 140         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 141     }
 142
 143     /// Parses an associative expression.
 144     ///
 145     /// This parses an expression accounting for associativity and precedence of the operators in
 146     /// the expression.
 147     #[inline]
 148     fn parse_assoc_expr(
 149         &mut self,
 150         already_parsed_attrs: Option<AttrWrapper>,
 151     ) -> PResult<'a, P<Expr>> {
 152         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 153     }
 154
 155     /// Parses an associative expression with operators of at least `min_prec` precedence.
 156     pub(super) fn parse_assoc_expr_with(
 157         &mut self,
 158         min_prec: usize,
 159         lhs: LhsExpr,
 160     ) -> PResult<'a, P<Expr>> {
 161         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 162             expr
 163         } else {
 164             let attrs = match lhs {
 165                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 166                 _ => None,
 167             };
 168             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 169                 return self.parse_prefix_range_expr(attrs);
 170             } else {
 171                 self.parse_prefix_expr(attrs)?
 172             }
 173         };
 174         let last_type_ascription_set = self.last_type_ascription.is_some();
 175
 176         if !self.should_continue_as_assoc_expr(&lhs) {
 177             self.last_type_ascription = None;
 178             return Ok(lhs);
 179         }
 180
 181         self.expected_tokens.push(TokenType::Operator);
 182         while let Some(op) = self.check_assoc_op() {
 183             // Adjust the span for interpolated LHS to point to the `$lhs` token
 184             // and not to what it refers to.
 185             let lhs_span = match self.prev_token.kind {
 186                 TokenKind::Interpolated(..) => self.prev_token.span,
 187                 _ => lhs.span,
 188             };
 189
 190             let cur_op_span = self.token.span;
 191             let restrictions = if op.node.is_assign_like() {
 192                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 193             } else {
 194                 self.restrictions
 195             };
 196             let prec = op.node.precedence();
 197             if prec < min_prec {
 198                 break;
 199             }
 200             // Check for deprecated `...` syntax
 201             if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
 202                 self.err_dotdotdot_syntax(self.token.span);
 203             }
 204
 205             if self.token == token::LArrow {
 206                 self.err_larrow_operator(self.token.span);
 207             }
 208
 209             self.bump();
 210             if op.node.is_comparison() {
 211                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 212                     return Ok(expr);
 213                 }
 214             }
 215
 216             // Look for JS' `===` and `!==` and recover
 217             if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
 218                 && self.token.kind == token::Eq
 219                 && self.prev_token.span.hi() == self.token.span.lo()
 220             {
 221                 let sp = op.span.to(self.token.span);
 222                 let sugg = match op.node {
 223                     AssocOp::Equal => "==",
 224                     AssocOp::NotEqual => "!=",
 225                     _ => unreachable!(),
 226                 };
 227                 self.struct_span_err(sp, &format!("invalid comparison operator `{}=`", sugg))
 228                     .span_suggestion_short(
 229                         sp,
 230                         &format!("`{s}=` is not a valid comparison operator, use `{s}`", s = sugg),
 231                         sugg.to_string(),
 232                         Applicability::MachineApplicable,
 233                     )
 234                     .emit();
 235                 self.bump();
 236             }
 237
 238             // Look for PHP's `<>` and recover
 239             if op.node == AssocOp::Less
 240                 && self.token.kind == token::Gt
 241                 && self.prev_token.span.hi() == self.token.span.lo()
 242             {
 243                 let sp = op.span.to(self.token.span);
 244                 self.struct_span_err(sp, "invalid comparison operator `<>`")
 245                     .span_suggestion_short(
 246                         sp,
 247                         "`<>` is not a valid comparison operator, use `!=`",
 248                         "!=".to_string(),
 249                         Applicability::MachineApplicable,
 250                     )
 251                     .emit();
 252                 self.bump();
 253             }
 254
 255             // Look for C++'s `<=>` and recover
 256             if op.node == AssocOp::LessEqual
 257                 && self.token.kind == token::Gt
 258                 && self.prev_token.span.hi() == self.token.span.lo()
 259             {
 260                 let sp = op.span.to(self.token.span);
 261                 self.struct_span_err(sp, "invalid comparison operator `<=>`")
 262                     .span_label(
 263                         sp,
 264                         "`<=>` is not a valid comparison operator, use `std::cmp::Ordering`",
 265                     )
 266                     .emit();
 267                 self.bump();
 268             }
 269
 270             let op = op.node;
 271             // Special cases:
 272             if op == AssocOp::As {
 273                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 274                 continue;
 275             } else if op == AssocOp::Colon {
 276                 lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
 277                 continue;
 278             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 279                 // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
 280                 // generalise it to the Fixity::None code.
 281                 lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?;
 282                 break;
 283             }
 284
 285             let fixity = op.fixity();
 286             let prec_adjustment = match fixity {
 287                 Fixity::Right => 0,
 288                 Fixity::Left => 1,
 289                 // We currently have no non-associative operators that are not handled above by
 290                 // the special cases. The code is here only for future convenience.
 291                 Fixity::None => 1,
 292             };
 293             let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
 294                 this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 295             })?;
 296
 297             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
 298             lhs = match op {
 299                 AssocOp::Add
 300                 | AssocOp::Subtract
 301                 | AssocOp::Multiply
 302                 | AssocOp::Divide
 303                 | AssocOp::Modulus
 304                 | AssocOp::LAnd
 305                 | AssocOp::LOr
 306                 | AssocOp::BitXor
 307                 | AssocOp::BitAnd
 308                 | AssocOp::BitOr
 309                 | AssocOp::ShiftLeft
 310                 | AssocOp::ShiftRight
 311                 | AssocOp::Equal
 312                 | AssocOp::Less
 313                 | AssocOp::LessEqual
 314                 | AssocOp::NotEqual
 315                 | AssocOp::Greater
 316                 | AssocOp::GreaterEqual => {
 317                     let ast_op = op.to_ast_binop().unwrap();
 318                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 319                     self.mk_expr(span, binary, AttrVec::new())
 320                 }
 321                 AssocOp::Assign => {
 322                     self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span), AttrVec::new())
 323                 }
 324                 AssocOp::AssignOp(k) => {
 325                     let aop = match k {
 326                         token::Plus => BinOpKind::Add,
 327                         token::Minus => BinOpKind::Sub,
 328                         token::Star => BinOpKind::Mul,
 329                         token::Slash => BinOpKind::Div,
 330                         token::Percent => BinOpKind::Rem,
 331                         token::Caret => BinOpKind::BitXor,
 332                         token::And => BinOpKind::BitAnd,
 333                         token::Or => BinOpKind::BitOr,
 334                         token::Shl => BinOpKind::Shl,
 335                         token::Shr => BinOpKind::Shr,
 336                     };
 337                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 338                     self.mk_expr(span, aopexpr, AttrVec::new())
 339                 }
 340                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 341                     self.span_bug(span, "AssocOp should have been handled by special case")
 342                 }
 343             };
 344
 345             if let Fixity::None = fixity {
 346                 break;
 347             }
 348         }
 349         if last_type_ascription_set {
 350             self.last_type_ascription = None;
 351         }
 352         Ok(lhs)
 353     }
 354
 355     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 356         match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
 357             // Semi-statement forms are odd:
 358             // See https://github.com/rust-lang/rust/issues/29071
 359             (true, None) => false,
 360             (false, _) => true, // Continue parsing the expression.
 361             // An exhaustive check is done in the following block, but these are checked first
 362             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 363             // want to keep their span info to improve diagnostics in these cases in a later stage.
 364             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 365             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 366             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 367             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 368             // `if x { a } else { b } && if y { c } else { d }`
 369             if !self.look_ahead(1, |t| t.is_used_keyword()) => {
 370                 // These cases are ambiguous and can't be identified in the parser alone.
 371                 let sp = self.sess.source_map().start_point(self.token.span);
 372                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 373                 false
 374             }
 375             (true, Some(AssocOp::LAnd)) |
 376             (true, Some(AssocOp::LOr)) |
 377             (true, Some(AssocOp::BitOr)) => {
 378                 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the
 379                 // above due to #74233.
 380                 // These cases are ambiguous and can't be identified in the parser alone.
 381                 //
 382                 // Bitwise AND is left out because guessing intent is hard. We can make
 383                 // suggestions based on the assumption that double-refs are rarely intentional,
 384                 // and closures are distinct enough that they don't get mixed up with their
 385                 // return value.
 386                 let sp = self.sess.source_map().start_point(self.token.span);
 387                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 388                 false
 389             }
 390             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 391             (true, Some(_)) => {
 392                 self.error_found_expr_would_be_stmt(lhs);
 393                 true
 394             }
 395         }
 396     }
 397
 398     /// We've found an expression that would be parsed as a statement,
 399     /// but the next token implies this should be parsed as an expression.
 400     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 401     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 402         let mut err = self.struct_span_err(
 403             self.token.span,
 404             &format!("expected expression, found `{}`", pprust::token_to_string(&self.token),),
 405         );
 406         err.span_label(self.token.span, "expected expression");
 407         self.sess.expr_parentheses_needed(&mut err, lhs.span);
 408         err.emit();
 409     }
 410
 411     /// Possibly translate the current token to an associative operator.
 412     /// The method does not advance the current token.
 413     ///
 414     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 415     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 416         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 417             // When parsing const expressions, stop parsing when encountering `>`.
 418             (
 419                 Some(
 420                     AssocOp::ShiftRight
 421                     | AssocOp::Greater
 422                     | AssocOp::GreaterEqual
 423                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 424                 ),
 425                 _,
 426             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 427                 return None;
 428             }
 429             (Some(op), _) => (op, self.token.span),
 430             (None, Some((Ident { name: sym::and, span }, false))) => {
 431                 self.error_bad_logical_op("and", "&&", "conjunction");
 432                 (AssocOp::LAnd, span)
 433             }
 434             (None, Some((Ident { name: sym::or, span }, false))) => {
 435                 self.error_bad_logical_op("or", "||", "disjunction");
 436                 (AssocOp::LOr, span)
 437             }
 438             _ => return None,
 439         };
 440         Some(source_map::respan(span, op))
 441     }
 442
 443     /// Error on `and` and `or` suggesting `&&` and `||` respectively.
 444     fn error_bad_logical_op(&self, bad: &str, good: &str, english: &str) {
 445         self.struct_span_err(self.token.span, &format!("`{}` is not a logical operator", bad))
 446             .span_suggestion_short(
 447                 self.token.span,
 448                 &format!("use `{}` to perform logical {}", good, english),
 449                 good.to_string(),
 450                 Applicability::MachineApplicable,
 451             )
 452             .note("unlike in e.g., python and PHP, `&&` and `||` are used for logical operators")
 453             .emit();
 454     }
 455
 456     /// Checks if this expression is a successfully parsed statement.
 457     fn expr_is_complete(&self, e: &Expr) -> bool {
 458         self.restrictions.contains(Restrictions::STMT_EXPR)
 459             && !classify::expr_requires_semi_to_be_stmt(e)
 460     }
 461
 462     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 463     /// The other two variants are handled in `parse_prefix_range_expr` below.
 464     fn parse_range_expr(
 465         &mut self,
 466         prec: usize,
 467         lhs: P<Expr>,
 468         op: AssocOp,
 469         cur_op_span: Span,
 470     ) -> PResult<'a, P<Expr>> {
 471         let rhs = if self.is_at_start_of_range_notation_rhs() {
 472             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 473         } else {
 474             None
 475         };
 476         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 477         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 478         let limits =
 479             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 480         let range = self.mk_range(Some(lhs), rhs, limits);
 481         Ok(self.mk_expr(span, range, AttrVec::new()))
 482     }
 483
 484     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 485         if self.token.can_begin_expr() {
 486             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 487             if self.token == token::OpenDelim(token::Brace) {
 488                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 489             }
 490             true
 491         } else {
 492             false
 493         }
 494     }
 495
 496     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 497     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 498         // Check for deprecated `...` syntax.
 499         if self.token == token::DotDotDot {
 500             self.err_dotdotdot_syntax(self.token.span);
 501         }
 502
 503         debug_assert!(
 504             [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 505             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 506             self.token
 507         );
 508
 509         let limits = match self.token.kind {
 510             token::DotDot => RangeLimits::HalfOpen,
 511             _ => RangeLimits::Closed,
 512         };
 513         let op = AssocOp::from_token(&self.token);
 514         // FIXME: `parse_prefix_range_expr` is called when the current
 515         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 516         // parsed attributes, then trying to parse them here will always fail.
 517         // We should figure out how we want attributes on range expressions to work.
 518         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 519         self.collect_tokens_for_expr(attrs, |this, attrs| {
 520             let lo = this.token.span;
 521             this.bump();
 522             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 523                 // RHS must be parsed with more associativity than the dots.
 524                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 525                     .map(|x| (lo.to(x.span), Some(x)))?
 526             } else {
 527                 (lo, None)
 528             };
 529             let range = this.mk_range(None, opt_end, limits);
 530             Ok(this.mk_expr(span, range, attrs.into()))
 531         })
 532     }
 533
 534     /// Parses a prefix-unary-operator expr.
 535     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 536         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 537         let lo = self.token.span;
 538
 539         macro_rules! make_it {
 540             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 541                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 542                     let (hi, ex) = $body?;
 543                     Ok($this.mk_expr(lo.to(hi), ex, attrs.into()))
 544                 })
 545             };
 546         }
 547
 548         let this = self;
 549
 550         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 551         match this.token.uninterpolate().kind {
 552             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr`
 553             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr`
 554             token::BinOp(token::Minus) => {
 555                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 556             } // `-expr`
 557             token::BinOp(token::Star) => {
 558                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 559             } // `*expr`
 560             token::BinOp(token::And) | token::AndAnd => {
 561                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 562             }
 563             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 564                 let mut err = this.struct_span_err(lo, "leading `+` is not supported");
 565                 err.span_label(lo, "unexpected `+`");
 566
 567                 // a block on the LHS might have been intended to be an expression instead
 568                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 569                     this.sess.expr_parentheses_needed(&mut err, *sp);
 570                 } else {
 571                     err.span_suggestion_verbose(
 572                         lo,
 573                         "try removing the `+`",
 574                         "".to_string(),
 575                         Applicability::MachineApplicable,
 576                     );
 577                 }
 578                 err.emit();
 579
 580                 this.bump();
 581                 this.parse_prefix_expr(None)
 582             } // `+expr`
 583             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 584                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 585             }
 586             token::Ident(..) if this.is_mistaken_not_ident_negation() => {
 587                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 588             }
 589             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 590         }
 591     }
 592
 593     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 594         self.bump();
 595         let expr = self.parse_prefix_expr(None);
 596         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 597         Ok((lo.to(span), expr))
 598     }
 599
 600     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 601         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 602         Ok((span, self.mk_unary(op, expr)))
 603     }
 604
 605     // Recover on `!` suggesting for bitwise negation instead.
 606     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 607         self.struct_span_err(lo, "`~` cannot be used as a unary operator")
 608             .span_suggestion_short(
 609                 lo,
 610                 "use `!` to perform bitwise not",
 611                 "!".to_owned(),
 612                 Applicability::MachineApplicable,
 613             )
 614             .emit();
 615
 616         self.parse_unary_expr(lo, UnOp::Not)
 617     }
 618
 619     /// Parse `box expr`.
 620     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 621         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 622         self.sess.gated_spans.gate(sym::box_syntax, span);
 623         Ok((span, ExprKind::Box(expr)))
 624     }
 625
 626     fn is_mistaken_not_ident_negation(&self) -> bool {
 627         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 628             // These tokens can start an expression after `!`, but
 629             // can't continue an expression after an ident
 630             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 631             token::Literal(..) | token::Pound => true,
 632             _ => t.is_whole_expr(),
 633         };
 634         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 635     }
 636
 637     /// Recover on `not expr` in favor of `!expr`.
 638     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 639         // Emit the error...
 640         let not_token = self.look_ahead(1, |t| t.clone());
 641         self.struct_span_err(
 642             not_token.span,
 643             &format!("unexpected {} after identifier", super::token_descr(&not_token)),
 644         )
 645         .span_suggestion_short(
 646             // Span the `not` plus trailing whitespace to avoid
 647             // trailing whitespace after the `!` in our suggestion
 648             self.sess.source_map().span_until_non_whitespace(lo.to(not_token.span)),
 649             "use `!` to perform logical negation",
 650             "!".to_owned(),
 651             Applicability::MachineApplicable,
 652         )
 653         .emit();
 654
 655         // ...and recover!
 656         self.parse_unary_expr(lo, UnOp::Not)
 657     }
 658
 659     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 660     fn interpolated_or_expr_span(
 661         &self,
 662         expr: PResult<'a, P<Expr>>,
 663     ) -> PResult<'a, (Span, P<Expr>)> {
 664         expr.map(|e| {
 665             (
 666                 match self.prev_token.kind {
 667                     TokenKind::Interpolated(..) => self.prev_token.span,
 668                     _ => e.span,
 669                 },
 670                 e,
 671             )
 672         })
 673     }
 674
 675     fn parse_assoc_op_cast(
 676         &mut self,
 677         lhs: P<Expr>,
 678         lhs_span: Span,
 679         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 680     ) -> PResult<'a, P<Expr>> {
 681         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 682             this.mk_expr(
 683                 this.mk_expr_sp(&lhs, lhs_span, rhs.span),
 684                 expr_kind(lhs, rhs),
 685                 AttrVec::new(),
 686             )
 687         };
 688
 689         // Save the state of the parser before parsing type normally, in case there is a
 690         // LessThan comparison after this cast.
 691         let parser_snapshot_before_type = self.clone();
 692         let cast_expr = match self.parse_as_cast_ty() {
 693             Ok(rhs) => mk_expr(self, lhs, rhs),
 694             Err(type_err) => {
 695                 // Rewind to before attempting to parse the type with generics, to recover
 696                 // from situations like `x as usize < y` in which we first tried to parse
 697                 // `usize < y` as a type with generic arguments.
 698                 let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
 699
 700                 // Check for typo of `'a: loop { break 'a }` with a missing `'`.
 701                 match (&lhs.kind, &self.token.kind) {
 702                     (
 703                         // `foo: `
 704                         ExprKind::Path(None, ast::Path { segments, .. }),
 705                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
 706                     ) if segments.len() == 1 => {
 707                         let snapshot = self.clone();
 708                         let label = Label {
 709                             ident: Ident::from_str_and_span(
 710                                 &format!("'{}", segments[0].ident),
 711                                 segments[0].ident.span,
 712                             ),
 713                         };
 714                         match self.parse_labeled_expr(label, AttrVec::new(), false) {
 715                             Ok(expr) => {
 716                                 type_err.cancel();
 717                                 self.struct_span_err(label.ident.span, "malformed loop label")
 718                                     .span_suggestion(
 719                                         label.ident.span,
 720                                         "use the correct loop label format",
 721                                         label.ident.to_string(),
 722                                         Applicability::MachineApplicable,
 723                                     )
 724                                     .emit();
 725                                 return Ok(expr);
 726                             }
 727                             Err(err) => {
 728                                 err.cancel();
 729                                 *self = snapshot;
 730                             }
 731                         }
 732                     }
 733                     _ => {}
 734                 }
 735
 736                 match self.parse_path(PathStyle::Expr) {
 737                     Ok(path) => {
 738                         let (op_noun, op_verb) = match self.token.kind {
 739                             token::Lt => ("comparison", "comparing"),
 740                             token::BinOp(token::Shl) => ("shift", "shifting"),
 741                             _ => {
 742                                 // We can end up here even without `<` being the next token, for
 743                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 744                                 // but `parse_path` returns `Ok` on them due to error recovery.
 745                                 // Return original error and parser state.
 746                                 *self = parser_snapshot_after_type;
 747                                 return Err(type_err);
 748                             }
 749                         };
 750
 751                         // Successfully parsed the type path leaving a `<` yet to parse.
 752                         type_err.cancel();
 753
 754                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 755                         // in AST and continue parsing.
 756                         let msg = format!(
 757                             "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
 758                             pprust::path_to_string(&path),
 759                             op_noun,
 760                         );
 761                         let span_after_type = parser_snapshot_after_type.token.span;
 762                         let expr =
 763                             mk_expr(self, lhs, self.mk_ty(path.span, TyKind::Path(None, path)));
 764
 765                         self.struct_span_err(self.token.span, &msg)
 766                             .span_label(
 767                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 768                                 "interpreted as generic arguments",
 769                             )
 770                             .span_label(self.token.span, format!("not interpreted as {}", op_noun))
 771                             .multipart_suggestion(
 772                                 &format!("try {} the cast value", op_verb),
 773                                 vec![
 774                                     (expr.span.shrink_to_lo(), "(".to_string()),
 775                                     (expr.span.shrink_to_hi(), ")".to_string()),
 776                                 ],
 777                                 Applicability::MachineApplicable,
 778                             )
 779                             .emit();
 780
 781                         expr
 782                     }
 783                     Err(path_err) => {
 784                         // Couldn't parse as a path, return original error and parser state.
 785                         path_err.cancel();
 786                         *self = parser_snapshot_after_type;
 787                         return Err(type_err);
 788                     }
 789                 }
 790             }
 791         };
 792
 793         self.parse_and_disallow_postfix_after_cast(cast_expr)
 794     }
 795
 796     /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
 797     /// then emits an error and returns the newly parsed tree.
 798     /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
 799     fn parse_and_disallow_postfix_after_cast(
 800         &mut self,
 801         cast_expr: P<Expr>,
 802     ) -> PResult<'a, P<Expr>> {
 803         // Save the memory location of expr before parsing any following postfix operators.
 804         // This will be compared with the memory location of the output expression.
 805         // If they different we can assume we parsed another expression because the existing expression is not reallocated.
 806         let addr_before = &*cast_expr as *const _ as usize;
 807         let span = cast_expr.span;
 808         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 809         let changed = addr_before != &*with_postfix as *const _ as usize;
 810
 811         // Check if an illegal postfix operator has been added after the cast.
 812         // If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator.
 813         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) || changed {
 814             let msg = format!(
 815                 "casts cannot be followed by {}",
 816                 match with_postfix.kind {
 817                     ExprKind::Index(_, _) => "indexing",
 818                     ExprKind::Try(_) => "`?`",
 819                     ExprKind::Field(_, _) => "a field access",
 820                     ExprKind::MethodCall(_, _, _) => "a method call",
 821                     ExprKind::Call(_, _) => "a function call",
 822                     ExprKind::Await(_) => "`.await`",
 823                     ExprKind::Err => return Ok(with_postfix),
 824                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 825                 }
 826             );
 827             let mut err = self.struct_span_err(span, &msg);
 828             // If type ascription is "likely an error", the user will already be getting a useful
 829             // help message, and doesn't need a second.
 830             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 831                 self.maybe_annotate_with_ascription(&mut err, false);
 832             } else {
 833                 let suggestions = vec![
 834                     (span.shrink_to_lo(), "(".to_string()),
 835                     (span.shrink_to_hi(), ")".to_string()),
 836                 ];
 837                 err.multipart_suggestion(
 838                     "try surrounding the expression in parentheses",
 839                     suggestions,
 840                     Applicability::MachineApplicable,
 841                 );
 842             }
 843             err.emit();
 844         };
 845         Ok(with_postfix)
 846     }
 847
 848     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 849         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 850         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 851         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 852         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 853         Ok(lhs)
 854     }
 855
 856     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 857     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 858         self.expect_and()?;
 859         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 860         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 861         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 862         let expr = self.parse_prefix_expr(None);
 863         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 864         let span = lo.to(hi);
 865         if let Some(lt) = lifetime {
 866             self.error_remove_borrow_lifetime(span, lt.ident.span);
 867         }
 868         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 869     }
 870
 871     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 872         self.struct_span_err(span, "borrow expressions cannot be annotated with lifetimes")
 873             .span_label(lt_span, "annotated with lifetime here")
 874             .span_suggestion(
 875                 lt_span,
 876                 "remove the lifetime annotation",
 877                 String::new(),
 878                 Applicability::MachineApplicable,
 879             )
 880             .emit();
 881     }
 882
 883     /// Parse `mut?` or `raw [ const | mut ]`.
 884     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 885         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 886             // `raw [ const | mut ]`.
 887             let found_raw = self.eat_keyword(kw::Raw);
 888             assert!(found_raw);
 889             let mutability = self.parse_const_or_mut().unwrap();
 890             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 891             (ast::BorrowKind::Raw, mutability)
 892         } else {
 893             // `mut?`
 894             (ast::BorrowKind::Ref, self.parse_mutability())
 895         }
 896     }
 897
 898     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 899     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 900         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 901         self.collect_tokens_for_expr(attrs, |this, attrs| {
 902             let base = this.parse_bottom_expr();
 903             let (span, base) = this.interpolated_or_expr_span(base)?;
 904             this.parse_dot_or_call_expr_with(base, span, attrs)
 905         })
 906     }
 907
 908     pub(super) fn parse_dot_or_call_expr_with(
 909         &mut self,
 910         e0: P<Expr>,
 911         lo: Span,
 912         mut attrs: Vec<ast::Attribute>,
 913     ) -> PResult<'a, P<Expr>> {
 914         // Stitch the list of outer attributes onto the return value.
 915         // A little bit ugly, but the best way given the current code
 916         // structure
 917         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| {
 918             expr.map(|mut expr| {
 919                 attrs.extend::<Vec<_>>(expr.attrs.into());
 920                 expr.attrs = attrs.into();
 921                 expr
 922             })
 923         })
 924     }
 925
 926     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 927         loop {
 928             if self.eat(&token::Question) {
 929                 // `expr?`
 930                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e), AttrVec::new());
 931                 continue;
 932             }
 933             if self.eat(&token::Dot) {
 934                 // expr.f
 935                 e = self.parse_dot_suffix_expr(lo, e)?;
 936                 continue;
 937             }
 938             if self.expr_is_complete(&e) {
 939                 return Ok(e);
 940             }
 941             e = match self.token.kind {
 942                 token::OpenDelim(token::Paren) => self.parse_fn_call_expr(lo, e),
 943                 token::OpenDelim(token::Bracket) => self.parse_index_expr(lo, e)?,
 944                 _ => return Ok(e),
 945             }
 946         }
 947     }
 948
 949     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
 950         self.look_ahead(1, |t| t.is_ident())
 951             && self.look_ahead(2, |t| t == &token::Colon)
 952             && self.look_ahead(3, |t| t.can_begin_expr())
 953     }
 954
 955     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
 956         match self.token.uninterpolate().kind {
 957             token::Ident(..) => self.parse_dot_suffix(base, lo),
 958             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 959                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
 960             }
 961             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
 962                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
 963             }
 964             _ => {
 965                 self.error_unexpected_after_dot();
 966                 Ok(base)
 967             }
 968         }
 969     }
 970
 971     fn error_unexpected_after_dot(&self) {
 972         // FIXME Could factor this out into non_fatal_unexpected or something.
 973         let actual = pprust::token_to_string(&self.token);
 974         self.struct_span_err(self.token.span, &format!("unexpected token: `{}`", actual)).emit();
 975     }
 976
 977     // We need an identifier or integer, but the next token is a float.
 978     // Break the float into components to extract the identifier or integer.
 979     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
 980     // parts unless those parts are processed immediately. `TokenCursor` should either
 981     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
 982     // we should break everything including floats into more basic proc-macro style
 983     // tokens in the lexer (probably preferable).
 984     fn parse_tuple_field_access_expr_float(
 985         &mut self,
 986         lo: Span,
 987         base: P<Expr>,
 988         float: Symbol,
 989         suffix: Option<Symbol>,
 990     ) -> P<Expr> {
 991         #[derive(Debug)]
 992         enum FloatComponent {
 993             IdentLike(String),
 994             Punct(char),
 995         }
 996         use FloatComponent::*;
 997
 998         let float_str = float.as_str();
 999         let mut components = Vec::new();
1000         let mut ident_like = String::new();
1001         for c in float_str.chars() {
1002             if c == '_' || c.is_ascii_alphanumeric() {
1003                 ident_like.push(c);
1004             } else if matches!(c, '.' | '+' | '-') {
1005                 if !ident_like.is_empty() {
1006                     components.push(IdentLike(mem::take(&mut ident_like)));
1007                 }
1008                 components.push(Punct(c));
1009             } else {
1010                 panic!("unexpected character in a float token: {:?}", c)
1011             }
1012         }
1013         if !ident_like.is_empty() {
1014             components.push(IdentLike(ident_like));
1015         }
1016
1017         // With proc macros the span can refer to anything, the source may be too short,
1018         // or too long, or non-ASCII. It only makes sense to break our span into components
1019         // if its underlying text is identical to our float literal.
1020         let span = self.token.span;
1021         let can_take_span_apart =
1022             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1023
1024         match &*components {
1025             // 1e2
1026             [IdentLike(i)] => {
1027                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1028             }
1029             // 1.
1030             [IdentLike(i), Punct('.')] => {
1031                 let (ident_span, dot_span) = if can_take_span_apart() {
1032                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1033                     let ident_span = span.with_hi(span.lo + ident_len);
1034                     let dot_span = span.with_lo(span.lo + ident_len);
1035                     (ident_span, dot_span)
1036                 } else {
1037                     (span, span)
1038                 };
1039                 assert!(suffix.is_none());
1040                 let symbol = Symbol::intern(&i);
1041                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1042                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1043                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1044             }
1045             // 1.2 | 1.2e3
1046             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1047                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1048                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1049                     let ident1_span = span.with_hi(span.lo + ident1_len);
1050                     let dot_span = span
1051                         .with_lo(span.lo + ident1_len)
1052                         .with_hi(span.lo + ident1_len + BytePos(1));
1053                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1054                     (ident1_span, dot_span, ident2_span)
1055                 } else {
1056                     (span, span, span)
1057                 };
1058                 let symbol1 = Symbol::intern(&i1);
1059                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1060                 // This needs to be `Spacing::Alone` to prevent regressions.
1061                 // See issue #76399 and PR #76285 for more details
1062                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1063                 let base1 =
1064                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1065                 let symbol2 = Symbol::intern(&i2);
1066                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1067                 self.bump_with((next_token2, self.token_spacing)); // `.`
1068                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1069             }
1070             // 1e+ | 1e- (recovered)
1071             [IdentLike(_), Punct('+' | '-')] |
1072             // 1e+2 | 1e-2
1073             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1074             // 1.2e+ | 1.2e-
1075             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1076             // 1.2e+3 | 1.2e-3
1077             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1078                 // See the FIXME about `TokenCursor` above.
1079                 self.error_unexpected_after_dot();
1080                 base
1081             }
1082             _ => panic!("unexpected components in a float token: {:?}", components),
1083         }
1084     }
1085
1086     fn parse_tuple_field_access_expr(
1087         &mut self,
1088         lo: Span,
1089         base: P<Expr>,
1090         field: Symbol,
1091         suffix: Option<Symbol>,
1092         next_token: Option<(Token, Spacing)>,
1093     ) -> P<Expr> {
1094         match next_token {
1095             Some(next_token) => self.bump_with(next_token),
1096             None => self.bump(),
1097         }
1098         let span = self.prev_token.span;
1099         let field = ExprKind::Field(base, Ident::new(field, span));
1100         self.expect_no_suffix(span, "a tuple index", suffix);
1101         self.mk_expr(lo.to(span), field, AttrVec::new())
1102     }
1103
1104     /// Parse a function call expression, `expr(...)`.
1105     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1106         let snapshot = if self.token.kind == token::OpenDelim(token::Paren)
1107             && self.look_ahead_type_ascription_as_field()
1108         {
1109             Some((self.clone(), fun.kind.clone()))
1110         } else {
1111             None
1112         };
1113         let open_paren = self.token.span;
1114
1115         let mut seq = self.parse_paren_expr_seq().map(|args| {
1116             self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new())
1117         });
1118         if let Some(expr) =
1119             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1120         {
1121             return expr;
1122         }
1123         self.recover_seq_parse_error(token::Paren, lo, seq)
1124     }
1125
1126     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1127     /// parentheses instead of braces, recover the parser state and provide suggestions.
1128     #[instrument(skip(self, seq, snapshot), level = "trace")]
1129     fn maybe_recover_struct_lit_bad_delims(
1130         &mut self,
1131         lo: Span,
1132         open_paren: Span,
1133         seq: &mut PResult<'a, P<Expr>>,
1134         snapshot: Option<(Self, ExprKind)>,
1135     ) -> Option<P<Expr>> {
1136         match (seq.as_mut(), snapshot) {
1137             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1138                 let name = pprust::path_to_string(&path);
1139                 snapshot.bump(); // `(`
1140                 match snapshot.parse_struct_fields(path, false, token::Paren) {
1141                     Ok((fields, ..)) if snapshot.eat(&token::CloseDelim(token::Paren)) => {
1142                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1143                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1144                         *self = snapshot;
1145                         let close_paren = self.prev_token.span;
1146                         let span = lo.to(self.prev_token.span);
1147                         if !fields.is_empty() {
1148                             let replacement_err = self.struct_span_err(
1149                                 span,
1150                                 "invalid `struct` delimiters or `fn` call arguments",
1151                             );
1152                             mem::replace(err, replacement_err).cancel();
1153
1154                             err.multipart_suggestion(
1155                                 &format!("if `{}` is a struct, use braces as delimiters", name),
1156                                 vec![
1157                                     (open_paren, " { ".to_string()),
1158                                     (close_paren, " }".to_string()),
1159                                 ],
1160                                 Applicability::MaybeIncorrect,
1161                             );
1162                             err.multipart_suggestion(
1163                                 &format!("if `{}` is a function, use the arguments directly", name),
1164                                 fields
1165                                     .into_iter()
1166                                     .map(|field| (field.span.until(field.expr.span), String::new()))
1167                                     .collect(),
1168                                 Applicability::MaybeIncorrect,
1169                             );
1170                             err.emit();
1171                         } else {
1172                             err.emit();
1173                         }
1174                         return Some(self.mk_expr_err(span));
1175                     }
1176                     Ok(_) => {}
1177                     Err(mut err) => {
1178                         err.emit();
1179                     }
1180                 }
1181             }
1182             _ => {}
1183         }
1184         None
1185     }
1186
1187     /// Parse an indexing expression `expr[...]`.
1188     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1189         self.bump(); // `[`
1190         let index = self.parse_expr()?;
1191         self.expect(&token::CloseDelim(token::Bracket))?;
1192         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new()))
1193     }
1194
1195     /// Assuming we have just parsed `.`, continue parsing into an expression.
1196     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1197         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1198             return Ok(self.mk_await_expr(self_arg, lo));
1199         }
1200
1201         let fn_span_lo = self.token.span;
1202         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1203         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(token::Paren)]);
1204         self.check_turbofish_missing_angle_brackets(&mut segment);
1205
1206         if self.check(&token::OpenDelim(token::Paren)) {
1207             // Method call `expr.f()`
1208             let mut args = self.parse_paren_expr_seq()?;
1209             args.insert(0, self_arg);
1210
1211             let fn_span = fn_span_lo.to(self.prev_token.span);
1212             let span = lo.to(self.prev_token.span);
1213             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new()))
1214         } else {
1215             // Field access `expr.f`
1216             if let Some(args) = segment.args {
1217                 self.struct_span_err(
1218                     args.span(),
1219                     "field expressions cannot have generic arguments",
1220                 )
1221                 .emit();
1222             }
1223
1224             let span = lo.to(self.prev_token.span);
1225             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new()))
1226         }
1227     }
1228
1229     /// At the bottom (top?) of the precedence hierarchy,
1230     /// Parses things like parenthesized exprs, macros, `return`, etc.
1231     ///
1232     /// N.B., this does not parse outer attributes, and is private because it only works
1233     /// correctly if called from `parse_dot_or_call_expr()`.
1234     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1235         maybe_recover_from_interpolated_ty_qpath!(self, true);
1236         maybe_whole_expr!(self);
1237
1238         // Outer attributes are already parsed and will be
1239         // added to the return value after the fact.
1240         //
1241         // Therefore, prevent sub-parser from parsing
1242         // attributes by giving them an empty "already-parsed" list.
1243         let attrs = AttrVec::new();
1244
1245         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1246         let lo = self.token.span;
1247         if let token::Literal(_) = self.token.kind {
1248             // This match arm is a special-case of the `_` match arm below and
1249             // could be removed without changing functionality, but it's faster
1250             // to have it here, especially for programs with large constants.
1251             self.parse_lit_expr(attrs)
1252         } else if self.check(&token::OpenDelim(token::Paren)) {
1253             self.parse_tuple_parens_expr(attrs)
1254         } else if self.check(&token::OpenDelim(token::Brace)) {
1255             self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs)
1256         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1257             self.parse_closure_expr(attrs).map_err(|mut err| {
1258                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1259                 // then suggest parens around the lhs.
1260                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1261                     self.sess.expr_parentheses_needed(&mut err, *sp);
1262                 }
1263                 err
1264             })
1265         } else if self.check(&token::OpenDelim(token::Bracket)) {
1266             self.parse_array_or_repeat_expr(attrs, token::Bracket)
1267         } else if self.check_path() {
1268             self.parse_path_start_expr(attrs)
1269         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1270             self.parse_closure_expr(attrs)
1271         } else if self.eat_keyword(kw::If) {
1272             self.parse_if_expr(attrs)
1273         } else if self.check_keyword(kw::For) {
1274             if self.choose_generics_over_qpath(1) {
1275                 // NOTE(Centril, eddyb): DO NOT REMOVE! Beyond providing parser recovery,
1276                 // this is an insurance policy in case we allow qpaths in (tuple-)struct patterns.
1277                 // When `for <Foo as Bar>::Proj in $expr $block` is wanted,
1278                 // you can disambiguate in favor of a pattern with `(...)`.
1279                 self.recover_quantified_closure_expr(attrs)
1280             } else {
1281                 assert!(self.eat_keyword(kw::For));
1282                 self.parse_for_expr(None, self.prev_token.span, attrs)
1283             }
1284         } else if self.eat_keyword(kw::While) {
1285             self.parse_while_expr(None, self.prev_token.span, attrs)
1286         } else if let Some(label) = self.eat_label() {
1287             self.parse_labeled_expr(label, attrs, true)
1288         } else if self.eat_keyword(kw::Loop) {
1289             self.parse_loop_expr(None, self.prev_token.span, attrs)
1290         } else if self.eat_keyword(kw::Continue) {
1291             let kind = ExprKind::Continue(self.eat_label());
1292             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1293         } else if self.eat_keyword(kw::Match) {
1294             let match_sp = self.prev_token.span;
1295             self.parse_match_expr(attrs).map_err(|mut err| {
1296                 err.span_label(match_sp, "while parsing this match expression");
1297                 err
1298             })
1299         } else if self.eat_keyword(kw::Unsafe) {
1300             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1301         } else if self.check_inline_const(0) {
1302             self.parse_const_block(lo.to(self.token.span), false)
1303         } else if self.is_do_catch_block() {
1304             self.recover_do_catch(attrs)
1305         } else if self.is_try_block() {
1306             self.expect_keyword(kw::Try)?;
1307             self.parse_try_block(lo, attrs)
1308         } else if self.eat_keyword(kw::Return) {
1309             self.parse_return_expr(attrs)
1310         } else if self.eat_keyword(kw::Break) {
1311             self.parse_break_expr(attrs)
1312         } else if self.eat_keyword(kw::Yield) {
1313             self.parse_yield_expr(attrs)
1314         } else if self.eat_keyword(kw::Let) {
1315             self.parse_let_expr(attrs)
1316         } else if self.eat_keyword(kw::Underscore) {
1317             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1318         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1319             // Don't complain about bare semicolons after unclosed braces
1320             // recovery in order to keep the error count down. Fixing the
1321             // delimiters will possibly also fix the bare semicolon found in
1322             // expression context. For example, silence the following error:
1323             //
1324             //     error: expected expression, found `;`
1325             //      --> file.rs:2:13
1326             //       |
1327             //     2 |     foo(bar(;
1328             //       |             ^ expected expression
1329             self.bump();
1330             Ok(self.mk_expr_err(self.token.span))
1331         } else if self.token.uninterpolated_span().rust_2018() {
1332             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1333             if self.check_keyword(kw::Async) {
1334                 if self.is_async_block() {
1335                     // Check for `async {` and `async move {`.
1336                     self.parse_async_block(attrs)
1337                 } else {
1338                     self.parse_closure_expr(attrs)
1339                 }
1340             } else if self.eat_keyword(kw::Await) {
1341                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1342             } else {
1343                 self.parse_lit_expr(attrs)
1344             }
1345         } else {
1346             self.parse_lit_expr(attrs)
1347         }
1348     }
1349
1350     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1351         let lo = self.token.span;
1352         match self.parse_opt_lit() {
1353             Some(literal) => {
1354                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1355                 self.maybe_recover_from_bad_qpath(expr, true)
1356             }
1357             None => self.try_macro_suggestion(),
1358         }
1359     }
1360
1361     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1362         let lo = self.token.span;
1363         self.expect(&token::OpenDelim(token::Paren))?;
1364         let (es, trailing_comma) = match self.parse_seq_to_end(
1365             &token::CloseDelim(token::Paren),
1366             SeqSep::trailing_allowed(token::Comma),
1367             |p| p.parse_expr_catch_underscore(),
1368         ) {
1369             Ok(x) => x,
1370             Err(err) => return Ok(self.recover_seq_parse_error(token::Paren, lo, Err(err))),
1371         };
1372         let kind = if es.len() == 1 && !trailing_comma {
1373             // `(e)` is parenthesized `e`.
1374             ExprKind::Paren(es.into_iter().next().unwrap())
1375         } else {
1376             // `(e,)` is a tuple with only one field, `e`.
1377             ExprKind::Tup(es)
1378         };
1379         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1380         self.maybe_recover_from_bad_qpath(expr, true)
1381     }
1382
1383     fn parse_array_or_repeat_expr(
1384         &mut self,
1385         attrs: AttrVec,
1386         close_delim: token::DelimToken,
1387     ) -> PResult<'a, P<Expr>> {
1388         let lo = self.token.span;
1389         self.bump(); // `[` or other open delim
1390
1391         let close = &token::CloseDelim(close_delim);
1392         let kind = if self.eat(close) {
1393             // Empty vector
1394             ExprKind::Array(Vec::new())
1395         } else {
1396             // Non-empty vector
1397             let first_expr = self.parse_expr()?;
1398             if self.eat(&token::Semi) {
1399                 // Repeating array syntax: `[ 0; 512 ]`
1400                 let count = self.parse_anon_const_expr()?;
1401                 self.expect(close)?;
1402                 ExprKind::Repeat(first_expr, count)
1403             } else if self.eat(&token::Comma) {
1404                 // Vector with two or more elements.
1405                 let sep = SeqSep::trailing_allowed(token::Comma);
1406                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1407                 let mut exprs = vec![first_expr];
1408                 exprs.extend(remaining_exprs);
1409                 ExprKind::Array(exprs)
1410             } else {
1411                 // Vector with one element
1412                 self.expect(close)?;
1413                 ExprKind::Array(vec![first_expr])
1414             }
1415         };
1416         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1417         self.maybe_recover_from_bad_qpath(expr, true)
1418     }
1419
1420     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1421         let (qself, path) = if self.eat_lt() {
1422             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1423             (Some(qself), path)
1424         } else {
1425             (None, self.parse_path(PathStyle::Expr)?)
1426         };
1427         let lo = path.span;
1428
1429         // `!`, as an operator, is prefix, so we know this isn't that.
1430         let (hi, kind) = if self.eat(&token::Not) {
1431             // MACRO INVOCATION expression
1432             if qself.is_some() {
1433                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1434             }
1435             let mac = MacCall {
1436                 path,
1437                 args: self.parse_mac_args()?,
1438                 prior_type_ascription: self.last_type_ascription,
1439             };
1440             (self.prev_token.span, ExprKind::MacCall(mac))
1441         } else if self.check(&token::OpenDelim(token::Brace)) {
1442             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1443                 if qself.is_some() {
1444                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1445                 }
1446                 return expr;
1447             } else {
1448                 (path.span, ExprKind::Path(qself, path))
1449             }
1450         } else {
1451             (path.span, ExprKind::Path(qself, path))
1452         };
1453
1454         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1455         self.maybe_recover_from_bad_qpath(expr, true)
1456     }
1457
1458     /// Parse `'label: $expr`. The label is already parsed.
1459     fn parse_labeled_expr(
1460         &mut self,
1461         label: Label,
1462         attrs: AttrVec,
1463         mut consume_colon: bool,
1464     ) -> PResult<'a, P<Expr>> {
1465         let lo = label.ident.span;
1466         let label = Some(label);
1467         let ate_colon = self.eat(&token::Colon);
1468         let expr = if self.eat_keyword(kw::While) {
1469             self.parse_while_expr(label, lo, attrs)
1470         } else if self.eat_keyword(kw::For) {
1471             self.parse_for_expr(label, lo, attrs)
1472         } else if self.eat_keyword(kw::Loop) {
1473             self.parse_loop_expr(label, lo, attrs)
1474         } else if self.check(&token::OpenDelim(token::Brace)) || self.token.is_whole_block() {
1475             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1476         } else if !ate_colon && (self.check(&TokenKind::Comma) || self.check(&TokenKind::Gt)) {
1477             // We're probably inside of a `Path<'a>` that needs a turbofish
1478             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1479             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1480             consume_colon = false;
1481             Ok(self.mk_expr_err(lo))
1482         } else {
1483             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1484             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1485             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1486             self.parse_expr()
1487         }?;
1488
1489         if !ate_colon && consume_colon {
1490             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1491         }
1492
1493         Ok(expr)
1494     }
1495
1496     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1497         self.struct_span_err(span, "labeled expression must be followed by `:`")
1498             .span_label(lo, "the label")
1499             .span_suggestion_short(
1500                 lo.shrink_to_hi(),
1501                 "add `:` after the label",
1502                 ": ".to_string(),
1503                 Applicability::MachineApplicable,
1504             )
1505             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1506             .emit();
1507     }
1508
1509     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1510     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1511         let lo = self.token.span;
1512
1513         self.bump(); // `do`
1514         self.bump(); // `catch`
1515
1516         let span_dc = lo.to(self.prev_token.span);
1517         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1518             .span_suggestion(
1519                 span_dc,
1520                 "replace with the new syntax",
1521                 "try".to_string(),
1522                 Applicability::MachineApplicable,
1523             )
1524             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1525             .emit();
1526
1527         self.parse_try_block(lo, attrs)
1528     }
1529
1530     /// Parse an expression if the token can begin one.
1531     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1532         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1533     }
1534
1535     /// Parse `"return" expr?`.
1536     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1537         let lo = self.prev_token.span;
1538         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1539         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1540         self.maybe_recover_from_bad_qpath(expr, true)
1541     }
1542
1543     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1544     /// If the label is followed immediately by a `:` token, the label and `:` are
1545     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1546     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1547     /// the break expression of an unlabeled break is a labeled loop (as in
1548     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1549     /// expression only gets a warning for compatibility reasons; and a labeled break
1550     /// with a labeled loop does not even get a warning because there is no ambiguity.
1551     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1552         let lo = self.prev_token.span;
1553         let mut label = self.eat_label();
1554         let kind = if label.is_some() && self.token == token::Colon {
1555             // The value expression can be a labeled loop, see issue #86948, e.g.:
1556             // `loop { break 'label: loop { break 'label 42; }; }`
1557             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1558             self.struct_span_err(
1559                 lexpr.span,
1560                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1561             )
1562             .multipart_suggestion(
1563                 "wrap the expression in parentheses",
1564                 vec![
1565                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1566                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1567                 ],
1568                 Applicability::MachineApplicable,
1569             )
1570             .emit();
1571             Some(lexpr)
1572         } else if self.token != token::OpenDelim(token::Brace)
1573             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1574         {
1575             let expr = self.parse_expr_opt()?;
1576             if let Some(ref expr) = expr {
1577                 if label.is_some()
1578                     && matches!(
1579                         expr.kind,
1580                         ExprKind::While(_, _, None)
1581                             | ExprKind::ForLoop(_, _, _, None)
1582                             | ExprKind::Loop(_, None)
1583                             | ExprKind::Block(_, None)
1584                     )
1585                 {
1586                     self.sess.buffer_lint_with_diagnostic(
1587                         BREAK_WITH_LABEL_AND_LOOP,
1588                         lo.to(expr.span),
1589                         ast::CRATE_NODE_ID,
1590                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1591                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1592                     );
1593                 }
1594             }
1595             expr
1596         } else {
1597             None
1598         };
1599         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1600         self.maybe_recover_from_bad_qpath(expr, true)
1601     }
1602
1603     /// Parse `"yield" expr?`.
1604     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1605         let lo = self.prev_token.span;
1606         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1607         let span = lo.to(self.prev_token.span);
1608         self.sess.gated_spans.gate(sym::generators, span);
1609         let expr = self.mk_expr(span, kind, attrs);
1610         self.maybe_recover_from_bad_qpath(expr, true)
1611     }
1612
1613     /// Returns a string literal if the next token is a string literal.
1614     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1615     /// and returns `None` if the next token is not literal at all.
1616     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1617         match self.parse_opt_lit() {
1618             Some(lit) => match lit.kind {
1619                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1620                     style,
1621                     symbol: lit.token.symbol,
1622                     suffix: lit.token.suffix,
1623                     span: lit.span,
1624                     symbol_unescaped,
1625                 }),
1626                 _ => Err(Some(lit)),
1627             },
1628             None => Err(None),
1629         }
1630     }
1631
1632     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1633         self.parse_opt_lit().ok_or_else(|| {
1634             if let token::Interpolated(inner) = &self.token.kind {
1635                 let expr = match inner.as_ref() {
1636                     token::NtExpr(expr) => Some(expr),
1637                     token::NtLiteral(expr) => Some(expr),
1638                     _ => None,
1639                 };
1640                 if let Some(expr) = expr {
1641                     if matches!(expr.kind, ExprKind::Err) {
1642                         let mut err = self
1643                             .diagnostic()
1644                             .struct_span_err(self.token.span, &"invalid interpolated expression");
1645                         err.downgrade_to_delayed_bug();
1646                         return err;
1647                     }
1648                 }
1649             }
1650             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1651             self.struct_span_err(self.token.span, &msg)
1652         })
1653     }
1654
1655     /// Matches `lit = true | false | token_lit`.
1656     /// Returns `None` if the next token is not a literal.
1657     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1658         let mut recovered = None;
1659         if self.token == token::Dot {
1660             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1661             // dot would follow an optional literal, so we do this unconditionally.
1662             recovered = self.look_ahead(1, |next_token| {
1663                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1664                     next_token.kind
1665                 {
1666                     if self.token.span.hi() == next_token.span.lo() {
1667                         let s = String::from("0.") + symbol.as_str();
1668                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1669                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1670                     }
1671                 }
1672                 None
1673             });
1674             if let Some(token) = &recovered {
1675                 self.bump();
1676                 self.error_float_lits_must_have_int_part(&token);
1677             }
1678         }
1679
1680         let token = recovered.as_ref().unwrap_or(&self.token);
1681         match Lit::from_token(token) {
1682             Ok(lit) => {
1683                 self.bump();
1684                 Some(lit)
1685             }
1686             Err(LitError::NotLiteral) => None,
1687             Err(err) => {
1688                 let span = token.span;
1689                 let token::Literal(lit) = token.kind else {
1690                     unreachable!();
1691                 };
1692                 self.bump();
1693                 self.report_lit_error(err, lit, span);
1694                 // Pack possible quotes and prefixes from the original literal into
1695                 // the error literal's symbol so they can be pretty-printed faithfully.
1696                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1697                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1698                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1699                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1700             }
1701         }
1702     }
1703
1704     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1705         self.struct_span_err(token.span, "float literals must have an integer part")
1706             .span_suggestion(
1707                 token.span,
1708                 "must have an integer part",
1709                 pprust::token_to_string(token).into(),
1710                 Applicability::MachineApplicable,
1711             )
1712             .emit();
1713     }
1714
1715     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1716         // Checks if `s` looks like i32 or u1234 etc.
1717         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1718             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1719         }
1720
1721         // Try to lowercase the prefix if it's a valid base prefix.
1722         fn fix_base_capitalisation(s: &str) -> Option<String> {
1723             if let Some(stripped) = s.strip_prefix('B') {
1724                 Some(format!("0b{stripped}"))
1725             } else if let Some(stripped) = s.strip_prefix('O') {
1726                 Some(format!("0o{stripped}"))
1727             } else if let Some(stripped) = s.strip_prefix('X') {
1728                 Some(format!("0x{stripped}"))
1729             } else {
1730                 None
1731             }
1732         }
1733
1734         let token::Lit { kind, suffix, .. } = lit;
1735         match err {
1736             // `NotLiteral` is not an error by itself, so we don't report
1737             // it and give the parser opportunity to try something else.
1738             LitError::NotLiteral => {}
1739             // `LexerError` *is* an error, but it was already reported
1740             // by lexer, so here we don't report it the second time.
1741             LitError::LexerError => {}
1742             LitError::InvalidSuffix => {
1743                 self.expect_no_suffix(
1744                     span,
1745                     &format!("{} {} literal", kind.article(), kind.descr()),
1746                     suffix,
1747                 );
1748             }
1749             LitError::InvalidIntSuffix => {
1750                 let suf = suffix.expect("suffix error with no suffix");
1751                 let suf = suf.as_str();
1752                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1753                     // If it looks like a width, try to be helpful.
1754                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1755                     self.struct_span_err(span, &msg)
1756                         .help("valid widths are 8, 16, 32, 64 and 128")
1757                         .emit();
1758                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1759                     let msg = "invalid base prefix for number literal";
1760
1761                     self.struct_span_err(span, &msg)
1762                         .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase")
1763                         .span_suggestion(
1764                             span,
1765                             "try making the prefix lowercase",
1766                             fixed,
1767                             Applicability::MaybeIncorrect,
1768                         )
1769                         .emit();
1770                 } else {
1771                     let msg = format!("invalid suffix `{}` for number literal", suf);
1772                     self.struct_span_err(span, &msg)
1773                         .span_label(span, format!("invalid suffix `{}`", suf))
1774                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1775                         .emit();
1776                 }
1777             }
1778             LitError::InvalidFloatSuffix => {
1779                 let suf = suffix.expect("suffix error with no suffix");
1780                 let suf = suf.as_str();
1781                 if looks_like_width_suffix(&['f'], suf) {
1782                     // If it looks like a width, try to be helpful.
1783                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1784                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1785                 } else {
1786                     let msg = format!("invalid suffix `{}` for float literal", suf);
1787                     self.struct_span_err(span, &msg)
1788                         .span_label(span, format!("invalid suffix `{}`", suf))
1789                         .help("valid suffixes are `f32` and `f64`")
1790                         .emit();
1791                 }
1792             }
1793             LitError::NonDecimalFloat(base) => {
1794                 let descr = match base {
1795                     16 => "hexadecimal",
1796                     8 => "octal",
1797                     2 => "binary",
1798                     _ => unreachable!(),
1799                 };
1800                 self.struct_span_err(span, &format!("{} float literal is not supported", descr))
1801                     .span_label(span, "not supported")
1802                     .emit();
1803             }
1804             LitError::IntTooLarge => {
1805                 self.struct_span_err(span, "integer literal is too large").emit();
1806             }
1807         }
1808     }
1809
1810     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1811         if let Some(suf) = suffix {
1812             let mut err = if kind == "a tuple index"
1813                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1814             {
1815                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1816                 // through the ecosystem when people fix their macros
1817                 let mut err = self
1818                     .sess
1819                     .span_diagnostic
1820                     .struct_span_warn(sp, &format!("suffixes on {} are invalid", kind));
1821                 err.note(&format!(
1822                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1823                         incorrectly accepted on stable for a few releases",
1824                     suf,
1825                 ));
1826                 err.help(
1827                     "on proc macros, you'll want to use `syn::Index::from` or \
1828                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1829                         to tuple field access",
1830                 );
1831                 err.note(
1832                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1833                      for more information",
1834                 );
1835                 err
1836             } else {
1837                 self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
1838                     .forget_guarantee()
1839             };
1840             err.span_label(sp, format!("invalid suffix `{}`", suf));
1841             err.emit();
1842         }
1843     }
1844
1845     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1846     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1847     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1848         maybe_whole_expr!(self);
1849
1850         let lo = self.token.span;
1851         let minus_present = self.eat(&token::BinOp(token::Minus));
1852         let lit = self.parse_lit()?;
1853         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
1854
1855         if minus_present {
1856             Ok(self.mk_expr(
1857                 lo.to(self.prev_token.span),
1858                 self.mk_unary(UnOp::Neg, expr),
1859                 AttrVec::new(),
1860             ))
1861         } else {
1862             Ok(expr)
1863         }
1864     }
1865
1866     fn is_array_like_block(&mut self) -> bool {
1867         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1868             && self.look_ahead(2, |t| t == &token::Comma)
1869             && self.look_ahead(3, |t| t.can_begin_expr())
1870     }
1871
1872     /// Emits a suggestion if it looks like the user meant an array but
1873     /// accidentally used braces, causing the code to be interpreted as a block
1874     /// expression.
1875     fn maybe_suggest_brackets_instead_of_braces(
1876         &mut self,
1877         lo: Span,
1878         attrs: AttrVec,
1879     ) -> Option<P<Expr>> {
1880         let mut snapshot = self.clone();
1881         match snapshot.parse_array_or_repeat_expr(attrs, token::Brace) {
1882             Ok(arr) => {
1883                 let hi = snapshot.prev_token.span;
1884                 self.struct_span_err(
1885                     arr.span,
1886                     "this code is interpreted as a block expression, not an array",
1887                 )
1888                 .multipart_suggestion(
1889                     "try using [] instead of {}",
1890                     vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
1891                     Applicability::MaybeIncorrect,
1892                 )
1893                 .note("to define an array, one would use square brackets instead of curly braces")
1894                 .emit();
1895
1896                 *self = snapshot;
1897                 Some(self.mk_expr_err(arr.span))
1898             }
1899             Err(e) => {
1900                 e.cancel();
1901                 None
1902             }
1903         }
1904     }
1905
1906     /// Parses a block or unsafe block.
1907     pub(super) fn parse_block_expr(
1908         &mut self,
1909         opt_label: Option<Label>,
1910         lo: Span,
1911         blk_mode: BlockCheckMode,
1912         mut attrs: AttrVec,
1913     ) -> PResult<'a, P<Expr>> {
1914         if self.is_array_like_block() {
1915             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) {
1916                 return Ok(arr);
1917             }
1918         }
1919
1920         if let Some(label) = opt_label {
1921             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
1922         }
1923
1924         if self.token.is_whole_block() {
1925             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
1926                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
1927                 .emit();
1928         }
1929
1930         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
1931         attrs.extend(inner_attrs);
1932         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1933     }
1934
1935     /// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`.
1936     fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1937         let lo = self.token.span;
1938         let _ = self.parse_late_bound_lifetime_defs()?;
1939         let span_for = lo.to(self.prev_token.span);
1940         let closure = self.parse_closure_expr(attrs)?;
1941
1942         self.struct_span_err(span_for, "cannot introduce explicit parameters for a closure")
1943             .span_label(closure.span, "the parameters are attached to this closure")
1944             .span_suggestion(
1945                 span_for,
1946                 "remove the parameters",
1947                 String::new(),
1948                 Applicability::MachineApplicable,
1949             )
1950             .emit();
1951
1952         Ok(self.mk_expr_err(lo.to(closure.span)))
1953     }
1954
1955     /// Parses a closure expression (e.g., `move |args| expr`).
1956     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1957         let lo = self.token.span;
1958
1959         let movability =
1960             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
1961
1962         let asyncness = if self.token.uninterpolated_span().rust_2018() {
1963             self.parse_asyncness()
1964         } else {
1965             Async::No
1966         };
1967
1968         let capture_clause = self.parse_capture_clause()?;
1969         let decl = self.parse_fn_block_decl()?;
1970         let decl_hi = self.prev_token.span;
1971         let mut body = match decl.output {
1972             FnRetTy::Default(_) => {
1973                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1974                 self.parse_expr_res(restrictions, None)?
1975             }
1976             _ => {
1977                 // If an explicit return type is given, require a block to appear (RFC 968).
1978                 let body_lo = self.token.span;
1979                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
1980             }
1981         };
1982
1983         if let Async::Yes { span, .. } = asyncness {
1984             // Feature-gate `async ||` closures.
1985             self.sess.gated_spans.gate(sym::async_closure, span);
1986         }
1987
1988         if self.token.kind == TokenKind::Semi && self.token_cursor.frame.delim == DelimToken::Paren
1989         {
1990             // It is likely that the closure body is a block but where the
1991             // braces have been removed. We will recover and eat the next
1992             // statements later in the parsing process.
1993             body = self.mk_expr_err(body.span);
1994         }
1995
1996         let body_span = body.span;
1997
1998         let closure = self.mk_expr(
1999             lo.to(body.span),
2000             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
2001             attrs,
2002         );
2003
2004         // Disable recovery for closure body
2005         let spans =
2006             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2007         self.current_closure = Some(spans);
2008
2009         Ok(closure)
2010     }
2011
2012     /// Parses an optional `move` prefix to a closure-like construct.
2013     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2014         if self.eat_keyword(kw::Move) {
2015             // Check for `move async` and recover
2016             if self.check_keyword(kw::Async) {
2017                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2018                 Err(self.incorrect_move_async_order_found(move_async_span))
2019             } else {
2020                 Ok(CaptureBy::Value)
2021             }
2022         } else {
2023             Ok(CaptureBy::Ref)
2024         }
2025     }
2026
2027     /// Parses the `|arg, arg|` header of a closure.
2028     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2029         let inputs = if self.eat(&token::OrOr) {
2030             Vec::new()
2031         } else {
2032             self.expect(&token::BinOp(token::Or))?;
2033             let args = self
2034                 .parse_seq_to_before_tokens(
2035                     &[&token::BinOp(token::Or), &token::OrOr],
2036                     SeqSep::trailing_allowed(token::Comma),
2037                     TokenExpectType::NoExpect,
2038                     |p| p.parse_fn_block_param(),
2039                 )?
2040                 .0;
2041             self.expect_or()?;
2042             args
2043         };
2044         let output =
2045             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2046
2047         Ok(P(FnDecl { inputs, output }))
2048     }
2049
2050     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2051     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2052         let lo = self.token.span;
2053         let attrs = self.parse_outer_attributes()?;
2054         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2055             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2056             let ty = if this.eat(&token::Colon) {
2057                 this.parse_ty()?
2058             } else {
2059                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2060             };
2061
2062             Ok((
2063                 Param {
2064                     attrs: attrs.into(),
2065                     ty,
2066                     pat,
2067                     span: lo.to(this.token.span),
2068                     id: DUMMY_NODE_ID,
2069                     is_placeholder: false,
2070                 },
2071                 TrailingToken::MaybeComma,
2072             ))
2073         })
2074     }
2075
2076     /// Parses an `if` expression (`if` token already eaten).
2077     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2078         let lo = self.prev_token.span;
2079         let cond = self.parse_cond_expr()?;
2080
2081         let missing_then_block_binop_span = || {
2082             match cond.kind {
2083                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, ref right)
2084                     if let ExprKind::Block(..) = right.kind => Some(binop_span),
2085                 _ => None
2086             }
2087         };
2088
2089         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
2090         // verify that the last statement is either an implicit return (no `;`) or an explicit
2091         // return. This won't catch blocks with an explicit `return`, but that would be caught by
2092         // the dead code lint.
2093         let thn = if self.token.is_keyword(kw::Else) || !cond.returns() {
2094             if let Some(binop_span) = missing_then_block_binop_span() {
2095                 self.error_missing_if_then_block(lo, None, Some(binop_span)).emit();
2096                 self.mk_block_err(cond.span)
2097             } else {
2098                 self.error_missing_if_cond(lo, cond.span)
2099             }
2100         } else {
2101             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2102             let not_block = self.token != token::OpenDelim(token::Brace);
2103             let block = self.parse_block().map_err(|err| {
2104                 if not_block {
2105                     self.error_missing_if_then_block(lo, Some(err), missing_then_block_binop_span())
2106                 } else {
2107                     err
2108                 }
2109             })?;
2110             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2111             block
2112         };
2113         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2114         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
2115     }
2116
2117     fn error_missing_if_then_block(
2118         &self,
2119         if_span: Span,
2120         err: Option<DiagnosticBuilder<'a, ErrorReported>>,
2121         binop_span: Option<Span>,
2122     ) -> DiagnosticBuilder<'a, ErrorReported> {
2123         let msg = "this `if` expression has a condition, but no block";
2124
2125         let mut err = if let Some(mut err) = err {
2126             err.span_label(if_span, msg);
2127             err
2128         } else {
2129             self.struct_span_err(if_span, msg)
2130         };
2131
2132         if let Some(binop_span) = binop_span {
2133             err.span_help(binop_span, "maybe you forgot the right operand of the condition?");
2134         }
2135
2136         err
2137     }
2138
2139     fn error_missing_if_cond(&self, lo: Span, span: Span) -> P<ast::Block> {
2140         let sp = self.sess.source_map().next_point(lo);
2141         self.struct_span_err(sp, "missing condition for `if` expression")
2142             .span_label(sp, "expected if condition here")
2143             .emit();
2144         self.mk_block_err(span)
2145     }
2146
2147     /// Parses the condition of a `if` or `while` expression.
2148     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2149         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2150
2151         if let ExprKind::Let(..) = cond.kind {
2152             // Remove the last feature gating of a `let` expression since it's stable.
2153             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2154         }
2155
2156         Ok(cond)
2157     }
2158
2159     /// Parses a `let $pat = $expr` pseudo-expression.
2160     /// The `let` token has already been eaten.
2161     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2162         let lo = self.prev_token.span;
2163         let pat = self.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
2164         self.expect(&token::Eq)?;
2165         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2166             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2167         })?;
2168         let span = lo.to(expr.span);
2169         self.sess.gated_spans.gate(sym::let_chains, span);
2170         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
2171     }
2172
2173     /// Parses an `else { ... }` expression (`else` token already eaten).
2174     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2175         let ctx_span = self.prev_token.span; // `else`
2176         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2177         let expr = if self.eat_keyword(kw::If) {
2178             self.parse_if_expr(AttrVec::new())?
2179         } else {
2180             let blk = self.parse_block()?;
2181             self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())
2182         };
2183         self.error_on_if_block_attrs(ctx_span, true, expr.span, &attrs);
2184         Ok(expr)
2185     }
2186
2187     fn error_on_if_block_attrs(
2188         &self,
2189         ctx_span: Span,
2190         is_ctx_else: bool,
2191         branch_span: Span,
2192         attrs: &[ast::Attribute],
2193     ) {
2194         let (span, last) = match attrs {
2195             [] => return,
2196             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2197         };
2198         let ctx = if is_ctx_else { "else" } else { "if" };
2199         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
2200             .span_label(branch_span, "the attributes are attached to this branch")
2201             .span_label(ctx_span, format!("the branch belongs to this `{}`", ctx))
2202             .span_suggestion(
2203                 span,
2204                 "remove the attributes",
2205                 String::new(),
2206                 Applicability::MachineApplicable,
2207             )
2208             .emit();
2209     }
2210
2211     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2212     fn parse_for_expr(
2213         &mut self,
2214         opt_label: Option<Label>,
2215         lo: Span,
2216         mut attrs: AttrVec,
2217     ) -> PResult<'a, P<Expr>> {
2218         // Record whether we are about to parse `for (`.
2219         // This is used below for recovery in case of `for ( $stuff ) $block`
2220         // in which case we will suggest `for $stuff $block`.
2221         let begin_paren = match self.token.kind {
2222             token::OpenDelim(token::Paren) => Some(self.token.span),
2223             _ => None,
2224         };
2225
2226         let pat = self.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
2227         if !self.eat_keyword(kw::In) {
2228             self.error_missing_in_for_loop();
2229         }
2230         self.check_for_for_in_in_typo(self.prev_token.span);
2231         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2232
2233         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2234
2235         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
2236         attrs.extend(iattrs);
2237
2238         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2239         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2240     }
2241
2242     fn error_missing_in_for_loop(&mut self) {
2243         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
2244             // Possibly using JS syntax (#75311).
2245             let span = self.token.span;
2246             self.bump();
2247             (span, "try using `in` here instead", "in")
2248         } else {
2249             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
2250         };
2251         self.struct_span_err(span, "missing `in` in `for` loop")
2252             .span_suggestion_short(
2253                 span,
2254                 msg,
2255                 sugg.into(),
2256                 // Has been misleading, at least in the past (closed Issue #48492).
2257                 Applicability::MaybeIncorrect,
2258             )
2259             .emit();
2260     }
2261
2262     /// Parses a `while` or `while let` expression (`while` token already eaten).
2263     fn parse_while_expr(
2264         &mut self,
2265         opt_label: Option<Label>,
2266         lo: Span,
2267         mut attrs: AttrVec,
2268     ) -> PResult<'a, P<Expr>> {
2269         let cond = self.parse_cond_expr()?;
2270         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2271         attrs.extend(iattrs);
2272         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2273     }
2274
2275     /// Parses `loop { ... }` (`loop` token already eaten).
2276     fn parse_loop_expr(
2277         &mut self,
2278         opt_label: Option<Label>,
2279         lo: Span,
2280         mut attrs: AttrVec,
2281     ) -> PResult<'a, P<Expr>> {
2282         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2283         attrs.extend(iattrs);
2284         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2285     }
2286
2287     fn eat_label(&mut self) -> Option<Label> {
2288         self.token.lifetime().map(|ident| {
2289             self.bump();
2290             Label { ident }
2291         })
2292     }
2293
2294     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2295     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2296         let match_span = self.prev_token.span;
2297         let lo = self.prev_token.span;
2298         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2299         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
2300             if self.token == token::Semi {
2301                 e.span_suggestion_short(
2302                     match_span,
2303                     "try removing this `match`",
2304                     String::new(),
2305                     Applicability::MaybeIncorrect, // speculative
2306                 );
2307             }
2308             return Err(e);
2309         }
2310         attrs.extend(self.parse_inner_attributes()?);
2311
2312         let mut arms: Vec<Arm> = Vec::new();
2313         while self.token != token::CloseDelim(token::Brace) {
2314             match self.parse_arm() {
2315                 Ok(arm) => arms.push(arm),
2316                 Err(mut e) => {
2317                     // Recover by skipping to the end of the block.
2318                     e.emit();
2319                     self.recover_stmt();
2320                     let span = lo.to(self.token.span);
2321                     if self.token == token::CloseDelim(token::Brace) {
2322                         self.bump();
2323                     }
2324                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2325                 }
2326             }
2327         }
2328         let hi = self.token.span;
2329         self.bump();
2330         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2331     }
2332
2333     /// Attempt to recover from match arm body with statements and no surrounding braces.
2334     fn parse_arm_body_missing_braces(
2335         &mut self,
2336         first_expr: &P<Expr>,
2337         arrow_span: Span,
2338     ) -> Option<P<Expr>> {
2339         if self.token.kind != token::Semi {
2340             return None;
2341         }
2342         let start_snapshot = self.clone();
2343         let semi_sp = self.token.span;
2344         self.bump(); // `;`
2345         let mut stmts =
2346             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2347         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2348             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2349             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2350             let (these, s, are) =
2351                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2352             err.span_label(
2353                 span,
2354                 &format!(
2355                     "{these} statement{s} {are} not surrounded by a body",
2356                     these = these,
2357                     s = s,
2358                     are = are
2359                 ),
2360             );
2361             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2362             if stmts.len() > 1 {
2363                 err.multipart_suggestion(
2364                     &format!("surround the statement{} with a body", s),
2365                     vec![
2366                         (span.shrink_to_lo(), "{ ".to_string()),
2367                         (span.shrink_to_hi(), " }".to_string()),
2368                     ],
2369                     Applicability::MachineApplicable,
2370                 );
2371             } else {
2372                 err.span_suggestion(
2373                     semi_sp,
2374                     "use a comma to end a `match` arm expression",
2375                     ",".to_string(),
2376                     Applicability::MachineApplicable,
2377                 );
2378             }
2379             err.emit();
2380             this.mk_expr_err(span)
2381         };
2382         // We might have either a `,` -> `;` typo, or a block without braces. We need
2383         // a more subtle parsing strategy.
2384         loop {
2385             if self.token.kind == token::CloseDelim(token::Brace) {
2386                 // We have reached the closing brace of the `match` expression.
2387                 return Some(err(self, stmts));
2388             }
2389             if self.token.kind == token::Comma {
2390                 *self = start_snapshot;
2391                 return None;
2392             }
2393             let pre_pat_snapshot = self.clone();
2394             match self.parse_pat_no_top_alt(None) {
2395                 Ok(_pat) => {
2396                     if self.token.kind == token::FatArrow {
2397                         // Reached arm end.
2398                         *self = pre_pat_snapshot;
2399                         return Some(err(self, stmts));
2400                     }
2401                 }
2402                 Err(err) => {
2403                     err.cancel();
2404                 }
2405             }
2406
2407             *self = pre_pat_snapshot;
2408             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2409                 // Consume statements for as long as possible.
2410                 Ok(Some(stmt)) => {
2411                     stmts.push(stmt);
2412                 }
2413                 Ok(None) => {
2414                     *self = start_snapshot;
2415                     break;
2416                 }
2417                 // We couldn't parse either yet another statement missing it's
2418                 // enclosing block nor the next arm's pattern or closing brace.
2419                 Err(stmt_err) => {
2420                     stmt_err.cancel();
2421                     *self = start_snapshot;
2422                     break;
2423                 }
2424             }
2425         }
2426         None
2427     }
2428
2429     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2430         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2431             match expr.kind {
2432                 ExprKind::Binary(_, ref lhs, ref rhs) => {
2433                     let lhs_rslt = check_let_expr(lhs);
2434                     let rhs_rslt = check_let_expr(rhs);
2435                     (lhs_rslt.0 || rhs_rslt.0, false)
2436                 }
2437                 ExprKind::Let(..) => (true, true),
2438                 _ => (false, true),
2439             }
2440         }
2441         let attrs = self.parse_outer_attributes()?;
2442         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2443             let lo = this.token.span;
2444             let pat = this.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
2445             let guard = if this.eat_keyword(kw::If) {
2446                 let if_span = this.prev_token.span;
2447                 let cond = this.parse_expr()?;
2448                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2449                 if has_let_expr {
2450                     if does_not_have_bin_op {
2451                         // Remove the last feature gating of a `let` expression since it's stable.
2452                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2453                     }
2454                     let span = if_span.to(cond.span);
2455                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2456                 }
2457                 Some(cond)
2458             } else {
2459                 None
2460             };
2461             let arrow_span = this.token.span;
2462             if let Err(mut err) = this.expect(&token::FatArrow) {
2463                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2464                 if TokenKind::FatArrow
2465                     .similar_tokens()
2466                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2467                 {
2468                     err.span_suggestion(
2469                         this.token.span,
2470                         "try using a fat arrow here",
2471                         "=>".to_string(),
2472                         Applicability::MaybeIncorrect,
2473                     );
2474                     err.emit();
2475                     this.bump();
2476                 } else {
2477                     return Err(err);
2478                 }
2479             }
2480             let arm_start_span = this.token.span;
2481
2482             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2483                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2484                 err
2485             })?;
2486
2487             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2488                 && this.token != token::CloseDelim(token::Brace);
2489
2490             let hi = this.prev_token.span;
2491
2492             if require_comma {
2493                 let sm = this.sess.source_map();
2494                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2495                     let span = body.span;
2496                     return Ok((
2497                         ast::Arm {
2498                             attrs: attrs.into(),
2499                             pat,
2500                             guard,
2501                             body,
2502                             span,
2503                             id: DUMMY_NODE_ID,
2504                             is_placeholder: false,
2505                         },
2506                         TrailingToken::None,
2507                     ));
2508                 }
2509                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]).map_err(
2510                     |mut err| {
2511                         match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) {
2512                             (Ok(ref expr_lines), Ok(ref arm_start_lines))
2513                                 if arm_start_lines.lines[0].end_col
2514                                     == expr_lines.lines[0].end_col
2515                                     && expr_lines.lines.len() == 2
2516                                     && this.token == token::FatArrow =>
2517                             {
2518                                 // We check whether there's any trailing code in the parse span,
2519                                 // if there isn't, we very likely have the following:
2520                                 //
2521                                 // X |     &Y => "y"
2522                                 //   |        --    - missing comma
2523                                 //   |        |
2524                                 //   |        arrow_span
2525                                 // X |     &X => "x"
2526                                 //   |      - ^^ self.token.span
2527                                 //   |      |
2528                                 //   |      parsed until here as `"y" & X`
2529                                 err.span_suggestion_short(
2530                                     arm_start_span.shrink_to_hi(),
2531                                     "missing a comma here to end this `match` arm",
2532                                     ",".to_owned(),
2533                                     Applicability::MachineApplicable,
2534                                 );
2535                             }
2536                             _ => {
2537                                 err.span_label(
2538                                     arrow_span,
2539                                     "while parsing the `match` arm starting here",
2540                                 );
2541                             }
2542                         }
2543                         err
2544                     },
2545                 )?;
2546             } else {
2547                 this.eat(&token::Comma);
2548             }
2549
2550             Ok((
2551                 ast::Arm {
2552                     attrs: attrs.into(),
2553                     pat,
2554                     guard,
2555                     body: expr,
2556                     span: lo.to(hi),
2557                     id: DUMMY_NODE_ID,
2558                     is_placeholder: false,
2559                 },
2560                 TrailingToken::None,
2561             ))
2562         })
2563     }
2564
2565     /// Parses a `try {...}` expression (`try` token already eaten).
2566     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2567         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2568         attrs.extend(iattrs);
2569         if self.eat_keyword(kw::Catch) {
2570             let mut error = self.struct_span_err(
2571                 self.prev_token.span,
2572                 "keyword `catch` cannot follow a `try` block",
2573             );
2574             error.help("try using `match` on the result of the `try` block instead");
2575             error.emit();
2576             Err(error)
2577         } else {
2578             let span = span_lo.to(body.span);
2579             self.sess.gated_spans.gate(sym::try_blocks, span);
2580             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2581         }
2582     }
2583
2584     fn is_do_catch_block(&self) -> bool {
2585         self.token.is_keyword(kw::Do)
2586             && self.is_keyword_ahead(1, &[kw::Catch])
2587             && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2588             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2589     }
2590
2591     fn is_try_block(&self) -> bool {
2592         self.token.is_keyword(kw::Try)
2593             && self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2594             && self.token.uninterpolated_span().rust_2018()
2595     }
2596
2597     /// Parses an `async move? {...}` expression.
2598     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2599         let lo = self.token.span;
2600         self.expect_keyword(kw::Async)?;
2601         let capture_clause = self.parse_capture_clause()?;
2602         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2603         attrs.extend(iattrs);
2604         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2605         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2606     }
2607
2608     fn is_async_block(&self) -> bool {
2609         self.token.is_keyword(kw::Async)
2610             && ((
2611                 // `async move {`
2612                 self.is_keyword_ahead(1, &[kw::Move])
2613                     && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2614             ) || (
2615                 // `async {`
2616                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2617             ))
2618     }
2619
2620     fn is_certainly_not_a_block(&self) -> bool {
2621         self.look_ahead(1, |t| t.is_ident())
2622             && (
2623                 // `{ ident, ` cannot start a block.
2624                 self.look_ahead(2, |t| t == &token::Comma)
2625                     || self.look_ahead(2, |t| t == &token::Colon)
2626                         && (
2627                             // `{ ident: token, ` cannot start a block.
2628                             self.look_ahead(4, |t| t == &token::Comma) ||
2629                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2630                 self.look_ahead(3, |t| !t.can_begin_type())
2631                         )
2632             )
2633     }
2634
2635     fn maybe_parse_struct_expr(
2636         &mut self,
2637         qself: Option<&ast::QSelf>,
2638         path: &ast::Path,
2639         attrs: &AttrVec,
2640     ) -> Option<PResult<'a, P<Expr>>> {
2641         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2642         if struct_allowed || self.is_certainly_not_a_block() {
2643             if let Err(err) = self.expect(&token::OpenDelim(token::Brace)) {
2644                 return Some(Err(err));
2645             }
2646             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2647             if let (Ok(expr), false) = (&expr, struct_allowed) {
2648                 // This is a struct literal, but we don't can't accept them here.
2649                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2650             }
2651             return Some(expr);
2652         }
2653         None
2654     }
2655
2656     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2657         self.struct_span_err(sp, "struct literals are not allowed here")
2658             .multipart_suggestion(
2659                 "surround the struct literal with parentheses",
2660                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2661                 Applicability::MachineApplicable,
2662             )
2663             .emit();
2664     }
2665
2666     pub(super) fn parse_struct_fields(
2667         &mut self,
2668         pth: ast::Path,
2669         recover: bool,
2670         close_delim: token::DelimToken,
2671     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2672         let mut fields = Vec::new();
2673         let mut base = ast::StructRest::None;
2674         let mut recover_async = false;
2675
2676         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2677             recover_async = true;
2678             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2679             e.help(&format!("set `edition = \"{}\"` in `Cargo.toml`", LATEST_STABLE_EDITION));
2680             e.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
2681         };
2682
2683         while self.token != token::CloseDelim(close_delim) {
2684             if self.eat(&token::DotDot) {
2685                 let exp_span = self.prev_token.span;
2686                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2687                 if self.check(&token::CloseDelim(close_delim)) {
2688                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2689                     break;
2690                 }
2691                 match self.parse_expr() {
2692                     Ok(e) => base = ast::StructRest::Base(e),
2693                     Err(mut e) if recover => {
2694                         e.emit();
2695                         self.recover_stmt();
2696                     }
2697                     Err(e) => return Err(e),
2698                 }
2699                 self.recover_struct_comma_after_dotdot(exp_span);
2700                 break;
2701             }
2702
2703             let recovery_field = self.find_struct_error_after_field_looking_code();
2704             let parsed_field = match self.parse_expr_field() {
2705                 Ok(f) => Some(f),
2706                 Err(mut e) => {
2707                     if pth == kw::Async {
2708                         async_block_err(&mut e, pth.span);
2709                     } else {
2710                         e.span_label(pth.span, "while parsing this struct");
2711                     }
2712                     e.emit();
2713
2714                     // If the next token is a comma, then try to parse
2715                     // what comes next as additional fields, rather than
2716                     // bailing out until next `}`.
2717                     if self.token != token::Comma {
2718                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2719                         if self.token != token::Comma {
2720                             break;
2721                         }
2722                     }
2723                     None
2724                 }
2725             };
2726
2727             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2728                 Ok(_) => {
2729                     if let Some(f) = parsed_field.or(recovery_field) {
2730                         // Only include the field if there's no parse error for the field name.
2731                         fields.push(f);
2732                     }
2733                 }
2734                 Err(mut e) => {
2735                     if pth == kw::Async {
2736                         async_block_err(&mut e, pth.span);
2737                     } else {
2738                         e.span_label(pth.span, "while parsing this struct");
2739                         if let Some(f) = recovery_field {
2740                             fields.push(f);
2741                             e.span_suggestion(
2742                                 self.prev_token.span.shrink_to_hi(),
2743                                 "try adding a comma",
2744                                 ",".into(),
2745                                 Applicability::MachineApplicable,
2746                             );
2747                         }
2748                     }
2749                     if !recover {
2750                         return Err(e);
2751                     }
2752                     e.emit();
2753                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2754                     self.eat(&token::Comma);
2755                 }
2756             }
2757         }
2758         Ok((fields, base, recover_async))
2759     }
2760
2761     /// Precondition: already parsed the '{'.
2762     pub(super) fn parse_struct_expr(
2763         &mut self,
2764         qself: Option<ast::QSelf>,
2765         pth: ast::Path,
2766         attrs: AttrVec,
2767         recover: bool,
2768     ) -> PResult<'a, P<Expr>> {
2769         let lo = pth.span;
2770         let (fields, base, recover_async) =
2771             self.parse_struct_fields(pth.clone(), recover, token::Brace)?;
2772         let span = lo.to(self.token.span);
2773         self.expect(&token::CloseDelim(token::Brace))?;
2774         let expr = if recover_async {
2775             ExprKind::Err
2776         } else {
2777             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2778         };
2779         Ok(self.mk_expr(span, expr, attrs))
2780     }
2781
2782     /// Use in case of error after field-looking code: `S { foo: () with a }`.
2783     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
2784         match self.token.ident() {
2785             Some((ident, is_raw))
2786                 if (is_raw || !ident.is_reserved())
2787                     && self.look_ahead(1, |t| *t == token::Colon) =>
2788             {
2789                 Some(ast::ExprField {
2790                     ident,
2791                     span: self.token.span,
2792                     expr: self.mk_expr_err(self.token.span),
2793                     is_shorthand: false,
2794                     attrs: AttrVec::new(),
2795                     id: DUMMY_NODE_ID,
2796                     is_placeholder: false,
2797                 })
2798             }
2799             _ => None,
2800         }
2801     }
2802
2803     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
2804         if self.token != token::Comma {
2805             return;
2806         }
2807         self.struct_span_err(
2808             span.to(self.prev_token.span),
2809             "cannot use a comma after the base struct",
2810         )
2811         .span_suggestion_short(
2812             self.token.span,
2813             "remove this comma",
2814             String::new(),
2815             Applicability::MachineApplicable,
2816         )
2817         .note("the base struct must always be the last field")
2818         .emit();
2819         self.recover_stmt();
2820     }
2821
2822     /// Parses `ident (COLON expr)?`.
2823     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
2824         let attrs = self.parse_outer_attributes()?;
2825         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2826             let lo = this.token.span;
2827
2828             // Check if a colon exists one ahead. This means we're parsing a fieldname.
2829             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
2830             let (ident, expr) = if is_shorthand {
2831                 // Mimic `x: x` for the `x` field shorthand.
2832                 let ident = this.parse_ident_common(false)?;
2833                 let path = ast::Path::from_ident(ident);
2834                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
2835             } else {
2836                 let ident = this.parse_field_name()?;
2837                 this.error_on_eq_field_init(ident);
2838                 this.bump(); // `:`
2839                 (ident, this.parse_expr()?)
2840             };
2841
2842             Ok((
2843                 ast::ExprField {
2844                     ident,
2845                     span: lo.to(expr.span),
2846                     expr,
2847                     is_shorthand,
2848                     attrs: attrs.into(),
2849                     id: DUMMY_NODE_ID,
2850                     is_placeholder: false,
2851                 },
2852                 TrailingToken::MaybeComma,
2853             ))
2854         })
2855     }
2856
2857     /// Check for `=`. This means the source incorrectly attempts to
2858     /// initialize a field with an eq rather than a colon.
2859     fn error_on_eq_field_init(&self, field_name: Ident) {
2860         if self.token != token::Eq {
2861             return;
2862         }
2863
2864         self.struct_span_err(self.token.span, "expected `:`, found `=`")
2865             .span_suggestion(
2866                 field_name.span.shrink_to_hi().to(self.token.span),
2867                 "replace equals symbol with a colon",
2868                 ":".to_string(),
2869                 Applicability::MachineApplicable,
2870             )
2871             .emit();
2872     }
2873
2874     fn err_dotdotdot_syntax(&self, span: Span) {
2875         self.struct_span_err(span, "unexpected token: `...`")
2876             .span_suggestion(
2877                 span,
2878                 "use `..` for an exclusive range",
2879                 "..".to_owned(),
2880                 Applicability::MaybeIncorrect,
2881             )
2882             .span_suggestion(
2883                 span,
2884                 "or `..=` for an inclusive range",
2885                 "..=".to_owned(),
2886                 Applicability::MaybeIncorrect,
2887             )
2888             .emit();
2889     }
2890
2891     fn err_larrow_operator(&self, span: Span) {
2892         self.struct_span_err(span, "unexpected token: `<-`")
2893             .span_suggestion(
2894                 span,
2895                 "if you meant to write a comparison against a negative value, add a \
2896              space in between `<` and `-`",
2897                 "< -".to_string(),
2898                 Applicability::MaybeIncorrect,
2899             )
2900             .emit();
2901     }
2902
2903     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2904         ExprKind::AssignOp(binop, lhs, rhs)
2905     }
2906
2907     fn mk_range(
2908         &mut self,
2909         start: Option<P<Expr>>,
2910         end: Option<P<Expr>>,
2911         limits: RangeLimits,
2912     ) -> ExprKind {
2913         if end.is_none() && limits == RangeLimits::Closed {
2914             self.inclusive_range_with_incorrect_end(self.prev_token.span);
2915             ExprKind::Err
2916         } else {
2917             ExprKind::Range(start, end, limits)
2918         }
2919     }
2920
2921     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
2922         ExprKind::Unary(unop, expr)
2923     }
2924
2925     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2926         ExprKind::Binary(binop, lhs, rhs)
2927     }
2928
2929     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
2930         ExprKind::Index(expr, idx)
2931     }
2932
2933     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
2934         ExprKind::Call(f, args)
2935     }
2936
2937     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
2938         let span = lo.to(self.prev_token.span);
2939         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
2940         self.recover_from_await_method_call();
2941         await_expr
2942     }
2943
2944     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
2945         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
2946     }
2947
2948     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
2949         self.mk_expr(span, ExprKind::Err, AttrVec::new())
2950     }
2951
2952     /// Create expression span ensuring the span of the parent node
2953     /// is larger than the span of lhs and rhs, including the attributes.
2954     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
2955         lhs.attrs
2956             .iter()
2957             .find(|a| a.style == AttrStyle::Outer)
2958             .map_or(lhs_span, |a| a.span)
2959             .to(rhs_span)
2960     }
2961
2962     fn collect_tokens_for_expr(
2963         &mut self,
2964         attrs: AttrWrapper,
2965         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
2966     ) -> PResult<'a, P<Expr>> {
2967         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2968             let res = f(this, attrs)?;
2969             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
2970                 && this.token.kind == token::Semi
2971             {
2972                 TrailingToken::Semi
2973             } else {
2974                 // FIXME - pass this through from the place where we know
2975                 // we need a comma, rather than assuming that `#[attr] expr,`
2976                 // always captures a trailing comma
2977                 TrailingToken::MaybeComma
2978             };
2979             Ok((res, trailing))
2980         })
2981     }
2982 }