compiler/rustc_parse/src/parser/expr.rs

   1 use super::diagnostics::SnapshotParser;
   2 use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
   3 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   4 use super::{
   5     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
   6     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
   7 };
   8 use crate::maybe_recover_from_interpolated_ty_qpath;
   9
  10 use ast::token::DelimToken;
  11 use rustc_ast::ptr::P;
  12 use rustc_ast::token::{self, Token, TokenKind};
  13 use rustc_ast::tokenstream::Spacing;
  14 use rustc_ast::util::classify;
  15 use rustc_ast::util::literal::LitError;
  16 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  17 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  18 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  19 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  20 use rustc_ast_pretty::pprust;
  21 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, PResult};
  22 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  23 use rustc_session::lint::BuiltinLintDiagnostics;
  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!("`{bad}` is not a logical operator"))
 446             .span_suggestion_short(
 447                 self.token.span,
 448                 &format!("use `{good}` to perform logical {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.create_snapshot_for_diagnostic();
 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.restore_snapshot(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 {op_verb} the cast value"),
 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.create_snapshot_for_diagnostic(), 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<(SnapshotParser<'a>, 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.restore_snapshot(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 `{name}` is a struct, use braces as delimiters"),
1156                                 vec![
1157                                     (open_paren, " { ".to_string()),
1158                                     (close_paren, " }".to_string()),
1159                                 ],
1160                                 Applicability::MaybeIncorrect,
1161                             );
1162                             err.multipart_suggestion(
1163                                 &format!("if `{name}` is a function, use the arguments directly"),
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             let sp = self.prev_token.span;
1290             self.parse_loop_expr(None, self.prev_token.span, attrs).map_err(|mut err| {
1291                 err.span_label(sp, "while parsing this `loop` expression");
1292                 err
1293             })
1294         } else if self.eat_keyword(kw::Continue) {
1295             let kind = ExprKind::Continue(self.eat_label());
1296             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1297         } else if self.eat_keyword(kw::Match) {
1298             let match_sp = self.prev_token.span;
1299             self.parse_match_expr(attrs).map_err(|mut err| {
1300                 err.span_label(match_sp, "while parsing this `match` expression");
1301                 err
1302             })
1303         } else if self.eat_keyword(kw::Unsafe) {
1304             let sp = self.prev_token.span;
1305             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1306                 .map_err(|mut err| {
1307                     err.span_label(sp, "while parsing this `unsafe` expression");
1308                     err
1309                 })
1310         } else if self.check_inline_const(0) {
1311             self.parse_const_block(lo.to(self.token.span), false)
1312         } else if self.is_do_catch_block() {
1313             self.recover_do_catch(attrs)
1314         } else if self.is_try_block() {
1315             self.expect_keyword(kw::Try)?;
1316             self.parse_try_block(lo, attrs)
1317         } else if self.eat_keyword(kw::Return) {
1318             self.parse_return_expr(attrs)
1319         } else if self.eat_keyword(kw::Break) {
1320             self.parse_break_expr(attrs)
1321         } else if self.eat_keyword(kw::Yield) {
1322             self.parse_yield_expr(attrs)
1323         } else if self.eat_keyword(kw::Let) {
1324             self.parse_let_expr(attrs)
1325         } else if self.eat_keyword(kw::Underscore) {
1326             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1327         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1328             // Don't complain about bare semicolons after unclosed braces
1329             // recovery in order to keep the error count down. Fixing the
1330             // delimiters will possibly also fix the bare semicolon found in
1331             // expression context. For example, silence the following error:
1332             //
1333             //     error: expected expression, found `;`
1334             //      --> file.rs:2:13
1335             //       |
1336             //     2 |     foo(bar(;
1337             //       |             ^ expected expression
1338             self.bump();
1339             Ok(self.mk_expr_err(self.token.span))
1340         } else if self.token.uninterpolated_span().rust_2018() {
1341             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1342             if self.check_keyword(kw::Async) {
1343                 if self.is_async_block() {
1344                     // Check for `async {` and `async move {`.
1345                     self.parse_async_block(attrs)
1346                 } else {
1347                     self.parse_closure_expr(attrs)
1348                 }
1349             } else if self.eat_keyword(kw::Await) {
1350                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1351             } else {
1352                 self.parse_lit_expr(attrs)
1353             }
1354         } else {
1355             self.parse_lit_expr(attrs)
1356         }
1357     }
1358
1359     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1360         let lo = self.token.span;
1361         match self.parse_opt_lit() {
1362             Some(literal) => {
1363                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1364                 self.maybe_recover_from_bad_qpath(expr, true)
1365             }
1366             None => self.try_macro_suggestion(),
1367         }
1368     }
1369
1370     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1371         let lo = self.token.span;
1372         self.expect(&token::OpenDelim(token::Paren))?;
1373         let (es, trailing_comma) = match self.parse_seq_to_end(
1374             &token::CloseDelim(token::Paren),
1375             SeqSep::trailing_allowed(token::Comma),
1376             |p| p.parse_expr_catch_underscore(),
1377         ) {
1378             Ok(x) => x,
1379             Err(err) => return Ok(self.recover_seq_parse_error(token::Paren, lo, Err(err))),
1380         };
1381         let kind = if es.len() == 1 && !trailing_comma {
1382             // `(e)` is parenthesized `e`.
1383             ExprKind::Paren(es.into_iter().next().unwrap())
1384         } else {
1385             // `(e,)` is a tuple with only one field, `e`.
1386             ExprKind::Tup(es)
1387         };
1388         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1389         self.maybe_recover_from_bad_qpath(expr, true)
1390     }
1391
1392     fn parse_array_or_repeat_expr(
1393         &mut self,
1394         attrs: AttrVec,
1395         close_delim: token::DelimToken,
1396     ) -> PResult<'a, P<Expr>> {
1397         let lo = self.token.span;
1398         self.bump(); // `[` or other open delim
1399
1400         let close = &token::CloseDelim(close_delim);
1401         let kind = if self.eat(close) {
1402             // Empty vector
1403             ExprKind::Array(Vec::new())
1404         } else {
1405             // Non-empty vector
1406             let first_expr = self.parse_expr()?;
1407             if self.eat(&token::Semi) {
1408                 // Repeating array syntax: `[ 0; 512 ]`
1409                 let count = self.parse_anon_const_expr()?;
1410                 self.expect(close)?;
1411                 ExprKind::Repeat(first_expr, count)
1412             } else if self.eat(&token::Comma) {
1413                 // Vector with two or more elements.
1414                 let sep = SeqSep::trailing_allowed(token::Comma);
1415                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1416                 let mut exprs = vec![first_expr];
1417                 exprs.extend(remaining_exprs);
1418                 ExprKind::Array(exprs)
1419             } else {
1420                 // Vector with one element
1421                 self.expect(close)?;
1422                 ExprKind::Array(vec![first_expr])
1423             }
1424         };
1425         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1426         self.maybe_recover_from_bad_qpath(expr, true)
1427     }
1428
1429     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1430         let (qself, path) = if self.eat_lt() {
1431             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1432             (Some(qself), path)
1433         } else {
1434             (None, self.parse_path(PathStyle::Expr)?)
1435         };
1436         let lo = path.span;
1437
1438         // `!`, as an operator, is prefix, so we know this isn't that.
1439         let (hi, kind) = if self.eat(&token::Not) {
1440             // MACRO INVOCATION expression
1441             if qself.is_some() {
1442                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1443             }
1444             let mac = MacCall {
1445                 path,
1446                 args: self.parse_mac_args()?,
1447                 prior_type_ascription: self.last_type_ascription,
1448             };
1449             (self.prev_token.span, ExprKind::MacCall(mac))
1450         } else if self.check(&token::OpenDelim(token::Brace)) {
1451             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1452                 if qself.is_some() {
1453                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1454                 }
1455                 return expr;
1456             } else {
1457                 (path.span, ExprKind::Path(qself, path))
1458             }
1459         } else {
1460             (path.span, ExprKind::Path(qself, path))
1461         };
1462
1463         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1464         self.maybe_recover_from_bad_qpath(expr, true)
1465     }
1466
1467     /// Parse `'label: $expr`. The label is already parsed.
1468     fn parse_labeled_expr(
1469         &mut self,
1470         label: Label,
1471         attrs: AttrVec,
1472         mut consume_colon: bool,
1473     ) -> PResult<'a, P<Expr>> {
1474         let lo = label.ident.span;
1475         let label = Some(label);
1476         let ate_colon = self.eat(&token::Colon);
1477         let expr = if self.eat_keyword(kw::While) {
1478             self.parse_while_expr(label, lo, attrs)
1479         } else if self.eat_keyword(kw::For) {
1480             self.parse_for_expr(label, lo, attrs)
1481         } else if self.eat_keyword(kw::Loop) {
1482             self.parse_loop_expr(label, lo, attrs)
1483         } else if self.check(&token::OpenDelim(token::Brace)) || self.token.is_whole_block() {
1484             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1485         } else if !ate_colon && (self.check(&TokenKind::Comma) || self.check(&TokenKind::Gt)) {
1486             // We're probably inside of a `Path<'a>` that needs a turbofish
1487             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1488             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1489             consume_colon = false;
1490             Ok(self.mk_expr_err(lo))
1491         } else {
1492             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1493             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1494             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1495             self.parse_expr()
1496         }?;
1497
1498         if !ate_colon && consume_colon {
1499             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1500         }
1501
1502         Ok(expr)
1503     }
1504
1505     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1506         self.struct_span_err(span, "labeled expression must be followed by `:`")
1507             .span_label(lo, "the label")
1508             .span_suggestion_short(
1509                 lo.shrink_to_hi(),
1510                 "add `:` after the label",
1511                 ": ".to_string(),
1512                 Applicability::MachineApplicable,
1513             )
1514             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1515             .emit();
1516     }
1517
1518     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1519     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1520         let lo = self.token.span;
1521
1522         self.bump(); // `do`
1523         self.bump(); // `catch`
1524
1525         let span_dc = lo.to(self.prev_token.span);
1526         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1527             .span_suggestion(
1528                 span_dc,
1529                 "replace with the new syntax",
1530                 "try".to_string(),
1531                 Applicability::MachineApplicable,
1532             )
1533             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1534             .emit();
1535
1536         self.parse_try_block(lo, attrs)
1537     }
1538
1539     /// Parse an expression if the token can begin one.
1540     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1541         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1542     }
1543
1544     /// Parse `"return" expr?`.
1545     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1546         let lo = self.prev_token.span;
1547         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1548         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1549         self.maybe_recover_from_bad_qpath(expr, true)
1550     }
1551
1552     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1553     /// If the label is followed immediately by a `:` token, the label and `:` are
1554     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1555     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1556     /// the break expression of an unlabeled break is a labeled loop (as in
1557     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1558     /// expression only gets a warning for compatibility reasons; and a labeled break
1559     /// with a labeled loop does not even get a warning because there is no ambiguity.
1560     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1561         let lo = self.prev_token.span;
1562         let mut label = self.eat_label();
1563         let kind = if label.is_some() && self.token == token::Colon {
1564             // The value expression can be a labeled loop, see issue #86948, e.g.:
1565             // `loop { break 'label: loop { break 'label 42; }; }`
1566             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1567             self.struct_span_err(
1568                 lexpr.span,
1569                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1570             )
1571             .multipart_suggestion(
1572                 "wrap the expression in parentheses",
1573                 vec![
1574                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1575                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1576                 ],
1577                 Applicability::MachineApplicable,
1578             )
1579             .emit();
1580             Some(lexpr)
1581         } else if self.token != token::OpenDelim(token::Brace)
1582             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1583         {
1584             let expr = self.parse_expr_opt()?;
1585             if let Some(ref expr) = expr {
1586                 if label.is_some()
1587                     && matches!(
1588                         expr.kind,
1589                         ExprKind::While(_, _, None)
1590                             | ExprKind::ForLoop(_, _, _, None)
1591                             | ExprKind::Loop(_, None)
1592                             | ExprKind::Block(_, None)
1593                     )
1594                 {
1595                     self.sess.buffer_lint_with_diagnostic(
1596                         BREAK_WITH_LABEL_AND_LOOP,
1597                         lo.to(expr.span),
1598                         ast::CRATE_NODE_ID,
1599                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1600                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1601                     );
1602                 }
1603             }
1604             expr
1605         } else {
1606             None
1607         };
1608         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1609         self.maybe_recover_from_bad_qpath(expr, true)
1610     }
1611
1612     /// Parse `"yield" expr?`.
1613     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1614         let lo = self.prev_token.span;
1615         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1616         let span = lo.to(self.prev_token.span);
1617         self.sess.gated_spans.gate(sym::generators, span);
1618         let expr = self.mk_expr(span, kind, attrs);
1619         self.maybe_recover_from_bad_qpath(expr, true)
1620     }
1621
1622     /// Returns a string literal if the next token is a string literal.
1623     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1624     /// and returns `None` if the next token is not literal at all.
1625     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1626         match self.parse_opt_lit() {
1627             Some(lit) => match lit.kind {
1628                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1629                     style,
1630                     symbol: lit.token.symbol,
1631                     suffix: lit.token.suffix,
1632                     span: lit.span,
1633                     symbol_unescaped,
1634                 }),
1635                 _ => Err(Some(lit)),
1636             },
1637             None => Err(None),
1638         }
1639     }
1640
1641     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1642         self.parse_opt_lit().ok_or_else(|| {
1643             if let token::Interpolated(inner) = &self.token.kind {
1644                 let expr = match inner.as_ref() {
1645                     token::NtExpr(expr) => Some(expr),
1646                     token::NtLiteral(expr) => Some(expr),
1647                     _ => None,
1648                 };
1649                 if let Some(expr) = expr {
1650                     if matches!(expr.kind, ExprKind::Err) {
1651                         let mut err = self
1652                             .diagnostic()
1653                             .struct_span_err(self.token.span, &"invalid interpolated expression");
1654                         err.downgrade_to_delayed_bug();
1655                         return err;
1656                     }
1657                 }
1658             }
1659             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1660             self.struct_span_err(self.token.span, &msg)
1661         })
1662     }
1663
1664     /// Matches `lit = true | false | token_lit`.
1665     /// Returns `None` if the next token is not a literal.
1666     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1667         let mut recovered = None;
1668         if self.token == token::Dot {
1669             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1670             // dot would follow an optional literal, so we do this unconditionally.
1671             recovered = self.look_ahead(1, |next_token| {
1672                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1673                     next_token.kind
1674                 {
1675                     if self.token.span.hi() == next_token.span.lo() {
1676                         let s = String::from("0.") + symbol.as_str();
1677                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1678                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1679                     }
1680                 }
1681                 None
1682             });
1683             if let Some(token) = &recovered {
1684                 self.bump();
1685                 self.error_float_lits_must_have_int_part(&token);
1686             }
1687         }
1688
1689         let token = recovered.as_ref().unwrap_or(&self.token);
1690         match Lit::from_token(token) {
1691             Ok(lit) => {
1692                 self.bump();
1693                 Some(lit)
1694             }
1695             Err(LitError::NotLiteral) => None,
1696             Err(err) => {
1697                 let span = token.span;
1698                 let token::Literal(lit) = token.kind else {
1699                     unreachable!();
1700                 };
1701                 self.bump();
1702                 self.report_lit_error(err, lit, span);
1703                 // Pack possible quotes and prefixes from the original literal into
1704                 // the error literal's symbol so they can be pretty-printed faithfully.
1705                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1706                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1707                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1708                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1709             }
1710         }
1711     }
1712
1713     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1714         self.struct_span_err(token.span, "float literals must have an integer part")
1715             .span_suggestion(
1716                 token.span,
1717                 "must have an integer part",
1718                 pprust::token_to_string(token).into(),
1719                 Applicability::MachineApplicable,
1720             )
1721             .emit();
1722     }
1723
1724     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1725         // Checks if `s` looks like i32 or u1234 etc.
1726         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1727             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1728         }
1729
1730         // Try to lowercase the prefix if it's a valid base prefix.
1731         fn fix_base_capitalisation(s: &str) -> Option<String> {
1732             if let Some(stripped) = s.strip_prefix('B') {
1733                 Some(format!("0b{stripped}"))
1734             } else if let Some(stripped) = s.strip_prefix('O') {
1735                 Some(format!("0o{stripped}"))
1736             } else if let Some(stripped) = s.strip_prefix('X') {
1737                 Some(format!("0x{stripped}"))
1738             } else {
1739                 None
1740             }
1741         }
1742
1743         let token::Lit { kind, suffix, .. } = lit;
1744         match err {
1745             // `NotLiteral` is not an error by itself, so we don't report
1746             // it and give the parser opportunity to try something else.
1747             LitError::NotLiteral => {}
1748             // `LexerError` *is* an error, but it was already reported
1749             // by lexer, so here we don't report it the second time.
1750             LitError::LexerError => {}
1751             LitError::InvalidSuffix => {
1752                 self.expect_no_suffix(
1753                     span,
1754                     &format!("{} {} literal", kind.article(), kind.descr()),
1755                     suffix,
1756                 );
1757             }
1758             LitError::InvalidIntSuffix => {
1759                 let suf = suffix.expect("suffix error with no suffix");
1760                 let suf = suf.as_str();
1761                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1762                     // If it looks like a width, try to be helpful.
1763                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1764                     self.struct_span_err(span, &msg)
1765                         .help("valid widths are 8, 16, 32, 64 and 128")
1766                         .emit();
1767                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1768                     let msg = "invalid base prefix for number literal";
1769
1770                     self.struct_span_err(span, &msg)
1771                         .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase")
1772                         .span_suggestion(
1773                             span,
1774                             "try making the prefix lowercase",
1775                             fixed,
1776                             Applicability::MaybeIncorrect,
1777                         )
1778                         .emit();
1779                 } else {
1780                     let msg = format!("invalid suffix `{suf}` for number literal");
1781                     self.struct_span_err(span, &msg)
1782                         .span_label(span, format!("invalid suffix `{suf}`"))
1783                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1784                         .emit();
1785                 }
1786             }
1787             LitError::InvalidFloatSuffix => {
1788                 let suf = suffix.expect("suffix error with no suffix");
1789                 let suf = suf.as_str();
1790                 if looks_like_width_suffix(&['f'], suf) {
1791                     // If it looks like a width, try to be helpful.
1792                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1793                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1794                 } else {
1795                     let msg = format!("invalid suffix `{suf}` for float literal");
1796                     self.struct_span_err(span, &msg)
1797                         .span_label(span, format!("invalid suffix `{suf}`"))
1798                         .help("valid suffixes are `f32` and `f64`")
1799                         .emit();
1800                 }
1801             }
1802             LitError::NonDecimalFloat(base) => {
1803                 let descr = match base {
1804                     16 => "hexadecimal",
1805                     8 => "octal",
1806                     2 => "binary",
1807                     _ => unreachable!(),
1808                 };
1809                 self.struct_span_err(span, &format!("{descr} float literal is not supported"))
1810                     .span_label(span, "not supported")
1811                     .emit();
1812             }
1813             LitError::IntTooLarge => {
1814                 self.struct_span_err(span, "integer literal is too large").emit();
1815             }
1816         }
1817     }
1818
1819     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1820         if let Some(suf) = suffix {
1821             let mut err = if kind == "a tuple index"
1822                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1823             {
1824                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1825                 // through the ecosystem when people fix their macros
1826                 let mut err = self
1827                     .sess
1828                     .span_diagnostic
1829                     .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
1830                 err.note(&format!(
1831                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1832                         incorrectly accepted on stable for a few releases",
1833                     suf,
1834                 ));
1835                 err.help(
1836                     "on proc macros, you'll want to use `syn::Index::from` or \
1837                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1838                         to tuple field access",
1839                 );
1840                 err.note(
1841                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1842                      for more information",
1843                 );
1844                 err
1845             } else {
1846                 self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
1847                     .forget_guarantee()
1848             };
1849             err.span_label(sp, format!("invalid suffix `{suf}`"));
1850             err.emit();
1851         }
1852     }
1853
1854     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1855     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1856     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1857         maybe_whole_expr!(self);
1858
1859         let lo = self.token.span;
1860         let minus_present = self.eat(&token::BinOp(token::Minus));
1861         let lit = self.parse_lit()?;
1862         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
1863
1864         if minus_present {
1865             Ok(self.mk_expr(
1866                 lo.to(self.prev_token.span),
1867                 self.mk_unary(UnOp::Neg, expr),
1868                 AttrVec::new(),
1869             ))
1870         } else {
1871             Ok(expr)
1872         }
1873     }
1874
1875     fn is_array_like_block(&mut self) -> bool {
1876         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1877             && self.look_ahead(2, |t| t == &token::Comma)
1878             && self.look_ahead(3, |t| t.can_begin_expr())
1879     }
1880
1881     /// Emits a suggestion if it looks like the user meant an array but
1882     /// accidentally used braces, causing the code to be interpreted as a block
1883     /// expression.
1884     fn maybe_suggest_brackets_instead_of_braces(
1885         &mut self,
1886         lo: Span,
1887         attrs: AttrVec,
1888     ) -> Option<P<Expr>> {
1889         let mut snapshot = self.create_snapshot_for_diagnostic();
1890         match snapshot.parse_array_or_repeat_expr(attrs, token::Brace) {
1891             Ok(arr) => {
1892                 let hi = snapshot.prev_token.span;
1893                 self.struct_span_err(
1894                     arr.span,
1895                     "this code is interpreted as a block expression, not an array",
1896                 )
1897                 .multipart_suggestion(
1898                     "try using [] instead of {}",
1899                     vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
1900                     Applicability::MaybeIncorrect,
1901                 )
1902                 .note("to define an array, one would use square brackets instead of curly braces")
1903                 .emit();
1904
1905                 self.restore_snapshot(snapshot);
1906                 Some(self.mk_expr_err(arr.span))
1907             }
1908             Err(e) => {
1909                 e.cancel();
1910                 None
1911             }
1912         }
1913     }
1914
1915     /// Parses a block or unsafe block.
1916     pub(super) fn parse_block_expr(
1917         &mut self,
1918         opt_label: Option<Label>,
1919         lo: Span,
1920         blk_mode: BlockCheckMode,
1921         mut attrs: AttrVec,
1922     ) -> PResult<'a, P<Expr>> {
1923         if self.is_array_like_block() {
1924             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) {
1925                 return Ok(arr);
1926             }
1927         }
1928
1929         if let Some(label) = opt_label {
1930             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
1931         }
1932
1933         if self.token.is_whole_block() {
1934             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
1935                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
1936                 .emit();
1937         }
1938
1939         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
1940         attrs.extend(inner_attrs);
1941         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1942     }
1943
1944     /// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`.
1945     fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1946         let lo = self.token.span;
1947         let _ = self.parse_late_bound_lifetime_defs()?;
1948         let span_for = lo.to(self.prev_token.span);
1949         let closure = self.parse_closure_expr(attrs)?;
1950
1951         self.struct_span_err(span_for, "cannot introduce explicit parameters for a closure")
1952             .span_label(closure.span, "the parameters are attached to this closure")
1953             .span_suggestion(
1954                 span_for,
1955                 "remove the parameters",
1956                 String::new(),
1957                 Applicability::MachineApplicable,
1958             )
1959             .emit();
1960
1961         Ok(self.mk_expr_err(lo.to(closure.span)))
1962     }
1963
1964     /// Parses a closure expression (e.g., `move |args| expr`).
1965     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1966         let lo = self.token.span;
1967
1968         let movability =
1969             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
1970
1971         let asyncness = if self.token.uninterpolated_span().rust_2018() {
1972             self.parse_asyncness()
1973         } else {
1974             Async::No
1975         };
1976
1977         let capture_clause = self.parse_capture_clause()?;
1978         let decl = self.parse_fn_block_decl()?;
1979         let decl_hi = self.prev_token.span;
1980         let mut body = match decl.output {
1981             FnRetTy::Default(_) => {
1982                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1983                 self.parse_expr_res(restrictions, None)?
1984             }
1985             _ => {
1986                 // If an explicit return type is given, require a block to appear (RFC 968).
1987                 let body_lo = self.token.span;
1988                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
1989             }
1990         };
1991
1992         if let Async::Yes { span, .. } = asyncness {
1993             // Feature-gate `async ||` closures.
1994             self.sess.gated_spans.gate(sym::async_closure, span);
1995         }
1996
1997         if self.token.kind == TokenKind::Semi && self.token_cursor.frame.delim == DelimToken::Paren
1998         {
1999             // It is likely that the closure body is a block but where the
2000             // braces have been removed. We will recover and eat the next
2001             // statements later in the parsing process.
2002             body = self.mk_expr_err(body.span);
2003         }
2004
2005         let body_span = body.span;
2006
2007         let closure = self.mk_expr(
2008             lo.to(body.span),
2009             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
2010             attrs,
2011         );
2012
2013         // Disable recovery for closure body
2014         let spans =
2015             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2016         self.current_closure = Some(spans);
2017
2018         Ok(closure)
2019     }
2020
2021     /// Parses an optional `move` prefix to a closure-like construct.
2022     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2023         if self.eat_keyword(kw::Move) {
2024             // Check for `move async` and recover
2025             if self.check_keyword(kw::Async) {
2026                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2027                 Err(self.incorrect_move_async_order_found(move_async_span))
2028             } else {
2029                 Ok(CaptureBy::Value)
2030             }
2031         } else {
2032             Ok(CaptureBy::Ref)
2033         }
2034     }
2035
2036     /// Parses the `|arg, arg|` header of a closure.
2037     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2038         let inputs = if self.eat(&token::OrOr) {
2039             Vec::new()
2040         } else {
2041             self.expect(&token::BinOp(token::Or))?;
2042             let args = self
2043                 .parse_seq_to_before_tokens(
2044                     &[&token::BinOp(token::Or), &token::OrOr],
2045                     SeqSep::trailing_allowed(token::Comma),
2046                     TokenExpectType::NoExpect,
2047                     |p| p.parse_fn_block_param(),
2048                 )?
2049                 .0;
2050             self.expect_or()?;
2051             args
2052         };
2053         let output =
2054             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2055
2056         Ok(P(FnDecl { inputs, output }))
2057     }
2058
2059     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2060     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2061         let lo = self.token.span;
2062         let attrs = self.parse_outer_attributes()?;
2063         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2064             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2065             let ty = if this.eat(&token::Colon) {
2066                 this.parse_ty()?
2067             } else {
2068                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2069             };
2070
2071             Ok((
2072                 Param {
2073                     attrs: attrs.into(),
2074                     ty,
2075                     pat,
2076                     span: lo.to(this.token.span),
2077                     id: DUMMY_NODE_ID,
2078                     is_placeholder: false,
2079                 },
2080                 TrailingToken::MaybeComma,
2081             ))
2082         })
2083     }
2084
2085     /// Parses an `if` expression (`if` token already eaten).
2086     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2087         let lo = self.prev_token.span;
2088         let cond = self.parse_cond_expr()?;
2089
2090         let missing_then_block_binop_span = || {
2091             match cond.kind {
2092                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, ref right)
2093                     if let ExprKind::Block(..) = right.kind => Some(binop_span),
2094                 _ => None
2095             }
2096         };
2097
2098         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
2099         // verify that the last statement is either an implicit return (no `;`) or an explicit
2100         // return. This won't catch blocks with an explicit `return`, but that would be caught by
2101         // the dead code lint.
2102         let thn = if self.token.is_keyword(kw::Else) || !cond.returns() {
2103             if let Some(binop_span) = missing_then_block_binop_span() {
2104                 self.error_missing_if_then_block(lo, None, Some(binop_span)).emit();
2105                 self.mk_block_err(cond.span)
2106             } else {
2107                 self.error_missing_if_cond(lo, cond.span)
2108             }
2109         } else {
2110             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2111             let not_block = self.token != token::OpenDelim(token::Brace);
2112             let block = self.parse_block().map_err(|err| {
2113                 if not_block {
2114                     self.error_missing_if_then_block(lo, Some(err), missing_then_block_binop_span())
2115                 } else {
2116                     err
2117                 }
2118             })?;
2119             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2120             block
2121         };
2122         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2123         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
2124     }
2125
2126     fn error_missing_if_then_block(
2127         &self,
2128         if_span: Span,
2129         err: Option<DiagnosticBuilder<'a, ErrorGuaranteed>>,
2130         binop_span: Option<Span>,
2131     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2132         let msg = "this `if` expression has a condition, but no block";
2133
2134         let mut err = if let Some(mut err) = err {
2135             err.span_label(if_span, msg);
2136             err
2137         } else {
2138             self.struct_span_err(if_span, msg)
2139         };
2140
2141         if let Some(binop_span) = binop_span {
2142             err.span_help(binop_span, "maybe you forgot the right operand of the condition?");
2143         }
2144
2145         err
2146     }
2147
2148     fn error_missing_if_cond(&self, lo: Span, span: Span) -> P<ast::Block> {
2149         let sp = self.sess.source_map().next_point(lo);
2150         self.struct_span_err(sp, "missing condition for `if` expression")
2151             .span_label(sp, "expected if condition here")
2152             .emit();
2153         self.mk_block_err(span)
2154     }
2155
2156     /// Parses the condition of a `if` or `while` expression.
2157     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2158         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2159
2160         if let ExprKind::Let(..) = cond.kind {
2161             // Remove the last feature gating of a `let` expression since it's stable.
2162             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2163         }
2164
2165         Ok(cond)
2166     }
2167
2168     /// Parses a `let $pat = $expr` pseudo-expression.
2169     /// The `let` token has already been eaten.
2170     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2171         let lo = self.prev_token.span;
2172         let pat = self.parse_pat_allow_top_alt(
2173             None,
2174             RecoverComma::Yes,
2175             RecoverColon::Yes,
2176             CommaRecoveryMode::LikelyTuple,
2177         )?;
2178         self.expect(&token::Eq)?;
2179         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2180             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2181         })?;
2182         let span = lo.to(expr.span);
2183         self.sess.gated_spans.gate(sym::let_chains, span);
2184         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
2185     }
2186
2187     /// Parses an `else { ... }` expression (`else` token already eaten).
2188     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2189         let ctx_span = self.prev_token.span; // `else`
2190         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2191         let expr = if self.eat_keyword(kw::If) {
2192             self.parse_if_expr(AttrVec::new())?
2193         } else {
2194             let blk = self.parse_block()?;
2195             self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())
2196         };
2197         self.error_on_if_block_attrs(ctx_span, true, expr.span, &attrs);
2198         Ok(expr)
2199     }
2200
2201     fn error_on_if_block_attrs(
2202         &self,
2203         ctx_span: Span,
2204         is_ctx_else: bool,
2205         branch_span: Span,
2206         attrs: &[ast::Attribute],
2207     ) {
2208         let (span, last) = match attrs {
2209             [] => return,
2210             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2211         };
2212         let ctx = if is_ctx_else { "else" } else { "if" };
2213         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
2214             .span_label(branch_span, "the attributes are attached to this branch")
2215             .span_label(ctx_span, format!("the branch belongs to this `{ctx}`"))
2216             .span_suggestion(
2217                 span,
2218                 "remove the attributes",
2219                 String::new(),
2220                 Applicability::MachineApplicable,
2221             )
2222             .emit();
2223     }
2224
2225     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2226     fn parse_for_expr(
2227         &mut self,
2228         opt_label: Option<Label>,
2229         lo: Span,
2230         mut attrs: AttrVec,
2231     ) -> PResult<'a, P<Expr>> {
2232         // Record whether we are about to parse `for (`.
2233         // This is used below for recovery in case of `for ( $stuff ) $block`
2234         // in which case we will suggest `for $stuff $block`.
2235         let begin_paren = match self.token.kind {
2236             token::OpenDelim(token::Paren) => Some(self.token.span),
2237             _ => None,
2238         };
2239
2240         let pat = self.parse_pat_allow_top_alt(
2241             None,
2242             RecoverComma::Yes,
2243             RecoverColon::Yes,
2244             CommaRecoveryMode::LikelyTuple,
2245         )?;
2246         if !self.eat_keyword(kw::In) {
2247             self.error_missing_in_for_loop();
2248         }
2249         self.check_for_for_in_in_typo(self.prev_token.span);
2250         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2251
2252         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2253
2254         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
2255         attrs.extend(iattrs);
2256
2257         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2258         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2259     }
2260
2261     fn error_missing_in_for_loop(&mut self) {
2262         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
2263             // Possibly using JS syntax (#75311).
2264             let span = self.token.span;
2265             self.bump();
2266             (span, "try using `in` here instead", "in")
2267         } else {
2268             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
2269         };
2270         self.struct_span_err(span, "missing `in` in `for` loop")
2271             .span_suggestion_short(
2272                 span,
2273                 msg,
2274                 sugg.into(),
2275                 // Has been misleading, at least in the past (closed Issue #48492).
2276                 Applicability::MaybeIncorrect,
2277             )
2278             .emit();
2279     }
2280
2281     /// Parses a `while` or `while let` expression (`while` token already eaten).
2282     fn parse_while_expr(
2283         &mut self,
2284         opt_label: Option<Label>,
2285         lo: Span,
2286         mut attrs: AttrVec,
2287     ) -> PResult<'a, P<Expr>> {
2288         let cond = self.parse_cond_expr().map_err(|mut err| {
2289             err.span_label(lo, "while parsing the condition of this `while` expression");
2290             err
2291         })?;
2292         let (iattrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2293             err.span_label(lo, "while parsing the body of this `while` expression");
2294             err.span_label(cond.span, "this `while` condition successfully parsed");
2295             err
2296         })?;
2297         attrs.extend(iattrs);
2298         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2299     }
2300
2301     /// Parses `loop { ... }` (`loop` token already eaten).
2302     fn parse_loop_expr(
2303         &mut self,
2304         opt_label: Option<Label>,
2305         lo: Span,
2306         mut attrs: AttrVec,
2307     ) -> PResult<'a, P<Expr>> {
2308         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2309         attrs.extend(iattrs);
2310         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2311     }
2312
2313     crate fn eat_label(&mut self) -> Option<Label> {
2314         self.token.lifetime().map(|ident| {
2315             self.bump();
2316             Label { ident }
2317         })
2318     }
2319
2320     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2321     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2322         let match_span = self.prev_token.span;
2323         let lo = self.prev_token.span;
2324         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2325         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
2326             if self.token == token::Semi {
2327                 e.span_suggestion_short(
2328                     match_span,
2329                     "try removing this `match`",
2330                     String::new(),
2331                     Applicability::MaybeIncorrect, // speculative
2332                 );
2333             }
2334             if self.maybe_recover_unexpected_block_label() {
2335                 e.cancel();
2336                 self.bump();
2337             } else {
2338                 return Err(e);
2339             }
2340         }
2341         attrs.extend(self.parse_inner_attributes()?);
2342
2343         let mut arms: Vec<Arm> = Vec::new();
2344         while self.token != token::CloseDelim(token::Brace) {
2345             match self.parse_arm() {
2346                 Ok(arm) => arms.push(arm),
2347                 Err(mut e) => {
2348                     // Recover by skipping to the end of the block.
2349                     e.emit();
2350                     self.recover_stmt();
2351                     let span = lo.to(self.token.span);
2352                     if self.token == token::CloseDelim(token::Brace) {
2353                         self.bump();
2354                     }
2355                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2356                 }
2357             }
2358         }
2359         let hi = self.token.span;
2360         self.bump();
2361         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2362     }
2363
2364     /// Attempt to recover from match arm body with statements and no surrounding braces.
2365     fn parse_arm_body_missing_braces(
2366         &mut self,
2367         first_expr: &P<Expr>,
2368         arrow_span: Span,
2369     ) -> Option<P<Expr>> {
2370         if self.token.kind != token::Semi {
2371             return None;
2372         }
2373         let start_snapshot = self.create_snapshot_for_diagnostic();
2374         let semi_sp = self.token.span;
2375         self.bump(); // `;`
2376         let mut stmts =
2377             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2378         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2379             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2380             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2381             let (these, s, are) =
2382                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2383             err.span_label(
2384                 span,
2385                 &format!(
2386                     "{these} statement{s} {are} not surrounded by a body",
2387                     these = these,
2388                     s = s,
2389                     are = are
2390                 ),
2391             );
2392             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2393             if stmts.len() > 1 {
2394                 err.multipart_suggestion(
2395                     &format!("surround the statement{s} with a body"),
2396                     vec![
2397                         (span.shrink_to_lo(), "{ ".to_string()),
2398                         (span.shrink_to_hi(), " }".to_string()),
2399                     ],
2400                     Applicability::MachineApplicable,
2401                 );
2402             } else {
2403                 err.span_suggestion(
2404                     semi_sp,
2405                     "use a comma to end a `match` arm expression",
2406                     ",".to_string(),
2407                     Applicability::MachineApplicable,
2408                 );
2409             }
2410             err.emit();
2411             this.mk_expr_err(span)
2412         };
2413         // We might have either a `,` -> `;` typo, or a block without braces. We need
2414         // a more subtle parsing strategy.
2415         loop {
2416             if self.token.kind == token::CloseDelim(token::Brace) {
2417                 // We have reached the closing brace of the `match` expression.
2418                 return Some(err(self, stmts));
2419             }
2420             if self.token.kind == token::Comma {
2421                 self.restore_snapshot(start_snapshot);
2422                 return None;
2423             }
2424             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2425             match self.parse_pat_no_top_alt(None) {
2426                 Ok(_pat) => {
2427                     if self.token.kind == token::FatArrow {
2428                         // Reached arm end.
2429                         self.restore_snapshot(pre_pat_snapshot);
2430                         return Some(err(self, stmts));
2431                     }
2432                 }
2433                 Err(err) => {
2434                     err.cancel();
2435                 }
2436             }
2437
2438             self.restore_snapshot(pre_pat_snapshot);
2439             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2440                 // Consume statements for as long as possible.
2441                 Ok(Some(stmt)) => {
2442                     stmts.push(stmt);
2443                 }
2444                 Ok(None) => {
2445                     self.restore_snapshot(start_snapshot);
2446                     break;
2447                 }
2448                 // We couldn't parse either yet another statement missing it's
2449                 // enclosing block nor the next arm's pattern or closing brace.
2450                 Err(stmt_err) => {
2451                     stmt_err.cancel();
2452                     self.restore_snapshot(start_snapshot);
2453                     break;
2454                 }
2455             }
2456         }
2457         None
2458     }
2459
2460     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2461         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2462             match expr.kind {
2463                 ExprKind::Binary(_, ref lhs, ref rhs) => {
2464                     let lhs_rslt = check_let_expr(lhs);
2465                     let rhs_rslt = check_let_expr(rhs);
2466                     (lhs_rslt.0 || rhs_rslt.0, false)
2467                 }
2468                 ExprKind::Let(..) => (true, true),
2469                 _ => (false, true),
2470             }
2471         }
2472         let attrs = self.parse_outer_attributes()?;
2473         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2474             let lo = this.token.span;
2475             let pat = this.parse_pat_allow_top_alt(
2476                 None,
2477                 RecoverComma::Yes,
2478                 RecoverColon::Yes,
2479                 CommaRecoveryMode::EitherTupleOrPipe,
2480             )?;
2481             let guard = if this.eat_keyword(kw::If) {
2482                 let if_span = this.prev_token.span;
2483                 let cond = this.parse_expr()?;
2484                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2485                 if has_let_expr {
2486                     if does_not_have_bin_op {
2487                         // Remove the last feature gating of a `let` expression since it's stable.
2488                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2489                     }
2490                     let span = if_span.to(cond.span);
2491                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2492                 }
2493                 Some(cond)
2494             } else {
2495                 None
2496             };
2497             let arrow_span = this.token.span;
2498             if let Err(mut err) = this.expect(&token::FatArrow) {
2499                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2500                 if TokenKind::FatArrow
2501                     .similar_tokens()
2502                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2503                 {
2504                     err.span_suggestion(
2505                         this.token.span,
2506                         "try using a fat arrow here",
2507                         "=>".to_string(),
2508                         Applicability::MaybeIncorrect,
2509                     );
2510                     err.emit();
2511                     this.bump();
2512                 } else {
2513                     return Err(err);
2514                 }
2515             }
2516             let arm_start_span = this.token.span;
2517
2518             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2519                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2520                 err
2521             })?;
2522
2523             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2524                 && this.token != token::CloseDelim(token::Brace);
2525
2526             let hi = this.prev_token.span;
2527
2528             if require_comma {
2529                 let sm = this.sess.source_map();
2530                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2531                     let span = body.span;
2532                     return Ok((
2533                         ast::Arm {
2534                             attrs: attrs.into(),
2535                             pat,
2536                             guard,
2537                             body,
2538                             span,
2539                             id: DUMMY_NODE_ID,
2540                             is_placeholder: false,
2541                         },
2542                         TrailingToken::None,
2543                     ));
2544                 }
2545                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]).map_err(
2546                     |mut err| {
2547                         match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) {
2548                             (Ok(ref expr_lines), Ok(ref arm_start_lines))
2549                                 if arm_start_lines.lines[0].end_col
2550                                     == expr_lines.lines[0].end_col
2551                                     && expr_lines.lines.len() == 2
2552                                     && this.token == token::FatArrow =>
2553                             {
2554                                 // We check whether there's any trailing code in the parse span,
2555                                 // if there isn't, we very likely have the following:
2556                                 //
2557                                 // X |     &Y => "y"
2558                                 //   |        --    - missing comma
2559                                 //   |        |
2560                                 //   |        arrow_span
2561                                 // X |     &X => "x"
2562                                 //   |      - ^^ self.token.span
2563                                 //   |      |
2564                                 //   |      parsed until here as `"y" & X`
2565                                 err.span_suggestion_short(
2566                                     arm_start_span.shrink_to_hi(),
2567                                     "missing a comma here to end this `match` arm",
2568                                     ",".to_owned(),
2569                                     Applicability::MachineApplicable,
2570                                 );
2571                             }
2572                             _ => {
2573                                 err.span_label(
2574                                     arrow_span,
2575                                     "while parsing the `match` arm starting here",
2576                                 );
2577                             }
2578                         }
2579                         err
2580                     },
2581                 )?;
2582             } else {
2583                 this.eat(&token::Comma);
2584             }
2585
2586             Ok((
2587                 ast::Arm {
2588                     attrs: attrs.into(),
2589                     pat,
2590                     guard,
2591                     body: expr,
2592                     span: lo.to(hi),
2593                     id: DUMMY_NODE_ID,
2594                     is_placeholder: false,
2595                 },
2596                 TrailingToken::None,
2597             ))
2598         })
2599     }
2600
2601     /// Parses a `try {...}` expression (`try` token already eaten).
2602     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2603         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2604         attrs.extend(iattrs);
2605         if self.eat_keyword(kw::Catch) {
2606             let mut error = self.struct_span_err(
2607                 self.prev_token.span,
2608                 "keyword `catch` cannot follow a `try` block",
2609             );
2610             error.help("try using `match` on the result of the `try` block instead");
2611             error.emit();
2612             Err(error)
2613         } else {
2614             let span = span_lo.to(body.span);
2615             self.sess.gated_spans.gate(sym::try_blocks, span);
2616             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2617         }
2618     }
2619
2620     fn is_do_catch_block(&self) -> bool {
2621         self.token.is_keyword(kw::Do)
2622             && self.is_keyword_ahead(1, &[kw::Catch])
2623             && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2624             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2625     }
2626
2627     fn is_try_block(&self) -> bool {
2628         self.token.is_keyword(kw::Try)
2629             && self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2630             && self.token.uninterpolated_span().rust_2018()
2631     }
2632
2633     /// Parses an `async move? {...}` expression.
2634     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2635         let lo = self.token.span;
2636         self.expect_keyword(kw::Async)?;
2637         let capture_clause = self.parse_capture_clause()?;
2638         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2639         attrs.extend(iattrs);
2640         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2641         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2642     }
2643
2644     fn is_async_block(&self) -> bool {
2645         self.token.is_keyword(kw::Async)
2646             && ((
2647                 // `async move {`
2648                 self.is_keyword_ahead(1, &[kw::Move])
2649                     && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2650             ) || (
2651                 // `async {`
2652                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2653             ))
2654     }
2655
2656     fn is_certainly_not_a_block(&self) -> bool {
2657         self.look_ahead(1, |t| t.is_ident())
2658             && (
2659                 // `{ ident, ` cannot start a block.
2660                 self.look_ahead(2, |t| t == &token::Comma)
2661                     || self.look_ahead(2, |t| t == &token::Colon)
2662                         && (
2663                             // `{ ident: token, ` cannot start a block.
2664                             self.look_ahead(4, |t| t == &token::Comma) ||
2665                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2666                 self.look_ahead(3, |t| !t.can_begin_type())
2667                         )
2668             )
2669     }
2670
2671     fn maybe_parse_struct_expr(
2672         &mut self,
2673         qself: Option<&ast::QSelf>,
2674         path: &ast::Path,
2675         attrs: &AttrVec,
2676     ) -> Option<PResult<'a, P<Expr>>> {
2677         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2678         if struct_allowed || self.is_certainly_not_a_block() {
2679             if let Err(err) = self.expect(&token::OpenDelim(token::Brace)) {
2680                 return Some(Err(err));
2681             }
2682             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2683             if let (Ok(expr), false) = (&expr, struct_allowed) {
2684                 // This is a struct literal, but we don't can't accept them here.
2685                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2686             }
2687             return Some(expr);
2688         }
2689         None
2690     }
2691
2692     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2693         self.struct_span_err(sp, "struct literals are not allowed here")
2694             .multipart_suggestion(
2695                 "surround the struct literal with parentheses",
2696                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2697                 Applicability::MachineApplicable,
2698             )
2699             .emit();
2700     }
2701
2702     pub(super) fn parse_struct_fields(
2703         &mut self,
2704         pth: ast::Path,
2705         recover: bool,
2706         close_delim: token::DelimToken,
2707     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2708         let mut fields = Vec::new();
2709         let mut base = ast::StructRest::None;
2710         let mut recover_async = false;
2711
2712         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2713             recover_async = true;
2714             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2715             e.help_use_latest_edition();
2716         };
2717
2718         while self.token != token::CloseDelim(close_delim) {
2719             if self.eat(&token::DotDot) {
2720                 let exp_span = self.prev_token.span;
2721                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2722                 if self.check(&token::CloseDelim(close_delim)) {
2723                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2724                     break;
2725                 }
2726                 match self.parse_expr() {
2727                     Ok(e) => base = ast::StructRest::Base(e),
2728                     Err(mut e) if recover => {
2729                         e.emit();
2730                         self.recover_stmt();
2731                     }
2732                     Err(e) => return Err(e),
2733                 }
2734                 self.recover_struct_comma_after_dotdot(exp_span);
2735                 break;
2736             }
2737
2738             let recovery_field = self.find_struct_error_after_field_looking_code();
2739             let parsed_field = match self.parse_expr_field() {
2740                 Ok(f) => Some(f),
2741                 Err(mut e) => {
2742                     if pth == kw::Async {
2743                         async_block_err(&mut e, pth.span);
2744                     } else {
2745                         e.span_label(pth.span, "while parsing this struct");
2746                     }
2747                     e.emit();
2748
2749                     // If the next token is a comma, then try to parse
2750                     // what comes next as additional fields, rather than
2751                     // bailing out until next `}`.
2752                     if self.token != token::Comma {
2753                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2754                         if self.token != token::Comma {
2755                             break;
2756                         }
2757                     }
2758                     None
2759                 }
2760             };
2761
2762             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2763                 Ok(_) => {
2764                     if let Some(f) = parsed_field.or(recovery_field) {
2765                         // Only include the field if there's no parse error for the field name.
2766                         fields.push(f);
2767                     }
2768                 }
2769                 Err(mut e) => {
2770                     if pth == kw::Async {
2771                         async_block_err(&mut e, pth.span);
2772                     } else {
2773                         e.span_label(pth.span, "while parsing this struct");
2774                         if let Some(f) = recovery_field {
2775                             fields.push(f);
2776                             e.span_suggestion(
2777                                 self.prev_token.span.shrink_to_hi(),
2778                                 "try adding a comma",
2779                                 ",".into(),
2780                                 Applicability::MachineApplicable,
2781                             );
2782                         }
2783                     }
2784                     if !recover {
2785                         return Err(e);
2786                     }
2787                     e.emit();
2788                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2789                     self.eat(&token::Comma);
2790                 }
2791             }
2792         }
2793         Ok((fields, base, recover_async))
2794     }
2795
2796     /// Precondition: already parsed the '{'.
2797     pub(super) fn parse_struct_expr(
2798         &mut self,
2799         qself: Option<ast::QSelf>,
2800         pth: ast::Path,
2801         attrs: AttrVec,
2802         recover: bool,
2803     ) -> PResult<'a, P<Expr>> {
2804         let lo = pth.span;
2805         let (fields, base, recover_async) =
2806             self.parse_struct_fields(pth.clone(), recover, token::Brace)?;
2807         let span = lo.to(self.token.span);
2808         self.expect(&token::CloseDelim(token::Brace))?;
2809         let expr = if recover_async {
2810             ExprKind::Err
2811         } else {
2812             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2813         };
2814         Ok(self.mk_expr(span, expr, attrs))
2815     }
2816
2817     /// Use in case of error after field-looking code: `S { foo: () with a }`.
2818     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
2819         match self.token.ident() {
2820             Some((ident, is_raw))
2821                 if (is_raw || !ident.is_reserved())
2822                     && self.look_ahead(1, |t| *t == token::Colon) =>
2823             {
2824                 Some(ast::ExprField {
2825                     ident,
2826                     span: self.token.span,
2827                     expr: self.mk_expr_err(self.token.span),
2828                     is_shorthand: false,
2829                     attrs: AttrVec::new(),
2830                     id: DUMMY_NODE_ID,
2831                     is_placeholder: false,
2832                 })
2833             }
2834             _ => None,
2835         }
2836     }
2837
2838     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
2839         if self.token != token::Comma {
2840             return;
2841         }
2842         self.struct_span_err(
2843             span.to(self.prev_token.span),
2844             "cannot use a comma after the base struct",
2845         )
2846         .span_suggestion_short(
2847             self.token.span,
2848             "remove this comma",
2849             String::new(),
2850             Applicability::MachineApplicable,
2851         )
2852         .note("the base struct must always be the last field")
2853         .emit();
2854         self.recover_stmt();
2855     }
2856
2857     /// Parses `ident (COLON expr)?`.
2858     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
2859         let attrs = self.parse_outer_attributes()?;
2860         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2861             let lo = this.token.span;
2862
2863             // Check if a colon exists one ahead. This means we're parsing a fieldname.
2864             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
2865             let (ident, expr) = if is_shorthand {
2866                 // Mimic `x: x` for the `x` field shorthand.
2867                 let ident = this.parse_ident_common(false)?;
2868                 let path = ast::Path::from_ident(ident);
2869                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
2870             } else {
2871                 let ident = this.parse_field_name()?;
2872                 this.error_on_eq_field_init(ident);
2873                 this.bump(); // `:`
2874                 (ident, this.parse_expr()?)
2875             };
2876
2877             Ok((
2878                 ast::ExprField {
2879                     ident,
2880                     span: lo.to(expr.span),
2881                     expr,
2882                     is_shorthand,
2883                     attrs: attrs.into(),
2884                     id: DUMMY_NODE_ID,
2885                     is_placeholder: false,
2886                 },
2887                 TrailingToken::MaybeComma,
2888             ))
2889         })
2890     }
2891
2892     /// Check for `=`. This means the source incorrectly attempts to
2893     /// initialize a field with an eq rather than a colon.
2894     fn error_on_eq_field_init(&self, field_name: Ident) {
2895         if self.token != token::Eq {
2896             return;
2897         }
2898
2899         self.struct_span_err(self.token.span, "expected `:`, found `=`")
2900             .span_suggestion(
2901                 field_name.span.shrink_to_hi().to(self.token.span),
2902                 "replace equals symbol with a colon",
2903                 ":".to_string(),
2904                 Applicability::MachineApplicable,
2905             )
2906             .emit();
2907     }
2908
2909     fn err_dotdotdot_syntax(&self, span: Span) {
2910         self.struct_span_err(span, "unexpected token: `...`")
2911             .span_suggestion(
2912                 span,
2913                 "use `..` for an exclusive range",
2914                 "..".to_owned(),
2915                 Applicability::MaybeIncorrect,
2916             )
2917             .span_suggestion(
2918                 span,
2919                 "or `..=` for an inclusive range",
2920                 "..=".to_owned(),
2921                 Applicability::MaybeIncorrect,
2922             )
2923             .emit();
2924     }
2925
2926     fn err_larrow_operator(&self, span: Span) {
2927         self.struct_span_err(span, "unexpected token: `<-`")
2928             .span_suggestion(
2929                 span,
2930                 "if you meant to write a comparison against a negative value, add a \
2931              space in between `<` and `-`",
2932                 "< -".to_string(),
2933                 Applicability::MaybeIncorrect,
2934             )
2935             .emit();
2936     }
2937
2938     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2939         ExprKind::AssignOp(binop, lhs, rhs)
2940     }
2941
2942     fn mk_range(
2943         &mut self,
2944         start: Option<P<Expr>>,
2945         end: Option<P<Expr>>,
2946         limits: RangeLimits,
2947     ) -> ExprKind {
2948         if end.is_none() && limits == RangeLimits::Closed {
2949             self.inclusive_range_with_incorrect_end(self.prev_token.span);
2950             ExprKind::Err
2951         } else {
2952             ExprKind::Range(start, end, limits)
2953         }
2954     }
2955
2956     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
2957         ExprKind::Unary(unop, expr)
2958     }
2959
2960     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2961         ExprKind::Binary(binop, lhs, rhs)
2962     }
2963
2964     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
2965         ExprKind::Index(expr, idx)
2966     }
2967
2968     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
2969         ExprKind::Call(f, args)
2970     }
2971
2972     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
2973         let span = lo.to(self.prev_token.span);
2974         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
2975         self.recover_from_await_method_call();
2976         await_expr
2977     }
2978
2979     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
2980         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
2981     }
2982
2983     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
2984         self.mk_expr(span, ExprKind::Err, AttrVec::new())
2985     }
2986
2987     /// Create expression span ensuring the span of the parent node
2988     /// is larger than the span of lhs and rhs, including the attributes.
2989     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
2990         lhs.attrs
2991             .iter()
2992             .find(|a| a.style == AttrStyle::Outer)
2993             .map_or(lhs_span, |a| a.span)
2994             .to(rhs_span)
2995     }
2996
2997     fn collect_tokens_for_expr(
2998         &mut self,
2999         attrs: AttrWrapper,
3000         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
3001     ) -> PResult<'a, P<Expr>> {
3002         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3003             let res = f(this, attrs)?;
3004             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3005                 && this.token.kind == token::Semi
3006             {
3007                 TrailingToken::Semi
3008             } else {
3009                 // FIXME - pass this through from the place where we know
3010                 // we need a comma, rather than assuming that `#[attr] expr,`
3011                 // always captures a trailing comma
3012                 TrailingToken::MaybeComma
3013             };
3014             Ok((res, trailing))
3015         })
3016     }
3017 }