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 core::mem;
  11 use rustc_ast::ptr::P;
  12 use rustc_ast::token::{self, Delimiter, 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::visit::Visitor;
  18 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  19 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  20 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  21 use rustc_ast::{ClosureBinder, StmtKind};
  22 use rustc_ast_pretty::pprust;
  23 use rustc_data_structures::thin_vec::ThinVec;
  24 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, PResult};
  25 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  26 use rustc_session::lint::BuiltinLintDiagnostics;
  27 use rustc_span::source_map::{self, Span, Spanned};
  28 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  29 use rustc_span::{BytePos, Pos};
  30
  31 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  32 /// dropped into the token stream, which happens while parsing the result of
  33 /// macro expansion). Placement of these is not as complex as I feared it would
  34 /// be. The important thing is to make sure that lookahead doesn't balk at
  35 /// `token::Interpolated` tokens.
  36 macro_rules! maybe_whole_expr {
  37     ($p:expr) => {
  38         if let token::Interpolated(nt) = &$p.token.kind {
  39             match &**nt {
  40                 token::NtExpr(e) | token::NtLiteral(e) => {
  41                     let e = e.clone();
  42                     $p.bump();
  43                     return Ok(e);
  44                 }
  45                 token::NtPath(path) => {
  46                     let path = (**path).clone();
  47                     $p.bump();
  48                     return Ok($p.mk_expr(
  49                         $p.prev_token.span,
  50                         ExprKind::Path(None, path),
  51                         AttrVec::new(),
  52                     ));
  53                 }
  54                 token::NtBlock(block) => {
  55                     let block = block.clone();
  56                     $p.bump();
  57                     return Ok($p.mk_expr(
  58                         $p.prev_token.span,
  59                         ExprKind::Block(block, None),
  60                         AttrVec::new(),
  61                     ));
  62                 }
  63                 _ => {}
  64             };
  65         }
  66     };
  67 }
  68
  69 #[derive(Debug)]
  70 pub(super) enum LhsExpr {
  71     NotYetParsed,
  72     AttributesParsed(AttrWrapper),
  73     AlreadyParsed(P<Expr>),
  74 }
  75
  76 impl From<Option<AttrWrapper>> for LhsExpr {
  77     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  78     /// and `None` into `LhsExpr::NotYetParsed`.
  79     ///
  80     /// This conversion does not allocate.
  81     fn from(o: Option<AttrWrapper>) -> Self {
  82         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
  83     }
  84 }
  85
  86 impl From<P<Expr>> for LhsExpr {
  87     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
  88     ///
  89     /// This conversion does not allocate.
  90     fn from(expr: P<Expr>) -> Self {
  91         LhsExpr::AlreadyParsed(expr)
  92     }
  93 }
  94
  95 impl<'a> Parser<'a> {
  96     /// Parses an expression.
  97     #[inline]
  98     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
  99         self.current_closure.take();
 100
 101         self.parse_expr_res(Restrictions::empty(), None)
 102     }
 103
 104     /// Parses an expression, forcing tokens to be collected
 105     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 106         self.collect_tokens_no_attrs(|this| this.parse_expr())
 107     }
 108
 109     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 110         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 111     }
 112
 113     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 114         match self.parse_expr() {
 115             Ok(expr) => Ok(expr),
 116             Err(mut err) => match self.token.ident() {
 117                 Some((Ident { name: kw::Underscore, .. }, false))
 118                     if self.look_ahead(1, |t| t == &token::Comma) =>
 119                 {
 120                     // Special-case handling of `foo(_, _, _)`
 121                     err.emit();
 122                     self.bump();
 123                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err, AttrVec::new()))
 124                 }
 125                 _ => Err(err),
 126             },
 127         }
 128     }
 129
 130     /// Parses a sequence of expressions delimited by parentheses.
 131     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 132         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 133     }
 134
 135     /// Parses an expression, subject to the given restrictions.
 136     #[inline]
 137     pub(super) fn parse_expr_res(
 138         &mut self,
 139         r: Restrictions,
 140         already_parsed_attrs: Option<AttrWrapper>,
 141     ) -> PResult<'a, P<Expr>> {
 142         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 143     }
 144
 145     /// Parses an associative expression.
 146     ///
 147     /// This parses an expression accounting for associativity and precedence of the operators in
 148     /// the expression.
 149     #[inline]
 150     fn parse_assoc_expr(
 151         &mut self,
 152         already_parsed_attrs: Option<AttrWrapper>,
 153     ) -> PResult<'a, P<Expr>> {
 154         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 155     }
 156
 157     /// Parses an associative expression with operators of at least `min_prec` precedence.
 158     pub(super) fn parse_assoc_expr_with(
 159         &mut self,
 160         min_prec: usize,
 161         lhs: LhsExpr,
 162     ) -> PResult<'a, P<Expr>> {
 163         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 164             expr
 165         } else {
 166             let attrs = match lhs {
 167                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 168                 _ => None,
 169             };
 170             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 171                 return self.parse_prefix_range_expr(attrs);
 172             } else {
 173                 self.parse_prefix_expr(attrs)?
 174             }
 175         };
 176         let last_type_ascription_set = self.last_type_ascription.is_some();
 177
 178         if !self.should_continue_as_assoc_expr(&lhs) {
 179             self.last_type_ascription = None;
 180             return Ok(lhs);
 181         }
 182
 183         self.expected_tokens.push(TokenType::Operator);
 184         while let Some(op) = self.check_assoc_op() {
 185             // Adjust the span for interpolated LHS to point to the `$lhs` token
 186             // and not to what it refers to.
 187             let lhs_span = match self.prev_token.kind {
 188                 TokenKind::Interpolated(..) => self.prev_token.span,
 189                 _ => lhs.span,
 190             };
 191
 192             let cur_op_span = self.token.span;
 193             let restrictions = if op.node.is_assign_like() {
 194                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 195             } else {
 196                 self.restrictions
 197             };
 198             let prec = op.node.precedence();
 199             if prec < min_prec {
 200                 break;
 201             }
 202             // Check for deprecated `...` syntax
 203             if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
 204                 self.err_dotdotdot_syntax(self.token.span);
 205             }
 206
 207             if self.token == token::LArrow {
 208                 self.err_larrow_operator(self.token.span);
 209             }
 210
 211             self.bump();
 212             if op.node.is_comparison() {
 213                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 214                     return Ok(expr);
 215                 }
 216             }
 217
 218             // Look for JS' `===` and `!==` and recover
 219             if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
 220                 && self.token.kind == token::Eq
 221                 && self.prev_token.span.hi() == self.token.span.lo()
 222             {
 223                 let sp = op.span.to(self.token.span);
 224                 let sugg = match op.node {
 225                     AssocOp::Equal => "==",
 226                     AssocOp::NotEqual => "!=",
 227                     _ => unreachable!(),
 228                 };
 229                 self.struct_span_err(sp, &format!("invalid comparison operator `{sugg}=`"))
 230                     .span_suggestion_short(
 231                         sp,
 232                         &format!("`{s}=` is not a valid comparison operator, use `{s}`", s = sugg),
 233                         sugg,
 234                         Applicability::MachineApplicable,
 235                     )
 236                     .emit();
 237                 self.bump();
 238             }
 239
 240             // Look for PHP's `<>` and recover
 241             if op.node == AssocOp::Less
 242                 && self.token.kind == token::Gt
 243                 && self.prev_token.span.hi() == self.token.span.lo()
 244             {
 245                 let sp = op.span.to(self.token.span);
 246                 self.struct_span_err(sp, "invalid comparison operator `<>`")
 247                     .span_suggestion_short(
 248                         sp,
 249                         "`<>` is not a valid comparison operator, use `!=`",
 250                         "!=",
 251                         Applicability::MachineApplicable,
 252                     )
 253                     .emit();
 254                 self.bump();
 255             }
 256
 257             // Look for C++'s `<=>` and recover
 258             if op.node == AssocOp::LessEqual
 259                 && self.token.kind == token::Gt
 260                 && self.prev_token.span.hi() == self.token.span.lo()
 261             {
 262                 let sp = op.span.to(self.token.span);
 263                 self.struct_span_err(sp, "invalid comparison operator `<=>`")
 264                     .span_label(
 265                         sp,
 266                         "`<=>` is not a valid comparison operator, use `std::cmp::Ordering`",
 267                     )
 268                     .emit();
 269                 self.bump();
 270             }
 271
 272             if self.prev_token == token::BinOp(token::Plus)
 273                 && self.token == token::BinOp(token::Plus)
 274                 && self.prev_token.span.between(self.token.span).is_empty()
 275             {
 276                 let op_span = self.prev_token.span.to(self.token.span);
 277                 // Eat the second `+`
 278                 self.bump();
 279                 lhs = self.recover_from_postfix_increment(lhs, op_span)?;
 280                 continue;
 281             }
 282
 283             let op = op.node;
 284             // Special cases:
 285             if op == AssocOp::As {
 286                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 287                 continue;
 288             } else if op == AssocOp::Colon {
 289                 lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
 290                 continue;
 291             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 292                 // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
 293                 // generalise it to the Fixity::None code.
 294                 lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?;
 295                 break;
 296             }
 297
 298             let fixity = op.fixity();
 299             let prec_adjustment = match fixity {
 300                 Fixity::Right => 0,
 301                 Fixity::Left => 1,
 302                 // We currently have no non-associative operators that are not handled above by
 303                 // the special cases. The code is here only for future convenience.
 304                 Fixity::None => 1,
 305             };
 306             let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
 307                 this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 308             })?;
 309
 310             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
 311             lhs = match op {
 312                 AssocOp::Add
 313                 | AssocOp::Subtract
 314                 | AssocOp::Multiply
 315                 | AssocOp::Divide
 316                 | AssocOp::Modulus
 317                 | AssocOp::LAnd
 318                 | AssocOp::LOr
 319                 | AssocOp::BitXor
 320                 | AssocOp::BitAnd
 321                 | AssocOp::BitOr
 322                 | AssocOp::ShiftLeft
 323                 | AssocOp::ShiftRight
 324                 | AssocOp::Equal
 325                 | AssocOp::Less
 326                 | AssocOp::LessEqual
 327                 | AssocOp::NotEqual
 328                 | AssocOp::Greater
 329                 | AssocOp::GreaterEqual => {
 330                     let ast_op = op.to_ast_binop().unwrap();
 331                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 332                     self.mk_expr(span, binary, AttrVec::new())
 333                 }
 334                 AssocOp::Assign => {
 335                     self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span), AttrVec::new())
 336                 }
 337                 AssocOp::AssignOp(k) => {
 338                     let aop = match k {
 339                         token::Plus => BinOpKind::Add,
 340                         token::Minus => BinOpKind::Sub,
 341                         token::Star => BinOpKind::Mul,
 342                         token::Slash => BinOpKind::Div,
 343                         token::Percent => BinOpKind::Rem,
 344                         token::Caret => BinOpKind::BitXor,
 345                         token::And => BinOpKind::BitAnd,
 346                         token::Or => BinOpKind::BitOr,
 347                         token::Shl => BinOpKind::Shl,
 348                         token::Shr => BinOpKind::Shr,
 349                     };
 350                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 351                     self.mk_expr(span, aopexpr, AttrVec::new())
 352                 }
 353                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 354                     self.span_bug(span, "AssocOp should have been handled by special case")
 355                 }
 356             };
 357
 358             if let Fixity::None = fixity {
 359                 break;
 360             }
 361         }
 362         if last_type_ascription_set {
 363             self.last_type_ascription = None;
 364         }
 365         Ok(lhs)
 366     }
 367
 368     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 369         match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
 370             // Semi-statement forms are odd:
 371             // See https://github.com/rust-lang/rust/issues/29071
 372             (true, None) => false,
 373             (false, _) => true, // Continue parsing the expression.
 374             // An exhaustive check is done in the following block, but these are checked first
 375             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 376             // want to keep their span info to improve diagnostics in these cases in a later stage.
 377             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 378             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 379             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 380             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 381             // `if x { a } else { b } && if y { c } else { d }`
 382             if !self.look_ahead(1, |t| t.is_used_keyword()) => {
 383                 // These cases are ambiguous and can't be identified in the parser alone.
 384                 let sp = self.sess.source_map().start_point(self.token.span);
 385                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 386                 false
 387             }
 388             (true, Some(AssocOp::LAnd)) |
 389             (true, Some(AssocOp::LOr)) |
 390             (true, Some(AssocOp::BitOr)) => {
 391                 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the
 392                 // above due to #74233.
 393                 // These cases are ambiguous and can't be identified in the parser alone.
 394                 //
 395                 // Bitwise AND is left out because guessing intent is hard. We can make
 396                 // suggestions based on the assumption that double-refs are rarely intentional,
 397                 // and closures are distinct enough that they don't get mixed up with their
 398                 // return value.
 399                 let sp = self.sess.source_map().start_point(self.token.span);
 400                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 401                 false
 402             }
 403             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 404             (true, Some(_)) => {
 405                 self.error_found_expr_would_be_stmt(lhs);
 406                 true
 407             }
 408         }
 409     }
 410
 411     /// We've found an expression that would be parsed as a statement,
 412     /// but the next token implies this should be parsed as an expression.
 413     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 414     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 415         let mut err = self.struct_span_err(
 416             self.token.span,
 417             &format!("expected expression, found `{}`", pprust::token_to_string(&self.token),),
 418         );
 419         err.span_label(self.token.span, "expected expression");
 420         self.sess.expr_parentheses_needed(&mut err, lhs.span);
 421         err.emit();
 422     }
 423
 424     /// Possibly translate the current token to an associative operator.
 425     /// The method does not advance the current token.
 426     ///
 427     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 428     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 429         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 430             // When parsing const expressions, stop parsing when encountering `>`.
 431             (
 432                 Some(
 433                     AssocOp::ShiftRight
 434                     | AssocOp::Greater
 435                     | AssocOp::GreaterEqual
 436                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 437                 ),
 438                 _,
 439             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 440                 return None;
 441             }
 442             (Some(op), _) => (op, self.token.span),
 443             (None, Some((Ident { name: sym::and, span }, false))) => {
 444                 self.error_bad_logical_op("and", "&&", "conjunction");
 445                 (AssocOp::LAnd, span)
 446             }
 447             (None, Some((Ident { name: sym::or, span }, false))) => {
 448                 self.error_bad_logical_op("or", "||", "disjunction");
 449                 (AssocOp::LOr, span)
 450             }
 451             _ => return None,
 452         };
 453         Some(source_map::respan(span, op))
 454     }
 455
 456     /// Error on `and` and `or` suggesting `&&` and `||` respectively.
 457     fn error_bad_logical_op(&self, bad: &str, good: &str, english: &str) {
 458         self.struct_span_err(self.token.span, &format!("`{bad}` is not a logical operator"))
 459             .span_suggestion_short(
 460                 self.token.span,
 461                 &format!("use `{good}` to perform logical {english}"),
 462                 good,
 463                 Applicability::MachineApplicable,
 464             )
 465             .note("unlike in e.g., python and PHP, `&&` and `||` are used for logical operators")
 466             .emit();
 467     }
 468
 469     /// Checks if this expression is a successfully parsed statement.
 470     fn expr_is_complete(&self, e: &Expr) -> bool {
 471         self.restrictions.contains(Restrictions::STMT_EXPR)
 472             && !classify::expr_requires_semi_to_be_stmt(e)
 473     }
 474
 475     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 476     /// The other two variants are handled in `parse_prefix_range_expr` below.
 477     fn parse_range_expr(
 478         &mut self,
 479         prec: usize,
 480         lhs: P<Expr>,
 481         op: AssocOp,
 482         cur_op_span: Span,
 483     ) -> PResult<'a, P<Expr>> {
 484         let rhs = if self.is_at_start_of_range_notation_rhs() {
 485             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 486         } else {
 487             None
 488         };
 489         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 490         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 491         let limits =
 492             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 493         let range = self.mk_range(Some(lhs), rhs, limits);
 494         Ok(self.mk_expr(span, range, AttrVec::new()))
 495     }
 496
 497     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 498         if self.token.can_begin_expr() {
 499             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 500             if self.token == token::OpenDelim(Delimiter::Brace) {
 501                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 502             }
 503             true
 504         } else {
 505             false
 506         }
 507     }
 508
 509     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 510     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 511         // Check for deprecated `...` syntax.
 512         if self.token == token::DotDotDot {
 513             self.err_dotdotdot_syntax(self.token.span);
 514         }
 515
 516         debug_assert!(
 517             [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 518             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 519             self.token
 520         );
 521
 522         let limits = match self.token.kind {
 523             token::DotDot => RangeLimits::HalfOpen,
 524             _ => RangeLimits::Closed,
 525         };
 526         let op = AssocOp::from_token(&self.token);
 527         // FIXME: `parse_prefix_range_expr` is called when the current
 528         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 529         // parsed attributes, then trying to parse them here will always fail.
 530         // We should figure out how we want attributes on range expressions to work.
 531         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 532         self.collect_tokens_for_expr(attrs, |this, attrs| {
 533             let lo = this.token.span;
 534             this.bump();
 535             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 536                 // RHS must be parsed with more associativity than the dots.
 537                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 538                     .map(|x| (lo.to(x.span), Some(x)))?
 539             } else {
 540                 (lo, None)
 541             };
 542             let range = this.mk_range(None, opt_end, limits);
 543             Ok(this.mk_expr(span, range, attrs.into()))
 544         })
 545     }
 546
 547     /// Parses a prefix-unary-operator expr.
 548     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 549         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 550         let lo = self.token.span;
 551
 552         macro_rules! make_it {
 553             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 554                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 555                     let (hi, ex) = $body?;
 556                     Ok($this.mk_expr(lo.to(hi), ex, attrs.into()))
 557                 })
 558             };
 559         }
 560
 561         let this = self;
 562
 563         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 564         match this.token.uninterpolate().kind {
 565             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr`
 566             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr`
 567             token::BinOp(token::Minus) => {
 568                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 569             } // `-expr`
 570             token::BinOp(token::Star) => {
 571                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 572             } // `*expr`
 573             token::BinOp(token::And) | token::AndAnd => {
 574                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 575             }
 576             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 577                 let mut err = this.struct_span_err(lo, "leading `+` is not supported");
 578                 err.span_label(lo, "unexpected `+`");
 579
 580                 // a block on the LHS might have been intended to be an expression instead
 581                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 582                     this.sess.expr_parentheses_needed(&mut err, *sp);
 583                 } else {
 584                     err.span_suggestion_verbose(
 585                         lo,
 586                         "try removing the `+`",
 587                         "",
 588                         Applicability::MachineApplicable,
 589                     );
 590                 }
 591                 err.emit();
 592
 593                 this.bump();
 594                 this.parse_prefix_expr(None)
 595             } // `+expr`
 596             // Recover from `++x`:
 597             token::BinOp(token::Plus)
 598                 if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
 599             {
 600                 let prev_is_semi = this.prev_token == token::Semi;
 601                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
 602                 // Eat both `+`s.
 603                 this.bump();
 604                 this.bump();
 605
 606                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
 607                 this.recover_from_prefix_increment(operand_expr, pre_span, prev_is_semi)
 608             }
 609             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 610                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 611             }
 612             token::Ident(..) if this.is_mistaken_not_ident_negation() => {
 613                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 614             }
 615             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 616         }
 617     }
 618
 619     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 620         self.bump();
 621         let expr = self.parse_prefix_expr(None);
 622         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 623         Ok((lo.to(span), expr))
 624     }
 625
 626     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 627         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 628         Ok((span, self.mk_unary(op, expr)))
 629     }
 630
 631     // Recover on `!` suggesting for bitwise negation instead.
 632     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 633         self.struct_span_err(lo, "`~` cannot be used as a unary operator")
 634             .span_suggestion_short(
 635                 lo,
 636                 "use `!` to perform bitwise not",
 637                 "!",
 638                 Applicability::MachineApplicable,
 639             )
 640             .emit();
 641
 642         self.parse_unary_expr(lo, UnOp::Not)
 643     }
 644
 645     /// Parse `box expr`.
 646     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 647         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 648         self.sess.gated_spans.gate(sym::box_syntax, span);
 649         Ok((span, ExprKind::Box(expr)))
 650     }
 651
 652     fn is_mistaken_not_ident_negation(&self) -> bool {
 653         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 654             // These tokens can start an expression after `!`, but
 655             // can't continue an expression after an ident
 656             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 657             token::Literal(..) | token::Pound => true,
 658             _ => t.is_whole_expr(),
 659         };
 660         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 661     }
 662
 663     /// Recover on `not expr` in favor of `!expr`.
 664     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 665         // Emit the error...
 666         let not_token = self.look_ahead(1, |t| t.clone());
 667         self.struct_span_err(
 668             not_token.span,
 669             &format!("unexpected {} after identifier", super::token_descr(&not_token)),
 670         )
 671         .span_suggestion_short(
 672             // Span the `not` plus trailing whitespace to avoid
 673             // trailing whitespace after the `!` in our suggestion
 674             self.sess.source_map().span_until_non_whitespace(lo.to(not_token.span)),
 675             "use `!` to perform logical negation",
 676             "!",
 677             Applicability::MachineApplicable,
 678         )
 679         .emit();
 680
 681         // ...and recover!
 682         self.parse_unary_expr(lo, UnOp::Not)
 683     }
 684
 685     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 686     fn interpolated_or_expr_span(
 687         &self,
 688         expr: PResult<'a, P<Expr>>,
 689     ) -> PResult<'a, (Span, P<Expr>)> {
 690         expr.map(|e| {
 691             (
 692                 match self.prev_token.kind {
 693                     TokenKind::Interpolated(..) => self.prev_token.span,
 694                     _ => e.span,
 695                 },
 696                 e,
 697             )
 698         })
 699     }
 700
 701     fn parse_assoc_op_cast(
 702         &mut self,
 703         lhs: P<Expr>,
 704         lhs_span: Span,
 705         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 706     ) -> PResult<'a, P<Expr>> {
 707         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 708             this.mk_expr(
 709                 this.mk_expr_sp(&lhs, lhs_span, rhs.span),
 710                 expr_kind(lhs, rhs),
 711                 AttrVec::new(),
 712             )
 713         };
 714
 715         // Save the state of the parser before parsing type normally, in case there is a
 716         // LessThan comparison after this cast.
 717         let parser_snapshot_before_type = self.clone();
 718         let cast_expr = match self.parse_as_cast_ty() {
 719             Ok(rhs) => mk_expr(self, lhs, rhs),
 720             Err(type_err) => {
 721                 // Rewind to before attempting to parse the type with generics, to recover
 722                 // from situations like `x as usize < y` in which we first tried to parse
 723                 // `usize < y` as a type with generic arguments.
 724                 let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
 725
 726                 // Check for typo of `'a: loop { break 'a }` with a missing `'`.
 727                 match (&lhs.kind, &self.token.kind) {
 728                     (
 729                         // `foo: `
 730                         ExprKind::Path(None, ast::Path { segments, .. }),
 731                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
 732                     ) if segments.len() == 1 => {
 733                         let snapshot = self.create_snapshot_for_diagnostic();
 734                         let label = Label {
 735                             ident: Ident::from_str_and_span(
 736                                 &format!("'{}", segments[0].ident),
 737                                 segments[0].ident.span,
 738                             ),
 739                         };
 740                         match self.parse_labeled_expr(label, AttrVec::new(), false) {
 741                             Ok(expr) => {
 742                                 type_err.cancel();
 743                                 self.struct_span_err(label.ident.span, "malformed loop label")
 744                                     .span_suggestion(
 745                                         label.ident.span,
 746                                         "use the correct loop label format",
 747                                         label.ident,
 748                                         Applicability::MachineApplicable,
 749                                     )
 750                                     .emit();
 751                                 return Ok(expr);
 752                             }
 753                             Err(err) => {
 754                                 err.cancel();
 755                                 self.restore_snapshot(snapshot);
 756                             }
 757                         }
 758                     }
 759                     _ => {}
 760                 }
 761
 762                 match self.parse_path(PathStyle::Expr) {
 763                     Ok(path) => {
 764                         let (op_noun, op_verb) = match self.token.kind {
 765                             token::Lt => ("comparison", "comparing"),
 766                             token::BinOp(token::Shl) => ("shift", "shifting"),
 767                             _ => {
 768                                 // We can end up here even without `<` being the next token, for
 769                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 770                                 // but `parse_path` returns `Ok` on them due to error recovery.
 771                                 // Return original error and parser state.
 772                                 *self = parser_snapshot_after_type;
 773                                 return Err(type_err);
 774                             }
 775                         };
 776
 777                         // Successfully parsed the type path leaving a `<` yet to parse.
 778                         type_err.cancel();
 779
 780                         // Report non-fatal diagnostics, keep `x as usize` as an expression
 781                         // in AST and continue parsing.
 782                         let msg = format!(
 783                             "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
 784                             pprust::path_to_string(&path),
 785                             op_noun,
 786                         );
 787                         let span_after_type = parser_snapshot_after_type.token.span;
 788                         let expr =
 789                             mk_expr(self, lhs, self.mk_ty(path.span, TyKind::Path(None, path)));
 790
 791                         self.struct_span_err(self.token.span, &msg)
 792                             .span_label(
 793                                 self.look_ahead(1, |t| t.span).to(span_after_type),
 794                                 "interpreted as generic arguments",
 795                             )
 796                             .span_label(self.token.span, format!("not interpreted as {op_noun}"))
 797                             .multipart_suggestion(
 798                                 &format!("try {op_verb} the cast value"),
 799                                 vec![
 800                                     (expr.span.shrink_to_lo(), "(".to_string()),
 801                                     (expr.span.shrink_to_hi(), ")".to_string()),
 802                                 ],
 803                                 Applicability::MachineApplicable,
 804                             )
 805                             .emit();
 806
 807                         expr
 808                     }
 809                     Err(path_err) => {
 810                         // Couldn't parse as a path, return original error and parser state.
 811                         path_err.cancel();
 812                         *self = parser_snapshot_after_type;
 813                         return Err(type_err);
 814                     }
 815                 }
 816             }
 817         };
 818
 819         self.parse_and_disallow_postfix_after_cast(cast_expr)
 820     }
 821
 822     /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
 823     /// then emits an error and returns the newly parsed tree.
 824     /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
 825     fn parse_and_disallow_postfix_after_cast(
 826         &mut self,
 827         cast_expr: P<Expr>,
 828     ) -> PResult<'a, P<Expr>> {
 829         let span = cast_expr.span;
 830         let maybe_ascription_span = if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
 831             Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi()))
 832         } else {
 833             None
 834         };
 835
 836         // Save the memory location of expr before parsing any following postfix operators.
 837         // This will be compared with the memory location of the output expression.
 838         // If they different we can assume we parsed another expression because the existing expression is not reallocated.
 839         let addr_before = &*cast_expr as *const _ as usize;
 840         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 841         let changed = addr_before != &*with_postfix as *const _ as usize;
 842
 843         // Check if an illegal postfix operator has been added after the cast.
 844         // If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator.
 845         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) || changed {
 846             let msg = format!(
 847                 "casts cannot be followed by {}",
 848                 match with_postfix.kind {
 849                     ExprKind::Index(_, _) => "indexing",
 850                     ExprKind::Try(_) => "`?`",
 851                     ExprKind::Field(_, _) => "a field access",
 852                     ExprKind::MethodCall(_, _, _) => "a method call",
 853                     ExprKind::Call(_, _) => "a function call",
 854                     ExprKind::Await(_) => "`.await`",
 855                     ExprKind::Err => return Ok(with_postfix),
 856                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 857                 }
 858             );
 859             let mut err = self.struct_span_err(span, &msg);
 860
 861             let suggest_parens = |err: &mut DiagnosticBuilder<'_, _>| {
 862                 let suggestions = vec![
 863                     (span.shrink_to_lo(), "(".to_string()),
 864                     (span.shrink_to_hi(), ")".to_string()),
 865                 ];
 866                 err.multipart_suggestion(
 867                     "try surrounding the expression in parentheses",
 868                     suggestions,
 869                     Applicability::MachineApplicable,
 870                 );
 871             };
 872
 873             // If type ascription is "likely an error", the user will already be getting a useful
 874             // help message, and doesn't need a second.
 875             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 876                 self.maybe_annotate_with_ascription(&mut err, false);
 877             } else if let Some(ascription_span) = maybe_ascription_span {
 878                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 879                 if is_nightly {
 880                     suggest_parens(&mut err);
 881                 }
 882                 err.span_suggestion(
 883                     ascription_span,
 884                     &format!(
 885                         "{}remove the type ascription",
 886                         if is_nightly { "alternatively, " } else { "" }
 887                     ),
 888                     "",
 889                     if is_nightly {
 890                         Applicability::MaybeIncorrect
 891                     } else {
 892                         Applicability::MachineApplicable
 893                     },
 894                 );
 895             } else {
 896                 suggest_parens(&mut err);
 897             }
 898             err.emit();
 899         };
 900         Ok(with_postfix)
 901     }
 902
 903     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 904         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 905         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 906         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 907         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 908         Ok(lhs)
 909     }
 910
 911     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 912     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 913         self.expect_and()?;
 914         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 915         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 916         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 917         let expr = self.parse_prefix_expr(None);
 918         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 919         let span = lo.to(hi);
 920         if let Some(lt) = lifetime {
 921             self.error_remove_borrow_lifetime(span, lt.ident.span);
 922         }
 923         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 924     }
 925
 926     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 927         self.struct_span_err(span, "borrow expressions cannot be annotated with lifetimes")
 928             .span_label(lt_span, "annotated with lifetime here")
 929             .span_suggestion(
 930                 lt_span,
 931                 "remove the lifetime annotation",
 932                 "",
 933                 Applicability::MachineApplicable,
 934             )
 935             .emit();
 936     }
 937
 938     /// Parse `mut?` or `raw [ const | mut ]`.
 939     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 940         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 941             // `raw [ const | mut ]`.
 942             let found_raw = self.eat_keyword(kw::Raw);
 943             assert!(found_raw);
 944             let mutability = self.parse_const_or_mut().unwrap();
 945             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 946             (ast::BorrowKind::Raw, mutability)
 947         } else {
 948             // `mut?`
 949             (ast::BorrowKind::Ref, self.parse_mutability())
 950         }
 951     }
 952
 953     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 954     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 955         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 956         self.collect_tokens_for_expr(attrs, |this, attrs| {
 957             let base = this.parse_bottom_expr();
 958             let (span, base) = this.interpolated_or_expr_span(base)?;
 959             this.parse_dot_or_call_expr_with(base, span, attrs)
 960         })
 961     }
 962
 963     pub(super) fn parse_dot_or_call_expr_with(
 964         &mut self,
 965         e0: P<Expr>,
 966         lo: Span,
 967         mut attrs: Vec<ast::Attribute>,
 968     ) -> PResult<'a, P<Expr>> {
 969         // Stitch the list of outer attributes onto the return value.
 970         // A little bit ugly, but the best way given the current code
 971         // structure
 972         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| {
 973             expr.map(|mut expr| {
 974                 attrs.extend::<Vec<_>>(expr.attrs.into());
 975                 expr.attrs = attrs.into();
 976                 expr
 977             })
 978         })
 979     }
 980
 981     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 982         loop {
 983             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 984                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 985                 // which could be suggested otherwise
 986                 self.eat_noexpect(&token::Question)
 987             } else {
 988                 self.eat(&token::Question)
 989             };
 990             if has_question {
 991                 // `expr?`
 992                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e), AttrVec::new());
 993                 continue;
 994             }
 995             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 996                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 997                 // which could be suggested otherwise
 998                 self.eat_noexpect(&token::Dot)
 999             } else {
1000                 self.eat(&token::Dot)
1001             };
1002             if has_dot {
1003                 // expr.f
1004                 e = self.parse_dot_suffix_expr(lo, e)?;
1005                 continue;
1006             }
1007             if self.expr_is_complete(&e) {
1008                 return Ok(e);
1009             }
1010             e = match self.token.kind {
1011                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1012                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1013                 _ => return Ok(e),
1014             }
1015         }
1016     }
1017
1018     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1019         self.look_ahead(1, |t| t.is_ident())
1020             && self.look_ahead(2, |t| t == &token::Colon)
1021             && self.look_ahead(3, |t| t.can_begin_expr())
1022     }
1023
1024     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1025         match self.token.uninterpolate().kind {
1026             token::Ident(..) => self.parse_dot_suffix(base, lo),
1027             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1028                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1029             }
1030             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1031                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1032             }
1033             _ => {
1034                 self.error_unexpected_after_dot();
1035                 Ok(base)
1036             }
1037         }
1038     }
1039
1040     fn error_unexpected_after_dot(&self) {
1041         // FIXME Could factor this out into non_fatal_unexpected or something.
1042         let actual = pprust::token_to_string(&self.token);
1043         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1044     }
1045
1046     // We need an identifier or integer, but the next token is a float.
1047     // Break the float into components to extract the identifier or integer.
1048     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1049     // parts unless those parts are processed immediately. `TokenCursor` should either
1050     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1051     // we should break everything including floats into more basic proc-macro style
1052     // tokens in the lexer (probably preferable).
1053     fn parse_tuple_field_access_expr_float(
1054         &mut self,
1055         lo: Span,
1056         base: P<Expr>,
1057         float: Symbol,
1058         suffix: Option<Symbol>,
1059     ) -> P<Expr> {
1060         #[derive(Debug)]
1061         enum FloatComponent {
1062             IdentLike(String),
1063             Punct(char),
1064         }
1065         use FloatComponent::*;
1066
1067         let float_str = float.as_str();
1068         let mut components = Vec::new();
1069         let mut ident_like = String::new();
1070         for c in float_str.chars() {
1071             if c == '_' || c.is_ascii_alphanumeric() {
1072                 ident_like.push(c);
1073             } else if matches!(c, '.' | '+' | '-') {
1074                 if !ident_like.is_empty() {
1075                     components.push(IdentLike(mem::take(&mut ident_like)));
1076                 }
1077                 components.push(Punct(c));
1078             } else {
1079                 panic!("unexpected character in a float token: {:?}", c)
1080             }
1081         }
1082         if !ident_like.is_empty() {
1083             components.push(IdentLike(ident_like));
1084         }
1085
1086         // With proc macros the span can refer to anything, the source may be too short,
1087         // or too long, or non-ASCII. It only makes sense to break our span into components
1088         // if its underlying text is identical to our float literal.
1089         let span = self.token.span;
1090         let can_take_span_apart =
1091             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1092
1093         match &*components {
1094             // 1e2
1095             [IdentLike(i)] => {
1096                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1097             }
1098             // 1.
1099             [IdentLike(i), Punct('.')] => {
1100                 let (ident_span, dot_span) = if can_take_span_apart() {
1101                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1102                     let ident_span = span.with_hi(span.lo + ident_len);
1103                     let dot_span = span.with_lo(span.lo + ident_len);
1104                     (ident_span, dot_span)
1105                 } else {
1106                     (span, span)
1107                 };
1108                 assert!(suffix.is_none());
1109                 let symbol = Symbol::intern(&i);
1110                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1111                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1112                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1113             }
1114             // 1.2 | 1.2e3
1115             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1116                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1117                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1118                     let ident1_span = span.with_hi(span.lo + ident1_len);
1119                     let dot_span = span
1120                         .with_lo(span.lo + ident1_len)
1121                         .with_hi(span.lo + ident1_len + BytePos(1));
1122                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1123                     (ident1_span, dot_span, ident2_span)
1124                 } else {
1125                     (span, span, span)
1126                 };
1127                 let symbol1 = Symbol::intern(&i1);
1128                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1129                 // This needs to be `Spacing::Alone` to prevent regressions.
1130                 // See issue #76399 and PR #76285 for more details
1131                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1132                 let base1 =
1133                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1134                 let symbol2 = Symbol::intern(&i2);
1135                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1136                 self.bump_with((next_token2, self.token_spacing)); // `.`
1137                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1138             }
1139             // 1e+ | 1e- (recovered)
1140             [IdentLike(_), Punct('+' | '-')] |
1141             // 1e+2 | 1e-2
1142             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1143             // 1.2e+ | 1.2e-
1144             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1145             // 1.2e+3 | 1.2e-3
1146             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1147                 // See the FIXME about `TokenCursor` above.
1148                 self.error_unexpected_after_dot();
1149                 base
1150             }
1151             _ => panic!("unexpected components in a float token: {:?}", components),
1152         }
1153     }
1154
1155     fn parse_tuple_field_access_expr(
1156         &mut self,
1157         lo: Span,
1158         base: P<Expr>,
1159         field: Symbol,
1160         suffix: Option<Symbol>,
1161         next_token: Option<(Token, Spacing)>,
1162     ) -> P<Expr> {
1163         match next_token {
1164             Some(next_token) => self.bump_with(next_token),
1165             None => self.bump(),
1166         }
1167         let span = self.prev_token.span;
1168         let field = ExprKind::Field(base, Ident::new(field, span));
1169         self.expect_no_suffix(span, "a tuple index", suffix);
1170         self.mk_expr(lo.to(span), field, AttrVec::new())
1171     }
1172
1173     /// Parse a function call expression, `expr(...)`.
1174     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1175         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1176             && self.look_ahead_type_ascription_as_field()
1177         {
1178             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1179         } else {
1180             None
1181         };
1182         let open_paren = self.token.span;
1183
1184         let mut seq = self.parse_paren_expr_seq().map(|args| {
1185             self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new())
1186         });
1187         if let Some(expr) =
1188             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1189         {
1190             return expr;
1191         }
1192         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1193     }
1194
1195     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1196     /// parentheses instead of braces, recover the parser state and provide suggestions.
1197     #[instrument(skip(self, seq, snapshot), level = "trace")]
1198     fn maybe_recover_struct_lit_bad_delims(
1199         &mut self,
1200         lo: Span,
1201         open_paren: Span,
1202         seq: &mut PResult<'a, P<Expr>>,
1203         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1204     ) -> Option<P<Expr>> {
1205         match (seq.as_mut(), snapshot) {
1206             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1207                 let name = pprust::path_to_string(&path);
1208                 snapshot.bump(); // `(`
1209                 match snapshot.parse_struct_fields(path, false, Delimiter::Parenthesis) {
1210                     Ok((fields, ..))
1211                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1212                     {
1213                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1214                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1215                         self.restore_snapshot(snapshot);
1216                         let close_paren = self.prev_token.span;
1217                         let span = lo.to(self.prev_token.span);
1218                         if !fields.is_empty() {
1219                             let replacement_err = self.struct_span_err(
1220                                 span,
1221                                 "invalid `struct` delimiters or `fn` call arguments",
1222                             );
1223                             mem::replace(err, replacement_err).cancel();
1224
1225                             err.multipart_suggestion(
1226                                 &format!("if `{name}` is a struct, use braces as delimiters"),
1227                                 vec![
1228                                     (open_paren, " { ".to_string()),
1229                                     (close_paren, " }".to_string()),
1230                                 ],
1231                                 Applicability::MaybeIncorrect,
1232                             );
1233                             err.multipart_suggestion(
1234                                 &format!("if `{name}` is a function, use the arguments directly"),
1235                                 fields
1236                                     .into_iter()
1237                                     .map(|field| (field.span.until(field.expr.span), String::new()))
1238                                     .collect(),
1239                                 Applicability::MaybeIncorrect,
1240                             );
1241                             err.emit();
1242                         } else {
1243                             err.emit();
1244                         }
1245                         return Some(self.mk_expr_err(span));
1246                     }
1247                     Ok(_) => {}
1248                     Err(mut err) => {
1249                         err.emit();
1250                     }
1251                 }
1252             }
1253             _ => {}
1254         }
1255         None
1256     }
1257
1258     /// Parse an indexing expression `expr[...]`.
1259     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1260         self.bump(); // `[`
1261         let index = self.parse_expr()?;
1262         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1263         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new()))
1264     }
1265
1266     /// Assuming we have just parsed `.`, continue parsing into an expression.
1267     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1268         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1269             return Ok(self.mk_await_expr(self_arg, lo));
1270         }
1271
1272         let fn_span_lo = self.token.span;
1273         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1274         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1275         self.check_turbofish_missing_angle_brackets(&mut segment);
1276
1277         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1278             // Method call `expr.f()`
1279             let mut args = self.parse_paren_expr_seq()?;
1280             args.insert(0, self_arg);
1281
1282             let fn_span = fn_span_lo.to(self.prev_token.span);
1283             let span = lo.to(self.prev_token.span);
1284             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new()))
1285         } else {
1286             // Field access `expr.f`
1287             if let Some(args) = segment.args {
1288                 self.struct_span_err(
1289                     args.span(),
1290                     "field expressions cannot have generic arguments",
1291                 )
1292                 .emit();
1293             }
1294
1295             let span = lo.to(self.prev_token.span);
1296             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new()))
1297         }
1298     }
1299
1300     /// At the bottom (top?) of the precedence hierarchy,
1301     /// Parses things like parenthesized exprs, macros, `return`, etc.
1302     ///
1303     /// N.B., this does not parse outer attributes, and is private because it only works
1304     /// correctly if called from `parse_dot_or_call_expr()`.
1305     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1306         maybe_recover_from_interpolated_ty_qpath!(self, true);
1307         maybe_whole_expr!(self);
1308
1309         // Outer attributes are already parsed and will be
1310         // added to the return value after the fact.
1311         //
1312         // Therefore, prevent sub-parser from parsing
1313         // attributes by giving them an empty "already-parsed" list.
1314         let attrs = AttrVec::new();
1315
1316         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1317         let lo = self.token.span;
1318         if let token::Literal(_) = self.token.kind {
1319             // This match arm is a special-case of the `_` match arm below and
1320             // could be removed without changing functionality, but it's faster
1321             // to have it here, especially for programs with large constants.
1322             self.parse_lit_expr(attrs)
1323         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1324             self.parse_tuple_parens_expr(attrs)
1325         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1326             self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs)
1327         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1328             self.parse_closure_expr(attrs).map_err(|mut err| {
1329                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1330                 // then suggest parens around the lhs.
1331                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1332                     self.sess.expr_parentheses_needed(&mut err, *sp);
1333                 }
1334                 err
1335             })
1336         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1337             self.parse_array_or_repeat_expr(attrs, Delimiter::Bracket)
1338         } else if self.check_path() {
1339             self.parse_path_start_expr(attrs)
1340         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1341             self.parse_closure_expr(attrs)
1342         } else if self.eat_keyword(kw::If) {
1343             self.parse_if_expr(attrs)
1344         } else if self.check_keyword(kw::For) {
1345             if self.choose_generics_over_qpath(1) {
1346                 self.parse_closure_expr(attrs)
1347             } else {
1348                 assert!(self.eat_keyword(kw::For));
1349                 self.parse_for_expr(None, self.prev_token.span, attrs)
1350             }
1351         } else if self.eat_keyword(kw::While) {
1352             self.parse_while_expr(None, self.prev_token.span, attrs)
1353         } else if let Some(label) = self.eat_label() {
1354             self.parse_labeled_expr(label, attrs, true)
1355         } else if self.eat_keyword(kw::Loop) {
1356             let sp = self.prev_token.span;
1357             self.parse_loop_expr(None, self.prev_token.span, attrs).map_err(|mut err| {
1358                 err.span_label(sp, "while parsing this `loop` expression");
1359                 err
1360             })
1361         } else if self.eat_keyword(kw::Continue) {
1362             let kind = ExprKind::Continue(self.eat_label());
1363             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1364         } else if self.eat_keyword(kw::Match) {
1365             let match_sp = self.prev_token.span;
1366             self.parse_match_expr(attrs).map_err(|mut err| {
1367                 err.span_label(match_sp, "while parsing this `match` expression");
1368                 err
1369             })
1370         } else if self.eat_keyword(kw::Unsafe) {
1371             let sp = self.prev_token.span;
1372             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1373                 .map_err(|mut err| {
1374                     err.span_label(sp, "while parsing this `unsafe` expression");
1375                     err
1376                 })
1377         } else if self.check_inline_const(0) {
1378             self.parse_const_block(lo.to(self.token.span), false)
1379         } else if self.is_do_catch_block() {
1380             self.recover_do_catch(attrs)
1381         } else if self.is_try_block() {
1382             self.expect_keyword(kw::Try)?;
1383             self.parse_try_block(lo, attrs)
1384         } else if self.eat_keyword(kw::Return) {
1385             self.parse_return_expr(attrs)
1386         } else if self.eat_keyword(kw::Break) {
1387             self.parse_break_expr(attrs)
1388         } else if self.eat_keyword(kw::Yield) {
1389             self.parse_yield_expr(attrs)
1390         } else if self.is_do_yeet() {
1391             self.parse_yeet_expr(attrs)
1392         } else if self.check_keyword(kw::Let) {
1393             self.manage_let_chains_context();
1394             self.bump();
1395             self.parse_let_expr(attrs)
1396         } else if self.eat_keyword(kw::Underscore) {
1397             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1398         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1399             // Don't complain about bare semicolons after unclosed braces
1400             // recovery in order to keep the error count down. Fixing the
1401             // delimiters will possibly also fix the bare semicolon found in
1402             // expression context. For example, silence the following error:
1403             //
1404             //     error: expected expression, found `;`
1405             //      --> file.rs:2:13
1406             //       |
1407             //     2 |     foo(bar(;
1408             //       |             ^ expected expression
1409             self.bump();
1410             Ok(self.mk_expr_err(self.token.span))
1411         } else if self.token.uninterpolated_span().rust_2018() {
1412             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1413             if self.check_keyword(kw::Async) {
1414                 if self.is_async_block() {
1415                     // Check for `async {` and `async move {`.
1416                     self.parse_async_block(attrs)
1417                 } else {
1418                     self.parse_closure_expr(attrs)
1419                 }
1420             } else if self.eat_keyword(kw::Await) {
1421                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1422             } else {
1423                 self.parse_lit_expr(attrs)
1424             }
1425         } else {
1426             self.parse_lit_expr(attrs)
1427         }
1428     }
1429
1430     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1431         let lo = self.token.span;
1432         match self.parse_opt_lit() {
1433             Some(literal) => {
1434                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1435                 self.maybe_recover_from_bad_qpath(expr)
1436             }
1437             None => self.try_macro_suggestion(),
1438         }
1439     }
1440
1441     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1442         let lo = self.token.span;
1443         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1444         let (es, trailing_comma) = match self.parse_seq_to_end(
1445             &token::CloseDelim(Delimiter::Parenthesis),
1446             SeqSep::trailing_allowed(token::Comma),
1447             |p| p.parse_expr_catch_underscore(),
1448         ) {
1449             Ok(x) => x,
1450             Err(err) => {
1451                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1452             }
1453         };
1454         let kind = if es.len() == 1 && !trailing_comma {
1455             // `(e)` is parenthesized `e`.
1456             ExprKind::Paren(es.into_iter().next().unwrap())
1457         } else {
1458             // `(e,)` is a tuple with only one field, `e`.
1459             ExprKind::Tup(es)
1460         };
1461         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1462         self.maybe_recover_from_bad_qpath(expr)
1463     }
1464
1465     fn parse_array_or_repeat_expr(
1466         &mut self,
1467         attrs: AttrVec,
1468         close_delim: Delimiter,
1469     ) -> PResult<'a, P<Expr>> {
1470         let lo = self.token.span;
1471         self.bump(); // `[` or other open delim
1472
1473         let close = &token::CloseDelim(close_delim);
1474         let kind = if self.eat(close) {
1475             // Empty vector
1476             ExprKind::Array(Vec::new())
1477         } else {
1478             // Non-empty vector
1479             let first_expr = self.parse_expr()?;
1480             if self.eat(&token::Semi) {
1481                 // Repeating array syntax: `[ 0; 512 ]`
1482                 let count = self.parse_anon_const_expr()?;
1483                 self.expect(close)?;
1484                 ExprKind::Repeat(first_expr, count)
1485             } else if self.eat(&token::Comma) {
1486                 // Vector with two or more elements.
1487                 let sep = SeqSep::trailing_allowed(token::Comma);
1488                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1489                 let mut exprs = vec![first_expr];
1490                 exprs.extend(remaining_exprs);
1491                 ExprKind::Array(exprs)
1492             } else {
1493                 // Vector with one element
1494                 self.expect(close)?;
1495                 ExprKind::Array(vec![first_expr])
1496             }
1497         };
1498         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1499         self.maybe_recover_from_bad_qpath(expr)
1500     }
1501
1502     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1503         let (qself, path) = if self.eat_lt() {
1504             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1505             (Some(qself), path)
1506         } else {
1507             (None, self.parse_path(PathStyle::Expr)?)
1508         };
1509         let lo = path.span;
1510
1511         // `!`, as an operator, is prefix, so we know this isn't that.
1512         let (hi, kind) = if self.eat(&token::Not) {
1513             // MACRO INVOCATION expression
1514             if qself.is_some() {
1515                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1516             }
1517             let mac = MacCall {
1518                 path,
1519                 args: self.parse_mac_args()?,
1520                 prior_type_ascription: self.last_type_ascription,
1521             };
1522             (self.prev_token.span, ExprKind::MacCall(mac))
1523         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1524             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1525                 if qself.is_some() {
1526                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1527                 }
1528                 return expr;
1529             } else {
1530                 (path.span, ExprKind::Path(qself, path))
1531             }
1532         } else {
1533             (path.span, ExprKind::Path(qself, path))
1534         };
1535
1536         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1537         self.maybe_recover_from_bad_qpath(expr)
1538     }
1539
1540     /// Parse `'label: $expr`. The label is already parsed.
1541     fn parse_labeled_expr(
1542         &mut self,
1543         label: Label,
1544         attrs: AttrVec,
1545         mut consume_colon: bool,
1546     ) -> PResult<'a, P<Expr>> {
1547         let lo = label.ident.span;
1548         let label = Some(label);
1549         let ate_colon = self.eat(&token::Colon);
1550         let expr = if self.eat_keyword(kw::While) {
1551             self.parse_while_expr(label, lo, attrs)
1552         } else if self.eat_keyword(kw::For) {
1553             self.parse_for_expr(label, lo, attrs)
1554         } else if self.eat_keyword(kw::Loop) {
1555             self.parse_loop_expr(label, lo, attrs)
1556         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1557             || self.token.is_whole_block()
1558         {
1559             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1560         } else if !ate_colon
1561             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1562         {
1563             // We're probably inside of a `Path<'a>` that needs a turbofish
1564             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1565             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1566             consume_colon = false;
1567             Ok(self.mk_expr_err(lo))
1568         } else {
1569             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1570
1571             let mut err = self.struct_span_err(self.token.span, msg);
1572             err.span_label(self.token.span, msg);
1573
1574             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1575             let expr = self.parse_expr().map(|expr| {
1576                 let span = expr.span;
1577
1578                 let found_labeled_breaks = {
1579                     struct FindLabeledBreaksVisitor(bool);
1580
1581                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1582                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1583                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1584                                 self.0 = true;
1585                             }
1586                         }
1587                     }
1588
1589                     let mut vis = FindLabeledBreaksVisitor(false);
1590                     vis.visit_expr(&expr);
1591                     vis.0
1592                 };
1593
1594                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1595                 //
1596                 // If there are no breaks that may use this label, suggest removing the label and
1597                 // recover to the unmodified expression.
1598                 if !found_labeled_breaks {
1599                     let msg = "consider removing the label";
1600                     err.span_suggestion_verbose(
1601                         lo.until(span),
1602                         msg,
1603                         "",
1604                         Applicability::MachineApplicable,
1605                     );
1606
1607                     return expr;
1608                 }
1609
1610                 let sugg_msg = "consider enclosing expression in a block";
1611                 let suggestions = vec![
1612                     (span.shrink_to_lo(), "{ ".to_owned()),
1613                     (span.shrink_to_hi(), " }".to_owned()),
1614                 ];
1615
1616                 err.multipart_suggestion_verbose(
1617                     sugg_msg,
1618                     suggestions,
1619                     Applicability::MachineApplicable,
1620                 );
1621
1622                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to supress future errors about `break 'label`.
1623                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1624                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1625                 self.mk_expr(span, ExprKind::Block(blk, label), ThinVec::new())
1626             });
1627
1628             err.emit();
1629             expr
1630         }?;
1631
1632         if !ate_colon && consume_colon {
1633             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1634         }
1635
1636         Ok(expr)
1637     }
1638
1639     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1640         self.struct_span_err(span, "labeled expression must be followed by `:`")
1641             .span_label(lo, "the label")
1642             .span_suggestion_short(
1643                 lo.shrink_to_hi(),
1644                 "add `:` after the label",
1645                 ": ",
1646                 Applicability::MachineApplicable,
1647             )
1648             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1649             .emit();
1650     }
1651
1652     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1653     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1654         let lo = self.token.span;
1655
1656         self.bump(); // `do`
1657         self.bump(); // `catch`
1658
1659         let span_dc = lo.to(self.prev_token.span);
1660         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1661             .span_suggestion(
1662                 span_dc,
1663                 "replace with the new syntax",
1664                 "try",
1665                 Applicability::MachineApplicable,
1666             )
1667             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1668             .emit();
1669
1670         self.parse_try_block(lo, attrs)
1671     }
1672
1673     /// Parse an expression if the token can begin one.
1674     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1675         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1676     }
1677
1678     /// Parse `"return" expr?`.
1679     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1680         let lo = self.prev_token.span;
1681         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1682         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1683         self.maybe_recover_from_bad_qpath(expr)
1684     }
1685
1686     /// Parse `"do" "yeet" expr?`.
1687     fn parse_yeet_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1688         let lo = self.token.span;
1689
1690         self.bump(); // `do`
1691         self.bump(); // `yeet`
1692
1693         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1694
1695         let span = lo.to(self.prev_token.span);
1696         self.sess.gated_spans.gate(sym::yeet_expr, span);
1697         let expr = self.mk_expr(span, kind, attrs);
1698         self.maybe_recover_from_bad_qpath(expr)
1699     }
1700
1701     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1702     /// If the label is followed immediately by a `:` token, the label and `:` are
1703     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1704     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1705     /// the break expression of an unlabeled break is a labeled loop (as in
1706     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1707     /// expression only gets a warning for compatibility reasons; and a labeled break
1708     /// with a labeled loop does not even get a warning because there is no ambiguity.
1709     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1710         let lo = self.prev_token.span;
1711         let mut label = self.eat_label();
1712         let kind = if label.is_some() && self.token == token::Colon {
1713             // The value expression can be a labeled loop, see issue #86948, e.g.:
1714             // `loop { break 'label: loop { break 'label 42; }; }`
1715             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1716             self.struct_span_err(
1717                 lexpr.span,
1718                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1719             )
1720             .multipart_suggestion(
1721                 "wrap the expression in parentheses",
1722                 vec![
1723                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1724                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1725                 ],
1726                 Applicability::MachineApplicable,
1727             )
1728             .emit();
1729             Some(lexpr)
1730         } else if self.token != token::OpenDelim(Delimiter::Brace)
1731             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1732         {
1733             let expr = self.parse_expr_opt()?;
1734             if let Some(ref expr) = expr {
1735                 if label.is_some()
1736                     && matches!(
1737                         expr.kind,
1738                         ExprKind::While(_, _, None)
1739                             | ExprKind::ForLoop(_, _, _, None)
1740                             | ExprKind::Loop(_, None)
1741                             | ExprKind::Block(_, None)
1742                     )
1743                 {
1744                     self.sess.buffer_lint_with_diagnostic(
1745                         BREAK_WITH_LABEL_AND_LOOP,
1746                         lo.to(expr.span),
1747                         ast::CRATE_NODE_ID,
1748                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1749                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1750                     );
1751                 }
1752             }
1753             expr
1754         } else {
1755             None
1756         };
1757         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1758         self.maybe_recover_from_bad_qpath(expr)
1759     }
1760
1761     /// Parse `"yield" expr?`.
1762     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1763         let lo = self.prev_token.span;
1764         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1765         let span = lo.to(self.prev_token.span);
1766         self.sess.gated_spans.gate(sym::generators, span);
1767         let expr = self.mk_expr(span, kind, attrs);
1768         self.maybe_recover_from_bad_qpath(expr)
1769     }
1770
1771     /// Returns a string literal if the next token is a string literal.
1772     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1773     /// and returns `None` if the next token is not literal at all.
1774     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1775         match self.parse_opt_lit() {
1776             Some(lit) => match lit.kind {
1777                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1778                     style,
1779                     symbol: lit.token.symbol,
1780                     suffix: lit.token.suffix,
1781                     span: lit.span,
1782                     symbol_unescaped,
1783                 }),
1784                 _ => Err(Some(lit)),
1785             },
1786             None => Err(None),
1787         }
1788     }
1789
1790     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1791         self.parse_opt_lit().ok_or_else(|| {
1792             if let token::Interpolated(inner) = &self.token.kind {
1793                 let expr = match inner.as_ref() {
1794                     token::NtExpr(expr) => Some(expr),
1795                     token::NtLiteral(expr) => Some(expr),
1796                     _ => None,
1797                 };
1798                 if let Some(expr) = expr {
1799                     if matches!(expr.kind, ExprKind::Err) {
1800                         let mut err = self
1801                             .diagnostic()
1802                             .struct_span_err(self.token.span, "invalid interpolated expression");
1803                         err.downgrade_to_delayed_bug();
1804                         return err;
1805                     }
1806                 }
1807             }
1808             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1809             self.struct_span_err(self.token.span, &msg)
1810         })
1811     }
1812
1813     /// Matches `lit = true | false | token_lit`.
1814     /// Returns `None` if the next token is not a literal.
1815     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1816         let mut recovered = None;
1817         if self.token == token::Dot {
1818             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1819             // dot would follow an optional literal, so we do this unconditionally.
1820             recovered = self.look_ahead(1, |next_token| {
1821                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1822                     next_token.kind
1823                 {
1824                     if self.token.span.hi() == next_token.span.lo() {
1825                         let s = String::from("0.") + symbol.as_str();
1826                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1827                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1828                     }
1829                 }
1830                 None
1831             });
1832             if let Some(token) = &recovered {
1833                 self.bump();
1834                 self.error_float_lits_must_have_int_part(&token);
1835             }
1836         }
1837
1838         let token = recovered.as_ref().unwrap_or(&self.token);
1839         match Lit::from_token(token) {
1840             Ok(lit) => {
1841                 self.bump();
1842                 Some(lit)
1843             }
1844             Err(LitError::NotLiteral) => None,
1845             Err(err) => {
1846                 let span = token.span;
1847                 let token::Literal(lit) = token.kind else {
1848                     unreachable!();
1849                 };
1850                 self.bump();
1851                 self.report_lit_error(err, lit, span);
1852                 // Pack possible quotes and prefixes from the original literal into
1853                 // the error literal's symbol so they can be pretty-printed faithfully.
1854                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1855                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1856                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1857                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1858             }
1859         }
1860     }
1861
1862     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1863         self.struct_span_err(token.span, "float literals must have an integer part")
1864             .span_suggestion(
1865                 token.span,
1866                 "must have an integer part",
1867                 pprust::token_to_string(token),
1868                 Applicability::MachineApplicable,
1869             )
1870             .emit();
1871     }
1872
1873     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1874         // Checks if `s` looks like i32 or u1234 etc.
1875         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1876             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1877         }
1878
1879         // Try to lowercase the prefix if it's a valid base prefix.
1880         fn fix_base_capitalisation(s: &str) -> Option<String> {
1881             if let Some(stripped) = s.strip_prefix('B') {
1882                 Some(format!("0b{stripped}"))
1883             } else if let Some(stripped) = s.strip_prefix('O') {
1884                 Some(format!("0o{stripped}"))
1885             } else if let Some(stripped) = s.strip_prefix('X') {
1886                 Some(format!("0x{stripped}"))
1887             } else {
1888                 None
1889             }
1890         }
1891
1892         let token::Lit { kind, suffix, .. } = lit;
1893         match err {
1894             // `NotLiteral` is not an error by itself, so we don't report
1895             // it and give the parser opportunity to try something else.
1896             LitError::NotLiteral => {}
1897             // `LexerError` *is* an error, but it was already reported
1898             // by lexer, so here we don't report it the second time.
1899             LitError::LexerError => {}
1900             LitError::InvalidSuffix => {
1901                 self.expect_no_suffix(
1902                     span,
1903                     &format!("{} {} literal", kind.article(), kind.descr()),
1904                     suffix,
1905                 );
1906             }
1907             LitError::InvalidIntSuffix => {
1908                 let suf = suffix.expect("suffix error with no suffix");
1909                 let suf = suf.as_str();
1910                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1911                     // If it looks like a width, try to be helpful.
1912                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1913                     self.struct_span_err(span, &msg)
1914                         .help("valid widths are 8, 16, 32, 64 and 128")
1915                         .emit();
1916                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1917                     let msg = "invalid base prefix for number literal";
1918
1919                     self.struct_span_err(span, msg)
1920                         .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase")
1921                         .span_suggestion(
1922                             span,
1923                             "try making the prefix lowercase",
1924                             fixed,
1925                             Applicability::MaybeIncorrect,
1926                         )
1927                         .emit();
1928                 } else {
1929                     let msg = format!("invalid suffix `{suf}` for number literal");
1930                     self.struct_span_err(span, &msg)
1931                         .span_label(span, format!("invalid suffix `{suf}`"))
1932                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1933                         .emit();
1934                 }
1935             }
1936             LitError::InvalidFloatSuffix => {
1937                 let suf = suffix.expect("suffix error with no suffix");
1938                 let suf = suf.as_str();
1939                 if looks_like_width_suffix(&['f'], suf) {
1940                     // If it looks like a width, try to be helpful.
1941                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1942                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1943                 } else {
1944                     let msg = format!("invalid suffix `{suf}` for float literal");
1945                     self.struct_span_err(span, &msg)
1946                         .span_label(span, format!("invalid suffix `{suf}`"))
1947                         .help("valid suffixes are `f32` and `f64`")
1948                         .emit();
1949                 }
1950             }
1951             LitError::NonDecimalFloat(base) => {
1952                 let descr = match base {
1953                     16 => "hexadecimal",
1954                     8 => "octal",
1955                     2 => "binary",
1956                     _ => unreachable!(),
1957                 };
1958                 self.struct_span_err(span, &format!("{descr} float literal is not supported"))
1959                     .span_label(span, "not supported")
1960                     .emit();
1961             }
1962             LitError::IntTooLarge => {
1963                 self.struct_span_err(span, "integer literal is too large").emit();
1964             }
1965         }
1966     }
1967
1968     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1969         if let Some(suf) = suffix {
1970             let mut err = if kind == "a tuple index"
1971                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1972             {
1973                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1974                 // through the ecosystem when people fix their macros
1975                 let mut err = self
1976                     .sess
1977                     .span_diagnostic
1978                     .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
1979                 err.note(&format!(
1980                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1981                         incorrectly accepted on stable for a few releases",
1982                     suf,
1983                 ));
1984                 err.help(
1985                     "on proc macros, you'll want to use `syn::Index::from` or \
1986                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1987                         to tuple field access",
1988                 );
1989                 err.note(
1990                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1991                      for more information",
1992                 );
1993                 err
1994             } else {
1995                 self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
1996                     .forget_guarantee()
1997             };
1998             err.span_label(sp, format!("invalid suffix `{suf}`"));
1999             err.emit();
2000         }
2001     }
2002
2003     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
2004     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
2005     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
2006         maybe_whole_expr!(self);
2007
2008         let lo = self.token.span;
2009         let minus_present = self.eat(&token::BinOp(token::Minus));
2010         let lit = self.parse_lit()?;
2011         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
2012
2013         if minus_present {
2014             Ok(self.mk_expr(
2015                 lo.to(self.prev_token.span),
2016                 self.mk_unary(UnOp::Neg, expr),
2017                 AttrVec::new(),
2018             ))
2019         } else {
2020             Ok(expr)
2021         }
2022     }
2023
2024     fn is_array_like_block(&mut self) -> bool {
2025         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
2026             && self.look_ahead(2, |t| t == &token::Comma)
2027             && self.look_ahead(3, |t| t.can_begin_expr())
2028     }
2029
2030     /// Emits a suggestion if it looks like the user meant an array but
2031     /// accidentally used braces, causing the code to be interpreted as a block
2032     /// expression.
2033     fn maybe_suggest_brackets_instead_of_braces(
2034         &mut self,
2035         lo: Span,
2036         attrs: AttrVec,
2037     ) -> Option<P<Expr>> {
2038         let mut snapshot = self.create_snapshot_for_diagnostic();
2039         match snapshot.parse_array_or_repeat_expr(attrs, Delimiter::Brace) {
2040             Ok(arr) => {
2041                 let hi = snapshot.prev_token.span;
2042                 self.struct_span_err(arr.span, "this is a block expression, not an array")
2043                     .multipart_suggestion(
2044                         "to make an array, use square brackets instead of curly braces",
2045                         vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
2046                         Applicability::MaybeIncorrect,
2047                     )
2048                     .emit();
2049
2050                 self.restore_snapshot(snapshot);
2051                 Some(self.mk_expr_err(arr.span))
2052             }
2053             Err(e) => {
2054                 e.cancel();
2055                 None
2056             }
2057         }
2058     }
2059
2060     /// Parses a block or unsafe block.
2061     pub(super) fn parse_block_expr(
2062         &mut self,
2063         opt_label: Option<Label>,
2064         lo: Span,
2065         blk_mode: BlockCheckMode,
2066         mut attrs: AttrVec,
2067     ) -> PResult<'a, P<Expr>> {
2068         if self.is_array_like_block() {
2069             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) {
2070                 return Ok(arr);
2071             }
2072         }
2073
2074         if let Some(label) = opt_label {
2075             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
2076         }
2077
2078         if self.token.is_whole_block() {
2079             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
2080                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
2081                 .emit();
2082         }
2083
2084         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
2085         attrs.extend(inner_attrs);
2086         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
2087     }
2088
2089     /// Parse a block which takes no attributes and has no label
2090     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2091         let blk = self.parse_block()?;
2092         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()))
2093     }
2094
2095     /// Parses a closure expression (e.g., `move |args| expr`).
2096     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2097         let lo = self.token.span;
2098
2099         let binder = if self.check_keyword(kw::For) {
2100             let lo = self.token.span;
2101             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2102             let span = lo.to(self.prev_token.span);
2103
2104             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2105
2106             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2107         } else {
2108             ClosureBinder::NotPresent
2109         };
2110
2111         let movability =
2112             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2113
2114         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2115             self.parse_asyncness()
2116         } else {
2117             Async::No
2118         };
2119
2120         let capture_clause = self.parse_capture_clause()?;
2121         let decl = self.parse_fn_block_decl()?;
2122         let decl_hi = self.prev_token.span;
2123         let mut body = match decl.output {
2124             FnRetTy::Default(_) => {
2125                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2126                 self.parse_expr_res(restrictions, None)?
2127             }
2128             _ => {
2129                 // If an explicit return type is given, require a block to appear (RFC 968).
2130                 let body_lo = self.token.span;
2131                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
2132             }
2133         };
2134
2135         if let Async::Yes { span, .. } = asyncness {
2136             // Feature-gate `async ||` closures.
2137             self.sess.gated_spans.gate(sym::async_closure, span);
2138         }
2139
2140         if self.token.kind == TokenKind::Semi
2141             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2142         {
2143             // It is likely that the closure body is a block but where the
2144             // braces have been removed. We will recover and eat the next
2145             // statements later in the parsing process.
2146             body = self.mk_expr_err(body.span);
2147         }
2148
2149         let body_span = body.span;
2150
2151         let closure = self.mk_expr(
2152             lo.to(body.span),
2153             ExprKind::Closure(
2154                 binder,
2155                 capture_clause,
2156                 asyncness,
2157                 movability,
2158                 decl,
2159                 body,
2160                 lo.to(decl_hi),
2161             ),
2162             attrs,
2163         );
2164
2165         // Disable recovery for closure body
2166         let spans =
2167             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2168         self.current_closure = Some(spans);
2169
2170         Ok(closure)
2171     }
2172
2173     /// Parses an optional `move` prefix to a closure-like construct.
2174     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2175         if self.eat_keyword(kw::Move) {
2176             // Check for `move async` and recover
2177             if self.check_keyword(kw::Async) {
2178                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2179                 Err(self.incorrect_move_async_order_found(move_async_span))
2180             } else {
2181                 Ok(CaptureBy::Value)
2182             }
2183         } else {
2184             Ok(CaptureBy::Ref)
2185         }
2186     }
2187
2188     /// Parses the `|arg, arg|` header of a closure.
2189     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2190         let inputs = if self.eat(&token::OrOr) {
2191             Vec::new()
2192         } else {
2193             self.expect(&token::BinOp(token::Or))?;
2194             let args = self
2195                 .parse_seq_to_before_tokens(
2196                     &[&token::BinOp(token::Or), &token::OrOr],
2197                     SeqSep::trailing_allowed(token::Comma),
2198                     TokenExpectType::NoExpect,
2199                     |p| p.parse_fn_block_param(),
2200                 )?
2201                 .0;
2202             self.expect_or()?;
2203             args
2204         };
2205         let output =
2206             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2207
2208         Ok(P(FnDecl { inputs, output }))
2209     }
2210
2211     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2212     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2213         let lo = self.token.span;
2214         let attrs = self.parse_outer_attributes()?;
2215         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2216             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2217             let ty = if this.eat(&token::Colon) {
2218                 this.parse_ty()?
2219             } else {
2220                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2221             };
2222
2223             Ok((
2224                 Param {
2225                     attrs: attrs.into(),
2226                     ty,
2227                     pat,
2228                     span: lo.to(this.token.span),
2229                     id: DUMMY_NODE_ID,
2230                     is_placeholder: false,
2231                 },
2232                 TrailingToken::MaybeComma,
2233             ))
2234         })
2235     }
2236
2237     /// Parses an `if` expression (`if` token already eaten).
2238     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2239         let lo = self.prev_token.span;
2240         let cond = self.parse_cond_expr()?;
2241
2242         self.parse_if_after_cond(attrs, lo, cond)
2243     }
2244
2245     fn parse_if_after_cond(
2246         &mut self,
2247         attrs: AttrVec,
2248         lo: Span,
2249         mut cond: P<Expr>,
2250     ) -> PResult<'a, P<Expr>> {
2251         let cond_span = cond.span;
2252         // Tries to interpret `cond` as either a missing expression if it's a block,
2253         // or as an unfinished expression if it's a binop and the RHS is a block.
2254         // We could probably add more recoveries here too...
2255         let mut recover_block_from_condition = |this: &mut Self| {
2256             let block = match &mut cond.kind {
2257                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2258                     if let ExprKind::Block(_, None) = right.kind => {
2259                         this.error_missing_if_then_block(lo, cond_span.shrink_to_lo().to(*binop_span), true).emit();
2260                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2261                     },
2262                 ExprKind::Block(_, None) => {
2263                     this.error_missing_if_cond(lo, cond_span).emit();
2264                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2265                 }
2266                 _ => {
2267                     return None;
2268                 }
2269             };
2270             if let ExprKind::Block(block, _) = &block.kind {
2271                 Some(block.clone())
2272             } else {
2273                 unreachable!()
2274             }
2275         };
2276         // Parse then block
2277         let thn = if self.token.is_keyword(kw::Else) {
2278             if let Some(block) = recover_block_from_condition(self) {
2279                 block
2280             } else {
2281                 self.error_missing_if_then_block(lo, cond_span, false).emit();
2282                 self.mk_block_err(cond_span.shrink_to_hi())
2283             }
2284         } else {
2285             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2286             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2287                 self.parse_block()?
2288             } else {
2289                 if let Some(block) = recover_block_from_condition(self) {
2290                     block
2291                 } else {
2292                     // Parse block, which will always fail, but we can add a nice note to the error
2293                     self.parse_block().map_err(|mut err| {
2294                         err.span_note(
2295                             cond_span,
2296                             "the `if` expression is missing a block after this condition",
2297                         );
2298                         err
2299                     })?
2300                 }
2301             };
2302             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2303             block
2304         };
2305         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2306         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
2307     }
2308
2309     fn error_missing_if_then_block(
2310         &self,
2311         if_span: Span,
2312         cond_span: Span,
2313         is_unfinished: bool,
2314     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2315         let mut err = self.struct_span_err(
2316             if_span,
2317             "this `if` expression is missing a block after the condition",
2318         );
2319         if is_unfinished {
2320             err.span_help(cond_span, "this binary operation is possibly unfinished");
2321         } else {
2322             err.span_help(cond_span.shrink_to_hi(), "add a block here");
2323         }
2324         err
2325     }
2326
2327     fn error_missing_if_cond(
2328         &self,
2329         lo: Span,
2330         span: Span,
2331     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2332         let next_span = self.sess.source_map().next_point(lo);
2333         let mut err = self.struct_span_err(next_span, "missing condition for `if` expression");
2334         err.span_label(next_span, "expected condition here");
2335         err.span_label(
2336             self.sess.source_map().start_point(span),
2337             "if this block is the condition of the `if` expression, then it must be followed by another block"
2338         );
2339         err
2340     }
2341
2342     /// Parses the condition of a `if` or `while` expression.
2343     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2344         self.with_let_management(true, |local_self| {
2345             local_self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)
2346         })
2347     }
2348
2349     // Checks if `let` is in an invalid position like `let x = let y = 1;` or
2350     // if the current `let` is in a let_chains context but nested in another
2351     // expression like `if let Some(_) = _opt && [1, 2, 3][let _ = ()] = 1`.
2352     //
2353     // This method expects that the current token is `let`.
2354     fn manage_let_chains_context(&mut self) {
2355         debug_assert!(matches!(self.token.kind, TokenKind::Ident(kw::Let, _)));
2356         let is_in_a_let_chains_context_but_nested_in_other_expr = self.let_expr_allowed
2357             && !matches!(
2358                 self.prev_token.kind,
2359                 TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2360             );
2361         if !self.let_expr_allowed || is_in_a_let_chains_context_but_nested_in_other_expr {
2362             self.struct_span_err(self.token.span, "expected expression, found `let` statement")
2363                 .emit();
2364         }
2365     }
2366
2367     /// Parses a `let $pat = $expr` pseudo-expression.
2368     /// The `let` token has already been eaten.
2369     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2370         let lo = self.prev_token.span;
2371         let pat = self.parse_pat_allow_top_alt(
2372             None,
2373             RecoverComma::Yes,
2374             RecoverColon::Yes,
2375             CommaRecoveryMode::LikelyTuple,
2376         )?;
2377         self.expect(&token::Eq)?;
2378         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2379             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2380         })?;
2381         let span = lo.to(expr.span);
2382         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
2383     }
2384
2385     /// Parses an `else { ... }` expression (`else` token already eaten).
2386     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2387         let else_span = self.prev_token.span; // `else`
2388         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2389         let expr = if self.eat_keyword(kw::If) {
2390             self.parse_if_expr(AttrVec::new())?
2391         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2392             self.parse_simple_block()?
2393         } else {
2394             let snapshot = self.create_snapshot_for_diagnostic();
2395             let first_tok = super::token_descr(&self.token);
2396             let first_tok_span = self.token.span;
2397             match self.parse_expr() {
2398                 Ok(cond)
2399                 // If it's not a free-standing expression, and is followed by a block,
2400                 // then it's very likely the condition to an `else if`.
2401                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2402                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2403                 {
2404                     self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}"))
2405                         .span_label(else_span, "expected an `if` or a block after this `else`")
2406                         .span_suggestion(
2407                             cond.span.shrink_to_lo(),
2408                             "add an `if` if this is the condition of a chained `else if` statement",
2409                             "if ",
2410                             Applicability::MaybeIncorrect,
2411                         )
2412                         .emit();
2413                     self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)?
2414                 }
2415                 Err(e) => {
2416                     e.cancel();
2417                     self.restore_snapshot(snapshot);
2418                     self.parse_simple_block()?
2419                 },
2420                 Ok(_) => {
2421                     self.restore_snapshot(snapshot);
2422                     self.parse_simple_block()?
2423                 },
2424             }
2425         };
2426         self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
2427         Ok(expr)
2428     }
2429
2430     fn error_on_if_block_attrs(
2431         &self,
2432         ctx_span: Span,
2433         is_ctx_else: bool,
2434         branch_span: Span,
2435         attrs: &[ast::Attribute],
2436     ) {
2437         let (span, last) = match attrs {
2438             [] => return,
2439             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2440         };
2441         let ctx = if is_ctx_else { "else" } else { "if" };
2442         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
2443             .span_label(branch_span, "the attributes are attached to this branch")
2444             .span_label(ctx_span, format!("the branch belongs to this `{ctx}`"))
2445             .span_suggestion(span, "remove the attributes", "", Applicability::MachineApplicable)
2446             .emit();
2447     }
2448
2449     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2450     fn parse_for_expr(
2451         &mut self,
2452         opt_label: Option<Label>,
2453         lo: Span,
2454         mut attrs: AttrVec,
2455     ) -> PResult<'a, P<Expr>> {
2456         // Record whether we are about to parse `for (`.
2457         // This is used below for recovery in case of `for ( $stuff ) $block`
2458         // in which case we will suggest `for $stuff $block`.
2459         let begin_paren = match self.token.kind {
2460             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2461             _ => None,
2462         };
2463
2464         let pat = self.parse_pat_allow_top_alt(
2465             None,
2466             RecoverComma::Yes,
2467             RecoverColon::Yes,
2468             CommaRecoveryMode::LikelyTuple,
2469         )?;
2470         if !self.eat_keyword(kw::In) {
2471             self.error_missing_in_for_loop();
2472         }
2473         self.check_for_for_in_in_typo(self.prev_token.span);
2474         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2475
2476         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2477
2478         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
2479         attrs.extend(iattrs);
2480
2481         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2482         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2483     }
2484
2485     fn error_missing_in_for_loop(&mut self) {
2486         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
2487             // Possibly using JS syntax (#75311).
2488             let span = self.token.span;
2489             self.bump();
2490             (span, "try using `in` here instead", "in")
2491         } else {
2492             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
2493         };
2494         self.struct_span_err(span, "missing `in` in `for` loop")
2495             .span_suggestion_short(
2496                 span,
2497                 msg,
2498                 sugg,
2499                 // Has been misleading, at least in the past (closed Issue #48492).
2500                 Applicability::MaybeIncorrect,
2501             )
2502             .emit();
2503     }
2504
2505     /// Parses a `while` or `while let` expression (`while` token already eaten).
2506     fn parse_while_expr(
2507         &mut self,
2508         opt_label: Option<Label>,
2509         lo: Span,
2510         mut attrs: AttrVec,
2511     ) -> PResult<'a, P<Expr>> {
2512         let cond = self.parse_cond_expr().map_err(|mut err| {
2513             err.span_label(lo, "while parsing the condition of this `while` expression");
2514             err
2515         })?;
2516         let (iattrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2517             err.span_label(lo, "while parsing the body of this `while` expression");
2518             err.span_label(cond.span, "this `while` condition successfully parsed");
2519             err
2520         })?;
2521         attrs.extend(iattrs);
2522         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2523     }
2524
2525     /// Parses `loop { ... }` (`loop` token already eaten).
2526     fn parse_loop_expr(
2527         &mut self,
2528         opt_label: Option<Label>,
2529         lo: Span,
2530         mut attrs: AttrVec,
2531     ) -> PResult<'a, P<Expr>> {
2532         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2533         attrs.extend(iattrs);
2534         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2535     }
2536
2537     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2538         self.token.lifetime().map(|ident| {
2539             self.bump();
2540             Label { ident }
2541         })
2542     }
2543
2544     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2545     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2546         let match_span = self.prev_token.span;
2547         let lo = self.prev_token.span;
2548         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2549         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2550             if self.token == token::Semi {
2551                 e.span_suggestion_short(
2552                     match_span,
2553                     "try removing this `match`",
2554                     "",
2555                     Applicability::MaybeIncorrect, // speculative
2556                 );
2557             }
2558             if self.maybe_recover_unexpected_block_label() {
2559                 e.cancel();
2560                 self.bump();
2561             } else {
2562                 return Err(e);
2563             }
2564         }
2565         attrs.extend(self.parse_inner_attributes()?);
2566
2567         let mut arms: Vec<Arm> = Vec::new();
2568         while self.token != token::CloseDelim(Delimiter::Brace) {
2569             match self.parse_arm() {
2570                 Ok(arm) => arms.push(arm),
2571                 Err(mut e) => {
2572                     // Recover by skipping to the end of the block.
2573                     e.emit();
2574                     self.recover_stmt();
2575                     let span = lo.to(self.token.span);
2576                     if self.token == token::CloseDelim(Delimiter::Brace) {
2577                         self.bump();
2578                     }
2579                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2580                 }
2581             }
2582         }
2583         let hi = self.token.span;
2584         self.bump();
2585         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2586     }
2587
2588     /// Attempt to recover from match arm body with statements and no surrounding braces.
2589     fn parse_arm_body_missing_braces(
2590         &mut self,
2591         first_expr: &P<Expr>,
2592         arrow_span: Span,
2593     ) -> Option<P<Expr>> {
2594         if self.token.kind != token::Semi {
2595             return None;
2596         }
2597         let start_snapshot = self.create_snapshot_for_diagnostic();
2598         let semi_sp = self.token.span;
2599         self.bump(); // `;`
2600         let mut stmts =
2601             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2602         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2603             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2604             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2605             let (these, s, are) =
2606                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2607             err.span_label(
2608                 span,
2609                 &format!(
2610                     "{these} statement{s} {are} not surrounded by a body",
2611                     these = these,
2612                     s = s,
2613                     are = are
2614                 ),
2615             );
2616             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2617             if stmts.len() > 1 {
2618                 err.multipart_suggestion(
2619                     &format!("surround the statement{s} with a body"),
2620                     vec![
2621                         (span.shrink_to_lo(), "{ ".to_string()),
2622                         (span.shrink_to_hi(), " }".to_string()),
2623                     ],
2624                     Applicability::MachineApplicable,
2625                 );
2626             } else {
2627                 err.span_suggestion(
2628                     semi_sp,
2629                     "use a comma to end a `match` arm expression",
2630                     ",",
2631                     Applicability::MachineApplicable,
2632                 );
2633             }
2634             err.emit();
2635             this.mk_expr_err(span)
2636         };
2637         // We might have either a `,` -> `;` typo, or a block without braces. We need
2638         // a more subtle parsing strategy.
2639         loop {
2640             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2641                 // We have reached the closing brace of the `match` expression.
2642                 return Some(err(self, stmts));
2643             }
2644             if self.token.kind == token::Comma {
2645                 self.restore_snapshot(start_snapshot);
2646                 return None;
2647             }
2648             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2649             match self.parse_pat_no_top_alt(None) {
2650                 Ok(_pat) => {
2651                     if self.token.kind == token::FatArrow {
2652                         // Reached arm end.
2653                         self.restore_snapshot(pre_pat_snapshot);
2654                         return Some(err(self, stmts));
2655                     }
2656                 }
2657                 Err(err) => {
2658                     err.cancel();
2659                 }
2660             }
2661
2662             self.restore_snapshot(pre_pat_snapshot);
2663             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2664                 // Consume statements for as long as possible.
2665                 Ok(Some(stmt)) => {
2666                     stmts.push(stmt);
2667                 }
2668                 Ok(None) => {
2669                     self.restore_snapshot(start_snapshot);
2670                     break;
2671                 }
2672                 // We couldn't parse either yet another statement missing it's
2673                 // enclosing block nor the next arm's pattern or closing brace.
2674                 Err(stmt_err) => {
2675                     stmt_err.cancel();
2676                     self.restore_snapshot(start_snapshot);
2677                     break;
2678                 }
2679             }
2680         }
2681         None
2682     }
2683
2684     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2685         // Used to check the `let_chains` and `if_let_guard` features mostly by scaning
2686         // `&&` tokens.
2687         fn check_let_expr(expr: &Expr) -> bool {
2688             match expr.kind {
2689                 ExprKind::Binary(_, ref lhs, ref rhs) => check_let_expr(lhs) || check_let_expr(rhs),
2690                 ExprKind::Let(..) => true,
2691                 _ => false,
2692             }
2693         }
2694         let attrs = self.parse_outer_attributes()?;
2695         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2696             let lo = this.token.span;
2697             let pat = this.parse_pat_allow_top_alt(
2698                 None,
2699                 RecoverComma::Yes,
2700                 RecoverColon::Yes,
2701                 CommaRecoveryMode::EitherTupleOrPipe,
2702             )?;
2703             let guard = if this.eat_keyword(kw::If) {
2704                 let if_span = this.prev_token.span;
2705                 let cond = this.with_let_management(true, |local_this| local_this.parse_expr())?;
2706                 let has_let_expr = check_let_expr(&cond);
2707                 if has_let_expr {
2708                     let span = if_span.to(cond.span);
2709                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2710                 }
2711                 Some(cond)
2712             } else {
2713                 None
2714             };
2715             let arrow_span = this.token.span;
2716             if let Err(mut err) = this.expect(&token::FatArrow) {
2717                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2718                 if TokenKind::FatArrow
2719                     .similar_tokens()
2720                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2721                 {
2722                     err.span_suggestion(
2723                         this.token.span,
2724                         "try using a fat arrow here",
2725                         "=>",
2726                         Applicability::MaybeIncorrect,
2727                     );
2728                     err.emit();
2729                     this.bump();
2730                 } else {
2731                     return Err(err);
2732                 }
2733             }
2734             let arm_start_span = this.token.span;
2735
2736             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2737                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2738                 err
2739             })?;
2740
2741             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2742                 && this.token != token::CloseDelim(Delimiter::Brace);
2743
2744             let hi = this.prev_token.span;
2745
2746             if require_comma {
2747                 let sm = this.sess.source_map();
2748                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2749                     let span = body.span;
2750                     return Ok((
2751                         ast::Arm {
2752                             attrs: attrs.into(),
2753                             pat,
2754                             guard,
2755                             body,
2756                             span,
2757                             id: DUMMY_NODE_ID,
2758                             is_placeholder: false,
2759                         },
2760                         TrailingToken::None,
2761                     ));
2762                 }
2763                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2764                     .or_else(|mut err| {
2765                         if this.token == token::FatArrow {
2766                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2767                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2768                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2769                             && expr_lines.lines.len() == 2
2770                             {
2771                                 // We check whether there's any trailing code in the parse span,
2772                                 // if there isn't, we very likely have the following:
2773                                 //
2774                                 // X |     &Y => "y"
2775                                 //   |        --    - missing comma
2776                                 //   |        |
2777                                 //   |        arrow_span
2778                                 // X |     &X => "x"
2779                                 //   |      - ^^ self.token.span
2780                                 //   |      |
2781                                 //   |      parsed until here as `"y" & X`
2782                                 err.span_suggestion_short(
2783                                     arm_start_span.shrink_to_hi(),
2784                                     "missing a comma here to end this `match` arm",
2785                                     ",",
2786                                     Applicability::MachineApplicable,
2787                                 );
2788                                 return Err(err);
2789                             }
2790                         } else {
2791                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2792
2793                             // Try to parse a following `PAT =>`, if successful
2794                             // then we should recover.
2795                             let mut snapshot = this.create_snapshot_for_diagnostic();
2796                             let pattern_follows = snapshot
2797                                 .parse_pat_allow_top_alt(
2798                                     None,
2799                                     RecoverComma::Yes,
2800                                     RecoverColon::Yes,
2801                                     CommaRecoveryMode::EitherTupleOrPipe,
2802                                 )
2803                                 .map_err(|err| err.cancel())
2804                                 .is_ok();
2805                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2806                                 err.cancel();
2807                                 this.struct_span_err(
2808                                     hi.shrink_to_hi(),
2809                                     "expected `,` following `match` arm",
2810                                 )
2811                                 .span_suggestion(
2812                                     hi.shrink_to_hi(),
2813                                     "missing a comma here to end this `match` arm",
2814                                     ",",
2815                                     Applicability::MachineApplicable,
2816                                 )
2817                                 .emit();
2818                                 return Ok(true);
2819                             }
2820                         }
2821                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2822                         Err(err)
2823                     })?;
2824             } else {
2825                 this.eat(&token::Comma);
2826             }
2827
2828             Ok((
2829                 ast::Arm {
2830                     attrs: attrs.into(),
2831                     pat,
2832                     guard,
2833                     body: expr,
2834                     span: lo.to(hi),
2835                     id: DUMMY_NODE_ID,
2836                     is_placeholder: false,
2837                 },
2838                 TrailingToken::None,
2839             ))
2840         })
2841     }
2842
2843     /// Parses a `try {...}` expression (`try` token already eaten).
2844     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2845         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2846         attrs.extend(iattrs);
2847         if self.eat_keyword(kw::Catch) {
2848             let mut error = self.struct_span_err(
2849                 self.prev_token.span,
2850                 "keyword `catch` cannot follow a `try` block",
2851             );
2852             error.help("try using `match` on the result of the `try` block instead");
2853             error.emit();
2854             Err(error)
2855         } else {
2856             let span = span_lo.to(body.span);
2857             self.sess.gated_spans.gate(sym::try_blocks, span);
2858             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2859         }
2860     }
2861
2862     fn is_do_catch_block(&self) -> bool {
2863         self.token.is_keyword(kw::Do)
2864             && self.is_keyword_ahead(1, &[kw::Catch])
2865             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2866             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2867     }
2868
2869     fn is_do_yeet(&self) -> bool {
2870         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2871     }
2872
2873     fn is_try_block(&self) -> bool {
2874         self.token.is_keyword(kw::Try)
2875             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2876             && self.token.uninterpolated_span().rust_2018()
2877     }
2878
2879     /// Parses an `async move? {...}` expression.
2880     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2881         let lo = self.token.span;
2882         self.expect_keyword(kw::Async)?;
2883         let capture_clause = self.parse_capture_clause()?;
2884         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2885         attrs.extend(iattrs);
2886         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2887         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2888     }
2889
2890     fn is_async_block(&self) -> bool {
2891         self.token.is_keyword(kw::Async)
2892             && ((
2893                 // `async move {`
2894                 self.is_keyword_ahead(1, &[kw::Move])
2895                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2896             ) || (
2897                 // `async {`
2898                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2899             ))
2900     }
2901
2902     fn is_certainly_not_a_block(&self) -> bool {
2903         self.look_ahead(1, |t| t.is_ident())
2904             && (
2905                 // `{ ident, ` cannot start a block.
2906                 self.look_ahead(2, |t| t == &token::Comma)
2907                     || self.look_ahead(2, |t| t == &token::Colon)
2908                         && (
2909                             // `{ ident: token, ` cannot start a block.
2910                             self.look_ahead(4, |t| t == &token::Comma) ||
2911                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2912                 self.look_ahead(3, |t| !t.can_begin_type())
2913                         )
2914             )
2915     }
2916
2917     fn maybe_parse_struct_expr(
2918         &mut self,
2919         qself: Option<&ast::QSelf>,
2920         path: &ast::Path,
2921         attrs: &AttrVec,
2922     ) -> Option<PResult<'a, P<Expr>>> {
2923         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2924         if struct_allowed || self.is_certainly_not_a_block() {
2925             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2926                 return Some(Err(err));
2927             }
2928             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2929             if let (Ok(expr), false) = (&expr, struct_allowed) {
2930                 // This is a struct literal, but we don't can't accept them here.
2931                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2932             }
2933             return Some(expr);
2934         }
2935         None
2936     }
2937
2938     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2939         self.struct_span_err(sp, "struct literals are not allowed here")
2940             .multipart_suggestion(
2941                 "surround the struct literal with parentheses",
2942                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2943                 Applicability::MachineApplicable,
2944             )
2945             .emit();
2946     }
2947
2948     pub(super) fn parse_struct_fields(
2949         &mut self,
2950         pth: ast::Path,
2951         recover: bool,
2952         close_delim: Delimiter,
2953     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2954         let mut fields = Vec::new();
2955         let mut base = ast::StructRest::None;
2956         let mut recover_async = false;
2957
2958         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2959             recover_async = true;
2960             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2961             e.help_use_latest_edition();
2962         };
2963
2964         while self.token != token::CloseDelim(close_delim) {
2965             if self.eat(&token::DotDot) {
2966                 let exp_span = self.prev_token.span;
2967                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2968                 if self.check(&token::CloseDelim(close_delim)) {
2969                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2970                     break;
2971                 }
2972                 match self.parse_expr() {
2973                     Ok(e) => base = ast::StructRest::Base(e),
2974                     Err(mut e) if recover => {
2975                         e.emit();
2976                         self.recover_stmt();
2977                     }
2978                     Err(e) => return Err(e),
2979                 }
2980                 self.recover_struct_comma_after_dotdot(exp_span);
2981                 break;
2982             }
2983
2984             let recovery_field = self.find_struct_error_after_field_looking_code();
2985             let parsed_field = match self.parse_expr_field() {
2986                 Ok(f) => Some(f),
2987                 Err(mut e) => {
2988                     if pth == kw::Async {
2989                         async_block_err(&mut e, pth.span);
2990                     } else {
2991                         e.span_label(pth.span, "while parsing this struct");
2992                     }
2993                     e.emit();
2994
2995                     // If the next token is a comma, then try to parse
2996                     // what comes next as additional fields, rather than
2997                     // bailing out until next `}`.
2998                     if self.token != token::Comma {
2999                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3000                         if self.token != token::Comma {
3001                             break;
3002                         }
3003                     }
3004                     None
3005                 }
3006             };
3007
3008             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
3009             // A shorthand field can be turned into a full field with `:`.
3010             // We should point this out.
3011             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
3012
3013             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
3014                 Ok(_) => {
3015                     if let Some(f) = parsed_field.or(recovery_field) {
3016                         // Only include the field if there's no parse error for the field name.
3017                         fields.push(f);
3018                     }
3019                 }
3020                 Err(mut e) => {
3021                     if pth == kw::Async {
3022                         async_block_err(&mut e, pth.span);
3023                     } else {
3024                         e.span_label(pth.span, "while parsing this struct");
3025                         if let Some(f) = recovery_field {
3026                             fields.push(f);
3027                             e.span_suggestion(
3028                                 self.prev_token.span.shrink_to_hi(),
3029                                 "try adding a comma",
3030                                 ",",
3031                                 Applicability::MachineApplicable,
3032                             );
3033                         } else if is_shorthand
3034                             && (AssocOp::from_token(&self.token).is_some()
3035                                 || matches!(&self.token.kind, token::OpenDelim(_))
3036                                 || self.token.kind == token::Dot)
3037                         {
3038                             // Looks like they tried to write a shorthand, complex expression.
3039                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
3040                             e.span_suggestion(
3041                                 ident.span.shrink_to_lo(),
3042                                 "try naming a field",
3043                                 &format!("{ident}: "),
3044                                 Applicability::HasPlaceholders,
3045                             );
3046                         }
3047                     }
3048                     if !recover {
3049                         return Err(e);
3050                     }
3051                     e.emit();
3052                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3053                     self.eat(&token::Comma);
3054                 }
3055             }
3056         }
3057         Ok((fields, base, recover_async))
3058     }
3059
3060     /// Precondition: already parsed the '{'.
3061     pub(super) fn parse_struct_expr(
3062         &mut self,
3063         qself: Option<ast::QSelf>,
3064         pth: ast::Path,
3065         attrs: AttrVec,
3066         recover: bool,
3067     ) -> PResult<'a, P<Expr>> {
3068         let lo = pth.span;
3069         let (fields, base, recover_async) =
3070             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
3071         let span = lo.to(self.token.span);
3072         self.expect(&token::CloseDelim(Delimiter::Brace))?;
3073         let expr = if recover_async {
3074             ExprKind::Err
3075         } else {
3076             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
3077         };
3078         Ok(self.mk_expr(span, expr, attrs))
3079     }
3080
3081     /// Use in case of error after field-looking code: `S { foo: () with a }`.
3082     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
3083         match self.token.ident() {
3084             Some((ident, is_raw))
3085                 if (is_raw || !ident.is_reserved())
3086                     && self.look_ahead(1, |t| *t == token::Colon) =>
3087             {
3088                 Some(ast::ExprField {
3089                     ident,
3090                     span: self.token.span,
3091                     expr: self.mk_expr_err(self.token.span),
3092                     is_shorthand: false,
3093                     attrs: AttrVec::new(),
3094                     id: DUMMY_NODE_ID,
3095                     is_placeholder: false,
3096                 })
3097             }
3098             _ => None,
3099         }
3100     }
3101
3102     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
3103         if self.token != token::Comma {
3104             return;
3105         }
3106         self.struct_span_err(
3107             span.to(self.prev_token.span),
3108             "cannot use a comma after the base struct",
3109         )
3110         .span_suggestion_short(
3111             self.token.span,
3112             "remove this comma",
3113             "",
3114             Applicability::MachineApplicable,
3115         )
3116         .note("the base struct must always be the last field")
3117         .emit();
3118         self.recover_stmt();
3119     }
3120
3121     /// Parses `ident (COLON expr)?`.
3122     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3123         let attrs = self.parse_outer_attributes()?;
3124         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3125             let lo = this.token.span;
3126
3127             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3128             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3129             let (ident, expr) = if is_shorthand {
3130                 // Mimic `x: x` for the `x` field shorthand.
3131                 let ident = this.parse_ident_common(false)?;
3132                 let path = ast::Path::from_ident(ident);
3133                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
3134             } else {
3135                 let ident = this.parse_field_name()?;
3136                 this.error_on_eq_field_init(ident);
3137                 this.bump(); // `:`
3138                 (ident, this.parse_expr()?)
3139             };
3140
3141             Ok((
3142                 ast::ExprField {
3143                     ident,
3144                     span: lo.to(expr.span),
3145                     expr,
3146                     is_shorthand,
3147                     attrs: attrs.into(),
3148                     id: DUMMY_NODE_ID,
3149                     is_placeholder: false,
3150                 },
3151                 TrailingToken::MaybeComma,
3152             ))
3153         })
3154     }
3155
3156     /// Check for `=`. This means the source incorrectly attempts to
3157     /// initialize a field with an eq rather than a colon.
3158     fn error_on_eq_field_init(&self, field_name: Ident) {
3159         if self.token != token::Eq {
3160             return;
3161         }
3162
3163         self.struct_span_err(self.token.span, "expected `:`, found `=`")
3164             .span_suggestion(
3165                 field_name.span.shrink_to_hi().to(self.token.span),
3166                 "replace equals symbol with a colon",
3167                 ":",
3168                 Applicability::MachineApplicable,
3169             )
3170             .emit();
3171     }
3172
3173     fn err_dotdotdot_syntax(&self, span: Span) {
3174         self.struct_span_err(span, "unexpected token: `...`")
3175             .span_suggestion(
3176                 span,
3177                 "use `..` for an exclusive range",
3178                 "..",
3179                 Applicability::MaybeIncorrect,
3180             )
3181             .span_suggestion(
3182                 span,
3183                 "or `..=` for an inclusive range",
3184                 "..=",
3185                 Applicability::MaybeIncorrect,
3186             )
3187             .emit();
3188     }
3189
3190     fn err_larrow_operator(&self, span: Span) {
3191         self.struct_span_err(span, "unexpected token: `<-`")
3192             .span_suggestion(
3193                 span,
3194                 "if you meant to write a comparison against a negative value, add a \
3195              space in between `<` and `-`",
3196                 "< -",
3197                 Applicability::MaybeIncorrect,
3198             )
3199             .emit();
3200     }
3201
3202     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3203         ExprKind::AssignOp(binop, lhs, rhs)
3204     }
3205
3206     fn mk_range(
3207         &mut self,
3208         start: Option<P<Expr>>,
3209         end: Option<P<Expr>>,
3210         limits: RangeLimits,
3211     ) -> ExprKind {
3212         if end.is_none() && limits == RangeLimits::Closed {
3213             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3214             ExprKind::Err
3215         } else {
3216             ExprKind::Range(start, end, limits)
3217         }
3218     }
3219
3220     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3221         ExprKind::Unary(unop, expr)
3222     }
3223
3224     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3225         ExprKind::Binary(binop, lhs, rhs)
3226     }
3227
3228     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3229         ExprKind::Index(expr, idx)
3230     }
3231
3232     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3233         ExprKind::Call(f, args)
3234     }
3235
3236     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3237         let span = lo.to(self.prev_token.span);
3238         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
3239         self.recover_from_await_method_call();
3240         await_expr
3241     }
3242
3243     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3244         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3245     }
3246
3247     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3248         self.mk_expr(span, ExprKind::Err, AttrVec::new())
3249     }
3250
3251     /// Create expression span ensuring the span of the parent node
3252     /// is larger than the span of lhs and rhs, including the attributes.
3253     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3254         lhs.attrs
3255             .iter()
3256             .find(|a| a.style == AttrStyle::Outer)
3257             .map_or(lhs_span, |a| a.span)
3258             .to(rhs_span)
3259     }
3260
3261     fn collect_tokens_for_expr(
3262         &mut self,
3263         attrs: AttrWrapper,
3264         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
3265     ) -> PResult<'a, P<Expr>> {
3266         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3267             let res = f(this, attrs)?;
3268             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3269                 && this.token.kind == token::Semi
3270             {
3271                 TrailingToken::Semi
3272             } else {
3273                 // FIXME - pass this through from the place where we know
3274                 // we need a comma, rather than assuming that `#[attr] expr,`
3275                 // always captures a trailing comma
3276                 TrailingToken::MaybeComma
3277             };
3278             Ok((res, trailing))
3279         })
3280     }
3281
3282     // Calls `f` with the internal `let_expr_allowed` set to `let_expr_allowed` and then
3283     // sets the internal `let_expr_allowed` back to its original value.
3284     fn with_let_management<T>(
3285         &mut self,
3286         let_expr_allowed: bool,
3287         f: impl FnOnce(&mut Self) -> T,
3288     ) -> T {
3289         let last_let_expr_allowed = mem::replace(&mut self.let_expr_allowed, let_expr_allowed);
3290         let rslt = f(self);
3291         self.let_expr_allowed = last_let_expr_allowed;
3292         rslt
3293     }
3294 }