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 (cast_kind, maybe_ascription_span) =
 831             if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
 832                 ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi())))
 833             } else {
 834                 ("cast", None)
 835             };
 836
 837         // Save the memory location of expr before parsing any following postfix operators.
 838         // This will be compared with the memory location of the output expression.
 839         // If they different we can assume we parsed another expression because the existing expression is not reallocated.
 840         let addr_before = &*cast_expr as *const _ as usize;
 841         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 842         let changed = addr_before != &*with_postfix as *const _ as usize;
 843
 844         // Check if an illegal postfix operator has been added after the cast.
 845         // If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator.
 846         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) || changed {
 847             let msg = format!(
 848                 "{cast_kind} cannot be followed by {}",
 849                 match with_postfix.kind {
 850                     ExprKind::Index(_, _) => "indexing",
 851                     ExprKind::Try(_) => "`?`",
 852                     ExprKind::Field(_, _) => "a field access",
 853                     ExprKind::MethodCall(_, _, _) => "a method call",
 854                     ExprKind::Call(_, _) => "a function call",
 855                     ExprKind::Await(_) => "`.await`",
 856                     ExprKind::Err => return Ok(with_postfix),
 857                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 858                 }
 859             );
 860             let mut err = self.struct_span_err(span, &msg);
 861
 862             let suggest_parens = |err: &mut DiagnosticBuilder<'_, _>| {
 863                 let suggestions = vec![
 864                     (span.shrink_to_lo(), "(".to_string()),
 865                     (span.shrink_to_hi(), ")".to_string()),
 866                 ];
 867                 err.multipart_suggestion(
 868                     "try surrounding the expression in parentheses",
 869                     suggestions,
 870                     Applicability::MachineApplicable,
 871                 );
 872             };
 873
 874             // If type ascription is "likely an error", the user will already be getting a useful
 875             // help message, and doesn't need a second.
 876             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 877                 self.maybe_annotate_with_ascription(&mut err, false);
 878             } else if let Some(ascription_span) = maybe_ascription_span {
 879                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 880                 if is_nightly {
 881                     suggest_parens(&mut err);
 882                 }
 883                 err.span_suggestion(
 884                     ascription_span,
 885                     &format!(
 886                         "{}remove the type ascription",
 887                         if is_nightly { "alternatively, " } else { "" }
 888                     ),
 889                     "",
 890                     if is_nightly {
 891                         Applicability::MaybeIncorrect
 892                     } else {
 893                         Applicability::MachineApplicable
 894                     },
 895                 );
 896             } else {
 897                 suggest_parens(&mut err);
 898             }
 899             err.emit();
 900         };
 901         Ok(with_postfix)
 902     }
 903
 904     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 905         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 906         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 907         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 908         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 909         Ok(lhs)
 910     }
 911
 912     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 913     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 914         self.expect_and()?;
 915         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 916         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 917         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 918         let expr = self.parse_prefix_expr(None);
 919         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 920         let span = lo.to(hi);
 921         if let Some(lt) = lifetime {
 922             self.error_remove_borrow_lifetime(span, lt.ident.span);
 923         }
 924         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 925     }
 926
 927     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 928         self.struct_span_err(span, "borrow expressions cannot be annotated with lifetimes")
 929             .span_label(lt_span, "annotated with lifetime here")
 930             .span_suggestion(
 931                 lt_span,
 932                 "remove the lifetime annotation",
 933                 "",
 934                 Applicability::MachineApplicable,
 935             )
 936             .emit();
 937     }
 938
 939     /// Parse `mut?` or `raw [ const | mut ]`.
 940     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 941         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 942             // `raw [ const | mut ]`.
 943             let found_raw = self.eat_keyword(kw::Raw);
 944             assert!(found_raw);
 945             let mutability = self.parse_const_or_mut().unwrap();
 946             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 947             (ast::BorrowKind::Raw, mutability)
 948         } else {
 949             // `mut?`
 950             (ast::BorrowKind::Ref, self.parse_mutability())
 951         }
 952     }
 953
 954     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 955     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 956         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 957         self.collect_tokens_for_expr(attrs, |this, attrs| {
 958             let base = this.parse_bottom_expr();
 959             let (span, base) = this.interpolated_or_expr_span(base)?;
 960             this.parse_dot_or_call_expr_with(base, span, attrs)
 961         })
 962     }
 963
 964     pub(super) fn parse_dot_or_call_expr_with(
 965         &mut self,
 966         e0: P<Expr>,
 967         lo: Span,
 968         mut attrs: Vec<ast::Attribute>,
 969     ) -> PResult<'a, P<Expr>> {
 970         // Stitch the list of outer attributes onto the return value.
 971         // A little bit ugly, but the best way given the current code
 972         // structure
 973         self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| {
 974             expr.map(|mut expr| {
 975                 attrs.extend::<Vec<_>>(expr.attrs.into());
 976                 expr.attrs = attrs.into();
 977                 expr
 978             })
 979         })
 980     }
 981
 982     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 983         loop {
 984             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 985                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 986                 // which could be suggested otherwise
 987                 self.eat_noexpect(&token::Question)
 988             } else {
 989                 self.eat(&token::Question)
 990             };
 991             if has_question {
 992                 // `expr?`
 993                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e), AttrVec::new());
 994                 continue;
 995             }
 996             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 997                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 998                 // which could be suggested otherwise
 999                 self.eat_noexpect(&token::Dot)
1000             } else {
1001                 self.eat(&token::Dot)
1002             };
1003             if has_dot {
1004                 // expr.f
1005                 e = self.parse_dot_suffix_expr(lo, e)?;
1006                 continue;
1007             }
1008             if self.expr_is_complete(&e) {
1009                 return Ok(e);
1010             }
1011             e = match self.token.kind {
1012                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1013                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1014                 _ => return Ok(e),
1015             }
1016         }
1017     }
1018
1019     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1020         self.look_ahead(1, |t| t.is_ident())
1021             && self.look_ahead(2, |t| t == &token::Colon)
1022             && self.look_ahead(3, |t| t.can_begin_expr())
1023     }
1024
1025     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1026         match self.token.uninterpolate().kind {
1027             token::Ident(..) => self.parse_dot_suffix(base, lo),
1028             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1029                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1030             }
1031             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1032                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1033             }
1034             _ => {
1035                 self.error_unexpected_after_dot();
1036                 Ok(base)
1037             }
1038         }
1039     }
1040
1041     fn error_unexpected_after_dot(&self) {
1042         // FIXME Could factor this out into non_fatal_unexpected or something.
1043         let actual = pprust::token_to_string(&self.token);
1044         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1045     }
1046
1047     // We need an identifier or integer, but the next token is a float.
1048     // Break the float into components to extract the identifier or integer.
1049     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1050     // parts unless those parts are processed immediately. `TokenCursor` should either
1051     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1052     // we should break everything including floats into more basic proc-macro style
1053     // tokens in the lexer (probably preferable).
1054     fn parse_tuple_field_access_expr_float(
1055         &mut self,
1056         lo: Span,
1057         base: P<Expr>,
1058         float: Symbol,
1059         suffix: Option<Symbol>,
1060     ) -> P<Expr> {
1061         #[derive(Debug)]
1062         enum FloatComponent {
1063             IdentLike(String),
1064             Punct(char),
1065         }
1066         use FloatComponent::*;
1067
1068         let float_str = float.as_str();
1069         let mut components = Vec::new();
1070         let mut ident_like = String::new();
1071         for c in float_str.chars() {
1072             if c == '_' || c.is_ascii_alphanumeric() {
1073                 ident_like.push(c);
1074             } else if matches!(c, '.' | '+' | '-') {
1075                 if !ident_like.is_empty() {
1076                     components.push(IdentLike(mem::take(&mut ident_like)));
1077                 }
1078                 components.push(Punct(c));
1079             } else {
1080                 panic!("unexpected character in a float token: {:?}", c)
1081             }
1082         }
1083         if !ident_like.is_empty() {
1084             components.push(IdentLike(ident_like));
1085         }
1086
1087         // With proc macros the span can refer to anything, the source may be too short,
1088         // or too long, or non-ASCII. It only makes sense to break our span into components
1089         // if its underlying text is identical to our float literal.
1090         let span = self.token.span;
1091         let can_take_span_apart =
1092             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1093
1094         match &*components {
1095             // 1e2
1096             [IdentLike(i)] => {
1097                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1098             }
1099             // 1.
1100             [IdentLike(i), Punct('.')] => {
1101                 let (ident_span, dot_span) = if can_take_span_apart() {
1102                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1103                     let ident_span = span.with_hi(span.lo + ident_len);
1104                     let dot_span = span.with_lo(span.lo + ident_len);
1105                     (ident_span, dot_span)
1106                 } else {
1107                     (span, span)
1108                 };
1109                 assert!(suffix.is_none());
1110                 let symbol = Symbol::intern(&i);
1111                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1112                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1113                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1114             }
1115             // 1.2 | 1.2e3
1116             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1117                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1118                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1119                     let ident1_span = span.with_hi(span.lo + ident1_len);
1120                     let dot_span = span
1121                         .with_lo(span.lo + ident1_len)
1122                         .with_hi(span.lo + ident1_len + BytePos(1));
1123                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1124                     (ident1_span, dot_span, ident2_span)
1125                 } else {
1126                     (span, span, span)
1127                 };
1128                 let symbol1 = Symbol::intern(&i1);
1129                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1130                 // This needs to be `Spacing::Alone` to prevent regressions.
1131                 // See issue #76399 and PR #76285 for more details
1132                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1133                 let base1 =
1134                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1135                 let symbol2 = Symbol::intern(&i2);
1136                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1137                 self.bump_with((next_token2, self.token_spacing)); // `.`
1138                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1139             }
1140             // 1e+ | 1e- (recovered)
1141             [IdentLike(_), Punct('+' | '-')] |
1142             // 1e+2 | 1e-2
1143             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1144             // 1.2e+ | 1.2e-
1145             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1146             // 1.2e+3 | 1.2e-3
1147             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1148                 // See the FIXME about `TokenCursor` above.
1149                 self.error_unexpected_after_dot();
1150                 base
1151             }
1152             _ => panic!("unexpected components in a float token: {:?}", components),
1153         }
1154     }
1155
1156     fn parse_tuple_field_access_expr(
1157         &mut self,
1158         lo: Span,
1159         base: P<Expr>,
1160         field: Symbol,
1161         suffix: Option<Symbol>,
1162         next_token: Option<(Token, Spacing)>,
1163     ) -> P<Expr> {
1164         match next_token {
1165             Some(next_token) => self.bump_with(next_token),
1166             None => self.bump(),
1167         }
1168         let span = self.prev_token.span;
1169         let field = ExprKind::Field(base, Ident::new(field, span));
1170         self.expect_no_suffix(span, "a tuple index", suffix);
1171         self.mk_expr(lo.to(span), field, AttrVec::new())
1172     }
1173
1174     /// Parse a function call expression, `expr(...)`.
1175     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1176         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1177             && self.look_ahead_type_ascription_as_field()
1178         {
1179             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1180         } else {
1181             None
1182         };
1183         let open_paren = self.token.span;
1184
1185         let mut seq = self.parse_paren_expr_seq().map(|args| {
1186             self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new())
1187         });
1188         if let Some(expr) =
1189             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1190         {
1191             return expr;
1192         }
1193         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1194     }
1195
1196     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1197     /// parentheses instead of braces, recover the parser state and provide suggestions.
1198     #[instrument(skip(self, seq, snapshot), level = "trace")]
1199     fn maybe_recover_struct_lit_bad_delims(
1200         &mut self,
1201         lo: Span,
1202         open_paren: Span,
1203         seq: &mut PResult<'a, P<Expr>>,
1204         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1205     ) -> Option<P<Expr>> {
1206         match (seq.as_mut(), snapshot) {
1207             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1208                 let name = pprust::path_to_string(&path);
1209                 snapshot.bump(); // `(`
1210                 match snapshot.parse_struct_fields(path, false, Delimiter::Parenthesis) {
1211                     Ok((fields, ..))
1212                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1213                     {
1214                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1215                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1216                         self.restore_snapshot(snapshot);
1217                         let close_paren = self.prev_token.span;
1218                         let span = lo.to(self.prev_token.span);
1219                         if !fields.is_empty() {
1220                             let replacement_err = self.struct_span_err(
1221                                 span,
1222                                 "invalid `struct` delimiters or `fn` call arguments",
1223                             );
1224                             mem::replace(err, replacement_err).cancel();
1225
1226                             err.multipart_suggestion(
1227                                 &format!("if `{name}` is a struct, use braces as delimiters"),
1228                                 vec![
1229                                     (open_paren, " { ".to_string()),
1230                                     (close_paren, " }".to_string()),
1231                                 ],
1232                                 Applicability::MaybeIncorrect,
1233                             );
1234                             err.multipart_suggestion(
1235                                 &format!("if `{name}` is a function, use the arguments directly"),
1236                                 fields
1237                                     .into_iter()
1238                                     .map(|field| (field.span.until(field.expr.span), String::new()))
1239                                     .collect(),
1240                                 Applicability::MaybeIncorrect,
1241                             );
1242                             err.emit();
1243                         } else {
1244                             err.emit();
1245                         }
1246                         return Some(self.mk_expr_err(span));
1247                     }
1248                     Ok(_) => {}
1249                     Err(mut err) => {
1250                         err.emit();
1251                     }
1252                 }
1253             }
1254             _ => {}
1255         }
1256         None
1257     }
1258
1259     /// Parse an indexing expression `expr[...]`.
1260     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1261         self.bump(); // `[`
1262         let index = self.parse_expr()?;
1263         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1264         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new()))
1265     }
1266
1267     /// Assuming we have just parsed `.`, continue parsing into an expression.
1268     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1269         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1270             return Ok(self.mk_await_expr(self_arg, lo));
1271         }
1272
1273         let fn_span_lo = self.token.span;
1274         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1275         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1276         self.check_turbofish_missing_angle_brackets(&mut segment);
1277
1278         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1279             // Method call `expr.f()`
1280             let mut args = self.parse_paren_expr_seq()?;
1281             args.insert(0, self_arg);
1282
1283             let fn_span = fn_span_lo.to(self.prev_token.span);
1284             let span = lo.to(self.prev_token.span);
1285             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new()))
1286         } else {
1287             // Field access `expr.f`
1288             if let Some(args) = segment.args {
1289                 self.struct_span_err(
1290                     args.span(),
1291                     "field expressions cannot have generic arguments",
1292                 )
1293                 .emit();
1294             }
1295
1296             let span = lo.to(self.prev_token.span);
1297             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new()))
1298         }
1299     }
1300
1301     /// At the bottom (top?) of the precedence hierarchy,
1302     /// Parses things like parenthesized exprs, macros, `return`, etc.
1303     ///
1304     /// N.B., this does not parse outer attributes, and is private because it only works
1305     /// correctly if called from `parse_dot_or_call_expr()`.
1306     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1307         maybe_recover_from_interpolated_ty_qpath!(self, true);
1308         maybe_whole_expr!(self);
1309
1310         // Outer attributes are already parsed and will be
1311         // added to the return value after the fact.
1312         //
1313         // Therefore, prevent sub-parser from parsing
1314         // attributes by giving them an empty "already-parsed" list.
1315         let attrs = AttrVec::new();
1316
1317         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1318         let lo = self.token.span;
1319         if let token::Literal(_) = self.token.kind {
1320             // This match arm is a special-case of the `_` match arm below and
1321             // could be removed without changing functionality, but it's faster
1322             // to have it here, especially for programs with large constants.
1323             self.parse_lit_expr(attrs)
1324         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1325             self.parse_tuple_parens_expr(attrs)
1326         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1327             self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs)
1328         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1329             self.parse_closure_expr(attrs).map_err(|mut err| {
1330                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1331                 // then suggest parens around the lhs.
1332                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1333                     self.sess.expr_parentheses_needed(&mut err, *sp);
1334                 }
1335                 err
1336             })
1337         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1338             self.parse_array_or_repeat_expr(attrs, Delimiter::Bracket)
1339         } else if self.check_path() {
1340             self.parse_path_start_expr(attrs)
1341         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1342             self.parse_closure_expr(attrs)
1343         } else if self.eat_keyword(kw::If) {
1344             self.parse_if_expr(attrs)
1345         } else if self.check_keyword(kw::For) {
1346             if self.choose_generics_over_qpath(1) {
1347                 self.parse_closure_expr(attrs)
1348             } else {
1349                 assert!(self.eat_keyword(kw::For));
1350                 self.parse_for_expr(None, self.prev_token.span, attrs)
1351             }
1352         } else if self.eat_keyword(kw::While) {
1353             self.parse_while_expr(None, self.prev_token.span, attrs)
1354         } else if let Some(label) = self.eat_label() {
1355             self.parse_labeled_expr(label, attrs, true)
1356         } else if self.eat_keyword(kw::Loop) {
1357             let sp = self.prev_token.span;
1358             self.parse_loop_expr(None, self.prev_token.span, attrs).map_err(|mut err| {
1359                 err.span_label(sp, "while parsing this `loop` expression");
1360                 err
1361             })
1362         } else if self.eat_keyword(kw::Continue) {
1363             let kind = ExprKind::Continue(self.eat_label());
1364             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1365         } else if self.eat_keyword(kw::Match) {
1366             let match_sp = self.prev_token.span;
1367             self.parse_match_expr(attrs).map_err(|mut err| {
1368                 err.span_label(match_sp, "while parsing this `match` expression");
1369                 err
1370             })
1371         } else if self.eat_keyword(kw::Unsafe) {
1372             let sp = self.prev_token.span;
1373             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1374                 .map_err(|mut err| {
1375                     err.span_label(sp, "while parsing this `unsafe` expression");
1376                     err
1377                 })
1378         } else if self.check_inline_const(0) {
1379             self.parse_const_block(lo.to(self.token.span), false)
1380         } else if self.is_do_catch_block() {
1381             self.recover_do_catch(attrs)
1382         } else if self.is_try_block() {
1383             self.expect_keyword(kw::Try)?;
1384             self.parse_try_block(lo, attrs)
1385         } else if self.eat_keyword(kw::Return) {
1386             self.parse_return_expr(attrs)
1387         } else if self.eat_keyword(kw::Break) {
1388             self.parse_break_expr(attrs)
1389         } else if self.eat_keyword(kw::Yield) {
1390             self.parse_yield_expr(attrs)
1391         } else if self.is_do_yeet() {
1392             self.parse_yeet_expr(attrs)
1393         } else if self.check_keyword(kw::Let) {
1394             self.manage_let_chains_context();
1395             self.bump();
1396             self.parse_let_expr(attrs)
1397         } else if self.eat_keyword(kw::Underscore) {
1398             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1399         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1400             // Don't complain about bare semicolons after unclosed braces
1401             // recovery in order to keep the error count down. Fixing the
1402             // delimiters will possibly also fix the bare semicolon found in
1403             // expression context. For example, silence the following error:
1404             //
1405             //     error: expected expression, found `;`
1406             //      --> file.rs:2:13
1407             //       |
1408             //     2 |     foo(bar(;
1409             //       |             ^ expected expression
1410             self.bump();
1411             Ok(self.mk_expr_err(self.token.span))
1412         } else if self.token.uninterpolated_span().rust_2018() {
1413             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1414             if self.check_keyword(kw::Async) {
1415                 if self.is_async_block() {
1416                     // Check for `async {` and `async move {`.
1417                     self.parse_async_block(attrs)
1418                 } else {
1419                     self.parse_closure_expr(attrs)
1420                 }
1421             } else if self.eat_keyword(kw::Await) {
1422                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1423             } else {
1424                 self.parse_lit_expr(attrs)
1425             }
1426         } else {
1427             self.parse_lit_expr(attrs)
1428         }
1429     }
1430
1431     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1432         let lo = self.token.span;
1433         match self.parse_opt_lit() {
1434             Some(literal) => {
1435                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1436                 self.maybe_recover_from_bad_qpath(expr)
1437             }
1438             None => self.try_macro_suggestion(),
1439         }
1440     }
1441
1442     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1443         let lo = self.token.span;
1444         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1445         let (es, trailing_comma) = match self.parse_seq_to_end(
1446             &token::CloseDelim(Delimiter::Parenthesis),
1447             SeqSep::trailing_allowed(token::Comma),
1448             |p| p.parse_expr_catch_underscore(),
1449         ) {
1450             Ok(x) => x,
1451             Err(err) => {
1452                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1453             }
1454         };
1455         let kind = if es.len() == 1 && !trailing_comma {
1456             // `(e)` is parenthesized `e`.
1457             ExprKind::Paren(es.into_iter().next().unwrap())
1458         } else {
1459             // `(e,)` is a tuple with only one field, `e`.
1460             ExprKind::Tup(es)
1461         };
1462         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1463         self.maybe_recover_from_bad_qpath(expr)
1464     }
1465
1466     fn parse_array_or_repeat_expr(
1467         &mut self,
1468         attrs: AttrVec,
1469         close_delim: Delimiter,
1470     ) -> PResult<'a, P<Expr>> {
1471         let lo = self.token.span;
1472         self.bump(); // `[` or other open delim
1473
1474         let close = &token::CloseDelim(close_delim);
1475         let kind = if self.eat(close) {
1476             // Empty vector
1477             ExprKind::Array(Vec::new())
1478         } else {
1479             // Non-empty vector
1480             let first_expr = self.parse_expr()?;
1481             if self.eat(&token::Semi) {
1482                 // Repeating array syntax: `[ 0; 512 ]`
1483                 let count = self.parse_anon_const_expr()?;
1484                 self.expect(close)?;
1485                 ExprKind::Repeat(first_expr, count)
1486             } else if self.eat(&token::Comma) {
1487                 // Vector with two or more elements.
1488                 let sep = SeqSep::trailing_allowed(token::Comma);
1489                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1490                 let mut exprs = vec![first_expr];
1491                 exprs.extend(remaining_exprs);
1492                 ExprKind::Array(exprs)
1493             } else {
1494                 // Vector with one element
1495                 self.expect(close)?;
1496                 ExprKind::Array(vec![first_expr])
1497             }
1498         };
1499         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1500         self.maybe_recover_from_bad_qpath(expr)
1501     }
1502
1503     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1504         let (qself, path) = if self.eat_lt() {
1505             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1506             (Some(qself), path)
1507         } else {
1508             (None, self.parse_path(PathStyle::Expr)?)
1509         };
1510         let lo = path.span;
1511
1512         // `!`, as an operator, is prefix, so we know this isn't that.
1513         let (hi, kind) = if self.eat(&token::Not) {
1514             // MACRO INVOCATION expression
1515             if qself.is_some() {
1516                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1517             }
1518             let mac = MacCall {
1519                 path,
1520                 args: self.parse_mac_args()?,
1521                 prior_type_ascription: self.last_type_ascription,
1522             };
1523             (self.prev_token.span, ExprKind::MacCall(mac))
1524         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1525             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1526                 if qself.is_some() {
1527                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1528                 }
1529                 return expr;
1530             } else {
1531                 (path.span, ExprKind::Path(qself, path))
1532             }
1533         } else {
1534             (path.span, ExprKind::Path(qself, path))
1535         };
1536
1537         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1538         self.maybe_recover_from_bad_qpath(expr)
1539     }
1540
1541     /// Parse `'label: $expr`. The label is already parsed.
1542     fn parse_labeled_expr(
1543         &mut self,
1544         label: Label,
1545         attrs: AttrVec,
1546         mut consume_colon: bool,
1547     ) -> PResult<'a, P<Expr>> {
1548         let lo = label.ident.span;
1549         let label = Some(label);
1550         let ate_colon = self.eat(&token::Colon);
1551         let expr = if self.eat_keyword(kw::While) {
1552             self.parse_while_expr(label, lo, attrs)
1553         } else if self.eat_keyword(kw::For) {
1554             self.parse_for_expr(label, lo, attrs)
1555         } else if self.eat_keyword(kw::Loop) {
1556             self.parse_loop_expr(label, lo, attrs)
1557         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1558             || self.token.is_whole_block()
1559         {
1560             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1561         } else if !ate_colon
1562             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1563         {
1564             // We're probably inside of a `Path<'a>` that needs a turbofish
1565             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1566             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1567             consume_colon = false;
1568             Ok(self.mk_expr_err(lo))
1569         } else {
1570             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1571
1572             let mut err = self.struct_span_err(self.token.span, msg);
1573             err.span_label(self.token.span, msg);
1574
1575             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1576             let expr = self.parse_expr().map(|expr| {
1577                 let span = expr.span;
1578
1579                 let found_labeled_breaks = {
1580                     struct FindLabeledBreaksVisitor(bool);
1581
1582                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1583                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1584                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1585                                 self.0 = true;
1586                             }
1587                         }
1588                     }
1589
1590                     let mut vis = FindLabeledBreaksVisitor(false);
1591                     vis.visit_expr(&expr);
1592                     vis.0
1593                 };
1594
1595                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1596                 //
1597                 // If there are no breaks that may use this label, suggest removing the label and
1598                 // recover to the unmodified expression.
1599                 if !found_labeled_breaks {
1600                     let msg = "consider removing the label";
1601                     err.span_suggestion_verbose(
1602                         lo.until(span),
1603                         msg,
1604                         "",
1605                         Applicability::MachineApplicable,
1606                     );
1607
1608                     return expr;
1609                 }
1610
1611                 let sugg_msg = "consider enclosing expression in a block";
1612                 let suggestions = vec![
1613                     (span.shrink_to_lo(), "{ ".to_owned()),
1614                     (span.shrink_to_hi(), " }".to_owned()),
1615                 ];
1616
1617                 err.multipart_suggestion_verbose(
1618                     sugg_msg,
1619                     suggestions,
1620                     Applicability::MachineApplicable,
1621                 );
1622
1623                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to supress future errors about `break 'label`.
1624                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1625                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1626                 self.mk_expr(span, ExprKind::Block(blk, label), ThinVec::new())
1627             });
1628
1629             err.emit();
1630             expr
1631         }?;
1632
1633         if !ate_colon && consume_colon {
1634             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1635         }
1636
1637         Ok(expr)
1638     }
1639
1640     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1641         self.struct_span_err(span, "labeled expression must be followed by `:`")
1642             .span_label(lo, "the label")
1643             .span_suggestion_short(
1644                 lo.shrink_to_hi(),
1645                 "add `:` after the label",
1646                 ": ",
1647                 Applicability::MachineApplicable,
1648             )
1649             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1650             .emit();
1651     }
1652
1653     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1654     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1655         let lo = self.token.span;
1656
1657         self.bump(); // `do`
1658         self.bump(); // `catch`
1659
1660         let span_dc = lo.to(self.prev_token.span);
1661         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1662             .span_suggestion(
1663                 span_dc,
1664                 "replace with the new syntax",
1665                 "try",
1666                 Applicability::MachineApplicable,
1667             )
1668             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1669             .emit();
1670
1671         self.parse_try_block(lo, attrs)
1672     }
1673
1674     /// Parse an expression if the token can begin one.
1675     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1676         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1677     }
1678
1679     /// Parse `"return" expr?`.
1680     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1681         let lo = self.prev_token.span;
1682         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1683         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1684         self.maybe_recover_from_bad_qpath(expr)
1685     }
1686
1687     /// Parse `"do" "yeet" expr?`.
1688     fn parse_yeet_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1689         let lo = self.token.span;
1690
1691         self.bump(); // `do`
1692         self.bump(); // `yeet`
1693
1694         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1695
1696         let span = lo.to(self.prev_token.span);
1697         self.sess.gated_spans.gate(sym::yeet_expr, span);
1698         let expr = self.mk_expr(span, kind, attrs);
1699         self.maybe_recover_from_bad_qpath(expr)
1700     }
1701
1702     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1703     /// If the label is followed immediately by a `:` token, the label and `:` are
1704     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1705     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1706     /// the break expression of an unlabeled break is a labeled loop (as in
1707     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1708     /// expression only gets a warning for compatibility reasons; and a labeled break
1709     /// with a labeled loop does not even get a warning because there is no ambiguity.
1710     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1711         let lo = self.prev_token.span;
1712         let mut label = self.eat_label();
1713         let kind = if label.is_some() && self.token == token::Colon {
1714             // The value expression can be a labeled loop, see issue #86948, e.g.:
1715             // `loop { break 'label: loop { break 'label 42; }; }`
1716             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1717             self.struct_span_err(
1718                 lexpr.span,
1719                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1720             )
1721             .multipart_suggestion(
1722                 "wrap the expression in parentheses",
1723                 vec![
1724                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1725                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1726                 ],
1727                 Applicability::MachineApplicable,
1728             )
1729             .emit();
1730             Some(lexpr)
1731         } else if self.token != token::OpenDelim(Delimiter::Brace)
1732             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1733         {
1734             let expr = self.parse_expr_opt()?;
1735             if let Some(ref expr) = expr {
1736                 if label.is_some()
1737                     && matches!(
1738                         expr.kind,
1739                         ExprKind::While(_, _, None)
1740                             | ExprKind::ForLoop(_, _, _, None)
1741                             | ExprKind::Loop(_, None)
1742                             | ExprKind::Block(_, None)
1743                     )
1744                 {
1745                     self.sess.buffer_lint_with_diagnostic(
1746                         BREAK_WITH_LABEL_AND_LOOP,
1747                         lo.to(expr.span),
1748                         ast::CRATE_NODE_ID,
1749                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1750                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1751                     );
1752                 }
1753             }
1754             expr
1755         } else {
1756             None
1757         };
1758         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1759         self.maybe_recover_from_bad_qpath(expr)
1760     }
1761
1762     /// Parse `"yield" expr?`.
1763     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1764         let lo = self.prev_token.span;
1765         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1766         let span = lo.to(self.prev_token.span);
1767         self.sess.gated_spans.gate(sym::generators, span);
1768         let expr = self.mk_expr(span, kind, attrs);
1769         self.maybe_recover_from_bad_qpath(expr)
1770     }
1771
1772     /// Returns a string literal if the next token is a string literal.
1773     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1774     /// and returns `None` if the next token is not literal at all.
1775     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1776         match self.parse_opt_lit() {
1777             Some(lit) => match lit.kind {
1778                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1779                     style,
1780                     symbol: lit.token.symbol,
1781                     suffix: lit.token.suffix,
1782                     span: lit.span,
1783                     symbol_unescaped,
1784                 }),
1785                 _ => Err(Some(lit)),
1786             },
1787             None => Err(None),
1788         }
1789     }
1790
1791     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1792         self.parse_opt_lit().ok_or_else(|| {
1793             if let token::Interpolated(inner) = &self.token.kind {
1794                 let expr = match inner.as_ref() {
1795                     token::NtExpr(expr) => Some(expr),
1796                     token::NtLiteral(expr) => Some(expr),
1797                     _ => None,
1798                 };
1799                 if let Some(expr) = expr {
1800                     if matches!(expr.kind, ExprKind::Err) {
1801                         let mut err = self
1802                             .diagnostic()
1803                             .struct_span_err(self.token.span, "invalid interpolated expression");
1804                         err.downgrade_to_delayed_bug();
1805                         return err;
1806                     }
1807                 }
1808             }
1809             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1810             self.struct_span_err(self.token.span, &msg)
1811         })
1812     }
1813
1814     /// Matches `lit = true | false | token_lit`.
1815     /// Returns `None` if the next token is not a literal.
1816     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1817         let mut recovered = None;
1818         if self.token == token::Dot {
1819             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1820             // dot would follow an optional literal, so we do this unconditionally.
1821             recovered = self.look_ahead(1, |next_token| {
1822                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1823                     next_token.kind
1824                 {
1825                     if self.token.span.hi() == next_token.span.lo() {
1826                         let s = String::from("0.") + symbol.as_str();
1827                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1828                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1829                     }
1830                 }
1831                 None
1832             });
1833             if let Some(token) = &recovered {
1834                 self.bump();
1835                 self.error_float_lits_must_have_int_part(&token);
1836             }
1837         }
1838
1839         let token = recovered.as_ref().unwrap_or(&self.token);
1840         match Lit::from_token(token) {
1841             Ok(lit) => {
1842                 self.bump();
1843                 Some(lit)
1844             }
1845             Err(LitError::NotLiteral) => None,
1846             Err(err) => {
1847                 let span = token.span;
1848                 let token::Literal(lit) = token.kind else {
1849                     unreachable!();
1850                 };
1851                 self.bump();
1852                 self.report_lit_error(err, lit, span);
1853                 // Pack possible quotes and prefixes from the original literal into
1854                 // the error literal's symbol so they can be pretty-printed faithfully.
1855                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1856                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1857                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1858                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1859             }
1860         }
1861     }
1862
1863     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1864         self.struct_span_err(token.span, "float literals must have an integer part")
1865             .span_suggestion(
1866                 token.span,
1867                 "must have an integer part",
1868                 pprust::token_to_string(token),
1869                 Applicability::MachineApplicable,
1870             )
1871             .emit();
1872     }
1873
1874     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1875         // Checks if `s` looks like i32 or u1234 etc.
1876         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1877             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1878         }
1879
1880         // Try to lowercase the prefix if it's a valid base prefix.
1881         fn fix_base_capitalisation(s: &str) -> Option<String> {
1882             if let Some(stripped) = s.strip_prefix('B') {
1883                 Some(format!("0b{stripped}"))
1884             } else if let Some(stripped) = s.strip_prefix('O') {
1885                 Some(format!("0o{stripped}"))
1886             } else if let Some(stripped) = s.strip_prefix('X') {
1887                 Some(format!("0x{stripped}"))
1888             } else {
1889                 None
1890             }
1891         }
1892
1893         let token::Lit { kind, suffix, .. } = lit;
1894         match err {
1895             // `NotLiteral` is not an error by itself, so we don't report
1896             // it and give the parser opportunity to try something else.
1897             LitError::NotLiteral => {}
1898             // `LexerError` *is* an error, but it was already reported
1899             // by lexer, so here we don't report it the second time.
1900             LitError::LexerError => {}
1901             LitError::InvalidSuffix => {
1902                 self.expect_no_suffix(
1903                     span,
1904                     &format!("{} {} literal", kind.article(), kind.descr()),
1905                     suffix,
1906                 );
1907             }
1908             LitError::InvalidIntSuffix => {
1909                 let suf = suffix.expect("suffix error with no suffix");
1910                 let suf = suf.as_str();
1911                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1912                     // If it looks like a width, try to be helpful.
1913                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1914                     self.struct_span_err(span, &msg)
1915                         .help("valid widths are 8, 16, 32, 64 and 128")
1916                         .emit();
1917                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1918                     let msg = "invalid base prefix for number literal";
1919
1920                     self.struct_span_err(span, msg)
1921                         .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase")
1922                         .span_suggestion(
1923                             span,
1924                             "try making the prefix lowercase",
1925                             fixed,
1926                             Applicability::MaybeIncorrect,
1927                         )
1928                         .emit();
1929                 } else {
1930                     let msg = format!("invalid suffix `{suf}` for number literal");
1931                     self.struct_span_err(span, &msg)
1932                         .span_label(span, format!("invalid suffix `{suf}`"))
1933                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1934                         .emit();
1935                 }
1936             }
1937             LitError::InvalidFloatSuffix => {
1938                 let suf = suffix.expect("suffix error with no suffix");
1939                 let suf = suf.as_str();
1940                 if looks_like_width_suffix(&['f'], suf) {
1941                     // If it looks like a width, try to be helpful.
1942                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1943                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1944                 } else {
1945                     let msg = format!("invalid suffix `{suf}` for float literal");
1946                     self.struct_span_err(span, &msg)
1947                         .span_label(span, format!("invalid suffix `{suf}`"))
1948                         .help("valid suffixes are `f32` and `f64`")
1949                         .emit();
1950                 }
1951             }
1952             LitError::NonDecimalFloat(base) => {
1953                 let descr = match base {
1954                     16 => "hexadecimal",
1955                     8 => "octal",
1956                     2 => "binary",
1957                     _ => unreachable!(),
1958                 };
1959                 self.struct_span_err(span, &format!("{descr} float literal is not supported"))
1960                     .span_label(span, "not supported")
1961                     .emit();
1962             }
1963             LitError::IntTooLarge => {
1964                 self.struct_span_err(span, "integer literal is too large").emit();
1965             }
1966         }
1967     }
1968
1969     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1970         if let Some(suf) = suffix {
1971             let mut err = if kind == "a tuple index"
1972                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1973             {
1974                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1975                 // through the ecosystem when people fix their macros
1976                 let mut err = self
1977                     .sess
1978                     .span_diagnostic
1979                     .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
1980                 err.note(&format!(
1981                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1982                         incorrectly accepted on stable for a few releases",
1983                     suf,
1984                 ));
1985                 err.help(
1986                     "on proc macros, you'll want to use `syn::Index::from` or \
1987                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1988                         to tuple field access",
1989                 );
1990                 err.note(
1991                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1992                      for more information",
1993                 );
1994                 err
1995             } else {
1996                 self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
1997                     .forget_guarantee()
1998             };
1999             err.span_label(sp, format!("invalid suffix `{suf}`"));
2000             err.emit();
2001         }
2002     }
2003
2004     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
2005     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
2006     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
2007         maybe_whole_expr!(self);
2008
2009         let lo = self.token.span;
2010         let minus_present = self.eat(&token::BinOp(token::Minus));
2011         let lit = self.parse_lit()?;
2012         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
2013
2014         if minus_present {
2015             Ok(self.mk_expr(
2016                 lo.to(self.prev_token.span),
2017                 self.mk_unary(UnOp::Neg, expr),
2018                 AttrVec::new(),
2019             ))
2020         } else {
2021             Ok(expr)
2022         }
2023     }
2024
2025     fn is_array_like_block(&mut self) -> bool {
2026         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
2027             && self.look_ahead(2, |t| t == &token::Comma)
2028             && self.look_ahead(3, |t| t.can_begin_expr())
2029     }
2030
2031     /// Emits a suggestion if it looks like the user meant an array but
2032     /// accidentally used braces, causing the code to be interpreted as a block
2033     /// expression.
2034     fn maybe_suggest_brackets_instead_of_braces(
2035         &mut self,
2036         lo: Span,
2037         attrs: AttrVec,
2038     ) -> Option<P<Expr>> {
2039         let mut snapshot = self.create_snapshot_for_diagnostic();
2040         match snapshot.parse_array_or_repeat_expr(attrs, Delimiter::Brace) {
2041             Ok(arr) => {
2042                 let hi = snapshot.prev_token.span;
2043                 self.struct_span_err(arr.span, "this is a block expression, not an array")
2044                     .multipart_suggestion(
2045                         "to make an array, use square brackets instead of curly braces",
2046                         vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
2047                         Applicability::MaybeIncorrect,
2048                     )
2049                     .emit();
2050
2051                 self.restore_snapshot(snapshot);
2052                 Some(self.mk_expr_err(arr.span))
2053             }
2054             Err(e) => {
2055                 e.cancel();
2056                 None
2057             }
2058         }
2059     }
2060
2061     /// Parses a block or unsafe block.
2062     pub(super) fn parse_block_expr(
2063         &mut self,
2064         opt_label: Option<Label>,
2065         lo: Span,
2066         blk_mode: BlockCheckMode,
2067         mut attrs: AttrVec,
2068     ) -> PResult<'a, P<Expr>> {
2069         if self.is_array_like_block() {
2070             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) {
2071                 return Ok(arr);
2072             }
2073         }
2074
2075         if let Some(label) = opt_label {
2076             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
2077         }
2078
2079         if self.token.is_whole_block() {
2080             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
2081                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
2082                 .emit();
2083         }
2084
2085         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
2086         attrs.extend(inner_attrs);
2087         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
2088     }
2089
2090     /// Parse a block which takes no attributes and has no label
2091     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2092         let blk = self.parse_block()?;
2093         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()))
2094     }
2095
2096     /// Parses a closure expression (e.g., `move |args| expr`).
2097     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2098         let lo = self.token.span;
2099
2100         let binder = if self.check_keyword(kw::For) {
2101             let lo = self.token.span;
2102             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2103             let span = lo.to(self.prev_token.span);
2104
2105             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2106
2107             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2108         } else {
2109             ClosureBinder::NotPresent
2110         };
2111
2112         let movability =
2113             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2114
2115         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2116             self.parse_asyncness()
2117         } else {
2118             Async::No
2119         };
2120
2121         let capture_clause = self.parse_capture_clause()?;
2122         let decl = self.parse_fn_block_decl()?;
2123         let decl_hi = self.prev_token.span;
2124         let mut body = match decl.output {
2125             FnRetTy::Default(_) => {
2126                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2127                 self.parse_expr_res(restrictions, None)?
2128             }
2129             _ => {
2130                 // If an explicit return type is given, require a block to appear (RFC 968).
2131                 let body_lo = self.token.span;
2132                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
2133             }
2134         };
2135
2136         if let Async::Yes { span, .. } = asyncness {
2137             // Feature-gate `async ||` closures.
2138             self.sess.gated_spans.gate(sym::async_closure, span);
2139         }
2140
2141         if self.token.kind == TokenKind::Semi
2142             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2143         {
2144             // It is likely that the closure body is a block but where the
2145             // braces have been removed. We will recover and eat the next
2146             // statements later in the parsing process.
2147             body = self.mk_expr_err(body.span);
2148         }
2149
2150         let body_span = body.span;
2151
2152         let closure = self.mk_expr(
2153             lo.to(body.span),
2154             ExprKind::Closure(
2155                 binder,
2156                 capture_clause,
2157                 asyncness,
2158                 movability,
2159                 decl,
2160                 body,
2161                 lo.to(decl_hi),
2162             ),
2163             attrs,
2164         );
2165
2166         // Disable recovery for closure body
2167         let spans =
2168             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2169         self.current_closure = Some(spans);
2170
2171         Ok(closure)
2172     }
2173
2174     /// Parses an optional `move` prefix to a closure-like construct.
2175     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2176         if self.eat_keyword(kw::Move) {
2177             // Check for `move async` and recover
2178             if self.check_keyword(kw::Async) {
2179                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2180                 Err(self.incorrect_move_async_order_found(move_async_span))
2181             } else {
2182                 Ok(CaptureBy::Value)
2183             }
2184         } else {
2185             Ok(CaptureBy::Ref)
2186         }
2187     }
2188
2189     /// Parses the `|arg, arg|` header of a closure.
2190     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2191         let inputs = if self.eat(&token::OrOr) {
2192             Vec::new()
2193         } else {
2194             self.expect(&token::BinOp(token::Or))?;
2195             let args = self
2196                 .parse_seq_to_before_tokens(
2197                     &[&token::BinOp(token::Or), &token::OrOr],
2198                     SeqSep::trailing_allowed(token::Comma),
2199                     TokenExpectType::NoExpect,
2200                     |p| p.parse_fn_block_param(),
2201                 )?
2202                 .0;
2203             self.expect_or()?;
2204             args
2205         };
2206         let output =
2207             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2208
2209         Ok(P(FnDecl { inputs, output }))
2210     }
2211
2212     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2213     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2214         let lo = self.token.span;
2215         let attrs = self.parse_outer_attributes()?;
2216         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2217             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2218             let ty = if this.eat(&token::Colon) {
2219                 this.parse_ty()?
2220             } else {
2221                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2222             };
2223
2224             Ok((
2225                 Param {
2226                     attrs: attrs.into(),
2227                     ty,
2228                     pat,
2229                     span: lo.to(this.token.span),
2230                     id: DUMMY_NODE_ID,
2231                     is_placeholder: false,
2232                 },
2233                 TrailingToken::MaybeComma,
2234             ))
2235         })
2236     }
2237
2238     /// Parses an `if` expression (`if` token already eaten).
2239     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2240         let lo = self.prev_token.span;
2241         let cond = self.parse_cond_expr()?;
2242
2243         self.parse_if_after_cond(attrs, lo, cond)
2244     }
2245
2246     fn parse_if_after_cond(
2247         &mut self,
2248         attrs: AttrVec,
2249         lo: Span,
2250         mut cond: P<Expr>,
2251     ) -> PResult<'a, P<Expr>> {
2252         let cond_span = cond.span;
2253         // Tries to interpret `cond` as either a missing expression if it's a block,
2254         // or as an unfinished expression if it's a binop and the RHS is a block.
2255         // We could probably add more recoveries here too...
2256         let mut recover_block_from_condition = |this: &mut Self| {
2257             let block = match &mut cond.kind {
2258                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2259                     if let ExprKind::Block(_, None) = right.kind => {
2260                         this.error_missing_if_then_block(lo, cond_span.shrink_to_lo().to(*binop_span), true).emit();
2261                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2262                     },
2263                 ExprKind::Block(_, None) => {
2264                     this.error_missing_if_cond(lo, cond_span).emit();
2265                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2266                 }
2267                 _ => {
2268                     return None;
2269                 }
2270             };
2271             if let ExprKind::Block(block, _) = &block.kind {
2272                 Some(block.clone())
2273             } else {
2274                 unreachable!()
2275             }
2276         };
2277         // Parse then block
2278         let thn = if self.token.is_keyword(kw::Else) {
2279             if let Some(block) = recover_block_from_condition(self) {
2280                 block
2281             } else {
2282                 self.error_missing_if_then_block(lo, cond_span, false).emit();
2283                 self.mk_block_err(cond_span.shrink_to_hi())
2284             }
2285         } else {
2286             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2287             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2288                 self.parse_block()?
2289             } else {
2290                 if let Some(block) = recover_block_from_condition(self) {
2291                     block
2292                 } else {
2293                     // Parse block, which will always fail, but we can add a nice note to the error
2294                     self.parse_block().map_err(|mut err| {
2295                         err.span_note(
2296                             cond_span,
2297                             "the `if` expression is missing a block after this condition",
2298                         );
2299                         err
2300                     })?
2301                 }
2302             };
2303             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2304             block
2305         };
2306         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2307         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
2308     }
2309
2310     fn error_missing_if_then_block(
2311         &self,
2312         if_span: Span,
2313         cond_span: Span,
2314         is_unfinished: bool,
2315     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2316         let mut err = self.struct_span_err(
2317             if_span,
2318             "this `if` expression is missing a block after the condition",
2319         );
2320         if is_unfinished {
2321             err.span_help(cond_span, "this binary operation is possibly unfinished");
2322         } else {
2323             err.span_help(cond_span.shrink_to_hi(), "add a block here");
2324         }
2325         err
2326     }
2327
2328     fn error_missing_if_cond(
2329         &self,
2330         lo: Span,
2331         span: Span,
2332     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2333         let next_span = self.sess.source_map().next_point(lo);
2334         let mut err = self.struct_span_err(next_span, "missing condition for `if` expression");
2335         err.span_label(next_span, "expected condition here");
2336         err.span_label(
2337             self.sess.source_map().start_point(span),
2338             "if this block is the condition of the `if` expression, then it must be followed by another block"
2339         );
2340         err
2341     }
2342
2343     /// Parses the condition of a `if` or `while` expression.
2344     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2345         self.with_let_management(true, |local_self| {
2346             local_self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)
2347         })
2348     }
2349
2350     // Checks if `let` is in an invalid position like `let x = let y = 1;` or
2351     // if the current `let` is in a let_chains context but nested in another
2352     // expression like `if let Some(_) = _opt && [1, 2, 3][let _ = ()] = 1`.
2353     //
2354     // This method expects that the current token is `let`.
2355     fn manage_let_chains_context(&mut self) {
2356         debug_assert!(matches!(self.token.kind, TokenKind::Ident(kw::Let, _)));
2357         let is_in_a_let_chains_context_but_nested_in_other_expr = self.let_expr_allowed
2358             && !matches!(
2359                 self.prev_token.kind,
2360                 TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2361             );
2362         if !self.let_expr_allowed || is_in_a_let_chains_context_but_nested_in_other_expr {
2363             self.struct_span_err(self.token.span, "expected expression, found `let` statement")
2364                 .emit();
2365         }
2366     }
2367
2368     /// Parses a `let $pat = $expr` pseudo-expression.
2369     /// The `let` token has already been eaten.
2370     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2371         let lo = self.prev_token.span;
2372         let pat = self.parse_pat_allow_top_alt(
2373             None,
2374             RecoverComma::Yes,
2375             RecoverColon::Yes,
2376             CommaRecoveryMode::LikelyTuple,
2377         )?;
2378         self.expect(&token::Eq)?;
2379         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2380             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2381         })?;
2382         let span = lo.to(expr.span);
2383         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
2384     }
2385
2386     /// Parses an `else { ... }` expression (`else` token already eaten).
2387     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2388         let else_span = self.prev_token.span; // `else`
2389         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2390         let expr = if self.eat_keyword(kw::If) {
2391             self.parse_if_expr(AttrVec::new())?
2392         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2393             self.parse_simple_block()?
2394         } else {
2395             let snapshot = self.create_snapshot_for_diagnostic();
2396             let first_tok = super::token_descr(&self.token);
2397             let first_tok_span = self.token.span;
2398             match self.parse_expr() {
2399                 Ok(cond)
2400                 // If it's not a free-standing expression, and is followed by a block,
2401                 // then it's very likely the condition to an `else if`.
2402                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2403                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2404                 {
2405                     self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}"))
2406                         .span_label(else_span, "expected an `if` or a block after this `else`")
2407                         .span_suggestion(
2408                             cond.span.shrink_to_lo(),
2409                             "add an `if` if this is the condition of a chained `else if` statement",
2410                             "if ",
2411                             Applicability::MaybeIncorrect,
2412                         )
2413                         .emit();
2414                     self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)?
2415                 }
2416                 Err(e) => {
2417                     e.cancel();
2418                     self.restore_snapshot(snapshot);
2419                     self.parse_simple_block()?
2420                 },
2421                 Ok(_) => {
2422                     self.restore_snapshot(snapshot);
2423                     self.parse_simple_block()?
2424                 },
2425             }
2426         };
2427         self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
2428         Ok(expr)
2429     }
2430
2431     fn error_on_if_block_attrs(
2432         &self,
2433         ctx_span: Span,
2434         is_ctx_else: bool,
2435         branch_span: Span,
2436         attrs: &[ast::Attribute],
2437     ) {
2438         let (span, last) = match attrs {
2439             [] => return,
2440             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2441         };
2442         let ctx = if is_ctx_else { "else" } else { "if" };
2443         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
2444             .span_label(branch_span, "the attributes are attached to this branch")
2445             .span_label(ctx_span, format!("the branch belongs to this `{ctx}`"))
2446             .span_suggestion(span, "remove the attributes", "", Applicability::MachineApplicable)
2447             .emit();
2448     }
2449
2450     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2451     fn parse_for_expr(
2452         &mut self,
2453         opt_label: Option<Label>,
2454         lo: Span,
2455         mut attrs: AttrVec,
2456     ) -> PResult<'a, P<Expr>> {
2457         // Record whether we are about to parse `for (`.
2458         // This is used below for recovery in case of `for ( $stuff ) $block`
2459         // in which case we will suggest `for $stuff $block`.
2460         let begin_paren = match self.token.kind {
2461             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2462             _ => None,
2463         };
2464
2465         let pat = self.parse_pat_allow_top_alt(
2466             None,
2467             RecoverComma::Yes,
2468             RecoverColon::Yes,
2469             CommaRecoveryMode::LikelyTuple,
2470         )?;
2471         if !self.eat_keyword(kw::In) {
2472             self.error_missing_in_for_loop();
2473         }
2474         self.check_for_for_in_in_typo(self.prev_token.span);
2475         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2476
2477         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2478
2479         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
2480         attrs.extend(iattrs);
2481
2482         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2483         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2484     }
2485
2486     fn error_missing_in_for_loop(&mut self) {
2487         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
2488             // Possibly using JS syntax (#75311).
2489             let span = self.token.span;
2490             self.bump();
2491             (span, "try using `in` here instead", "in")
2492         } else {
2493             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
2494         };
2495         self.struct_span_err(span, "missing `in` in `for` loop")
2496             .span_suggestion_short(
2497                 span,
2498                 msg,
2499                 sugg,
2500                 // Has been misleading, at least in the past (closed Issue #48492).
2501                 Applicability::MaybeIncorrect,
2502             )
2503             .emit();
2504     }
2505
2506     /// Parses a `while` or `while let` expression (`while` token already eaten).
2507     fn parse_while_expr(
2508         &mut self,
2509         opt_label: Option<Label>,
2510         lo: Span,
2511         mut attrs: AttrVec,
2512     ) -> PResult<'a, P<Expr>> {
2513         let cond = self.parse_cond_expr().map_err(|mut err| {
2514             err.span_label(lo, "while parsing the condition of this `while` expression");
2515             err
2516         })?;
2517         let (iattrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2518             err.span_label(lo, "while parsing the body of this `while` expression");
2519             err.span_label(cond.span, "this `while` condition successfully parsed");
2520             err
2521         })?;
2522         attrs.extend(iattrs);
2523         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2524     }
2525
2526     /// Parses `loop { ... }` (`loop` token already eaten).
2527     fn parse_loop_expr(
2528         &mut self,
2529         opt_label: Option<Label>,
2530         lo: Span,
2531         mut attrs: AttrVec,
2532     ) -> PResult<'a, P<Expr>> {
2533         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2534         attrs.extend(iattrs);
2535         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2536     }
2537
2538     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2539         self.token.lifetime().map(|ident| {
2540             self.bump();
2541             Label { ident }
2542         })
2543     }
2544
2545     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2546     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2547         let match_span = self.prev_token.span;
2548         let lo = self.prev_token.span;
2549         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2550         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2551             if self.token == token::Semi {
2552                 e.span_suggestion_short(
2553                     match_span,
2554                     "try removing this `match`",
2555                     "",
2556                     Applicability::MaybeIncorrect, // speculative
2557                 );
2558             }
2559             if self.maybe_recover_unexpected_block_label() {
2560                 e.cancel();
2561                 self.bump();
2562             } else {
2563                 return Err(e);
2564             }
2565         }
2566         attrs.extend(self.parse_inner_attributes()?);
2567
2568         let mut arms: Vec<Arm> = Vec::new();
2569         while self.token != token::CloseDelim(Delimiter::Brace) {
2570             match self.parse_arm() {
2571                 Ok(arm) => arms.push(arm),
2572                 Err(mut e) => {
2573                     // Recover by skipping to the end of the block.
2574                     e.emit();
2575                     self.recover_stmt();
2576                     let span = lo.to(self.token.span);
2577                     if self.token == token::CloseDelim(Delimiter::Brace) {
2578                         self.bump();
2579                     }
2580                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2581                 }
2582             }
2583         }
2584         let hi = self.token.span;
2585         self.bump();
2586         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2587     }
2588
2589     /// Attempt to recover from match arm body with statements and no surrounding braces.
2590     fn parse_arm_body_missing_braces(
2591         &mut self,
2592         first_expr: &P<Expr>,
2593         arrow_span: Span,
2594     ) -> Option<P<Expr>> {
2595         if self.token.kind != token::Semi {
2596             return None;
2597         }
2598         let start_snapshot = self.create_snapshot_for_diagnostic();
2599         let semi_sp = self.token.span;
2600         self.bump(); // `;`
2601         let mut stmts =
2602             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2603         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2604             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2605             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2606             let (these, s, are) =
2607                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2608             err.span_label(
2609                 span,
2610                 &format!(
2611                     "{these} statement{s} {are} not surrounded by a body",
2612                     these = these,
2613                     s = s,
2614                     are = are
2615                 ),
2616             );
2617             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2618             if stmts.len() > 1 {
2619                 err.multipart_suggestion(
2620                     &format!("surround the statement{s} with a body"),
2621                     vec![
2622                         (span.shrink_to_lo(), "{ ".to_string()),
2623                         (span.shrink_to_hi(), " }".to_string()),
2624                     ],
2625                     Applicability::MachineApplicable,
2626                 );
2627             } else {
2628                 err.span_suggestion(
2629                     semi_sp,
2630                     "use a comma to end a `match` arm expression",
2631                     ",",
2632                     Applicability::MachineApplicable,
2633                 );
2634             }
2635             err.emit();
2636             this.mk_expr_err(span)
2637         };
2638         // We might have either a `,` -> `;` typo, or a block without braces. We need
2639         // a more subtle parsing strategy.
2640         loop {
2641             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2642                 // We have reached the closing brace of the `match` expression.
2643                 return Some(err(self, stmts));
2644             }
2645             if self.token.kind == token::Comma {
2646                 self.restore_snapshot(start_snapshot);
2647                 return None;
2648             }
2649             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2650             match self.parse_pat_no_top_alt(None) {
2651                 Ok(_pat) => {
2652                     if self.token.kind == token::FatArrow {
2653                         // Reached arm end.
2654                         self.restore_snapshot(pre_pat_snapshot);
2655                         return Some(err(self, stmts));
2656                     }
2657                 }
2658                 Err(err) => {
2659                     err.cancel();
2660                 }
2661             }
2662
2663             self.restore_snapshot(pre_pat_snapshot);
2664             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2665                 // Consume statements for as long as possible.
2666                 Ok(Some(stmt)) => {
2667                     stmts.push(stmt);
2668                 }
2669                 Ok(None) => {
2670                     self.restore_snapshot(start_snapshot);
2671                     break;
2672                 }
2673                 // We couldn't parse either yet another statement missing it's
2674                 // enclosing block nor the next arm's pattern or closing brace.
2675                 Err(stmt_err) => {
2676                     stmt_err.cancel();
2677                     self.restore_snapshot(start_snapshot);
2678                     break;
2679                 }
2680             }
2681         }
2682         None
2683     }
2684
2685     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2686         // Used to check the `let_chains` and `if_let_guard` features mostly by scaning
2687         // `&&` tokens.
2688         fn check_let_expr(expr: &Expr) -> bool {
2689             match expr.kind {
2690                 ExprKind::Binary(_, ref lhs, ref rhs) => check_let_expr(lhs) || check_let_expr(rhs),
2691                 ExprKind::Let(..) => true,
2692                 _ => false,
2693             }
2694         }
2695         let attrs = self.parse_outer_attributes()?;
2696         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2697             let lo = this.token.span;
2698             let pat = this.parse_pat_allow_top_alt(
2699                 None,
2700                 RecoverComma::Yes,
2701                 RecoverColon::Yes,
2702                 CommaRecoveryMode::EitherTupleOrPipe,
2703             )?;
2704             let guard = if this.eat_keyword(kw::If) {
2705                 let if_span = this.prev_token.span;
2706                 let cond = this.with_let_management(true, |local_this| local_this.parse_expr())?;
2707                 let has_let_expr = check_let_expr(&cond);
2708                 if has_let_expr {
2709                     let span = if_span.to(cond.span);
2710                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2711                 }
2712                 Some(cond)
2713             } else {
2714                 None
2715             };
2716             let arrow_span = this.token.span;
2717             if let Err(mut err) = this.expect(&token::FatArrow) {
2718                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2719                 if TokenKind::FatArrow
2720                     .similar_tokens()
2721                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2722                 {
2723                     err.span_suggestion(
2724                         this.token.span,
2725                         "try using a fat arrow here",
2726                         "=>",
2727                         Applicability::MaybeIncorrect,
2728                     );
2729                     err.emit();
2730                     this.bump();
2731                 } else {
2732                     return Err(err);
2733                 }
2734             }
2735             let arm_start_span = this.token.span;
2736
2737             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2738                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2739                 err
2740             })?;
2741
2742             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2743                 && this.token != token::CloseDelim(Delimiter::Brace);
2744
2745             let hi = this.prev_token.span;
2746
2747             if require_comma {
2748                 let sm = this.sess.source_map();
2749                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2750                     let span = body.span;
2751                     return Ok((
2752                         ast::Arm {
2753                             attrs: attrs.into(),
2754                             pat,
2755                             guard,
2756                             body,
2757                             span,
2758                             id: DUMMY_NODE_ID,
2759                             is_placeholder: false,
2760                         },
2761                         TrailingToken::None,
2762                     ));
2763                 }
2764                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2765                     .or_else(|mut err| {
2766                         if this.token == token::FatArrow {
2767                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2768                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2769                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2770                             && expr_lines.lines.len() == 2
2771                             {
2772                                 // We check whether there's any trailing code in the parse span,
2773                                 // if there isn't, we very likely have the following:
2774                                 //
2775                                 // X |     &Y => "y"
2776                                 //   |        --    - missing comma
2777                                 //   |        |
2778                                 //   |        arrow_span
2779                                 // X |     &X => "x"
2780                                 //   |      - ^^ self.token.span
2781                                 //   |      |
2782                                 //   |      parsed until here as `"y" & X`
2783                                 err.span_suggestion_short(
2784                                     arm_start_span.shrink_to_hi(),
2785                                     "missing a comma here to end this `match` arm",
2786                                     ",",
2787                                     Applicability::MachineApplicable,
2788                                 );
2789                                 return Err(err);
2790                             }
2791                         } else {
2792                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2793
2794                             // Try to parse a following `PAT =>`, if successful
2795                             // then we should recover.
2796                             let mut snapshot = this.create_snapshot_for_diagnostic();
2797                             let pattern_follows = snapshot
2798                                 .parse_pat_allow_top_alt(
2799                                     None,
2800                                     RecoverComma::Yes,
2801                                     RecoverColon::Yes,
2802                                     CommaRecoveryMode::EitherTupleOrPipe,
2803                                 )
2804                                 .map_err(|err| err.cancel())
2805                                 .is_ok();
2806                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2807                                 err.cancel();
2808                                 this.struct_span_err(
2809                                     hi.shrink_to_hi(),
2810                                     "expected `,` following `match` arm",
2811                                 )
2812                                 .span_suggestion(
2813                                     hi.shrink_to_hi(),
2814                                     "missing a comma here to end this `match` arm",
2815                                     ",",
2816                                     Applicability::MachineApplicable,
2817                                 )
2818                                 .emit();
2819                                 return Ok(true);
2820                             }
2821                         }
2822                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2823                         Err(err)
2824                     })?;
2825             } else {
2826                 this.eat(&token::Comma);
2827             }
2828
2829             Ok((
2830                 ast::Arm {
2831                     attrs: attrs.into(),
2832                     pat,
2833                     guard,
2834                     body: expr,
2835                     span: lo.to(hi),
2836                     id: DUMMY_NODE_ID,
2837                     is_placeholder: false,
2838                 },
2839                 TrailingToken::None,
2840             ))
2841         })
2842     }
2843
2844     /// Parses a `try {...}` expression (`try` token already eaten).
2845     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2846         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2847         attrs.extend(iattrs);
2848         if self.eat_keyword(kw::Catch) {
2849             let mut error = self.struct_span_err(
2850                 self.prev_token.span,
2851                 "keyword `catch` cannot follow a `try` block",
2852             );
2853             error.help("try using `match` on the result of the `try` block instead");
2854             error.emit();
2855             Err(error)
2856         } else {
2857             let span = span_lo.to(body.span);
2858             self.sess.gated_spans.gate(sym::try_blocks, span);
2859             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2860         }
2861     }
2862
2863     fn is_do_catch_block(&self) -> bool {
2864         self.token.is_keyword(kw::Do)
2865             && self.is_keyword_ahead(1, &[kw::Catch])
2866             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2867             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2868     }
2869
2870     fn is_do_yeet(&self) -> bool {
2871         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2872     }
2873
2874     fn is_try_block(&self) -> bool {
2875         self.token.is_keyword(kw::Try)
2876             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2877             && self.token.uninterpolated_span().rust_2018()
2878     }
2879
2880     /// Parses an `async move? {...}` expression.
2881     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2882         let lo = self.token.span;
2883         self.expect_keyword(kw::Async)?;
2884         let capture_clause = self.parse_capture_clause()?;
2885         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2886         attrs.extend(iattrs);
2887         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2888         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2889     }
2890
2891     fn is_async_block(&self) -> bool {
2892         self.token.is_keyword(kw::Async)
2893             && ((
2894                 // `async move {`
2895                 self.is_keyword_ahead(1, &[kw::Move])
2896                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2897             ) || (
2898                 // `async {`
2899                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2900             ))
2901     }
2902
2903     fn is_certainly_not_a_block(&self) -> bool {
2904         self.look_ahead(1, |t| t.is_ident())
2905             && (
2906                 // `{ ident, ` cannot start a block.
2907                 self.look_ahead(2, |t| t == &token::Comma)
2908                     || self.look_ahead(2, |t| t == &token::Colon)
2909                         && (
2910                             // `{ ident: token, ` cannot start a block.
2911                             self.look_ahead(4, |t| t == &token::Comma) ||
2912                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2913                 self.look_ahead(3, |t| !t.can_begin_type())
2914                         )
2915             )
2916     }
2917
2918     fn maybe_parse_struct_expr(
2919         &mut self,
2920         qself: Option<&ast::QSelf>,
2921         path: &ast::Path,
2922         attrs: &AttrVec,
2923     ) -> Option<PResult<'a, P<Expr>>> {
2924         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2925         if struct_allowed || self.is_certainly_not_a_block() {
2926             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2927                 return Some(Err(err));
2928             }
2929             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2930             if let (Ok(expr), false) = (&expr, struct_allowed) {
2931                 // This is a struct literal, but we don't can't accept them here.
2932                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2933             }
2934             return Some(expr);
2935         }
2936         None
2937     }
2938
2939     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2940         self.struct_span_err(sp, "struct literals are not allowed here")
2941             .multipart_suggestion(
2942                 "surround the struct literal with parentheses",
2943                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2944                 Applicability::MachineApplicable,
2945             )
2946             .emit();
2947     }
2948
2949     pub(super) fn parse_struct_fields(
2950         &mut self,
2951         pth: ast::Path,
2952         recover: bool,
2953         close_delim: Delimiter,
2954     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2955         let mut fields = Vec::new();
2956         let mut base = ast::StructRest::None;
2957         let mut recover_async = false;
2958
2959         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2960             recover_async = true;
2961             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2962             e.help_use_latest_edition();
2963         };
2964
2965         while self.token != token::CloseDelim(close_delim) {
2966             if self.eat(&token::DotDot) {
2967                 let exp_span = self.prev_token.span;
2968                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2969                 if self.check(&token::CloseDelim(close_delim)) {
2970                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2971                     break;
2972                 }
2973                 match self.parse_expr() {
2974                     Ok(e) => base = ast::StructRest::Base(e),
2975                     Err(mut e) if recover => {
2976                         e.emit();
2977                         self.recover_stmt();
2978                     }
2979                     Err(e) => return Err(e),
2980                 }
2981                 self.recover_struct_comma_after_dotdot(exp_span);
2982                 break;
2983             }
2984
2985             let recovery_field = self.find_struct_error_after_field_looking_code();
2986             let parsed_field = match self.parse_expr_field() {
2987                 Ok(f) => Some(f),
2988                 Err(mut e) => {
2989                     if pth == kw::Async {
2990                         async_block_err(&mut e, pth.span);
2991                     } else {
2992                         e.span_label(pth.span, "while parsing this struct");
2993                     }
2994                     e.emit();
2995
2996                     // If the next token is a comma, then try to parse
2997                     // what comes next as additional fields, rather than
2998                     // bailing out until next `}`.
2999                     if self.token != token::Comma {
3000                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3001                         if self.token != token::Comma {
3002                             break;
3003                         }
3004                     }
3005                     None
3006                 }
3007             };
3008
3009             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
3010             // A shorthand field can be turned into a full field with `:`.
3011             // We should point this out.
3012             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
3013
3014             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
3015                 Ok(_) => {
3016                     if let Some(f) = parsed_field.or(recovery_field) {
3017                         // Only include the field if there's no parse error for the field name.
3018                         fields.push(f);
3019                     }
3020                 }
3021                 Err(mut e) => {
3022                     if pth == kw::Async {
3023                         async_block_err(&mut e, pth.span);
3024                     } else {
3025                         e.span_label(pth.span, "while parsing this struct");
3026                         if let Some(f) = recovery_field {
3027                             fields.push(f);
3028                             e.span_suggestion(
3029                                 self.prev_token.span.shrink_to_hi(),
3030                                 "try adding a comma",
3031                                 ",",
3032                                 Applicability::MachineApplicable,
3033                             );
3034                         } else if is_shorthand
3035                             && (AssocOp::from_token(&self.token).is_some()
3036                                 || matches!(&self.token.kind, token::OpenDelim(_))
3037                                 || self.token.kind == token::Dot)
3038                         {
3039                             // Looks like they tried to write a shorthand, complex expression.
3040                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
3041                             e.span_suggestion(
3042                                 ident.span.shrink_to_lo(),
3043                                 "try naming a field",
3044                                 &format!("{ident}: "),
3045                                 Applicability::HasPlaceholders,
3046                             );
3047                         }
3048                     }
3049                     if !recover {
3050                         return Err(e);
3051                     }
3052                     e.emit();
3053                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3054                     self.eat(&token::Comma);
3055                 }
3056             }
3057         }
3058         Ok((fields, base, recover_async))
3059     }
3060
3061     /// Precondition: already parsed the '{'.
3062     pub(super) fn parse_struct_expr(
3063         &mut self,
3064         qself: Option<ast::QSelf>,
3065         pth: ast::Path,
3066         attrs: AttrVec,
3067         recover: bool,
3068     ) -> PResult<'a, P<Expr>> {
3069         let lo = pth.span;
3070         let (fields, base, recover_async) =
3071             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
3072         let span = lo.to(self.token.span);
3073         self.expect(&token::CloseDelim(Delimiter::Brace))?;
3074         let expr = if recover_async {
3075             ExprKind::Err
3076         } else {
3077             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
3078         };
3079         Ok(self.mk_expr(span, expr, attrs))
3080     }
3081
3082     /// Use in case of error after field-looking code: `S { foo: () with a }`.
3083     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
3084         match self.token.ident() {
3085             Some((ident, is_raw))
3086                 if (is_raw || !ident.is_reserved())
3087                     && self.look_ahead(1, |t| *t == token::Colon) =>
3088             {
3089                 Some(ast::ExprField {
3090                     ident,
3091                     span: self.token.span,
3092                     expr: self.mk_expr_err(self.token.span),
3093                     is_shorthand: false,
3094                     attrs: AttrVec::new(),
3095                     id: DUMMY_NODE_ID,
3096                     is_placeholder: false,
3097                 })
3098             }
3099             _ => None,
3100         }
3101     }
3102
3103     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
3104         if self.token != token::Comma {
3105             return;
3106         }
3107         self.struct_span_err(
3108             span.to(self.prev_token.span),
3109             "cannot use a comma after the base struct",
3110         )
3111         .span_suggestion_short(
3112             self.token.span,
3113             "remove this comma",
3114             "",
3115             Applicability::MachineApplicable,
3116         )
3117         .note("the base struct must always be the last field")
3118         .emit();
3119         self.recover_stmt();
3120     }
3121
3122     /// Parses `ident (COLON expr)?`.
3123     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3124         let attrs = self.parse_outer_attributes()?;
3125         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3126             let lo = this.token.span;
3127
3128             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3129             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3130             let (ident, expr) = if is_shorthand {
3131                 // Mimic `x: x` for the `x` field shorthand.
3132                 let ident = this.parse_ident_common(false)?;
3133                 let path = ast::Path::from_ident(ident);
3134                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
3135             } else {
3136                 let ident = this.parse_field_name()?;
3137                 this.error_on_eq_field_init(ident);
3138                 this.bump(); // `:`
3139                 (ident, this.parse_expr()?)
3140             };
3141
3142             Ok((
3143                 ast::ExprField {
3144                     ident,
3145                     span: lo.to(expr.span),
3146                     expr,
3147                     is_shorthand,
3148                     attrs: attrs.into(),
3149                     id: DUMMY_NODE_ID,
3150                     is_placeholder: false,
3151                 },
3152                 TrailingToken::MaybeComma,
3153             ))
3154         })
3155     }
3156
3157     /// Check for `=`. This means the source incorrectly attempts to
3158     /// initialize a field with an eq rather than a colon.
3159     fn error_on_eq_field_init(&self, field_name: Ident) {
3160         if self.token != token::Eq {
3161             return;
3162         }
3163
3164         self.struct_span_err(self.token.span, "expected `:`, found `=`")
3165             .span_suggestion(
3166                 field_name.span.shrink_to_hi().to(self.token.span),
3167                 "replace equals symbol with a colon",
3168                 ":",
3169                 Applicability::MachineApplicable,
3170             )
3171             .emit();
3172     }
3173
3174     fn err_dotdotdot_syntax(&self, span: Span) {
3175         self.struct_span_err(span, "unexpected token: `...`")
3176             .span_suggestion(
3177                 span,
3178                 "use `..` for an exclusive range",
3179                 "..",
3180                 Applicability::MaybeIncorrect,
3181             )
3182             .span_suggestion(
3183                 span,
3184                 "or `..=` for an inclusive range",
3185                 "..=",
3186                 Applicability::MaybeIncorrect,
3187             )
3188             .emit();
3189     }
3190
3191     fn err_larrow_operator(&self, span: Span) {
3192         self.struct_span_err(span, "unexpected token: `<-`")
3193             .span_suggestion(
3194                 span,
3195                 "if you meant to write a comparison against a negative value, add a \
3196              space in between `<` and `-`",
3197                 "< -",
3198                 Applicability::MaybeIncorrect,
3199             )
3200             .emit();
3201     }
3202
3203     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3204         ExprKind::AssignOp(binop, lhs, rhs)
3205     }
3206
3207     fn mk_range(
3208         &mut self,
3209         start: Option<P<Expr>>,
3210         end: Option<P<Expr>>,
3211         limits: RangeLimits,
3212     ) -> ExprKind {
3213         if end.is_none() && limits == RangeLimits::Closed {
3214             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3215             ExprKind::Err
3216         } else {
3217             ExprKind::Range(start, end, limits)
3218         }
3219     }
3220
3221     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3222         ExprKind::Unary(unop, expr)
3223     }
3224
3225     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3226         ExprKind::Binary(binop, lhs, rhs)
3227     }
3228
3229     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3230         ExprKind::Index(expr, idx)
3231     }
3232
3233     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3234         ExprKind::Call(f, args)
3235     }
3236
3237     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3238         let span = lo.to(self.prev_token.span);
3239         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
3240         self.recover_from_await_method_call();
3241         await_expr
3242     }
3243
3244     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3245         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3246     }
3247
3248     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3249         self.mk_expr(span, ExprKind::Err, AttrVec::new())
3250     }
3251
3252     /// Create expression span ensuring the span of the parent node
3253     /// is larger than the span of lhs and rhs, including the attributes.
3254     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3255         lhs.attrs
3256             .iter()
3257             .find(|a| a.style == AttrStyle::Outer)
3258             .map_or(lhs_span, |a| a.span)
3259             .to(rhs_span)
3260     }
3261
3262     fn collect_tokens_for_expr(
3263         &mut self,
3264         attrs: AttrWrapper,
3265         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
3266     ) -> PResult<'a, P<Expr>> {
3267         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3268             let res = f(this, attrs)?;
3269             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3270                 && this.token.kind == token::Semi
3271             {
3272                 TrailingToken::Semi
3273             } else {
3274                 // FIXME - pass this through from the place where we know
3275                 // we need a comma, rather than assuming that `#[attr] expr,`
3276                 // always captures a trailing comma
3277                 TrailingToken::MaybeComma
3278             };
3279             Ok((res, trailing))
3280         })
3281     }
3282
3283     // Calls `f` with the internal `let_expr_allowed` set to `let_expr_allowed` and then
3284     // sets the internal `let_expr_allowed` back to its original value.
3285     fn with_let_management<T>(
3286         &mut self,
3287         let_expr_allowed: bool,
3288         f: impl FnOnce(&mut Self) -> T,
3289     ) -> T {
3290         let last_let_expr_allowed = mem::replace(&mut self.let_expr_allowed, let_expr_allowed);
3291         let rslt = f(self);
3292         self.let_expr_allowed = last_let_expr_allowed;
3293         rslt
3294     }
3295 }