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 Diagnostic| {
 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         let prev_span = self.prev_token.span;
1262         let open_delim_span = self.token.span;
1263         self.bump(); // `[`
1264         let index = self.parse_expr()?;
1265         self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
1266         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1267         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new()))
1268     }
1269
1270     /// Assuming we have just parsed `.`, continue parsing into an expression.
1271     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1272         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1273             return Ok(self.mk_await_expr(self_arg, lo));
1274         }
1275
1276         let fn_span_lo = self.token.span;
1277         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1278         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1279         self.check_turbofish_missing_angle_brackets(&mut segment);
1280
1281         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1282             // Method call `expr.f()`
1283             let args = self.parse_paren_expr_seq()?;
1284             let fn_span = fn_span_lo.to(self.prev_token.span);
1285             let span = lo.to(self.prev_token.span);
1286             Ok(self.mk_expr(
1287                 span,
1288                 ExprKind::MethodCall(segment, self_arg, args, fn_span),
1289                 AttrVec::new(),
1290             ))
1291         } else {
1292             // Field access `expr.f`
1293             if let Some(args) = segment.args {
1294                 self.struct_span_err(
1295                     args.span(),
1296                     "field expressions cannot have generic arguments",
1297                 )
1298                 .emit();
1299             }
1300
1301             let span = lo.to(self.prev_token.span);
1302             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new()))
1303         }
1304     }
1305
1306     /// At the bottom (top?) of the precedence hierarchy,
1307     /// Parses things like parenthesized exprs, macros, `return`, etc.
1308     ///
1309     /// N.B., this does not parse outer attributes, and is private because it only works
1310     /// correctly if called from `parse_dot_or_call_expr()`.
1311     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1312         maybe_recover_from_interpolated_ty_qpath!(self, true);
1313         maybe_whole_expr!(self);
1314
1315         // Outer attributes are already parsed and will be
1316         // added to the return value after the fact.
1317         //
1318         // Therefore, prevent sub-parser from parsing
1319         // attributes by giving them an empty "already-parsed" list.
1320         let attrs = AttrVec::new();
1321
1322         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1323         let lo = self.token.span;
1324         if let token::Literal(_) = self.token.kind {
1325             // This match arm is a special-case of the `_` match arm below and
1326             // could be removed without changing functionality, but it's faster
1327             // to have it here, especially for programs with large constants.
1328             self.parse_lit_expr(attrs)
1329         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1330             self.parse_tuple_parens_expr(attrs)
1331         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1332             self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs)
1333         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1334             self.parse_closure_expr(attrs).map_err(|mut err| {
1335                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1336                 // then suggest parens around the lhs.
1337                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1338                     self.sess.expr_parentheses_needed(&mut err, *sp);
1339                 }
1340                 err
1341             })
1342         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1343             self.parse_array_or_repeat_expr(attrs, Delimiter::Bracket)
1344         } else if self.check_path() {
1345             self.parse_path_start_expr(attrs)
1346         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1347             self.parse_closure_expr(attrs)
1348         } else if self.eat_keyword(kw::If) {
1349             self.parse_if_expr(attrs)
1350         } else if self.check_keyword(kw::For) {
1351             if self.choose_generics_over_qpath(1) {
1352                 self.parse_closure_expr(attrs)
1353             } else {
1354                 assert!(self.eat_keyword(kw::For));
1355                 self.parse_for_expr(None, self.prev_token.span, attrs)
1356             }
1357         } else if self.eat_keyword(kw::While) {
1358             self.parse_while_expr(None, self.prev_token.span, attrs)
1359         } else if let Some(label) = self.eat_label() {
1360             self.parse_labeled_expr(label, attrs, true)
1361         } else if self.eat_keyword(kw::Loop) {
1362             let sp = self.prev_token.span;
1363             self.parse_loop_expr(None, self.prev_token.span, attrs).map_err(|mut err| {
1364                 err.span_label(sp, "while parsing this `loop` expression");
1365                 err
1366             })
1367         } else if self.eat_keyword(kw::Continue) {
1368             let kind = ExprKind::Continue(self.eat_label());
1369             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1370         } else if self.eat_keyword(kw::Match) {
1371             let match_sp = self.prev_token.span;
1372             self.parse_match_expr(attrs).map_err(|mut err| {
1373                 err.span_label(match_sp, "while parsing this `match` expression");
1374                 err
1375             })
1376         } else if self.eat_keyword(kw::Unsafe) {
1377             let sp = self.prev_token.span;
1378             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1379                 .map_err(|mut err| {
1380                     err.span_label(sp, "while parsing this `unsafe` expression");
1381                     err
1382                 })
1383         } else if self.check_inline_const(0) {
1384             self.parse_const_block(lo.to(self.token.span), false)
1385         } else if self.is_do_catch_block() {
1386             self.recover_do_catch(attrs)
1387         } else if self.is_try_block() {
1388             self.expect_keyword(kw::Try)?;
1389             self.parse_try_block(lo, attrs)
1390         } else if self.eat_keyword(kw::Return) {
1391             self.parse_return_expr(attrs)
1392         } else if self.eat_keyword(kw::Break) {
1393             self.parse_break_expr(attrs)
1394         } else if self.eat_keyword(kw::Yield) {
1395             self.parse_yield_expr(attrs)
1396         } else if self.is_do_yeet() {
1397             self.parse_yeet_expr(attrs)
1398         } else if self.check_keyword(kw::Let) {
1399             self.parse_let_expr(attrs)
1400         } else if self.eat_keyword(kw::Underscore) {
1401             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1402         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1403             // Don't complain about bare semicolons after unclosed braces
1404             // recovery in order to keep the error count down. Fixing the
1405             // delimiters will possibly also fix the bare semicolon found in
1406             // expression context. For example, silence the following error:
1407             //
1408             //     error: expected expression, found `;`
1409             //      --> file.rs:2:13
1410             //       |
1411             //     2 |     foo(bar(;
1412             //       |             ^ expected expression
1413             self.bump();
1414             Ok(self.mk_expr_err(self.token.span))
1415         } else if self.token.uninterpolated_span().rust_2018() {
1416             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1417             if self.check_keyword(kw::Async) {
1418                 if self.is_async_block() {
1419                     // Check for `async {` and `async move {`.
1420                     self.parse_async_block(attrs)
1421                 } else {
1422                     self.parse_closure_expr(attrs)
1423                 }
1424             } else if self.eat_keyword(kw::Await) {
1425                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1426             } else {
1427                 self.parse_lit_expr(attrs)
1428             }
1429         } else {
1430             self.parse_lit_expr(attrs)
1431         }
1432     }
1433
1434     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1435         let lo = self.token.span;
1436         match self.parse_opt_lit() {
1437             Some(literal) => {
1438                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1439                 self.maybe_recover_from_bad_qpath(expr)
1440             }
1441             None => self.try_macro_suggestion(),
1442         }
1443     }
1444
1445     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1446         let lo = self.token.span;
1447         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1448         let (es, trailing_comma) = match self.parse_seq_to_end(
1449             &token::CloseDelim(Delimiter::Parenthesis),
1450             SeqSep::trailing_allowed(token::Comma),
1451             |p| p.parse_expr_catch_underscore(),
1452         ) {
1453             Ok(x) => x,
1454             Err(err) => {
1455                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1456             }
1457         };
1458         let kind = if es.len() == 1 && !trailing_comma {
1459             // `(e)` is parenthesized `e`.
1460             ExprKind::Paren(es.into_iter().next().unwrap())
1461         } else {
1462             // `(e,)` is a tuple with only one field, `e`.
1463             ExprKind::Tup(es)
1464         };
1465         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1466         self.maybe_recover_from_bad_qpath(expr)
1467     }
1468
1469     fn parse_array_or_repeat_expr(
1470         &mut self,
1471         attrs: AttrVec,
1472         close_delim: Delimiter,
1473     ) -> PResult<'a, P<Expr>> {
1474         let lo = self.token.span;
1475         self.bump(); // `[` or other open delim
1476
1477         let close = &token::CloseDelim(close_delim);
1478         let kind = if self.eat(close) {
1479             // Empty vector
1480             ExprKind::Array(Vec::new())
1481         } else {
1482             // Non-empty vector
1483             let first_expr = self.parse_expr()?;
1484             if self.eat(&token::Semi) {
1485                 // Repeating array syntax: `[ 0; 512 ]`
1486                 let count = self.parse_anon_const_expr()?;
1487                 self.expect(close)?;
1488                 ExprKind::Repeat(first_expr, count)
1489             } else if self.eat(&token::Comma) {
1490                 // Vector with two or more elements.
1491                 let sep = SeqSep::trailing_allowed(token::Comma);
1492                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1493                 let mut exprs = vec![first_expr];
1494                 exprs.extend(remaining_exprs);
1495                 ExprKind::Array(exprs)
1496             } else {
1497                 // Vector with one element
1498                 self.expect(close)?;
1499                 ExprKind::Array(vec![first_expr])
1500             }
1501         };
1502         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1503         self.maybe_recover_from_bad_qpath(expr)
1504     }
1505
1506     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1507         let (qself, path) = if self.eat_lt() {
1508             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1509             (Some(qself), path)
1510         } else {
1511             (None, self.parse_path(PathStyle::Expr)?)
1512         };
1513         let lo = path.span;
1514
1515         // `!`, as an operator, is prefix, so we know this isn't that.
1516         let (hi, kind) = if self.eat(&token::Not) {
1517             // MACRO INVOCATION expression
1518             if qself.is_some() {
1519                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1520             }
1521             let mac = MacCall {
1522                 path,
1523                 args: self.parse_mac_args()?,
1524                 prior_type_ascription: self.last_type_ascription,
1525             };
1526             (self.prev_token.span, ExprKind::MacCall(mac))
1527         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1528             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1529                 if qself.is_some() {
1530                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1531                 }
1532                 return expr;
1533             } else {
1534                 (path.span, ExprKind::Path(qself, path))
1535             }
1536         } else {
1537             (path.span, ExprKind::Path(qself, path))
1538         };
1539
1540         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1541         self.maybe_recover_from_bad_qpath(expr)
1542     }
1543
1544     /// Parse `'label: $expr`. The label is already parsed.
1545     fn parse_labeled_expr(
1546         &mut self,
1547         label: Label,
1548         attrs: AttrVec,
1549         mut consume_colon: bool,
1550     ) -> PResult<'a, P<Expr>> {
1551         let lo = label.ident.span;
1552         let label = Some(label);
1553         let ate_colon = self.eat(&token::Colon);
1554         let expr = if self.eat_keyword(kw::While) {
1555             self.parse_while_expr(label, lo, attrs)
1556         } else if self.eat_keyword(kw::For) {
1557             self.parse_for_expr(label, lo, attrs)
1558         } else if self.eat_keyword(kw::Loop) {
1559             self.parse_loop_expr(label, lo, attrs)
1560         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1561             || self.token.is_whole_block()
1562         {
1563             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1564         } else if !ate_colon
1565             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1566         {
1567             // We're probably inside of a `Path<'a>` that needs a turbofish
1568             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1569             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1570             consume_colon = false;
1571             Ok(self.mk_expr_err(lo))
1572         } else {
1573             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1574
1575             let mut err = self.struct_span_err(self.token.span, msg);
1576             err.span_label(self.token.span, msg);
1577
1578             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1579             let expr = self.parse_expr().map(|expr| {
1580                 let span = expr.span;
1581
1582                 let found_labeled_breaks = {
1583                     struct FindLabeledBreaksVisitor(bool);
1584
1585                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1586                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1587                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1588                                 self.0 = true;
1589                             }
1590                         }
1591                     }
1592
1593                     let mut vis = FindLabeledBreaksVisitor(false);
1594                     vis.visit_expr(&expr);
1595                     vis.0
1596                 };
1597
1598                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1599                 //
1600                 // If there are no breaks that may use this label, suggest removing the label and
1601                 // recover to the unmodified expression.
1602                 if !found_labeled_breaks {
1603                     let msg = "consider removing the label";
1604                     err.span_suggestion_verbose(
1605                         lo.until(span),
1606                         msg,
1607                         "",
1608                         Applicability::MachineApplicable,
1609                     );
1610
1611                     return expr;
1612                 }
1613
1614                 let sugg_msg = "consider enclosing expression in a block";
1615                 let suggestions = vec![
1616                     (span.shrink_to_lo(), "{ ".to_owned()),
1617                     (span.shrink_to_hi(), " }".to_owned()),
1618                 ];
1619
1620                 err.multipart_suggestion_verbose(
1621                     sugg_msg,
1622                     suggestions,
1623                     Applicability::MachineApplicable,
1624                 );
1625
1626                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to supress future errors about `break 'label`.
1627                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1628                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1629                 self.mk_expr(span, ExprKind::Block(blk, label), ThinVec::new())
1630             });
1631
1632             err.emit();
1633             expr
1634         }?;
1635
1636         if !ate_colon && consume_colon {
1637             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1638         }
1639
1640         Ok(expr)
1641     }
1642
1643     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1644         self.struct_span_err(span, "labeled expression must be followed by `:`")
1645             .span_label(lo, "the label")
1646             .span_suggestion_short(
1647                 lo.shrink_to_hi(),
1648                 "add `:` after the label",
1649                 ": ",
1650                 Applicability::MachineApplicable,
1651             )
1652             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1653             .emit();
1654     }
1655
1656     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1657     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1658         let lo = self.token.span;
1659
1660         self.bump(); // `do`
1661         self.bump(); // `catch`
1662
1663         let span_dc = lo.to(self.prev_token.span);
1664         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1665             .span_suggestion(
1666                 span_dc,
1667                 "replace with the new syntax",
1668                 "try",
1669                 Applicability::MachineApplicable,
1670             )
1671             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1672             .emit();
1673
1674         self.parse_try_block(lo, attrs)
1675     }
1676
1677     /// Parse an expression if the token can begin one.
1678     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1679         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1680     }
1681
1682     /// Parse `"return" expr?`.
1683     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1684         let lo = self.prev_token.span;
1685         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1686         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1687         self.maybe_recover_from_bad_qpath(expr)
1688     }
1689
1690     /// Parse `"do" "yeet" expr?`.
1691     fn parse_yeet_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1692         let lo = self.token.span;
1693
1694         self.bump(); // `do`
1695         self.bump(); // `yeet`
1696
1697         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1698
1699         let span = lo.to(self.prev_token.span);
1700         self.sess.gated_spans.gate(sym::yeet_expr, span);
1701         let expr = self.mk_expr(span, kind, attrs);
1702         self.maybe_recover_from_bad_qpath(expr)
1703     }
1704
1705     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1706     /// If the label is followed immediately by a `:` token, the label and `:` are
1707     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1708     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1709     /// the break expression of an unlabeled break is a labeled loop (as in
1710     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1711     /// expression only gets a warning for compatibility reasons; and a labeled break
1712     /// with a labeled loop does not even get a warning because there is no ambiguity.
1713     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1714         let lo = self.prev_token.span;
1715         let mut label = self.eat_label();
1716         let kind = if label.is_some() && self.token == token::Colon {
1717             // The value expression can be a labeled loop, see issue #86948, e.g.:
1718             // `loop { break 'label: loop { break 'label 42; }; }`
1719             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1720             self.struct_span_err(
1721                 lexpr.span,
1722                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1723             )
1724             .multipart_suggestion(
1725                 "wrap the expression in parentheses",
1726                 vec![
1727                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1728                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1729                 ],
1730                 Applicability::MachineApplicable,
1731             )
1732             .emit();
1733             Some(lexpr)
1734         } else if self.token != token::OpenDelim(Delimiter::Brace)
1735             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1736         {
1737             let expr = self.parse_expr_opt()?;
1738             if let Some(ref expr) = expr {
1739                 if label.is_some()
1740                     && matches!(
1741                         expr.kind,
1742                         ExprKind::While(_, _, None)
1743                             | ExprKind::ForLoop(_, _, _, None)
1744                             | ExprKind::Loop(_, None)
1745                             | ExprKind::Block(_, None)
1746                     )
1747                 {
1748                     self.sess.buffer_lint_with_diagnostic(
1749                         BREAK_WITH_LABEL_AND_LOOP,
1750                         lo.to(expr.span),
1751                         ast::CRATE_NODE_ID,
1752                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1753                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1754                     );
1755                 }
1756             }
1757             expr
1758         } else {
1759             None
1760         };
1761         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1762         self.maybe_recover_from_bad_qpath(expr)
1763     }
1764
1765     /// Parse `"yield" expr?`.
1766     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1767         let lo = self.prev_token.span;
1768         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1769         let span = lo.to(self.prev_token.span);
1770         self.sess.gated_spans.gate(sym::generators, span);
1771         let expr = self.mk_expr(span, kind, attrs);
1772         self.maybe_recover_from_bad_qpath(expr)
1773     }
1774
1775     /// Returns a string literal if the next token is a string literal.
1776     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1777     /// and returns `None` if the next token is not literal at all.
1778     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1779         match self.parse_opt_lit() {
1780             Some(lit) => match lit.kind {
1781                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1782                     style,
1783                     symbol: lit.token.symbol,
1784                     suffix: lit.token.suffix,
1785                     span: lit.span,
1786                     symbol_unescaped,
1787                 }),
1788                 _ => Err(Some(lit)),
1789             },
1790             None => Err(None),
1791         }
1792     }
1793
1794     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1795         self.parse_opt_lit().ok_or_else(|| {
1796             if let token::Interpolated(inner) = &self.token.kind {
1797                 let expr = match inner.as_ref() {
1798                     token::NtExpr(expr) => Some(expr),
1799                     token::NtLiteral(expr) => Some(expr),
1800                     _ => None,
1801                 };
1802                 if let Some(expr) = expr {
1803                     if matches!(expr.kind, ExprKind::Err) {
1804                         let mut err = self
1805                             .diagnostic()
1806                             .struct_span_err(self.token.span, "invalid interpolated expression");
1807                         err.downgrade_to_delayed_bug();
1808                         return err;
1809                     }
1810                 }
1811             }
1812             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1813             self.struct_span_err(self.token.span, &msg)
1814         })
1815     }
1816
1817     /// Matches `lit = true | false | token_lit`.
1818     /// Returns `None` if the next token is not a literal.
1819     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1820         let mut recovered = None;
1821         if self.token == token::Dot {
1822             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1823             // dot would follow an optional literal, so we do this unconditionally.
1824             recovered = self.look_ahead(1, |next_token| {
1825                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1826                     next_token.kind
1827                 {
1828                     if self.token.span.hi() == next_token.span.lo() {
1829                         let s = String::from("0.") + symbol.as_str();
1830                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1831                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1832                     }
1833                 }
1834                 None
1835             });
1836             if let Some(token) = &recovered {
1837                 self.bump();
1838                 self.error_float_lits_must_have_int_part(&token);
1839             }
1840         }
1841
1842         let token = recovered.as_ref().unwrap_or(&self.token);
1843         match Lit::from_token(token) {
1844             Ok(lit) => {
1845                 self.bump();
1846                 Some(lit)
1847             }
1848             Err(LitError::NotLiteral) => None,
1849             Err(err) => {
1850                 let span = token.span;
1851                 let token::Literal(lit) = token.kind else {
1852                     unreachable!();
1853                 };
1854                 self.bump();
1855                 self.report_lit_error(err, lit, span);
1856                 // Pack possible quotes and prefixes from the original literal into
1857                 // the error literal's symbol so they can be pretty-printed faithfully.
1858                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1859                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1860                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1861                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1862             }
1863         }
1864     }
1865
1866     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1867         self.struct_span_err(token.span, "float literals must have an integer part")
1868             .span_suggestion(
1869                 token.span,
1870                 "must have an integer part",
1871                 pprust::token_to_string(token),
1872                 Applicability::MachineApplicable,
1873             )
1874             .emit();
1875     }
1876
1877     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1878         // Checks if `s` looks like i32 or u1234 etc.
1879         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1880             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1881         }
1882
1883         // Try to lowercase the prefix if it's a valid base prefix.
1884         fn fix_base_capitalisation(s: &str) -> Option<String> {
1885             if let Some(stripped) = s.strip_prefix('B') {
1886                 Some(format!("0b{stripped}"))
1887             } else if let Some(stripped) = s.strip_prefix('O') {
1888                 Some(format!("0o{stripped}"))
1889             } else if let Some(stripped) = s.strip_prefix('X') {
1890                 Some(format!("0x{stripped}"))
1891             } else {
1892                 None
1893             }
1894         }
1895
1896         let token::Lit { kind, suffix, .. } = lit;
1897         match err {
1898             // `NotLiteral` is not an error by itself, so we don't report
1899             // it and give the parser opportunity to try something else.
1900             LitError::NotLiteral => {}
1901             // `LexerError` *is* an error, but it was already reported
1902             // by lexer, so here we don't report it the second time.
1903             LitError::LexerError => {}
1904             LitError::InvalidSuffix => {
1905                 self.expect_no_suffix(
1906                     span,
1907                     &format!("{} {} literal", kind.article(), kind.descr()),
1908                     suffix,
1909                 );
1910             }
1911             LitError::InvalidIntSuffix => {
1912                 let suf = suffix.expect("suffix error with no suffix");
1913                 let suf = suf.as_str();
1914                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1915                     // If it looks like a width, try to be helpful.
1916                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1917                     self.struct_span_err(span, &msg)
1918                         .help("valid widths are 8, 16, 32, 64 and 128")
1919                         .emit();
1920                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1921                     let msg = "invalid base prefix for number literal";
1922
1923                     self.struct_span_err(span, msg)
1924                         .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase")
1925                         .span_suggestion(
1926                             span,
1927                             "try making the prefix lowercase",
1928                             fixed,
1929                             Applicability::MaybeIncorrect,
1930                         )
1931                         .emit();
1932                 } else {
1933                     let msg = format!("invalid suffix `{suf}` for number literal");
1934                     self.struct_span_err(span, &msg)
1935                         .span_label(span, format!("invalid suffix `{suf}`"))
1936                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1937                         .emit();
1938                 }
1939             }
1940             LitError::InvalidFloatSuffix => {
1941                 let suf = suffix.expect("suffix error with no suffix");
1942                 let suf = suf.as_str();
1943                 if looks_like_width_suffix(&['f'], suf) {
1944                     // If it looks like a width, try to be helpful.
1945                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1946                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1947                 } else {
1948                     let msg = format!("invalid suffix `{suf}` for float literal");
1949                     self.struct_span_err(span, &msg)
1950                         .span_label(span, format!("invalid suffix `{suf}`"))
1951                         .help("valid suffixes are `f32` and `f64`")
1952                         .emit();
1953                 }
1954             }
1955             LitError::NonDecimalFloat(base) => {
1956                 let descr = match base {
1957                     16 => "hexadecimal",
1958                     8 => "octal",
1959                     2 => "binary",
1960                     _ => unreachable!(),
1961                 };
1962                 self.struct_span_err(span, &format!("{descr} float literal is not supported"))
1963                     .span_label(span, "not supported")
1964                     .emit();
1965             }
1966             LitError::IntTooLarge => {
1967                 self.struct_span_err(span, "integer literal is too large").emit();
1968             }
1969         }
1970     }
1971
1972     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1973         if let Some(suf) = suffix {
1974             let mut err = if kind == "a tuple index"
1975                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1976             {
1977                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1978                 // through the ecosystem when people fix their macros
1979                 let mut err = self
1980                     .sess
1981                     .span_diagnostic
1982                     .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
1983                 err.note(&format!(
1984                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1985                         incorrectly accepted on stable for a few releases",
1986                     suf,
1987                 ));
1988                 err.help(
1989                     "on proc macros, you'll want to use `syn::Index::from` or \
1990                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1991                         to tuple field access",
1992                 );
1993                 err.note(
1994                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1995                      for more information",
1996                 );
1997                 err
1998             } else {
1999                 self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
2000                     .forget_guarantee()
2001             };
2002             err.span_label(sp, format!("invalid suffix `{suf}`"));
2003             err.emit();
2004         }
2005     }
2006
2007     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
2008     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
2009     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
2010         maybe_whole_expr!(self);
2011
2012         let lo = self.token.span;
2013         let minus_present = self.eat(&token::BinOp(token::Minus));
2014         let lit = self.parse_lit()?;
2015         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
2016
2017         if minus_present {
2018             Ok(self.mk_expr(
2019                 lo.to(self.prev_token.span),
2020                 self.mk_unary(UnOp::Neg, expr),
2021                 AttrVec::new(),
2022             ))
2023         } else {
2024             Ok(expr)
2025         }
2026     }
2027
2028     fn is_array_like_block(&mut self) -> bool {
2029         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
2030             && self.look_ahead(2, |t| t == &token::Comma)
2031             && self.look_ahead(3, |t| t.can_begin_expr())
2032     }
2033
2034     /// Emits a suggestion if it looks like the user meant an array but
2035     /// accidentally used braces, causing the code to be interpreted as a block
2036     /// expression.
2037     fn maybe_suggest_brackets_instead_of_braces(
2038         &mut self,
2039         lo: Span,
2040         attrs: AttrVec,
2041     ) -> Option<P<Expr>> {
2042         let mut snapshot = self.create_snapshot_for_diagnostic();
2043         match snapshot.parse_array_or_repeat_expr(attrs, Delimiter::Brace) {
2044             Ok(arr) => {
2045                 let hi = snapshot.prev_token.span;
2046                 self.struct_span_err(arr.span, "this is a block expression, not an array")
2047                     .multipart_suggestion(
2048                         "to make an array, use square brackets instead of curly braces",
2049                         vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
2050                         Applicability::MaybeIncorrect,
2051                     )
2052                     .emit();
2053
2054                 self.restore_snapshot(snapshot);
2055                 Some(self.mk_expr_err(arr.span))
2056             }
2057             Err(e) => {
2058                 e.cancel();
2059                 None
2060             }
2061         }
2062     }
2063
2064     fn suggest_missing_semicolon_before_array(
2065         &self,
2066         prev_span: Span,
2067         open_delim_span: Span,
2068     ) -> PResult<'a, ()> {
2069         if self.token.kind == token::Comma {
2070             let mut snapshot = self.create_snapshot_for_diagnostic();
2071             snapshot.bump();
2072             match snapshot.parse_seq_to_before_end(
2073                 &token::CloseDelim(Delimiter::Bracket),
2074                 SeqSep::trailing_allowed(token::Comma),
2075                 |p| p.parse_expr(),
2076             ) {
2077                 Ok(_)
2078                     // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
2079                     // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
2080                     // This is because the `token.kind` of the close delim is treated as the same as
2081                     // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
2082                     // Therefore, `token.kind` should not be compared here.
2083                     if snapshot
2084                         .span_to_snippet(snapshot.token.span)
2085                         .map_or(false, |snippet| snippet == "]") =>
2086                 {
2087                     let mut err = self.struct_span_err(open_delim_span, "expected `;`, found `[`");
2088                     err.span_suggestion_verbose(
2089                         prev_span.shrink_to_hi(),
2090                         "consider adding `;` here",
2091                         ';',
2092                         Applicability::MaybeIncorrect,
2093                     );
2094                     return Err(err);
2095                 }
2096                 Ok(_) => (),
2097                 Err(err) => err.cancel(),
2098             }
2099         }
2100         Ok(())
2101     }
2102
2103     /// Parses a block or unsafe block.
2104     pub(super) fn parse_block_expr(
2105         &mut self,
2106         opt_label: Option<Label>,
2107         lo: Span,
2108         blk_mode: BlockCheckMode,
2109         mut attrs: AttrVec,
2110     ) -> PResult<'a, P<Expr>> {
2111         if self.is_array_like_block() {
2112             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) {
2113                 return Ok(arr);
2114             }
2115         }
2116
2117         if let Some(label) = opt_label {
2118             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
2119         }
2120
2121         if self.token.is_whole_block() {
2122             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
2123                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
2124                 .emit();
2125         }
2126
2127         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
2128         attrs.extend(inner_attrs);
2129         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
2130     }
2131
2132     /// Parse a block which takes no attributes and has no label
2133     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2134         let blk = self.parse_block()?;
2135         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()))
2136     }
2137
2138     /// Parses a closure expression (e.g., `move |args| expr`).
2139     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2140         let lo = self.token.span;
2141
2142         let binder = if self.check_keyword(kw::For) {
2143             let lo = self.token.span;
2144             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2145             let span = lo.to(self.prev_token.span);
2146
2147             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2148
2149             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2150         } else {
2151             ClosureBinder::NotPresent
2152         };
2153
2154         let movability =
2155             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2156
2157         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2158             self.parse_asyncness()
2159         } else {
2160             Async::No
2161         };
2162
2163         let capture_clause = self.parse_capture_clause()?;
2164         let decl = self.parse_fn_block_decl()?;
2165         let decl_hi = self.prev_token.span;
2166         let mut body = match decl.output {
2167             FnRetTy::Default(_) => {
2168                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2169                 self.parse_expr_res(restrictions, None)?
2170             }
2171             _ => {
2172                 // If an explicit return type is given, require a block to appear (RFC 968).
2173                 let body_lo = self.token.span;
2174                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
2175             }
2176         };
2177
2178         if let Async::Yes { span, .. } = asyncness {
2179             // Feature-gate `async ||` closures.
2180             self.sess.gated_spans.gate(sym::async_closure, span);
2181         }
2182
2183         if self.token.kind == TokenKind::Semi
2184             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2185         {
2186             // It is likely that the closure body is a block but where the
2187             // braces have been removed. We will recover and eat the next
2188             // statements later in the parsing process.
2189             body = self.mk_expr_err(body.span);
2190         }
2191
2192         let body_span = body.span;
2193
2194         let closure = self.mk_expr(
2195             lo.to(body.span),
2196             ExprKind::Closure(
2197                 binder,
2198                 capture_clause,
2199                 asyncness,
2200                 movability,
2201                 decl,
2202                 body,
2203                 lo.to(decl_hi),
2204             ),
2205             attrs,
2206         );
2207
2208         // Disable recovery for closure body
2209         let spans =
2210             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2211         self.current_closure = Some(spans);
2212
2213         Ok(closure)
2214     }
2215
2216     /// Parses an optional `move` prefix to a closure-like construct.
2217     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2218         if self.eat_keyword(kw::Move) {
2219             // Check for `move async` and recover
2220             if self.check_keyword(kw::Async) {
2221                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2222                 Err(self.incorrect_move_async_order_found(move_async_span))
2223             } else {
2224                 Ok(CaptureBy::Value)
2225             }
2226         } else {
2227             Ok(CaptureBy::Ref)
2228         }
2229     }
2230
2231     /// Parses the `|arg, arg|` header of a closure.
2232     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2233         let inputs = if self.eat(&token::OrOr) {
2234             Vec::new()
2235         } else {
2236             self.expect(&token::BinOp(token::Or))?;
2237             let args = self
2238                 .parse_seq_to_before_tokens(
2239                     &[&token::BinOp(token::Or), &token::OrOr],
2240                     SeqSep::trailing_allowed(token::Comma),
2241                     TokenExpectType::NoExpect,
2242                     |p| p.parse_fn_block_param(),
2243                 )?
2244                 .0;
2245             self.expect_or()?;
2246             args
2247         };
2248         let output =
2249             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2250
2251         Ok(P(FnDecl { inputs, output }))
2252     }
2253
2254     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2255     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2256         let lo = self.token.span;
2257         let attrs = self.parse_outer_attributes()?;
2258         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2259             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2260             let ty = if this.eat(&token::Colon) {
2261                 this.parse_ty()?
2262             } else {
2263                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2264             };
2265
2266             Ok((
2267                 Param {
2268                     attrs: attrs.into(),
2269                     ty,
2270                     pat,
2271                     span: lo.to(this.token.span),
2272                     id: DUMMY_NODE_ID,
2273                     is_placeholder: false,
2274                 },
2275                 TrailingToken::MaybeComma,
2276             ))
2277         })
2278     }
2279
2280     /// Parses an `if` expression (`if` token already eaten).
2281     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2282         let lo = self.prev_token.span;
2283         let cond = self.parse_cond_expr()?;
2284
2285         self.parse_if_after_cond(attrs, lo, cond)
2286     }
2287
2288     fn parse_if_after_cond(
2289         &mut self,
2290         attrs: AttrVec,
2291         lo: Span,
2292         mut cond: P<Expr>,
2293     ) -> PResult<'a, P<Expr>> {
2294         let cond_span = cond.span;
2295         // Tries to interpret `cond` as either a missing expression if it's a block,
2296         // or as an unfinished expression if it's a binop and the RHS is a block.
2297         // We could probably add more recoveries here too...
2298         let mut recover_block_from_condition = |this: &mut Self| {
2299             let block = match &mut cond.kind {
2300                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2301                     if let ExprKind::Block(_, None) = right.kind => {
2302                         this.error_missing_if_then_block(lo, cond_span.shrink_to_lo().to(*binop_span), true).emit();
2303                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2304                     },
2305                 ExprKind::Block(_, None) => {
2306                     this.error_missing_if_cond(lo, cond_span).emit();
2307                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2308                 }
2309                 _ => {
2310                     return None;
2311                 }
2312             };
2313             if let ExprKind::Block(block, _) = &block.kind {
2314                 Some(block.clone())
2315             } else {
2316                 unreachable!()
2317             }
2318         };
2319         // Parse then block
2320         let thn = if self.token.is_keyword(kw::Else) {
2321             if let Some(block) = recover_block_from_condition(self) {
2322                 block
2323             } else {
2324                 self.error_missing_if_then_block(lo, cond_span, false).emit();
2325                 self.mk_block_err(cond_span.shrink_to_hi())
2326             }
2327         } else {
2328             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2329             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2330                 self.parse_block()?
2331             } else {
2332                 if let Some(block) = recover_block_from_condition(self) {
2333                     block
2334                 } else {
2335                     // Parse block, which will always fail, but we can add a nice note to the error
2336                     self.parse_block().map_err(|mut err| {
2337                         err.span_note(
2338                             cond_span,
2339                             "the `if` expression is missing a block after this condition",
2340                         );
2341                         err
2342                     })?
2343                 }
2344             };
2345             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2346             block
2347         };
2348         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2349         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
2350     }
2351
2352     fn error_missing_if_then_block(
2353         &self,
2354         if_span: Span,
2355         cond_span: Span,
2356         is_unfinished: bool,
2357     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2358         let mut err = self.struct_span_err(
2359             if_span,
2360             "this `if` expression is missing a block after the condition",
2361         );
2362         if is_unfinished {
2363             err.span_help(cond_span, "this binary operation is possibly unfinished");
2364         } else {
2365             err.span_help(cond_span.shrink_to_hi(), "add a block here");
2366         }
2367         err
2368     }
2369
2370     fn error_missing_if_cond(
2371         &self,
2372         lo: Span,
2373         span: Span,
2374     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2375         let next_span = self.sess.source_map().next_point(lo);
2376         let mut err = self.struct_span_err(next_span, "missing condition for `if` expression");
2377         err.span_label(next_span, "expected condition here");
2378         err.span_label(
2379             self.sess.source_map().start_point(span),
2380             "if this block is the condition of the `if` expression, then it must be followed by another block"
2381         );
2382         err
2383     }
2384
2385     /// Parses the condition of a `if` or `while` expression.
2386     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2387         self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)
2388     }
2389
2390     /// Parses a `let $pat = $expr` pseudo-expression.
2391     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
2392         // This is a *approximate* heuristic that detects if `let` chains are
2393         // being parsed in the right position. It's approximate because it
2394         // doesn't deny all invalid `let` expressions, just completely wrong usages.
2395         let not_in_chain = !matches!(
2396             self.prev_token.kind,
2397             TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2398         );
2399         if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
2400             self.struct_span_err(self.token.span, "expected expression, found `let` statement")
2401                 .emit();
2402         }
2403
2404         self.bump(); // Eat `let` token
2405         let lo = self.prev_token.span;
2406         let pat = self.parse_pat_allow_top_alt(
2407             None,
2408             RecoverComma::Yes,
2409             RecoverColon::Yes,
2410             CommaRecoveryMode::LikelyTuple,
2411         )?;
2412         self.expect(&token::Eq)?;
2413         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2414             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2415         })?;
2416         let span = lo.to(expr.span);
2417         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
2418     }
2419
2420     /// Parses an `else { ... }` expression (`else` token already eaten).
2421     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2422         let else_span = self.prev_token.span; // `else`
2423         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2424         let expr = if self.eat_keyword(kw::If) {
2425             self.parse_if_expr(AttrVec::new())?
2426         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2427             self.parse_simple_block()?
2428         } else {
2429             let snapshot = self.create_snapshot_for_diagnostic();
2430             let first_tok = super::token_descr(&self.token);
2431             let first_tok_span = self.token.span;
2432             match self.parse_expr() {
2433                 Ok(cond)
2434                 // If it's not a free-standing expression, and is followed by a block,
2435                 // then it's very likely the condition to an `else if`.
2436                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2437                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2438                 {
2439                     self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}"))
2440                         .span_label(else_span, "expected an `if` or a block after this `else`")
2441                         .span_suggestion(
2442                             cond.span.shrink_to_lo(),
2443                             "add an `if` if this is the condition of a chained `else if` statement",
2444                             "if ",
2445                             Applicability::MaybeIncorrect,
2446                         )
2447                         .emit();
2448                     self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)?
2449                 }
2450                 Err(e) => {
2451                     e.cancel();
2452                     self.restore_snapshot(snapshot);
2453                     self.parse_simple_block()?
2454                 },
2455                 Ok(_) => {
2456                     self.restore_snapshot(snapshot);
2457                     self.parse_simple_block()?
2458                 },
2459             }
2460         };
2461         self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
2462         Ok(expr)
2463     }
2464
2465     fn error_on_if_block_attrs(
2466         &self,
2467         ctx_span: Span,
2468         is_ctx_else: bool,
2469         branch_span: Span,
2470         attrs: &[ast::Attribute],
2471     ) {
2472         let (span, last) = match attrs {
2473             [] => return,
2474             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2475         };
2476         let ctx = if is_ctx_else { "else" } else { "if" };
2477         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
2478             .span_label(branch_span, "the attributes are attached to this branch")
2479             .span_label(ctx_span, format!("the branch belongs to this `{ctx}`"))
2480             .span_suggestion(span, "remove the attributes", "", Applicability::MachineApplicable)
2481             .emit();
2482     }
2483
2484     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2485     fn parse_for_expr(
2486         &mut self,
2487         opt_label: Option<Label>,
2488         lo: Span,
2489         mut attrs: AttrVec,
2490     ) -> PResult<'a, P<Expr>> {
2491         // Record whether we are about to parse `for (`.
2492         // This is used below for recovery in case of `for ( $stuff ) $block`
2493         // in which case we will suggest `for $stuff $block`.
2494         let begin_paren = match self.token.kind {
2495             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2496             _ => None,
2497         };
2498
2499         let pat = self.parse_pat_allow_top_alt(
2500             None,
2501             RecoverComma::Yes,
2502             RecoverColon::Yes,
2503             CommaRecoveryMode::LikelyTuple,
2504         )?;
2505         if !self.eat_keyword(kw::In) {
2506             self.error_missing_in_for_loop();
2507         }
2508         self.check_for_for_in_in_typo(self.prev_token.span);
2509         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2510
2511         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2512
2513         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
2514         attrs.extend(iattrs);
2515
2516         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2517         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2518     }
2519
2520     fn error_missing_in_for_loop(&mut self) {
2521         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
2522             // Possibly using JS syntax (#75311).
2523             let span = self.token.span;
2524             self.bump();
2525             (span, "try using `in` here instead", "in")
2526         } else {
2527             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
2528         };
2529         self.struct_span_err(span, "missing `in` in `for` loop")
2530             .span_suggestion_short(
2531                 span,
2532                 msg,
2533                 sugg,
2534                 // Has been misleading, at least in the past (closed Issue #48492).
2535                 Applicability::MaybeIncorrect,
2536             )
2537             .emit();
2538     }
2539
2540     /// Parses a `while` or `while let` expression (`while` token already eaten).
2541     fn parse_while_expr(
2542         &mut self,
2543         opt_label: Option<Label>,
2544         lo: Span,
2545         mut attrs: AttrVec,
2546     ) -> PResult<'a, P<Expr>> {
2547         let cond = self.parse_cond_expr().map_err(|mut err| {
2548             err.span_label(lo, "while parsing the condition of this `while` expression");
2549             err
2550         })?;
2551         let (iattrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2552             err.span_label(lo, "while parsing the body of this `while` expression");
2553             err.span_label(cond.span, "this `while` condition successfully parsed");
2554             err
2555         })?;
2556         attrs.extend(iattrs);
2557         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2558     }
2559
2560     /// Parses `loop { ... }` (`loop` token already eaten).
2561     fn parse_loop_expr(
2562         &mut self,
2563         opt_label: Option<Label>,
2564         lo: Span,
2565         mut attrs: AttrVec,
2566     ) -> PResult<'a, P<Expr>> {
2567         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2568         attrs.extend(iattrs);
2569         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2570     }
2571
2572     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2573         self.token.lifetime().map(|ident| {
2574             self.bump();
2575             Label { ident }
2576         })
2577     }
2578
2579     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2580     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2581         let match_span = self.prev_token.span;
2582         let lo = self.prev_token.span;
2583         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2584         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2585             if self.token == token::Semi {
2586                 e.span_suggestion_short(
2587                     match_span,
2588                     "try removing this `match`",
2589                     "",
2590                     Applicability::MaybeIncorrect, // speculative
2591                 );
2592             }
2593             if self.maybe_recover_unexpected_block_label() {
2594                 e.cancel();
2595                 self.bump();
2596             } else {
2597                 return Err(e);
2598             }
2599         }
2600         attrs.extend(self.parse_inner_attributes()?);
2601
2602         let mut arms: Vec<Arm> = Vec::new();
2603         while self.token != token::CloseDelim(Delimiter::Brace) {
2604             match self.parse_arm() {
2605                 Ok(arm) => arms.push(arm),
2606                 Err(mut e) => {
2607                     // Recover by skipping to the end of the block.
2608                     e.emit();
2609                     self.recover_stmt();
2610                     let span = lo.to(self.token.span);
2611                     if self.token == token::CloseDelim(Delimiter::Brace) {
2612                         self.bump();
2613                     }
2614                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2615                 }
2616             }
2617         }
2618         let hi = self.token.span;
2619         self.bump();
2620         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2621     }
2622
2623     /// Attempt to recover from match arm body with statements and no surrounding braces.
2624     fn parse_arm_body_missing_braces(
2625         &mut self,
2626         first_expr: &P<Expr>,
2627         arrow_span: Span,
2628     ) -> Option<P<Expr>> {
2629         if self.token.kind != token::Semi {
2630             return None;
2631         }
2632         let start_snapshot = self.create_snapshot_for_diagnostic();
2633         let semi_sp = self.token.span;
2634         self.bump(); // `;`
2635         let mut stmts =
2636             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2637         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2638             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2639             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2640             let (these, s, are) =
2641                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2642             err.span_label(
2643                 span,
2644                 &format!(
2645                     "{these} statement{s} {are} not surrounded by a body",
2646                     these = these,
2647                     s = s,
2648                     are = are
2649                 ),
2650             );
2651             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2652             if stmts.len() > 1 {
2653                 err.multipart_suggestion(
2654                     &format!("surround the statement{s} with a body"),
2655                     vec![
2656                         (span.shrink_to_lo(), "{ ".to_string()),
2657                         (span.shrink_to_hi(), " }".to_string()),
2658                     ],
2659                     Applicability::MachineApplicable,
2660                 );
2661             } else {
2662                 err.span_suggestion(
2663                     semi_sp,
2664                     "use a comma to end a `match` arm expression",
2665                     ",",
2666                     Applicability::MachineApplicable,
2667                 );
2668             }
2669             err.emit();
2670             this.mk_expr_err(span)
2671         };
2672         // We might have either a `,` -> `;` typo, or a block without braces. We need
2673         // a more subtle parsing strategy.
2674         loop {
2675             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2676                 // We have reached the closing brace of the `match` expression.
2677                 return Some(err(self, stmts));
2678             }
2679             if self.token.kind == token::Comma {
2680                 self.restore_snapshot(start_snapshot);
2681                 return None;
2682             }
2683             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2684             match self.parse_pat_no_top_alt(None) {
2685                 Ok(_pat) => {
2686                     if self.token.kind == token::FatArrow {
2687                         // Reached arm end.
2688                         self.restore_snapshot(pre_pat_snapshot);
2689                         return Some(err(self, stmts));
2690                     }
2691                 }
2692                 Err(err) => {
2693                     err.cancel();
2694                 }
2695             }
2696
2697             self.restore_snapshot(pre_pat_snapshot);
2698             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2699                 // Consume statements for as long as possible.
2700                 Ok(Some(stmt)) => {
2701                     stmts.push(stmt);
2702                 }
2703                 Ok(None) => {
2704                     self.restore_snapshot(start_snapshot);
2705                     break;
2706                 }
2707                 // We couldn't parse either yet another statement missing it's
2708                 // enclosing block nor the next arm's pattern or closing brace.
2709                 Err(stmt_err) => {
2710                     stmt_err.cancel();
2711                     self.restore_snapshot(start_snapshot);
2712                     break;
2713                 }
2714             }
2715         }
2716         None
2717     }
2718
2719     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2720         // Used to check the `let_chains` and `if_let_guard` features mostly by scaning
2721         // `&&` tokens.
2722         fn check_let_expr(expr: &Expr) -> bool {
2723             match expr.kind {
2724                 ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, ref lhs, ref rhs) => {
2725                     check_let_expr(lhs) || check_let_expr(rhs)
2726                 }
2727                 ExprKind::Let(..) => true,
2728                 _ => false,
2729             }
2730         }
2731         let attrs = self.parse_outer_attributes()?;
2732         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2733             let lo = this.token.span;
2734             let pat = this.parse_pat_allow_top_alt(
2735                 None,
2736                 RecoverComma::Yes,
2737                 RecoverColon::Yes,
2738                 CommaRecoveryMode::EitherTupleOrPipe,
2739             )?;
2740             let guard = if this.eat_keyword(kw::If) {
2741                 let if_span = this.prev_token.span;
2742                 let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
2743                 if check_let_expr(&cond) {
2744                     let span = if_span.to(cond.span);
2745                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2746                 }
2747                 Some(cond)
2748             } else {
2749                 None
2750             };
2751             let arrow_span = this.token.span;
2752             if let Err(mut err) = this.expect(&token::FatArrow) {
2753                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2754                 if TokenKind::FatArrow
2755                     .similar_tokens()
2756                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2757                 {
2758                     err.span_suggestion(
2759                         this.token.span,
2760                         "try using a fat arrow here",
2761                         "=>",
2762                         Applicability::MaybeIncorrect,
2763                     );
2764                     err.emit();
2765                     this.bump();
2766                 } else {
2767                     return Err(err);
2768                 }
2769             }
2770             let arm_start_span = this.token.span;
2771
2772             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2773                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2774                 err
2775             })?;
2776
2777             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2778                 && this.token != token::CloseDelim(Delimiter::Brace);
2779
2780             let hi = this.prev_token.span;
2781
2782             if require_comma {
2783                 let sm = this.sess.source_map();
2784                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2785                     let span = body.span;
2786                     return Ok((
2787                         ast::Arm {
2788                             attrs: attrs.into(),
2789                             pat,
2790                             guard,
2791                             body,
2792                             span,
2793                             id: DUMMY_NODE_ID,
2794                             is_placeholder: false,
2795                         },
2796                         TrailingToken::None,
2797                     ));
2798                 }
2799                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2800                     .or_else(|mut err| {
2801                         if this.token == token::FatArrow {
2802                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2803                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2804                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2805                             && expr_lines.lines.len() == 2
2806                             {
2807                                 // We check whether there's any trailing code in the parse span,
2808                                 // if there isn't, we very likely have the following:
2809                                 //
2810                                 // X |     &Y => "y"
2811                                 //   |        --    - missing comma
2812                                 //   |        |
2813                                 //   |        arrow_span
2814                                 // X |     &X => "x"
2815                                 //   |      - ^^ self.token.span
2816                                 //   |      |
2817                                 //   |      parsed until here as `"y" & X`
2818                                 err.span_suggestion_short(
2819                                     arm_start_span.shrink_to_hi(),
2820                                     "missing a comma here to end this `match` arm",
2821                                     ",",
2822                                     Applicability::MachineApplicable,
2823                                 );
2824                                 return Err(err);
2825                             }
2826                         } else {
2827                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2828
2829                             // Try to parse a following `PAT =>`, if successful
2830                             // then we should recover.
2831                             let mut snapshot = this.create_snapshot_for_diagnostic();
2832                             let pattern_follows = snapshot
2833                                 .parse_pat_allow_top_alt(
2834                                     None,
2835                                     RecoverComma::Yes,
2836                                     RecoverColon::Yes,
2837                                     CommaRecoveryMode::EitherTupleOrPipe,
2838                                 )
2839                                 .map_err(|err| err.cancel())
2840                                 .is_ok();
2841                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2842                                 err.cancel();
2843                                 this.struct_span_err(
2844                                     hi.shrink_to_hi(),
2845                                     "expected `,` following `match` arm",
2846                                 )
2847                                 .span_suggestion(
2848                                     hi.shrink_to_hi(),
2849                                     "missing a comma here to end this `match` arm",
2850                                     ",",
2851                                     Applicability::MachineApplicable,
2852                                 )
2853                                 .emit();
2854                                 return Ok(true);
2855                             }
2856                         }
2857                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2858                         Err(err)
2859                     })?;
2860             } else {
2861                 this.eat(&token::Comma);
2862             }
2863
2864             Ok((
2865                 ast::Arm {
2866                     attrs: attrs.into(),
2867                     pat,
2868                     guard,
2869                     body: expr,
2870                     span: lo.to(hi),
2871                     id: DUMMY_NODE_ID,
2872                     is_placeholder: false,
2873                 },
2874                 TrailingToken::None,
2875             ))
2876         })
2877     }
2878
2879     /// Parses a `try {...}` expression (`try` token already eaten).
2880     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2881         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2882         attrs.extend(iattrs);
2883         if self.eat_keyword(kw::Catch) {
2884             let mut error = self.struct_span_err(
2885                 self.prev_token.span,
2886                 "keyword `catch` cannot follow a `try` block",
2887             );
2888             error.help("try using `match` on the result of the `try` block instead");
2889             error.emit();
2890             Err(error)
2891         } else {
2892             let span = span_lo.to(body.span);
2893             self.sess.gated_spans.gate(sym::try_blocks, span);
2894             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2895         }
2896     }
2897
2898     fn is_do_catch_block(&self) -> bool {
2899         self.token.is_keyword(kw::Do)
2900             && self.is_keyword_ahead(1, &[kw::Catch])
2901             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2902             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2903     }
2904
2905     fn is_do_yeet(&self) -> bool {
2906         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2907     }
2908
2909     fn is_try_block(&self) -> bool {
2910         self.token.is_keyword(kw::Try)
2911             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2912             && self.token.uninterpolated_span().rust_2018()
2913     }
2914
2915     /// Parses an `async move? {...}` expression.
2916     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2917         let lo = self.token.span;
2918         self.expect_keyword(kw::Async)?;
2919         let capture_clause = self.parse_capture_clause()?;
2920         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2921         attrs.extend(iattrs);
2922         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2923         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2924     }
2925
2926     fn is_async_block(&self) -> bool {
2927         self.token.is_keyword(kw::Async)
2928             && ((
2929                 // `async move {`
2930                 self.is_keyword_ahead(1, &[kw::Move])
2931                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2932             ) || (
2933                 // `async {`
2934                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2935             ))
2936     }
2937
2938     fn is_certainly_not_a_block(&self) -> bool {
2939         self.look_ahead(1, |t| t.is_ident())
2940             && (
2941                 // `{ ident, ` cannot start a block.
2942                 self.look_ahead(2, |t| t == &token::Comma)
2943                     || self.look_ahead(2, |t| t == &token::Colon)
2944                         && (
2945                             // `{ ident: token, ` cannot start a block.
2946                             self.look_ahead(4, |t| t == &token::Comma) ||
2947                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2948                 self.look_ahead(3, |t| !t.can_begin_type())
2949                         )
2950             )
2951     }
2952
2953     fn maybe_parse_struct_expr(
2954         &mut self,
2955         qself: Option<&ast::QSelf>,
2956         path: &ast::Path,
2957         attrs: &AttrVec,
2958     ) -> Option<PResult<'a, P<Expr>>> {
2959         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2960         if struct_allowed || self.is_certainly_not_a_block() {
2961             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2962                 return Some(Err(err));
2963             }
2964             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2965             if let (Ok(expr), false) = (&expr, struct_allowed) {
2966                 // This is a struct literal, but we don't can't accept them here.
2967                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2968             }
2969             return Some(expr);
2970         }
2971         None
2972     }
2973
2974     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2975         self.struct_span_err(sp, "struct literals are not allowed here")
2976             .multipart_suggestion(
2977                 "surround the struct literal with parentheses",
2978                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2979                 Applicability::MachineApplicable,
2980             )
2981             .emit();
2982     }
2983
2984     pub(super) fn parse_struct_fields(
2985         &mut self,
2986         pth: ast::Path,
2987         recover: bool,
2988         close_delim: Delimiter,
2989     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2990         let mut fields = Vec::new();
2991         let mut base = ast::StructRest::None;
2992         let mut recover_async = false;
2993
2994         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2995             recover_async = true;
2996             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2997             e.help_use_latest_edition();
2998         };
2999
3000         while self.token != token::CloseDelim(close_delim) {
3001             if self.eat(&token::DotDot) {
3002                 let exp_span = self.prev_token.span;
3003                 // We permit `.. }` on the left-hand side of a destructuring assignment.
3004                 if self.check(&token::CloseDelim(close_delim)) {
3005                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
3006                     break;
3007                 }
3008                 match self.parse_expr() {
3009                     Ok(e) => base = ast::StructRest::Base(e),
3010                     Err(mut e) if recover => {
3011                         e.emit();
3012                         self.recover_stmt();
3013                     }
3014                     Err(e) => return Err(e),
3015                 }
3016                 self.recover_struct_comma_after_dotdot(exp_span);
3017                 break;
3018             }
3019
3020             let recovery_field = self.find_struct_error_after_field_looking_code();
3021             let parsed_field = match self.parse_expr_field() {
3022                 Ok(f) => Some(f),
3023                 Err(mut e) => {
3024                     if pth == kw::Async {
3025                         async_block_err(&mut e, pth.span);
3026                     } else {
3027                         e.span_label(pth.span, "while parsing this struct");
3028                     }
3029                     e.emit();
3030
3031                     // If the next token is a comma, then try to parse
3032                     // what comes next as additional fields, rather than
3033                     // bailing out until next `}`.
3034                     if self.token != token::Comma {
3035                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3036                         if self.token != token::Comma {
3037                             break;
3038                         }
3039                     }
3040                     None
3041                 }
3042             };
3043
3044             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
3045             // A shorthand field can be turned into a full field with `:`.
3046             // We should point this out.
3047             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
3048
3049             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
3050                 Ok(_) => {
3051                     if let Some(f) = parsed_field.or(recovery_field) {
3052                         // Only include the field if there's no parse error for the field name.
3053                         fields.push(f);
3054                     }
3055                 }
3056                 Err(mut e) => {
3057                     if pth == kw::Async {
3058                         async_block_err(&mut e, pth.span);
3059                     } else {
3060                         e.span_label(pth.span, "while parsing this struct");
3061                         if let Some(f) = recovery_field {
3062                             fields.push(f);
3063                             e.span_suggestion(
3064                                 self.prev_token.span.shrink_to_hi(),
3065                                 "try adding a comma",
3066                                 ",",
3067                                 Applicability::MachineApplicable,
3068                             );
3069                         } else if is_shorthand
3070                             && (AssocOp::from_token(&self.token).is_some()
3071                                 || matches!(&self.token.kind, token::OpenDelim(_))
3072                                 || self.token.kind == token::Dot)
3073                         {
3074                             // Looks like they tried to write a shorthand, complex expression.
3075                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
3076                             e.span_suggestion(
3077                                 ident.span.shrink_to_lo(),
3078                                 "try naming a field",
3079                                 &format!("{ident}: "),
3080                                 Applicability::HasPlaceholders,
3081                             );
3082                         }
3083                     }
3084                     if !recover {
3085                         return Err(e);
3086                     }
3087                     e.emit();
3088                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
3089                     self.eat(&token::Comma);
3090                 }
3091             }
3092         }
3093         Ok((fields, base, recover_async))
3094     }
3095
3096     /// Precondition: already parsed the '{'.
3097     pub(super) fn parse_struct_expr(
3098         &mut self,
3099         qself: Option<ast::QSelf>,
3100         pth: ast::Path,
3101         attrs: AttrVec,
3102         recover: bool,
3103     ) -> PResult<'a, P<Expr>> {
3104         let lo = pth.span;
3105         let (fields, base, recover_async) =
3106             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
3107         let span = lo.to(self.token.span);
3108         self.expect(&token::CloseDelim(Delimiter::Brace))?;
3109         let expr = if recover_async {
3110             ExprKind::Err
3111         } else {
3112             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
3113         };
3114         Ok(self.mk_expr(span, expr, attrs))
3115     }
3116
3117     /// Use in case of error after field-looking code: `S { foo: () with a }`.
3118     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
3119         match self.token.ident() {
3120             Some((ident, is_raw))
3121                 if (is_raw || !ident.is_reserved())
3122                     && self.look_ahead(1, |t| *t == token::Colon) =>
3123             {
3124                 Some(ast::ExprField {
3125                     ident,
3126                     span: self.token.span,
3127                     expr: self.mk_expr_err(self.token.span),
3128                     is_shorthand: false,
3129                     attrs: AttrVec::new(),
3130                     id: DUMMY_NODE_ID,
3131                     is_placeholder: false,
3132                 })
3133             }
3134             _ => None,
3135         }
3136     }
3137
3138     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
3139         if self.token != token::Comma {
3140             return;
3141         }
3142         self.struct_span_err(
3143             span.to(self.prev_token.span),
3144             "cannot use a comma after the base struct",
3145         )
3146         .span_suggestion_short(
3147             self.token.span,
3148             "remove this comma",
3149             "",
3150             Applicability::MachineApplicable,
3151         )
3152         .note("the base struct must always be the last field")
3153         .emit();
3154         self.recover_stmt();
3155     }
3156
3157     /// Parses `ident (COLON expr)?`.
3158     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3159         let attrs = self.parse_outer_attributes()?;
3160         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3161             let lo = this.token.span;
3162
3163             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3164             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3165             let (ident, expr) = if is_shorthand {
3166                 // Mimic `x: x` for the `x` field shorthand.
3167                 let ident = this.parse_ident_common(false)?;
3168                 let path = ast::Path::from_ident(ident);
3169                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
3170             } else {
3171                 let ident = this.parse_field_name()?;
3172                 this.error_on_eq_field_init(ident);
3173                 this.bump(); // `:`
3174                 (ident, this.parse_expr()?)
3175             };
3176
3177             Ok((
3178                 ast::ExprField {
3179                     ident,
3180                     span: lo.to(expr.span),
3181                     expr,
3182                     is_shorthand,
3183                     attrs: attrs.into(),
3184                     id: DUMMY_NODE_ID,
3185                     is_placeholder: false,
3186                 },
3187                 TrailingToken::MaybeComma,
3188             ))
3189         })
3190     }
3191
3192     /// Check for `=`. This means the source incorrectly attempts to
3193     /// initialize a field with an eq rather than a colon.
3194     fn error_on_eq_field_init(&self, field_name: Ident) {
3195         if self.token != token::Eq {
3196             return;
3197         }
3198
3199         self.struct_span_err(self.token.span, "expected `:`, found `=`")
3200             .span_suggestion(
3201                 field_name.span.shrink_to_hi().to(self.token.span),
3202                 "replace equals symbol with a colon",
3203                 ":",
3204                 Applicability::MachineApplicable,
3205             )
3206             .emit();
3207     }
3208
3209     fn err_dotdotdot_syntax(&self, span: Span) {
3210         self.struct_span_err(span, "unexpected token: `...`")
3211             .span_suggestion(
3212                 span,
3213                 "use `..` for an exclusive range",
3214                 "..",
3215                 Applicability::MaybeIncorrect,
3216             )
3217             .span_suggestion(
3218                 span,
3219                 "or `..=` for an inclusive range",
3220                 "..=",
3221                 Applicability::MaybeIncorrect,
3222             )
3223             .emit();
3224     }
3225
3226     fn err_larrow_operator(&self, span: Span) {
3227         self.struct_span_err(span, "unexpected token: `<-`")
3228             .span_suggestion(
3229                 span,
3230                 "if you meant to write a comparison against a negative value, add a \
3231              space in between `<` and `-`",
3232                 "< -",
3233                 Applicability::MaybeIncorrect,
3234             )
3235             .emit();
3236     }
3237
3238     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3239         ExprKind::AssignOp(binop, lhs, rhs)
3240     }
3241
3242     fn mk_range(
3243         &mut self,
3244         start: Option<P<Expr>>,
3245         end: Option<P<Expr>>,
3246         limits: RangeLimits,
3247     ) -> ExprKind {
3248         if end.is_none() && limits == RangeLimits::Closed {
3249             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3250             ExprKind::Err
3251         } else {
3252             ExprKind::Range(start, end, limits)
3253         }
3254     }
3255
3256     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3257         ExprKind::Unary(unop, expr)
3258     }
3259
3260     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3261         ExprKind::Binary(binop, lhs, rhs)
3262     }
3263
3264     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3265         ExprKind::Index(expr, idx)
3266     }
3267
3268     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3269         ExprKind::Call(f, args)
3270     }
3271
3272     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3273         let span = lo.to(self.prev_token.span);
3274         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
3275         self.recover_from_await_method_call();
3276         await_expr
3277     }
3278
3279     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3280         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3281     }
3282
3283     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3284         self.mk_expr(span, ExprKind::Err, AttrVec::new())
3285     }
3286
3287     /// Create expression span ensuring the span of the parent node
3288     /// is larger than the span of lhs and rhs, including the attributes.
3289     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3290         lhs.attrs
3291             .iter()
3292             .find(|a| a.style == AttrStyle::Outer)
3293             .map_or(lhs_span, |a| a.span)
3294             .to(rhs_span)
3295     }
3296
3297     fn collect_tokens_for_expr(
3298         &mut self,
3299         attrs: AttrWrapper,
3300         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
3301     ) -> PResult<'a, P<Expr>> {
3302         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3303             let res = f(this, attrs)?;
3304             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3305                 && this.token.kind == token::Semi
3306             {
3307                 TrailingToken::Semi
3308             } else {
3309                 // FIXME - pass this through from the place where we know
3310                 // we need a comma, rather than assuming that `#[attr] expr,`
3311                 // always captures a trailing comma
3312                 TrailingToken::MaybeComma
3313             };
3314             Ok((res, trailing))
3315         })
3316     }
3317 }