compiler/rustc_parse/src/parser/expr.rs

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