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 parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
 911         match self.token.uninterpolate().kind {
 912             token::Ident(..) => self.parse_dot_suffix(base, lo),
 913             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
 914                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
 915             }
 916             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
 917                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
 918             }
 919             _ => {
 920                 self.error_unexpected_after_dot();
 921                 Ok(base)
 922             }
 923         }
 924     }
 925
 926     fn error_unexpected_after_dot(&self) {
 927         // FIXME Could factor this out into non_fatal_unexpected or something.
 928         let actual = pprust::token_to_string(&self.token);
 929         self.struct_span_err(self.token.span, &format!("unexpected token: `{}`", actual)).emit();
 930     }
 931
 932     // We need an identifier or integer, but the next token is a float.
 933     // Break the float into components to extract the identifier or integer.
 934     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
 935     // parts unless those parts are processed immediately. `TokenCursor` should either
 936     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
 937     // we should break everything including floats into more basic proc-macro style
 938     // tokens in the lexer (probably preferable).
 939     fn parse_tuple_field_access_expr_float(
 940         &mut self,
 941         lo: Span,
 942         base: P<Expr>,
 943         float: Symbol,
 944         suffix: Option<Symbol>,
 945     ) -> P<Expr> {
 946         #[derive(Debug)]
 947         enum FloatComponent {
 948             IdentLike(String),
 949             Punct(char),
 950         }
 951         use FloatComponent::*;
 952
 953         let float_str = float.as_str();
 954         let mut components = Vec::new();
 955         let mut ident_like = String::new();
 956         for c in float_str.chars() {
 957             if c == '_' || c.is_ascii_alphanumeric() {
 958                 ident_like.push(c);
 959             } else if matches!(c, '.' | '+' | '-') {
 960                 if !ident_like.is_empty() {
 961                     components.push(IdentLike(mem::take(&mut ident_like)));
 962                 }
 963                 components.push(Punct(c));
 964             } else {
 965                 panic!("unexpected character in a float token: {:?}", c)
 966             }
 967         }
 968         if !ident_like.is_empty() {
 969             components.push(IdentLike(ident_like));
 970         }
 971
 972         // With proc macros the span can refer to anything, the source may be too short,
 973         // or too long, or non-ASCII. It only makes sense to break our span into components
 974         // if its underlying text is identical to our float literal.
 975         let span = self.token.span;
 976         let can_take_span_apart =
 977             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
 978
 979         match &*components {
 980             // 1e2
 981             [IdentLike(i)] => {
 982                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
 983             }
 984             // 1.
 985             [IdentLike(i), Punct('.')] => {
 986                 let (ident_span, dot_span) = if can_take_span_apart() {
 987                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
 988                     let ident_span = span.with_hi(span.lo + ident_len);
 989                     let dot_span = span.with_lo(span.lo + ident_len);
 990                     (ident_span, dot_span)
 991                 } else {
 992                     (span, span)
 993                 };
 994                 assert!(suffix.is_none());
 995                 let symbol = Symbol::intern(&i);
 996                 self.token = Token::new(token::Ident(symbol, false), ident_span);
 997                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
 998                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
 999             }
1000             // 1.2 | 1.2e3
1001             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1002                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1003                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1004                     let ident1_span = span.with_hi(span.lo + ident1_len);
1005                     let dot_span = span
1006                         .with_lo(span.lo + ident1_len)
1007                         .with_hi(span.lo + ident1_len + BytePos(1));
1008                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1009                     (ident1_span, dot_span, ident2_span)
1010                 } else {
1011                     (span, span, span)
1012                 };
1013                 let symbol1 = Symbol::intern(&i1);
1014                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1015                 // This needs to be `Spacing::Alone` to prevent regressions.
1016                 // See issue #76399 and PR #76285 for more details
1017                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1018                 let base1 =
1019                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1020                 let symbol2 = Symbol::intern(&i2);
1021                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1022                 self.bump_with((next_token2, self.token_spacing)); // `.`
1023                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1024             }
1025             // 1e+ | 1e- (recovered)
1026             [IdentLike(_), Punct('+' | '-')] |
1027             // 1e+2 | 1e-2
1028             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1029             // 1.2e+3 | 1.2e-3
1030             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1031                 // See the FIXME about `TokenCursor` above.
1032                 self.error_unexpected_after_dot();
1033                 base
1034             }
1035             _ => panic!("unexpected components in a float token: {:?}", components),
1036         }
1037     }
1038
1039     fn parse_tuple_field_access_expr(
1040         &mut self,
1041         lo: Span,
1042         base: P<Expr>,
1043         field: Symbol,
1044         suffix: Option<Symbol>,
1045         next_token: Option<(Token, Spacing)>,
1046     ) -> P<Expr> {
1047         match next_token {
1048             Some(next_token) => self.bump_with(next_token),
1049             None => self.bump(),
1050         }
1051         let span = self.prev_token.span;
1052         let field = ExprKind::Field(base, Ident::new(field, span));
1053         self.expect_no_suffix(span, "a tuple index", suffix);
1054         self.mk_expr(lo.to(span), field, AttrVec::new())
1055     }
1056
1057     /// Parse a function call expression, `expr(...)`.
1058     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1059         let seq = self.parse_paren_expr_seq().map(|args| {
1060             self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new())
1061         });
1062         self.recover_seq_parse_error(token::Paren, lo, seq)
1063     }
1064
1065     /// Parse an indexing expression `expr[...]`.
1066     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1067         self.bump(); // `[`
1068         let index = self.parse_expr()?;
1069         self.expect(&token::CloseDelim(token::Bracket))?;
1070         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new()))
1071     }
1072
1073     /// Assuming we have just parsed `.`, continue parsing into an expression.
1074     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1075         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1076             return Ok(self.mk_await_expr(self_arg, lo));
1077         }
1078
1079         let fn_span_lo = self.token.span;
1080         let mut segment = self.parse_path_segment(PathStyle::Expr)?;
1081         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(token::Paren)]);
1082         self.check_turbofish_missing_angle_brackets(&mut segment);
1083
1084         if self.check(&token::OpenDelim(token::Paren)) {
1085             // Method call `expr.f()`
1086             let mut args = self.parse_paren_expr_seq()?;
1087             args.insert(0, self_arg);
1088
1089             let fn_span = fn_span_lo.to(self.prev_token.span);
1090             let span = lo.to(self.prev_token.span);
1091             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new()))
1092         } else {
1093             // Field access `expr.f`
1094             if let Some(args) = segment.args {
1095                 self.struct_span_err(
1096                     args.span(),
1097                     "field expressions cannot have generic arguments",
1098                 )
1099                 .emit();
1100             }
1101
1102             let span = lo.to(self.prev_token.span);
1103             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new()))
1104         }
1105     }
1106
1107     /// At the bottom (top?) of the precedence hierarchy,
1108     /// Parses things like parenthesized exprs, macros, `return`, etc.
1109     ///
1110     /// N.B., this does not parse outer attributes, and is private because it only works
1111     /// correctly if called from `parse_dot_or_call_expr()`.
1112     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1113         maybe_recover_from_interpolated_ty_qpath!(self, true);
1114         maybe_whole_expr!(self);
1115
1116         // Outer attributes are already parsed and will be
1117         // added to the return value after the fact.
1118         //
1119         // Therefore, prevent sub-parser from parsing
1120         // attributes by giving them an empty "already-parsed" list.
1121         let attrs = AttrVec::new();
1122
1123         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1124         let lo = self.token.span;
1125         if let token::Literal(_) = self.token.kind {
1126             // This match arm is a special-case of the `_` match arm below and
1127             // could be removed without changing functionality, but it's faster
1128             // to have it here, especially for programs with large constants.
1129             self.parse_lit_expr(attrs)
1130         } else if self.check(&token::OpenDelim(token::Paren)) {
1131             self.parse_tuple_parens_expr(attrs)
1132         } else if self.check(&token::OpenDelim(token::Brace)) {
1133             self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs)
1134         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1135             self.parse_closure_expr(attrs)
1136         } else if self.check(&token::OpenDelim(token::Bracket)) {
1137             self.parse_array_or_repeat_expr(attrs)
1138         } else if self.check_path() {
1139             self.parse_path_start_expr(attrs)
1140         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1141             self.parse_closure_expr(attrs)
1142         } else if self.eat_keyword(kw::If) {
1143             self.parse_if_expr(attrs)
1144         } else if self.check_keyword(kw::For) {
1145             if self.choose_generics_over_qpath(1) {
1146                 // NOTE(Centril, eddyb): DO NOT REMOVE! Beyond providing parser recovery,
1147                 // this is an insurance policy in case we allow qpaths in (tuple-)struct patterns.
1148                 // When `for <Foo as Bar>::Proj in $expr $block` is wanted,
1149                 // you can disambiguate in favor of a pattern with `(...)`.
1150                 self.recover_quantified_closure_expr(attrs)
1151             } else {
1152                 assert!(self.eat_keyword(kw::For));
1153                 self.parse_for_expr(None, self.prev_token.span, attrs)
1154             }
1155         } else if self.eat_keyword(kw::While) {
1156             self.parse_while_expr(None, self.prev_token.span, attrs)
1157         } else if let Some(label) = self.eat_label() {
1158             self.parse_labeled_expr(label, attrs, true)
1159         } else if self.eat_keyword(kw::Loop) {
1160             self.parse_loop_expr(None, self.prev_token.span, attrs)
1161         } else if self.eat_keyword(kw::Continue) {
1162             let kind = ExprKind::Continue(self.eat_label());
1163             Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1164         } else if self.eat_keyword(kw::Match) {
1165             let match_sp = self.prev_token.span;
1166             self.parse_match_expr(attrs).map_err(|mut err| {
1167                 err.span_label(match_sp, "while parsing this match expression");
1168                 err
1169             })
1170         } else if self.eat_keyword(kw::Unsafe) {
1171             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
1172         } else if self.check_inline_const(0) {
1173             self.parse_const_block(lo.to(self.token.span))
1174         } else if self.is_do_catch_block() {
1175             self.recover_do_catch(attrs)
1176         } else if self.is_try_block() {
1177             self.expect_keyword(kw::Try)?;
1178             self.parse_try_block(lo, attrs)
1179         } else if self.eat_keyword(kw::Return) {
1180             self.parse_return_expr(attrs)
1181         } else if self.eat_keyword(kw::Break) {
1182             self.parse_break_expr(attrs)
1183         } else if self.eat_keyword(kw::Yield) {
1184             self.parse_yield_expr(attrs)
1185         } else if self.eat_keyword(kw::Let) {
1186             self.parse_let_expr(attrs)
1187         } else if self.eat_keyword(kw::Underscore) {
1188             self.sess.gated_spans.gate(sym::destructuring_assignment, self.prev_token.span);
1189             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
1190         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1191             // Don't complain about bare semicolons after unclosed braces
1192             // recovery in order to keep the error count down. Fixing the
1193             // delimiters will possibly also fix the bare semicolon found in
1194             // expression context. For example, silence the following error:
1195             //
1196             //     error: expected expression, found `;`
1197             //      --> file.rs:2:13
1198             //       |
1199             //     2 |     foo(bar(;
1200             //       |             ^ expected expression
1201             self.bump();
1202             Ok(self.mk_expr_err(self.token.span))
1203         } else if self.token.uninterpolated_span().rust_2018() {
1204             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1205             if self.check_keyword(kw::Async) {
1206                 if self.is_async_block() {
1207                     // Check for `async {` and `async move {`.
1208                     self.parse_async_block(attrs)
1209                 } else {
1210                     self.parse_closure_expr(attrs)
1211                 }
1212             } else if self.eat_keyword(kw::Await) {
1213                 self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs)
1214             } else {
1215                 self.parse_lit_expr(attrs)
1216             }
1217         } else {
1218             self.parse_lit_expr(attrs)
1219         }
1220     }
1221
1222     fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1223         let lo = self.token.span;
1224         match self.parse_opt_lit() {
1225             Some(literal) => {
1226                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs);
1227                 self.maybe_recover_from_bad_qpath(expr, true)
1228             }
1229             None => self.try_macro_suggestion(),
1230         }
1231     }
1232
1233     fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1234         let lo = self.token.span;
1235         self.expect(&token::OpenDelim(token::Paren))?;
1236         let (es, trailing_comma) = match self.parse_seq_to_end(
1237             &token::CloseDelim(token::Paren),
1238             SeqSep::trailing_allowed(token::Comma),
1239             |p| p.parse_expr_catch_underscore(),
1240         ) {
1241             Ok(x) => x,
1242             Err(err) => return Ok(self.recover_seq_parse_error(token::Paren, lo, Err(err))),
1243         };
1244         let kind = if es.len() == 1 && !trailing_comma {
1245             // `(e)` is parenthesized `e`.
1246             ExprKind::Paren(es.into_iter().next().unwrap())
1247         } else {
1248             // `(e,)` is a tuple with only one field, `e`.
1249             ExprKind::Tup(es)
1250         };
1251         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1252         self.maybe_recover_from_bad_qpath(expr, true)
1253     }
1254
1255     fn parse_array_or_repeat_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1256         let lo = self.token.span;
1257         self.bump(); // `[`
1258
1259         let close = &token::CloseDelim(token::Bracket);
1260         let kind = if self.eat(close) {
1261             // Empty vector
1262             ExprKind::Array(Vec::new())
1263         } else {
1264             // Non-empty vector
1265             let first_expr = self.parse_expr()?;
1266             if self.eat(&token::Semi) {
1267                 // Repeating array syntax: `[ 0; 512 ]`
1268                 let count = self.parse_anon_const_expr()?;
1269                 self.expect(close)?;
1270                 ExprKind::Repeat(first_expr, count)
1271             } else if self.eat(&token::Comma) {
1272                 // Vector with two or more elements.
1273                 let sep = SeqSep::trailing_allowed(token::Comma);
1274                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1275                 let mut exprs = vec![first_expr];
1276                 exprs.extend(remaining_exprs);
1277                 ExprKind::Array(exprs)
1278             } else {
1279                 // Vector with one element
1280                 self.expect(close)?;
1281                 ExprKind::Array(vec![first_expr])
1282             }
1283         };
1284         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1285         self.maybe_recover_from_bad_qpath(expr, true)
1286     }
1287
1288     fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1289         let (qself, path) = if self.eat_lt() {
1290             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1291             (Some(qself), path)
1292         } else {
1293             (None, self.parse_path(PathStyle::Expr)?)
1294         };
1295         let lo = path.span;
1296
1297         // `!`, as an operator, is prefix, so we know this isn't that.
1298         let (hi, kind) = if self.eat(&token::Not) {
1299             // MACRO INVOCATION expression
1300             if qself.is_some() {
1301                 self.struct_span_err(path.span, "macros cannot use qualified paths").emit();
1302             }
1303             let mac = MacCall {
1304                 path,
1305                 args: self.parse_mac_args()?,
1306                 prior_type_ascription: self.last_type_ascription,
1307             };
1308             (self.prev_token.span, ExprKind::MacCall(mac))
1309         } else if self.check(&token::OpenDelim(token::Brace)) {
1310             if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) {
1311                 if qself.is_some() {
1312                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1313                 }
1314                 return expr;
1315             } else {
1316                 (path.span, ExprKind::Path(qself, path))
1317             }
1318         } else {
1319             (path.span, ExprKind::Path(qself, path))
1320         };
1321
1322         let expr = self.mk_expr(lo.to(hi), kind, attrs);
1323         self.maybe_recover_from_bad_qpath(expr, true)
1324     }
1325
1326     /// Parse `'label: $expr`. The label is already parsed.
1327     fn parse_labeled_expr(
1328         &mut self,
1329         label: Label,
1330         attrs: AttrVec,
1331         consume_colon: bool,
1332     ) -> PResult<'a, P<Expr>> {
1333         let lo = label.ident.span;
1334         let label = Some(label);
1335         let ate_colon = self.eat(&token::Colon);
1336         let expr = if self.eat_keyword(kw::While) {
1337             self.parse_while_expr(label, lo, attrs)
1338         } else if self.eat_keyword(kw::For) {
1339             self.parse_for_expr(label, lo, attrs)
1340         } else if self.eat_keyword(kw::Loop) {
1341             self.parse_loop_expr(label, lo, attrs)
1342         } else if self.check(&token::OpenDelim(token::Brace)) || self.token.is_whole_block() {
1343             self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs)
1344         } else {
1345             let msg = "expected `while`, `for`, `loop` or `{` after a label";
1346             self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
1347             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1348             self.parse_expr()
1349         }?;
1350
1351         if !ate_colon && consume_colon {
1352             self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span);
1353         }
1354
1355         Ok(expr)
1356     }
1357
1358     fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) {
1359         self.struct_span_err(span, "labeled expression must be followed by `:`")
1360             .span_label(lo, "the label")
1361             .span_suggestion_short(
1362                 lo.shrink_to_hi(),
1363                 "add `:` after the label",
1364                 ": ".to_string(),
1365                 Applicability::MachineApplicable,
1366             )
1367             .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them")
1368             .emit();
1369     }
1370
1371     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1372     fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1373         let lo = self.token.span;
1374
1375         self.bump(); // `do`
1376         self.bump(); // `catch`
1377
1378         let span_dc = lo.to(self.prev_token.span);
1379         self.struct_span_err(span_dc, "found removed `do catch` syntax")
1380             .span_suggestion(
1381                 span_dc,
1382                 "replace with the new syntax",
1383                 "try".to_string(),
1384                 Applicability::MachineApplicable,
1385             )
1386             .note("following RFC #2388, the new non-placeholder syntax is `try`")
1387             .emit();
1388
1389         self.parse_try_block(lo, attrs)
1390     }
1391
1392     /// Parse an expression if the token can begin one.
1393     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1394         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1395     }
1396
1397     /// Parse `"return" expr?`.
1398     fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1399         let lo = self.prev_token.span;
1400         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1401         let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs);
1402         self.maybe_recover_from_bad_qpath(expr, true)
1403     }
1404
1405     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1406     /// If the label is followed immediately by a `:` token, the label and `:` are
1407     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1408     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1409     /// the break expression of an unlabeled break is a labeled loop (as in
1410     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1411     /// expression only gets a warning for compatibility reasons; and a labeled break
1412     /// with a labeled loop does not even get a warning because there is no ambiguity.
1413     fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1414         let lo = self.prev_token.span;
1415         let mut label = self.eat_label();
1416         let kind = if label.is_some() && self.token == token::Colon {
1417             // The value expression can be a labeled loop, see issue #86948, e.g.:
1418             // `loop { break 'label: loop { break 'label 42; }; }`
1419             let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?;
1420             self.struct_span_err(
1421                 lexpr.span,
1422                 "parentheses are required around this expression to avoid confusion with a labeled break expression",
1423             )
1424             .multipart_suggestion(
1425                 "wrap the expression in parentheses",
1426                 vec![
1427                     (lexpr.span.shrink_to_lo(), "(".to_string()),
1428                     (lexpr.span.shrink_to_hi(), ")".to_string()),
1429                 ],
1430                 Applicability::MachineApplicable,
1431             )
1432             .emit();
1433             Some(lexpr)
1434         } else if self.token != token::OpenDelim(token::Brace)
1435             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1436         {
1437             let expr = self.parse_expr_opt()?;
1438             if let Some(ref expr) = expr {
1439                 if label.is_some()
1440                     && matches!(
1441                         expr.kind,
1442                         ExprKind::While(_, _, None)
1443                             | ExprKind::ForLoop(_, _, _, None)
1444                             | ExprKind::Loop(_, None)
1445                             | ExprKind::Block(_, None)
1446                     )
1447                 {
1448                     self.sess.buffer_lint_with_diagnostic(
1449                         BREAK_WITH_LABEL_AND_LOOP,
1450                         lo.to(expr.span),
1451                         ast::CRATE_NODE_ID,
1452                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1453                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1454                     );
1455                 }
1456             }
1457             expr
1458         } else {
1459             None
1460         };
1461         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs);
1462         self.maybe_recover_from_bad_qpath(expr, true)
1463     }
1464
1465     /// Parse `"yield" expr?`.
1466     fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1467         let lo = self.prev_token.span;
1468         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1469         let span = lo.to(self.prev_token.span);
1470         self.sess.gated_spans.gate(sym::generators, span);
1471         let expr = self.mk_expr(span, kind, attrs);
1472         self.maybe_recover_from_bad_qpath(expr, true)
1473     }
1474
1475     /// Returns a string literal if the next token is a string literal.
1476     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1477     /// and returns `None` if the next token is not literal at all.
1478     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1479         match self.parse_opt_lit() {
1480             Some(lit) => match lit.kind {
1481                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1482                     style,
1483                     symbol: lit.token.symbol,
1484                     suffix: lit.token.suffix,
1485                     span: lit.span,
1486                     symbol_unescaped,
1487                 }),
1488                 _ => Err(Some(lit)),
1489             },
1490             None => Err(None),
1491         }
1492     }
1493
1494     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1495         self.parse_opt_lit().ok_or_else(|| {
1496             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1497             self.struct_span_err(self.token.span, &msg)
1498         })
1499     }
1500
1501     /// Matches `lit = true | false | token_lit`.
1502     /// Returns `None` if the next token is not a literal.
1503     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1504         let mut recovered = None;
1505         if self.token == token::Dot {
1506             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1507             // dot would follow an optional literal, so we do this unconditionally.
1508             recovered = self.look_ahead(1, |next_token| {
1509                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1510                     next_token.kind
1511                 {
1512                     if self.token.span.hi() == next_token.span.lo() {
1513                         let s = String::from("0.") + &symbol.as_str();
1514                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1515                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1516                     }
1517                 }
1518                 None
1519             });
1520             if let Some(token) = &recovered {
1521                 self.bump();
1522                 self.error_float_lits_must_have_int_part(&token);
1523             }
1524         }
1525
1526         let token = recovered.as_ref().unwrap_or(&self.token);
1527         match Lit::from_token(token) {
1528             Ok(lit) => {
1529                 self.bump();
1530                 Some(lit)
1531             }
1532             Err(LitError::NotLiteral) => None,
1533             Err(err) => {
1534                 let span = token.span;
1535                 let lit = match token.kind {
1536                     token::Literal(lit) => lit,
1537                     _ => unreachable!(),
1538                 };
1539                 self.bump();
1540                 self.report_lit_error(err, lit, span);
1541                 // Pack possible quotes and prefixes from the original literal into
1542                 // the error literal's symbol so they can be pretty-printed faithfully.
1543                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1544                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1545                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1546                 Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!()))
1547             }
1548         }
1549     }
1550
1551     fn error_float_lits_must_have_int_part(&self, token: &Token) {
1552         self.struct_span_err(token.span, "float literals must have an integer part")
1553             .span_suggestion(
1554                 token.span,
1555                 "must have an integer part",
1556                 pprust::token_to_string(token).into(),
1557                 Applicability::MachineApplicable,
1558             )
1559             .emit();
1560     }
1561
1562     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1563         // Checks if `s` looks like i32 or u1234 etc.
1564         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1565             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1566         }
1567
1568         let token::Lit { kind, suffix, .. } = lit;
1569         match err {
1570             // `NotLiteral` is not an error by itself, so we don't report
1571             // it and give the parser opportunity to try something else.
1572             LitError::NotLiteral => {}
1573             // `LexerError` *is* an error, but it was already reported
1574             // by lexer, so here we don't report it the second time.
1575             LitError::LexerError => {}
1576             LitError::InvalidSuffix => {
1577                 self.expect_no_suffix(
1578                     span,
1579                     &format!("{} {} literal", kind.article(), kind.descr()),
1580                     suffix,
1581                 );
1582             }
1583             LitError::InvalidIntSuffix => {
1584                 let suf = suffix.expect("suffix error with no suffix").as_str();
1585                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1586                     // If it looks like a width, try to be helpful.
1587                     let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
1588                     self.struct_span_err(span, &msg)
1589                         .help("valid widths are 8, 16, 32, 64 and 128")
1590                         .emit();
1591                 } else {
1592                     let msg = format!("invalid suffix `{}` for number literal", suf);
1593                     self.struct_span_err(span, &msg)
1594                         .span_label(span, format!("invalid suffix `{}`", suf))
1595                         .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)")
1596                         .emit();
1597                 }
1598             }
1599             LitError::InvalidFloatSuffix => {
1600                 let suf = suffix.expect("suffix error with no suffix").as_str();
1601                 if looks_like_width_suffix(&['f'], &suf) {
1602                     // If it looks like a width, try to be helpful.
1603                     let msg = format!("invalid width `{}` for float literal", &suf[1..]);
1604                     self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit();
1605                 } else {
1606                     let msg = format!("invalid suffix `{}` for float literal", suf);
1607                     self.struct_span_err(span, &msg)
1608                         .span_label(span, format!("invalid suffix `{}`", suf))
1609                         .help("valid suffixes are `f32` and `f64`")
1610                         .emit();
1611                 }
1612             }
1613             LitError::NonDecimalFloat(base) => {
1614                 let descr = match base {
1615                     16 => "hexadecimal",
1616                     8 => "octal",
1617                     2 => "binary",
1618                     _ => unreachable!(),
1619                 };
1620                 self.struct_span_err(span, &format!("{} float literal is not supported", descr))
1621                     .span_label(span, "not supported")
1622                     .emit();
1623             }
1624             LitError::IntTooLarge => {
1625                 self.struct_span_err(span, "integer literal is too large").emit();
1626             }
1627         }
1628     }
1629
1630     pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
1631         if let Some(suf) = suffix {
1632             let mut err = if kind == "a tuple index"
1633                 && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
1634             {
1635                 // #59553: warn instead of reject out of hand to allow the fix to percolate
1636                 // through the ecosystem when people fix their macros
1637                 let mut err = self
1638                     .sess
1639                     .span_diagnostic
1640                     .struct_span_warn(sp, &format!("suffixes on {} are invalid", kind));
1641                 err.note(&format!(
1642                     "`{}` is *temporarily* accepted on tuple index fields as it was \
1643                         incorrectly accepted on stable for a few releases",
1644                     suf,
1645                 ));
1646                 err.help(
1647                     "on proc macros, you'll want to use `syn::Index::from` or \
1648                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
1649                         to tuple field access",
1650                 );
1651                 err.note(
1652                     "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
1653                      for more information",
1654                 );
1655                 err
1656             } else {
1657                 self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
1658             };
1659             err.span_label(sp, format!("invalid suffix `{}`", suf));
1660             err.emit();
1661         }
1662     }
1663
1664     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1665     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1666     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1667         maybe_whole_expr!(self);
1668
1669         let lo = self.token.span;
1670         let minus_present = self.eat(&token::BinOp(token::Minus));
1671         let lit = self.parse_lit()?;
1672         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new());
1673
1674         if minus_present {
1675             Ok(self.mk_expr(
1676                 lo.to(self.prev_token.span),
1677                 self.mk_unary(UnOp::Neg, expr),
1678                 AttrVec::new(),
1679             ))
1680         } else {
1681             Ok(expr)
1682         }
1683     }
1684
1685     /// Parses a block or unsafe block.
1686     pub(super) fn parse_block_expr(
1687         &mut self,
1688         opt_label: Option<Label>,
1689         lo: Span,
1690         blk_mode: BlockCheckMode,
1691         mut attrs: AttrVec,
1692     ) -> PResult<'a, P<Expr>> {
1693         if let Some(label) = opt_label {
1694             self.sess.gated_spans.gate(sym::label_break_value, label.ident.span);
1695         }
1696
1697         if self.token.is_whole_block() {
1698             self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here")
1699                 .span_label(lo.to(self.token.span), "the `block` fragment is within this context")
1700                 .emit();
1701         }
1702
1703         let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?;
1704         attrs.extend(inner_attrs);
1705         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
1706     }
1707
1708     /// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`.
1709     fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1710         let lo = self.token.span;
1711         let _ = self.parse_late_bound_lifetime_defs()?;
1712         let span_for = lo.to(self.prev_token.span);
1713         let closure = self.parse_closure_expr(attrs)?;
1714
1715         self.struct_span_err(span_for, "cannot introduce explicit parameters for a closure")
1716             .span_label(closure.span, "the parameters are attached to this closure")
1717             .span_suggestion(
1718                 span_for,
1719                 "remove the parameters",
1720                 String::new(),
1721                 Applicability::MachineApplicable,
1722             )
1723             .emit();
1724
1725         Ok(self.mk_expr_err(lo.to(closure.span)))
1726     }
1727
1728     /// Parses a closure expression (e.g., `move |args| expr`).
1729     fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1730         let lo = self.token.span;
1731
1732         let movability =
1733             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
1734
1735         let asyncness = if self.token.uninterpolated_span().rust_2018() {
1736             self.parse_asyncness()
1737         } else {
1738             Async::No
1739         };
1740
1741         let capture_clause = self.parse_capture_clause()?;
1742         let decl = self.parse_fn_block_decl()?;
1743         let decl_hi = self.prev_token.span;
1744         let mut body = match decl.output {
1745             FnRetTy::Default(_) => {
1746                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
1747                 self.parse_expr_res(restrictions, None)?
1748             }
1749             _ => {
1750                 // If an explicit return type is given, require a block to appear (RFC 968).
1751                 let body_lo = self.token.span;
1752                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())?
1753             }
1754         };
1755
1756         if let Async::Yes { span, .. } = asyncness {
1757             // Feature-gate `async ||` closures.
1758             self.sess.gated_spans.gate(sym::async_closure, span);
1759         }
1760
1761         if self.token.kind == TokenKind::Semi && self.token_cursor.frame.delim == DelimToken::Paren
1762         {
1763             // It is likely that the closure body is a block but where the
1764             // braces have been removed. We will recover and eat the next
1765             // statements later in the parsing process.
1766             body = self.mk_expr_err(body.span);
1767         }
1768
1769         let body_span = body.span;
1770
1771         let closure = self.mk_expr(
1772             lo.to(body.span),
1773             ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
1774             attrs,
1775         );
1776
1777         // Disable recovery for closure body
1778         let spans =
1779             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
1780         self.current_closure = Some(spans);
1781
1782         Ok(closure)
1783     }
1784
1785     /// Parses an optional `move` prefix to a closure-like construct.
1786     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
1787         if self.eat_keyword(kw::Move) {
1788             // Check for `move async` and recover
1789             if self.check_keyword(kw::Async) {
1790                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
1791                 Err(self.incorrect_move_async_order_found(move_async_span))
1792             } else {
1793                 Ok(CaptureBy::Value)
1794             }
1795         } else {
1796             Ok(CaptureBy::Ref)
1797         }
1798     }
1799
1800     /// Parses the `|arg, arg|` header of a closure.
1801     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
1802         let inputs = if self.eat(&token::OrOr) {
1803             Vec::new()
1804         } else {
1805             self.expect(&token::BinOp(token::Or))?;
1806             let args = self
1807                 .parse_seq_to_before_tokens(
1808                     &[&token::BinOp(token::Or), &token::OrOr],
1809                     SeqSep::trailing_allowed(token::Comma),
1810                     TokenExpectType::NoExpect,
1811                     |p| p.parse_fn_block_param(),
1812                 )?
1813                 .0;
1814             self.expect_or()?;
1815             args
1816         };
1817         let output =
1818             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
1819
1820         Ok(P(FnDecl { inputs, output }))
1821     }
1822
1823     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
1824     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
1825         let lo = self.token.span;
1826         let attrs = self.parse_outer_attributes()?;
1827         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
1828             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
1829             let ty = if this.eat(&token::Colon) {
1830                 this.parse_ty()?
1831             } else {
1832                 this.mk_ty(this.prev_token.span, TyKind::Infer)
1833             };
1834
1835             Ok((
1836                 Param {
1837                     attrs: attrs.into(),
1838                     ty,
1839                     pat,
1840                     span: lo.to(this.token.span),
1841                     id: DUMMY_NODE_ID,
1842                     is_placeholder: false,
1843                 },
1844                 TrailingToken::MaybeComma,
1845             ))
1846         })
1847     }
1848
1849     /// Parses an `if` expression (`if` token already eaten).
1850     fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1851         let lo = self.prev_token.span;
1852         let cond = self.parse_cond_expr()?;
1853
1854         // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
1855         // verify that the last statement is either an implicit return (no `;`) or an explicit
1856         // return. This won't catch blocks with an explicit `return`, but that would be caught by
1857         // the dead code lint.
1858         let thn = if self.eat_keyword(kw::Else) || !cond.returns() {
1859             self.error_missing_if_cond(lo, cond.span)
1860         } else {
1861             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
1862             let not_block = self.token != token::OpenDelim(token::Brace);
1863             let block = self.parse_block().map_err(|mut err| {
1864                 if not_block {
1865                     err.span_label(lo, "this `if` expression has a condition, but no block");
1866                     if let ExprKind::Binary(_, _, ref right) = cond.kind {
1867                         if let ExprKind::Block(_, _) = right.kind {
1868                             err.help("maybe you forgot the right operand of the condition?");
1869                         }
1870                     }
1871                 }
1872                 err
1873             })?;
1874             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
1875             block
1876         };
1877         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
1878         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs))
1879     }
1880
1881     fn error_missing_if_cond(&self, lo: Span, span: Span) -> P<ast::Block> {
1882         let sp = self.sess.source_map().next_point(lo);
1883         self.struct_span_err(sp, "missing condition for `if` expression")
1884             .span_label(sp, "expected if condition here")
1885             .emit();
1886         self.mk_block_err(span)
1887     }
1888
1889     /// Parses the condition of a `if` or `while` expression.
1890     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
1891         let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1892
1893         if let ExprKind::Let(..) = cond.kind {
1894             // Remove the last feature gating of a `let` expression since it's stable.
1895             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
1896         }
1897
1898         Ok(cond)
1899     }
1900
1901     /// Parses a `let $pat = $expr` pseudo-expression.
1902     /// The `let` token has already been eaten.
1903     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
1904         let lo = self.prev_token.span;
1905         let pat = self.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
1906         self.expect(&token::Eq)?;
1907         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
1908             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
1909         })?;
1910         let span = lo.to(expr.span);
1911         self.sess.gated_spans.gate(sym::let_chains, span);
1912         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs))
1913     }
1914
1915     /// Parses an `else { ... }` expression (`else` token already eaten).
1916     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
1917         let ctx_span = self.prev_token.span; // `else`
1918         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
1919         let expr = if self.eat_keyword(kw::If) {
1920             self.parse_if_expr(AttrVec::new())?
1921         } else {
1922             let blk = self.parse_block()?;
1923             self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())
1924         };
1925         self.error_on_if_block_attrs(ctx_span, true, expr.span, &attrs);
1926         Ok(expr)
1927     }
1928
1929     fn error_on_if_block_attrs(
1930         &self,
1931         ctx_span: Span,
1932         is_ctx_else: bool,
1933         branch_span: Span,
1934         attrs: &[ast::Attribute],
1935     ) {
1936         let (span, last) = match attrs {
1937             [] => return,
1938             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
1939         };
1940         let ctx = if is_ctx_else { "else" } else { "if" };
1941         self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches")
1942             .span_label(branch_span, "the attributes are attached to this branch")
1943             .span_label(ctx_span, format!("the branch belongs to this `{}`", ctx))
1944             .span_suggestion(
1945                 span,
1946                 "remove the attributes",
1947                 String::new(),
1948                 Applicability::MachineApplicable,
1949             )
1950             .emit();
1951     }
1952
1953     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
1954     fn parse_for_expr(
1955         &mut self,
1956         opt_label: Option<Label>,
1957         lo: Span,
1958         mut attrs: AttrVec,
1959     ) -> PResult<'a, P<Expr>> {
1960         // Record whether we are about to parse `for (`.
1961         // This is used below for recovery in case of `for ( $stuff ) $block`
1962         // in which case we will suggest `for $stuff $block`.
1963         let begin_paren = match self.token.kind {
1964             token::OpenDelim(token::Paren) => Some(self.token.span),
1965             _ => None,
1966         };
1967
1968         let pat = self.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
1969         if !self.eat_keyword(kw::In) {
1970             self.error_missing_in_for_loop();
1971         }
1972         self.check_for_for_in_in_typo(self.prev_token.span);
1973         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
1974
1975         let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
1976
1977         let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
1978         attrs.extend(iattrs);
1979
1980         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
1981         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
1982     }
1983
1984     fn error_missing_in_for_loop(&mut self) {
1985         let (span, msg, sugg) = if self.token.is_ident_named(sym::of) {
1986             // Possibly using JS syntax (#75311).
1987             let span = self.token.span;
1988             self.bump();
1989             (span, "try using `in` here instead", "in")
1990         } else {
1991             (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ")
1992         };
1993         self.struct_span_err(span, "missing `in` in `for` loop")
1994             .span_suggestion_short(
1995                 span,
1996                 msg,
1997                 sugg.into(),
1998                 // Has been misleading, at least in the past (closed Issue #48492).
1999                 Applicability::MaybeIncorrect,
2000             )
2001             .emit();
2002     }
2003
2004     /// Parses a `while` or `while let` expression (`while` token already eaten).
2005     fn parse_while_expr(
2006         &mut self,
2007         opt_label: Option<Label>,
2008         lo: Span,
2009         mut attrs: AttrVec,
2010     ) -> PResult<'a, P<Expr>> {
2011         let cond = self.parse_cond_expr()?;
2012         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2013         attrs.extend(iattrs);
2014         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs))
2015     }
2016
2017     /// Parses `loop { ... }` (`loop` token already eaten).
2018     fn parse_loop_expr(
2019         &mut self,
2020         opt_label: Option<Label>,
2021         lo: Span,
2022         mut attrs: AttrVec,
2023     ) -> PResult<'a, P<Expr>> {
2024         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2025         attrs.extend(iattrs);
2026         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs))
2027     }
2028
2029     fn eat_label(&mut self) -> Option<Label> {
2030         self.token.lifetime().map(|ident| {
2031             self.bump();
2032             Label { ident }
2033         })
2034     }
2035
2036     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2037     fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2038         let match_span = self.prev_token.span;
2039         let lo = self.prev_token.span;
2040         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2041         if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
2042             if self.token == token::Semi {
2043                 e.span_suggestion_short(
2044                     match_span,
2045                     "try removing this `match`",
2046                     String::new(),
2047                     Applicability::MaybeIncorrect, // speculative
2048                 );
2049             }
2050             return Err(e);
2051         }
2052         attrs.extend(self.parse_inner_attributes()?);
2053
2054         let mut arms: Vec<Arm> = Vec::new();
2055         while self.token != token::CloseDelim(token::Brace) {
2056             match self.parse_arm() {
2057                 Ok(arm) => arms.push(arm),
2058                 Err(mut e) => {
2059                     // Recover by skipping to the end of the block.
2060                     e.emit();
2061                     self.recover_stmt();
2062                     let span = lo.to(self.token.span);
2063                     if self.token == token::CloseDelim(token::Brace) {
2064                         self.bump();
2065                     }
2066                     return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs));
2067                 }
2068             }
2069         }
2070         let hi = self.token.span;
2071         self.bump();
2072         Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2073     }
2074
2075     /// Attempt to recover from match arm body with statements and no surrounding braces.
2076     fn parse_arm_body_missing_braces(
2077         &mut self,
2078         first_expr: &P<Expr>,
2079         arrow_span: Span,
2080     ) -> Option<P<Expr>> {
2081         if self.token.kind != token::Semi {
2082             return None;
2083         }
2084         let start_snapshot = self.clone();
2085         let semi_sp = self.token.span;
2086         self.bump(); // `;`
2087         let mut stmts =
2088             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2089         let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
2090             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2091             let mut err = this.struct_span_err(span, "`match` arm body without braces");
2092             let (these, s, are) =
2093                 if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
2094             err.span_label(
2095                 span,
2096                 &format!(
2097                     "{these} statement{s} {are} not surrounded by a body",
2098                     these = these,
2099                     s = s,
2100                     are = are
2101                 ),
2102             );
2103             err.span_label(arrow_span, "while parsing the `match` arm starting here");
2104             if stmts.len() > 1 {
2105                 err.multipart_suggestion(
2106                     &format!("surround the statement{} with a body", s),
2107                     vec![
2108                         (span.shrink_to_lo(), "{ ".to_string()),
2109                         (span.shrink_to_hi(), " }".to_string()),
2110                     ],
2111                     Applicability::MachineApplicable,
2112                 );
2113             } else {
2114                 err.span_suggestion(
2115                     semi_sp,
2116                     "use a comma to end a `match` arm expression",
2117                     ",".to_string(),
2118                     Applicability::MachineApplicable,
2119                 );
2120             }
2121             err.emit();
2122             this.mk_expr_err(span)
2123         };
2124         // We might have either a `,` -> `;` typo, or a block without braces. We need
2125         // a more subtle parsing strategy.
2126         loop {
2127             if self.token.kind == token::CloseDelim(token::Brace) {
2128                 // We have reached the closing brace of the `match` expression.
2129                 return Some(err(self, stmts));
2130             }
2131             if self.token.kind == token::Comma {
2132                 *self = start_snapshot;
2133                 return None;
2134             }
2135             let pre_pat_snapshot = self.clone();
2136             match self.parse_pat_no_top_alt(None) {
2137                 Ok(_pat) => {
2138                     if self.token.kind == token::FatArrow {
2139                         // Reached arm end.
2140                         *self = pre_pat_snapshot;
2141                         return Some(err(self, stmts));
2142                     }
2143                 }
2144                 Err(mut err) => {
2145                     err.cancel();
2146                 }
2147             }
2148
2149             *self = pre_pat_snapshot;
2150             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2151                 // Consume statements for as long as possible.
2152                 Ok(Some(stmt)) => {
2153                     stmts.push(stmt);
2154                 }
2155                 Ok(None) => {
2156                     *self = start_snapshot;
2157                     break;
2158                 }
2159                 // We couldn't parse either yet another statement missing it's
2160                 // enclosing block nor the next arm's pattern or closing brace.
2161                 Err(mut stmt_err) => {
2162                     stmt_err.cancel();
2163                     *self = start_snapshot;
2164                     break;
2165                 }
2166             }
2167         }
2168         None
2169     }
2170
2171     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2172         let attrs = self.parse_outer_attributes()?;
2173         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2174             let lo = this.token.span;
2175             let pat = this.parse_pat_allow_top_alt(None, RecoverComma::Yes, RecoverColon::Yes)?;
2176             let guard = if this.eat_keyword(kw::If) {
2177                 let if_span = this.prev_token.span;
2178                 let cond = this.parse_expr()?;
2179                 if let ExprKind::Let(..) = cond.kind {
2180                     // Remove the last feature gating of a `let` expression since it's stable.
2181                     this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2182                     let span = if_span.to(cond.span);
2183                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2184                 }
2185                 Some(cond)
2186             } else {
2187                 None
2188             };
2189             let arrow_span = this.token.span;
2190             this.expect(&token::FatArrow)?;
2191             let arm_start_span = this.token.span;
2192
2193             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2194                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2195                 err
2196             })?;
2197
2198             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2199                 && this.token != token::CloseDelim(token::Brace);
2200
2201             let hi = this.prev_token.span;
2202
2203             if require_comma {
2204                 let sm = this.sess.source_map();
2205                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2206                     let span = body.span;
2207                     return Ok((
2208                         ast::Arm {
2209                             attrs: attrs.into(),
2210                             pat,
2211                             guard,
2212                             body,
2213                             span,
2214                             id: DUMMY_NODE_ID,
2215                             is_placeholder: false,
2216                         },
2217                         TrailingToken::None,
2218                     ));
2219                 }
2220                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]).map_err(
2221                     |mut err| {
2222                         match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) {
2223                             (Ok(ref expr_lines), Ok(ref arm_start_lines))
2224                                 if arm_start_lines.lines[0].end_col
2225                                     == expr_lines.lines[0].end_col
2226                                     && expr_lines.lines.len() == 2
2227                                     && this.token == token::FatArrow =>
2228                             {
2229                                 // We check whether there's any trailing code in the parse span,
2230                                 // if there isn't, we very likely have the following:
2231                                 //
2232                                 // X |     &Y => "y"
2233                                 //   |        --    - missing comma
2234                                 //   |        |
2235                                 //   |        arrow_span
2236                                 // X |     &X => "x"
2237                                 //   |      - ^^ self.token.span
2238                                 //   |      |
2239                                 //   |      parsed until here as `"y" & X`
2240                                 err.span_suggestion_short(
2241                                     arm_start_span.shrink_to_hi(),
2242                                     "missing a comma here to end this `match` arm",
2243                                     ",".to_owned(),
2244                                     Applicability::MachineApplicable,
2245                                 );
2246                             }
2247                             _ => {
2248                                 err.span_label(
2249                                     arrow_span,
2250                                     "while parsing the `match` arm starting here",
2251                                 );
2252                             }
2253                         }
2254                         err
2255                     },
2256                 )?;
2257             } else {
2258                 this.eat(&token::Comma);
2259             }
2260
2261             Ok((
2262                 ast::Arm {
2263                     attrs: attrs.into(),
2264                     pat,
2265                     guard,
2266                     body: expr,
2267                     span: lo.to(hi),
2268                     id: DUMMY_NODE_ID,
2269                     is_placeholder: false,
2270                 },
2271                 TrailingToken::None,
2272             ))
2273         })
2274     }
2275
2276     /// Parses a `try {...}` expression (`try` token already eaten).
2277     fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2278         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2279         attrs.extend(iattrs);
2280         if self.eat_keyword(kw::Catch) {
2281             let mut error = self.struct_span_err(
2282                 self.prev_token.span,
2283                 "keyword `catch` cannot follow a `try` block",
2284             );
2285             error.help("try using `match` on the result of the `try` block instead");
2286             error.emit();
2287             Err(error)
2288         } else {
2289             let span = span_lo.to(body.span);
2290             self.sess.gated_spans.gate(sym::try_blocks, span);
2291             Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs))
2292         }
2293     }
2294
2295     fn is_do_catch_block(&self) -> bool {
2296         self.token.is_keyword(kw::Do)
2297             && self.is_keyword_ahead(1, &[kw::Catch])
2298             && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2299             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2300     }
2301
2302     fn is_try_block(&self) -> bool {
2303         self.token.is_keyword(kw::Try)
2304             && self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2305             && self.token.uninterpolated_span().rust_2018()
2306     }
2307
2308     /// Parses an `async move? {...}` expression.
2309     fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
2310         let lo = self.token.span;
2311         self.expect_keyword(kw::Async)?;
2312         let capture_clause = self.parse_capture_clause()?;
2313         let (iattrs, body) = self.parse_inner_attrs_and_block()?;
2314         attrs.extend(iattrs);
2315         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2316         Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs))
2317     }
2318
2319     fn is_async_block(&self) -> bool {
2320         self.token.is_keyword(kw::Async)
2321             && ((
2322                 // `async move {`
2323                 self.is_keyword_ahead(1, &[kw::Move])
2324                     && self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
2325             ) || (
2326                 // `async {`
2327                 self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
2328             ))
2329     }
2330
2331     fn is_certainly_not_a_block(&self) -> bool {
2332         self.look_ahead(1, |t| t.is_ident())
2333             && (
2334                 // `{ ident, ` cannot start a block.
2335                 self.look_ahead(2, |t| t == &token::Comma)
2336                     || self.look_ahead(2, |t| t == &token::Colon)
2337                         && (
2338                             // `{ ident: token, ` cannot start a block.
2339                             self.look_ahead(4, |t| t == &token::Comma) ||
2340                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2341                 self.look_ahead(3, |t| !t.can_begin_type())
2342                         )
2343             )
2344     }
2345
2346     fn maybe_parse_struct_expr(
2347         &mut self,
2348         qself: Option<&ast::QSelf>,
2349         path: &ast::Path,
2350         attrs: &AttrVec,
2351     ) -> Option<PResult<'a, P<Expr>>> {
2352         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2353         if struct_allowed || self.is_certainly_not_a_block() {
2354             if let Err(err) = self.expect(&token::OpenDelim(token::Brace)) {
2355                 return Some(Err(err));
2356             }
2357             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true);
2358             if let (Ok(expr), false) = (&expr, struct_allowed) {
2359                 // This is a struct literal, but we don't can't accept them here.
2360                 self.error_struct_lit_not_allowed_here(path.span, expr.span);
2361             }
2362             return Some(expr);
2363         }
2364         None
2365     }
2366
2367     fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
2368         self.struct_span_err(sp, "struct literals are not allowed here")
2369             .multipart_suggestion(
2370                 "surround the struct literal with parentheses",
2371                 vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
2372                 Applicability::MachineApplicable,
2373             )
2374             .emit();
2375     }
2376
2377     /// Precondition: already parsed the '{'.
2378     pub(super) fn parse_struct_expr(
2379         &mut self,
2380         qself: Option<ast::QSelf>,
2381         pth: ast::Path,
2382         attrs: AttrVec,
2383         recover: bool,
2384     ) -> PResult<'a, P<Expr>> {
2385         let mut fields = Vec::new();
2386         let mut base = ast::StructRest::None;
2387         let mut recover_async = false;
2388
2389         let mut async_block_err = |e: &mut DiagnosticBuilder<'_>, span: Span| {
2390             recover_async = true;
2391             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2392             e.help(&format!("set `edition = \"{}\"` in `Cargo.toml`", LATEST_STABLE_EDITION));
2393             e.note("for more on editions, read https://doc.rust-lang.org/edition-guide");
2394         };
2395
2396         while self.token != token::CloseDelim(token::Brace) {
2397             if self.eat(&token::DotDot) {
2398                 let exp_span = self.prev_token.span;
2399                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2400                 if self.check(&token::CloseDelim(token::Brace)) {
2401                     self.sess.gated_spans.gate(sym::destructuring_assignment, self.prev_token.span);
2402                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2403                     break;
2404                 }
2405                 match self.parse_expr() {
2406                     Ok(e) => base = ast::StructRest::Base(e),
2407                     Err(mut e) if recover => {
2408                         e.emit();
2409                         self.recover_stmt();
2410                     }
2411                     Err(e) => return Err(e),
2412                 }
2413                 self.recover_struct_comma_after_dotdot(exp_span);
2414                 break;
2415             }
2416
2417             let recovery_field = self.find_struct_error_after_field_looking_code();
2418             let parsed_field = match self.parse_expr_field() {
2419                 Ok(f) => Some(f),
2420                 Err(mut e) => {
2421                     if pth == kw::Async {
2422                         async_block_err(&mut e, pth.span);
2423                     } else {
2424                         e.span_label(pth.span, "while parsing this struct");
2425                     }
2426                     e.emit();
2427
2428                     // If the next token is a comma, then try to parse
2429                     // what comes next as additional fields, rather than
2430                     // bailing out until next `}`.
2431                     if self.token != token::Comma {
2432                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2433                         if self.token != token::Comma {
2434                             break;
2435                         }
2436                     }
2437                     None
2438                 }
2439             };
2440
2441             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]) {
2442                 Ok(_) => {
2443                     if let Some(f) = parsed_field.or(recovery_field) {
2444                         // Only include the field if there's no parse error for the field name.
2445                         fields.push(f);
2446                     }
2447                 }
2448                 Err(mut e) => {
2449                     if pth == kw::Async {
2450                         async_block_err(&mut e, pth.span);
2451                     } else {
2452                         e.span_label(pth.span, "while parsing this struct");
2453                         if let Some(f) = recovery_field {
2454                             fields.push(f);
2455                             e.span_suggestion(
2456                                 self.prev_token.span.shrink_to_hi(),
2457                                 "try adding a comma",
2458                                 ",".into(),
2459                                 Applicability::MachineApplicable,
2460                             );
2461                         }
2462                     }
2463                     if !recover {
2464                         return Err(e);
2465                     }
2466                     e.emit();
2467                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2468                     self.eat(&token::Comma);
2469                 }
2470             }
2471         }
2472
2473         let span = pth.span.to(self.token.span);
2474         self.expect(&token::CloseDelim(token::Brace))?;
2475         let expr = if recover_async {
2476             ExprKind::Err
2477         } else {
2478             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2479         };
2480         Ok(self.mk_expr(span, expr, attrs))
2481     }
2482
2483     /// Use in case of error after field-looking code: `S { foo: () with a }`.
2484     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
2485         match self.token.ident() {
2486             Some((ident, is_raw))
2487                 if (is_raw || !ident.is_reserved())
2488                     && self.look_ahead(1, |t| *t == token::Colon) =>
2489             {
2490                 Some(ast::ExprField {
2491                     ident,
2492                     span: self.token.span,
2493                     expr: self.mk_expr_err(self.token.span),
2494                     is_shorthand: false,
2495                     attrs: AttrVec::new(),
2496                     id: DUMMY_NODE_ID,
2497                     is_placeholder: false,
2498                 })
2499             }
2500             _ => None,
2501         }
2502     }
2503
2504     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
2505         if self.token != token::Comma {
2506             return;
2507         }
2508         self.struct_span_err(
2509             span.to(self.prev_token.span),
2510             "cannot use a comma after the base struct",
2511         )
2512         .span_suggestion_short(
2513             self.token.span,
2514             "remove this comma",
2515             String::new(),
2516             Applicability::MachineApplicable,
2517         )
2518         .note("the base struct must always be the last field")
2519         .emit();
2520         self.recover_stmt();
2521     }
2522
2523     /// Parses `ident (COLON expr)?`.
2524     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
2525         let attrs = self.parse_outer_attributes()?;
2526         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2527             let lo = this.token.span;
2528
2529             // Check if a colon exists one ahead. This means we're parsing a fieldname.
2530             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
2531             let (ident, expr) = if is_shorthand {
2532                 // Mimic `x: x` for the `x` field shorthand.
2533                 let ident = this.parse_ident_common(false)?;
2534                 let path = ast::Path::from_ident(ident);
2535                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new()))
2536             } else {
2537                 let ident = this.parse_field_name()?;
2538                 this.error_on_eq_field_init(ident);
2539                 this.bump(); // `:`
2540                 (ident, this.parse_expr()?)
2541             };
2542
2543             Ok((
2544                 ast::ExprField {
2545                     ident,
2546                     span: lo.to(expr.span),
2547                     expr,
2548                     is_shorthand,
2549                     attrs: attrs.into(),
2550                     id: DUMMY_NODE_ID,
2551                     is_placeholder: false,
2552                 },
2553                 TrailingToken::MaybeComma,
2554             ))
2555         })
2556     }
2557
2558     /// Check for `=`. This means the source incorrectly attempts to
2559     /// initialize a field with an eq rather than a colon.
2560     fn error_on_eq_field_init(&self, field_name: Ident) {
2561         if self.token != token::Eq {
2562             return;
2563         }
2564
2565         self.struct_span_err(self.token.span, "expected `:`, found `=`")
2566             .span_suggestion(
2567                 field_name.span.shrink_to_hi().to(self.token.span),
2568                 "replace equals symbol with a colon",
2569                 ":".to_string(),
2570                 Applicability::MachineApplicable,
2571             )
2572             .emit();
2573     }
2574
2575     fn err_dotdotdot_syntax(&self, span: Span) {
2576         self.struct_span_err(span, "unexpected token: `...`")
2577             .span_suggestion(
2578                 span,
2579                 "use `..` for an exclusive range",
2580                 "..".to_owned(),
2581                 Applicability::MaybeIncorrect,
2582             )
2583             .span_suggestion(
2584                 span,
2585                 "or `..=` for an inclusive range",
2586                 "..=".to_owned(),
2587                 Applicability::MaybeIncorrect,
2588             )
2589             .emit();
2590     }
2591
2592     fn err_larrow_operator(&self, span: Span) {
2593         self.struct_span_err(span, "unexpected token: `<-`")
2594             .span_suggestion(
2595                 span,
2596                 "if you meant to write a comparison against a negative value, add a \
2597              space in between `<` and `-`",
2598                 "< -".to_string(),
2599                 Applicability::MaybeIncorrect,
2600             )
2601             .emit();
2602     }
2603
2604     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2605         ExprKind::AssignOp(binop, lhs, rhs)
2606     }
2607
2608     fn mk_range(
2609         &mut self,
2610         start: Option<P<Expr>>,
2611         end: Option<P<Expr>>,
2612         limits: RangeLimits,
2613     ) -> ExprKind {
2614         if end.is_none() && limits == RangeLimits::Closed {
2615             self.inclusive_range_with_incorrect_end(self.prev_token.span);
2616             ExprKind::Err
2617         } else {
2618             ExprKind::Range(start, end, limits)
2619         }
2620     }
2621
2622     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
2623         ExprKind::Unary(unop, expr)
2624     }
2625
2626     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
2627         ExprKind::Binary(binop, lhs, rhs)
2628     }
2629
2630     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
2631         ExprKind::Index(expr, idx)
2632     }
2633
2634     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
2635         ExprKind::Call(f, args)
2636     }
2637
2638     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
2639         let span = lo.to(self.prev_token.span);
2640         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new());
2641         self.recover_from_await_method_call();
2642         await_expr
2643     }
2644
2645     crate fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
2646         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
2647     }
2648
2649     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
2650         self.mk_expr(span, ExprKind::Err, AttrVec::new())
2651     }
2652
2653     /// Create expression span ensuring the span of the parent node
2654     /// is larger than the span of lhs and rhs, including the attributes.
2655     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
2656         lhs.attrs
2657             .iter()
2658             .find(|a| a.style == AttrStyle::Outer)
2659             .map_or(lhs_span, |a| a.span)
2660             .to(rhs_span)
2661     }
2662
2663     fn collect_tokens_for_expr(
2664         &mut self,
2665         attrs: AttrWrapper,
2666         f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>,
2667     ) -> PResult<'a, P<Expr>> {
2668         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2669             let res = f(this, attrs)?;
2670             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
2671                 && this.token.kind == token::Semi
2672             {
2673                 TrailingToken::Semi
2674             } else {
2675                 // FIXME - pass this through from the place where we know
2676                 // we need a comma, rather than assuming that `#[attr] expr,`
2677                 // always captures a trailing comma
2678                 TrailingToken::MaybeComma
2679             };
2680             Ok((res, trailing))
2681         })
2682     }
2683 }