compiler/rustc_parse/src/parser/expr.rs

   1 use super::diagnostics::SnapshotParser;
   2 use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
   3 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   4 use super::{
   5     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
   6     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
   7 };
   8 use crate::errors::{
   9     ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
  10     BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct, ComparisonInterpretedAsGeneric,
  11     ComparisonOrShiftInterpretedAsGenericSugg, DoCatchSyntaxRemoved, DotDotDot, EqFieldInit,
  12     ExpectedElseBlock, ExpectedEqForLetExpr, ExpectedExpressionFoundLet,
  13     FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
  14     IfExpressionMissingCondition, IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub,
  15     InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
  16     InvalidInterpolatedExpression, InvalidLiteralSuffixOnTupleIndex, InvalidLogicalOperator,
  17     InvalidLogicalOperatorSub, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
  18     LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
  19     MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
  20     MissingDotDot, MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray,
  21     NoFieldsForFnCall, NotAsNegationOperator, NotAsNegationOperatorSub,
  22     OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
  23     RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
  24     StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedIfWithIf,
  25     UnexpectedTokenAfterLabel, UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
  26 };
  27 use crate::maybe_recover_from_interpolated_ty_qpath;
  28 use core::mem;
  29 use rustc_ast::ptr::P;
  30 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
  31 use rustc_ast::tokenstream::Spacing;
  32 use rustc_ast::util::case::Case;
  33 use rustc_ast::util::classify;
  34 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  35 use rustc_ast::visit::Visitor;
  36 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  37 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  38 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  39 use rustc_ast::{ClosureBinder, StmtKind};
  40 use rustc_ast_pretty::pprust;
  41 use rustc_errors::{
  42     Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
  43     StashKey,
  44 };
  45 use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
  46 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  47 use rustc_session::lint::BuiltinLintDiagnostics;
  48 use rustc_span::source_map::{self, Span, Spanned};
  49 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  50 use rustc_span::{BytePos, Pos};
  51
  52 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  53 /// dropped into the token stream, which happens while parsing the result of
  54 /// macro expansion). Placement of these is not as complex as I feared it would
  55 /// be. The important thing is to make sure that lookahead doesn't balk at
  56 /// `token::Interpolated` tokens.
  57 macro_rules! maybe_whole_expr {
  58     ($p:expr) => {
  59         if let token::Interpolated(nt) = &$p.token.kind {
  60             match &**nt {
  61                 token::NtExpr(e) | token::NtLiteral(e) => {
  62                     let e = e.clone();
  63                     $p.bump();
  64                     return Ok(e);
  65                 }
  66                 token::NtPath(path) => {
  67                     let path = (**path).clone();
  68                     $p.bump();
  69                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Path(None, path)));
  70                 }
  71                 token::NtBlock(block) => {
  72                     let block = block.clone();
  73                     $p.bump();
  74                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Block(block, None)));
  75                 }
  76                 _ => {}
  77             };
  78         }
  79     };
  80 }
  81
  82 #[derive(Debug)]
  83 pub(super) enum LhsExpr {
  84     NotYetParsed,
  85     AttributesParsed(AttrWrapper),
  86     AlreadyParsed(P<Expr>),
  87 }
  88
  89 impl From<Option<AttrWrapper>> for LhsExpr {
  90     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  91     /// and `None` into `LhsExpr::NotYetParsed`.
  92     ///
  93     /// This conversion does not allocate.
  94     fn from(o: Option<AttrWrapper>) -> Self {
  95         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
  96     }
  97 }
  98
  99 impl From<P<Expr>> for LhsExpr {
 100     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
 101     ///
 102     /// This conversion does not allocate.
 103     fn from(expr: P<Expr>) -> Self {
 104         LhsExpr::AlreadyParsed(expr)
 105     }
 106 }
 107
 108 impl<'a> Parser<'a> {
 109     /// Parses an expression.
 110     #[inline]
 111     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
 112         self.current_closure.take();
 113
 114         self.parse_expr_res(Restrictions::empty(), None)
 115     }
 116
 117     /// Parses an expression, forcing tokens to be collected
 118     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 119         self.collect_tokens_no_attrs(|this| this.parse_expr())
 120     }
 121
 122     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 123         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 124     }
 125
 126     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 127         match self.parse_expr() {
 128             Ok(expr) => Ok(expr),
 129             Err(mut err) => match self.token.ident() {
 130                 Some((Ident { name: kw::Underscore, .. }, false))
 131                     if self.may_recover() && self.look_ahead(1, |t| t == &token::Comma) =>
 132                 {
 133                     // Special-case handling of `foo(_, _, _)`
 134                     err.emit();
 135                     self.bump();
 136                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err))
 137                 }
 138                 _ => Err(err),
 139             },
 140         }
 141     }
 142
 143     /// Parses a sequence of expressions delimited by parentheses.
 144     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 145         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 146     }
 147
 148     /// Parses an expression, subject to the given restrictions.
 149     #[inline]
 150     pub(super) fn parse_expr_res(
 151         &mut self,
 152         r: Restrictions,
 153         already_parsed_attrs: Option<AttrWrapper>,
 154     ) -> PResult<'a, P<Expr>> {
 155         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 156     }
 157
 158     /// Parses an associative expression.
 159     ///
 160     /// This parses an expression accounting for associativity and precedence of the operators in
 161     /// the expression.
 162     #[inline]
 163     fn parse_assoc_expr(
 164         &mut self,
 165         already_parsed_attrs: Option<AttrWrapper>,
 166     ) -> PResult<'a, P<Expr>> {
 167         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 168     }
 169
 170     /// Parses an associative expression with operators of at least `min_prec` precedence.
 171     pub(super) fn parse_assoc_expr_with(
 172         &mut self,
 173         min_prec: usize,
 174         lhs: LhsExpr,
 175     ) -> PResult<'a, P<Expr>> {
 176         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 177             expr
 178         } else {
 179             let attrs = match lhs {
 180                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 181                 _ => None,
 182             };
 183             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 184                 return self.parse_prefix_range_expr(attrs);
 185             } else {
 186                 self.parse_prefix_expr(attrs)?
 187             }
 188         };
 189         let last_type_ascription_set = self.last_type_ascription.is_some();
 190
 191         if !self.should_continue_as_assoc_expr(&lhs) {
 192             self.last_type_ascription = None;
 193             return Ok(lhs);
 194         }
 195
 196         self.expected_tokens.push(TokenType::Operator);
 197         while let Some(op) = self.check_assoc_op() {
 198             // Adjust the span for interpolated LHS to point to the `$lhs` token
 199             // and not to what it refers to.
 200             let lhs_span = match self.prev_token.kind {
 201                 TokenKind::Interpolated(..) => self.prev_token.span,
 202                 _ => lhs.span,
 203             };
 204
 205             let cur_op_span = self.token.span;
 206             let restrictions = if op.node.is_assign_like() {
 207                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 208             } else {
 209                 self.restrictions
 210             };
 211             let prec = op.node.precedence();
 212             if prec < min_prec {
 213                 break;
 214             }
 215             // Check for deprecated `...` syntax
 216             if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
 217                 self.err_dotdotdot_syntax(self.token.span);
 218             }
 219
 220             if self.token == token::LArrow {
 221                 self.err_larrow_operator(self.token.span);
 222             }
 223
 224             self.bump();
 225             if op.node.is_comparison() {
 226                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 227                     return Ok(expr);
 228                 }
 229             }
 230
 231             // Look for JS' `===` and `!==` and recover
 232             if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
 233                 && self.token.kind == token::Eq
 234                 && self.prev_token.span.hi() == self.token.span.lo()
 235             {
 236                 let sp = op.span.to(self.token.span);
 237                 let sugg = match op.node {
 238                     AssocOp::Equal => "==",
 239                     AssocOp::NotEqual => "!=",
 240                     _ => unreachable!(),
 241                 }
 242                 .into();
 243                 let invalid = format!("{}=", &sugg);
 244                 self.sess.emit_err(InvalidComparisonOperator {
 245                     span: sp,
 246                     invalid: invalid.clone(),
 247                     sub: InvalidComparisonOperatorSub::Correctable {
 248                         span: sp,
 249                         invalid,
 250                         correct: sugg,
 251                     },
 252                 });
 253                 self.bump();
 254             }
 255
 256             // Look for PHP's `<>` and recover
 257             if op.node == AssocOp::Less
 258                 && self.token.kind == token::Gt
 259                 && self.prev_token.span.hi() == self.token.span.lo()
 260             {
 261                 let sp = op.span.to(self.token.span);
 262                 self.sess.emit_err(InvalidComparisonOperator {
 263                     span: sp,
 264                     invalid: "<>".into(),
 265                     sub: InvalidComparisonOperatorSub::Correctable {
 266                         span: sp,
 267                         invalid: "<>".into(),
 268                         correct: "!=".into(),
 269                     },
 270                 });
 271                 self.bump();
 272             }
 273
 274             // Look for C++'s `<=>` and recover
 275             if op.node == AssocOp::LessEqual
 276                 && self.token.kind == token::Gt
 277                 && self.prev_token.span.hi() == self.token.span.lo()
 278             {
 279                 let sp = op.span.to(self.token.span);
 280                 self.sess.emit_err(InvalidComparisonOperator {
 281                     span: sp,
 282                     invalid: "<=>".into(),
 283                     sub: InvalidComparisonOperatorSub::Spaceship(sp),
 284                 });
 285                 self.bump();
 286             }
 287
 288             if self.prev_token == token::BinOp(token::Plus)
 289                 && self.token == token::BinOp(token::Plus)
 290                 && self.prev_token.span.between(self.token.span).is_empty()
 291             {
 292                 let op_span = self.prev_token.span.to(self.token.span);
 293                 // Eat the second `+`
 294                 self.bump();
 295                 lhs = self.recover_from_postfix_increment(lhs, op_span)?;
 296                 continue;
 297             }
 298
 299             let op = op.node;
 300             // Special cases:
 301             if op == AssocOp::As {
 302                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 303                 continue;
 304             } else if op == AssocOp::Colon {
 305                 lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
 306                 continue;
 307             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 308                 // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
 309                 // generalise it to the Fixity::None code.
 310                 lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?;
 311                 break;
 312             }
 313
 314             let fixity = op.fixity();
 315             let prec_adjustment = match fixity {
 316                 Fixity::Right => 0,
 317                 Fixity::Left => 1,
 318                 // We currently have no non-associative operators that are not handled above by
 319                 // the special cases. The code is here only for future convenience.
 320                 Fixity::None => 1,
 321             };
 322             let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
 323                 this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 324             })?;
 325
 326             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
 327             lhs = match op {
 328                 AssocOp::Add
 329                 | AssocOp::Subtract
 330                 | AssocOp::Multiply
 331                 | AssocOp::Divide
 332                 | AssocOp::Modulus
 333                 | AssocOp::LAnd
 334                 | AssocOp::LOr
 335                 | AssocOp::BitXor
 336                 | AssocOp::BitAnd
 337                 | AssocOp::BitOr
 338                 | AssocOp::ShiftLeft
 339                 | AssocOp::ShiftRight
 340                 | AssocOp::Equal
 341                 | AssocOp::Less
 342                 | AssocOp::LessEqual
 343                 | AssocOp::NotEqual
 344                 | AssocOp::Greater
 345                 | AssocOp::GreaterEqual => {
 346                     let ast_op = op.to_ast_binop().unwrap();
 347                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 348                     self.mk_expr(span, binary)
 349                 }
 350                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span)),
 351                 AssocOp::AssignOp(k) => {
 352                     let aop = match k {
 353                         token::Plus => BinOpKind::Add,
 354                         token::Minus => BinOpKind::Sub,
 355                         token::Star => BinOpKind::Mul,
 356                         token::Slash => BinOpKind::Div,
 357                         token::Percent => BinOpKind::Rem,
 358                         token::Caret => BinOpKind::BitXor,
 359                         token::And => BinOpKind::BitAnd,
 360                         token::Or => BinOpKind::BitOr,
 361                         token::Shl => BinOpKind::Shl,
 362                         token::Shr => BinOpKind::Shr,
 363                     };
 364                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 365                     self.mk_expr(span, aopexpr)
 366                 }
 367                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 368                     self.span_bug(span, "AssocOp should have been handled by special case")
 369                 }
 370             };
 371
 372             if let Fixity::None = fixity {
 373                 break;
 374             }
 375         }
 376         if last_type_ascription_set {
 377             self.last_type_ascription = None;
 378         }
 379         Ok(lhs)
 380     }
 381
 382     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 383         match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
 384             // Semi-statement forms are odd:
 385             // See https://github.com/rust-lang/rust/issues/29071
 386             (true, None) => false,
 387             (false, _) => true, // Continue parsing the expression.
 388             // An exhaustive check is done in the following block, but these are checked first
 389             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 390             // want to keep their span info to improve diagnostics in these cases in a later stage.
 391             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 392             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 393             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 394             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 395             // `if x { a } else { b } && if y { c } else { d }`
 396             if !self.look_ahead(1, |t| t.is_used_keyword()) => {
 397                 // These cases are ambiguous and can't be identified in the parser alone.
 398                 let sp = self.sess.source_map().start_point(self.token.span);
 399                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 400                 false
 401             }
 402             (true, Some(AssocOp::LAnd)) |
 403             (true, Some(AssocOp::LOr)) |
 404             (true, Some(AssocOp::BitOr)) => {
 405                 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the
 406                 // above due to #74233.
 407                 // These cases are ambiguous and can't be identified in the parser alone.
 408                 //
 409                 // Bitwise AND is left out because guessing intent is hard. We can make
 410                 // suggestions based on the assumption that double-refs are rarely intentional,
 411                 // and closures are distinct enough that they don't get mixed up with their
 412                 // return value.
 413                 let sp = self.sess.source_map().start_point(self.token.span);
 414                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 415                 false
 416             }
 417             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 418             (true, Some(_)) => {
 419                 self.error_found_expr_would_be_stmt(lhs);
 420                 true
 421             }
 422         }
 423     }
 424
 425     /// We've found an expression that would be parsed as a statement,
 426     /// but the next token implies this should be parsed as an expression.
 427     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 428     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 429         self.sess.emit_err(FoundExprWouldBeStmt {
 430             span: self.token.span,
 431             token: self.token.clone(),
 432             suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
 433         });
 434     }
 435
 436     /// Possibly translate the current token to an associative operator.
 437     /// The method does not advance the current token.
 438     ///
 439     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 440     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 441         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 442             // When parsing const expressions, stop parsing when encountering `>`.
 443             (
 444                 Some(
 445                     AssocOp::ShiftRight
 446                     | AssocOp::Greater
 447                     | AssocOp::GreaterEqual
 448                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 449                 ),
 450                 _,
 451             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 452                 return None;
 453             }
 454             (Some(op), _) => (op, self.token.span),
 455             (None, Some((Ident { name: sym::and, span }, false))) if self.may_recover() => {
 456                 self.sess.emit_err(InvalidLogicalOperator {
 457                     span: self.token.span,
 458                     incorrect: "and".into(),
 459                     sub: InvalidLogicalOperatorSub::Conjunction(self.token.span),
 460                 });
 461                 (AssocOp::LAnd, span)
 462             }
 463             (None, Some((Ident { name: sym::or, span }, false))) if self.may_recover() => {
 464                 self.sess.emit_err(InvalidLogicalOperator {
 465                     span: self.token.span,
 466                     incorrect: "or".into(),
 467                     sub: InvalidLogicalOperatorSub::Disjunction(self.token.span),
 468                 });
 469                 (AssocOp::LOr, span)
 470             }
 471             _ => return None,
 472         };
 473         Some(source_map::respan(span, op))
 474     }
 475
 476     /// Checks if this expression is a successfully parsed statement.
 477     fn expr_is_complete(&self, e: &Expr) -> bool {
 478         self.restrictions.contains(Restrictions::STMT_EXPR)
 479             && !classify::expr_requires_semi_to_be_stmt(e)
 480     }
 481
 482     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 483     /// The other two variants are handled in `parse_prefix_range_expr` below.
 484     fn parse_range_expr(
 485         &mut self,
 486         prec: usize,
 487         lhs: P<Expr>,
 488         op: AssocOp,
 489         cur_op_span: Span,
 490     ) -> PResult<'a, P<Expr>> {
 491         let rhs = if self.is_at_start_of_range_notation_rhs() {
 492             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 493         } else {
 494             None
 495         };
 496         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 497         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 498         let limits =
 499             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 500         let range = self.mk_range(Some(lhs), rhs, limits);
 501         Ok(self.mk_expr(span, range))
 502     }
 503
 504     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 505         if self.token.can_begin_expr() {
 506             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 507             if self.token == token::OpenDelim(Delimiter::Brace) {
 508                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 509             }
 510             true
 511         } else {
 512             false
 513         }
 514     }
 515
 516     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 517     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 518         // Check for deprecated `...` syntax.
 519         if self.token == token::DotDotDot {
 520             self.err_dotdotdot_syntax(self.token.span);
 521         }
 522
 523         debug_assert!(
 524             [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 525             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 526             self.token
 527         );
 528
 529         let limits = match self.token.kind {
 530             token::DotDot => RangeLimits::HalfOpen,
 531             _ => RangeLimits::Closed,
 532         };
 533         let op = AssocOp::from_token(&self.token);
 534         // FIXME: `parse_prefix_range_expr` is called when the current
 535         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 536         // parsed attributes, then trying to parse them here will always fail.
 537         // We should figure out how we want attributes on range expressions to work.
 538         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 539         self.collect_tokens_for_expr(attrs, |this, attrs| {
 540             let lo = this.token.span;
 541             this.bump();
 542             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 543                 // RHS must be parsed with more associativity than the dots.
 544                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 545                     .map(|x| (lo.to(x.span), Some(x)))?
 546             } else {
 547                 (lo, None)
 548             };
 549             let range = this.mk_range(None, opt_end, limits);
 550             Ok(this.mk_expr_with_attrs(span, range, attrs))
 551         })
 552     }
 553
 554     /// Parses a prefix-unary-operator expr.
 555     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 556         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 557         let lo = self.token.span;
 558
 559         macro_rules! make_it {
 560             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 561                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 562                     let (hi, ex) = $body?;
 563                     Ok($this.mk_expr_with_attrs(lo.to(hi), ex, attrs))
 564                 })
 565             };
 566         }
 567
 568         let this = self;
 569
 570         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 571         match this.token.uninterpolate().kind {
 572             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr`
 573             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr`
 574             token::BinOp(token::Minus) => {
 575                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 576             } // `-expr`
 577             token::BinOp(token::Star) => {
 578                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 579             } // `*expr`
 580             token::BinOp(token::And) | token::AndAnd => {
 581                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 582             }
 583             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 584                 let mut err =
 585                     LeadingPlusNotSupported { span: lo, remove_plus: None, add_parentheses: None };
 586
 587                 // a block on the LHS might have been intended to be an expression instead
 588                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 589                     err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
 590                 } else {
 591                     err.remove_plus = Some(lo);
 592                 }
 593                 this.sess.emit_err(err);
 594
 595                 this.bump();
 596                 this.parse_prefix_expr(None)
 597             } // `+expr`
 598             // Recover from `++x`:
 599             token::BinOp(token::Plus)
 600                 if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
 601             {
 602                 let prev_is_semi = this.prev_token == token::Semi;
 603                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
 604                 // Eat both `+`s.
 605                 this.bump();
 606                 this.bump();
 607
 608                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
 609                 this.recover_from_prefix_increment(operand_expr, pre_span, prev_is_semi)
 610             }
 611             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 612                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 613             }
 614             token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
 615                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 616             }
 617             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 618         }
 619     }
 620
 621     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 622         self.bump();
 623         let expr = self.parse_prefix_expr(None);
 624         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 625         Ok((lo.to(span), expr))
 626     }
 627
 628     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 629         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 630         Ok((span, self.mk_unary(op, expr)))
 631     }
 632
 633     // Recover on `!` suggesting for bitwise negation instead.
 634     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 635         self.sess.emit_err(TildeAsUnaryOperator(lo));
 636
 637         self.parse_unary_expr(lo, UnOp::Not)
 638     }
 639
 640     /// Parse `box expr`.
 641     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 642         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 643         self.sess.gated_spans.gate(sym::box_syntax, span);
 644         Ok((span, ExprKind::Box(expr)))
 645     }
 646
 647     fn is_mistaken_not_ident_negation(&self) -> bool {
 648         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 649             // These tokens can start an expression after `!`, but
 650             // can't continue an expression after an ident
 651             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 652             token::Literal(..) | token::Pound => true,
 653             _ => t.is_whole_expr(),
 654         };
 655         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 656     }
 657
 658     /// Recover on `not expr` in favor of `!expr`.
 659     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 660         // Emit the error...
 661         let negated_token = self.look_ahead(1, |t| t.clone());
 662
 663         let sub_diag = if negated_token.is_numeric_lit() {
 664             NotAsNegationOperatorSub::SuggestNotBitwise
 665         } else if negated_token.is_bool_lit() {
 666             NotAsNegationOperatorSub::SuggestNotLogical
 667         } else {
 668             NotAsNegationOperatorSub::SuggestNotDefault
 669         };
 670
 671         self.sess.emit_err(NotAsNegationOperator {
 672             negated: negated_token.span,
 673             negated_desc: super::token_descr(&negated_token),
 674             // Span the `not` plus trailing whitespace to avoid
 675             // trailing whitespace after the `!` in our suggestion
 676             sub: sub_diag(
 677                 self.sess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
 678             ),
 679         });
 680
 681         // ...and recover!
 682         self.parse_unary_expr(lo, UnOp::Not)
 683     }
 684
 685     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 686     fn interpolated_or_expr_span(
 687         &self,
 688         expr: PResult<'a, P<Expr>>,
 689     ) -> PResult<'a, (Span, P<Expr>)> {
 690         expr.map(|e| {
 691             (
 692                 match self.prev_token.kind {
 693                     TokenKind::Interpolated(..) => self.prev_token.span,
 694                     _ => e.span,
 695                 },
 696                 e,
 697             )
 698         })
 699     }
 700
 701     fn parse_assoc_op_cast(
 702         &mut self,
 703         lhs: P<Expr>,
 704         lhs_span: Span,
 705         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 706     ) -> PResult<'a, P<Expr>> {
 707         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 708             this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, rhs.span), expr_kind(lhs, rhs))
 709         };
 710
 711         // Save the state of the parser before parsing type normally, in case there is a
 712         // LessThan comparison after this cast.
 713         let parser_snapshot_before_type = self.clone();
 714         let cast_expr = match self.parse_as_cast_ty() {
 715             Ok(rhs) => mk_expr(self, lhs, rhs),
 716             Err(type_err) => {
 717                 if !self.may_recover() {
 718                     return Err(type_err);
 719                 }
 720
 721                 // Rewind to before attempting to parse the type with generics, to recover
 722                 // from situations like `x as usize < y` in which we first tried to parse
 723                 // `usize < y` as a type with generic arguments.
 724                 let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
 725
 726                 // Check for typo of `'a: loop { break 'a }` with a missing `'`.
 727                 match (&lhs.kind, &self.token.kind) {
 728                     (
 729                         // `foo: `
 730                         ExprKind::Path(None, ast::Path { segments, .. }),
 731                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
 732                     ) if segments.len() == 1 => {
 733                         let snapshot = self.create_snapshot_for_diagnostic();
 734                         let label = Label {
 735                             ident: Ident::from_str_and_span(
 736                                 &format!("'{}", segments[0].ident),
 737                                 segments[0].ident.span,
 738                             ),
 739                         };
 740                         match self.parse_labeled_expr(label, false) {
 741                             Ok(expr) => {
 742                                 type_err.cancel();
 743                                 self.sess.emit_err(MalformedLoopLabel {
 744                                     span: label.ident.span,
 745                                     correct_label: label.ident,
 746                                 });
 747                                 return Ok(expr);
 748                             }
 749                             Err(err) => {
 750                                 err.cancel();
 751                                 self.restore_snapshot(snapshot);
 752                             }
 753                         }
 754                     }
 755                     _ => {}
 756                 }
 757
 758                 match self.parse_path(PathStyle::Expr) {
 759                     Ok(path) => {
 760                         let span_after_type = parser_snapshot_after_type.token.span;
 761                         let expr = mk_expr(
 762                             self,
 763                             lhs,
 764                             self.mk_ty(path.span, TyKind::Path(None, path.clone())),
 765                         );
 766
 767                         let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
 768                         let suggestion = ComparisonOrShiftInterpretedAsGenericSugg {
 769                             left: expr.span.shrink_to_lo(),
 770                             right: expr.span.shrink_to_hi(),
 771                         };
 772
 773                         match self.token.kind {
 774                             token::Lt => self.sess.emit_err(ComparisonInterpretedAsGeneric {
 775                                 comparison: self.token.span,
 776                                 r#type: path,
 777                                 args: args_span,
 778                                 suggestion,
 779                             }),
 780                             token::BinOp(token::Shl) => {
 781                                 self.sess.emit_err(ShiftInterpretedAsGeneric {
 782                                     shift: self.token.span,
 783                                     r#type: path,
 784                                     args: args_span,
 785                                     suggestion,
 786                                 })
 787                             }
 788                             _ => {
 789                                 // We can end up here even without `<` being the next token, for
 790                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 791                                 // but `parse_path` returns `Ok` on them due to error recovery.
 792                                 // Return original error and parser state.
 793                                 *self = parser_snapshot_after_type;
 794                                 return Err(type_err);
 795                             }
 796                         };
 797
 798                         // Successfully parsed the type path leaving a `<` yet to parse.
 799                         type_err.cancel();
 800
 801                         // Keep `x as usize` as an expression in AST and continue parsing.
 802                         expr
 803                     }
 804                     Err(path_err) => {
 805                         // Couldn't parse as a path, return original error and parser state.
 806                         path_err.cancel();
 807                         *self = parser_snapshot_after_type;
 808                         return Err(type_err);
 809                     }
 810                 }
 811             }
 812         };
 813
 814         self.parse_and_disallow_postfix_after_cast(cast_expr)
 815     }
 816
 817     /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
 818     /// then emits an error and returns the newly parsed tree.
 819     /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
 820     fn parse_and_disallow_postfix_after_cast(
 821         &mut self,
 822         cast_expr: P<Expr>,
 823     ) -> PResult<'a, P<Expr>> {
 824         let span = cast_expr.span;
 825         let (cast_kind, maybe_ascription_span) =
 826             if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
 827                 ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi())))
 828             } else {
 829                 ("cast", None)
 830             };
 831
 832         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 833
 834         // Check if an illegal postfix operator has been added after the cast.
 835         // If the resulting expression is not a cast, it is an illegal postfix operator.
 836         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) {
 837             let msg = format!(
 838                 "{cast_kind} cannot be followed by {}",
 839                 match with_postfix.kind {
 840                     ExprKind::Index(_, _) => "indexing",
 841                     ExprKind::Try(_) => "`?`",
 842                     ExprKind::Field(_, _) => "a field access",
 843                     ExprKind::MethodCall(_, _, _, _) => "a method call",
 844                     ExprKind::Call(_, _) => "a function call",
 845                     ExprKind::Await(_) => "`.await`",
 846                     ExprKind::Err => return Ok(with_postfix),
 847                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 848                 }
 849             );
 850             let mut err = self.struct_span_err(span, &msg);
 851
 852             let suggest_parens = |err: &mut Diagnostic| {
 853                 let suggestions = vec![
 854                     (span.shrink_to_lo(), "(".to_string()),
 855                     (span.shrink_to_hi(), ")".to_string()),
 856                 ];
 857                 err.multipart_suggestion(
 858                     "try surrounding the expression in parentheses",
 859                     suggestions,
 860                     Applicability::MachineApplicable,
 861                 );
 862             };
 863
 864             // If type ascription is "likely an error", the user will already be getting a useful
 865             // help message, and doesn't need a second.
 866             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 867                 self.maybe_annotate_with_ascription(&mut err, false);
 868             } else if let Some(ascription_span) = maybe_ascription_span {
 869                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 870                 if is_nightly {
 871                     suggest_parens(&mut err);
 872                 }
 873                 err.span_suggestion(
 874                     ascription_span,
 875                     &format!(
 876                         "{}remove the type ascription",
 877                         if is_nightly { "alternatively, " } else { "" }
 878                     ),
 879                     "",
 880                     if is_nightly {
 881                         Applicability::MaybeIncorrect
 882                     } else {
 883                         Applicability::MachineApplicable
 884                     },
 885                 );
 886             } else {
 887                 suggest_parens(&mut err);
 888             }
 889             err.emit();
 890         };
 891         Ok(with_postfix)
 892     }
 893
 894     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 895         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 896         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 897         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 898         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 899         Ok(lhs)
 900     }
 901
 902     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 903     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 904         self.expect_and()?;
 905         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 906         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 907         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 908         let expr = self.parse_prefix_expr(None);
 909         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 910         let span = lo.to(hi);
 911         if let Some(lt) = lifetime {
 912             self.error_remove_borrow_lifetime(span, lt.ident.span);
 913         }
 914         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 915     }
 916
 917     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 918         self.sess.emit_err(LifetimeInBorrowExpression { span, lifetime_span: lt_span });
 919     }
 920
 921     /// Parse `mut?` or `raw [ const | mut ]`.
 922     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 923         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 924             // `raw [ const | mut ]`.
 925             let found_raw = self.eat_keyword(kw::Raw);
 926             assert!(found_raw);
 927             let mutability = self.parse_const_or_mut().unwrap();
 928             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 929             (ast::BorrowKind::Raw, mutability)
 930         } else {
 931             // `mut?`
 932             (ast::BorrowKind::Ref, self.parse_mutability())
 933         }
 934     }
 935
 936     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 937     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 938         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 939         self.collect_tokens_for_expr(attrs, |this, attrs| {
 940             let base = this.parse_bottom_expr();
 941             let (span, base) = this.interpolated_or_expr_span(base)?;
 942             this.parse_dot_or_call_expr_with(base, span, attrs)
 943         })
 944     }
 945
 946     pub(super) fn parse_dot_or_call_expr_with(
 947         &mut self,
 948         e0: P<Expr>,
 949         lo: Span,
 950         mut attrs: ast::AttrVec,
 951     ) -> PResult<'a, P<Expr>> {
 952         // Stitch the list of outer attributes onto the return value.
 953         // A little bit ugly, but the best way given the current code
 954         // structure
 955         let res = self.parse_dot_or_call_expr_with_(e0, lo);
 956         if attrs.is_empty() {
 957             res
 958         } else {
 959             res.map(|expr| {
 960                 expr.map(|mut expr| {
 961                     attrs.extend(expr.attrs);
 962                     expr.attrs = attrs;
 963                     expr
 964                 })
 965             })
 966         }
 967     }
 968
 969     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 970         loop {
 971             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 972                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 973                 // which could be suggested otherwise
 974                 self.eat_noexpect(&token::Question)
 975             } else {
 976                 self.eat(&token::Question)
 977             };
 978             if has_question {
 979                 // `expr?`
 980                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
 981                 continue;
 982             }
 983             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 984                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 985                 // which could be suggested otherwise
 986                 self.eat_noexpect(&token::Dot)
 987             } else {
 988                 self.eat(&token::Dot)
 989             };
 990             if has_dot {
 991                 // expr.f
 992                 e = self.parse_dot_suffix_expr(lo, e)?;
 993                 continue;
 994             }
 995             if self.expr_is_complete(&e) {
 996                 return Ok(e);
 997             }
 998             e = match self.token.kind {
 999                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1000                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1001                 _ => return Ok(e),
1002             }
1003         }
1004     }
1005
1006     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1007         self.look_ahead(1, |t| t.is_ident())
1008             && self.look_ahead(2, |t| t == &token::Colon)
1009             && self.look_ahead(3, |t| t.can_begin_expr())
1010     }
1011
1012     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1013         match self.token.uninterpolate().kind {
1014             token::Ident(..) => self.parse_dot_suffix(base, lo),
1015             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1016                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1017             }
1018             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1019                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1020             }
1021             _ => {
1022                 self.error_unexpected_after_dot();
1023                 Ok(base)
1024             }
1025         }
1026     }
1027
1028     fn error_unexpected_after_dot(&self) {
1029         // FIXME Could factor this out into non_fatal_unexpected or something.
1030         let actual = pprust::token_to_string(&self.token);
1031         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1032     }
1033
1034     // We need an identifier or integer, but the next token is a float.
1035     // Break the float into components to extract the identifier or integer.
1036     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1037     // parts unless those parts are processed immediately. `TokenCursor` should either
1038     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1039     // we should break everything including floats into more basic proc-macro style
1040     // tokens in the lexer (probably preferable).
1041     fn parse_tuple_field_access_expr_float(
1042         &mut self,
1043         lo: Span,
1044         base: P<Expr>,
1045         float: Symbol,
1046         suffix: Option<Symbol>,
1047     ) -> P<Expr> {
1048         #[derive(Debug)]
1049         enum FloatComponent {
1050             IdentLike(String),
1051             Punct(char),
1052         }
1053         use FloatComponent::*;
1054
1055         let float_str = float.as_str();
1056         let mut components = Vec::new();
1057         let mut ident_like = String::new();
1058         for c in float_str.chars() {
1059             if c == '_' || c.is_ascii_alphanumeric() {
1060                 ident_like.push(c);
1061             } else if matches!(c, '.' | '+' | '-') {
1062                 if !ident_like.is_empty() {
1063                     components.push(IdentLike(mem::take(&mut ident_like)));
1064                 }
1065                 components.push(Punct(c));
1066             } else {
1067                 panic!("unexpected character in a float token: {:?}", c)
1068             }
1069         }
1070         if !ident_like.is_empty() {
1071             components.push(IdentLike(ident_like));
1072         }
1073
1074         // With proc macros the span can refer to anything, the source may be too short,
1075         // or too long, or non-ASCII. It only makes sense to break our span into components
1076         // if its underlying text is identical to our float literal.
1077         let span = self.token.span;
1078         let can_take_span_apart =
1079             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1080
1081         match &*components {
1082             // 1e2
1083             [IdentLike(i)] => {
1084                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1085             }
1086             // 1.
1087             [IdentLike(i), Punct('.')] => {
1088                 let (ident_span, dot_span) = if can_take_span_apart() {
1089                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1090                     let ident_span = span.with_hi(span.lo + ident_len);
1091                     let dot_span = span.with_lo(span.lo + ident_len);
1092                     (ident_span, dot_span)
1093                 } else {
1094                     (span, span)
1095                 };
1096                 assert!(suffix.is_none());
1097                 let symbol = Symbol::intern(&i);
1098                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1099                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1100                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1101             }
1102             // 1.2 | 1.2e3
1103             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1104                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1105                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1106                     let ident1_span = span.with_hi(span.lo + ident1_len);
1107                     let dot_span = span
1108                         .with_lo(span.lo + ident1_len)
1109                         .with_hi(span.lo + ident1_len + BytePos(1));
1110                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1111                     (ident1_span, dot_span, ident2_span)
1112                 } else {
1113                     (span, span, span)
1114                 };
1115                 let symbol1 = Symbol::intern(&i1);
1116                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1117                 // This needs to be `Spacing::Alone` to prevent regressions.
1118                 // See issue #76399 and PR #76285 for more details
1119                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1120                 let base1 =
1121                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1122                 let symbol2 = Symbol::intern(&i2);
1123                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1124                 self.bump_with((next_token2, self.token_spacing)); // `.`
1125                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1126             }
1127             // 1e+ | 1e- (recovered)
1128             [IdentLike(_), Punct('+' | '-')] |
1129             // 1e+2 | 1e-2
1130             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1131             // 1.2e+ | 1.2e-
1132             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1133             // 1.2e+3 | 1.2e-3
1134             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1135                 // See the FIXME about `TokenCursor` above.
1136                 self.error_unexpected_after_dot();
1137                 base
1138             }
1139             _ => panic!("unexpected components in a float token: {:?}", components),
1140         }
1141     }
1142
1143     fn parse_tuple_field_access_expr(
1144         &mut self,
1145         lo: Span,
1146         base: P<Expr>,
1147         field: Symbol,
1148         suffix: Option<Symbol>,
1149         next_token: Option<(Token, Spacing)>,
1150     ) -> P<Expr> {
1151         match next_token {
1152             Some(next_token) => self.bump_with(next_token),
1153             None => self.bump(),
1154         }
1155         let span = self.prev_token.span;
1156         let field = ExprKind::Field(base, Ident::new(field, span));
1157         if let Some(suffix) = suffix {
1158             self.expect_no_tuple_index_suffix(span, suffix);
1159         }
1160         self.mk_expr(lo.to(span), field)
1161     }
1162
1163     /// Parse a function call expression, `expr(...)`.
1164     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1165         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1166             && self.look_ahead_type_ascription_as_field()
1167         {
1168             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1169         } else {
1170             None
1171         };
1172         let open_paren = self.token.span;
1173
1174         let mut seq = self
1175             .parse_paren_expr_seq()
1176             .map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
1177         if let Some(expr) =
1178             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1179         {
1180             return expr;
1181         }
1182         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1183     }
1184
1185     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1186     /// parentheses instead of braces, recover the parser state and provide suggestions.
1187     #[instrument(skip(self, seq, snapshot), level = "trace")]
1188     fn maybe_recover_struct_lit_bad_delims(
1189         &mut self,
1190         lo: Span,
1191         open_paren: Span,
1192         seq: &mut PResult<'a, P<Expr>>,
1193         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1194     ) -> Option<P<Expr>> {
1195         if !self.may_recover() {
1196             return None;
1197         }
1198
1199         match (seq.as_mut(), snapshot) {
1200             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1201                 snapshot.bump(); // `(`
1202                 match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
1203                     Ok((fields, ..))
1204                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1205                     {
1206                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1207                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1208                         self.restore_snapshot(snapshot);
1209                         let close_paren = self.prev_token.span;
1210                         let span = lo.to(self.prev_token.span);
1211                         if !fields.is_empty() {
1212                             let mut replacement_err = ParenthesesWithStructFields {
1213                                 span,
1214                                 r#type: path,
1215                                 braces_for_struct: BracesForStructLiteral {
1216                                     first: open_paren,
1217                                     second: close_paren,
1218                                 },
1219                                 no_fields_for_fn: NoFieldsForFnCall {
1220                                     fields: fields
1221                                         .into_iter()
1222                                         .map(|field| field.span.until(field.expr.span))
1223                                         .collect(),
1224                                 },
1225                             }
1226                             .into_diagnostic(&self.sess.span_diagnostic);
1227                             replacement_err.emit();
1228
1229                             let old_err = mem::replace(err, replacement_err);
1230                             old_err.cancel();
1231                         } else {
1232                             err.emit();
1233                         }
1234                         return Some(self.mk_expr_err(span));
1235                     }
1236                     Ok(_) => {}
1237                     Err(mut err) => {
1238                         err.emit();
1239                     }
1240                 }
1241             }
1242             _ => {}
1243         }
1244         None
1245     }
1246
1247     /// Parse an indexing expression `expr[...]`.
1248     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1249         let prev_span = self.prev_token.span;
1250         let open_delim_span = self.token.span;
1251         self.bump(); // `[`
1252         let index = self.parse_expr()?;
1253         self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
1254         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1255         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index)))
1256     }
1257
1258     /// Assuming we have just parsed `.`, continue parsing into an expression.
1259     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1260         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1261             return Ok(self.mk_await_expr(self_arg, lo));
1262         }
1263
1264         let fn_span_lo = self.token.span;
1265         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1266         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1267         self.check_turbofish_missing_angle_brackets(&mut segment);
1268
1269         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1270             // Method call `expr.f()`
1271             let args = self.parse_paren_expr_seq()?;
1272             let fn_span = fn_span_lo.to(self.prev_token.span);
1273             let span = lo.to(self.prev_token.span);
1274             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, self_arg, args, fn_span)))
1275         } else {
1276             // Field access `expr.f`
1277             if let Some(args) = segment.args {
1278                 self.sess.emit_err(FieldExpressionWithGeneric(args.span()));
1279             }
1280
1281             let span = lo.to(self.prev_token.span);
1282             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident)))
1283         }
1284     }
1285
1286     /// At the bottom (top?) of the precedence hierarchy,
1287     /// Parses things like parenthesized exprs, macros, `return`, etc.
1288     ///
1289     /// N.B., this does not parse outer attributes, and is private because it only works
1290     /// correctly if called from `parse_dot_or_call_expr()`.
1291     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1292         maybe_recover_from_interpolated_ty_qpath!(self, true);
1293         maybe_whole_expr!(self);
1294
1295         // Outer attributes are already parsed and will be
1296         // added to the return value after the fact.
1297
1298         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1299         let lo = self.token.span;
1300         if let token::Literal(_) = self.token.kind {
1301             // This match arm is a special-case of the `_` match arm below and
1302             // could be removed without changing functionality, but it's faster
1303             // to have it here, especially for programs with large constants.
1304             self.parse_lit_expr()
1305         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1306             self.parse_tuple_parens_expr()
1307         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1308             self.parse_block_expr(None, lo, BlockCheckMode::Default)
1309         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1310             self.parse_closure_expr().map_err(|mut err| {
1311                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1312                 // then suggest parens around the lhs.
1313                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1314                     err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
1315                 }
1316                 err
1317             })
1318         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1319             self.parse_array_or_repeat_expr(Delimiter::Bracket)
1320         } else if self.check_path() {
1321             self.parse_path_start_expr()
1322         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1323             self.parse_closure_expr()
1324         } else if self.eat_keyword(kw::If) {
1325             self.parse_if_expr()
1326         } else if self.check_keyword(kw::For) {
1327             if self.choose_generics_over_qpath(1) {
1328                 self.parse_closure_expr()
1329             } else {
1330                 assert!(self.eat_keyword(kw::For));
1331                 self.parse_for_expr(None, self.prev_token.span)
1332             }
1333         } else if self.eat_keyword(kw::While) {
1334             self.parse_while_expr(None, self.prev_token.span)
1335         } else if let Some(label) = self.eat_label() {
1336             self.parse_labeled_expr(label, true)
1337         } else if self.eat_keyword(kw::Loop) {
1338             let sp = self.prev_token.span;
1339             self.parse_loop_expr(None, self.prev_token.span).map_err(|mut err| {
1340                 err.span_label(sp, "while parsing this `loop` expression");
1341                 err
1342             })
1343         } else if self.eat_keyword(kw::Continue) {
1344             let kind = ExprKind::Continue(self.eat_label());
1345             Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
1346         } else if self.eat_keyword(kw::Match) {
1347             let match_sp = self.prev_token.span;
1348             self.parse_match_expr().map_err(|mut err| {
1349                 err.span_label(match_sp, "while parsing this `match` expression");
1350                 err
1351             })
1352         } else if self.eat_keyword(kw::Unsafe) {
1353             let sp = self.prev_token.span;
1354             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
1355                 |mut err| {
1356                     err.span_label(sp, "while parsing this `unsafe` expression");
1357                     err
1358                 },
1359             )
1360         } else if self.check_inline_const(0) {
1361             self.parse_const_block(lo.to(self.token.span), false)
1362         } else if self.may_recover() && self.is_do_catch_block() {
1363             self.recover_do_catch()
1364         } else if self.is_try_block() {
1365             self.expect_keyword(kw::Try)?;
1366             self.parse_try_block(lo)
1367         } else if self.eat_keyword(kw::Return) {
1368             self.parse_return_expr()
1369         } else if self.eat_keyword(kw::Break) {
1370             self.parse_break_expr()
1371         } else if self.eat_keyword(kw::Yield) {
1372             self.parse_yield_expr()
1373         } else if self.is_do_yeet() {
1374             self.parse_yeet_expr()
1375         } else if self.check_keyword(kw::Let) {
1376             self.parse_let_expr()
1377         } else if self.eat_keyword(kw::Underscore) {
1378             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore))
1379         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1380             // Don't complain about bare semicolons after unclosed braces
1381             // recovery in order to keep the error count down. Fixing the
1382             // delimiters will possibly also fix the bare semicolon found in
1383             // expression context. For example, silence the following error:
1384             //
1385             //     error: expected expression, found `;`
1386             //      --> file.rs:2:13
1387             //       |
1388             //     2 |     foo(bar(;
1389             //       |             ^ expected expression
1390             self.bump();
1391             Ok(self.mk_expr_err(self.token.span))
1392         } else if self.token.uninterpolated_span().rust_2018() {
1393             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1394             if self.check_keyword(kw::Async) {
1395                 if self.is_async_block() {
1396                     // Check for `async {` and `async move {`.
1397                     self.parse_async_block()
1398                 } else {
1399                     self.parse_closure_expr()
1400                 }
1401             } else if self.eat_keyword(kw::Await) {
1402                 self.recover_incorrect_await_syntax(lo, self.prev_token.span)
1403             } else {
1404                 self.parse_lit_expr()
1405             }
1406         } else {
1407             self.parse_lit_expr()
1408         }
1409     }
1410
1411     fn parse_lit_expr(&mut self) -> PResult<'a, P<Expr>> {
1412         let lo = self.token.span;
1413         match self.parse_opt_token_lit() {
1414             Some((token_lit, _)) => {
1415                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(token_lit));
1416                 self.maybe_recover_from_bad_qpath(expr)
1417             }
1418             None => self.try_macro_suggestion(),
1419         }
1420     }
1421
1422     fn parse_tuple_parens_expr(&mut self) -> PResult<'a, P<Expr>> {
1423         let lo = self.token.span;
1424         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1425         let (es, trailing_comma) = match self.parse_seq_to_end(
1426             &token::CloseDelim(Delimiter::Parenthesis),
1427             SeqSep::trailing_allowed(token::Comma),
1428             |p| p.parse_expr_catch_underscore(),
1429         ) {
1430             Ok(x) => x,
1431             Err(err) => {
1432                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1433             }
1434         };
1435         let kind = if es.len() == 1 && !trailing_comma {
1436             // `(e)` is parenthesized `e`.
1437             ExprKind::Paren(es.into_iter().next().unwrap())
1438         } else {
1439             // `(e,)` is a tuple with only one field, `e`.
1440             ExprKind::Tup(es)
1441         };
1442         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1443         self.maybe_recover_from_bad_qpath(expr)
1444     }
1445
1446     fn parse_array_or_repeat_expr(&mut self, close_delim: Delimiter) -> PResult<'a, P<Expr>> {
1447         let lo = self.token.span;
1448         self.bump(); // `[` or other open delim
1449
1450         let close = &token::CloseDelim(close_delim);
1451         let kind = if self.eat(close) {
1452             // Empty vector
1453             ExprKind::Array(Vec::new())
1454         } else {
1455             // Non-empty vector
1456             let first_expr = self.parse_expr()?;
1457             if self.eat(&token::Semi) {
1458                 // Repeating array syntax: `[ 0; 512 ]`
1459                 let count = self.parse_anon_const_expr()?;
1460                 self.expect(close)?;
1461                 ExprKind::Repeat(first_expr, count)
1462             } else if self.eat(&token::Comma) {
1463                 // Vector with two or more elements.
1464                 let sep = SeqSep::trailing_allowed(token::Comma);
1465                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1466                 let mut exprs = vec![first_expr];
1467                 exprs.extend(remaining_exprs);
1468                 ExprKind::Array(exprs)
1469             } else {
1470                 // Vector with one element
1471                 self.expect(close)?;
1472                 ExprKind::Array(vec![first_expr])
1473             }
1474         };
1475         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1476         self.maybe_recover_from_bad_qpath(expr)
1477     }
1478
1479     fn parse_path_start_expr(&mut self) -> PResult<'a, P<Expr>> {
1480         let (qself, path) = if self.eat_lt() {
1481             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1482             (Some(qself), path)
1483         } else {
1484             (None, self.parse_path(PathStyle::Expr)?)
1485         };
1486
1487         // `!`, as an operator, is prefix, so we know this isn't that.
1488         let (span, kind) = if self.eat(&token::Not) {
1489             // MACRO INVOCATION expression
1490             if qself.is_some() {
1491                 self.sess.emit_err(MacroInvocationWithQualifiedPath(path.span));
1492             }
1493             let lo = path.span;
1494             let mac = P(MacCall {
1495                 path,
1496                 args: self.parse_mac_args()?,
1497                 prior_type_ascription: self.last_type_ascription,
1498             });
1499             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
1500         } else if self.check(&token::OpenDelim(Delimiter::Brace)) &&
1501             let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path) {
1502                 if qself.is_some() {
1503                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1504                 }
1505                 return expr;
1506         } else {
1507             (path.span, ExprKind::Path(qself, path))
1508         };
1509
1510         let expr = self.mk_expr(span, kind);
1511         self.maybe_recover_from_bad_qpath(expr)
1512     }
1513
1514     /// Parse `'label: $expr`. The label is already parsed.
1515     fn parse_labeled_expr(
1516         &mut self,
1517         label_: Label,
1518         mut consume_colon: bool,
1519     ) -> PResult<'a, P<Expr>> {
1520         let lo = label_.ident.span;
1521         let label = Some(label_);
1522         let ate_colon = self.eat(&token::Colon);
1523         let expr = if self.eat_keyword(kw::While) {
1524             self.parse_while_expr(label, lo)
1525         } else if self.eat_keyword(kw::For) {
1526             self.parse_for_expr(label, lo)
1527         } else if self.eat_keyword(kw::Loop) {
1528             self.parse_loop_expr(label, lo)
1529         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1530             || self.token.is_whole_block()
1531         {
1532             self.parse_block_expr(label, lo, BlockCheckMode::Default)
1533         } else if !ate_colon
1534             && self.may_recover()
1535             && (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
1536                 || self.token.is_op())
1537         {
1538             let lit = self.recover_unclosed_char(label_.ident, |self_| {
1539                 self_.sess.create_err(UnexpectedTokenAfterLabel {
1540                     span: self_.token.span,
1541                     remove_label: None,
1542                     enclose_in_block: None,
1543                 })
1544             });
1545             consume_colon = false;
1546             Ok(self.mk_expr(lo, ExprKind::Lit(lit.token_lit)))
1547         } else if !ate_colon
1548             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1549         {
1550             // We're probably inside of a `Path<'a>` that needs a turbofish
1551             self.sess.emit_err(UnexpectedTokenAfterLabel {
1552                 span: self.token.span,
1553                 remove_label: None,
1554                 enclose_in_block: None,
1555             });
1556             consume_colon = false;
1557             Ok(self.mk_expr_err(lo))
1558         } else {
1559             let mut err = UnexpectedTokenAfterLabel {
1560                 span: self.token.span,
1561                 remove_label: None,
1562                 enclose_in_block: None,
1563             };
1564
1565             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1566             let expr = self.parse_expr().map(|expr| {
1567                 let span = expr.span;
1568
1569                 let found_labeled_breaks = {
1570                     struct FindLabeledBreaksVisitor(bool);
1571
1572                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1573                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1574                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1575                                 self.0 = true;
1576                             }
1577                         }
1578                     }
1579
1580                     let mut vis = FindLabeledBreaksVisitor(false);
1581                     vis.visit_expr(&expr);
1582                     vis.0
1583                 };
1584
1585                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1586                 //
1587                 // If there are no breaks that may use this label, suggest removing the label and
1588                 // recover to the unmodified expression.
1589                 if !found_labeled_breaks {
1590                     err.remove_label = Some(lo.until(span));
1591
1592                     return expr;
1593                 }
1594
1595                 err.enclose_in_block = Some(UnexpectedTokenAfterLabelSugg {
1596                     left: span.shrink_to_lo(),
1597                     right: span.shrink_to_hi(),
1598                 });
1599
1600                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
1601                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1602                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1603                 self.mk_expr(span, ExprKind::Block(blk, label))
1604             });
1605
1606             self.sess.emit_err(err);
1607             expr
1608         }?;
1609
1610         if !ate_colon && consume_colon {
1611             self.sess.emit_err(RequireColonAfterLabeledExpression {
1612                 span: expr.span,
1613                 label: lo,
1614                 label_end: lo.shrink_to_hi(),
1615             });
1616         }
1617
1618         Ok(expr)
1619     }
1620
1621     /// Emit an error when a char is parsed as a lifetime because of a missing quote
1622     pub(super) fn recover_unclosed_char(
1623         &self,
1624         lifetime: Ident,
1625         err: impl FnOnce(&Self) -> DiagnosticBuilder<'a, ErrorGuaranteed>,
1626     ) -> ast::Lit {
1627         if let Some(mut diag) =
1628             self.sess.span_diagnostic.steal_diagnostic(lifetime.span, StashKey::LifetimeIsChar)
1629         {
1630             diag.span_suggestion_verbose(
1631                 lifetime.span.shrink_to_hi(),
1632                 "add `'` to close the char literal",
1633                 "'",
1634                 Applicability::MaybeIncorrect,
1635             )
1636             .emit();
1637         } else {
1638             err(self)
1639                 .span_suggestion_verbose(
1640                     lifetime.span.shrink_to_hi(),
1641                     "add `'` to close the char literal",
1642                     "'",
1643                     Applicability::MaybeIncorrect,
1644                 )
1645                 .emit();
1646         }
1647         let name = lifetime.without_first_quote().name;
1648         ast::Lit {
1649             token_lit: token::Lit::new(token::LitKind::Char, name, None),
1650             kind: ast::LitKind::Char(name.as_str().chars().next().unwrap_or('_')),
1651             span: lifetime.span,
1652         }
1653     }
1654
1655     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1656     fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
1657         let lo = self.token.span;
1658
1659         self.bump(); // `do`
1660         self.bump(); // `catch`
1661
1662         let span = lo.to(self.prev_token.span);
1663         self.sess.emit_err(DoCatchSyntaxRemoved { span });
1664
1665         self.parse_try_block(lo)
1666     }
1667
1668     /// Parse an expression if the token can begin one.
1669     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1670         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1671     }
1672
1673     /// Parse `"return" expr?`.
1674     fn parse_return_expr(&mut self) -> PResult<'a, P<Expr>> {
1675         let lo = self.prev_token.span;
1676         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1677         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1678         self.maybe_recover_from_bad_qpath(expr)
1679     }
1680
1681     /// Parse `"do" "yeet" expr?`.
1682     fn parse_yeet_expr(&mut self) -> PResult<'a, P<Expr>> {
1683         let lo = self.token.span;
1684
1685         self.bump(); // `do`
1686         self.bump(); // `yeet`
1687
1688         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1689
1690         let span = lo.to(self.prev_token.span);
1691         self.sess.gated_spans.gate(sym::yeet_expr, span);
1692         let expr = self.mk_expr(span, kind);
1693         self.maybe_recover_from_bad_qpath(expr)
1694     }
1695
1696     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1697     /// If the label is followed immediately by a `:` token, the label and `:` are
1698     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1699     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1700     /// the break expression of an unlabeled break is a labeled loop (as in
1701     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1702     /// expression only gets a warning for compatibility reasons; and a labeled break
1703     /// with a labeled loop does not even get a warning because there is no ambiguity.
1704     fn parse_break_expr(&mut self) -> PResult<'a, P<Expr>> {
1705         let lo = self.prev_token.span;
1706         let mut label = self.eat_label();
1707         let kind = if label.is_some() && self.token == token::Colon {
1708             // The value expression can be a labeled loop, see issue #86948, e.g.:
1709             // `loop { break 'label: loop { break 'label 42; }; }`
1710             let lexpr = self.parse_labeled_expr(label.take().unwrap(), true)?;
1711             self.sess.emit_err(LabeledLoopInBreak {
1712                 span: lexpr.span,
1713                 sub: WrapExpressionInParentheses {
1714                     left: lexpr.span.shrink_to_lo(),
1715                     right: lexpr.span.shrink_to_hi(),
1716                 },
1717             });
1718             Some(lexpr)
1719         } else if self.token != token::OpenDelim(Delimiter::Brace)
1720             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1721         {
1722             let expr = self.parse_expr_opt()?;
1723             if let Some(ref expr) = expr {
1724                 if label.is_some()
1725                     && matches!(
1726                         expr.kind,
1727                         ExprKind::While(_, _, None)
1728                             | ExprKind::ForLoop(_, _, _, None)
1729                             | ExprKind::Loop(_, None)
1730                             | ExprKind::Block(_, None)
1731                     )
1732                 {
1733                     self.sess.buffer_lint_with_diagnostic(
1734                         BREAK_WITH_LABEL_AND_LOOP,
1735                         lo.to(expr.span),
1736                         ast::CRATE_NODE_ID,
1737                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1738                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1739                     );
1740                 }
1741             }
1742             expr
1743         } else {
1744             None
1745         };
1746         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
1747         self.maybe_recover_from_bad_qpath(expr)
1748     }
1749
1750     /// Parse `"yield" expr?`.
1751     fn parse_yield_expr(&mut self) -> PResult<'a, P<Expr>> {
1752         let lo = self.prev_token.span;
1753         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1754         let span = lo.to(self.prev_token.span);
1755         self.sess.gated_spans.gate(sym::generators, span);
1756         let expr = self.mk_expr(span, kind);
1757         self.maybe_recover_from_bad_qpath(expr)
1758     }
1759
1760     /// Returns a string literal if the next token is a string literal.
1761     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1762     /// and returns `None` if the next token is not literal at all.
1763     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1764         match self.parse_opt_ast_lit() {
1765             Some(lit) => match lit.kind {
1766                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1767                     style,
1768                     symbol: lit.token_lit.symbol,
1769                     suffix: lit.token_lit.suffix,
1770                     span: lit.span,
1771                     symbol_unescaped,
1772                 }),
1773                 _ => Err(Some(lit)),
1774             },
1775             None => Err(None),
1776         }
1777     }
1778
1779     fn handle_missing_lit(&mut self) -> PResult<'a, Lit> {
1780         if let token::Interpolated(inner) = &self.token.kind {
1781             let expr = match inner.as_ref() {
1782                 token::NtExpr(expr) => Some(expr),
1783                 token::NtLiteral(expr) => Some(expr),
1784                 _ => None,
1785             };
1786             if let Some(expr) = expr {
1787                 if matches!(expr.kind, ExprKind::Err) {
1788                     let mut err = InvalidInterpolatedExpression { span: self.token.span }
1789                         .into_diagnostic(&self.sess.span_diagnostic);
1790                     err.downgrade_to_delayed_bug();
1791                     return Err(err);
1792                 }
1793             }
1794         }
1795         let token = self.token.clone();
1796         let err = |self_: &Self| {
1797             let msg = format!("unexpected token: {}", super::token_descr(&token));
1798             self_.struct_span_err(token.span, &msg)
1799         };
1800         // On an error path, eagerly consider a lifetime to be an unclosed character lit
1801         if self.token.is_lifetime() {
1802             let lt = self.expect_lifetime();
1803             Ok(self.recover_unclosed_char(lt.ident, err))
1804         } else {
1805             Err(err(self))
1806         }
1807     }
1808
1809     pub(super) fn parse_token_lit(&mut self) -> PResult<'a, (token::Lit, Span)> {
1810         self.parse_opt_token_lit()
1811             .ok_or(())
1812             .or_else(|()| self.handle_missing_lit().map(|lit| (lit.token_lit, lit.span)))
1813     }
1814
1815     pub(super) fn parse_ast_lit(&mut self) -> PResult<'a, Lit> {
1816         self.parse_opt_ast_lit().ok_or(()).or_else(|()| self.handle_missing_lit())
1817     }
1818
1819     fn recover_after_dot(&mut self) -> Option<Token> {
1820         let mut recovered = None;
1821         if self.token == token::Dot {
1822             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1823             // dot would follow an optional literal, so we do this unconditionally.
1824             recovered = self.look_ahead(1, |next_token| {
1825                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1826                     next_token.kind
1827                 {
1828                     if self.token.span.hi() == next_token.span.lo() {
1829                         let s = String::from("0.") + symbol.as_str();
1830                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1831                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1832                     }
1833                 }
1834                 None
1835             });
1836             if let Some(token) = &recovered {
1837                 self.bump();
1838                 self.sess.emit_err(FloatLiteralRequiresIntegerPart {
1839                     span: token.span,
1840                     correct: pprust::token_to_string(token).into_owned(),
1841                 });
1842             }
1843         }
1844
1845         recovered
1846     }
1847
1848     /// Matches `lit = true | false | token_lit`.
1849     /// Returns `None` if the next token is not a literal.
1850     pub(super) fn parse_opt_token_lit(&mut self) -> Option<(token::Lit, Span)> {
1851         let recovered = self.recover_after_dot();
1852         let token = recovered.as_ref().unwrap_or(&self.token);
1853         let span = token.span;
1854         token::Lit::from_token(token).map(|token_lit| {
1855             self.bump();
1856             (token_lit, span)
1857         })
1858     }
1859
1860     /// Matches `lit = true | false | token_lit`.
1861     /// Returns `None` if the next token is not a literal.
1862     pub(super) fn parse_opt_ast_lit(&mut self) -> Option<Lit> {
1863         let recovered = self.recover_after_dot();
1864         let token = recovered.as_ref().unwrap_or(&self.token);
1865         match token::Lit::from_token(token) {
1866             Some(token_lit) => {
1867                 match Lit::from_token_lit(token_lit, token.span) {
1868                     Ok(lit) => {
1869                         self.bump();
1870                         Some(lit)
1871                     }
1872                     Err(err) => {
1873                         let span = token.span;
1874                         let token::Literal(lit) = token.kind else {
1875                             unreachable!();
1876                         };
1877                         self.bump();
1878                         report_lit_error(&self.sess, err, lit, span);
1879                         // Pack possible quotes and prefixes from the original literal into
1880                         // the error literal's symbol so they can be pretty-printed faithfully.
1881                         let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1882                         let symbol = Symbol::intern(&suffixless_lit.to_string());
1883                         let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1884                         Some(Lit::from_token_lit(lit, span).unwrap_or_else(|_| unreachable!()))
1885                     }
1886                 }
1887             }
1888             None => None,
1889         }
1890     }
1891
1892     pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
1893         if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
1894             // #59553: warn instead of reject out of hand to allow the fix to percolate
1895             // through the ecosystem when people fix their macros
1896             self.sess.emit_warning(InvalidLiteralSuffixOnTupleIndex {
1897                 span,
1898                 suffix,
1899                 exception: Some(()),
1900             });
1901         } else {
1902             self.sess.emit_err(InvalidLiteralSuffixOnTupleIndex { span, suffix, exception: None });
1903         }
1904     }
1905
1906     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1907     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1908     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1909         maybe_whole_expr!(self);
1910
1911         let lo = self.token.span;
1912         let minus_present = self.eat(&token::BinOp(token::Minus));
1913         let (token_lit, span) = self.parse_token_lit()?;
1914         let expr = self.mk_expr(span, ExprKind::Lit(token_lit));
1915
1916         if minus_present {
1917             Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
1918         } else {
1919             Ok(expr)
1920         }
1921     }
1922
1923     fn is_array_like_block(&mut self) -> bool {
1924         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1925             && self.look_ahead(2, |t| t == &token::Comma)
1926             && self.look_ahead(3, |t| t.can_begin_expr())
1927     }
1928
1929     /// Emits a suggestion if it looks like the user meant an array but
1930     /// accidentally used braces, causing the code to be interpreted as a block
1931     /// expression.
1932     fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
1933         let mut snapshot = self.create_snapshot_for_diagnostic();
1934         match snapshot.parse_array_or_repeat_expr(Delimiter::Brace) {
1935             Ok(arr) => {
1936                 self.sess.emit_err(ArrayBracketsInsteadOfSpaces {
1937                     span: arr.span,
1938                     sub: ArrayBracketsInsteadOfSpacesSugg {
1939                         left: lo,
1940                         right: snapshot.prev_token.span,
1941                     },
1942                 });
1943
1944                 self.restore_snapshot(snapshot);
1945                 Some(self.mk_expr_err(arr.span))
1946             }
1947             Err(e) => {
1948                 e.cancel();
1949                 None
1950             }
1951         }
1952     }
1953
1954     fn suggest_missing_semicolon_before_array(
1955         &self,
1956         prev_span: Span,
1957         open_delim_span: Span,
1958     ) -> PResult<'a, ()> {
1959         if !self.may_recover() {
1960             return Ok(());
1961         }
1962
1963         if self.token.kind == token::Comma {
1964             if !self.sess.source_map().is_multiline(prev_span.until(self.token.span)) {
1965                 return Ok(());
1966             }
1967             let mut snapshot = self.create_snapshot_for_diagnostic();
1968             snapshot.bump();
1969             match snapshot.parse_seq_to_before_end(
1970                 &token::CloseDelim(Delimiter::Bracket),
1971                 SeqSep::trailing_allowed(token::Comma),
1972                 |p| p.parse_expr(),
1973             ) {
1974                 Ok(_)
1975                     // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
1976                     // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
1977                     // This is because the `token.kind` of the close delim is treated as the same as
1978                     // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
1979                     // Therefore, `token.kind` should not be compared here.
1980                     if snapshot
1981                         .span_to_snippet(snapshot.token.span)
1982                         .map_or(false, |snippet| snippet == "]") =>
1983                 {
1984                     return Err(MissingSemicolonBeforeArray {
1985                         open_delim: open_delim_span,
1986                         semicolon: prev_span.shrink_to_hi(),
1987                     }.into_diagnostic(&self.sess.span_diagnostic));
1988                 }
1989                 Ok(_) => (),
1990                 Err(err) => err.cancel(),
1991             }
1992         }
1993         Ok(())
1994     }
1995
1996     /// Parses a block or unsafe block.
1997     pub(super) fn parse_block_expr(
1998         &mut self,
1999         opt_label: Option<Label>,
2000         lo: Span,
2001         blk_mode: BlockCheckMode,
2002     ) -> PResult<'a, P<Expr>> {
2003         if self.may_recover() && self.is_array_like_block() {
2004             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
2005                 return Ok(arr);
2006             }
2007         }
2008
2009         if self.token.is_whole_block() {
2010             self.sess.emit_err(InvalidBlockMacroSegment {
2011                 span: self.token.span,
2012                 context: lo.to(self.token.span),
2013             });
2014         }
2015
2016         let (attrs, blk) = self.parse_block_common(lo, blk_mode)?;
2017         Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
2018     }
2019
2020     /// Parse a block which takes no attributes and has no label
2021     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2022         let blk = self.parse_block()?;
2023         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
2024     }
2025
2026     /// Parses a closure expression (e.g., `move |args| expr`).
2027     fn parse_closure_expr(&mut self) -> PResult<'a, P<Expr>> {
2028         let lo = self.token.span;
2029
2030         let binder = if self.check_keyword(kw::For) {
2031             let lo = self.token.span;
2032             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2033             let span = lo.to(self.prev_token.span);
2034
2035             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2036
2037             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2038         } else {
2039             ClosureBinder::NotPresent
2040         };
2041
2042         let movability =
2043             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2044
2045         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2046             self.parse_asyncness(Case::Sensitive)
2047         } else {
2048             Async::No
2049         };
2050
2051         let capture_clause = self.parse_capture_clause()?;
2052         let decl = self.parse_fn_block_decl()?;
2053         let decl_hi = self.prev_token.span;
2054         let mut body = match decl.output {
2055             FnRetTy::Default(_) => {
2056                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2057                 self.parse_expr_res(restrictions, None)?
2058             }
2059             _ => {
2060                 // If an explicit return type is given, require a block to appear (RFC 968).
2061                 let body_lo = self.token.span;
2062                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default)?
2063             }
2064         };
2065
2066         if let Async::Yes { span, .. } = asyncness {
2067             // Feature-gate `async ||` closures.
2068             self.sess.gated_spans.gate(sym::async_closure, span);
2069         }
2070
2071         if self.token.kind == TokenKind::Semi
2072             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2073             // HACK: This is needed so we can detect whether we're inside a macro,
2074             // where regular assumptions about what tokens can follow other tokens
2075             // don't necessarily apply.
2076             && self.may_recover()
2077             // FIXME(Nilstrieb): Remove this check once `may_recover` actually stops recovery
2078             && self.subparser_name.is_none()
2079         {
2080             // It is likely that the closure body is a block but where the
2081             // braces have been removed. We will recover and eat the next
2082             // statements later in the parsing process.
2083             body = self.mk_expr_err(body.span);
2084         }
2085
2086         let body_span = body.span;
2087
2088         let closure = self.mk_expr(
2089             lo.to(body.span),
2090             ExprKind::Closure(
2091                 binder,
2092                 capture_clause,
2093                 asyncness,
2094                 movability,
2095                 decl,
2096                 body,
2097                 lo.to(decl_hi),
2098             ),
2099         );
2100
2101         // Disable recovery for closure body
2102         let spans =
2103             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2104         self.current_closure = Some(spans);
2105
2106         Ok(closure)
2107     }
2108
2109     /// Parses an optional `move` prefix to a closure-like construct.
2110     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2111         if self.eat_keyword(kw::Move) {
2112             // Check for `move async` and recover
2113             if self.check_keyword(kw::Async) {
2114                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2115                 Err(AsyncMoveOrderIncorrect { span: move_async_span }
2116                     .into_diagnostic(&self.sess.span_diagnostic))
2117             } else {
2118                 Ok(CaptureBy::Value)
2119             }
2120         } else {
2121             Ok(CaptureBy::Ref)
2122         }
2123     }
2124
2125     /// Parses the `|arg, arg|` header of a closure.
2126     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2127         let inputs = if self.eat(&token::OrOr) {
2128             Vec::new()
2129         } else {
2130             self.expect(&token::BinOp(token::Or))?;
2131             let args = self
2132                 .parse_seq_to_before_tokens(
2133                     &[&token::BinOp(token::Or), &token::OrOr],
2134                     SeqSep::trailing_allowed(token::Comma),
2135                     TokenExpectType::NoExpect,
2136                     |p| p.parse_fn_block_param(),
2137                 )?
2138                 .0;
2139             self.expect_or()?;
2140             args
2141         };
2142         let output =
2143             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2144
2145         Ok(P(FnDecl { inputs, output }))
2146     }
2147
2148     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2149     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2150         let lo = self.token.span;
2151         let attrs = self.parse_outer_attributes()?;
2152         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2153             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2154             let ty = if this.eat(&token::Colon) {
2155                 this.parse_ty()?
2156             } else {
2157                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2158             };
2159
2160             Ok((
2161                 Param {
2162                     attrs,
2163                     ty,
2164                     pat,
2165                     span: lo.to(this.prev_token.span),
2166                     id: DUMMY_NODE_ID,
2167                     is_placeholder: false,
2168                 },
2169                 TrailingToken::MaybeComma,
2170             ))
2171         })
2172     }
2173
2174     /// Parses an `if` expression (`if` token already eaten).
2175     fn parse_if_expr(&mut self) -> PResult<'a, P<Expr>> {
2176         let lo = self.prev_token.span;
2177         let cond = self.parse_cond_expr()?;
2178         self.parse_if_after_cond(lo, cond)
2179     }
2180
2181     fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
2182         let cond_span = cond.span;
2183         // Tries to interpret `cond` as either a missing expression if it's a block,
2184         // or as an unfinished expression if it's a binop and the RHS is a block.
2185         // We could probably add more recoveries here too...
2186         let mut recover_block_from_condition = |this: &mut Self| {
2187             let block = match &mut cond.kind {
2188                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2189                     if let ExprKind::Block(_, None) = right.kind => {
2190                         self.sess.emit_err(IfExpressionMissingThenBlock {
2191                             if_span: lo,
2192                             sub: IfExpressionMissingThenBlockSub::UnfinishedCondition(
2193                                 cond_span.shrink_to_lo().to(*binop_span)
2194                             ),
2195                         });
2196                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2197                     },
2198                 ExprKind::Block(_, None) => {
2199                     self.sess.emit_err(IfExpressionMissingCondition {
2200                         if_span: lo.shrink_to_hi(),
2201                         block_span: self.sess.source_map().start_point(cond_span),
2202                     });
2203                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2204                 }
2205                 _ => {
2206                     return None;
2207                 }
2208             };
2209             if let ExprKind::Block(block, _) = &block.kind {
2210                 Some(block.clone())
2211             } else {
2212                 unreachable!()
2213             }
2214         };
2215         // Parse then block
2216         let thn = if self.token.is_keyword(kw::Else) {
2217             if let Some(block) = recover_block_from_condition(self) {
2218                 block
2219             } else {
2220                 self.sess.emit_err(IfExpressionMissingThenBlock {
2221                     if_span: lo,
2222                     sub: IfExpressionMissingThenBlockSub::AddThenBlock(cond_span.shrink_to_hi()),
2223                 });
2224                 self.mk_block_err(cond_span.shrink_to_hi())
2225             }
2226         } else {
2227             let attrs = self.parse_outer_attributes()?; // For recovery.
2228             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2229                 self.parse_block()?
2230             } else {
2231                 if let Some(block) = recover_block_from_condition(self) {
2232                     block
2233                 } else {
2234                     self.error_on_extra_if(&cond)?;
2235                     // Parse block, which will always fail, but we can add a nice note to the error
2236                     self.parse_block().map_err(|mut err| {
2237                         err.span_note(
2238                             cond_span,
2239                             "the `if` expression is missing a block after this condition",
2240                         );
2241                         err
2242                     })?
2243                 }
2244             };
2245             self.error_on_if_block_attrs(lo, false, block.span, attrs);
2246             block
2247         };
2248         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2249         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
2250     }
2251
2252     /// Parses the condition of a `if` or `while` expression.
2253     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2254         let cond =
2255             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
2256
2257         if let ExprKind::Let(..) = cond.kind {
2258             // Remove the last feature gating of a `let` expression since it's stable.
2259             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2260         }
2261
2262         Ok(cond)
2263     }
2264
2265     /// Parses a `let $pat = $expr` pseudo-expression.
2266     fn parse_let_expr(&mut self) -> PResult<'a, P<Expr>> {
2267         // This is a *approximate* heuristic that detects if `let` chains are
2268         // being parsed in the right position. It's approximate because it
2269         // doesn't deny all invalid `let` expressions, just completely wrong usages.
2270         let not_in_chain = !matches!(
2271             self.prev_token.kind,
2272             TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2273         );
2274         if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
2275             self.sess.emit_err(ExpectedExpressionFoundLet { span: self.token.span });
2276         }
2277
2278         self.bump(); // Eat `let` token
2279         let lo = self.prev_token.span;
2280         let pat = self.parse_pat_allow_top_alt(
2281             None,
2282             RecoverComma::Yes,
2283             RecoverColon::Yes,
2284             CommaRecoveryMode::LikelyTuple,
2285         )?;
2286         if self.token == token::EqEq {
2287             self.sess.emit_err(ExpectedEqForLetExpr {
2288                 span: self.token.span,
2289                 sugg_span: self.token.span,
2290             });
2291             self.bump();
2292         } else {
2293             self.expect(&token::Eq)?;
2294         }
2295         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2296             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2297         })?;
2298         let span = lo.to(expr.span);
2299         self.sess.gated_spans.gate(sym::let_chains, span);
2300         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span)))
2301     }
2302
2303     /// Parses an `else { ... }` expression (`else` token already eaten).
2304     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2305         let else_span = self.prev_token.span; // `else`
2306         let attrs = self.parse_outer_attributes()?; // For recovery.
2307         let expr = if self.eat_keyword(kw::If) {
2308             self.parse_if_expr()?
2309         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2310             self.parse_simple_block()?
2311         } else {
2312             let snapshot = self.create_snapshot_for_diagnostic();
2313             let first_tok = super::token_descr(&self.token);
2314             let first_tok_span = self.token.span;
2315             match self.parse_expr() {
2316                 Ok(cond)
2317                 // If it's not a free-standing expression, and is followed by a block,
2318                 // then it's very likely the condition to an `else if`.
2319                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2320                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2321                 {
2322                     self.sess.emit_err(ExpectedElseBlock {
2323                         first_tok_span,
2324                         first_tok,
2325                         else_span,
2326                         condition_start: cond.span.shrink_to_lo(),
2327                     });
2328                     self.parse_if_after_cond(cond.span.shrink_to_lo(), cond)?
2329                 }
2330                 Err(e) => {
2331                     e.cancel();
2332                     self.restore_snapshot(snapshot);
2333                     self.parse_simple_block()?
2334                 },
2335                 Ok(_) => {
2336                     self.restore_snapshot(snapshot);
2337                     self.parse_simple_block()?
2338                 },
2339             }
2340         };
2341         self.error_on_if_block_attrs(else_span, true, expr.span, attrs);
2342         Ok(expr)
2343     }
2344
2345     fn error_on_if_block_attrs(
2346         &self,
2347         ctx_span: Span,
2348         is_ctx_else: bool,
2349         branch_span: Span,
2350         attrs: AttrWrapper,
2351     ) {
2352         if attrs.is_empty() {
2353             return;
2354         }
2355
2356         let attrs: &[ast::Attribute] = &attrs.take_for_recovery(self.sess);
2357         let (attributes, last) = match attrs {
2358             [] => return,
2359             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2360         };
2361         let ctx = if is_ctx_else { "else" } else { "if" };
2362         self.sess.emit_err(OuterAttributeNotAllowedOnIfElse {
2363             last,
2364             branch_span,
2365             ctx_span,
2366             ctx: ctx.to_string(),
2367             attributes,
2368         });
2369     }
2370
2371     fn error_on_extra_if(&mut self, cond: &P<Expr>) -> PResult<'a, ()> {
2372         if let ExprKind::Binary(Spanned { span: binop_span, node: binop}, _, right) = &cond.kind &&
2373             let BinOpKind::And = binop &&
2374             let ExprKind::If(cond, ..) = &right.kind {
2375                     Err(self.sess.create_err(UnexpectedIfWithIf(binop_span.shrink_to_hi().to(cond.span.shrink_to_lo()))))
2376             } else {
2377                 Ok(())
2378             }
2379     }
2380
2381     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2382     fn parse_for_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2383         // Record whether we are about to parse `for (`.
2384         // This is used below for recovery in case of `for ( $stuff ) $block`
2385         // in which case we will suggest `for $stuff $block`.
2386         let begin_paren = match self.token.kind {
2387             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2388             _ => None,
2389         };
2390
2391         let pat = self.parse_pat_allow_top_alt(
2392             None,
2393             RecoverComma::Yes,
2394             RecoverColon::Yes,
2395             CommaRecoveryMode::LikelyTuple,
2396         )?;
2397         if !self.eat_keyword(kw::In) {
2398             self.error_missing_in_for_loop();
2399         }
2400         self.check_for_for_in_in_typo(self.prev_token.span);
2401         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2402
2403         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2404
2405         let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
2406
2407         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2408         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2409     }
2410
2411     fn error_missing_in_for_loop(&mut self) {
2412         let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
2413             // Possibly using JS syntax (#75311).
2414             let span = self.token.span;
2415             self.bump();
2416             (span, MissingInInForLoopSub::InNotOf)
2417         } else {
2418             (self.prev_token.span.between(self.token.span), MissingInInForLoopSub::AddIn)
2419         };
2420
2421         self.sess.emit_err(MissingInInForLoop { span, sub: sub(span) });
2422     }
2423
2424     /// Parses a `while` or `while let` expression (`while` token already eaten).
2425     fn parse_while_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2426         let cond = self.parse_cond_expr().map_err(|mut err| {
2427             err.span_label(lo, "while parsing the condition of this `while` expression");
2428             err
2429         })?;
2430         let (attrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2431             err.span_label(lo, "while parsing the body of this `while` expression");
2432             err.span_label(cond.span, "this `while` condition successfully parsed");
2433             err
2434         })?;
2435         Ok(self.mk_expr_with_attrs(
2436             lo.to(self.prev_token.span),
2437             ExprKind::While(cond, body, opt_label),
2438             attrs,
2439         ))
2440     }
2441
2442     /// Parses `loop { ... }` (`loop` token already eaten).
2443     fn parse_loop_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2444         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2445         Ok(self.mk_expr_with_attrs(
2446             lo.to(self.prev_token.span),
2447             ExprKind::Loop(body, opt_label),
2448             attrs,
2449         ))
2450     }
2451
2452     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2453         self.token.lifetime().map(|ident| {
2454             self.bump();
2455             Label { ident }
2456         })
2457     }
2458
2459     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2460     fn parse_match_expr(&mut self) -> PResult<'a, P<Expr>> {
2461         let match_span = self.prev_token.span;
2462         let lo = self.prev_token.span;
2463         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2464         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2465             if self.token == token::Semi {
2466                 e.span_suggestion_short(
2467                     match_span,
2468                     "try removing this `match`",
2469                     "",
2470                     Applicability::MaybeIncorrect, // speculative
2471                 );
2472             }
2473             if self.maybe_recover_unexpected_block_label() {
2474                 e.cancel();
2475                 self.bump();
2476             } else {
2477                 return Err(e);
2478             }
2479         }
2480         let attrs = self.parse_inner_attributes()?;
2481
2482         let mut arms: Vec<Arm> = Vec::new();
2483         while self.token != token::CloseDelim(Delimiter::Brace) {
2484             match self.parse_arm() {
2485                 Ok(arm) => arms.push(arm),
2486                 Err(mut e) => {
2487                     // Recover by skipping to the end of the block.
2488                     e.emit();
2489                     self.recover_stmt();
2490                     let span = lo.to(self.token.span);
2491                     if self.token == token::CloseDelim(Delimiter::Brace) {
2492                         self.bump();
2493                     }
2494                     return Ok(self.mk_expr_with_attrs(
2495                         span,
2496                         ExprKind::Match(scrutinee, arms),
2497                         attrs,
2498                     ));
2499                 }
2500             }
2501         }
2502         let hi = self.token.span;
2503         self.bump();
2504         Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2505     }
2506
2507     /// Attempt to recover from match arm body with statements and no surrounding braces.
2508     fn parse_arm_body_missing_braces(
2509         &mut self,
2510         first_expr: &P<Expr>,
2511         arrow_span: Span,
2512     ) -> Option<P<Expr>> {
2513         if self.token.kind != token::Semi {
2514             return None;
2515         }
2516         let start_snapshot = self.create_snapshot_for_diagnostic();
2517         let semi_sp = self.token.span;
2518         self.bump(); // `;`
2519         let mut stmts =
2520             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2521         let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
2522             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2523
2524             this.sess.emit_err(MatchArmBodyWithoutBraces {
2525                 statements: span,
2526                 arrow: arrow_span,
2527                 num_statements: stmts.len(),
2528                 sub: if stmts.len() > 1 {
2529                     MatchArmBodyWithoutBracesSugg::AddBraces {
2530                         left: span.shrink_to_lo(),
2531                         right: span.shrink_to_hi(),
2532                     }
2533                 } else {
2534                     MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
2535                 },
2536             });
2537             this.mk_expr_err(span)
2538         };
2539         // We might have either a `,` -> `;` typo, or a block without braces. We need
2540         // a more subtle parsing strategy.
2541         loop {
2542             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2543                 // We have reached the closing brace of the `match` expression.
2544                 return Some(err(self, stmts));
2545             }
2546             if self.token.kind == token::Comma {
2547                 self.restore_snapshot(start_snapshot);
2548                 return None;
2549             }
2550             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2551             match self.parse_pat_no_top_alt(None) {
2552                 Ok(_pat) => {
2553                     if self.token.kind == token::FatArrow {
2554                         // Reached arm end.
2555                         self.restore_snapshot(pre_pat_snapshot);
2556                         return Some(err(self, stmts));
2557                     }
2558                 }
2559                 Err(err) => {
2560                     err.cancel();
2561                 }
2562             }
2563
2564             self.restore_snapshot(pre_pat_snapshot);
2565             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2566                 // Consume statements for as long as possible.
2567                 Ok(Some(stmt)) => {
2568                     stmts.push(stmt);
2569                 }
2570                 Ok(None) => {
2571                     self.restore_snapshot(start_snapshot);
2572                     break;
2573                 }
2574                 // We couldn't parse either yet another statement missing it's
2575                 // enclosing block nor the next arm's pattern or closing brace.
2576                 Err(stmt_err) => {
2577                     stmt_err.cancel();
2578                     self.restore_snapshot(start_snapshot);
2579                     break;
2580                 }
2581             }
2582         }
2583         None
2584     }
2585
2586     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2587         // Used to check the `let_chains` and `if_let_guard` features mostly by scanning
2588         // `&&` tokens.
2589         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2590             match expr.kind {
2591                 ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, ref lhs, ref rhs) => {
2592                     let lhs_rslt = check_let_expr(lhs);
2593                     let rhs_rslt = check_let_expr(rhs);
2594                     (lhs_rslt.0 || rhs_rslt.0, false)
2595                 }
2596                 ExprKind::Let(..) => (true, true),
2597                 _ => (false, true),
2598             }
2599         }
2600         let attrs = self.parse_outer_attributes()?;
2601         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2602             let lo = this.token.span;
2603             let pat = this.parse_pat_allow_top_alt(
2604                 None,
2605                 RecoverComma::Yes,
2606                 RecoverColon::Yes,
2607                 CommaRecoveryMode::EitherTupleOrPipe,
2608             )?;
2609             let guard = if this.eat_keyword(kw::If) {
2610                 let if_span = this.prev_token.span;
2611                 let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
2612                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2613                 if has_let_expr {
2614                     if does_not_have_bin_op {
2615                         // Remove the last feature gating of a `let` expression since it's stable.
2616                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2617                     }
2618                     let span = if_span.to(cond.span);
2619                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2620                 }
2621                 Some(cond)
2622             } else {
2623                 None
2624             };
2625             let arrow_span = this.token.span;
2626             if let Err(mut err) = this.expect(&token::FatArrow) {
2627                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2628                 if TokenKind::FatArrow
2629                     .similar_tokens()
2630                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2631                 {
2632                     err.span_suggestion(
2633                         this.token.span,
2634                         "try using a fat arrow here",
2635                         "=>",
2636                         Applicability::MaybeIncorrect,
2637                     );
2638                     err.emit();
2639                     this.bump();
2640                 } else {
2641                     return Err(err);
2642                 }
2643             }
2644             let arm_start_span = this.token.span;
2645
2646             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2647                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2648                 err
2649             })?;
2650
2651             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2652                 && this.token != token::CloseDelim(Delimiter::Brace);
2653
2654             let hi = this.prev_token.span;
2655
2656             if require_comma {
2657                 let sm = this.sess.source_map();
2658                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2659                     let span = body.span;
2660                     return Ok((
2661                         ast::Arm {
2662                             attrs,
2663                             pat,
2664                             guard,
2665                             body,
2666                             span,
2667                             id: DUMMY_NODE_ID,
2668                             is_placeholder: false,
2669                         },
2670                         TrailingToken::None,
2671                     ));
2672                 }
2673                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2674                     .or_else(|mut err| {
2675                         if this.token == token::FatArrow {
2676                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2677                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2678                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2679                             && expr_lines.lines.len() == 2
2680                             {
2681                                 // We check whether there's any trailing code in the parse span,
2682                                 // if there isn't, we very likely have the following:
2683                                 //
2684                                 // X |     &Y => "y"
2685                                 //   |        --    - missing comma
2686                                 //   |        |
2687                                 //   |        arrow_span
2688                                 // X |     &X => "x"
2689                                 //   |      - ^^ self.token.span
2690                                 //   |      |
2691                                 //   |      parsed until here as `"y" & X`
2692                                 err.span_suggestion_short(
2693                                     arm_start_span.shrink_to_hi(),
2694                                     "missing a comma here to end this `match` arm",
2695                                     ",",
2696                                     Applicability::MachineApplicable,
2697                                 );
2698                                 return Err(err);
2699                             }
2700                         } else {
2701                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2702
2703                             // Try to parse a following `PAT =>`, if successful
2704                             // then we should recover.
2705                             let mut snapshot = this.create_snapshot_for_diagnostic();
2706                             let pattern_follows = snapshot
2707                                 .parse_pat_allow_top_alt(
2708                                     None,
2709                                     RecoverComma::Yes,
2710                                     RecoverColon::Yes,
2711                                     CommaRecoveryMode::EitherTupleOrPipe,
2712                                 )
2713                                 .map_err(|err| err.cancel())
2714                                 .is_ok();
2715                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2716                                 err.cancel();
2717                                 this.sess.emit_err(MissingCommaAfterMatchArm {
2718                                     span: hi.shrink_to_hi(),
2719                                 });
2720                                 return Ok(true);
2721                             }
2722                         }
2723                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2724                         Err(err)
2725                     })?;
2726             } else {
2727                 this.eat(&token::Comma);
2728             }
2729
2730             Ok((
2731                 ast::Arm {
2732                     attrs,
2733                     pat,
2734                     guard,
2735                     body: expr,
2736                     span: lo.to(hi),
2737                     id: DUMMY_NODE_ID,
2738                     is_placeholder: false,
2739                 },
2740                 TrailingToken::None,
2741             ))
2742         })
2743     }
2744
2745     /// Parses a `try {...}` expression (`try` token already eaten).
2746     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
2747         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2748         if self.eat_keyword(kw::Catch) {
2749             Err(CatchAfterTry { span: self.prev_token.span }
2750                 .into_diagnostic(&self.sess.span_diagnostic))
2751         } else {
2752             let span = span_lo.to(body.span);
2753             self.sess.gated_spans.gate(sym::try_blocks, span);
2754             Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body), attrs))
2755         }
2756     }
2757
2758     fn is_do_catch_block(&self) -> bool {
2759         self.token.is_keyword(kw::Do)
2760             && self.is_keyword_ahead(1, &[kw::Catch])
2761             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2762             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2763     }
2764
2765     fn is_do_yeet(&self) -> bool {
2766         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2767     }
2768
2769     fn is_try_block(&self) -> bool {
2770         self.token.is_keyword(kw::Try)
2771             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2772             && self.token.uninterpolated_span().rust_2018()
2773     }
2774
2775     /// Parses an `async move? {...}` expression.
2776     fn parse_async_block(&mut self) -> PResult<'a, P<Expr>> {
2777         let lo = self.token.span;
2778         self.expect_keyword(kw::Async)?;
2779         let capture_clause = self.parse_capture_clause()?;
2780         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2781         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2782         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2783     }
2784
2785     fn is_async_block(&self) -> bool {
2786         self.token.is_keyword(kw::Async)
2787             && ((
2788                 // `async move {`
2789                 self.is_keyword_ahead(1, &[kw::Move])
2790                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2791             ) || (
2792                 // `async {`
2793                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2794             ))
2795     }
2796
2797     fn is_certainly_not_a_block(&self) -> bool {
2798         self.look_ahead(1, |t| t.is_ident())
2799             && (
2800                 // `{ ident, ` cannot start a block.
2801                 self.look_ahead(2, |t| t == &token::Comma)
2802                     || self.look_ahead(2, |t| t == &token::Colon)
2803                         && (
2804                             // `{ ident: token, ` cannot start a block.
2805                             self.look_ahead(4, |t| t == &token::Comma) ||
2806                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2807                 self.look_ahead(3, |t| !t.can_begin_type())
2808                         )
2809             )
2810     }
2811
2812     fn maybe_parse_struct_expr(
2813         &mut self,
2814         qself: Option<&ast::QSelf>,
2815         path: &ast::Path,
2816     ) -> Option<PResult<'a, P<Expr>>> {
2817         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2818         if struct_allowed || self.is_certainly_not_a_block() {
2819             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2820                 return Some(Err(err));
2821             }
2822             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), true);
2823             if let (Ok(expr), false) = (&expr, struct_allowed) {
2824                 // This is a struct literal, but we don't can't accept them here.
2825                 self.sess.emit_err(StructLiteralNotAllowedHere {
2826                     span: expr.span,
2827                     sub: StructLiteralNotAllowedHereSugg {
2828                         left: path.span.shrink_to_lo(),
2829                         right: expr.span.shrink_to_hi(),
2830                     },
2831                 });
2832             }
2833             return Some(expr);
2834         }
2835         None
2836     }
2837
2838     pub(super) fn parse_struct_fields(
2839         &mut self,
2840         pth: ast::Path,
2841         recover: bool,
2842         close_delim: Delimiter,
2843     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2844         let mut fields = Vec::new();
2845         let mut base = ast::StructRest::None;
2846         let mut recover_async = false;
2847
2848         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2849             recover_async = true;
2850             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2851             e.help_use_latest_edition();
2852         };
2853
2854         while self.token != token::CloseDelim(close_delim) {
2855             if self.eat(&token::DotDot) || self.recover_struct_field_dots(close_delim) {
2856                 let exp_span = self.prev_token.span;
2857                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2858                 if self.check(&token::CloseDelim(close_delim)) {
2859                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2860                     break;
2861                 }
2862                 match self.parse_expr() {
2863                     Ok(e) => base = ast::StructRest::Base(e),
2864                     Err(mut e) if recover => {
2865                         e.emit();
2866                         self.recover_stmt();
2867                     }
2868                     Err(e) => return Err(e),
2869                 }
2870                 self.recover_struct_comma_after_dotdot(exp_span);
2871                 break;
2872             }
2873
2874             let recovery_field = self.find_struct_error_after_field_looking_code();
2875             let parsed_field = match self.parse_expr_field() {
2876                 Ok(f) => Some(f),
2877                 Err(mut e) => {
2878                     if pth == kw::Async {
2879                         async_block_err(&mut e, pth.span);
2880                     } else {
2881                         e.span_label(pth.span, "while parsing this struct");
2882                     }
2883                     e.emit();
2884
2885                     // If the next token is a comma, then try to parse
2886                     // what comes next as additional fields, rather than
2887                     // bailing out until next `}`.
2888                     if self.token != token::Comma {
2889                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2890                         if self.token != token::Comma {
2891                             break;
2892                         }
2893                     }
2894                     None
2895                 }
2896             };
2897
2898             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
2899             // A shorthand field can be turned into a full field with `:`.
2900             // We should point this out.
2901             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
2902
2903             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2904                 Ok(_) => {
2905                     if let Some(f) = parsed_field.or(recovery_field) {
2906                         // Only include the field if there's no parse error for the field name.
2907                         fields.push(f);
2908                     }
2909                 }
2910                 Err(mut e) => {
2911                     if pth == kw::Async {
2912                         async_block_err(&mut e, pth.span);
2913                     } else {
2914                         e.span_label(pth.span, "while parsing this struct");
2915                         if let Some(f) = recovery_field {
2916                             fields.push(f);
2917                             e.span_suggestion(
2918                                 self.prev_token.span.shrink_to_hi(),
2919                                 "try adding a comma",
2920                                 ",",
2921                                 Applicability::MachineApplicable,
2922                             );
2923                         } else if is_shorthand
2924                             && (AssocOp::from_token(&self.token).is_some()
2925                                 || matches!(&self.token.kind, token::OpenDelim(_))
2926                                 || self.token.kind == token::Dot)
2927                         {
2928                             // Looks like they tried to write a shorthand, complex expression.
2929                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
2930                             e.span_suggestion(
2931                                 ident.span.shrink_to_lo(),
2932                                 "try naming a field",
2933                                 &format!("{ident}: "),
2934                                 Applicability::HasPlaceholders,
2935                             );
2936                         }
2937                     }
2938                     if !recover {
2939                         return Err(e);
2940                     }
2941                     e.emit();
2942                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2943                     self.eat(&token::Comma);
2944                 }
2945             }
2946         }
2947         Ok((fields, base, recover_async))
2948     }
2949
2950     /// Precondition: already parsed the '{'.
2951     pub(super) fn parse_struct_expr(
2952         &mut self,
2953         qself: Option<ast::QSelf>,
2954         pth: ast::Path,
2955         recover: bool,
2956     ) -> PResult<'a, P<Expr>> {
2957         let lo = pth.span;
2958         let (fields, base, recover_async) =
2959             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
2960         let span = lo.to(self.token.span);
2961         self.expect(&token::CloseDelim(Delimiter::Brace))?;
2962         let expr = if recover_async {
2963             ExprKind::Err
2964         } else {
2965             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2966         };
2967         Ok(self.mk_expr(span, expr))
2968     }
2969
2970     /// Use in case of error after field-looking code: `S { foo: () with a }`.
2971     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
2972         match self.token.ident() {
2973             Some((ident, is_raw))
2974                 if (is_raw || !ident.is_reserved())
2975                     && self.look_ahead(1, |t| *t == token::Colon) =>
2976             {
2977                 Some(ast::ExprField {
2978                     ident,
2979                     span: self.token.span,
2980                     expr: self.mk_expr_err(self.token.span),
2981                     is_shorthand: false,
2982                     attrs: AttrVec::new(),
2983                     id: DUMMY_NODE_ID,
2984                     is_placeholder: false,
2985                 })
2986             }
2987             _ => None,
2988         }
2989     }
2990
2991     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
2992         if self.token != token::Comma {
2993             return;
2994         }
2995         self.sess.emit_err(CommaAfterBaseStruct {
2996             span: span.to(self.prev_token.span),
2997             comma: self.token.span,
2998         });
2999         self.recover_stmt();
3000     }
3001
3002     fn recover_struct_field_dots(&mut self, close_delim: Delimiter) -> bool {
3003         if !self.look_ahead(1, |t| *t == token::CloseDelim(close_delim))
3004             && self.eat(&token::DotDotDot)
3005         {
3006             // recover from typo of `...`, suggest `..`
3007             let span = self.prev_token.span;
3008             self.sess.emit_err(MissingDotDot { token_span: span, sugg_span: span });
3009             return true;
3010         }
3011         false
3012     }
3013
3014     /// Parses `ident (COLON expr)?`.
3015     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3016         let attrs = self.parse_outer_attributes()?;
3017         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3018             let lo = this.token.span;
3019
3020             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3021             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3022             let (ident, expr) = if is_shorthand {
3023                 // Mimic `x: x` for the `x` field shorthand.
3024                 let ident = this.parse_ident_common(false)?;
3025                 let path = ast::Path::from_ident(ident);
3026                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path)))
3027             } else {
3028                 let ident = this.parse_field_name()?;
3029                 this.error_on_eq_field_init(ident);
3030                 this.bump(); // `:`
3031                 (ident, this.parse_expr()?)
3032             };
3033
3034             Ok((
3035                 ast::ExprField {
3036                     ident,
3037                     span: lo.to(expr.span),
3038                     expr,
3039                     is_shorthand,
3040                     attrs,
3041                     id: DUMMY_NODE_ID,
3042                     is_placeholder: false,
3043                 },
3044                 TrailingToken::MaybeComma,
3045             ))
3046         })
3047     }
3048
3049     /// Check for `=`. This means the source incorrectly attempts to
3050     /// initialize a field with an eq rather than a colon.
3051     fn error_on_eq_field_init(&self, field_name: Ident) {
3052         if self.token != token::Eq {
3053             return;
3054         }
3055
3056         self.sess.emit_err(EqFieldInit {
3057             span: self.token.span,
3058             eq: field_name.span.shrink_to_hi().to(self.token.span),
3059         });
3060     }
3061
3062     fn err_dotdotdot_syntax(&self, span: Span) {
3063         self.sess.emit_err(DotDotDot { span });
3064     }
3065
3066     fn err_larrow_operator(&self, span: Span) {
3067         self.sess.emit_err(LeftArrowOperator { span });
3068     }
3069
3070     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3071         ExprKind::AssignOp(binop, lhs, rhs)
3072     }
3073
3074     fn mk_range(
3075         &mut self,
3076         start: Option<P<Expr>>,
3077         end: Option<P<Expr>>,
3078         limits: RangeLimits,
3079     ) -> ExprKind {
3080         if end.is_none() && limits == RangeLimits::Closed {
3081             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3082             ExprKind::Err
3083         } else {
3084             ExprKind::Range(start, end, limits)
3085         }
3086     }
3087
3088     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3089         ExprKind::Unary(unop, expr)
3090     }
3091
3092     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3093         ExprKind::Binary(binop, lhs, rhs)
3094     }
3095
3096     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3097         ExprKind::Index(expr, idx)
3098     }
3099
3100     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3101         ExprKind::Call(f, args)
3102     }
3103
3104     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3105         let span = lo.to(self.prev_token.span);
3106         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg));
3107         self.recover_from_await_method_call();
3108         await_expr
3109     }
3110
3111     pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3112         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3113     }
3114
3115     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
3116         P(Expr { kind, span, attrs: AttrVec::new(), id: DUMMY_NODE_ID, tokens: None })
3117     }
3118
3119     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3120         self.mk_expr(span, ExprKind::Err)
3121     }
3122
3123     /// Create expression span ensuring the span of the parent node
3124     /// is larger than the span of lhs and rhs, including the attributes.
3125     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3126         lhs.attrs
3127             .iter()
3128             .find(|a| a.style == AttrStyle::Outer)
3129             .map_or(lhs_span, |a| a.span)
3130             .to(rhs_span)
3131     }
3132
3133     fn collect_tokens_for_expr(
3134         &mut self,
3135         attrs: AttrWrapper,
3136         f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
3137     ) -> PResult<'a, P<Expr>> {
3138         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3139             let res = f(this, attrs)?;
3140             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3141                 && this.token.kind == token::Semi
3142             {
3143                 TrailingToken::Semi
3144             } else if this.token.kind == token::Gt {
3145                 TrailingToken::Gt
3146             } else {
3147                 // FIXME - pass this through from the place where we know
3148                 // we need a comma, rather than assuming that `#[attr] expr,`
3149                 // always captures a trailing comma
3150                 TrailingToken::MaybeComma
3151             };
3152             Ok((res, trailing))
3153         })
3154     }
3155 }