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     BinaryFloatLiteralNotSupported, BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct,
  11     ComparisonInterpretedAsGeneric, ComparisonOrShiftInterpretedAsGenericSugg,
  12     DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedExpressionFoundLet,
  13     FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
  14     HexadecimalFloatLiteralNotSupported, IfExpressionMissingCondition,
  15     IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub, IntLiteralTooLarge,
  16     InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
  17     InvalidFloatLiteralSuffix, InvalidFloatLiteralWidth, InvalidIntLiteralWidth,
  18     InvalidInterpolatedExpression, InvalidLiteralSuffix, InvalidLiteralSuffixOnTupleIndex,
  19     InvalidLogicalOperator, InvalidLogicalOperatorSub, InvalidNumLiteralBasePrefix,
  20     InvalidNumLiteralSuffix, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
  21     LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
  22     MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
  23     MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray, NoFieldsForFnCall,
  24     NotAsNegationOperator, NotAsNegationOperatorSub, OctalFloatLiteralNotSupported,
  25     OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
  26     RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
  27     StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedTokenAfterLabel,
  28     UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
  29 };
  30 use crate::maybe_recover_from_interpolated_ty_qpath;
  31
  32 use core::mem;
  33 use rustc_ast::ptr::P;
  34 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
  35 use rustc_ast::tokenstream::Spacing;
  36 use rustc_ast::util::classify;
  37 use rustc_ast::util::literal::LitError;
  38 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  39 use rustc_ast::visit::Visitor;
  40 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  41 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  42 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  43 use rustc_ast::{ClosureBinder, StmtKind};
  44 use rustc_ast_pretty::pprust;
  45 use rustc_errors::IntoDiagnostic;
  46 use rustc_errors::{Applicability, Diagnostic, PResult};
  47 use rustc_session::errors::ExprParenthesesNeeded;
  48 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  49 use rustc_session::lint::BuiltinLintDiagnostics;
  50 use rustc_span::source_map::{self, Span, Spanned};
  51 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  52 use rustc_span::{BytePos, Pos};
  53
  54 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  55 /// dropped into the token stream, which happens while parsing the result of
  56 /// macro expansion). Placement of these is not as complex as I feared it would
  57 /// be. The important thing is to make sure that lookahead doesn't balk at
  58 /// `token::Interpolated` tokens.
  59 macro_rules! maybe_whole_expr {
  60     ($p:expr) => {
  61         if let token::Interpolated(nt) = &$p.token.kind {
  62             match &**nt {
  63                 token::NtExpr(e) | token::NtLiteral(e) => {
  64                     let e = e.clone();
  65                     $p.bump();
  66                     return Ok(e);
  67                 }
  68                 token::NtPath(path) => {
  69                     let path = (**path).clone();
  70                     $p.bump();
  71                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Path(None, path)));
  72                 }
  73                 token::NtBlock(block) => {
  74                     let block = block.clone();
  75                     $p.bump();
  76                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Block(block, None)));
  77                 }
  78                 _ => {}
  79             };
  80         }
  81     };
  82 }
  83
  84 #[derive(Debug)]
  85 pub(super) enum LhsExpr {
  86     NotYetParsed,
  87     AttributesParsed(AttrWrapper),
  88     AlreadyParsed(P<Expr>),
  89 }
  90
  91 impl From<Option<AttrWrapper>> for LhsExpr {
  92     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  93     /// and `None` into `LhsExpr::NotYetParsed`.
  94     ///
  95     /// This conversion does not allocate.
  96     fn from(o: Option<AttrWrapper>) -> Self {
  97         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
  98     }
  99 }
 100
 101 impl From<P<Expr>> for LhsExpr {
 102     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
 103     ///
 104     /// This conversion does not allocate.
 105     fn from(expr: P<Expr>) -> Self {
 106         LhsExpr::AlreadyParsed(expr)
 107     }
 108 }
 109
 110 impl<'a> Parser<'a> {
 111     /// Parses an expression.
 112     #[inline]
 113     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
 114         self.current_closure.take();
 115
 116         self.parse_expr_res(Restrictions::empty(), None)
 117     }
 118
 119     /// Parses an expression, forcing tokens to be collected
 120     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 121         self.collect_tokens_no_attrs(|this| this.parse_expr())
 122     }
 123
 124     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 125         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 126     }
 127
 128     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 129         match self.parse_expr() {
 130             Ok(expr) => Ok(expr),
 131             Err(mut err) => match self.token.ident() {
 132                 Some((Ident { name: kw::Underscore, .. }, false))
 133                     if self.look_ahead(1, |t| t == &token::Comma) =>
 134                 {
 135                     // Special-case handling of `foo(_, _, _)`
 136                     err.emit();
 137                     self.bump();
 138                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err))
 139                 }
 140                 _ => Err(err),
 141             },
 142         }
 143     }
 144
 145     /// Parses a sequence of expressions delimited by parentheses.
 146     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 147         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 148     }
 149
 150     /// Parses an expression, subject to the given restrictions.
 151     #[inline]
 152     pub(super) fn parse_expr_res(
 153         &mut self,
 154         r: Restrictions,
 155         already_parsed_attrs: Option<AttrWrapper>,
 156     ) -> PResult<'a, P<Expr>> {
 157         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 158     }
 159
 160     /// Parses an associative expression.
 161     ///
 162     /// This parses an expression accounting for associativity and precedence of the operators in
 163     /// the expression.
 164     #[inline]
 165     fn parse_assoc_expr(
 166         &mut self,
 167         already_parsed_attrs: Option<AttrWrapper>,
 168     ) -> PResult<'a, P<Expr>> {
 169         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 170     }
 171
 172     /// Parses an associative expression with operators of at least `min_prec` precedence.
 173     pub(super) fn parse_assoc_expr_with(
 174         &mut self,
 175         min_prec: usize,
 176         lhs: LhsExpr,
 177     ) -> PResult<'a, P<Expr>> {
 178         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 179             expr
 180         } else {
 181             let attrs = match lhs {
 182                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 183                 _ => None,
 184             };
 185             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 186                 return self.parse_prefix_range_expr(attrs);
 187             } else {
 188                 self.parse_prefix_expr(attrs)?
 189             }
 190         };
 191         let last_type_ascription_set = self.last_type_ascription.is_some();
 192
 193         if !self.should_continue_as_assoc_expr(&lhs) {
 194             self.last_type_ascription = None;
 195             return Ok(lhs);
 196         }
 197
 198         self.expected_tokens.push(TokenType::Operator);
 199         while let Some(op) = self.check_assoc_op() {
 200             // Adjust the span for interpolated LHS to point to the `$lhs` token
 201             // and not to what it refers to.
 202             let lhs_span = match self.prev_token.kind {
 203                 TokenKind::Interpolated(..) => self.prev_token.span,
 204                 _ => lhs.span,
 205             };
 206
 207             let cur_op_span = self.token.span;
 208             let restrictions = if op.node.is_assign_like() {
 209                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 210             } else {
 211                 self.restrictions
 212             };
 213             let prec = op.node.precedence();
 214             if prec < min_prec {
 215                 break;
 216             }
 217             // Check for deprecated `...` syntax
 218             if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
 219                 self.err_dotdotdot_syntax(self.token.span);
 220             }
 221
 222             if self.token == token::LArrow {
 223                 self.err_larrow_operator(self.token.span);
 224             }
 225
 226             self.bump();
 227             if op.node.is_comparison() {
 228                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 229                     return Ok(expr);
 230                 }
 231             }
 232
 233             // Look for JS' `===` and `!==` and recover
 234             if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
 235                 && self.token.kind == token::Eq
 236                 && self.prev_token.span.hi() == self.token.span.lo()
 237             {
 238                 let sp = op.span.to(self.token.span);
 239                 let sugg = match op.node {
 240                     AssocOp::Equal => "==",
 241                     AssocOp::NotEqual => "!=",
 242                     _ => unreachable!(),
 243                 }
 244                 .into();
 245                 let invalid = format!("{}=", &sugg);
 246                 self.sess.emit_err(InvalidComparisonOperator {
 247                     span: sp,
 248                     invalid: invalid.clone(),
 249                     sub: InvalidComparisonOperatorSub::Correctable {
 250                         span: sp,
 251                         invalid,
 252                         correct: sugg,
 253                     },
 254                 });
 255                 self.bump();
 256             }
 257
 258             // Look for PHP's `<>` and recover
 259             if op.node == AssocOp::Less
 260                 && self.token.kind == token::Gt
 261                 && self.prev_token.span.hi() == self.token.span.lo()
 262             {
 263                 let sp = op.span.to(self.token.span);
 264                 self.sess.emit_err(InvalidComparisonOperator {
 265                     span: sp,
 266                     invalid: "<>".into(),
 267                     sub: InvalidComparisonOperatorSub::Correctable {
 268                         span: sp,
 269                         invalid: "<>".into(),
 270                         correct: "!=".into(),
 271                     },
 272                 });
 273                 self.bump();
 274             }
 275
 276             // Look for C++'s `<=>` and recover
 277             if op.node == AssocOp::LessEqual
 278                 && self.token.kind == token::Gt
 279                 && self.prev_token.span.hi() == self.token.span.lo()
 280             {
 281                 let sp = op.span.to(self.token.span);
 282                 self.sess.emit_err(InvalidComparisonOperator {
 283                     span: sp,
 284                     invalid: "<=>".into(),
 285                     sub: InvalidComparisonOperatorSub::Spaceship(sp),
 286                 });
 287                 self.bump();
 288             }
 289
 290             if self.prev_token == token::BinOp(token::Plus)
 291                 && self.token == token::BinOp(token::Plus)
 292                 && self.prev_token.span.between(self.token.span).is_empty()
 293             {
 294                 let op_span = self.prev_token.span.to(self.token.span);
 295                 // Eat the second `+`
 296                 self.bump();
 297                 lhs = self.recover_from_postfix_increment(lhs, op_span)?;
 298                 continue;
 299             }
 300
 301             let op = op.node;
 302             // Special cases:
 303             if op == AssocOp::As {
 304                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 305                 continue;
 306             } else if op == AssocOp::Colon {
 307                 lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
 308                 continue;
 309             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 310                 // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
 311                 // generalise it to the Fixity::None code.
 312                 lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?;
 313                 break;
 314             }
 315
 316             let fixity = op.fixity();
 317             let prec_adjustment = match fixity {
 318                 Fixity::Right => 0,
 319                 Fixity::Left => 1,
 320                 // We currently have no non-associative operators that are not handled above by
 321                 // the special cases. The code is here only for future convenience.
 322                 Fixity::None => 1,
 323             };
 324             let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
 325                 this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 326             })?;
 327
 328             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
 329             lhs = match op {
 330                 AssocOp::Add
 331                 | AssocOp::Subtract
 332                 | AssocOp::Multiply
 333                 | AssocOp::Divide
 334                 | AssocOp::Modulus
 335                 | AssocOp::LAnd
 336                 | AssocOp::LOr
 337                 | AssocOp::BitXor
 338                 | AssocOp::BitAnd
 339                 | AssocOp::BitOr
 340                 | AssocOp::ShiftLeft
 341                 | AssocOp::ShiftRight
 342                 | AssocOp::Equal
 343                 | AssocOp::Less
 344                 | AssocOp::LessEqual
 345                 | AssocOp::NotEqual
 346                 | AssocOp::Greater
 347                 | AssocOp::GreaterEqual => {
 348                     let ast_op = op.to_ast_binop().unwrap();
 349                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 350                     self.mk_expr(span, binary)
 351                 }
 352                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span)),
 353                 AssocOp::AssignOp(k) => {
 354                     let aop = match k {
 355                         token::Plus => BinOpKind::Add,
 356                         token::Minus => BinOpKind::Sub,
 357                         token::Star => BinOpKind::Mul,
 358                         token::Slash => BinOpKind::Div,
 359                         token::Percent => BinOpKind::Rem,
 360                         token::Caret => BinOpKind::BitXor,
 361                         token::And => BinOpKind::BitAnd,
 362                         token::Or => BinOpKind::BitOr,
 363                         token::Shl => BinOpKind::Shl,
 364                         token::Shr => BinOpKind::Shr,
 365                     };
 366                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 367                     self.mk_expr(span, aopexpr)
 368                 }
 369                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 370                     self.span_bug(span, "AssocOp should have been handled by special case")
 371                 }
 372             };
 373
 374             if let Fixity::None = fixity {
 375                 break;
 376             }
 377         }
 378         if last_type_ascription_set {
 379             self.last_type_ascription = None;
 380         }
 381         Ok(lhs)
 382     }
 383
 384     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 385         match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
 386             // Semi-statement forms are odd:
 387             // See https://github.com/rust-lang/rust/issues/29071
 388             (true, None) => false,
 389             (false, _) => true, // Continue parsing the expression.
 390             // An exhaustive check is done in the following block, but these are checked first
 391             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 392             // want to keep their span info to improve diagnostics in these cases in a later stage.
 393             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 394             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 395             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 396             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 397             // `if x { a } else { b } && if y { c } else { d }`
 398             if !self.look_ahead(1, |t| t.is_used_keyword()) => {
 399                 // These cases are ambiguous and can't be identified in the parser alone.
 400                 let sp = self.sess.source_map().start_point(self.token.span);
 401                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 402                 false
 403             }
 404             (true, Some(AssocOp::LAnd)) |
 405             (true, Some(AssocOp::LOr)) |
 406             (true, Some(AssocOp::BitOr)) => {
 407                 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the
 408                 // above due to #74233.
 409                 // These cases are ambiguous and can't be identified in the parser alone.
 410                 //
 411                 // Bitwise AND is left out because guessing intent is hard. We can make
 412                 // suggestions based on the assumption that double-refs are rarely intentional,
 413                 // and closures are distinct enough that they don't get mixed up with their
 414                 // return value.
 415                 let sp = self.sess.source_map().start_point(self.token.span);
 416                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 417                 false
 418             }
 419             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 420             (true, Some(_)) => {
 421                 self.error_found_expr_would_be_stmt(lhs);
 422                 true
 423             }
 424         }
 425     }
 426
 427     /// We've found an expression that would be parsed as a statement,
 428     /// but the next token implies this should be parsed as an expression.
 429     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 430     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 431         self.sess.emit_err(FoundExprWouldBeStmt {
 432             span: self.token.span,
 433             token: self.token.clone(),
 434             suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
 435         });
 436     }
 437
 438     /// Possibly translate the current token to an associative operator.
 439     /// The method does not advance the current token.
 440     ///
 441     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 442     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 443         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 444             // When parsing const expressions, stop parsing when encountering `>`.
 445             (
 446                 Some(
 447                     AssocOp::ShiftRight
 448                     | AssocOp::Greater
 449                     | AssocOp::GreaterEqual
 450                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 451                 ),
 452                 _,
 453             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 454                 return None;
 455             }
 456             (Some(op), _) => (op, self.token.span),
 457             (None, Some((Ident { name: sym::and, span }, false))) => {
 458                 self.sess.emit_err(InvalidLogicalOperator {
 459                     span: self.token.span,
 460                     incorrect: "and".into(),
 461                     sub: InvalidLogicalOperatorSub::Conjunction(self.token.span),
 462                 });
 463                 (AssocOp::LAnd, span)
 464             }
 465             (None, Some((Ident { name: sym::or, span }, false))) => {
 466                 self.sess.emit_err(InvalidLogicalOperator {
 467                     span: self.token.span,
 468                     incorrect: "or".into(),
 469                     sub: InvalidLogicalOperatorSub::Disjunction(self.token.span),
 470                 });
 471                 (AssocOp::LOr, span)
 472             }
 473             _ => return None,
 474         };
 475         Some(source_map::respan(span, op))
 476     }
 477
 478     /// Checks if this expression is a successfully parsed statement.
 479     fn expr_is_complete(&self, e: &Expr) -> bool {
 480         self.restrictions.contains(Restrictions::STMT_EXPR)
 481             && !classify::expr_requires_semi_to_be_stmt(e)
 482     }
 483
 484     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 485     /// The other two variants are handled in `parse_prefix_range_expr` below.
 486     fn parse_range_expr(
 487         &mut self,
 488         prec: usize,
 489         lhs: P<Expr>,
 490         op: AssocOp,
 491         cur_op_span: Span,
 492     ) -> PResult<'a, P<Expr>> {
 493         let rhs = if self.is_at_start_of_range_notation_rhs() {
 494             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 495         } else {
 496             None
 497         };
 498         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 499         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 500         let limits =
 501             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 502         let range = self.mk_range(Some(lhs), rhs, limits);
 503         Ok(self.mk_expr(span, range))
 504     }
 505
 506     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 507         if self.token.can_begin_expr() {
 508             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 509             if self.token == token::OpenDelim(Delimiter::Brace) {
 510                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 511             }
 512             true
 513         } else {
 514             false
 515         }
 516     }
 517
 518     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 519     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 520         // Check for deprecated `...` syntax.
 521         if self.token == token::DotDotDot {
 522             self.err_dotdotdot_syntax(self.token.span);
 523         }
 524
 525         debug_assert!(
 526             [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 527             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 528             self.token
 529         );
 530
 531         let limits = match self.token.kind {
 532             token::DotDot => RangeLimits::HalfOpen,
 533             _ => RangeLimits::Closed,
 534         };
 535         let op = AssocOp::from_token(&self.token);
 536         // FIXME: `parse_prefix_range_expr` is called when the current
 537         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 538         // parsed attributes, then trying to parse them here will always fail.
 539         // We should figure out how we want attributes on range expressions to work.
 540         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 541         self.collect_tokens_for_expr(attrs, |this, attrs| {
 542             let lo = this.token.span;
 543             this.bump();
 544             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 545                 // RHS must be parsed with more associativity than the dots.
 546                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 547                     .map(|x| (lo.to(x.span), Some(x)))?
 548             } else {
 549                 (lo, None)
 550             };
 551             let range = this.mk_range(None, opt_end, limits);
 552             Ok(this.mk_expr_with_attrs(span, range, attrs))
 553         })
 554     }
 555
 556     /// Parses a prefix-unary-operator expr.
 557     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 558         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 559         let lo = self.token.span;
 560
 561         macro_rules! make_it {
 562             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 563                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 564                     let (hi, ex) = $body?;
 565                     Ok($this.mk_expr_with_attrs(lo.to(hi), ex, attrs))
 566                 })
 567             };
 568         }
 569
 570         let this = self;
 571
 572         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 573         match this.token.uninterpolate().kind {
 574             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr`
 575             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr`
 576             token::BinOp(token::Minus) => {
 577                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 578             } // `-expr`
 579             token::BinOp(token::Star) => {
 580                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 581             } // `*expr`
 582             token::BinOp(token::And) | token::AndAnd => {
 583                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 584             }
 585             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 586                 let mut err =
 587                     LeadingPlusNotSupported { span: lo, remove_plus: None, add_parentheses: None };
 588
 589                 // a block on the LHS might have been intended to be an expression instead
 590                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 591                     err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
 592                 } else {
 593                     err.remove_plus = Some(lo);
 594                 }
 595                 this.sess.emit_err(err);
 596
 597                 this.bump();
 598                 this.parse_prefix_expr(None)
 599             } // `+expr`
 600             // Recover from `++x`:
 601             token::BinOp(token::Plus)
 602                 if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
 603             {
 604                 let prev_is_semi = this.prev_token == token::Semi;
 605                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
 606                 // Eat both `+`s.
 607                 this.bump();
 608                 this.bump();
 609
 610                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
 611                 this.recover_from_prefix_increment(operand_expr, pre_span, prev_is_semi)
 612             }
 613             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 614                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 615             }
 616             token::Ident(..) if this.is_mistaken_not_ident_negation() => {
 617                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 618             }
 619             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 620         }
 621     }
 622
 623     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 624         self.bump();
 625         let expr = self.parse_prefix_expr(None);
 626         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 627         Ok((lo.to(span), expr))
 628     }
 629
 630     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 631         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 632         Ok((span, self.mk_unary(op, expr)))
 633     }
 634
 635     // Recover on `!` suggesting for bitwise negation instead.
 636     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 637         self.sess.emit_err(TildeAsUnaryOperator(lo));
 638
 639         self.parse_unary_expr(lo, UnOp::Not)
 640     }
 641
 642     /// Parse `box expr`.
 643     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 644         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 645         self.sess.gated_spans.gate(sym::box_syntax, span);
 646         Ok((span, ExprKind::Box(expr)))
 647     }
 648
 649     fn is_mistaken_not_ident_negation(&self) -> bool {
 650         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 651             // These tokens can start an expression after `!`, but
 652             // can't continue an expression after an ident
 653             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 654             token::Literal(..) | token::Pound => true,
 655             _ => t.is_whole_expr(),
 656         };
 657         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 658     }
 659
 660     /// Recover on `not expr` in favor of `!expr`.
 661     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 662         // Emit the error...
 663         let negated_token = self.look_ahead(1, |t| t.clone());
 664
 665         let sub_diag = if negated_token.is_numeric_lit() {
 666             NotAsNegationOperatorSub::SuggestNotBitwise
 667         } else if negated_token.is_bool_lit() {
 668             NotAsNegationOperatorSub::SuggestNotLogical
 669         } else {
 670             NotAsNegationOperatorSub::SuggestNotDefault
 671         };
 672
 673         self.sess.emit_err(NotAsNegationOperator {
 674             negated: negated_token.span,
 675             negated_desc: super::token_descr(&negated_token),
 676             // Span the `not` plus trailing whitespace to avoid
 677             // trailing whitespace after the `!` in our suggestion
 678             sub: sub_diag(
 679                 self.sess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
 680             ),
 681         });
 682
 683         // ...and recover!
 684         self.parse_unary_expr(lo, UnOp::Not)
 685     }
 686
 687     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 688     fn interpolated_or_expr_span(
 689         &self,
 690         expr: PResult<'a, P<Expr>>,
 691     ) -> PResult<'a, (Span, P<Expr>)> {
 692         expr.map(|e| {
 693             (
 694                 match self.prev_token.kind {
 695                     TokenKind::Interpolated(..) => self.prev_token.span,
 696                     _ => e.span,
 697                 },
 698                 e,
 699             )
 700         })
 701     }
 702
 703     fn parse_assoc_op_cast(
 704         &mut self,
 705         lhs: P<Expr>,
 706         lhs_span: Span,
 707         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 708     ) -> PResult<'a, P<Expr>> {
 709         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 710             this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, rhs.span), expr_kind(lhs, rhs))
 711         };
 712
 713         // Save the state of the parser before parsing type normally, in case there is a
 714         // LessThan comparison after this cast.
 715         let parser_snapshot_before_type = self.clone();
 716         let cast_expr = match self.parse_as_cast_ty() {
 717             Ok(rhs) => mk_expr(self, lhs, rhs),
 718             Err(type_err) => {
 719                 // Rewind to before attempting to parse the type with generics, to recover
 720                 // from situations like `x as usize < y` in which we first tried to parse
 721                 // `usize < y` as a type with generic arguments.
 722                 let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
 723
 724                 // Check for typo of `'a: loop { break 'a }` with a missing `'`.
 725                 match (&lhs.kind, &self.token.kind) {
 726                     (
 727                         // `foo: `
 728                         ExprKind::Path(None, ast::Path { segments, .. }),
 729                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
 730                     ) if segments.len() == 1 => {
 731                         let snapshot = self.create_snapshot_for_diagnostic();
 732                         let label = Label {
 733                             ident: Ident::from_str_and_span(
 734                                 &format!("'{}", segments[0].ident),
 735                                 segments[0].ident.span,
 736                             ),
 737                         };
 738                         match self.parse_labeled_expr(label, false) {
 739                             Ok(expr) => {
 740                                 type_err.cancel();
 741                                 self.sess.emit_err(MalformedLoopLabel {
 742                                     span: label.ident.span,
 743                                     correct_label: label.ident,
 744                                 });
 745                                 return Ok(expr);
 746                             }
 747                             Err(err) => {
 748                                 err.cancel();
 749                                 self.restore_snapshot(snapshot);
 750                             }
 751                         }
 752                     }
 753                     _ => {}
 754                 }
 755
 756                 match self.parse_path(PathStyle::Expr) {
 757                     Ok(path) => {
 758                         let span_after_type = parser_snapshot_after_type.token.span;
 759                         let expr = mk_expr(
 760                             self,
 761                             lhs,
 762                             self.mk_ty(path.span, TyKind::Path(None, path.clone())),
 763                         );
 764
 765                         let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
 766                         let suggestion = ComparisonOrShiftInterpretedAsGenericSugg {
 767                             left: expr.span.shrink_to_lo(),
 768                             right: expr.span.shrink_to_hi(),
 769                         };
 770
 771                         match self.token.kind {
 772                             token::Lt => self.sess.emit_err(ComparisonInterpretedAsGeneric {
 773                                 comparison: self.token.span,
 774                                 r#type: path,
 775                                 args: args_span,
 776                                 suggestion,
 777                             }),
 778                             token::BinOp(token::Shl) => {
 779                                 self.sess.emit_err(ShiftInterpretedAsGeneric {
 780                                     shift: self.token.span,
 781                                     r#type: path,
 782                                     args: args_span,
 783                                     suggestion,
 784                                 })
 785                             }
 786                             _ => {
 787                                 // We can end up here even without `<` being the next token, for
 788                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 789                                 // but `parse_path` returns `Ok` on them due to error recovery.
 790                                 // Return original error and parser state.
 791                                 *self = parser_snapshot_after_type;
 792                                 return Err(type_err);
 793                             }
 794                         };
 795
 796                         // Successfully parsed the type path leaving a `<` yet to parse.
 797                         type_err.cancel();
 798
 799                         // Keep `x as usize` as an expression in AST and continue parsing.
 800                         expr
 801                     }
 802                     Err(path_err) => {
 803                         // Couldn't parse as a path, return original error and parser state.
 804                         path_err.cancel();
 805                         *self = parser_snapshot_after_type;
 806                         return Err(type_err);
 807                     }
 808                 }
 809             }
 810         };
 811
 812         self.parse_and_disallow_postfix_after_cast(cast_expr)
 813     }
 814
 815     /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
 816     /// then emits an error and returns the newly parsed tree.
 817     /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
 818     fn parse_and_disallow_postfix_after_cast(
 819         &mut self,
 820         cast_expr: P<Expr>,
 821     ) -> PResult<'a, P<Expr>> {
 822         let span = cast_expr.span;
 823         let (cast_kind, maybe_ascription_span) =
 824             if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
 825                 ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi())))
 826             } else {
 827                 ("cast", None)
 828             };
 829
 830         // Save the memory location of expr before parsing any following postfix operators.
 831         // This will be compared with the memory location of the output expression.
 832         // If they different we can assume we parsed another expression because the existing expression is not reallocated.
 833         let addr_before = &*cast_expr as *const _ as usize;
 834         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 835         let changed = addr_before != &*with_postfix as *const _ as usize;
 836
 837         // Check if an illegal postfix operator has been added after the cast.
 838         // If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator.
 839         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) || changed {
 840             let msg = format!(
 841                 "{cast_kind} cannot be followed by {}",
 842                 match with_postfix.kind {
 843                     ExprKind::Index(_, _) => "indexing",
 844                     ExprKind::Try(_) => "`?`",
 845                     ExprKind::Field(_, _) => "a field access",
 846                     ExprKind::MethodCall(_, _, _, _) => "a method call",
 847                     ExprKind::Call(_, _) => "a function call",
 848                     ExprKind::Await(_) => "`.await`",
 849                     ExprKind::Err => return Ok(with_postfix),
 850                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 851                 }
 852             );
 853             let mut err = self.struct_span_err(span, &msg);
 854
 855             let suggest_parens = |err: &mut Diagnostic| {
 856                 let suggestions = vec![
 857                     (span.shrink_to_lo(), "(".to_string()),
 858                     (span.shrink_to_hi(), ")".to_string()),
 859                 ];
 860                 err.multipart_suggestion(
 861                     "try surrounding the expression in parentheses",
 862                     suggestions,
 863                     Applicability::MachineApplicable,
 864                 );
 865             };
 866
 867             // If type ascription is "likely an error", the user will already be getting a useful
 868             // help message, and doesn't need a second.
 869             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 870                 self.maybe_annotate_with_ascription(&mut err, false);
 871             } else if let Some(ascription_span) = maybe_ascription_span {
 872                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 873                 if is_nightly {
 874                     suggest_parens(&mut err);
 875                 }
 876                 err.span_suggestion(
 877                     ascription_span,
 878                     &format!(
 879                         "{}remove the type ascription",
 880                         if is_nightly { "alternatively, " } else { "" }
 881                     ),
 882                     "",
 883                     if is_nightly {
 884                         Applicability::MaybeIncorrect
 885                     } else {
 886                         Applicability::MachineApplicable
 887                     },
 888                 );
 889             } else {
 890                 suggest_parens(&mut err);
 891             }
 892             err.emit();
 893         };
 894         Ok(with_postfix)
 895     }
 896
 897     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 898         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 899         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 900         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 901         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 902         Ok(lhs)
 903     }
 904
 905     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 906     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 907         self.expect_and()?;
 908         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 909         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 910         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 911         let expr = self.parse_prefix_expr(None);
 912         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 913         let span = lo.to(hi);
 914         if let Some(lt) = lifetime {
 915             self.error_remove_borrow_lifetime(span, lt.ident.span);
 916         }
 917         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 918     }
 919
 920     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 921         self.sess.emit_err(LifetimeInBorrowExpression { span, lifetime_span: lt_span });
 922     }
 923
 924     /// Parse `mut?` or `raw [ const | mut ]`.
 925     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 926         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 927             // `raw [ const | mut ]`.
 928             let found_raw = self.eat_keyword(kw::Raw);
 929             assert!(found_raw);
 930             let mutability = self.parse_const_or_mut().unwrap();
 931             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 932             (ast::BorrowKind::Raw, mutability)
 933         } else {
 934             // `mut?`
 935             (ast::BorrowKind::Ref, self.parse_mutability())
 936         }
 937     }
 938
 939     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 940     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 941         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 942         self.collect_tokens_for_expr(attrs, |this, attrs| {
 943             let base = this.parse_bottom_expr();
 944             let (span, base) = this.interpolated_or_expr_span(base)?;
 945             this.parse_dot_or_call_expr_with(base, span, attrs)
 946         })
 947     }
 948
 949     pub(super) fn parse_dot_or_call_expr_with(
 950         &mut self,
 951         e0: P<Expr>,
 952         lo: Span,
 953         mut attrs: ast::AttrVec,
 954     ) -> PResult<'a, P<Expr>> {
 955         // Stitch the list of outer attributes onto the return value.
 956         // A little bit ugly, but the best way given the current code
 957         // structure
 958         let res = self.parse_dot_or_call_expr_with_(e0, lo);
 959         if attrs.is_empty() {
 960             res
 961         } else {
 962             res.map(|expr| {
 963                 expr.map(|mut expr| {
 964                     attrs.extend(expr.attrs);
 965                     expr.attrs = attrs;
 966                     expr
 967                 })
 968             })
 969         }
 970     }
 971
 972     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 973         loop {
 974             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 975                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 976                 // which could be suggested otherwise
 977                 self.eat_noexpect(&token::Question)
 978             } else {
 979                 self.eat(&token::Question)
 980             };
 981             if has_question {
 982                 // `expr?`
 983                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
 984                 continue;
 985             }
 986             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 987                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 988                 // which could be suggested otherwise
 989                 self.eat_noexpect(&token::Dot)
 990             } else {
 991                 self.eat(&token::Dot)
 992             };
 993             if has_dot {
 994                 // expr.f
 995                 e = self.parse_dot_suffix_expr(lo, e)?;
 996                 continue;
 997             }
 998             if self.expr_is_complete(&e) {
 999                 return Ok(e);
1000             }
1001             e = match self.token.kind {
1002                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1003                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1004                 _ => return Ok(e),
1005             }
1006         }
1007     }
1008
1009     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1010         self.look_ahead(1, |t| t.is_ident())
1011             && self.look_ahead(2, |t| t == &token::Colon)
1012             && self.look_ahead(3, |t| t.can_begin_expr())
1013     }
1014
1015     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1016         match self.token.uninterpolate().kind {
1017             token::Ident(..) => self.parse_dot_suffix(base, lo),
1018             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1019                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1020             }
1021             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1022                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1023             }
1024             _ => {
1025                 self.error_unexpected_after_dot();
1026                 Ok(base)
1027             }
1028         }
1029     }
1030
1031     fn error_unexpected_after_dot(&self) {
1032         // FIXME Could factor this out into non_fatal_unexpected or something.
1033         let actual = pprust::token_to_string(&self.token);
1034         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1035     }
1036
1037     // We need an identifier or integer, but the next token is a float.
1038     // Break the float into components to extract the identifier or integer.
1039     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1040     // parts unless those parts are processed immediately. `TokenCursor` should either
1041     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1042     // we should break everything including floats into more basic proc-macro style
1043     // tokens in the lexer (probably preferable).
1044     fn parse_tuple_field_access_expr_float(
1045         &mut self,
1046         lo: Span,
1047         base: P<Expr>,
1048         float: Symbol,
1049         suffix: Option<Symbol>,
1050     ) -> P<Expr> {
1051         #[derive(Debug)]
1052         enum FloatComponent {
1053             IdentLike(String),
1054             Punct(char),
1055         }
1056         use FloatComponent::*;
1057
1058         let float_str = float.as_str();
1059         let mut components = Vec::new();
1060         let mut ident_like = String::new();
1061         for c in float_str.chars() {
1062             if c == '_' || c.is_ascii_alphanumeric() {
1063                 ident_like.push(c);
1064             } else if matches!(c, '.' | '+' | '-') {
1065                 if !ident_like.is_empty() {
1066                     components.push(IdentLike(mem::take(&mut ident_like)));
1067                 }
1068                 components.push(Punct(c));
1069             } else {
1070                 panic!("unexpected character in a float token: {:?}", c)
1071             }
1072         }
1073         if !ident_like.is_empty() {
1074             components.push(IdentLike(ident_like));
1075         }
1076
1077         // With proc macros the span can refer to anything, the source may be too short,
1078         // or too long, or non-ASCII. It only makes sense to break our span into components
1079         // if its underlying text is identical to our float literal.
1080         let span = self.token.span;
1081         let can_take_span_apart =
1082             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1083
1084         match &*components {
1085             // 1e2
1086             [IdentLike(i)] => {
1087                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1088             }
1089             // 1.
1090             [IdentLike(i), Punct('.')] => {
1091                 let (ident_span, dot_span) = if can_take_span_apart() {
1092                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1093                     let ident_span = span.with_hi(span.lo + ident_len);
1094                     let dot_span = span.with_lo(span.lo + ident_len);
1095                     (ident_span, dot_span)
1096                 } else {
1097                     (span, span)
1098                 };
1099                 assert!(suffix.is_none());
1100                 let symbol = Symbol::intern(&i);
1101                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1102                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1103                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1104             }
1105             // 1.2 | 1.2e3
1106             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1107                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1108                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1109                     let ident1_span = span.with_hi(span.lo + ident1_len);
1110                     let dot_span = span
1111                         .with_lo(span.lo + ident1_len)
1112                         .with_hi(span.lo + ident1_len + BytePos(1));
1113                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1114                     (ident1_span, dot_span, ident2_span)
1115                 } else {
1116                     (span, span, span)
1117                 };
1118                 let symbol1 = Symbol::intern(&i1);
1119                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1120                 // This needs to be `Spacing::Alone` to prevent regressions.
1121                 // See issue #76399 and PR #76285 for more details
1122                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1123                 let base1 =
1124                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1125                 let symbol2 = Symbol::intern(&i2);
1126                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1127                 self.bump_with((next_token2, self.token_spacing)); // `.`
1128                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1129             }
1130             // 1e+ | 1e- (recovered)
1131             [IdentLike(_), Punct('+' | '-')] |
1132             // 1e+2 | 1e-2
1133             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1134             // 1.2e+ | 1.2e-
1135             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1136             // 1.2e+3 | 1.2e-3
1137             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1138                 // See the FIXME about `TokenCursor` above.
1139                 self.error_unexpected_after_dot();
1140                 base
1141             }
1142             _ => panic!("unexpected components in a float token: {:?}", components),
1143         }
1144     }
1145
1146     fn parse_tuple_field_access_expr(
1147         &mut self,
1148         lo: Span,
1149         base: P<Expr>,
1150         field: Symbol,
1151         suffix: Option<Symbol>,
1152         next_token: Option<(Token, Spacing)>,
1153     ) -> P<Expr> {
1154         match next_token {
1155             Some(next_token) => self.bump_with(next_token),
1156             None => self.bump(),
1157         }
1158         let span = self.prev_token.span;
1159         let field = ExprKind::Field(base, Ident::new(field, span));
1160         if let Some(suffix) = suffix {
1161             self.expect_no_tuple_index_suffix(span, suffix);
1162         }
1163         self.mk_expr(lo.to(span), field)
1164     }
1165
1166     /// Parse a function call expression, `expr(...)`.
1167     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1168         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1169             && self.look_ahead_type_ascription_as_field()
1170         {
1171             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1172         } else {
1173             None
1174         };
1175         let open_paren = self.token.span;
1176
1177         let mut seq = self
1178             .parse_paren_expr_seq()
1179             .map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
1180         if let Some(expr) =
1181             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1182         {
1183             return expr;
1184         }
1185         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1186     }
1187
1188     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1189     /// parentheses instead of braces, recover the parser state and provide suggestions.
1190     #[instrument(skip(self, seq, snapshot), level = "trace")]
1191     fn maybe_recover_struct_lit_bad_delims(
1192         &mut self,
1193         lo: Span,
1194         open_paren: Span,
1195         seq: &mut PResult<'a, P<Expr>>,
1196         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1197     ) -> Option<P<Expr>> {
1198         match (seq.as_mut(), snapshot) {
1199             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1200                 snapshot.bump(); // `(`
1201                 match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
1202                     Ok((fields, ..))
1203                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1204                     {
1205                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1206                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1207                         self.restore_snapshot(snapshot);
1208                         let close_paren = self.prev_token.span;
1209                         let span = lo.to(self.prev_token.span);
1210                         if !fields.is_empty() {
1211                             let mut replacement_err = ParenthesesWithStructFields {
1212                                 span,
1213                                 r#type: path,
1214                                 braces_for_struct: BracesForStructLiteral {
1215                                     first: open_paren,
1216                                     second: close_paren,
1217                                 },
1218                                 no_fields_for_fn: NoFieldsForFnCall {
1219                                     fields: fields
1220                                         .into_iter()
1221                                         .map(|field| field.span.until(field.expr.span))
1222                                         .collect(),
1223                                 },
1224                             }
1225                             .into_diagnostic(&self.sess.span_diagnostic);
1226                             replacement_err.emit();
1227
1228                             let old_err = mem::replace(err, replacement_err);
1229                             old_err.cancel();
1230                         } else {
1231                             err.emit();
1232                         }
1233                         return Some(self.mk_expr_err(span));
1234                     }
1235                     Ok(_) => {}
1236                     Err(mut err) => {
1237                         err.emit();
1238                     }
1239                 }
1240             }
1241             _ => {}
1242         }
1243         None
1244     }
1245
1246     /// Parse an indexing expression `expr[...]`.
1247     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1248         let prev_span = self.prev_token.span;
1249         let open_delim_span = self.token.span;
1250         self.bump(); // `[`
1251         let index = self.parse_expr()?;
1252         self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
1253         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1254         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index)))
1255     }
1256
1257     /// Assuming we have just parsed `.`, continue parsing into an expression.
1258     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1259         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1260             return Ok(self.mk_await_expr(self_arg, lo));
1261         }
1262
1263         let fn_span_lo = self.token.span;
1264         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1265         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1266         self.check_turbofish_missing_angle_brackets(&mut segment);
1267
1268         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1269             // Method call `expr.f()`
1270             let args = self.parse_paren_expr_seq()?;
1271             let fn_span = fn_span_lo.to(self.prev_token.span);
1272             let span = lo.to(self.prev_token.span);
1273             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, self_arg, args, fn_span)))
1274         } else {
1275             // Field access `expr.f`
1276             if let Some(args) = segment.args {
1277                 self.sess.emit_err(FieldExpressionWithGeneric(args.span()));
1278             }
1279
1280             let span = lo.to(self.prev_token.span);
1281             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident)))
1282         }
1283     }
1284
1285     /// At the bottom (top?) of the precedence hierarchy,
1286     /// Parses things like parenthesized exprs, macros, `return`, etc.
1287     ///
1288     /// N.B., this does not parse outer attributes, and is private because it only works
1289     /// correctly if called from `parse_dot_or_call_expr()`.
1290     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1291         maybe_recover_from_interpolated_ty_qpath!(self, true);
1292         maybe_whole_expr!(self);
1293
1294         // Outer attributes are already parsed and will be
1295         // added to the return value after the fact.
1296
1297         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1298         let lo = self.token.span;
1299         if let token::Literal(_) = self.token.kind {
1300             // This match arm is a special-case of the `_` match arm below and
1301             // could be removed without changing functionality, but it's faster
1302             // to have it here, especially for programs with large constants.
1303             self.parse_lit_expr()
1304         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1305             self.parse_tuple_parens_expr()
1306         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1307             self.parse_block_expr(None, lo, BlockCheckMode::Default)
1308         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1309             self.parse_closure_expr().map_err(|mut err| {
1310                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1311                 // then suggest parens around the lhs.
1312                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1313                     err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
1314                 }
1315                 err
1316             })
1317         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1318             self.parse_array_or_repeat_expr(Delimiter::Bracket)
1319         } else if self.check_path() {
1320             self.parse_path_start_expr()
1321         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1322             self.parse_closure_expr()
1323         } else if self.eat_keyword(kw::If) {
1324             self.parse_if_expr()
1325         } else if self.check_keyword(kw::For) {
1326             if self.choose_generics_over_qpath(1) {
1327                 self.parse_closure_expr()
1328             } else {
1329                 assert!(self.eat_keyword(kw::For));
1330                 self.parse_for_expr(None, self.prev_token.span)
1331             }
1332         } else if self.eat_keyword(kw::While) {
1333             self.parse_while_expr(None, self.prev_token.span)
1334         } else if let Some(label) = self.eat_label() {
1335             self.parse_labeled_expr(label, true)
1336         } else if self.eat_keyword(kw::Loop) {
1337             let sp = self.prev_token.span;
1338             self.parse_loop_expr(None, self.prev_token.span).map_err(|mut err| {
1339                 err.span_label(sp, "while parsing this `loop` expression");
1340                 err
1341             })
1342         } else if self.eat_keyword(kw::Continue) {
1343             let kind = ExprKind::Continue(self.eat_label());
1344             Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
1345         } else if self.eat_keyword(kw::Match) {
1346             let match_sp = self.prev_token.span;
1347             self.parse_match_expr().map_err(|mut err| {
1348                 err.span_label(match_sp, "while parsing this `match` expression");
1349                 err
1350             })
1351         } else if self.eat_keyword(kw::Unsafe) {
1352             let sp = self.prev_token.span;
1353             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
1354                 |mut err| {
1355                     err.span_label(sp, "while parsing this `unsafe` expression");
1356                     err
1357                 },
1358             )
1359         } else if self.check_inline_const(0) {
1360             self.parse_const_block(lo.to(self.token.span), false)
1361         } else if self.is_do_catch_block() {
1362             self.recover_do_catch()
1363         } else if self.is_try_block() {
1364             self.expect_keyword(kw::Try)?;
1365             self.parse_try_block(lo)
1366         } else if self.eat_keyword(kw::Return) {
1367             self.parse_return_expr()
1368         } else if self.eat_keyword(kw::Break) {
1369             self.parse_break_expr()
1370         } else if self.eat_keyword(kw::Yield) {
1371             self.parse_yield_expr()
1372         } else if self.is_do_yeet() {
1373             self.parse_yeet_expr()
1374         } else if self.check_keyword(kw::Let) {
1375             self.parse_let_expr()
1376         } else if self.eat_keyword(kw::Underscore) {
1377             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore))
1378         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1379             // Don't complain about bare semicolons after unclosed braces
1380             // recovery in order to keep the error count down. Fixing the
1381             // delimiters will possibly also fix the bare semicolon found in
1382             // expression context. For example, silence the following error:
1383             //
1384             //     error: expected expression, found `;`
1385             //      --> file.rs:2:13
1386             //       |
1387             //     2 |     foo(bar(;
1388             //       |             ^ expected expression
1389             self.bump();
1390             Ok(self.mk_expr_err(self.token.span))
1391         } else if self.token.uninterpolated_span().rust_2018() {
1392             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1393             if self.check_keyword(kw::Async) {
1394                 if self.is_async_block() {
1395                     // Check for `async {` and `async move {`.
1396                     self.parse_async_block()
1397                 } else {
1398                     self.parse_closure_expr()
1399                 }
1400             } else if self.eat_keyword(kw::Await) {
1401                 self.recover_incorrect_await_syntax(lo, self.prev_token.span)
1402             } else {
1403                 self.parse_lit_expr()
1404             }
1405         } else {
1406             self.parse_lit_expr()
1407         }
1408     }
1409
1410     fn parse_lit_expr(&mut self) -> PResult<'a, P<Expr>> {
1411         let lo = self.token.span;
1412         match self.parse_opt_lit() {
1413             Some(literal) => {
1414                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal));
1415                 self.maybe_recover_from_bad_qpath(expr)
1416             }
1417             None => self.try_macro_suggestion(),
1418         }
1419     }
1420
1421     fn parse_tuple_parens_expr(&mut self) -> PResult<'a, P<Expr>> {
1422         let lo = self.token.span;
1423         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1424         let (es, trailing_comma) = match self.parse_seq_to_end(
1425             &token::CloseDelim(Delimiter::Parenthesis),
1426             SeqSep::trailing_allowed(token::Comma),
1427             |p| p.parse_expr_catch_underscore(),
1428         ) {
1429             Ok(x) => x,
1430             Err(err) => {
1431                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1432             }
1433         };
1434         let kind = if es.len() == 1 && !trailing_comma {
1435             // `(e)` is parenthesized `e`.
1436             ExprKind::Paren(es.into_iter().next().unwrap())
1437         } else {
1438             // `(e,)` is a tuple with only one field, `e`.
1439             ExprKind::Tup(es)
1440         };
1441         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1442         self.maybe_recover_from_bad_qpath(expr)
1443     }
1444
1445     fn parse_array_or_repeat_expr(&mut self, close_delim: Delimiter) -> PResult<'a, P<Expr>> {
1446         let lo = self.token.span;
1447         self.bump(); // `[` or other open delim
1448
1449         let close = &token::CloseDelim(close_delim);
1450         let kind = if self.eat(close) {
1451             // Empty vector
1452             ExprKind::Array(Vec::new())
1453         } else {
1454             // Non-empty vector
1455             let first_expr = self.parse_expr()?;
1456             if self.eat(&token::Semi) {
1457                 // Repeating array syntax: `[ 0; 512 ]`
1458                 let count = self.parse_anon_const_expr()?;
1459                 self.expect(close)?;
1460                 ExprKind::Repeat(first_expr, count)
1461             } else if self.eat(&token::Comma) {
1462                 // Vector with two or more elements.
1463                 let sep = SeqSep::trailing_allowed(token::Comma);
1464                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1465                 let mut exprs = vec![first_expr];
1466                 exprs.extend(remaining_exprs);
1467                 ExprKind::Array(exprs)
1468             } else {
1469                 // Vector with one element
1470                 self.expect(close)?;
1471                 ExprKind::Array(vec![first_expr])
1472             }
1473         };
1474         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1475         self.maybe_recover_from_bad_qpath(expr)
1476     }
1477
1478     fn parse_path_start_expr(&mut self) -> PResult<'a, P<Expr>> {
1479         let (qself, path) = if self.eat_lt() {
1480             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1481             (Some(qself), path)
1482         } else {
1483             (None, self.parse_path(PathStyle::Expr)?)
1484         };
1485
1486         // `!`, as an operator, is prefix, so we know this isn't that.
1487         let (span, kind) = if self.eat(&token::Not) {
1488             // MACRO INVOCATION expression
1489             if qself.is_some() {
1490                 self.sess.emit_err(MacroInvocationWithQualifiedPath(path.span));
1491             }
1492             let lo = path.span;
1493             let mac = P(MacCall {
1494                 path,
1495                 args: self.parse_mac_args()?,
1496                 prior_type_ascription: self.last_type_ascription,
1497             });
1498             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
1499         } else if self.check(&token::OpenDelim(Delimiter::Brace)) &&
1500             let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path) {
1501                 if qself.is_some() {
1502                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1503                 }
1504                 return expr;
1505         } else {
1506             (path.span, ExprKind::Path(qself, path))
1507         };
1508
1509         let expr = self.mk_expr(span, kind);
1510         self.maybe_recover_from_bad_qpath(expr)
1511     }
1512
1513     /// Parse `'label: $expr`. The label is already parsed.
1514     fn parse_labeled_expr(
1515         &mut self,
1516         label: Label,
1517         mut consume_colon: bool,
1518     ) -> PResult<'a, P<Expr>> {
1519         let lo = label.ident.span;
1520         let label = Some(label);
1521         let ate_colon = self.eat(&token::Colon);
1522         let expr = if self.eat_keyword(kw::While) {
1523             self.parse_while_expr(label, lo)
1524         } else if self.eat_keyword(kw::For) {
1525             self.parse_for_expr(label, lo)
1526         } else if self.eat_keyword(kw::Loop) {
1527             self.parse_loop_expr(label, lo)
1528         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1529             || self.token.is_whole_block()
1530         {
1531             self.parse_block_expr(label, lo, BlockCheckMode::Default)
1532         } else if !ate_colon
1533             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1534         {
1535             // We're probably inside of a `Path<'a>` that needs a turbofish
1536             self.sess.emit_err(UnexpectedTokenAfterLabel {
1537                 span: self.token.span,
1538                 remove_label: None,
1539                 enclose_in_block: None,
1540             });
1541             consume_colon = false;
1542             Ok(self.mk_expr_err(lo))
1543         } else {
1544             let mut err = UnexpectedTokenAfterLabel {
1545                 span: self.token.span,
1546                 remove_label: None,
1547                 enclose_in_block: None,
1548             };
1549
1550             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1551             let expr = self.parse_expr().map(|expr| {
1552                 let span = expr.span;
1553
1554                 let found_labeled_breaks = {
1555                     struct FindLabeledBreaksVisitor(bool);
1556
1557                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1558                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1559                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1560                                 self.0 = true;
1561                             }
1562                         }
1563                     }
1564
1565                     let mut vis = FindLabeledBreaksVisitor(false);
1566                     vis.visit_expr(&expr);
1567                     vis.0
1568                 };
1569
1570                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1571                 //
1572                 // If there are no breaks that may use this label, suggest removing the label and
1573                 // recover to the unmodified expression.
1574                 if !found_labeled_breaks {
1575                     err.remove_label = Some(lo.until(span));
1576
1577                     return expr;
1578                 }
1579
1580                 err.enclose_in_block = Some(UnexpectedTokenAfterLabelSugg {
1581                     left: span.shrink_to_lo(),
1582                     right: span.shrink_to_hi(),
1583                 });
1584
1585                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
1586                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1587                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1588                 self.mk_expr(span, ExprKind::Block(blk, label))
1589             });
1590
1591             self.sess.emit_err(err);
1592             expr
1593         }?;
1594
1595         if !ate_colon && consume_colon {
1596             self.sess.emit_err(RequireColonAfterLabeledExpression {
1597                 span: expr.span,
1598                 label: lo,
1599                 label_end: lo.shrink_to_hi(),
1600             });
1601         }
1602
1603         Ok(expr)
1604     }
1605
1606     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1607     fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
1608         let lo = self.token.span;
1609
1610         self.bump(); // `do`
1611         self.bump(); // `catch`
1612
1613         let span = lo.to(self.prev_token.span);
1614         self.sess.emit_err(DoCatchSyntaxRemoved { span });
1615
1616         self.parse_try_block(lo)
1617     }
1618
1619     /// Parse an expression if the token can begin one.
1620     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1621         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1622     }
1623
1624     /// Parse `"return" expr?`.
1625     fn parse_return_expr(&mut self) -> PResult<'a, P<Expr>> {
1626         let lo = self.prev_token.span;
1627         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1628         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1629         self.maybe_recover_from_bad_qpath(expr)
1630     }
1631
1632     /// Parse `"do" "yeet" expr?`.
1633     fn parse_yeet_expr(&mut self) -> PResult<'a, P<Expr>> {
1634         let lo = self.token.span;
1635
1636         self.bump(); // `do`
1637         self.bump(); // `yeet`
1638
1639         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1640
1641         let span = lo.to(self.prev_token.span);
1642         self.sess.gated_spans.gate(sym::yeet_expr, span);
1643         let expr = self.mk_expr(span, kind);
1644         self.maybe_recover_from_bad_qpath(expr)
1645     }
1646
1647     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1648     /// If the label is followed immediately by a `:` token, the label and `:` are
1649     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1650     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1651     /// the break expression of an unlabeled break is a labeled loop (as in
1652     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1653     /// expression only gets a warning for compatibility reasons; and a labeled break
1654     /// with a labeled loop does not even get a warning because there is no ambiguity.
1655     fn parse_break_expr(&mut self) -> PResult<'a, P<Expr>> {
1656         let lo = self.prev_token.span;
1657         let mut label = self.eat_label();
1658         let kind = if label.is_some() && self.token == token::Colon {
1659             // The value expression can be a labeled loop, see issue #86948, e.g.:
1660             // `loop { break 'label: loop { break 'label 42; }; }`
1661             let lexpr = self.parse_labeled_expr(label.take().unwrap(), true)?;
1662             self.sess.emit_err(LabeledLoopInBreak {
1663                 span: lexpr.span,
1664                 sub: WrapExpressionInParentheses {
1665                     left: lexpr.span.shrink_to_lo(),
1666                     right: lexpr.span.shrink_to_hi(),
1667                 },
1668             });
1669             Some(lexpr)
1670         } else if self.token != token::OpenDelim(Delimiter::Brace)
1671             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1672         {
1673             let expr = self.parse_expr_opt()?;
1674             if let Some(ref expr) = expr {
1675                 if label.is_some()
1676                     && matches!(
1677                         expr.kind,
1678                         ExprKind::While(_, _, None)
1679                             | ExprKind::ForLoop(_, _, _, None)
1680                             | ExprKind::Loop(_, None)
1681                             | ExprKind::Block(_, None)
1682                     )
1683                 {
1684                     self.sess.buffer_lint_with_diagnostic(
1685                         BREAK_WITH_LABEL_AND_LOOP,
1686                         lo.to(expr.span),
1687                         ast::CRATE_NODE_ID,
1688                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1689                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1690                     );
1691                 }
1692             }
1693             expr
1694         } else {
1695             None
1696         };
1697         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
1698         self.maybe_recover_from_bad_qpath(expr)
1699     }
1700
1701     /// Parse `"yield" expr?`.
1702     fn parse_yield_expr(&mut self) -> PResult<'a, P<Expr>> {
1703         let lo = self.prev_token.span;
1704         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1705         let span = lo.to(self.prev_token.span);
1706         self.sess.gated_spans.gate(sym::generators, span);
1707         let expr = self.mk_expr(span, kind);
1708         self.maybe_recover_from_bad_qpath(expr)
1709     }
1710
1711     /// Returns a string literal if the next token is a string literal.
1712     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1713     /// and returns `None` if the next token is not literal at all.
1714     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1715         match self.parse_opt_lit() {
1716             Some(lit) => match lit.kind {
1717                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1718                     style,
1719                     symbol: lit.token_lit.symbol,
1720                     suffix: lit.token_lit.suffix,
1721                     span: lit.span,
1722                     symbol_unescaped,
1723                 }),
1724                 _ => Err(Some(lit)),
1725             },
1726             None => Err(None),
1727         }
1728     }
1729
1730     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1731         self.parse_opt_lit().ok_or_else(|| {
1732             if let token::Interpolated(inner) = &self.token.kind {
1733                 let expr = match inner.as_ref() {
1734                     token::NtExpr(expr) => Some(expr),
1735                     token::NtLiteral(expr) => Some(expr),
1736                     _ => None,
1737                 };
1738                 if let Some(expr) = expr {
1739                     if matches!(expr.kind, ExprKind::Err) {
1740                         let mut err = InvalidInterpolatedExpression { span: self.token.span }
1741                             .into_diagnostic(&self.sess.span_diagnostic);
1742                         err.downgrade_to_delayed_bug();
1743                         return err;
1744                     }
1745                 }
1746             }
1747             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
1748             self.struct_span_err(self.token.span, &msg)
1749         })
1750     }
1751
1752     /// Matches `lit = true | false | token_lit`.
1753     /// Returns `None` if the next token is not a literal.
1754     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1755         let mut recovered = None;
1756         if self.token == token::Dot {
1757             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1758             // dot would follow an optional literal, so we do this unconditionally.
1759             recovered = self.look_ahead(1, |next_token| {
1760                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1761                     next_token.kind
1762                 {
1763                     if self.token.span.hi() == next_token.span.lo() {
1764                         let s = String::from("0.") + symbol.as_str();
1765                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1766                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1767                     }
1768                 }
1769                 None
1770             });
1771             if let Some(token) = &recovered {
1772                 self.bump();
1773                 self.sess.emit_err(FloatLiteralRequiresIntegerPart {
1774                     span: token.span,
1775                     correct: pprust::token_to_string(token).into_owned(),
1776                 });
1777             }
1778         }
1779
1780         let token = recovered.as_ref().unwrap_or(&self.token);
1781         match Lit::from_token(token) {
1782             Ok(lit) => {
1783                 self.bump();
1784                 Some(lit)
1785             }
1786             Err(LitError::NotLiteral) => None,
1787             Err(err) => {
1788                 let span = token.span;
1789                 let token::Literal(lit) = token.kind else {
1790                     unreachable!();
1791                 };
1792                 self.bump();
1793                 self.report_lit_error(err, lit, span);
1794                 // Pack possible quotes and prefixes from the original literal into
1795                 // the error literal's symbol so they can be pretty-printed faithfully.
1796                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1797                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1798                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1799                 Some(Lit::from_token_lit(lit, span).unwrap_or_else(|_| unreachable!()))
1800             }
1801         }
1802     }
1803
1804     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1805         // Checks if `s` looks like i32 or u1234 etc.
1806         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1807             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1808         }
1809
1810         // Try to lowercase the prefix if it's a valid base prefix.
1811         fn fix_base_capitalisation(s: &str) -> Option<String> {
1812             if let Some(stripped) = s.strip_prefix('B') {
1813                 Some(format!("0b{stripped}"))
1814             } else if let Some(stripped) = s.strip_prefix('O') {
1815                 Some(format!("0o{stripped}"))
1816             } else if let Some(stripped) = s.strip_prefix('X') {
1817                 Some(format!("0x{stripped}"))
1818             } else {
1819                 None
1820             }
1821         }
1822
1823         let token::Lit { kind, suffix, .. } = lit;
1824         match err {
1825             // `NotLiteral` is not an error by itself, so we don't report
1826             // it and give the parser opportunity to try something else.
1827             LitError::NotLiteral => {}
1828             // `LexerError` *is* an error, but it was already reported
1829             // by lexer, so here we don't report it the second time.
1830             LitError::LexerError => {}
1831             LitError::InvalidSuffix => {
1832                 if let Some(suffix) = suffix {
1833                     self.sess.emit_err(InvalidLiteralSuffix {
1834                         span,
1835                         kind: format!("{}", kind.descr()),
1836                         suffix,
1837                     });
1838                 }
1839             }
1840             LitError::InvalidIntSuffix => {
1841                 let suf = suffix.expect("suffix error with no suffix");
1842                 let suf = suf.as_str();
1843                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1844                     // If it looks like a width, try to be helpful.
1845                     self.sess.emit_err(InvalidIntLiteralWidth { span, width: suf[1..].into() });
1846                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1847                     self.sess.emit_err(InvalidNumLiteralBasePrefix { span, fixed });
1848                 } else {
1849                     self.sess.emit_err(InvalidNumLiteralSuffix { span, suffix: suf.to_string() });
1850                 }
1851             }
1852             LitError::InvalidFloatSuffix => {
1853                 let suf = suffix.expect("suffix error with no suffix");
1854                 let suf = suf.as_str();
1855                 if looks_like_width_suffix(&['f'], suf) {
1856                     // If it looks like a width, try to be helpful.
1857                     self.sess
1858                         .emit_err(InvalidFloatLiteralWidth { span, width: suf[1..].to_string() });
1859                 } else {
1860                     self.sess.emit_err(InvalidFloatLiteralSuffix { span, suffix: suf.to_string() });
1861                 }
1862             }
1863             LitError::NonDecimalFloat(base) => {
1864                 match base {
1865                     16 => self.sess.emit_err(HexadecimalFloatLiteralNotSupported { span }),
1866                     8 => self.sess.emit_err(OctalFloatLiteralNotSupported { span }),
1867                     2 => self.sess.emit_err(BinaryFloatLiteralNotSupported { span }),
1868                     _ => unreachable!(),
1869                 };
1870             }
1871             LitError::IntTooLarge => {
1872                 self.sess.emit_err(IntLiteralTooLarge { span });
1873             }
1874         }
1875     }
1876
1877     pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
1878         if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
1879             // #59553: warn instead of reject out of hand to allow the fix to percolate
1880             // through the ecosystem when people fix their macros
1881             self.sess.emit_warning(InvalidLiteralSuffixOnTupleIndex {
1882                 span,
1883                 suffix,
1884                 exception: Some(()),
1885             });
1886         } else {
1887             self.sess.emit_err(InvalidLiteralSuffixOnTupleIndex { span, suffix, exception: None });
1888         }
1889     }
1890
1891     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1892     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1893     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1894         maybe_whole_expr!(self);
1895
1896         let lo = self.token.span;
1897         let minus_present = self.eat(&token::BinOp(token::Minus));
1898         let lit = self.parse_lit()?;
1899         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit));
1900
1901         if minus_present {
1902             Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
1903         } else {
1904             Ok(expr)
1905         }
1906     }
1907
1908     fn is_array_like_block(&mut self) -> bool {
1909         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1910             && self.look_ahead(2, |t| t == &token::Comma)
1911             && self.look_ahead(3, |t| t.can_begin_expr())
1912     }
1913
1914     /// Emits a suggestion if it looks like the user meant an array but
1915     /// accidentally used braces, causing the code to be interpreted as a block
1916     /// expression.
1917     fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
1918         let mut snapshot = self.create_snapshot_for_diagnostic();
1919         match snapshot.parse_array_or_repeat_expr(Delimiter::Brace) {
1920             Ok(arr) => {
1921                 self.sess.emit_err(ArrayBracketsInsteadOfSpaces {
1922                     span: arr.span,
1923                     sub: ArrayBracketsInsteadOfSpacesSugg {
1924                         left: lo,
1925                         right: snapshot.prev_token.span,
1926                     },
1927                 });
1928
1929                 self.restore_snapshot(snapshot);
1930                 Some(self.mk_expr_err(arr.span))
1931             }
1932             Err(e) => {
1933                 e.cancel();
1934                 None
1935             }
1936         }
1937     }
1938
1939     fn suggest_missing_semicolon_before_array(
1940         &self,
1941         prev_span: Span,
1942         open_delim_span: Span,
1943     ) -> PResult<'a, ()> {
1944         if self.token.kind == token::Comma {
1945             if !self.sess.source_map().is_multiline(prev_span.until(self.token.span)) {
1946                 return Ok(());
1947             }
1948             let mut snapshot = self.create_snapshot_for_diagnostic();
1949             snapshot.bump();
1950             match snapshot.parse_seq_to_before_end(
1951                 &token::CloseDelim(Delimiter::Bracket),
1952                 SeqSep::trailing_allowed(token::Comma),
1953                 |p| p.parse_expr(),
1954             ) {
1955                 Ok(_)
1956                     // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
1957                     // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
1958                     // This is because the `token.kind` of the close delim is treated as the same as
1959                     // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
1960                     // Therefore, `token.kind` should not be compared here.
1961                     if snapshot
1962                         .span_to_snippet(snapshot.token.span)
1963                         .map_or(false, |snippet| snippet == "]") =>
1964                 {
1965                     return Err(MissingSemicolonBeforeArray {
1966                         open_delim: open_delim_span,
1967                         semicolon: prev_span.shrink_to_hi(),
1968                     }.into_diagnostic(&self.sess.span_diagnostic));
1969                 }
1970                 Ok(_) => (),
1971                 Err(err) => err.cancel(),
1972             }
1973         }
1974         Ok(())
1975     }
1976
1977     /// Parses a block or unsafe block.
1978     pub(super) fn parse_block_expr(
1979         &mut self,
1980         opt_label: Option<Label>,
1981         lo: Span,
1982         blk_mode: BlockCheckMode,
1983     ) -> PResult<'a, P<Expr>> {
1984         if self.is_array_like_block() {
1985             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
1986                 return Ok(arr);
1987             }
1988         }
1989
1990         if self.token.is_whole_block() {
1991             self.sess.emit_err(InvalidBlockMacroSegment {
1992                 span: self.token.span,
1993                 context: lo.to(self.token.span),
1994             });
1995         }
1996
1997         let (attrs, blk) = self.parse_block_common(lo, blk_mode)?;
1998         Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
1999     }
2000
2001     /// Parse a block which takes no attributes and has no label
2002     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2003         let blk = self.parse_block()?;
2004         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
2005     }
2006
2007     /// Parses a closure expression (e.g., `move |args| expr`).
2008     fn parse_closure_expr(&mut self) -> PResult<'a, P<Expr>> {
2009         let lo = self.token.span;
2010
2011         let binder = if self.check_keyword(kw::For) {
2012             let lo = self.token.span;
2013             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2014             let span = lo.to(self.prev_token.span);
2015
2016             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2017
2018             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2019         } else {
2020             ClosureBinder::NotPresent
2021         };
2022
2023         let movability =
2024             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2025
2026         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2027             self.parse_asyncness()
2028         } else {
2029             Async::No
2030         };
2031
2032         let capture_clause = self.parse_capture_clause()?;
2033         let decl = self.parse_fn_block_decl()?;
2034         let decl_hi = self.prev_token.span;
2035         let mut body = match decl.output {
2036             FnRetTy::Default(_) => {
2037                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2038                 self.parse_expr_res(restrictions, None)?
2039             }
2040             _ => {
2041                 // If an explicit return type is given, require a block to appear (RFC 968).
2042                 let body_lo = self.token.span;
2043                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default)?
2044             }
2045         };
2046
2047         if let Async::Yes { span, .. } = asyncness {
2048             // Feature-gate `async ||` closures.
2049             self.sess.gated_spans.gate(sym::async_closure, span);
2050         }
2051
2052         if self.token.kind == TokenKind::Semi
2053             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2054         {
2055             // It is likely that the closure body is a block but where the
2056             // braces have been removed. We will recover and eat the next
2057             // statements later in the parsing process.
2058             body = self.mk_expr_err(body.span);
2059         }
2060
2061         let body_span = body.span;
2062
2063         let closure = self.mk_expr(
2064             lo.to(body.span),
2065             ExprKind::Closure(
2066                 binder,
2067                 capture_clause,
2068                 asyncness,
2069                 movability,
2070                 decl,
2071                 body,
2072                 lo.to(decl_hi),
2073             ),
2074         );
2075
2076         // Disable recovery for closure body
2077         let spans =
2078             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2079         self.current_closure = Some(spans);
2080
2081         Ok(closure)
2082     }
2083
2084     /// Parses an optional `move` prefix to a closure-like construct.
2085     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2086         if self.eat_keyword(kw::Move) {
2087             // Check for `move async` and recover
2088             if self.check_keyword(kw::Async) {
2089                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2090                 Err(AsyncMoveOrderIncorrect { span: move_async_span }
2091                     .into_diagnostic(&self.sess.span_diagnostic))
2092             } else {
2093                 Ok(CaptureBy::Value)
2094             }
2095         } else {
2096             Ok(CaptureBy::Ref)
2097         }
2098     }
2099
2100     /// Parses the `|arg, arg|` header of a closure.
2101     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2102         let inputs = if self.eat(&token::OrOr) {
2103             Vec::new()
2104         } else {
2105             self.expect(&token::BinOp(token::Or))?;
2106             let args = self
2107                 .parse_seq_to_before_tokens(
2108                     &[&token::BinOp(token::Or), &token::OrOr],
2109                     SeqSep::trailing_allowed(token::Comma),
2110                     TokenExpectType::NoExpect,
2111                     |p| p.parse_fn_block_param(),
2112                 )?
2113                 .0;
2114             self.expect_or()?;
2115             args
2116         };
2117         let output =
2118             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2119
2120         Ok(P(FnDecl { inputs, output }))
2121     }
2122
2123     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2124     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2125         let lo = self.token.span;
2126         let attrs = self.parse_outer_attributes()?;
2127         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2128             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2129             let ty = if this.eat(&token::Colon) {
2130                 this.parse_ty()?
2131             } else {
2132                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2133             };
2134
2135             Ok((
2136                 Param {
2137                     attrs,
2138                     ty,
2139                     pat,
2140                     span: lo.to(this.prev_token.span),
2141                     id: DUMMY_NODE_ID,
2142                     is_placeholder: false,
2143                 },
2144                 TrailingToken::MaybeComma,
2145             ))
2146         })
2147     }
2148
2149     /// Parses an `if` expression (`if` token already eaten).
2150     fn parse_if_expr(&mut self) -> PResult<'a, P<Expr>> {
2151         let lo = self.prev_token.span;
2152         let cond = self.parse_cond_expr()?;
2153         self.parse_if_after_cond(lo, cond)
2154     }
2155
2156     fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
2157         let cond_span = cond.span;
2158         // Tries to interpret `cond` as either a missing expression if it's a block,
2159         // or as an unfinished expression if it's a binop and the RHS is a block.
2160         // We could probably add more recoveries here too...
2161         let mut recover_block_from_condition = |this: &mut Self| {
2162             let block = match &mut cond.kind {
2163                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2164                     if let ExprKind::Block(_, None) = right.kind => {
2165                         self.sess.emit_err(IfExpressionMissingThenBlock {
2166                             if_span: lo,
2167                             sub: IfExpressionMissingThenBlockSub::UnfinishedCondition(
2168                                 cond_span.shrink_to_lo().to(*binop_span)
2169                             ),
2170                         });
2171                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2172                     },
2173                 ExprKind::Block(_, None) => {
2174                     self.sess.emit_err(IfExpressionMissingCondition {
2175                         if_span: self.sess.source_map().next_point(lo),
2176                         block_span: self.sess.source_map().start_point(cond_span),
2177                     });
2178                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2179                 }
2180                 _ => {
2181                     return None;
2182                 }
2183             };
2184             if let ExprKind::Block(block, _) = &block.kind {
2185                 Some(block.clone())
2186             } else {
2187                 unreachable!()
2188             }
2189         };
2190         // Parse then block
2191         let thn = if self.token.is_keyword(kw::Else) {
2192             if let Some(block) = recover_block_from_condition(self) {
2193                 block
2194             } else {
2195                 self.sess.emit_err(IfExpressionMissingThenBlock {
2196                     if_span: lo,
2197                     sub: IfExpressionMissingThenBlockSub::AddThenBlock(cond_span.shrink_to_hi()),
2198                 });
2199                 self.mk_block_err(cond_span.shrink_to_hi())
2200             }
2201         } else {
2202             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2203             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2204                 self.parse_block()?
2205             } else {
2206                 if let Some(block) = recover_block_from_condition(self) {
2207                     block
2208                 } else {
2209                     // Parse block, which will always fail, but we can add a nice note to the error
2210                     self.parse_block().map_err(|mut err| {
2211                         err.span_note(
2212                             cond_span,
2213                             "the `if` expression is missing a block after this condition",
2214                         );
2215                         err
2216                     })?
2217                 }
2218             };
2219             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2220             block
2221         };
2222         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2223         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
2224     }
2225
2226     /// Parses the condition of a `if` or `while` expression.
2227     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2228         let cond =
2229             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
2230
2231         if let ExprKind::Let(..) = cond.kind {
2232             // Remove the last feature gating of a `let` expression since it's stable.
2233             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2234         }
2235
2236         Ok(cond)
2237     }
2238
2239     /// Parses a `let $pat = $expr` pseudo-expression.
2240     fn parse_let_expr(&mut self) -> PResult<'a, P<Expr>> {
2241         // This is a *approximate* heuristic that detects if `let` chains are
2242         // being parsed in the right position. It's approximate because it
2243         // doesn't deny all invalid `let` expressions, just completely wrong usages.
2244         let not_in_chain = !matches!(
2245             self.prev_token.kind,
2246             TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2247         );
2248         if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
2249             self.sess.emit_err(ExpectedExpressionFoundLet { span: self.token.span });
2250         }
2251
2252         self.bump(); // Eat `let` token
2253         let lo = self.prev_token.span;
2254         let pat = self.parse_pat_allow_top_alt(
2255             None,
2256             RecoverComma::Yes,
2257             RecoverColon::Yes,
2258             CommaRecoveryMode::LikelyTuple,
2259         )?;
2260         self.expect(&token::Eq)?;
2261         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2262             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2263         })?;
2264         let span = lo.to(expr.span);
2265         self.sess.gated_spans.gate(sym::let_chains, span);
2266         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span)))
2267     }
2268
2269     /// Parses an `else { ... }` expression (`else` token already eaten).
2270     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2271         let else_span = self.prev_token.span; // `else`
2272         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2273         let expr = if self.eat_keyword(kw::If) {
2274             self.parse_if_expr()?
2275         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2276             self.parse_simple_block()?
2277         } else {
2278             let snapshot = self.create_snapshot_for_diagnostic();
2279             let first_tok = super::token_descr(&self.token);
2280             let first_tok_span = self.token.span;
2281             match self.parse_expr() {
2282                 Ok(cond)
2283                 // If it's not a free-standing expression, and is followed by a block,
2284                 // then it's very likely the condition to an `else if`.
2285                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2286                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2287                 {
2288                     self.sess.emit_err(ExpectedElseBlock {
2289                         first_tok_span,
2290                         first_tok,
2291                         else_span,
2292                         condition_start: cond.span.shrink_to_lo(),
2293                     });
2294                     self.parse_if_after_cond(cond.span.shrink_to_lo(), cond)?
2295                 }
2296                 Err(e) => {
2297                     e.cancel();
2298                     self.restore_snapshot(snapshot);
2299                     self.parse_simple_block()?
2300                 },
2301                 Ok(_) => {
2302                     self.restore_snapshot(snapshot);
2303                     self.parse_simple_block()?
2304                 },
2305             }
2306         };
2307         self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
2308         Ok(expr)
2309     }
2310
2311     fn error_on_if_block_attrs(
2312         &self,
2313         ctx_span: Span,
2314         is_ctx_else: bool,
2315         branch_span: Span,
2316         attrs: &[ast::Attribute],
2317     ) {
2318         let (attributes, last) = match attrs {
2319             [] => return,
2320             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2321         };
2322         let ctx = if is_ctx_else { "else" } else { "if" };
2323         self.sess.emit_err(OuterAttributeNotAllowedOnIfElse {
2324             last,
2325             branch_span,
2326             ctx_span,
2327             ctx: ctx.to_string(),
2328             attributes,
2329         });
2330     }
2331
2332     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2333     fn parse_for_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2334         // Record whether we are about to parse `for (`.
2335         // This is used below for recovery in case of `for ( $stuff ) $block`
2336         // in which case we will suggest `for $stuff $block`.
2337         let begin_paren = match self.token.kind {
2338             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2339             _ => None,
2340         };
2341
2342         let pat = self.parse_pat_allow_top_alt(
2343             None,
2344             RecoverComma::Yes,
2345             RecoverColon::Yes,
2346             CommaRecoveryMode::LikelyTuple,
2347         )?;
2348         if !self.eat_keyword(kw::In) {
2349             self.error_missing_in_for_loop();
2350         }
2351         self.check_for_for_in_in_typo(self.prev_token.span);
2352         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2353
2354         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2355
2356         let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
2357
2358         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2359         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2360     }
2361
2362     fn error_missing_in_for_loop(&mut self) {
2363         let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
2364             // Possibly using JS syntax (#75311).
2365             let span = self.token.span;
2366             self.bump();
2367             (span, MissingInInForLoopSub::InNotOf)
2368         } else {
2369             (self.prev_token.span.between(self.token.span), MissingInInForLoopSub::AddIn)
2370         };
2371
2372         self.sess.emit_err(MissingInInForLoop { span, sub: sub(span) });
2373     }
2374
2375     /// Parses a `while` or `while let` expression (`while` token already eaten).
2376     fn parse_while_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2377         let cond = self.parse_cond_expr().map_err(|mut err| {
2378             err.span_label(lo, "while parsing the condition of this `while` expression");
2379             err
2380         })?;
2381         let (attrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2382             err.span_label(lo, "while parsing the body of this `while` expression");
2383             err.span_label(cond.span, "this `while` condition successfully parsed");
2384             err
2385         })?;
2386         Ok(self.mk_expr_with_attrs(
2387             lo.to(self.prev_token.span),
2388             ExprKind::While(cond, body, opt_label),
2389             attrs,
2390         ))
2391     }
2392
2393     /// Parses `loop { ... }` (`loop` token already eaten).
2394     fn parse_loop_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2395         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2396         Ok(self.mk_expr_with_attrs(
2397             lo.to(self.prev_token.span),
2398             ExprKind::Loop(body, opt_label),
2399             attrs,
2400         ))
2401     }
2402
2403     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2404         self.token.lifetime().map(|ident| {
2405             self.bump();
2406             Label { ident }
2407         })
2408     }
2409
2410     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2411     fn parse_match_expr(&mut self) -> PResult<'a, P<Expr>> {
2412         let match_span = self.prev_token.span;
2413         let lo = self.prev_token.span;
2414         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2415         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2416             if self.token == token::Semi {
2417                 e.span_suggestion_short(
2418                     match_span,
2419                     "try removing this `match`",
2420                     "",
2421                     Applicability::MaybeIncorrect, // speculative
2422                 );
2423             }
2424             if self.maybe_recover_unexpected_block_label() {
2425                 e.cancel();
2426                 self.bump();
2427             } else {
2428                 return Err(e);
2429             }
2430         }
2431         let attrs = self.parse_inner_attributes()?;
2432
2433         let mut arms: Vec<Arm> = Vec::new();
2434         while self.token != token::CloseDelim(Delimiter::Brace) {
2435             match self.parse_arm() {
2436                 Ok(arm) => arms.push(arm),
2437                 Err(mut e) => {
2438                     // Recover by skipping to the end of the block.
2439                     e.emit();
2440                     self.recover_stmt();
2441                     let span = lo.to(self.token.span);
2442                     if self.token == token::CloseDelim(Delimiter::Brace) {
2443                         self.bump();
2444                     }
2445                     return Ok(self.mk_expr_with_attrs(
2446                         span,
2447                         ExprKind::Match(scrutinee, arms),
2448                         attrs,
2449                     ));
2450                 }
2451             }
2452         }
2453         let hi = self.token.span;
2454         self.bump();
2455         Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2456     }
2457
2458     /// Attempt to recover from match arm body with statements and no surrounding braces.
2459     fn parse_arm_body_missing_braces(
2460         &mut self,
2461         first_expr: &P<Expr>,
2462         arrow_span: Span,
2463     ) -> Option<P<Expr>> {
2464         if self.token.kind != token::Semi {
2465             return None;
2466         }
2467         let start_snapshot = self.create_snapshot_for_diagnostic();
2468         let semi_sp = self.token.span;
2469         self.bump(); // `;`
2470         let mut stmts =
2471             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2472         let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
2473             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2474
2475             this.sess.emit_err(MatchArmBodyWithoutBraces {
2476                 statements: span,
2477                 arrow: arrow_span,
2478                 num_statements: stmts.len(),
2479                 sub: if stmts.len() > 1 {
2480                     MatchArmBodyWithoutBracesSugg::AddBraces {
2481                         left: span.shrink_to_lo(),
2482                         right: span.shrink_to_hi(),
2483                     }
2484                 } else {
2485                     MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
2486                 },
2487             });
2488             this.mk_expr_err(span)
2489         };
2490         // We might have either a `,` -> `;` typo, or a block without braces. We need
2491         // a more subtle parsing strategy.
2492         loop {
2493             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2494                 // We have reached the closing brace of the `match` expression.
2495                 return Some(err(self, stmts));
2496             }
2497             if self.token.kind == token::Comma {
2498                 self.restore_snapshot(start_snapshot);
2499                 return None;
2500             }
2501             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2502             match self.parse_pat_no_top_alt(None) {
2503                 Ok(_pat) => {
2504                     if self.token.kind == token::FatArrow {
2505                         // Reached arm end.
2506                         self.restore_snapshot(pre_pat_snapshot);
2507                         return Some(err(self, stmts));
2508                     }
2509                 }
2510                 Err(err) => {
2511                     err.cancel();
2512                 }
2513             }
2514
2515             self.restore_snapshot(pre_pat_snapshot);
2516             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2517                 // Consume statements for as long as possible.
2518                 Ok(Some(stmt)) => {
2519                     stmts.push(stmt);
2520                 }
2521                 Ok(None) => {
2522                     self.restore_snapshot(start_snapshot);
2523                     break;
2524                 }
2525                 // We couldn't parse either yet another statement missing it's
2526                 // enclosing block nor the next arm's pattern or closing brace.
2527                 Err(stmt_err) => {
2528                     stmt_err.cancel();
2529                     self.restore_snapshot(start_snapshot);
2530                     break;
2531                 }
2532             }
2533         }
2534         None
2535     }
2536
2537     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2538         // Used to check the `let_chains` and `if_let_guard` features mostly by scanning
2539         // `&&` tokens.
2540         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2541             match expr.kind {
2542                 ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, ref lhs, ref rhs) => {
2543                     let lhs_rslt = check_let_expr(lhs);
2544                     let rhs_rslt = check_let_expr(rhs);
2545                     (lhs_rslt.0 || rhs_rslt.0, false)
2546                 }
2547                 ExprKind::Let(..) => (true, true),
2548                 _ => (false, true),
2549             }
2550         }
2551         let attrs = self.parse_outer_attributes()?;
2552         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2553             let lo = this.token.span;
2554             let pat = this.parse_pat_allow_top_alt(
2555                 None,
2556                 RecoverComma::Yes,
2557                 RecoverColon::Yes,
2558                 CommaRecoveryMode::EitherTupleOrPipe,
2559             )?;
2560             let guard = if this.eat_keyword(kw::If) {
2561                 let if_span = this.prev_token.span;
2562                 let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
2563                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2564                 if has_let_expr {
2565                     if does_not_have_bin_op {
2566                         // Remove the last feature gating of a `let` expression since it's stable.
2567                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2568                     }
2569                     let span = if_span.to(cond.span);
2570                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2571                 }
2572                 Some(cond)
2573             } else {
2574                 None
2575             };
2576             let arrow_span = this.token.span;
2577             if let Err(mut err) = this.expect(&token::FatArrow) {
2578                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2579                 if TokenKind::FatArrow
2580                     .similar_tokens()
2581                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2582                 {
2583                     err.span_suggestion(
2584                         this.token.span,
2585                         "try using a fat arrow here",
2586                         "=>",
2587                         Applicability::MaybeIncorrect,
2588                     );
2589                     err.emit();
2590                     this.bump();
2591                 } else {
2592                     return Err(err);
2593                 }
2594             }
2595             let arm_start_span = this.token.span;
2596
2597             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2598                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2599                 err
2600             })?;
2601
2602             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2603                 && this.token != token::CloseDelim(Delimiter::Brace);
2604
2605             let hi = this.prev_token.span;
2606
2607             if require_comma {
2608                 let sm = this.sess.source_map();
2609                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2610                     let span = body.span;
2611                     return Ok((
2612                         ast::Arm {
2613                             attrs,
2614                             pat,
2615                             guard,
2616                             body,
2617                             span,
2618                             id: DUMMY_NODE_ID,
2619                             is_placeholder: false,
2620                         },
2621                         TrailingToken::None,
2622                     ));
2623                 }
2624                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2625                     .or_else(|mut err| {
2626                         if this.token == token::FatArrow {
2627                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2628                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2629                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2630                             && expr_lines.lines.len() == 2
2631                             {
2632                                 // We check whether there's any trailing code in the parse span,
2633                                 // if there isn't, we very likely have the following:
2634                                 //
2635                                 // X |     &Y => "y"
2636                                 //   |        --    - missing comma
2637                                 //   |        |
2638                                 //   |        arrow_span
2639                                 // X |     &X => "x"
2640                                 //   |      - ^^ self.token.span
2641                                 //   |      |
2642                                 //   |      parsed until here as `"y" & X`
2643                                 err.span_suggestion_short(
2644                                     arm_start_span.shrink_to_hi(),
2645                                     "missing a comma here to end this `match` arm",
2646                                     ",",
2647                                     Applicability::MachineApplicable,
2648                                 );
2649                                 return Err(err);
2650                             }
2651                         } else {
2652                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2653
2654                             // Try to parse a following `PAT =>`, if successful
2655                             // then we should recover.
2656                             let mut snapshot = this.create_snapshot_for_diagnostic();
2657                             let pattern_follows = snapshot
2658                                 .parse_pat_allow_top_alt(
2659                                     None,
2660                                     RecoverComma::Yes,
2661                                     RecoverColon::Yes,
2662                                     CommaRecoveryMode::EitherTupleOrPipe,
2663                                 )
2664                                 .map_err(|err| err.cancel())
2665                                 .is_ok();
2666                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2667                                 err.cancel();
2668                                 this.sess.emit_err(MissingCommaAfterMatchArm {
2669                                     span: hi.shrink_to_hi(),
2670                                 });
2671                                 return Ok(true);
2672                             }
2673                         }
2674                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2675                         Err(err)
2676                     })?;
2677             } else {
2678                 this.eat(&token::Comma);
2679             }
2680
2681             Ok((
2682                 ast::Arm {
2683                     attrs,
2684                     pat,
2685                     guard,
2686                     body: expr,
2687                     span: lo.to(hi),
2688                     id: DUMMY_NODE_ID,
2689                     is_placeholder: false,
2690                 },
2691                 TrailingToken::None,
2692             ))
2693         })
2694     }
2695
2696     /// Parses a `try {...}` expression (`try` token already eaten).
2697     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
2698         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2699         if self.eat_keyword(kw::Catch) {
2700             Err(CatchAfterTry { span: self.prev_token.span }
2701                 .into_diagnostic(&self.sess.span_diagnostic))
2702         } else {
2703             let span = span_lo.to(body.span);
2704             self.sess.gated_spans.gate(sym::try_blocks, span);
2705             Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body), attrs))
2706         }
2707     }
2708
2709     fn is_do_catch_block(&self) -> bool {
2710         self.token.is_keyword(kw::Do)
2711             && self.is_keyword_ahead(1, &[kw::Catch])
2712             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2713             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2714     }
2715
2716     fn is_do_yeet(&self) -> bool {
2717         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2718     }
2719
2720     fn is_try_block(&self) -> bool {
2721         self.token.is_keyword(kw::Try)
2722             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2723             && self.token.uninterpolated_span().rust_2018()
2724     }
2725
2726     /// Parses an `async move? {...}` expression.
2727     fn parse_async_block(&mut self) -> PResult<'a, P<Expr>> {
2728         let lo = self.token.span;
2729         self.expect_keyword(kw::Async)?;
2730         let capture_clause = self.parse_capture_clause()?;
2731         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2732         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2733         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2734     }
2735
2736     fn is_async_block(&self) -> bool {
2737         self.token.is_keyword(kw::Async)
2738             && ((
2739                 // `async move {`
2740                 self.is_keyword_ahead(1, &[kw::Move])
2741                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2742             ) || (
2743                 // `async {`
2744                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2745             ))
2746     }
2747
2748     fn is_certainly_not_a_block(&self) -> bool {
2749         self.look_ahead(1, |t| t.is_ident())
2750             && (
2751                 // `{ ident, ` cannot start a block.
2752                 self.look_ahead(2, |t| t == &token::Comma)
2753                     || self.look_ahead(2, |t| t == &token::Colon)
2754                         && (
2755                             // `{ ident: token, ` cannot start a block.
2756                             self.look_ahead(4, |t| t == &token::Comma) ||
2757                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2758                 self.look_ahead(3, |t| !t.can_begin_type())
2759                         )
2760             )
2761     }
2762
2763     fn maybe_parse_struct_expr(
2764         &mut self,
2765         qself: Option<&ast::QSelf>,
2766         path: &ast::Path,
2767     ) -> Option<PResult<'a, P<Expr>>> {
2768         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2769         if struct_allowed || self.is_certainly_not_a_block() {
2770             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2771                 return Some(Err(err));
2772             }
2773             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), true);
2774             if let (Ok(expr), false) = (&expr, struct_allowed) {
2775                 // This is a struct literal, but we don't can't accept them here.
2776                 self.sess.emit_err(StructLiteralNotAllowedHere {
2777                     span: expr.span,
2778                     sub: StructLiteralNotAllowedHereSugg {
2779                         left: path.span.shrink_to_lo(),
2780                         right: expr.span.shrink_to_hi(),
2781                     },
2782                 });
2783             }
2784             return Some(expr);
2785         }
2786         None
2787     }
2788
2789     pub(super) fn parse_struct_fields(
2790         &mut self,
2791         pth: ast::Path,
2792         recover: bool,
2793         close_delim: Delimiter,
2794     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2795         let mut fields = Vec::new();
2796         let mut base = ast::StructRest::None;
2797         let mut recover_async = false;
2798
2799         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2800             recover_async = true;
2801             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2802             e.help_use_latest_edition();
2803         };
2804
2805         while self.token != token::CloseDelim(close_delim) {
2806             if self.eat(&token::DotDot) {
2807                 let exp_span = self.prev_token.span;
2808                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2809                 if self.check(&token::CloseDelim(close_delim)) {
2810                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2811                     break;
2812                 }
2813                 match self.parse_expr() {
2814                     Ok(e) => base = ast::StructRest::Base(e),
2815                     Err(mut e) if recover => {
2816                         e.emit();
2817                         self.recover_stmt();
2818                     }
2819                     Err(e) => return Err(e),
2820                 }
2821                 self.recover_struct_comma_after_dotdot(exp_span);
2822                 break;
2823             }
2824
2825             let recovery_field = self.find_struct_error_after_field_looking_code();
2826             let parsed_field = match self.parse_expr_field() {
2827                 Ok(f) => Some(f),
2828                 Err(mut e) => {
2829                     if pth == kw::Async {
2830                         async_block_err(&mut e, pth.span);
2831                     } else {
2832                         e.span_label(pth.span, "while parsing this struct");
2833                     }
2834                     e.emit();
2835
2836                     // If the next token is a comma, then try to parse
2837                     // what comes next as additional fields, rather than
2838                     // bailing out until next `}`.
2839                     if self.token != token::Comma {
2840                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2841                         if self.token != token::Comma {
2842                             break;
2843                         }
2844                     }
2845                     None
2846                 }
2847             };
2848
2849             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
2850             // A shorthand field can be turned into a full field with `:`.
2851             // We should point this out.
2852             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
2853
2854             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2855                 Ok(_) => {
2856                     if let Some(f) = parsed_field.or(recovery_field) {
2857                         // Only include the field if there's no parse error for the field name.
2858                         fields.push(f);
2859                     }
2860                 }
2861                 Err(mut e) => {
2862                     if pth == kw::Async {
2863                         async_block_err(&mut e, pth.span);
2864                     } else {
2865                         e.span_label(pth.span, "while parsing this struct");
2866                         if let Some(f) = recovery_field {
2867                             fields.push(f);
2868                             e.span_suggestion(
2869                                 self.prev_token.span.shrink_to_hi(),
2870                                 "try adding a comma",
2871                                 ",",
2872                                 Applicability::MachineApplicable,
2873                             );
2874                         } else if is_shorthand
2875                             && (AssocOp::from_token(&self.token).is_some()
2876                                 || matches!(&self.token.kind, token::OpenDelim(_))
2877                                 || self.token.kind == token::Dot)
2878                         {
2879                             // Looks like they tried to write a shorthand, complex expression.
2880                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
2881                             e.span_suggestion(
2882                                 ident.span.shrink_to_lo(),
2883                                 "try naming a field",
2884                                 &format!("{ident}: "),
2885                                 Applicability::HasPlaceholders,
2886                             );
2887                         }
2888                     }
2889                     if !recover {
2890                         return Err(e);
2891                     }
2892                     e.emit();
2893                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2894                     self.eat(&token::Comma);
2895                 }
2896             }
2897         }
2898         Ok((fields, base, recover_async))
2899     }
2900
2901     /// Precondition: already parsed the '{'.
2902     pub(super) fn parse_struct_expr(
2903         &mut self,
2904         qself: Option<ast::QSelf>,
2905         pth: ast::Path,
2906         recover: bool,
2907     ) -> PResult<'a, P<Expr>> {
2908         let lo = pth.span;
2909         let (fields, base, recover_async) =
2910             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
2911         let span = lo.to(self.token.span);
2912         self.expect(&token::CloseDelim(Delimiter::Brace))?;
2913         let expr = if recover_async {
2914             ExprKind::Err
2915         } else {
2916             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2917         };
2918         Ok(self.mk_expr(span, expr))
2919     }
2920
2921     /// Use in case of error after field-looking code: `S { foo: () with a }`.
2922     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
2923         match self.token.ident() {
2924             Some((ident, is_raw))
2925                 if (is_raw || !ident.is_reserved())
2926                     && self.look_ahead(1, |t| *t == token::Colon) =>
2927             {
2928                 Some(ast::ExprField {
2929                     ident,
2930                     span: self.token.span,
2931                     expr: self.mk_expr_err(self.token.span),
2932                     is_shorthand: false,
2933                     attrs: AttrVec::new(),
2934                     id: DUMMY_NODE_ID,
2935                     is_placeholder: false,
2936                 })
2937             }
2938             _ => None,
2939         }
2940     }
2941
2942     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
2943         if self.token != token::Comma {
2944             return;
2945         }
2946         self.sess.emit_err(CommaAfterBaseStruct {
2947             span: span.to(self.prev_token.span),
2948             comma: self.token.span,
2949         });
2950         self.recover_stmt();
2951     }
2952
2953     /// Parses `ident (COLON expr)?`.
2954     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
2955         let attrs = self.parse_outer_attributes()?;
2956         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2957             let lo = this.token.span;
2958
2959             // Check if a colon exists one ahead. This means we're parsing a fieldname.
2960             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
2961             let (ident, expr) = if is_shorthand {
2962                 // Mimic `x: x` for the `x` field shorthand.
2963                 let ident = this.parse_ident_common(false)?;
2964                 let path = ast::Path::from_ident(ident);
2965                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path)))
2966             } else {
2967                 let ident = this.parse_field_name()?;
2968                 this.error_on_eq_field_init(ident);
2969                 this.bump(); // `:`
2970                 (ident, this.parse_expr()?)
2971             };
2972
2973             Ok((
2974                 ast::ExprField {
2975                     ident,
2976                     span: lo.to(expr.span),
2977                     expr,
2978                     is_shorthand,
2979                     attrs,
2980                     id: DUMMY_NODE_ID,
2981                     is_placeholder: false,
2982                 },
2983                 TrailingToken::MaybeComma,
2984             ))
2985         })
2986     }
2987
2988     /// Check for `=`. This means the source incorrectly attempts to
2989     /// initialize a field with an eq rather than a colon.
2990     fn error_on_eq_field_init(&self, field_name: Ident) {
2991         if self.token != token::Eq {
2992             return;
2993         }
2994
2995         self.sess.emit_err(EqFieldInit {
2996             span: self.token.span,
2997             eq: field_name.span.shrink_to_hi().to(self.token.span),
2998         });
2999     }
3000
3001     fn err_dotdotdot_syntax(&self, span: Span) {
3002         self.sess.emit_err(DotDotDot { span });
3003     }
3004
3005     fn err_larrow_operator(&self, span: Span) {
3006         self.sess.emit_err(LeftArrowOperator { span });
3007     }
3008
3009     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3010         ExprKind::AssignOp(binop, lhs, rhs)
3011     }
3012
3013     fn mk_range(
3014         &mut self,
3015         start: Option<P<Expr>>,
3016         end: Option<P<Expr>>,
3017         limits: RangeLimits,
3018     ) -> ExprKind {
3019         if end.is_none() && limits == RangeLimits::Closed {
3020             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3021             ExprKind::Err
3022         } else {
3023             ExprKind::Range(start, end, limits)
3024         }
3025     }
3026
3027     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3028         ExprKind::Unary(unop, expr)
3029     }
3030
3031     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3032         ExprKind::Binary(binop, lhs, rhs)
3033     }
3034
3035     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3036         ExprKind::Index(expr, idx)
3037     }
3038
3039     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3040         ExprKind::Call(f, args)
3041     }
3042
3043     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3044         let span = lo.to(self.prev_token.span);
3045         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg));
3046         self.recover_from_await_method_call();
3047         await_expr
3048     }
3049
3050     pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3051         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3052     }
3053
3054     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
3055         P(Expr { kind, span, attrs: AttrVec::new(), id: DUMMY_NODE_ID, tokens: None })
3056     }
3057
3058     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3059         self.mk_expr(span, ExprKind::Err)
3060     }
3061
3062     /// Create expression span ensuring the span of the parent node
3063     /// is larger than the span of lhs and rhs, including the attributes.
3064     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3065         lhs.attrs
3066             .iter()
3067             .find(|a| a.style == AttrStyle::Outer)
3068             .map_or(lhs_span, |a| a.span)
3069             .to(rhs_span)
3070     }
3071
3072     fn collect_tokens_for_expr(
3073         &mut self,
3074         attrs: AttrWrapper,
3075         f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
3076     ) -> PResult<'a, P<Expr>> {
3077         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3078             let res = f(this, attrs)?;
3079             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3080                 && this.token.kind == token::Semi
3081             {
3082                 TrailingToken::Semi
3083             } else {
3084                 // FIXME - pass this through from the place where we know
3085                 // we need a comma, rather than assuming that `#[attr] expr,`
3086                 // always captures a trailing comma
3087                 TrailingToken::MaybeComma
3088             };
3089             Ok((res, trailing))
3090         })
3091     }
3092 }