compiler/rustc_parse/src/parser/expr.rs

   1 use super::diagnostics::SnapshotParser;
   2 use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
   3 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   4 use super::{
   5     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
   6     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
   7 };
   8 use crate::errors::{
   9     ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
  10     BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct, ComparisonInterpretedAsGeneric,
  11     ComparisonOrShiftInterpretedAsGenericSugg, DoCatchSyntaxRemoved, DotDotDot, EqFieldInit,
  12     ExpectedElseBlock, ExpectedEqForLetExpr, ExpectedExpressionFoundLet,
  13     FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
  14     IfExpressionMissingCondition, IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub,
  15     InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
  16     InvalidInterpolatedExpression, InvalidLiteralSuffixOnTupleIndex, InvalidLogicalOperator,
  17     InvalidLogicalOperatorSub, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
  18     LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
  19     MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
  20     MissingDotDot, MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray,
  21     NoFieldsForFnCall, NotAsNegationOperator, NotAsNegationOperatorSub,
  22     OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
  23     RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
  24     StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedIfWithIf,
  25     UnexpectedTokenAfterLabel, UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
  26 };
  27 use crate::maybe_recover_from_interpolated_ty_qpath;
  28 use core::mem;
  29 use rustc_ast::ptr::P;
  30 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
  31 use rustc_ast::tokenstream::Spacing;
  32 use rustc_ast::util::case::Case;
  33 use rustc_ast::util::classify;
  34 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  35 use rustc_ast::visit::Visitor;
  36 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, UnOp, DUMMY_NODE_ID};
  37 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  38 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  39 use rustc_ast::{ClosureBinder, MetaItemLit, StmtKind};
  40 use rustc_ast_pretty::pprust;
  41 use rustc_errors::{
  42     Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
  43     StashKey,
  44 };
  45 use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
  46 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  47 use rustc_session::lint::BuiltinLintDiagnostics;
  48 use rustc_span::source_map::{self, Span, Spanned};
  49 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  50 use rustc_span::{BytePos, Pos};
  51
  52 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  53 /// dropped into the token stream, which happens while parsing the result of
  54 /// macro expansion). Placement of these is not as complex as I feared it would
  55 /// be. The important thing is to make sure that lookahead doesn't balk at
  56 /// `token::Interpolated` tokens.
  57 macro_rules! maybe_whole_expr {
  58     ($p:expr) => {
  59         if let token::Interpolated(nt) = &$p.token.kind {
  60             match &**nt {
  61                 token::NtExpr(e) | token::NtLiteral(e) => {
  62                     let e = e.clone();
  63                     $p.bump();
  64                     return Ok(e);
  65                 }
  66                 token::NtPath(path) => {
  67                     let path = (**path).clone();
  68                     $p.bump();
  69                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Path(None, path)));
  70                 }
  71                 token::NtBlock(block) => {
  72                     let block = block.clone();
  73                     $p.bump();
  74                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Block(block, None)));
  75                 }
  76                 _ => {}
  77             };
  78         }
  79     };
  80 }
  81
  82 #[derive(Debug)]
  83 pub(super) enum LhsExpr {
  84     NotYetParsed,
  85     AttributesParsed(AttrWrapper),
  86     AlreadyParsed { expr: P<Expr>, starts_statement: bool },
  87 }
  88
  89 impl From<Option<AttrWrapper>> for LhsExpr {
  90     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  91     /// and `None` into `LhsExpr::NotYetParsed`.
  92     ///
  93     /// This conversion does not allocate.
  94     fn from(o: Option<AttrWrapper>) -> Self {
  95         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
  96     }
  97 }
  98
  99 impl From<P<Expr>> for LhsExpr {
 100     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed { expr, starts_statement: false }`.
 101     ///
 102     /// This conversion does not allocate.
 103     fn from(expr: P<Expr>) -> Self {
 104         LhsExpr::AlreadyParsed { expr, starts_statement: false }
 105     }
 106 }
 107
 108 impl<'a> Parser<'a> {
 109     /// Parses an expression.
 110     #[inline]
 111     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
 112         self.current_closure.take();
 113
 114         self.parse_expr_res(Restrictions::empty(), None)
 115     }
 116
 117     /// Parses an expression, forcing tokens to be collected
 118     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 119         self.collect_tokens_no_attrs(|this| this.parse_expr())
 120     }
 121
 122     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 123         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 124     }
 125
 126     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 127         match self.parse_expr() {
 128             Ok(expr) => Ok(expr),
 129             Err(mut err) => match self.token.ident() {
 130                 Some((Ident { name: kw::Underscore, .. }, false))
 131                     if self.may_recover() && self.look_ahead(1, |t| t == &token::Comma) =>
 132                 {
 133                     // Special-case handling of `foo(_, _, _)`
 134                     err.emit();
 135                     self.bump();
 136                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err))
 137                 }
 138                 _ => Err(err),
 139             },
 140         }
 141     }
 142
 143     /// Parses a sequence of expressions delimited by parentheses.
 144     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 145         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 146     }
 147
 148     /// Parses an expression, subject to the given restrictions.
 149     #[inline]
 150     pub(super) fn parse_expr_res(
 151         &mut self,
 152         r: Restrictions,
 153         already_parsed_attrs: Option<AttrWrapper>,
 154     ) -> PResult<'a, P<Expr>> {
 155         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 156     }
 157
 158     /// Parses an associative expression.
 159     ///
 160     /// This parses an expression accounting for associativity and precedence of the operators in
 161     /// the expression.
 162     #[inline]
 163     fn parse_assoc_expr(
 164         &mut self,
 165         already_parsed_attrs: Option<AttrWrapper>,
 166     ) -> PResult<'a, P<Expr>> {
 167         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 168     }
 169
 170     /// Parses an associative expression with operators of at least `min_prec` precedence.
 171     pub(super) fn parse_assoc_expr_with(
 172         &mut self,
 173         min_prec: usize,
 174         lhs: LhsExpr,
 175     ) -> PResult<'a, P<Expr>> {
 176         let mut starts_stmt = false;
 177         let mut lhs = if let LhsExpr::AlreadyParsed { expr, starts_statement } = lhs {
 178             starts_stmt = starts_statement;
 179             expr
 180         } else {
 181             let attrs = match lhs {
 182                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 183                 _ => None,
 184             };
 185             if self.token.is_range_separator() {
 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, starts_stmt)?;
 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` (unary plus)
 396             (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
 397             (true, Some(AssocOp::LOr)) | // `{ 42 } || 42` ("logical or" or closure)
 398             (true, Some(AssocOp::BitOr)) // `{ 42 } | 42` or `{ 42 } |x| 42`
 399             => {
 400                 // These cases are ambiguous and can't be identified in the parser alone.
 401                 //
 402                 // Bitwise AND is left out because guessing intent is hard. We can make
 403                 // suggestions based on the assumption that double-refs are rarely intentional,
 404                 // and closures are distinct enough that they don't get mixed up with their
 405                 // return value.
 406                 let sp = self.sess.source_map().start_point(self.token.span);
 407                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 408                 false
 409             }
 410             (true, Some(op)) if !op.can_continue_expr_unambiguously() => false,
 411             (true, Some(_)) => {
 412                 self.error_found_expr_would_be_stmt(lhs);
 413                 true
 414             }
 415         }
 416     }
 417
 418     /// We've found an expression that would be parsed as a statement,
 419     /// but the next token implies this should be parsed as an expression.
 420     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 421     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 422         self.sess.emit_err(FoundExprWouldBeStmt {
 423             span: self.token.span,
 424             token: self.token.clone(),
 425             suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
 426         });
 427     }
 428
 429     /// Possibly translate the current token to an associative operator.
 430     /// The method does not advance the current token.
 431     ///
 432     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 433     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 434         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 435             // When parsing const expressions, stop parsing when encountering `>`.
 436             (
 437                 Some(
 438                     AssocOp::ShiftRight
 439                     | AssocOp::Greater
 440                     | AssocOp::GreaterEqual
 441                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 442                 ),
 443                 _,
 444             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 445                 return None;
 446             }
 447             (Some(op), _) => (op, self.token.span),
 448             (None, Some((Ident { name: sym::and, span }, false))) if self.may_recover() => {
 449                 self.sess.emit_err(InvalidLogicalOperator {
 450                     span: self.token.span,
 451                     incorrect: "and".into(),
 452                     sub: InvalidLogicalOperatorSub::Conjunction(self.token.span),
 453                 });
 454                 (AssocOp::LAnd, span)
 455             }
 456             (None, Some((Ident { name: sym::or, span }, false))) if self.may_recover() => {
 457                 self.sess.emit_err(InvalidLogicalOperator {
 458                     span: self.token.span,
 459                     incorrect: "or".into(),
 460                     sub: InvalidLogicalOperatorSub::Disjunction(self.token.span),
 461                 });
 462                 (AssocOp::LOr, span)
 463             }
 464             _ => return None,
 465         };
 466         Some(source_map::respan(span, op))
 467     }
 468
 469     /// Checks if this expression is a successfully parsed statement.
 470     fn expr_is_complete(&self, e: &Expr) -> bool {
 471         self.restrictions.contains(Restrictions::STMT_EXPR)
 472             && !classify::expr_requires_semi_to_be_stmt(e)
 473     }
 474
 475     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 476     /// The other two variants are handled in `parse_prefix_range_expr` below.
 477     fn parse_range_expr(
 478         &mut self,
 479         prec: usize,
 480         lhs: P<Expr>,
 481         op: AssocOp,
 482         cur_op_span: Span,
 483     ) -> PResult<'a, P<Expr>> {
 484         let rhs = if self.is_at_start_of_range_notation_rhs() {
 485             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 486         } else {
 487             None
 488         };
 489         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 490         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 491         let limits =
 492             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 493         let range = self.mk_range(Some(lhs), rhs, limits);
 494         Ok(self.mk_expr(span, range))
 495     }
 496
 497     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 498         if self.token.can_begin_expr() {
 499             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 500             if self.token == token::OpenDelim(Delimiter::Brace) {
 501                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 502             }
 503             true
 504         } else {
 505             false
 506         }
 507     }
 508
 509     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 510     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 511         // Check for deprecated `...` syntax.
 512         if self.token == token::DotDotDot {
 513             self.err_dotdotdot_syntax(self.token.span);
 514         }
 515
 516         debug_assert!(
 517             self.token.is_range_separator(),
 518             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 519             self.token
 520         );
 521
 522         let limits = match self.token.kind {
 523             token::DotDot => RangeLimits::HalfOpen,
 524             _ => RangeLimits::Closed,
 525         };
 526         let op = AssocOp::from_token(&self.token);
 527         // FIXME: `parse_prefix_range_expr` is called when the current
 528         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 529         // parsed attributes, then trying to parse them here will always fail.
 530         // We should figure out how we want attributes on range expressions to work.
 531         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 532         self.collect_tokens_for_expr(attrs, |this, attrs| {
 533             let lo = this.token.span;
 534             this.bump();
 535             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 536                 // RHS must be parsed with more associativity than the dots.
 537                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 538                     .map(|x| (lo.to(x.span), Some(x)))?
 539             } else {
 540                 (lo, None)
 541             };
 542             let range = this.mk_range(None, opt_end, limits);
 543             Ok(this.mk_expr_with_attrs(span, range, attrs))
 544         })
 545     }
 546
 547     /// Parses a prefix-unary-operator expr.
 548     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 549         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 550         let lo = self.token.span;
 551
 552         macro_rules! make_it {
 553             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 554                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 555                     let (hi, ex) = $body?;
 556                     Ok($this.mk_expr_with_attrs(lo.to(hi), ex, attrs))
 557                 })
 558             };
 559         }
 560
 561         let this = self;
 562
 563         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 564         match this.token.uninterpolate().kind {
 565             // `!expr`
 566             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)),
 567             // `~expr`
 568             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)),
 569             // `-expr`
 570             token::BinOp(token::Minus) => {
 571                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 572             }
 573             // `*expr`
 574             token::BinOp(token::Star) => {
 575                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 576             }
 577             // `&expr` and `&&expr`
 578             token::BinOp(token::And) | token::AndAnd => {
 579                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 580             }
 581             // `+lit`
 582             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 583                 let mut err =
 584                     LeadingPlusNotSupported { span: lo, remove_plus: None, add_parentheses: None };
 585
 586                 // a block on the LHS might have been intended to be an expression instead
 587                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 588                     err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
 589                 } else {
 590                     err.remove_plus = Some(lo);
 591                 }
 592                 this.sess.emit_err(err);
 593
 594                 this.bump();
 595                 this.parse_prefix_expr(None)
 596             }
 597             // Recover from `++x`:
 598             token::BinOp(token::Plus)
 599                 if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
 600             {
 601                 let starts_stmt = this.prev_token == token::Semi
 602                     || this.prev_token == token::CloseDelim(Delimiter::Brace);
 603                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
 604                 // Eat both `+`s.
 605                 this.bump();
 606                 this.bump();
 607
 608                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
 609                 this.recover_from_prefix_increment(operand_expr, pre_span, starts_stmt)
 610             }
 611             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 612                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 613             }
 614             token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
 615                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 616             }
 617             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 618         }
 619     }
 620
 621     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 622         self.bump();
 623         let expr = self.parse_prefix_expr(None);
 624         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 625         Ok((lo.to(span), expr))
 626     }
 627
 628     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 629         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 630         Ok((span, self.mk_unary(op, expr)))
 631     }
 632
 633     /// Recover on `~expr` in favor of `!expr`.
 634     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 635         self.sess.emit_err(TildeAsUnaryOperator(lo));
 636
 637         self.parse_unary_expr(lo, UnOp::Not)
 638     }
 639
 640     /// Parse `box expr`.
 641     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 642         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 643         self.sess.gated_spans.gate(sym::box_syntax, span);
 644         Ok((span, ExprKind::Box(expr)))
 645     }
 646
 647     fn is_mistaken_not_ident_negation(&self) -> bool {
 648         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 649             // These tokens can start an expression after `!`, but
 650             // can't continue an expression after an ident
 651             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 652             token::Literal(..) | token::Pound => true,
 653             _ => t.is_whole_expr(),
 654         };
 655         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 656     }
 657
 658     /// Recover on `not expr` in favor of `!expr`.
 659     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 660         let negated_token = self.look_ahead(1, |t| t.clone());
 661
 662         let sub_diag = if negated_token.is_numeric_lit() {
 663             NotAsNegationOperatorSub::SuggestNotBitwise
 664         } else if negated_token.is_bool_lit() {
 665             NotAsNegationOperatorSub::SuggestNotLogical
 666         } else {
 667             NotAsNegationOperatorSub::SuggestNotDefault
 668         };
 669
 670         self.sess.emit_err(NotAsNegationOperator {
 671             negated: negated_token.span,
 672             negated_desc: super::token_descr(&negated_token),
 673             // Span the `not` plus trailing whitespace to avoid
 674             // trailing whitespace after the `!` in our suggestion
 675             sub: sub_diag(
 676                 self.sess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
 677             ),
 678         });
 679
 680         self.parse_unary_expr(lo, UnOp::Not)
 681     }
 682
 683     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 684     fn interpolated_or_expr_span(
 685         &self,
 686         expr: PResult<'a, P<Expr>>,
 687     ) -> PResult<'a, (Span, P<Expr>)> {
 688         expr.map(|e| {
 689             (
 690                 match self.prev_token.kind {
 691                     TokenKind::Interpolated(..) => self.prev_token.span,
 692                     _ => e.span,
 693                 },
 694                 e,
 695             )
 696         })
 697     }
 698
 699     fn parse_assoc_op_cast(
 700         &mut self,
 701         lhs: P<Expr>,
 702         lhs_span: Span,
 703         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 704     ) -> PResult<'a, P<Expr>> {
 705         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 706             this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, rhs.span), expr_kind(lhs, rhs))
 707         };
 708
 709         // Save the state of the parser before parsing type normally, in case there is a
 710         // LessThan comparison after this cast.
 711         let parser_snapshot_before_type = self.clone();
 712         let cast_expr = match self.parse_as_cast_ty() {
 713             Ok(rhs) => mk_expr(self, lhs, rhs),
 714             Err(type_err) => {
 715                 if !self.may_recover() {
 716                     return Err(type_err);
 717                 }
 718
 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         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 831
 832         // Check if an illegal postfix operator has been added after the cast.
 833         // If the resulting expression is not a cast, it is an illegal postfix operator.
 834         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) {
 835             let msg = format!(
 836                 "{cast_kind} cannot be followed by {}",
 837                 match with_postfix.kind {
 838                     ExprKind::Index(_, _) => "indexing",
 839                     ExprKind::Try(_) => "`?`",
 840                     ExprKind::Field(_, _) => "a field access",
 841                     ExprKind::MethodCall(_) => "a method call",
 842                     ExprKind::Call(_, _) => "a function call",
 843                     ExprKind::Await(_) => "`.await`",
 844                     ExprKind::Err => return Ok(with_postfix),
 845                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 846                 }
 847             );
 848             let mut err = self.struct_span_err(span, &msg);
 849
 850             let suggest_parens = |err: &mut Diagnostic| {
 851                 let suggestions = vec![
 852                     (span.shrink_to_lo(), "(".to_string()),
 853                     (span.shrink_to_hi(), ")".to_string()),
 854                 ];
 855                 err.multipart_suggestion(
 856                     "try surrounding the expression in parentheses",
 857                     suggestions,
 858                     Applicability::MachineApplicable,
 859                 );
 860             };
 861
 862             // If type ascription is "likely an error", the user will already be getting a useful
 863             // help message, and doesn't need a second.
 864             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 865                 self.maybe_annotate_with_ascription(&mut err, false);
 866             } else if let Some(ascription_span) = maybe_ascription_span {
 867                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 868                 if is_nightly {
 869                     suggest_parens(&mut err);
 870                 }
 871                 err.span_suggestion(
 872                     ascription_span,
 873                     &format!(
 874                         "{}remove the type ascription",
 875                         if is_nightly { "alternatively, " } else { "" }
 876                     ),
 877                     "",
 878                     if is_nightly {
 879                         Applicability::MaybeIncorrect
 880                     } else {
 881                         Applicability::MachineApplicable
 882                     },
 883                 );
 884             } else {
 885                 suggest_parens(&mut err);
 886             }
 887             err.emit();
 888         };
 889         Ok(with_postfix)
 890     }
 891
 892     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 893         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 894         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 895         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 896         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 897         Ok(lhs)
 898     }
 899
 900     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 901     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 902         self.expect_and()?;
 903         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 904         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 905         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 906         let expr = if self.token.is_range_separator() {
 907             self.parse_prefix_range_expr(None)
 908         } else {
 909             self.parse_prefix_expr(None)
 910         };
 911         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 912         let span = lo.to(hi);
 913         if let Some(lt) = lifetime {
 914             self.error_remove_borrow_lifetime(span, lt.ident.span);
 915         }
 916         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 917     }
 918
 919     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 920         self.sess.emit_err(LifetimeInBorrowExpression { span, lifetime_span: lt_span });
 921     }
 922
 923     /// Parse `mut?` or `raw [ const | mut ]`.
 924     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 925         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 926             // `raw [ const | mut ]`.
 927             let found_raw = self.eat_keyword(kw::Raw);
 928             assert!(found_raw);
 929             let mutability = self.parse_const_or_mut().unwrap();
 930             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 931             (ast::BorrowKind::Raw, mutability)
 932         } else {
 933             // `mut?`
 934             (ast::BorrowKind::Ref, self.parse_mutability())
 935         }
 936     }
 937
 938     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 939     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 940         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 941         self.collect_tokens_for_expr(attrs, |this, attrs| {
 942             let base = this.parse_bottom_expr();
 943             let (span, base) = this.interpolated_or_expr_span(base)?;
 944             this.parse_dot_or_call_expr_with(base, span, attrs)
 945         })
 946     }
 947
 948     pub(super) fn parse_dot_or_call_expr_with(
 949         &mut self,
 950         e0: P<Expr>,
 951         lo: Span,
 952         mut attrs: ast::AttrVec,
 953     ) -> PResult<'a, P<Expr>> {
 954         // Stitch the list of outer attributes onto the return value.
 955         // A little bit ugly, but the best way given the current code
 956         // structure
 957         let res = self.parse_dot_or_call_expr_with_(e0, lo);
 958         if attrs.is_empty() {
 959             res
 960         } else {
 961             res.map(|expr| {
 962                 expr.map(|mut expr| {
 963                     attrs.extend(expr.attrs);
 964                     expr.attrs = attrs;
 965                     expr
 966                 })
 967             })
 968         }
 969     }
 970
 971     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 972         loop {
 973             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 974                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 975                 // which could be suggested otherwise
 976                 self.eat_noexpect(&token::Question)
 977             } else {
 978                 self.eat(&token::Question)
 979             };
 980             if has_question {
 981                 // `expr?`
 982                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
 983                 continue;
 984             }
 985             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 986                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 987                 // which could be suggested otherwise
 988                 self.eat_noexpect(&token::Dot)
 989             } else {
 990                 self.eat(&token::Dot)
 991             };
 992             if has_dot {
 993                 // expr.f
 994                 e = self.parse_dot_suffix_expr(lo, e)?;
 995                 continue;
 996             }
 997             if self.expr_is_complete(&e) {
 998                 return Ok(e);
 999             }
1000             e = match self.token.kind {
1001                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1002                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1003                 _ => return Ok(e),
1004             }
1005         }
1006     }
1007
1008     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1009         self.look_ahead(1, |t| t.is_ident())
1010             && self.look_ahead(2, |t| t == &token::Colon)
1011             && self.look_ahead(3, |t| t.can_begin_expr())
1012     }
1013
1014     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1015         match self.token.uninterpolate().kind {
1016             token::Ident(..) => self.parse_dot_suffix(base, lo),
1017             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1018                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1019             }
1020             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1021                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1022             }
1023             _ => {
1024                 self.error_unexpected_after_dot();
1025                 Ok(base)
1026             }
1027         }
1028     }
1029
1030     fn error_unexpected_after_dot(&self) {
1031         // FIXME Could factor this out into non_fatal_unexpected or something.
1032         let actual = pprust::token_to_string(&self.token);
1033         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1034     }
1035
1036     // We need an identifier or integer, but the next token is a float.
1037     // Break the float into components to extract the identifier or integer.
1038     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1039     // parts unless those parts are processed immediately. `TokenCursor` should either
1040     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1041     // we should break everything including floats into more basic proc-macro style
1042     // tokens in the lexer (probably preferable).
1043     fn parse_tuple_field_access_expr_float(
1044         &mut self,
1045         lo: Span,
1046         base: P<Expr>,
1047         float: Symbol,
1048         suffix: Option<Symbol>,
1049     ) -> P<Expr> {
1050         #[derive(Debug)]
1051         enum FloatComponent {
1052             IdentLike(String),
1053             Punct(char),
1054         }
1055         use FloatComponent::*;
1056
1057         let float_str = float.as_str();
1058         let mut components = Vec::new();
1059         let mut ident_like = String::new();
1060         for c in float_str.chars() {
1061             if c == '_' || c.is_ascii_alphanumeric() {
1062                 ident_like.push(c);
1063             } else if matches!(c, '.' | '+' | '-') {
1064                 if !ident_like.is_empty() {
1065                     components.push(IdentLike(mem::take(&mut ident_like)));
1066                 }
1067                 components.push(Punct(c));
1068             } else {
1069                 panic!("unexpected character in a float token: {:?}", c)
1070             }
1071         }
1072         if !ident_like.is_empty() {
1073             components.push(IdentLike(ident_like));
1074         }
1075
1076         // With proc macros the span can refer to anything, the source may be too short,
1077         // or too long, or non-ASCII. It only makes sense to break our span into components
1078         // if its underlying text is identical to our float literal.
1079         let span = self.token.span;
1080         let can_take_span_apart =
1081             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1082
1083         match &*components {
1084             // 1e2
1085             [IdentLike(i)] => {
1086                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1087             }
1088             // 1.
1089             [IdentLike(i), Punct('.')] => {
1090                 let (ident_span, dot_span) = if can_take_span_apart() {
1091                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1092                     let ident_span = span.with_hi(span.lo + ident_len);
1093                     let dot_span = span.with_lo(span.lo + ident_len);
1094                     (ident_span, dot_span)
1095                 } else {
1096                     (span, span)
1097                 };
1098                 assert!(suffix.is_none());
1099                 let symbol = Symbol::intern(&i);
1100                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1101                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1102                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1103             }
1104             // 1.2 | 1.2e3
1105             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1106                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1107                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1108                     let ident1_span = span.with_hi(span.lo + ident1_len);
1109                     let dot_span = span
1110                         .with_lo(span.lo + ident1_len)
1111                         .with_hi(span.lo + ident1_len + BytePos(1));
1112                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1113                     (ident1_span, dot_span, ident2_span)
1114                 } else {
1115                     (span, span, span)
1116                 };
1117                 let symbol1 = Symbol::intern(&i1);
1118                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1119                 // This needs to be `Spacing::Alone` to prevent regressions.
1120                 // See issue #76399 and PR #76285 for more details
1121                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1122                 let base1 =
1123                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1124                 let symbol2 = Symbol::intern(&i2);
1125                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1126                 self.bump_with((next_token2, self.token_spacing)); // `.`
1127                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1128             }
1129             // 1e+ | 1e- (recovered)
1130             [IdentLike(_), Punct('+' | '-')] |
1131             // 1e+2 | 1e-2
1132             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1133             // 1.2e+ | 1.2e-
1134             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1135             // 1.2e+3 | 1.2e-3
1136             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1137                 // See the FIXME about `TokenCursor` above.
1138                 self.error_unexpected_after_dot();
1139                 base
1140             }
1141             _ => panic!("unexpected components in a float token: {:?}", components),
1142         }
1143     }
1144
1145     fn parse_tuple_field_access_expr(
1146         &mut self,
1147         lo: Span,
1148         base: P<Expr>,
1149         field: Symbol,
1150         suffix: Option<Symbol>,
1151         next_token: Option<(Token, Spacing)>,
1152     ) -> P<Expr> {
1153         match next_token {
1154             Some(next_token) => self.bump_with(next_token),
1155             None => self.bump(),
1156         }
1157         let span = self.prev_token.span;
1158         let field = ExprKind::Field(base, Ident::new(field, span));
1159         if let Some(suffix) = suffix {
1160             self.expect_no_tuple_index_suffix(span, suffix);
1161         }
1162         self.mk_expr(lo.to(span), field)
1163     }
1164
1165     /// Parse a function call expression, `expr(...)`.
1166     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1167         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1168             && self.look_ahead_type_ascription_as_field()
1169         {
1170             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1171         } else {
1172             None
1173         };
1174         let open_paren = self.token.span;
1175
1176         let mut seq = self
1177             .parse_paren_expr_seq()
1178             .map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
1179         if let Some(expr) =
1180             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1181         {
1182             return expr;
1183         }
1184         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1185     }
1186
1187     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1188     /// parentheses instead of braces, recover the parser state and provide suggestions.
1189     #[instrument(skip(self, seq, snapshot), level = "trace")]
1190     fn maybe_recover_struct_lit_bad_delims(
1191         &mut self,
1192         lo: Span,
1193         open_paren: Span,
1194         seq: &mut PResult<'a, P<Expr>>,
1195         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1196     ) -> Option<P<Expr>> {
1197         if !self.may_recover() {
1198             return None;
1199         }
1200
1201         match (seq.as_mut(), snapshot) {
1202             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1203                 snapshot.bump(); // `(`
1204                 match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
1205                     Ok((fields, ..))
1206                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1207                     {
1208                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1209                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1210                         self.restore_snapshot(snapshot);
1211                         let close_paren = self.prev_token.span;
1212                         let span = lo.to(self.prev_token.span);
1213                         if !fields.is_empty() {
1214                             let mut replacement_err = ParenthesesWithStructFields {
1215                                 span,
1216                                 r#type: path,
1217                                 braces_for_struct: BracesForStructLiteral {
1218                                     first: open_paren,
1219                                     second: close_paren,
1220                                 },
1221                                 no_fields_for_fn: NoFieldsForFnCall {
1222                                     fields: fields
1223                                         .into_iter()
1224                                         .map(|field| field.span.until(field.expr.span))
1225                                         .collect(),
1226                                 },
1227                             }
1228                             .into_diagnostic(&self.sess.span_diagnostic);
1229                             replacement_err.emit();
1230
1231                             let old_err = mem::replace(err, replacement_err);
1232                             old_err.cancel();
1233                         } else {
1234                             err.emit();
1235                         }
1236                         return Some(self.mk_expr_err(span));
1237                     }
1238                     Ok(_) => {}
1239                     Err(mut err) => {
1240                         err.emit();
1241                     }
1242                 }
1243             }
1244             _ => {}
1245         }
1246         None
1247     }
1248
1249     /// Parse an indexing expression `expr[...]`.
1250     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1251         let prev_span = self.prev_token.span;
1252         let open_delim_span = self.token.span;
1253         self.bump(); // `[`
1254         let index = self.parse_expr()?;
1255         self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
1256         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1257         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index)))
1258     }
1259
1260     /// Assuming we have just parsed `.`, continue parsing into an expression.
1261     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1262         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1263             return Ok(self.mk_await_expr(self_arg, lo));
1264         }
1265
1266         let fn_span_lo = self.token.span;
1267         let mut seg = self.parse_path_segment(PathStyle::Expr, None)?;
1268         self.check_trailing_angle_brackets(&seg, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1269         self.check_turbofish_missing_angle_brackets(&mut seg);
1270
1271         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1272             // Method call `expr.f()`
1273             let args = self.parse_paren_expr_seq()?;
1274             let fn_span = fn_span_lo.to(self.prev_token.span);
1275             let span = lo.to(self.prev_token.span);
1276             Ok(self.mk_expr(
1277                 span,
1278                 ExprKind::MethodCall(Box::new(ast::MethodCall {
1279                     seg,
1280                     receiver: self_arg,
1281                     args,
1282                     span: fn_span,
1283                 })),
1284             ))
1285         } else {
1286             // Field access `expr.f`
1287             if let Some(args) = seg.args {
1288                 self.sess.emit_err(FieldExpressionWithGeneric(args.span()));
1289             }
1290
1291             let span = lo.to(self.prev_token.span);
1292             Ok(self.mk_expr(span, ExprKind::Field(self_arg, seg.ident)))
1293         }
1294     }
1295
1296     /// At the bottom (top?) of the precedence hierarchy,
1297     /// Parses things like parenthesized exprs, macros, `return`, etc.
1298     ///
1299     /// N.B., this does not parse outer attributes, and is private because it only works
1300     /// correctly if called from `parse_dot_or_call_expr()`.
1301     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1302         maybe_recover_from_interpolated_ty_qpath!(self, true);
1303         maybe_whole_expr!(self);
1304
1305         // Outer attributes are already parsed and will be
1306         // added to the return value after the fact.
1307
1308         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1309         let lo = self.token.span;
1310         if let token::Literal(_) = self.token.kind {
1311             // This match arm is a special-case of the `_` match arm below and
1312             // could be removed without changing functionality, but it's faster
1313             // to have it here, especially for programs with large constants.
1314             self.parse_lit_expr()
1315         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1316             self.parse_tuple_parens_expr()
1317         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1318             self.parse_block_expr(None, lo, BlockCheckMode::Default)
1319         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1320             self.parse_closure_expr().map_err(|mut err| {
1321                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1322                 // then suggest parens around the lhs.
1323                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1324                     err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
1325                 }
1326                 err
1327             })
1328         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1329             self.parse_array_or_repeat_expr(Delimiter::Bracket)
1330         } else if self.check_path() {
1331             self.parse_path_start_expr()
1332         } else if self.check_keyword(kw::Move)
1333             || self.check_keyword(kw::Static)
1334             || self.check_const_closure()
1335         {
1336             self.parse_closure_expr()
1337         } else if self.eat_keyword(kw::If) {
1338             self.parse_if_expr()
1339         } else if self.check_keyword(kw::For) {
1340             if self.choose_generics_over_qpath(1) {
1341                 self.parse_closure_expr()
1342             } else {
1343                 assert!(self.eat_keyword(kw::For));
1344                 self.parse_for_expr(None, self.prev_token.span)
1345             }
1346         } else if self.eat_keyword(kw::While) {
1347             self.parse_while_expr(None, self.prev_token.span)
1348         } else if let Some(label) = self.eat_label() {
1349             self.parse_labeled_expr(label, true)
1350         } else if self.eat_keyword(kw::Loop) {
1351             let sp = self.prev_token.span;
1352             self.parse_loop_expr(None, self.prev_token.span).map_err(|mut err| {
1353                 err.span_label(sp, "while parsing this `loop` expression");
1354                 err
1355             })
1356         } else if self.eat_keyword(kw::Continue) {
1357             let kind = ExprKind::Continue(self.eat_label());
1358             Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
1359         } else if self.eat_keyword(kw::Match) {
1360             let match_sp = self.prev_token.span;
1361             self.parse_match_expr().map_err(|mut err| {
1362                 err.span_label(match_sp, "while parsing this `match` expression");
1363                 err
1364             })
1365         } else if self.eat_keyword(kw::Unsafe) {
1366             let sp = self.prev_token.span;
1367             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
1368                 |mut err| {
1369                     err.span_label(sp, "while parsing this `unsafe` expression");
1370                     err
1371                 },
1372             )
1373         } else if self.check_inline_const(0) {
1374             self.parse_const_block(lo.to(self.token.span), false)
1375         } else if self.may_recover() && self.is_do_catch_block() {
1376             self.recover_do_catch()
1377         } else if self.is_try_block() {
1378             self.expect_keyword(kw::Try)?;
1379             self.parse_try_block(lo)
1380         } else if self.eat_keyword(kw::Return) {
1381             self.parse_return_expr()
1382         } else if self.eat_keyword(kw::Break) {
1383             self.parse_break_expr()
1384         } else if self.eat_keyword(kw::Yield) {
1385             self.parse_yield_expr()
1386         } else if self.is_do_yeet() {
1387             self.parse_yeet_expr()
1388         } else if self.check_keyword(kw::Let) {
1389             self.parse_let_expr()
1390         } else if self.eat_keyword(kw::Underscore) {
1391             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore))
1392         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1393             // Don't complain about bare semicolons after unclosed braces
1394             // recovery in order to keep the error count down. Fixing the
1395             // delimiters will possibly also fix the bare semicolon found in
1396             // expression context. For example, silence the following error:
1397             //
1398             //     error: expected expression, found `;`
1399             //      --> file.rs:2:13
1400             //       |
1401             //     2 |     foo(bar(;
1402             //       |             ^ expected expression
1403             self.bump();
1404             Ok(self.mk_expr_err(self.token.span))
1405         } else if self.token.uninterpolated_span().rust_2018() {
1406             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1407             if self.check_keyword(kw::Async) {
1408                 if self.is_async_block() {
1409                     // Check for `async {` and `async move {`.
1410                     self.parse_async_block()
1411                 } else {
1412                     self.parse_closure_expr()
1413                 }
1414             } else if self.eat_keyword(kw::Await) {
1415                 self.recover_incorrect_await_syntax(lo, self.prev_token.span)
1416             } else {
1417                 self.parse_lit_expr()
1418             }
1419         } else {
1420             self.parse_lit_expr()
1421         }
1422     }
1423
1424     fn parse_lit_expr(&mut self) -> PResult<'a, P<Expr>> {
1425         let lo = self.token.span;
1426         match self.parse_opt_token_lit() {
1427             Some((token_lit, _)) => {
1428                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(token_lit));
1429                 self.maybe_recover_from_bad_qpath(expr)
1430             }
1431             None => self.try_macro_suggestion(),
1432         }
1433     }
1434
1435     fn parse_tuple_parens_expr(&mut self) -> PResult<'a, P<Expr>> {
1436         let lo = self.token.span;
1437         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1438         let (es, trailing_comma) = match self.parse_seq_to_end(
1439             &token::CloseDelim(Delimiter::Parenthesis),
1440             SeqSep::trailing_allowed(token::Comma),
1441             |p| p.parse_expr_catch_underscore(),
1442         ) {
1443             Ok(x) => x,
1444             Err(err) => {
1445                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1446             }
1447         };
1448         let kind = if es.len() == 1 && !trailing_comma {
1449             // `(e)` is parenthesized `e`.
1450             ExprKind::Paren(es.into_iter().next().unwrap())
1451         } else {
1452             // `(e,)` is a tuple with only one field, `e`.
1453             ExprKind::Tup(es)
1454         };
1455         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1456         self.maybe_recover_from_bad_qpath(expr)
1457     }
1458
1459     fn parse_array_or_repeat_expr(&mut self, close_delim: Delimiter) -> PResult<'a, P<Expr>> {
1460         let lo = self.token.span;
1461         self.bump(); // `[` or other open delim
1462
1463         let close = &token::CloseDelim(close_delim);
1464         let kind = if self.eat(close) {
1465             // Empty vector
1466             ExprKind::Array(Vec::new())
1467         } else {
1468             // Non-empty vector
1469             let first_expr = self.parse_expr()?;
1470             if self.eat(&token::Semi) {
1471                 // Repeating array syntax: `[ 0; 512 ]`
1472                 let count = self.parse_anon_const_expr()?;
1473                 self.expect(close)?;
1474                 ExprKind::Repeat(first_expr, count)
1475             } else if self.eat(&token::Comma) {
1476                 // Vector with two or more elements.
1477                 let sep = SeqSep::trailing_allowed(token::Comma);
1478                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1479                 let mut exprs = vec![first_expr];
1480                 exprs.extend(remaining_exprs);
1481                 ExprKind::Array(exprs)
1482             } else {
1483                 // Vector with one element
1484                 self.expect(close)?;
1485                 ExprKind::Array(vec![first_expr])
1486             }
1487         };
1488         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1489         self.maybe_recover_from_bad_qpath(expr)
1490     }
1491
1492     fn parse_path_start_expr(&mut self) -> PResult<'a, P<Expr>> {
1493         let (qself, path) = if self.eat_lt() {
1494             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1495             (Some(qself), path)
1496         } else {
1497             (None, self.parse_path(PathStyle::Expr)?)
1498         };
1499
1500         // `!`, as an operator, is prefix, so we know this isn't that.
1501         let (span, kind) = if self.eat(&token::Not) {
1502             // MACRO INVOCATION expression
1503             if qself.is_some() {
1504                 self.sess.emit_err(MacroInvocationWithQualifiedPath(path.span));
1505             }
1506             let lo = path.span;
1507             let mac = P(MacCall {
1508                 path,
1509                 args: self.parse_delim_args()?,
1510                 prior_type_ascription: self.last_type_ascription,
1511             });
1512             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
1513         } else if self.check(&token::OpenDelim(Delimiter::Brace))
1514             && let Some(expr) = self.maybe_parse_struct_expr(&qself, &path)
1515         {
1516             if qself.is_some() {
1517                 self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1518             }
1519             return expr;
1520         } else {
1521             (path.span, ExprKind::Path(qself, path))
1522         };
1523
1524         let expr = self.mk_expr(span, kind);
1525         self.maybe_recover_from_bad_qpath(expr)
1526     }
1527
1528     /// Parse `'label: $expr`. The label is already parsed.
1529     fn parse_labeled_expr(
1530         &mut self,
1531         label_: Label,
1532         mut consume_colon: bool,
1533     ) -> PResult<'a, P<Expr>> {
1534         let lo = label_.ident.span;
1535         let label = Some(label_);
1536         let ate_colon = self.eat(&token::Colon);
1537         let expr = if self.eat_keyword(kw::While) {
1538             self.parse_while_expr(label, lo)
1539         } else if self.eat_keyword(kw::For) {
1540             self.parse_for_expr(label, lo)
1541         } else if self.eat_keyword(kw::Loop) {
1542             self.parse_loop_expr(label, lo)
1543         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1544             || self.token.is_whole_block()
1545         {
1546             self.parse_block_expr(label, lo, BlockCheckMode::Default)
1547         } else if !ate_colon
1548             && self.may_recover()
1549             && (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
1550                 || self.token.is_op())
1551         {
1552             let (lit, _) =
1553                 self.recover_unclosed_char(label_.ident, Parser::mk_token_lit_char, |self_| {
1554                     self_.sess.create_err(UnexpectedTokenAfterLabel {
1555                         span: self_.token.span,
1556                         remove_label: None,
1557                         enclose_in_block: None,
1558                     })
1559                 });
1560             consume_colon = false;
1561             Ok(self.mk_expr(lo, ExprKind::Lit(lit)))
1562         } else if !ate_colon
1563             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1564         {
1565             // We're probably inside of a `Path<'a>` that needs a turbofish
1566             self.sess.emit_err(UnexpectedTokenAfterLabel {
1567                 span: self.token.span,
1568                 remove_label: None,
1569                 enclose_in_block: None,
1570             });
1571             consume_colon = false;
1572             Ok(self.mk_expr_err(lo))
1573         } else {
1574             let mut err = UnexpectedTokenAfterLabel {
1575                 span: self.token.span,
1576                 remove_label: None,
1577                 enclose_in_block: None,
1578             };
1579
1580             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1581             let expr = self.parse_expr().map(|expr| {
1582                 let span = expr.span;
1583
1584                 let found_labeled_breaks = {
1585                     struct FindLabeledBreaksVisitor(bool);
1586
1587                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1588                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1589                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1590                                 self.0 = true;
1591                             }
1592                         }
1593                     }
1594
1595                     let mut vis = FindLabeledBreaksVisitor(false);
1596                     vis.visit_expr(&expr);
1597                     vis.0
1598                 };
1599
1600                 // Suggestion involves adding a labeled block.
1601                 //
1602                 // If there are no breaks that may use this label, suggest removing the label and
1603                 // recover to the unmodified expression.
1604                 if !found_labeled_breaks {
1605                     err.remove_label = Some(lo.until(span));
1606
1607                     return expr;
1608                 }
1609
1610                 err.enclose_in_block = Some(UnexpectedTokenAfterLabelSugg {
1611                     left: span.shrink_to_lo(),
1612                     right: span.shrink_to_hi(),
1613                 });
1614
1615                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
1616                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1617                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1618                 self.mk_expr(span, ExprKind::Block(blk, label))
1619             });
1620
1621             self.sess.emit_err(err);
1622             expr
1623         }?;
1624
1625         if !ate_colon && consume_colon {
1626             self.sess.emit_err(RequireColonAfterLabeledExpression {
1627                 span: expr.span,
1628                 label: lo,
1629                 label_end: lo.shrink_to_hi(),
1630             });
1631         }
1632
1633         Ok(expr)
1634     }
1635
1636     /// Emit an error when a char is parsed as a lifetime because of a missing quote.
1637     pub(super) fn recover_unclosed_char<L>(
1638         &self,
1639         lifetime: Ident,
1640         mk_lit_char: impl FnOnce(Symbol, Span) -> L,
1641         err: impl FnOnce(&Self) -> DiagnosticBuilder<'a, ErrorGuaranteed>,
1642     ) -> L {
1643         if let Some(mut diag) =
1644             self.sess.span_diagnostic.steal_diagnostic(lifetime.span, StashKey::LifetimeIsChar)
1645         {
1646             diag.span_suggestion_verbose(
1647                 lifetime.span.shrink_to_hi(),
1648                 "add `'` to close the char literal",
1649                 "'",
1650                 Applicability::MaybeIncorrect,
1651             )
1652             .emit();
1653         } else {
1654             err(self)
1655                 .span_suggestion_verbose(
1656                     lifetime.span.shrink_to_hi(),
1657                     "add `'` to close the char literal",
1658                     "'",
1659                     Applicability::MaybeIncorrect,
1660                 )
1661                 .emit();
1662         }
1663         let name = lifetime.without_first_quote().name;
1664         mk_lit_char(name, lifetime.span)
1665     }
1666
1667     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1668     fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
1669         let lo = self.token.span;
1670
1671         self.bump(); // `do`
1672         self.bump(); // `catch`
1673
1674         let span = lo.to(self.prev_token.span);
1675         self.sess.emit_err(DoCatchSyntaxRemoved { span });
1676
1677         self.parse_try_block(lo)
1678     }
1679
1680     /// Parse an expression if the token can begin one.
1681     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1682         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1683     }
1684
1685     /// Parse `"return" expr?`.
1686     fn parse_return_expr(&mut self) -> PResult<'a, P<Expr>> {
1687         let lo = self.prev_token.span;
1688         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1689         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1690         self.maybe_recover_from_bad_qpath(expr)
1691     }
1692
1693     /// Parse `"do" "yeet" expr?`.
1694     fn parse_yeet_expr(&mut self) -> PResult<'a, P<Expr>> {
1695         let lo = self.token.span;
1696
1697         self.bump(); // `do`
1698         self.bump(); // `yeet`
1699
1700         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1701
1702         let span = lo.to(self.prev_token.span);
1703         self.sess.gated_spans.gate(sym::yeet_expr, span);
1704         let expr = self.mk_expr(span, kind);
1705         self.maybe_recover_from_bad_qpath(expr)
1706     }
1707
1708     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1709     /// If the label is followed immediately by a `:` token, the label and `:` are
1710     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1711     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1712     /// the break expression of an unlabeled break is a labeled loop (as in
1713     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1714     /// expression only gets a warning for compatibility reasons; and a labeled break
1715     /// with a labeled loop does not even get a warning because there is no ambiguity.
1716     fn parse_break_expr(&mut self) -> PResult<'a, P<Expr>> {
1717         let lo = self.prev_token.span;
1718         let mut label = self.eat_label();
1719         let kind = if label.is_some() && self.token == token::Colon {
1720             // The value expression can be a labeled loop, see issue #86948, e.g.:
1721             // `loop { break 'label: loop { break 'label 42; }; }`
1722             let lexpr = self.parse_labeled_expr(label.take().unwrap(), true)?;
1723             self.sess.emit_err(LabeledLoopInBreak {
1724                 span: lexpr.span,
1725                 sub: WrapExpressionInParentheses {
1726                     left: lexpr.span.shrink_to_lo(),
1727                     right: lexpr.span.shrink_to_hi(),
1728                 },
1729             });
1730             Some(lexpr)
1731         } else if self.token != token::OpenDelim(Delimiter::Brace)
1732             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1733         {
1734             let expr = self.parse_expr_opt()?;
1735             if let Some(expr) = &expr {
1736                 if label.is_some()
1737                     && matches!(
1738                         expr.kind,
1739                         ExprKind::While(_, _, None)
1740                             | ExprKind::ForLoop(_, _, _, None)
1741                             | ExprKind::Loop(_, None, _)
1742                             | ExprKind::Block(_, None)
1743                     )
1744                 {
1745                     self.sess.buffer_lint_with_diagnostic(
1746                         BREAK_WITH_LABEL_AND_LOOP,
1747                         lo.to(expr.span),
1748                         ast::CRATE_NODE_ID,
1749                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1750                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1751                     );
1752                 }
1753             }
1754             expr
1755         } else {
1756             None
1757         };
1758         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
1759         self.maybe_recover_from_bad_qpath(expr)
1760     }
1761
1762     /// Parse `"yield" expr?`.
1763     fn parse_yield_expr(&mut self) -> PResult<'a, P<Expr>> {
1764         let lo = self.prev_token.span;
1765         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1766         let span = lo.to(self.prev_token.span);
1767         self.sess.gated_spans.gate(sym::generators, span);
1768         let expr = self.mk_expr(span, kind);
1769         self.maybe_recover_from_bad_qpath(expr)
1770     }
1771
1772     /// Returns a string literal if the next token is a string literal.
1773     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1774     /// and returns `None` if the next token is not literal at all.
1775     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<MetaItemLit>> {
1776         match self.parse_opt_meta_item_lit() {
1777             Some(lit) => match lit.kind {
1778                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1779                     style,
1780                     symbol: lit.symbol,
1781                     suffix: lit.suffix,
1782                     span: lit.span,
1783                     symbol_unescaped,
1784                 }),
1785                 _ => Err(Some(lit)),
1786             },
1787             None => Err(None),
1788         }
1789     }
1790
1791     pub(crate) fn mk_token_lit_char(name: Symbol, span: Span) -> (token::Lit, Span) {
1792         (token::Lit { symbol: name, suffix: None, kind: token::Char }, span)
1793     }
1794
1795     fn mk_meta_item_lit_char(name: Symbol, span: Span) -> MetaItemLit {
1796         ast::MetaItemLit {
1797             symbol: name,
1798             suffix: None,
1799             kind: ast::LitKind::Char(name.as_str().chars().next().unwrap_or('_')),
1800             span,
1801         }
1802     }
1803
1804     fn handle_missing_lit<L>(
1805         &mut self,
1806         mk_lit_char: impl FnOnce(Symbol, Span) -> L,
1807     ) -> PResult<'a, L> {
1808         if let token::Interpolated(inner) = &self.token.kind {
1809             let expr = match inner.as_ref() {
1810                 token::NtExpr(expr) => Some(expr),
1811                 token::NtLiteral(expr) => Some(expr),
1812                 _ => None,
1813             };
1814             if let Some(expr) = expr {
1815                 if matches!(expr.kind, ExprKind::Err) {
1816                     let mut err = InvalidInterpolatedExpression { span: self.token.span }
1817                         .into_diagnostic(&self.sess.span_diagnostic);
1818                     err.downgrade_to_delayed_bug();
1819                     return Err(err);
1820                 }
1821             }
1822         }
1823         let token = self.token.clone();
1824         let err = |self_: &Self| {
1825             let msg = format!("unexpected token: {}", super::token_descr(&token));
1826             self_.struct_span_err(token.span, &msg)
1827         };
1828         // On an error path, eagerly consider a lifetime to be an unclosed character lit
1829         if self.token.is_lifetime() {
1830             let lt = self.expect_lifetime();
1831             Ok(self.recover_unclosed_char(lt.ident, mk_lit_char, err))
1832         } else {
1833             Err(err(self))
1834         }
1835     }
1836
1837     pub(super) fn parse_token_lit(&mut self) -> PResult<'a, (token::Lit, Span)> {
1838         self.parse_opt_token_lit()
1839             .ok_or(())
1840             .or_else(|()| self.handle_missing_lit(Parser::mk_token_lit_char))
1841     }
1842
1843     pub(super) fn parse_meta_item_lit(&mut self) -> PResult<'a, MetaItemLit> {
1844         self.parse_opt_meta_item_lit()
1845             .ok_or(())
1846             .or_else(|()| self.handle_missing_lit(Parser::mk_meta_item_lit_char))
1847     }
1848
1849     fn recover_after_dot(&mut self) -> Option<Token> {
1850         let mut recovered = None;
1851         if self.token == token::Dot {
1852             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1853             // dot would follow an optional literal, so we do this unconditionally.
1854             recovered = self.look_ahead(1, |next_token| {
1855                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1856                     next_token.kind
1857                 {
1858                     if self.token.span.hi() == next_token.span.lo() {
1859                         let s = String::from("0.") + symbol.as_str();
1860                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1861                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1862                     }
1863                 }
1864                 None
1865             });
1866             if let Some(token) = &recovered {
1867                 self.bump();
1868                 self.sess.emit_err(FloatLiteralRequiresIntegerPart {
1869                     span: token.span,
1870                     correct: pprust::token_to_string(token).into_owned(),
1871                 });
1872             }
1873         }
1874
1875         recovered
1876     }
1877
1878     /// Matches `lit = true | false | token_lit`.
1879     /// Returns `None` if the next token is not a literal.
1880     pub(super) fn parse_opt_token_lit(&mut self) -> Option<(token::Lit, Span)> {
1881         let recovered = self.recover_after_dot();
1882         let token = recovered.as_ref().unwrap_or(&self.token);
1883         let span = token.span;
1884         token::Lit::from_token(token).map(|token_lit| {
1885             self.bump();
1886             (token_lit, span)
1887         })
1888     }
1889
1890     /// Matches `lit = true | false | token_lit`.
1891     /// Returns `None` if the next token is not a literal.
1892     pub(super) fn parse_opt_meta_item_lit(&mut self) -> Option<MetaItemLit> {
1893         let recovered = self.recover_after_dot();
1894         let token = recovered.as_ref().unwrap_or(&self.token);
1895         match token::Lit::from_token(token) {
1896             Some(token_lit) => {
1897                 match MetaItemLit::from_token_lit(token_lit, token.span) {
1898                     Ok(lit) => {
1899                         self.bump();
1900                         Some(lit)
1901                     }
1902                     Err(err) => {
1903                         let span = token.span;
1904                         let token::Literal(lit) = token.kind else {
1905                             unreachable!();
1906                         };
1907                         self.bump();
1908                         report_lit_error(&self.sess, err, lit, span);
1909                         // Pack possible quotes and prefixes from the original literal into
1910                         // the error literal's symbol so they can be pretty-printed faithfully.
1911                         let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1912                         let symbol = Symbol::intern(&suffixless_lit.to_string());
1913                         let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1914                         Some(
1915                             MetaItemLit::from_token_lit(lit, span)
1916                                 .unwrap_or_else(|_| unreachable!()),
1917                         )
1918                     }
1919                 }
1920             }
1921             None => None,
1922         }
1923     }
1924
1925     pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
1926         if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
1927             // #59553: warn instead of reject out of hand to allow the fix to percolate
1928             // through the ecosystem when people fix their macros
1929             self.sess.emit_warning(InvalidLiteralSuffixOnTupleIndex {
1930                 span,
1931                 suffix,
1932                 exception: Some(()),
1933             });
1934         } else {
1935             self.sess.emit_err(InvalidLiteralSuffixOnTupleIndex { span, suffix, exception: None });
1936         }
1937     }
1938
1939     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1940     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1941     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1942         maybe_whole_expr!(self);
1943
1944         let lo = self.token.span;
1945         let minus_present = self.eat(&token::BinOp(token::Minus));
1946         let (token_lit, span) = self.parse_token_lit()?;
1947         let expr = self.mk_expr(span, ExprKind::Lit(token_lit));
1948
1949         if minus_present {
1950             Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
1951         } else {
1952             Ok(expr)
1953         }
1954     }
1955
1956     fn is_array_like_block(&mut self) -> bool {
1957         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1958             && self.look_ahead(2, |t| t == &token::Comma)
1959             && self.look_ahead(3, |t| t.can_begin_expr())
1960     }
1961
1962     /// Emits a suggestion if it looks like the user meant an array but
1963     /// accidentally used braces, causing the code to be interpreted as a block
1964     /// expression.
1965     fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
1966         let mut snapshot = self.create_snapshot_for_diagnostic();
1967         match snapshot.parse_array_or_repeat_expr(Delimiter::Brace) {
1968             Ok(arr) => {
1969                 self.sess.emit_err(ArrayBracketsInsteadOfSpaces {
1970                     span: arr.span,
1971                     sub: ArrayBracketsInsteadOfSpacesSugg {
1972                         left: lo,
1973                         right: snapshot.prev_token.span,
1974                     },
1975                 });
1976
1977                 self.restore_snapshot(snapshot);
1978                 Some(self.mk_expr_err(arr.span))
1979             }
1980             Err(e) => {
1981                 e.cancel();
1982                 None
1983             }
1984         }
1985     }
1986
1987     fn suggest_missing_semicolon_before_array(
1988         &self,
1989         prev_span: Span,
1990         open_delim_span: Span,
1991     ) -> PResult<'a, ()> {
1992         if !self.may_recover() {
1993             return Ok(());
1994         }
1995
1996         if self.token.kind == token::Comma {
1997             if !self.sess.source_map().is_multiline(prev_span.until(self.token.span)) {
1998                 return Ok(());
1999             }
2000             let mut snapshot = self.create_snapshot_for_diagnostic();
2001             snapshot.bump();
2002             match snapshot.parse_seq_to_before_end(
2003                 &token::CloseDelim(Delimiter::Bracket),
2004                 SeqSep::trailing_allowed(token::Comma),
2005                 |p| p.parse_expr(),
2006             ) {
2007                 Ok(_)
2008                     // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
2009                     // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
2010                     // This is because the `token.kind` of the close delim is treated as the same as
2011                     // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
2012                     // Therefore, `token.kind` should not be compared here.
2013                     if snapshot
2014                         .span_to_snippet(snapshot.token.span)
2015                         .map_or(false, |snippet| snippet == "]") =>
2016                 {
2017                     return Err(MissingSemicolonBeforeArray {
2018                         open_delim: open_delim_span,
2019                         semicolon: prev_span.shrink_to_hi(),
2020                     }.into_diagnostic(&self.sess.span_diagnostic));
2021                 }
2022                 Ok(_) => (),
2023                 Err(err) => err.cancel(),
2024             }
2025         }
2026         Ok(())
2027     }
2028
2029     /// Parses a block or unsafe block.
2030     pub(super) fn parse_block_expr(
2031         &mut self,
2032         opt_label: Option<Label>,
2033         lo: Span,
2034         blk_mode: BlockCheckMode,
2035     ) -> PResult<'a, P<Expr>> {
2036         if self.may_recover() && self.is_array_like_block() {
2037             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
2038                 return Ok(arr);
2039             }
2040         }
2041
2042         if self.token.is_whole_block() {
2043             self.sess.emit_err(InvalidBlockMacroSegment {
2044                 span: self.token.span,
2045                 context: lo.to(self.token.span),
2046             });
2047         }
2048
2049         let (attrs, blk) = self.parse_block_common(lo, blk_mode, true)?;
2050         Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
2051     }
2052
2053     /// Parse a block which takes no attributes and has no label
2054     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2055         let blk = self.parse_block()?;
2056         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
2057     }
2058
2059     /// Parses a closure expression (e.g., `move |args| expr`).
2060     fn parse_closure_expr(&mut self) -> PResult<'a, P<Expr>> {
2061         let lo = self.token.span;
2062
2063         let binder = if self.check_keyword(kw::For) {
2064             let lo = self.token.span;
2065             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2066             let span = lo.to(self.prev_token.span);
2067
2068             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2069
2070             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2071         } else {
2072             ClosureBinder::NotPresent
2073         };
2074
2075         let constness = self.parse_constness(Case::Sensitive);
2076
2077         let movability =
2078             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2079
2080         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2081             self.parse_asyncness(Case::Sensitive)
2082         } else {
2083             Async::No
2084         };
2085
2086         let capture_clause = self.parse_capture_clause()?;
2087         let (fn_decl, fn_arg_span) = self.parse_fn_block_decl()?;
2088         let decl_hi = self.prev_token.span;
2089         let mut body = match fn_decl.output {
2090             FnRetTy::Default(_) => {
2091                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2092                 self.parse_expr_res(restrictions, None)?
2093             }
2094             _ => {
2095                 // If an explicit return type is given, require a block to appear (RFC 968).
2096                 let body_lo = self.token.span;
2097                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default)?
2098             }
2099         };
2100
2101         if let Async::Yes { span, .. } = asyncness {
2102             // Feature-gate `async ||` closures.
2103             self.sess.gated_spans.gate(sym::async_closure, span);
2104         }
2105
2106         if self.token.kind == TokenKind::Semi
2107             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2108             && self.may_recover()
2109         {
2110             // It is likely that the closure body is a block but where the
2111             // braces have been removed. We will recover and eat the next
2112             // statements later in the parsing process.
2113             body = self.mk_expr_err(body.span);
2114         }
2115
2116         let body_span = body.span;
2117
2118         let closure = self.mk_expr(
2119             lo.to(body.span),
2120             ExprKind::Closure(Box::new(ast::Closure {
2121                 binder,
2122                 capture_clause,
2123                 constness,
2124                 asyncness,
2125                 movability,
2126                 fn_decl,
2127                 body,
2128                 fn_decl_span: lo.to(decl_hi),
2129                 fn_arg_span,
2130             })),
2131         );
2132
2133         // Disable recovery for closure body
2134         let spans =
2135             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2136         self.current_closure = Some(spans);
2137
2138         Ok(closure)
2139     }
2140
2141     /// Parses an optional `move` prefix to a closure-like construct.
2142     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2143         if self.eat_keyword(kw::Move) {
2144             // Check for `move async` and recover
2145             if self.check_keyword(kw::Async) {
2146                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2147                 Err(AsyncMoveOrderIncorrect { span: move_async_span }
2148                     .into_diagnostic(&self.sess.span_diagnostic))
2149             } else {
2150                 Ok(CaptureBy::Value)
2151             }
2152         } else {
2153             Ok(CaptureBy::Ref)
2154         }
2155     }
2156
2157     /// Parses the `|arg, arg|` header of a closure.
2158     fn parse_fn_block_decl(&mut self) -> PResult<'a, (P<FnDecl>, Span)> {
2159         let arg_start = self.token.span.lo();
2160
2161         let inputs = if self.eat(&token::OrOr) {
2162             Vec::new()
2163         } else {
2164             self.expect(&token::BinOp(token::Or))?;
2165             let args = self
2166                 .parse_seq_to_before_tokens(
2167                     &[&token::BinOp(token::Or), &token::OrOr],
2168                     SeqSep::trailing_allowed(token::Comma),
2169                     TokenExpectType::NoExpect,
2170                     |p| p.parse_fn_block_param(),
2171                 )?
2172                 .0;
2173             self.expect_or()?;
2174             args
2175         };
2176         let arg_span = self.prev_token.span.with_lo(arg_start);
2177         let output =
2178             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2179
2180         Ok((P(FnDecl { inputs, output }), arg_span))
2181     }
2182
2183     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2184     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2185         let lo = self.token.span;
2186         let attrs = self.parse_outer_attributes()?;
2187         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2188             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2189             let ty = if this.eat(&token::Colon) {
2190                 this.parse_ty()?
2191             } else {
2192                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2193             };
2194
2195             Ok((
2196                 Param {
2197                     attrs,
2198                     ty,
2199                     pat,
2200                     span: lo.to(this.prev_token.span),
2201                     id: DUMMY_NODE_ID,
2202                     is_placeholder: false,
2203                 },
2204                 TrailingToken::MaybeComma,
2205             ))
2206         })
2207     }
2208
2209     /// Parses an `if` expression (`if` token already eaten).
2210     fn parse_if_expr(&mut self) -> PResult<'a, P<Expr>> {
2211         let lo = self.prev_token.span;
2212         let cond = self.parse_cond_expr()?;
2213         self.parse_if_after_cond(lo, cond)
2214     }
2215
2216     fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
2217         let cond_span = cond.span;
2218         // Tries to interpret `cond` as either a missing expression if it's a block,
2219         // or as an unfinished expression if it's a binop and the RHS is a block.
2220         // We could probably add more recoveries here too...
2221         let mut recover_block_from_condition = |this: &mut Self| {
2222             let block = match &mut cond.kind {
2223                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2224                     if let ExprKind::Block(_, None) = right.kind => {
2225                         self.sess.emit_err(IfExpressionMissingThenBlock {
2226                             if_span: lo,
2227                             sub: IfExpressionMissingThenBlockSub::UnfinishedCondition(
2228                                 cond_span.shrink_to_lo().to(*binop_span)
2229                             ),
2230                         });
2231                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2232                     },
2233                 ExprKind::Block(_, None) => {
2234                     self.sess.emit_err(IfExpressionMissingCondition {
2235                         if_span: lo.shrink_to_hi(),
2236                         block_span: self.sess.source_map().start_point(cond_span),
2237                     });
2238                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2239                 }
2240                 _ => {
2241                     return None;
2242                 }
2243             };
2244             if let ExprKind::Block(block, _) = &block.kind {
2245                 Some(block.clone())
2246             } else {
2247                 unreachable!()
2248             }
2249         };
2250         // Parse then block
2251         let thn = if self.token.is_keyword(kw::Else) {
2252             if let Some(block) = recover_block_from_condition(self) {
2253                 block
2254             } else {
2255                 self.sess.emit_err(IfExpressionMissingThenBlock {
2256                     if_span: lo,
2257                     sub: IfExpressionMissingThenBlockSub::AddThenBlock(cond_span.shrink_to_hi()),
2258                 });
2259                 self.mk_block_err(cond_span.shrink_to_hi())
2260             }
2261         } else {
2262             let attrs = self.parse_outer_attributes()?; // For recovery.
2263             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2264                 self.parse_block()?
2265             } else {
2266                 if let Some(block) = recover_block_from_condition(self) {
2267                     block
2268                 } else {
2269                     self.error_on_extra_if(&cond)?;
2270                     // Parse block, which will always fail, but we can add a nice note to the error
2271                     self.parse_block().map_err(|mut err| {
2272                         err.span_note(
2273                             cond_span,
2274                             "the `if` expression is missing a block after this condition",
2275                         );
2276                         err
2277                     })?
2278                 }
2279             };
2280             self.error_on_if_block_attrs(lo, false, block.span, attrs);
2281             block
2282         };
2283         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2284         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
2285     }
2286
2287     /// Parses the condition of a `if` or `while` expression.
2288     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2289         let cond =
2290             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
2291
2292         if let ExprKind::Let(..) = cond.kind {
2293             // Remove the last feature gating of a `let` expression since it's stable.
2294             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2295         }
2296
2297         Ok(cond)
2298     }
2299
2300     /// Parses a `let $pat = $expr` pseudo-expression.
2301     fn parse_let_expr(&mut self) -> PResult<'a, P<Expr>> {
2302         // This is a *approximate* heuristic that detects if `let` chains are
2303         // being parsed in the right position. It's approximate because it
2304         // doesn't deny all invalid `let` expressions, just completely wrong usages.
2305         let not_in_chain = !matches!(
2306             self.prev_token.kind,
2307             TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2308         );
2309         if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
2310             self.sess.emit_err(ExpectedExpressionFoundLet { span: self.token.span });
2311         }
2312
2313         self.bump(); // Eat `let` token
2314         let lo = self.prev_token.span;
2315         let pat = self.parse_pat_allow_top_alt(
2316             None,
2317             RecoverComma::Yes,
2318             RecoverColon::Yes,
2319             CommaRecoveryMode::LikelyTuple,
2320         )?;
2321         if self.token == token::EqEq {
2322             self.sess.emit_err(ExpectedEqForLetExpr {
2323                 span: self.token.span,
2324                 sugg_span: self.token.span,
2325             });
2326             self.bump();
2327         } else {
2328             self.expect(&token::Eq)?;
2329         }
2330         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2331             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2332         })?;
2333         let span = lo.to(expr.span);
2334         self.sess.gated_spans.gate(sym::let_chains, span);
2335         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span)))
2336     }
2337
2338     /// Parses an `else { ... }` expression (`else` token already eaten).
2339     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2340         let else_span = self.prev_token.span; // `else`
2341         let attrs = self.parse_outer_attributes()?; // For recovery.
2342         let expr = if self.eat_keyword(kw::If) {
2343             self.parse_if_expr()?
2344         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2345             self.parse_simple_block()?
2346         } else {
2347             let snapshot = self.create_snapshot_for_diagnostic();
2348             let first_tok = super::token_descr(&self.token);
2349             let first_tok_span = self.token.span;
2350             match self.parse_expr() {
2351                 Ok(cond)
2352                 // If it's not a free-standing expression, and is followed by a block,
2353                 // then it's very likely the condition to an `else if`.
2354                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2355                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2356                 {
2357                     self.sess.emit_err(ExpectedElseBlock {
2358                         first_tok_span,
2359                         first_tok,
2360                         else_span,
2361                         condition_start: cond.span.shrink_to_lo(),
2362                     });
2363                     self.parse_if_after_cond(cond.span.shrink_to_lo(), cond)?
2364                 }
2365                 Err(e) => {
2366                     e.cancel();
2367                     self.restore_snapshot(snapshot);
2368                     self.parse_simple_block()?
2369                 },
2370                 Ok(_) => {
2371                     self.restore_snapshot(snapshot);
2372                     self.parse_simple_block()?
2373                 },
2374             }
2375         };
2376         self.error_on_if_block_attrs(else_span, true, expr.span, attrs);
2377         Ok(expr)
2378     }
2379
2380     fn error_on_if_block_attrs(
2381         &self,
2382         ctx_span: Span,
2383         is_ctx_else: bool,
2384         branch_span: Span,
2385         attrs: AttrWrapper,
2386     ) {
2387         if attrs.is_empty() {
2388             return;
2389         }
2390
2391         let attrs: &[ast::Attribute] = &attrs.take_for_recovery(self.sess);
2392         let (attributes, last) = match attrs {
2393             [] => return,
2394             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2395         };
2396         let ctx = if is_ctx_else { "else" } else { "if" };
2397         self.sess.emit_err(OuterAttributeNotAllowedOnIfElse {
2398             last,
2399             branch_span,
2400             ctx_span,
2401             ctx: ctx.to_string(),
2402             attributes,
2403         });
2404     }
2405
2406     fn error_on_extra_if(&mut self, cond: &P<Expr>) -> PResult<'a, ()> {
2407         if let ExprKind::Binary(Spanned { span: binop_span, node: binop}, _, right) = &cond.kind &&
2408             let BinOpKind::And = binop &&
2409             let ExprKind::If(cond, ..) = &right.kind {
2410                     Err(self.sess.create_err(UnexpectedIfWithIf(binop_span.shrink_to_hi().to(cond.span.shrink_to_lo()))))
2411             } else {
2412                 Ok(())
2413             }
2414     }
2415
2416     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2417     fn parse_for_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2418         // Record whether we are about to parse `for (`.
2419         // This is used below for recovery in case of `for ( $stuff ) $block`
2420         // in which case we will suggest `for $stuff $block`.
2421         let begin_paren = match self.token.kind {
2422             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2423             _ => None,
2424         };
2425
2426         let pat = self.parse_pat_allow_top_alt(
2427             None,
2428             RecoverComma::Yes,
2429             RecoverColon::Yes,
2430             CommaRecoveryMode::LikelyTuple,
2431         )?;
2432         if !self.eat_keyword(kw::In) {
2433             self.error_missing_in_for_loop();
2434         }
2435         self.check_for_for_in_in_typo(self.prev_token.span);
2436         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2437
2438         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2439
2440         let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
2441
2442         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2443         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2444     }
2445
2446     fn error_missing_in_for_loop(&mut self) {
2447         let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
2448             // Possibly using JS syntax (#75311).
2449             let span = self.token.span;
2450             self.bump();
2451             (span, MissingInInForLoopSub::InNotOf)
2452         } else {
2453             (self.prev_token.span.between(self.token.span), MissingInInForLoopSub::AddIn)
2454         };
2455
2456         self.sess.emit_err(MissingInInForLoop { span, sub: sub(span) });
2457     }
2458
2459     /// Parses a `while` or `while let` expression (`while` token already eaten).
2460     fn parse_while_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2461         let cond = self.parse_cond_expr().map_err(|mut err| {
2462             err.span_label(lo, "while parsing the condition of this `while` expression");
2463             err
2464         })?;
2465         let (attrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2466             err.span_label(lo, "while parsing the body of this `while` expression");
2467             err.span_label(cond.span, "this `while` condition successfully parsed");
2468             err
2469         })?;
2470         Ok(self.mk_expr_with_attrs(
2471             lo.to(self.prev_token.span),
2472             ExprKind::While(cond, body, opt_label),
2473             attrs,
2474         ))
2475     }
2476
2477     /// Parses `loop { ... }` (`loop` token already eaten).
2478     fn parse_loop_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2479         let loop_span = self.prev_token.span;
2480         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2481         Ok(self.mk_expr_with_attrs(
2482             lo.to(self.prev_token.span),
2483             ExprKind::Loop(body, opt_label, loop_span),
2484             attrs,
2485         ))
2486     }
2487
2488     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2489         self.token.lifetime().map(|ident| {
2490             self.bump();
2491             Label { ident }
2492         })
2493     }
2494
2495     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2496     fn parse_match_expr(&mut self) -> PResult<'a, P<Expr>> {
2497         let match_span = self.prev_token.span;
2498         let lo = self.prev_token.span;
2499         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2500         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2501             if self.token == token::Semi {
2502                 e.span_suggestion_short(
2503                     match_span,
2504                     "try removing this `match`",
2505                     "",
2506                     Applicability::MaybeIncorrect, // speculative
2507                 );
2508             }
2509             if self.maybe_recover_unexpected_block_label() {
2510                 e.cancel();
2511                 self.bump();
2512             } else {
2513                 return Err(e);
2514             }
2515         }
2516         let attrs = self.parse_inner_attributes()?;
2517
2518         let mut arms: Vec<Arm> = Vec::new();
2519         while self.token != token::CloseDelim(Delimiter::Brace) {
2520             match self.parse_arm() {
2521                 Ok(arm) => arms.push(arm),
2522                 Err(mut e) => {
2523                     // Recover by skipping to the end of the block.
2524                     e.emit();
2525                     self.recover_stmt();
2526                     let span = lo.to(self.token.span);
2527                     if self.token == token::CloseDelim(Delimiter::Brace) {
2528                         self.bump();
2529                     }
2530                     return Ok(self.mk_expr_with_attrs(
2531                         span,
2532                         ExprKind::Match(scrutinee, arms),
2533                         attrs,
2534                     ));
2535                 }
2536             }
2537         }
2538         let hi = self.token.span;
2539         self.bump();
2540         Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2541     }
2542
2543     /// Attempt to recover from match arm body with statements and no surrounding braces.
2544     fn parse_arm_body_missing_braces(
2545         &mut self,
2546         first_expr: &P<Expr>,
2547         arrow_span: Span,
2548     ) -> Option<P<Expr>> {
2549         if self.token.kind != token::Semi {
2550             return None;
2551         }
2552         let start_snapshot = self.create_snapshot_for_diagnostic();
2553         let semi_sp = self.token.span;
2554         self.bump(); // `;`
2555         let mut stmts =
2556             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2557         let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
2558             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2559
2560             this.sess.emit_err(MatchArmBodyWithoutBraces {
2561                 statements: span,
2562                 arrow: arrow_span,
2563                 num_statements: stmts.len(),
2564                 sub: if stmts.len() > 1 {
2565                     MatchArmBodyWithoutBracesSugg::AddBraces {
2566                         left: span.shrink_to_lo(),
2567                         right: span.shrink_to_hi(),
2568                     }
2569                 } else {
2570                     MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
2571                 },
2572             });
2573             this.mk_expr_err(span)
2574         };
2575         // We might have either a `,` -> `;` typo, or a block without braces. We need
2576         // a more subtle parsing strategy.
2577         loop {
2578             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2579                 // We have reached the closing brace of the `match` expression.
2580                 return Some(err(self, stmts));
2581             }
2582             if self.token.kind == token::Comma {
2583                 self.restore_snapshot(start_snapshot);
2584                 return None;
2585             }
2586             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2587             match self.parse_pat_no_top_alt(None) {
2588                 Ok(_pat) => {
2589                     if self.token.kind == token::FatArrow {
2590                         // Reached arm end.
2591                         self.restore_snapshot(pre_pat_snapshot);
2592                         return Some(err(self, stmts));
2593                     }
2594                 }
2595                 Err(err) => {
2596                     err.cancel();
2597                 }
2598             }
2599
2600             self.restore_snapshot(pre_pat_snapshot);
2601             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2602                 // Consume statements for as long as possible.
2603                 Ok(Some(stmt)) => {
2604                     stmts.push(stmt);
2605                 }
2606                 Ok(None) => {
2607                     self.restore_snapshot(start_snapshot);
2608                     break;
2609                 }
2610                 // We couldn't parse either yet another statement missing it's
2611                 // enclosing block nor the next arm's pattern or closing brace.
2612                 Err(stmt_err) => {
2613                     stmt_err.cancel();
2614                     self.restore_snapshot(start_snapshot);
2615                     break;
2616                 }
2617             }
2618         }
2619         None
2620     }
2621
2622     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2623         // Used to check the `let_chains` and `if_let_guard` features mostly by scanning
2624         // `&&` tokens.
2625         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2626             match &expr.kind {
2627                 ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, lhs, rhs) => {
2628                     let lhs_rslt = check_let_expr(lhs);
2629                     let rhs_rslt = check_let_expr(rhs);
2630                     (lhs_rslt.0 || rhs_rslt.0, false)
2631                 }
2632                 ExprKind::Let(..) => (true, true),
2633                 _ => (false, true),
2634             }
2635         }
2636         let attrs = self.parse_outer_attributes()?;
2637         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2638             let lo = this.token.span;
2639             let pat = this.parse_pat_allow_top_alt(
2640                 None,
2641                 RecoverComma::Yes,
2642                 RecoverColon::Yes,
2643                 CommaRecoveryMode::EitherTupleOrPipe,
2644             )?;
2645             let guard = if this.eat_keyword(kw::If) {
2646                 let if_span = this.prev_token.span;
2647                 let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
2648                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2649                 if has_let_expr {
2650                     if does_not_have_bin_op {
2651                         // Remove the last feature gating of a `let` expression since it's stable.
2652                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2653                     }
2654                     let span = if_span.to(cond.span);
2655                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2656                 }
2657                 Some(cond)
2658             } else {
2659                 None
2660             };
2661             let arrow_span = this.token.span;
2662             if let Err(mut err) = this.expect(&token::FatArrow) {
2663                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2664                 if TokenKind::FatArrow
2665                     .similar_tokens()
2666                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2667                 {
2668                     err.span_suggestion(
2669                         this.token.span,
2670                         "try using a fat arrow here",
2671                         "=>",
2672                         Applicability::MaybeIncorrect,
2673                     );
2674                     err.emit();
2675                     this.bump();
2676                 } else {
2677                     return Err(err);
2678                 }
2679             }
2680             let arm_start_span = this.token.span;
2681
2682             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2683                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2684                 err
2685             })?;
2686
2687             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2688                 && this.token != token::CloseDelim(Delimiter::Brace);
2689
2690             let hi = this.prev_token.span;
2691
2692             if require_comma {
2693                 let sm = this.sess.source_map();
2694                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2695                     let span = body.span;
2696                     return Ok((
2697                         ast::Arm {
2698                             attrs,
2699                             pat,
2700                             guard,
2701                             body,
2702                             span,
2703                             id: DUMMY_NODE_ID,
2704                             is_placeholder: false,
2705                         },
2706                         TrailingToken::None,
2707                     ));
2708                 }
2709                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2710                     .or_else(|mut err| {
2711                         if this.token == token::FatArrow {
2712                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2713                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2714                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2715                             && expr_lines.lines.len() == 2
2716                             {
2717                                 // We check whether there's any trailing code in the parse span,
2718                                 // if there isn't, we very likely have the following:
2719                                 //
2720                                 // X |     &Y => "y"
2721                                 //   |        --    - missing comma
2722                                 //   |        |
2723                                 //   |        arrow_span
2724                                 // X |     &X => "x"
2725                                 //   |      - ^^ self.token.span
2726                                 //   |      |
2727                                 //   |      parsed until here as `"y" & X`
2728                                 err.span_suggestion_short(
2729                                     arm_start_span.shrink_to_hi(),
2730                                     "missing a comma here to end this `match` arm",
2731                                     ",",
2732                                     Applicability::MachineApplicable,
2733                                 );
2734                                 return Err(err);
2735                             }
2736                         } else {
2737                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2738
2739                             // Try to parse a following `PAT =>`, if successful
2740                             // then we should recover.
2741                             let mut snapshot = this.create_snapshot_for_diagnostic();
2742                             let pattern_follows = snapshot
2743                                 .parse_pat_allow_top_alt(
2744                                     None,
2745                                     RecoverComma::Yes,
2746                                     RecoverColon::Yes,
2747                                     CommaRecoveryMode::EitherTupleOrPipe,
2748                                 )
2749                                 .map_err(|err| err.cancel())
2750                                 .is_ok();
2751                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2752                                 err.cancel();
2753                                 this.sess.emit_err(MissingCommaAfterMatchArm {
2754                                     span: hi.shrink_to_hi(),
2755                                 });
2756                                 return Ok(true);
2757                             }
2758                         }
2759                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2760                         Err(err)
2761                     })?;
2762             } else {
2763                 this.eat(&token::Comma);
2764             }
2765
2766             Ok((
2767                 ast::Arm {
2768                     attrs,
2769                     pat,
2770                     guard,
2771                     body: expr,
2772                     span: lo.to(hi),
2773                     id: DUMMY_NODE_ID,
2774                     is_placeholder: false,
2775                 },
2776                 TrailingToken::None,
2777             ))
2778         })
2779     }
2780
2781     /// Parses a `try {...}` expression (`try` token already eaten).
2782     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
2783         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2784         if self.eat_keyword(kw::Catch) {
2785             Err(CatchAfterTry { span: self.prev_token.span }
2786                 .into_diagnostic(&self.sess.span_diagnostic))
2787         } else {
2788             let span = span_lo.to(body.span);
2789             self.sess.gated_spans.gate(sym::try_blocks, span);
2790             Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body), attrs))
2791         }
2792     }
2793
2794     fn is_do_catch_block(&self) -> bool {
2795         self.token.is_keyword(kw::Do)
2796             && self.is_keyword_ahead(1, &[kw::Catch])
2797             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2798             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2799     }
2800
2801     fn is_do_yeet(&self) -> bool {
2802         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2803     }
2804
2805     fn is_try_block(&self) -> bool {
2806         self.token.is_keyword(kw::Try)
2807             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2808             && self.token.uninterpolated_span().rust_2018()
2809     }
2810
2811     /// Parses an `async move? {...}` expression.
2812     fn parse_async_block(&mut self) -> PResult<'a, P<Expr>> {
2813         let lo = self.token.span;
2814         self.expect_keyword(kw::Async)?;
2815         let capture_clause = self.parse_capture_clause()?;
2816         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2817         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2818         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2819     }
2820
2821     fn is_async_block(&self) -> bool {
2822         self.token.is_keyword(kw::Async)
2823             && ((
2824                 // `async move {`
2825                 self.is_keyword_ahead(1, &[kw::Move])
2826                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2827             ) || (
2828                 // `async {`
2829                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2830             ))
2831     }
2832
2833     fn is_certainly_not_a_block(&self) -> bool {
2834         self.look_ahead(1, |t| t.is_ident())
2835             && (
2836                 // `{ ident, ` cannot start a block.
2837                 self.look_ahead(2, |t| t == &token::Comma)
2838                     || self.look_ahead(2, |t| t == &token::Colon)
2839                         && (
2840                             // `{ ident: token, ` cannot start a block.
2841                             self.look_ahead(4, |t| t == &token::Comma) ||
2842                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2843                 self.look_ahead(3, |t| !t.can_begin_type())
2844                         )
2845             )
2846     }
2847
2848     fn maybe_parse_struct_expr(
2849         &mut self,
2850         qself: &Option<P<ast::QSelf>>,
2851         path: &ast::Path,
2852     ) -> Option<PResult<'a, P<Expr>>> {
2853         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2854         if struct_allowed || self.is_certainly_not_a_block() {
2855             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2856                 return Some(Err(err));
2857             }
2858             let expr = self.parse_struct_expr(qself.clone(), path.clone(), true);
2859             if let (Ok(expr), false) = (&expr, struct_allowed) {
2860                 // This is a struct literal, but we don't can't accept them here.
2861                 self.sess.emit_err(StructLiteralNotAllowedHere {
2862                     span: expr.span,
2863                     sub: StructLiteralNotAllowedHereSugg {
2864                         left: path.span.shrink_to_lo(),
2865                         right: expr.span.shrink_to_hi(),
2866                     },
2867                 });
2868             }
2869             return Some(expr);
2870         }
2871         None
2872     }
2873
2874     pub(super) fn parse_struct_fields(
2875         &mut self,
2876         pth: ast::Path,
2877         recover: bool,
2878         close_delim: Delimiter,
2879     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2880         let mut fields = Vec::new();
2881         let mut base = ast::StructRest::None;
2882         let mut recover_async = false;
2883
2884         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2885             recover_async = true;
2886             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2887             e.help_use_latest_edition();
2888         };
2889
2890         while self.token != token::CloseDelim(close_delim) {
2891             if self.eat(&token::DotDot) || self.recover_struct_field_dots(close_delim) {
2892                 let exp_span = self.prev_token.span;
2893                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2894                 if self.check(&token::CloseDelim(close_delim)) {
2895                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2896                     break;
2897                 }
2898                 match self.parse_expr() {
2899                     Ok(e) => base = ast::StructRest::Base(e),
2900                     Err(mut e) if recover => {
2901                         e.emit();
2902                         self.recover_stmt();
2903                     }
2904                     Err(e) => return Err(e),
2905                 }
2906                 self.recover_struct_comma_after_dotdot(exp_span);
2907                 break;
2908             }
2909
2910             let recovery_field = self.find_struct_error_after_field_looking_code();
2911             let parsed_field = match self.parse_expr_field() {
2912                 Ok(f) => Some(f),
2913                 Err(mut e) => {
2914                     if pth == kw::Async {
2915                         async_block_err(&mut e, pth.span);
2916                     } else {
2917                         e.span_label(pth.span, "while parsing this struct");
2918                     }
2919                     e.emit();
2920
2921                     // If the next token is a comma, then try to parse
2922                     // what comes next as additional fields, rather than
2923                     // bailing out until next `}`.
2924                     if self.token != token::Comma {
2925                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2926                         if self.token != token::Comma {
2927                             break;
2928                         }
2929                     }
2930                     None
2931                 }
2932             };
2933
2934             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
2935             // A shorthand field can be turned into a full field with `:`.
2936             // We should point this out.
2937             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
2938
2939             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2940                 Ok(_) => {
2941                     if let Some(f) = parsed_field.or(recovery_field) {
2942                         // Only include the field if there's no parse error for the field name.
2943                         fields.push(f);
2944                     }
2945                 }
2946                 Err(mut e) => {
2947                     if pth == kw::Async {
2948                         async_block_err(&mut e, pth.span);
2949                     } else {
2950                         e.span_label(pth.span, "while parsing this struct");
2951                         if let Some(f) = recovery_field {
2952                             fields.push(f);
2953                             e.span_suggestion(
2954                                 self.prev_token.span.shrink_to_hi(),
2955                                 "try adding a comma",
2956                                 ",",
2957                                 Applicability::MachineApplicable,
2958                             );
2959                         } else if is_shorthand
2960                             && (AssocOp::from_token(&self.token).is_some()
2961                                 || matches!(&self.token.kind, token::OpenDelim(_))
2962                                 || self.token.kind == token::Dot)
2963                         {
2964                             // Looks like they tried to write a shorthand, complex expression.
2965                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
2966                             e.span_suggestion(
2967                                 ident.span.shrink_to_lo(),
2968                                 "try naming a field",
2969                                 &format!("{ident}: "),
2970                                 Applicability::HasPlaceholders,
2971                             );
2972                         }
2973                     }
2974                     if !recover {
2975                         return Err(e);
2976                     }
2977                     e.emit();
2978                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2979                     self.eat(&token::Comma);
2980                 }
2981             }
2982         }
2983         Ok((fields, base, recover_async))
2984     }
2985
2986     /// Precondition: already parsed the '{'.
2987     pub(super) fn parse_struct_expr(
2988         &mut self,
2989         qself: Option<P<ast::QSelf>>,
2990         pth: ast::Path,
2991         recover: bool,
2992     ) -> PResult<'a, P<Expr>> {
2993         let lo = pth.span;
2994         let (fields, base, recover_async) =
2995             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
2996         let span = lo.to(self.token.span);
2997         self.expect(&token::CloseDelim(Delimiter::Brace))?;
2998         let expr = if recover_async {
2999             ExprKind::Err
3000         } else {
3001             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
3002         };
3003         Ok(self.mk_expr(span, expr))
3004     }
3005
3006     /// Use in case of error after field-looking code: `S { foo: () with a }`.
3007     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
3008         match self.token.ident() {
3009             Some((ident, is_raw))
3010                 if (is_raw || !ident.is_reserved())
3011                     && self.look_ahead(1, |t| *t == token::Colon) =>
3012             {
3013                 Some(ast::ExprField {
3014                     ident,
3015                     span: self.token.span,
3016                     expr: self.mk_expr_err(self.token.span),
3017                     is_shorthand: false,
3018                     attrs: AttrVec::new(),
3019                     id: DUMMY_NODE_ID,
3020                     is_placeholder: false,
3021                 })
3022             }
3023             _ => None,
3024         }
3025     }
3026
3027     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
3028         if self.token != token::Comma {
3029             return;
3030         }
3031         self.sess.emit_err(CommaAfterBaseStruct {
3032             span: span.to(self.prev_token.span),
3033             comma: self.token.span,
3034         });
3035         self.recover_stmt();
3036     }
3037
3038     fn recover_struct_field_dots(&mut self, close_delim: Delimiter) -> bool {
3039         if !self.look_ahead(1, |t| *t == token::CloseDelim(close_delim))
3040             && self.eat(&token::DotDotDot)
3041         {
3042             // recover from typo of `...`, suggest `..`
3043             let span = self.prev_token.span;
3044             self.sess.emit_err(MissingDotDot { token_span: span, sugg_span: span });
3045             return true;
3046         }
3047         false
3048     }
3049
3050     /// Parses `ident (COLON expr)?`.
3051     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3052         let attrs = self.parse_outer_attributes()?;
3053         self.recover_diff_marker();
3054         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3055             let lo = this.token.span;
3056
3057             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3058             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3059             let (ident, expr) = if is_shorthand {
3060                 // Mimic `x: x` for the `x` field shorthand.
3061                 let ident = this.parse_ident_common(false)?;
3062                 let path = ast::Path::from_ident(ident);
3063                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path)))
3064             } else {
3065                 let ident = this.parse_field_name()?;
3066                 this.error_on_eq_field_init(ident);
3067                 this.bump(); // `:`
3068                 (ident, this.parse_expr()?)
3069             };
3070
3071             Ok((
3072                 ast::ExprField {
3073                     ident,
3074                     span: lo.to(expr.span),
3075                     expr,
3076                     is_shorthand,
3077                     attrs,
3078                     id: DUMMY_NODE_ID,
3079                     is_placeholder: false,
3080                 },
3081                 TrailingToken::MaybeComma,
3082             ))
3083         })
3084     }
3085
3086     /// Check for `=`. This means the source incorrectly attempts to
3087     /// initialize a field with an eq rather than a colon.
3088     fn error_on_eq_field_init(&self, field_name: Ident) {
3089         if self.token != token::Eq {
3090             return;
3091         }
3092
3093         self.sess.emit_err(EqFieldInit {
3094             span: self.token.span,
3095             eq: field_name.span.shrink_to_hi().to(self.token.span),
3096         });
3097     }
3098
3099     fn err_dotdotdot_syntax(&self, span: Span) {
3100         self.sess.emit_err(DotDotDot { span });
3101     }
3102
3103     fn err_larrow_operator(&self, span: Span) {
3104         self.sess.emit_err(LeftArrowOperator { span });
3105     }
3106
3107     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3108         ExprKind::AssignOp(binop, lhs, rhs)
3109     }
3110
3111     fn mk_range(
3112         &mut self,
3113         start: Option<P<Expr>>,
3114         end: Option<P<Expr>>,
3115         limits: RangeLimits,
3116     ) -> ExprKind {
3117         if end.is_none() && limits == RangeLimits::Closed {
3118             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3119             ExprKind::Err
3120         } else {
3121             ExprKind::Range(start, end, limits)
3122         }
3123     }
3124
3125     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3126         ExprKind::Unary(unop, expr)
3127     }
3128
3129     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3130         ExprKind::Binary(binop, lhs, rhs)
3131     }
3132
3133     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3134         ExprKind::Index(expr, idx)
3135     }
3136
3137     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3138         ExprKind::Call(f, args)
3139     }
3140
3141     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3142         let span = lo.to(self.prev_token.span);
3143         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg));
3144         self.recover_from_await_method_call();
3145         await_expr
3146     }
3147
3148     pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3149         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3150     }
3151
3152     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
3153         P(Expr { kind, span, attrs: AttrVec::new(), id: DUMMY_NODE_ID, tokens: None })
3154     }
3155
3156     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3157         self.mk_expr(span, ExprKind::Err)
3158     }
3159
3160     /// Create expression span ensuring the span of the parent node
3161     /// is larger than the span of lhs and rhs, including the attributes.
3162     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3163         lhs.attrs
3164             .iter()
3165             .find(|a| a.style == AttrStyle::Outer)
3166             .map_or(lhs_span, |a| a.span)
3167             .to(rhs_span)
3168     }
3169
3170     fn collect_tokens_for_expr(
3171         &mut self,
3172         attrs: AttrWrapper,
3173         f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
3174     ) -> PResult<'a, P<Expr>> {
3175         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3176             let res = f(this, attrs)?;
3177             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3178                 && this.token.kind == token::Semi
3179             {
3180                 TrailingToken::Semi
3181             } else if this.token.kind == token::Gt {
3182                 TrailingToken::Gt
3183             } else {
3184                 // FIXME - pass this through from the place where we know
3185                 // we need a comma, rather than assuming that `#[attr] expr,`
3186                 // always captures a trailing comma
3187                 TrailingToken::MaybeComma
3188             };
3189             Ok((res, trailing))
3190         })
3191     }
3192 }