compiler/rustc_parse/src/parser/expr.rs

   1 use super::diagnostics::SnapshotParser;
   2 use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
   3 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   4 use super::{
   5     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
   6     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
   7 };
   8 use crate::errors::{
   9     ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
  10     BinaryFloatLiteralNotSupported, BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct,
  11     ComparisonInterpretedAsGeneric, ComparisonOrShiftInterpretedAsGenericSugg,
  12     DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedEqForLetExpr,
  13     ExpectedExpressionFoundLet, FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart,
  14     FoundExprWouldBeStmt, HexadecimalFloatLiteralNotSupported, IfExpressionMissingCondition,
  15     IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub, IntLiteralTooLarge,
  16     InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
  17     InvalidFloatLiteralSuffix, InvalidFloatLiteralWidth, InvalidIntLiteralWidth,
  18     InvalidInterpolatedExpression, InvalidLiteralSuffix, InvalidLiteralSuffixOnTupleIndex,
  19     InvalidLogicalOperator, InvalidLogicalOperatorSub, InvalidNumLiteralBasePrefix,
  20     InvalidNumLiteralSuffix, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
  21     LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
  22     MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
  23     MissingDotDot, MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray,
  24     NoFieldsForFnCall, NotAsNegationOperator, NotAsNegationOperatorSub,
  25     OctalFloatLiteralNotSupported, OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
  26     RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
  27     StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedTokenAfterLabel,
  28     UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
  29 };
  30 use crate::maybe_recover_from_interpolated_ty_qpath;
  31
  32 use core::mem;
  33 use rustc_ast::ptr::P;
  34 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
  35 use rustc_ast::tokenstream::Spacing;
  36 use rustc_ast::util::classify;
  37 use rustc_ast::util::literal::LitError;
  38 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
  39 use rustc_ast::visit::Visitor;
  40 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
  41 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
  42 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
  43 use rustc_ast::{ClosureBinder, StmtKind};
  44 use rustc_ast_pretty::pprust;
  45 use rustc_errors::{
  46     Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
  47     StashKey,
  48 };
  49 use rustc_session::errors::ExprParenthesesNeeded;
  50 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
  51 use rustc_session::lint::BuiltinLintDiagnostics;
  52 use rustc_span::source_map::{self, Span, Spanned};
  53 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  54 use rustc_span::{BytePos, Pos};
  55
  56 /// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
  57 /// dropped into the token stream, which happens while parsing the result of
  58 /// macro expansion). Placement of these is not as complex as I feared it would
  59 /// be. The important thing is to make sure that lookahead doesn't balk at
  60 /// `token::Interpolated` tokens.
  61 macro_rules! maybe_whole_expr {
  62     ($p:expr) => {
  63         if let token::Interpolated(nt) = &$p.token.kind {
  64             match &**nt {
  65                 token::NtExpr(e) | token::NtLiteral(e) => {
  66                     let e = e.clone();
  67                     $p.bump();
  68                     return Ok(e);
  69                 }
  70                 token::NtPath(path) => {
  71                     let path = (**path).clone();
  72                     $p.bump();
  73                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Path(None, path)));
  74                 }
  75                 token::NtBlock(block) => {
  76                     let block = block.clone();
  77                     $p.bump();
  78                     return Ok($p.mk_expr($p.prev_token.span, ExprKind::Block(block, None)));
  79                 }
  80                 _ => {}
  81             };
  82         }
  83     };
  84 }
  85
  86 #[derive(Debug)]
  87 pub(super) enum LhsExpr {
  88     NotYetParsed,
  89     AttributesParsed(AttrWrapper),
  90     AlreadyParsed(P<Expr>),
  91 }
  92
  93 impl From<Option<AttrWrapper>> for LhsExpr {
  94     /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
  95     /// and `None` into `LhsExpr::NotYetParsed`.
  96     ///
  97     /// This conversion does not allocate.
  98     fn from(o: Option<AttrWrapper>) -> Self {
  99         if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
 100     }
 101 }
 102
 103 impl From<P<Expr>> for LhsExpr {
 104     /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`.
 105     ///
 106     /// This conversion does not allocate.
 107     fn from(expr: P<Expr>) -> Self {
 108         LhsExpr::AlreadyParsed(expr)
 109     }
 110 }
 111
 112 impl<'a> Parser<'a> {
 113     /// Parses an expression.
 114     #[inline]
 115     pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
 116         self.current_closure.take();
 117
 118         self.parse_expr_res(Restrictions::empty(), None)
 119     }
 120
 121     /// Parses an expression, forcing tokens to be collected
 122     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
 123         self.collect_tokens_no_attrs(|this| this.parse_expr())
 124     }
 125
 126     pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> {
 127         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
 128     }
 129
 130     fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
 131         match self.parse_expr() {
 132             Ok(expr) => Ok(expr),
 133             Err(mut err) => match self.token.ident() {
 134                 Some((Ident { name: kw::Underscore, .. }, false))
 135                     if self.may_recover() && self.look_ahead(1, |t| t == &token::Comma) =>
 136                 {
 137                     // Special-case handling of `foo(_, _, _)`
 138                     err.emit();
 139                     self.bump();
 140                     Ok(self.mk_expr(self.prev_token.span, ExprKind::Err))
 141                 }
 142                 _ => Err(err),
 143             },
 144         }
 145     }
 146
 147     /// Parses a sequence of expressions delimited by parentheses.
 148     fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
 149         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
 150     }
 151
 152     /// Parses an expression, subject to the given restrictions.
 153     #[inline]
 154     pub(super) fn parse_expr_res(
 155         &mut self,
 156         r: Restrictions,
 157         already_parsed_attrs: Option<AttrWrapper>,
 158     ) -> PResult<'a, P<Expr>> {
 159         self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
 160     }
 161
 162     /// Parses an associative expression.
 163     ///
 164     /// This parses an expression accounting for associativity and precedence of the operators in
 165     /// the expression.
 166     #[inline]
 167     fn parse_assoc_expr(
 168         &mut self,
 169         already_parsed_attrs: Option<AttrWrapper>,
 170     ) -> PResult<'a, P<Expr>> {
 171         self.parse_assoc_expr_with(0, already_parsed_attrs.into())
 172     }
 173
 174     /// Parses an associative expression with operators of at least `min_prec` precedence.
 175     pub(super) fn parse_assoc_expr_with(
 176         &mut self,
 177         min_prec: usize,
 178         lhs: LhsExpr,
 179     ) -> PResult<'a, P<Expr>> {
 180         let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
 181             expr
 182         } else {
 183             let attrs = match lhs {
 184                 LhsExpr::AttributesParsed(attrs) => Some(attrs),
 185                 _ => None,
 186             };
 187             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
 188                 return self.parse_prefix_range_expr(attrs);
 189             } else {
 190                 self.parse_prefix_expr(attrs)?
 191             }
 192         };
 193         let last_type_ascription_set = self.last_type_ascription.is_some();
 194
 195         if !self.should_continue_as_assoc_expr(&lhs) {
 196             self.last_type_ascription = None;
 197             return Ok(lhs);
 198         }
 199
 200         self.expected_tokens.push(TokenType::Operator);
 201         while let Some(op) = self.check_assoc_op() {
 202             // Adjust the span for interpolated LHS to point to the `$lhs` token
 203             // and not to what it refers to.
 204             let lhs_span = match self.prev_token.kind {
 205                 TokenKind::Interpolated(..) => self.prev_token.span,
 206                 _ => lhs.span,
 207             };
 208
 209             let cur_op_span = self.token.span;
 210             let restrictions = if op.node.is_assign_like() {
 211                 self.restrictions & Restrictions::NO_STRUCT_LITERAL
 212             } else {
 213                 self.restrictions
 214             };
 215             let prec = op.node.precedence();
 216             if prec < min_prec {
 217                 break;
 218             }
 219             // Check for deprecated `...` syntax
 220             if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
 221                 self.err_dotdotdot_syntax(self.token.span);
 222             }
 223
 224             if self.token == token::LArrow {
 225                 self.err_larrow_operator(self.token.span);
 226             }
 227
 228             self.bump();
 229             if op.node.is_comparison() {
 230                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
 231                     return Ok(expr);
 232                 }
 233             }
 234
 235             // Look for JS' `===` and `!==` and recover
 236             if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
 237                 && self.token.kind == token::Eq
 238                 && self.prev_token.span.hi() == self.token.span.lo()
 239             {
 240                 let sp = op.span.to(self.token.span);
 241                 let sugg = match op.node {
 242                     AssocOp::Equal => "==",
 243                     AssocOp::NotEqual => "!=",
 244                     _ => unreachable!(),
 245                 }
 246                 .into();
 247                 let invalid = format!("{}=", &sugg);
 248                 self.sess.emit_err(InvalidComparisonOperator {
 249                     span: sp,
 250                     invalid: invalid.clone(),
 251                     sub: InvalidComparisonOperatorSub::Correctable {
 252                         span: sp,
 253                         invalid,
 254                         correct: sugg,
 255                     },
 256                 });
 257                 self.bump();
 258             }
 259
 260             // Look for PHP's `<>` and recover
 261             if op.node == AssocOp::Less
 262                 && self.token.kind == token::Gt
 263                 && self.prev_token.span.hi() == self.token.span.lo()
 264             {
 265                 let sp = op.span.to(self.token.span);
 266                 self.sess.emit_err(InvalidComparisonOperator {
 267                     span: sp,
 268                     invalid: "<>".into(),
 269                     sub: InvalidComparisonOperatorSub::Correctable {
 270                         span: sp,
 271                         invalid: "<>".into(),
 272                         correct: "!=".into(),
 273                     },
 274                 });
 275                 self.bump();
 276             }
 277
 278             // Look for C++'s `<=>` and recover
 279             if op.node == AssocOp::LessEqual
 280                 && self.token.kind == token::Gt
 281                 && self.prev_token.span.hi() == self.token.span.lo()
 282             {
 283                 let sp = op.span.to(self.token.span);
 284                 self.sess.emit_err(InvalidComparisonOperator {
 285                     span: sp,
 286                     invalid: "<=>".into(),
 287                     sub: InvalidComparisonOperatorSub::Spaceship(sp),
 288                 });
 289                 self.bump();
 290             }
 291
 292             if self.prev_token == token::BinOp(token::Plus)
 293                 && self.token == token::BinOp(token::Plus)
 294                 && self.prev_token.span.between(self.token.span).is_empty()
 295             {
 296                 let op_span = self.prev_token.span.to(self.token.span);
 297                 // Eat the second `+`
 298                 self.bump();
 299                 lhs = self.recover_from_postfix_increment(lhs, op_span)?;
 300                 continue;
 301             }
 302
 303             let op = op.node;
 304             // Special cases:
 305             if op == AssocOp::As {
 306                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
 307                 continue;
 308             } else if op == AssocOp::Colon {
 309                 lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
 310                 continue;
 311             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
 312                 // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
 313                 // generalise it to the Fixity::None code.
 314                 lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?;
 315                 break;
 316             }
 317
 318             let fixity = op.fixity();
 319             let prec_adjustment = match fixity {
 320                 Fixity::Right => 0,
 321                 Fixity::Left => 1,
 322                 // We currently have no non-associative operators that are not handled above by
 323                 // the special cases. The code is here only for future convenience.
 324                 Fixity::None => 1,
 325             };
 326             let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
 327                 this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
 328             })?;
 329
 330             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
 331             lhs = match op {
 332                 AssocOp::Add
 333                 | AssocOp::Subtract
 334                 | AssocOp::Multiply
 335                 | AssocOp::Divide
 336                 | AssocOp::Modulus
 337                 | AssocOp::LAnd
 338                 | AssocOp::LOr
 339                 | AssocOp::BitXor
 340                 | AssocOp::BitAnd
 341                 | AssocOp::BitOr
 342                 | AssocOp::ShiftLeft
 343                 | AssocOp::ShiftRight
 344                 | AssocOp::Equal
 345                 | AssocOp::Less
 346                 | AssocOp::LessEqual
 347                 | AssocOp::NotEqual
 348                 | AssocOp::Greater
 349                 | AssocOp::GreaterEqual => {
 350                     let ast_op = op.to_ast_binop().unwrap();
 351                     let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
 352                     self.mk_expr(span, binary)
 353                 }
 354                 AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span)),
 355                 AssocOp::AssignOp(k) => {
 356                     let aop = match k {
 357                         token::Plus => BinOpKind::Add,
 358                         token::Minus => BinOpKind::Sub,
 359                         token::Star => BinOpKind::Mul,
 360                         token::Slash => BinOpKind::Div,
 361                         token::Percent => BinOpKind::Rem,
 362                         token::Caret => BinOpKind::BitXor,
 363                         token::And => BinOpKind::BitAnd,
 364                         token::Or => BinOpKind::BitOr,
 365                         token::Shl => BinOpKind::Shl,
 366                         token::Shr => BinOpKind::Shr,
 367                     };
 368                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
 369                     self.mk_expr(span, aopexpr)
 370                 }
 371                 AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
 372                     self.span_bug(span, "AssocOp should have been handled by special case")
 373                 }
 374             };
 375
 376             if let Fixity::None = fixity {
 377                 break;
 378             }
 379         }
 380         if last_type_ascription_set {
 381             self.last_type_ascription = None;
 382         }
 383         Ok(lhs)
 384     }
 385
 386     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
 387         match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
 388             // Semi-statement forms are odd:
 389             // See https://github.com/rust-lang/rust/issues/29071
 390             (true, None) => false,
 391             (false, _) => true, // Continue parsing the expression.
 392             // An exhaustive check is done in the following block, but these are checked first
 393             // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
 394             // want to keep their span info to improve diagnostics in these cases in a later stage.
 395             (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
 396             (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
 397             (true, Some(AssocOp::Add)) // `{ 42 } + 42
 398             // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
 399             // `if x { a } else { b } && if y { c } else { d }`
 400             if !self.look_ahead(1, |t| t.is_used_keyword()) => {
 401                 // These cases are ambiguous and can't be identified in the parser alone.
 402                 let sp = self.sess.source_map().start_point(self.token.span);
 403                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 404                 false
 405             }
 406             (true, Some(AssocOp::LAnd)) |
 407             (true, Some(AssocOp::LOr)) |
 408             (true, Some(AssocOp::BitOr)) => {
 409                 // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the
 410                 // above due to #74233.
 411                 // These cases are ambiguous and can't be identified in the parser alone.
 412                 //
 413                 // Bitwise AND is left out because guessing intent is hard. We can make
 414                 // suggestions based on the assumption that double-refs are rarely intentional,
 415                 // and closures are distinct enough that they don't get mixed up with their
 416                 // return value.
 417                 let sp = self.sess.source_map().start_point(self.token.span);
 418                 self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
 419                 false
 420             }
 421             (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false,
 422             (true, Some(_)) => {
 423                 self.error_found_expr_would_be_stmt(lhs);
 424                 true
 425             }
 426         }
 427     }
 428
 429     /// We've found an expression that would be parsed as a statement,
 430     /// but the next token implies this should be parsed as an expression.
 431     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
 432     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
 433         self.sess.emit_err(FoundExprWouldBeStmt {
 434             span: self.token.span,
 435             token: self.token.clone(),
 436             suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
 437         });
 438     }
 439
 440     /// Possibly translate the current token to an associative operator.
 441     /// The method does not advance the current token.
 442     ///
 443     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
 444     fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
 445         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
 446             // When parsing const expressions, stop parsing when encountering `>`.
 447             (
 448                 Some(
 449                     AssocOp::ShiftRight
 450                     | AssocOp::Greater
 451                     | AssocOp::GreaterEqual
 452                     | AssocOp::AssignOp(token::BinOpToken::Shr),
 453                 ),
 454                 _,
 455             ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
 456                 return None;
 457             }
 458             (Some(op), _) => (op, self.token.span),
 459             (None, Some((Ident { name: sym::and, span }, false))) if self.may_recover() => {
 460                 self.sess.emit_err(InvalidLogicalOperator {
 461                     span: self.token.span,
 462                     incorrect: "and".into(),
 463                     sub: InvalidLogicalOperatorSub::Conjunction(self.token.span),
 464                 });
 465                 (AssocOp::LAnd, span)
 466             }
 467             (None, Some((Ident { name: sym::or, span }, false))) if self.may_recover() => {
 468                 self.sess.emit_err(InvalidLogicalOperator {
 469                     span: self.token.span,
 470                     incorrect: "or".into(),
 471                     sub: InvalidLogicalOperatorSub::Disjunction(self.token.span),
 472                 });
 473                 (AssocOp::LOr, span)
 474             }
 475             _ => return None,
 476         };
 477         Some(source_map::respan(span, op))
 478     }
 479
 480     /// Checks if this expression is a successfully parsed statement.
 481     fn expr_is_complete(&self, e: &Expr) -> bool {
 482         self.restrictions.contains(Restrictions::STMT_EXPR)
 483             && !classify::expr_requires_semi_to_be_stmt(e)
 484     }
 485
 486     /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
 487     /// The other two variants are handled in `parse_prefix_range_expr` below.
 488     fn parse_range_expr(
 489         &mut self,
 490         prec: usize,
 491         lhs: P<Expr>,
 492         op: AssocOp,
 493         cur_op_span: Span,
 494     ) -> PResult<'a, P<Expr>> {
 495         let rhs = if self.is_at_start_of_range_notation_rhs() {
 496             Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
 497         } else {
 498             None
 499         };
 500         let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
 501         let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span);
 502         let limits =
 503             if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
 504         let range = self.mk_range(Some(lhs), rhs, limits);
 505         Ok(self.mk_expr(span, range))
 506     }
 507
 508     fn is_at_start_of_range_notation_rhs(&self) -> bool {
 509         if self.token.can_begin_expr() {
 510             // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
 511             if self.token == token::OpenDelim(Delimiter::Brace) {
 512                 return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
 513             }
 514             true
 515         } else {
 516             false
 517         }
 518     }
 519
 520     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
 521     fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 522         // Check for deprecated `...` syntax.
 523         if self.token == token::DotDotDot {
 524             self.err_dotdotdot_syntax(self.token.span);
 525         }
 526
 527         debug_assert!(
 528             [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
 529             "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
 530             self.token
 531         );
 532
 533         let limits = match self.token.kind {
 534             token::DotDot => RangeLimits::HalfOpen,
 535             _ => RangeLimits::Closed,
 536         };
 537         let op = AssocOp::from_token(&self.token);
 538         // FIXME: `parse_prefix_range_expr` is called when the current
 539         // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
 540         // parsed attributes, then trying to parse them here will always fail.
 541         // We should figure out how we want attributes on range expressions to work.
 542         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 543         self.collect_tokens_for_expr(attrs, |this, attrs| {
 544             let lo = this.token.span;
 545             this.bump();
 546             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
 547                 // RHS must be parsed with more associativity than the dots.
 548                 this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
 549                     .map(|x| (lo.to(x.span), Some(x)))?
 550             } else {
 551                 (lo, None)
 552             };
 553             let range = this.mk_range(None, opt_end, limits);
 554             Ok(this.mk_expr_with_attrs(span, range, attrs))
 555         })
 556     }
 557
 558     /// Parses a prefix-unary-operator expr.
 559     fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 560         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 561         let lo = self.token.span;
 562
 563         macro_rules! make_it {
 564             ($this:ident, $attrs:expr, |this, _| $body:expr) => {
 565                 $this.collect_tokens_for_expr($attrs, |$this, attrs| {
 566                     let (hi, ex) = $body?;
 567                     Ok($this.mk_expr_with_attrs(lo.to(hi), ex, attrs))
 568                 })
 569             };
 570         }
 571
 572         let this = self;
 573
 574         // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
 575         match this.token.uninterpolate().kind {
 576             token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr`
 577             token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr`
 578             token::BinOp(token::Minus) => {
 579                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg))
 580             } // `-expr`
 581             token::BinOp(token::Star) => {
 582                 make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref))
 583             } // `*expr`
 584             token::BinOp(token::And) | token::AndAnd => {
 585                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
 586             }
 587             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
 588                 let mut err =
 589                     LeadingPlusNotSupported { span: lo, remove_plus: None, add_parentheses: None };
 590
 591                 // a block on the LHS might have been intended to be an expression instead
 592                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
 593                     err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
 594                 } else {
 595                     err.remove_plus = Some(lo);
 596                 }
 597                 this.sess.emit_err(err);
 598
 599                 this.bump();
 600                 this.parse_prefix_expr(None)
 601             } // `+expr`
 602             // Recover from `++x`:
 603             token::BinOp(token::Plus)
 604                 if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
 605             {
 606                 let prev_is_semi = this.prev_token == token::Semi;
 607                 let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
 608                 // Eat both `+`s.
 609                 this.bump();
 610                 this.bump();
 611
 612                 let operand_expr = this.parse_dot_or_call_expr(Default::default())?;
 613                 this.recover_from_prefix_increment(operand_expr, pre_span, prev_is_semi)
 614             }
 615             token::Ident(..) if this.token.is_keyword(kw::Box) => {
 616                 make_it!(this, attrs, |this, _| this.parse_box_expr(lo))
 617             }
 618             token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
 619                 make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
 620             }
 621             _ => return this.parse_dot_or_call_expr(Some(attrs)),
 622         }
 623     }
 624
 625     fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
 626         self.bump();
 627         let expr = self.parse_prefix_expr(None);
 628         let (span, expr) = self.interpolated_or_expr_span(expr)?;
 629         Ok((lo.to(span), expr))
 630     }
 631
 632     fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
 633         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 634         Ok((span, self.mk_unary(op, expr)))
 635     }
 636
 637     // Recover on `!` suggesting for bitwise negation instead.
 638     fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 639         self.sess.emit_err(TildeAsUnaryOperator(lo));
 640
 641         self.parse_unary_expr(lo, UnOp::Not)
 642     }
 643
 644     /// Parse `box expr`.
 645     fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 646         let (span, expr) = self.parse_prefix_expr_common(lo)?;
 647         self.sess.gated_spans.gate(sym::box_syntax, span);
 648         Ok((span, ExprKind::Box(expr)))
 649     }
 650
 651     fn is_mistaken_not_ident_negation(&self) -> bool {
 652         let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
 653             // These tokens can start an expression after `!`, but
 654             // can't continue an expression after an ident
 655             token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
 656             token::Literal(..) | token::Pound => true,
 657             _ => t.is_whole_expr(),
 658         };
 659         self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
 660     }
 661
 662     /// Recover on `not expr` in favor of `!expr`.
 663     fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 664         // Emit the error...
 665         let negated_token = self.look_ahead(1, |t| t.clone());
 666
 667         let sub_diag = if negated_token.is_numeric_lit() {
 668             NotAsNegationOperatorSub::SuggestNotBitwise
 669         } else if negated_token.is_bool_lit() {
 670             NotAsNegationOperatorSub::SuggestNotLogical
 671         } else {
 672             NotAsNegationOperatorSub::SuggestNotDefault
 673         };
 674
 675         self.sess.emit_err(NotAsNegationOperator {
 676             negated: negated_token.span,
 677             negated_desc: super::token_descr(&negated_token),
 678             // Span the `not` plus trailing whitespace to avoid
 679             // trailing whitespace after the `!` in our suggestion
 680             sub: sub_diag(
 681                 self.sess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
 682             ),
 683         });
 684
 685         // ...and recover!
 686         self.parse_unary_expr(lo, UnOp::Not)
 687     }
 688
 689     /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
 690     fn interpolated_or_expr_span(
 691         &self,
 692         expr: PResult<'a, P<Expr>>,
 693     ) -> PResult<'a, (Span, P<Expr>)> {
 694         expr.map(|e| {
 695             (
 696                 match self.prev_token.kind {
 697                     TokenKind::Interpolated(..) => self.prev_token.span,
 698                     _ => e.span,
 699                 },
 700                 e,
 701             )
 702         })
 703     }
 704
 705     fn parse_assoc_op_cast(
 706         &mut self,
 707         lhs: P<Expr>,
 708         lhs_span: Span,
 709         expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
 710     ) -> PResult<'a, P<Expr>> {
 711         let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
 712             this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, rhs.span), expr_kind(lhs, rhs))
 713         };
 714
 715         // Save the state of the parser before parsing type normally, in case there is a
 716         // LessThan comparison after this cast.
 717         let parser_snapshot_before_type = self.clone();
 718         let cast_expr = match self.parse_as_cast_ty() {
 719             Ok(rhs) => mk_expr(self, lhs, rhs),
 720             Err(type_err) => {
 721                 if !self.may_recover() {
 722                     return Err(type_err);
 723                 }
 724
 725                 // Rewind to before attempting to parse the type with generics, to recover
 726                 // from situations like `x as usize < y` in which we first tried to parse
 727                 // `usize < y` as a type with generic arguments.
 728                 let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
 729
 730                 // Check for typo of `'a: loop { break 'a }` with a missing `'`.
 731                 match (&lhs.kind, &self.token.kind) {
 732                     (
 733                         // `foo: `
 734                         ExprKind::Path(None, ast::Path { segments, .. }),
 735                         TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
 736                     ) if segments.len() == 1 => {
 737                         let snapshot = self.create_snapshot_for_diagnostic();
 738                         let label = Label {
 739                             ident: Ident::from_str_and_span(
 740                                 &format!("'{}", segments[0].ident),
 741                                 segments[0].ident.span,
 742                             ),
 743                         };
 744                         match self.parse_labeled_expr(label, false) {
 745                             Ok(expr) => {
 746                                 type_err.cancel();
 747                                 self.sess.emit_err(MalformedLoopLabel {
 748                                     span: label.ident.span,
 749                                     correct_label: label.ident,
 750                                 });
 751                                 return Ok(expr);
 752                             }
 753                             Err(err) => {
 754                                 err.cancel();
 755                                 self.restore_snapshot(snapshot);
 756                             }
 757                         }
 758                     }
 759                     _ => {}
 760                 }
 761
 762                 match self.parse_path(PathStyle::Expr) {
 763                     Ok(path) => {
 764                         let span_after_type = parser_snapshot_after_type.token.span;
 765                         let expr = mk_expr(
 766                             self,
 767                             lhs,
 768                             self.mk_ty(path.span, TyKind::Path(None, path.clone())),
 769                         );
 770
 771                         let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
 772                         let suggestion = ComparisonOrShiftInterpretedAsGenericSugg {
 773                             left: expr.span.shrink_to_lo(),
 774                             right: expr.span.shrink_to_hi(),
 775                         };
 776
 777                         match self.token.kind {
 778                             token::Lt => self.sess.emit_err(ComparisonInterpretedAsGeneric {
 779                                 comparison: self.token.span,
 780                                 r#type: path,
 781                                 args: args_span,
 782                                 suggestion,
 783                             }),
 784                             token::BinOp(token::Shl) => {
 785                                 self.sess.emit_err(ShiftInterpretedAsGeneric {
 786                                     shift: self.token.span,
 787                                     r#type: path,
 788                                     args: args_span,
 789                                     suggestion,
 790                                 })
 791                             }
 792                             _ => {
 793                                 // We can end up here even without `<` being the next token, for
 794                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
 795                                 // but `parse_path` returns `Ok` on them due to error recovery.
 796                                 // Return original error and parser state.
 797                                 *self = parser_snapshot_after_type;
 798                                 return Err(type_err);
 799                             }
 800                         };
 801
 802                         // Successfully parsed the type path leaving a `<` yet to parse.
 803                         type_err.cancel();
 804
 805                         // Keep `x as usize` as an expression in AST and continue parsing.
 806                         expr
 807                     }
 808                     Err(path_err) => {
 809                         // Couldn't parse as a path, return original error and parser state.
 810                         path_err.cancel();
 811                         *self = parser_snapshot_after_type;
 812                         return Err(type_err);
 813                     }
 814                 }
 815             }
 816         };
 817
 818         self.parse_and_disallow_postfix_after_cast(cast_expr)
 819     }
 820
 821     /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
 822     /// then emits an error and returns the newly parsed tree.
 823     /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
 824     fn parse_and_disallow_postfix_after_cast(
 825         &mut self,
 826         cast_expr: P<Expr>,
 827     ) -> PResult<'a, P<Expr>> {
 828         let span = cast_expr.span;
 829         let (cast_kind, maybe_ascription_span) =
 830             if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
 831                 ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi())))
 832             } else {
 833                 ("cast", None)
 834             };
 835
 836         let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;
 837
 838         // Check if an illegal postfix operator has been added after the cast.
 839         // If the resulting expression is not a cast, it is an illegal postfix operator.
 840         if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) {
 841             let msg = format!(
 842                 "{cast_kind} cannot be followed by {}",
 843                 match with_postfix.kind {
 844                     ExprKind::Index(_, _) => "indexing",
 845                     ExprKind::Try(_) => "`?`",
 846                     ExprKind::Field(_, _) => "a field access",
 847                     ExprKind::MethodCall(_, _, _, _) => "a method call",
 848                     ExprKind::Call(_, _) => "a function call",
 849                     ExprKind::Await(_) => "`.await`",
 850                     ExprKind::Err => return Ok(with_postfix),
 851                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
 852                 }
 853             );
 854             let mut err = self.struct_span_err(span, &msg);
 855
 856             let suggest_parens = |err: &mut Diagnostic| {
 857                 let suggestions = vec![
 858                     (span.shrink_to_lo(), "(".to_string()),
 859                     (span.shrink_to_hi(), ")".to_string()),
 860                 ];
 861                 err.multipart_suggestion(
 862                     "try surrounding the expression in parentheses",
 863                     suggestions,
 864                     Applicability::MachineApplicable,
 865                 );
 866             };
 867
 868             // If type ascription is "likely an error", the user will already be getting a useful
 869             // help message, and doesn't need a second.
 870             if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
 871                 self.maybe_annotate_with_ascription(&mut err, false);
 872             } else if let Some(ascription_span) = maybe_ascription_span {
 873                 let is_nightly = self.sess.unstable_features.is_nightly_build();
 874                 if is_nightly {
 875                     suggest_parens(&mut err);
 876                 }
 877                 err.span_suggestion(
 878                     ascription_span,
 879                     &format!(
 880                         "{}remove the type ascription",
 881                         if is_nightly { "alternatively, " } else { "" }
 882                     ),
 883                     "",
 884                     if is_nightly {
 885                         Applicability::MaybeIncorrect
 886                     } else {
 887                         Applicability::MachineApplicable
 888                     },
 889                 );
 890             } else {
 891                 suggest_parens(&mut err);
 892             }
 893             err.emit();
 894         };
 895         Ok(with_postfix)
 896     }
 897
 898     fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
 899         let maybe_path = self.could_ascription_be_path(&lhs.kind);
 900         self.last_type_ascription = Some((self.prev_token.span, maybe_path));
 901         let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
 902         self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
 903         Ok(lhs)
 904     }
 905
 906     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
 907     fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
 908         self.expect_and()?;
 909         let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
 910         let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
 911         let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
 912         let expr = self.parse_prefix_expr(None);
 913         let (hi, expr) = self.interpolated_or_expr_span(expr)?;
 914         let span = lo.to(hi);
 915         if let Some(lt) = lifetime {
 916             self.error_remove_borrow_lifetime(span, lt.ident.span);
 917         }
 918         Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
 919     }
 920
 921     fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
 922         self.sess.emit_err(LifetimeInBorrowExpression { span, lifetime_span: lt_span });
 923     }
 924
 925     /// Parse `mut?` or `raw [ const | mut ]`.
 926     fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
 927         if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
 928             // `raw [ const | mut ]`.
 929             let found_raw = self.eat_keyword(kw::Raw);
 930             assert!(found_raw);
 931             let mutability = self.parse_const_or_mut().unwrap();
 932             self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
 933             (ast::BorrowKind::Raw, mutability)
 934         } else {
 935             // `mut?`
 936             (ast::BorrowKind::Ref, self.parse_mutability())
 937         }
 938     }
 939
 940     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
 941     fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
 942         let attrs = self.parse_or_use_outer_attributes(attrs)?;
 943         self.collect_tokens_for_expr(attrs, |this, attrs| {
 944             let base = this.parse_bottom_expr();
 945             let (span, base) = this.interpolated_or_expr_span(base)?;
 946             this.parse_dot_or_call_expr_with(base, span, attrs)
 947         })
 948     }
 949
 950     pub(super) fn parse_dot_or_call_expr_with(
 951         &mut self,
 952         e0: P<Expr>,
 953         lo: Span,
 954         mut attrs: ast::AttrVec,
 955     ) -> PResult<'a, P<Expr>> {
 956         // Stitch the list of outer attributes onto the return value.
 957         // A little bit ugly, but the best way given the current code
 958         // structure
 959         let res = self.parse_dot_or_call_expr_with_(e0, lo);
 960         if attrs.is_empty() {
 961             res
 962         } else {
 963             res.map(|expr| {
 964                 expr.map(|mut expr| {
 965                     attrs.extend(expr.attrs);
 966                     expr.attrs = attrs;
 967                     expr
 968                 })
 969             })
 970         }
 971     }
 972
 973     fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
 974         loop {
 975             let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 976                 // we are using noexpect here because we don't expect a `?` directly after a `return`
 977                 // which could be suggested otherwise
 978                 self.eat_noexpect(&token::Question)
 979             } else {
 980                 self.eat(&token::Question)
 981             };
 982             if has_question {
 983                 // `expr?`
 984                 e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
 985                 continue;
 986             }
 987             let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) {
 988                 // we are using noexpect here because we don't expect a `.` directly after a `return`
 989                 // which could be suggested otherwise
 990                 self.eat_noexpect(&token::Dot)
 991             } else {
 992                 self.eat(&token::Dot)
 993             };
 994             if has_dot {
 995                 // expr.f
 996                 e = self.parse_dot_suffix_expr(lo, e)?;
 997                 continue;
 998             }
 999             if self.expr_is_complete(&e) {
1000                 return Ok(e);
1001             }
1002             e = match self.token.kind {
1003                 token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e),
1004                 token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?,
1005                 _ => return Ok(e),
1006             }
1007         }
1008     }
1009
1010     fn look_ahead_type_ascription_as_field(&mut self) -> bool {
1011         self.look_ahead(1, |t| t.is_ident())
1012             && self.look_ahead(2, |t| t == &token::Colon)
1013             && self.look_ahead(3, |t| t.can_begin_expr())
1014     }
1015
1016     fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1017         match self.token.uninterpolate().kind {
1018             token::Ident(..) => self.parse_dot_suffix(base, lo),
1019             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
1020                 Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None))
1021             }
1022             token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
1023                 Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix))
1024             }
1025             _ => {
1026                 self.error_unexpected_after_dot();
1027                 Ok(base)
1028             }
1029         }
1030     }
1031
1032     fn error_unexpected_after_dot(&self) {
1033         // FIXME Could factor this out into non_fatal_unexpected or something.
1034         let actual = pprust::token_to_string(&self.token);
1035         self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit();
1036     }
1037
1038     // We need an identifier or integer, but the next token is a float.
1039     // Break the float into components to extract the identifier or integer.
1040     // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
1041     // parts unless those parts are processed immediately. `TokenCursor` should either
1042     // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
1043     // we should break everything including floats into more basic proc-macro style
1044     // tokens in the lexer (probably preferable).
1045     fn parse_tuple_field_access_expr_float(
1046         &mut self,
1047         lo: Span,
1048         base: P<Expr>,
1049         float: Symbol,
1050         suffix: Option<Symbol>,
1051     ) -> P<Expr> {
1052         #[derive(Debug)]
1053         enum FloatComponent {
1054             IdentLike(String),
1055             Punct(char),
1056         }
1057         use FloatComponent::*;
1058
1059         let float_str = float.as_str();
1060         let mut components = Vec::new();
1061         let mut ident_like = String::new();
1062         for c in float_str.chars() {
1063             if c == '_' || c.is_ascii_alphanumeric() {
1064                 ident_like.push(c);
1065             } else if matches!(c, '.' | '+' | '-') {
1066                 if !ident_like.is_empty() {
1067                     components.push(IdentLike(mem::take(&mut ident_like)));
1068                 }
1069                 components.push(Punct(c));
1070             } else {
1071                 panic!("unexpected character in a float token: {:?}", c)
1072             }
1073         }
1074         if !ident_like.is_empty() {
1075             components.push(IdentLike(ident_like));
1076         }
1077
1078         // With proc macros the span can refer to anything, the source may be too short,
1079         // or too long, or non-ASCII. It only makes sense to break our span into components
1080         // if its underlying text is identical to our float literal.
1081         let span = self.token.span;
1082         let can_take_span_apart =
1083             || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
1084
1085         match &*components {
1086             // 1e2
1087             [IdentLike(i)] => {
1088                 self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None)
1089             }
1090             // 1.
1091             [IdentLike(i), Punct('.')] => {
1092                 let (ident_span, dot_span) = if can_take_span_apart() {
1093                     let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
1094                     let ident_span = span.with_hi(span.lo + ident_len);
1095                     let dot_span = span.with_lo(span.lo + ident_len);
1096                     (ident_span, dot_span)
1097                 } else {
1098                     (span, span)
1099                 };
1100                 assert!(suffix.is_none());
1101                 let symbol = Symbol::intern(&i);
1102                 self.token = Token::new(token::Ident(symbol, false), ident_span);
1103                 let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
1104                 self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token))
1105             }
1106             // 1.2 | 1.2e3
1107             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
1108                 let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
1109                     let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
1110                     let ident1_span = span.with_hi(span.lo + ident1_len);
1111                     let dot_span = span
1112                         .with_lo(span.lo + ident1_len)
1113                         .with_hi(span.lo + ident1_len + BytePos(1));
1114                     let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
1115                     (ident1_span, dot_span, ident2_span)
1116                 } else {
1117                     (span, span, span)
1118                 };
1119                 let symbol1 = Symbol::intern(&i1);
1120                 self.token = Token::new(token::Ident(symbol1, false), ident1_span);
1121                 // This needs to be `Spacing::Alone` to prevent regressions.
1122                 // See issue #76399 and PR #76285 for more details
1123                 let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
1124                 let base1 =
1125                     self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1));
1126                 let symbol2 = Symbol::intern(&i2);
1127                 let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
1128                 self.bump_with((next_token2, self.token_spacing)); // `.`
1129                 self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None)
1130             }
1131             // 1e+ | 1e- (recovered)
1132             [IdentLike(_), Punct('+' | '-')] |
1133             // 1e+2 | 1e-2
1134             [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
1135             // 1.2e+ | 1.2e-
1136             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
1137             // 1.2e+3 | 1.2e-3
1138             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
1139                 // See the FIXME about `TokenCursor` above.
1140                 self.error_unexpected_after_dot();
1141                 base
1142             }
1143             _ => panic!("unexpected components in a float token: {:?}", components),
1144         }
1145     }
1146
1147     fn parse_tuple_field_access_expr(
1148         &mut self,
1149         lo: Span,
1150         base: P<Expr>,
1151         field: Symbol,
1152         suffix: Option<Symbol>,
1153         next_token: Option<(Token, Spacing)>,
1154     ) -> P<Expr> {
1155         match next_token {
1156             Some(next_token) => self.bump_with(next_token),
1157             None => self.bump(),
1158         }
1159         let span = self.prev_token.span;
1160         let field = ExprKind::Field(base, Ident::new(field, span));
1161         if let Some(suffix) = suffix {
1162             self.expect_no_tuple_index_suffix(span, suffix);
1163         }
1164         self.mk_expr(lo.to(span), field)
1165     }
1166
1167     /// Parse a function call expression, `expr(...)`.
1168     fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
1169         let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
1170             && self.look_ahead_type_ascription_as_field()
1171         {
1172             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
1173         } else {
1174             None
1175         };
1176         let open_paren = self.token.span;
1177
1178         let mut seq = self
1179             .parse_paren_expr_seq()
1180             .map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
1181         if let Some(expr) =
1182             self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot)
1183         {
1184             return expr;
1185         }
1186         self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq)
1187     }
1188
1189     /// If we encounter a parser state that looks like the user has written a `struct` literal with
1190     /// parentheses instead of braces, recover the parser state and provide suggestions.
1191     #[instrument(skip(self, seq, snapshot), level = "trace")]
1192     fn maybe_recover_struct_lit_bad_delims(
1193         &mut self,
1194         lo: Span,
1195         open_paren: Span,
1196         seq: &mut PResult<'a, P<Expr>>,
1197         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
1198     ) -> Option<P<Expr>> {
1199         if !self.may_recover() {
1200             return None;
1201         }
1202
1203         match (seq.as_mut(), snapshot) {
1204             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
1205                 snapshot.bump(); // `(`
1206                 match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
1207                     Ok((fields, ..))
1208                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
1209                     {
1210                         // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
1211                         // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
1212                         self.restore_snapshot(snapshot);
1213                         let close_paren = self.prev_token.span;
1214                         let span = lo.to(self.prev_token.span);
1215                         if !fields.is_empty() {
1216                             let mut replacement_err = ParenthesesWithStructFields {
1217                                 span,
1218                                 r#type: path,
1219                                 braces_for_struct: BracesForStructLiteral {
1220                                     first: open_paren,
1221                                     second: close_paren,
1222                                 },
1223                                 no_fields_for_fn: NoFieldsForFnCall {
1224                                     fields: fields
1225                                         .into_iter()
1226                                         .map(|field| field.span.until(field.expr.span))
1227                                         .collect(),
1228                                 },
1229                             }
1230                             .into_diagnostic(&self.sess.span_diagnostic);
1231                             replacement_err.emit();
1232
1233                             let old_err = mem::replace(err, replacement_err);
1234                             old_err.cancel();
1235                         } else {
1236                             err.emit();
1237                         }
1238                         return Some(self.mk_expr_err(span));
1239                     }
1240                     Ok(_) => {}
1241                     Err(mut err) => {
1242                         err.emit();
1243                     }
1244                 }
1245             }
1246             _ => {}
1247         }
1248         None
1249     }
1250
1251     /// Parse an indexing expression `expr[...]`.
1252     fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
1253         let prev_span = self.prev_token.span;
1254         let open_delim_span = self.token.span;
1255         self.bump(); // `[`
1256         let index = self.parse_expr()?;
1257         self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
1258         self.expect(&token::CloseDelim(Delimiter::Bracket))?;
1259         Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index)))
1260     }
1261
1262     /// Assuming we have just parsed `.`, continue parsing into an expression.
1263     fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
1264         if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) {
1265             return Ok(self.mk_await_expr(self_arg, lo));
1266         }
1267
1268         let fn_span_lo = self.token.span;
1269         let mut segment = self.parse_path_segment(PathStyle::Expr, None)?;
1270         self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]);
1271         self.check_turbofish_missing_angle_brackets(&mut segment);
1272
1273         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1274             // Method call `expr.f()`
1275             let args = self.parse_paren_expr_seq()?;
1276             let fn_span = fn_span_lo.to(self.prev_token.span);
1277             let span = lo.to(self.prev_token.span);
1278             Ok(self.mk_expr(span, ExprKind::MethodCall(segment, self_arg, args, fn_span)))
1279         } else {
1280             // Field access `expr.f`
1281             if let Some(args) = segment.args {
1282                 self.sess.emit_err(FieldExpressionWithGeneric(args.span()));
1283             }
1284
1285             let span = lo.to(self.prev_token.span);
1286             Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident)))
1287         }
1288     }
1289
1290     /// At the bottom (top?) of the precedence hierarchy,
1291     /// Parses things like parenthesized exprs, macros, `return`, etc.
1292     ///
1293     /// N.B., this does not parse outer attributes, and is private because it only works
1294     /// correctly if called from `parse_dot_or_call_expr()`.
1295     fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
1296         maybe_recover_from_interpolated_ty_qpath!(self, true);
1297         maybe_whole_expr!(self);
1298
1299         // Outer attributes are already parsed and will be
1300         // added to the return value after the fact.
1301
1302         // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
1303         let lo = self.token.span;
1304         if let token::Literal(_) = self.token.kind {
1305             // This match arm is a special-case of the `_` match arm below and
1306             // could be removed without changing functionality, but it's faster
1307             // to have it here, especially for programs with large constants.
1308             self.parse_lit_expr()
1309         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1310             self.parse_tuple_parens_expr()
1311         } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
1312             self.parse_block_expr(None, lo, BlockCheckMode::Default)
1313         } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
1314             self.parse_closure_expr().map_err(|mut err| {
1315                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
1316                 // then suggest parens around the lhs.
1317                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
1318                     err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
1319                 }
1320                 err
1321             })
1322         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
1323             self.parse_array_or_repeat_expr(Delimiter::Bracket)
1324         } else if self.check_path() {
1325             self.parse_path_start_expr()
1326         } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
1327             self.parse_closure_expr()
1328         } else if self.eat_keyword(kw::If) {
1329             self.parse_if_expr()
1330         } else if self.check_keyword(kw::For) {
1331             if self.choose_generics_over_qpath(1) {
1332                 self.parse_closure_expr()
1333             } else {
1334                 assert!(self.eat_keyword(kw::For));
1335                 self.parse_for_expr(None, self.prev_token.span)
1336             }
1337         } else if self.eat_keyword(kw::While) {
1338             self.parse_while_expr(None, self.prev_token.span)
1339         } else if let Some(label) = self.eat_label() {
1340             self.parse_labeled_expr(label, true)
1341         } else if self.eat_keyword(kw::Loop) {
1342             let sp = self.prev_token.span;
1343             self.parse_loop_expr(None, self.prev_token.span).map_err(|mut err| {
1344                 err.span_label(sp, "while parsing this `loop` expression");
1345                 err
1346             })
1347         } else if self.eat_keyword(kw::Continue) {
1348             let kind = ExprKind::Continue(self.eat_label());
1349             Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
1350         } else if self.eat_keyword(kw::Match) {
1351             let match_sp = self.prev_token.span;
1352             self.parse_match_expr().map_err(|mut err| {
1353                 err.span_label(match_sp, "while parsing this `match` expression");
1354                 err
1355             })
1356         } else if self.eat_keyword(kw::Unsafe) {
1357             let sp = self.prev_token.span;
1358             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
1359                 |mut err| {
1360                     err.span_label(sp, "while parsing this `unsafe` expression");
1361                     err
1362                 },
1363             )
1364         } else if self.check_inline_const(0) {
1365             self.parse_const_block(lo.to(self.token.span), false)
1366         } else if self.may_recover() && self.is_do_catch_block() {
1367             self.recover_do_catch()
1368         } else if self.is_try_block() {
1369             self.expect_keyword(kw::Try)?;
1370             self.parse_try_block(lo)
1371         } else if self.eat_keyword(kw::Return) {
1372             self.parse_return_expr()
1373         } else if self.eat_keyword(kw::Break) {
1374             self.parse_break_expr()
1375         } else if self.eat_keyword(kw::Yield) {
1376             self.parse_yield_expr()
1377         } else if self.is_do_yeet() {
1378             self.parse_yeet_expr()
1379         } else if self.check_keyword(kw::Let) {
1380             self.parse_let_expr()
1381         } else if self.eat_keyword(kw::Underscore) {
1382             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore))
1383         } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
1384             // Don't complain about bare semicolons after unclosed braces
1385             // recovery in order to keep the error count down. Fixing the
1386             // delimiters will possibly also fix the bare semicolon found in
1387             // expression context. For example, silence the following error:
1388             //
1389             //     error: expected expression, found `;`
1390             //      --> file.rs:2:13
1391             //       |
1392             //     2 |     foo(bar(;
1393             //       |             ^ expected expression
1394             self.bump();
1395             Ok(self.mk_expr_err(self.token.span))
1396         } else if self.token.uninterpolated_span().rust_2018() {
1397             // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly.
1398             if self.check_keyword(kw::Async) {
1399                 if self.is_async_block() {
1400                     // Check for `async {` and `async move {`.
1401                     self.parse_async_block()
1402                 } else {
1403                     self.parse_closure_expr()
1404                 }
1405             } else if self.eat_keyword(kw::Await) {
1406                 self.recover_incorrect_await_syntax(lo, self.prev_token.span)
1407             } else {
1408                 self.parse_lit_expr()
1409             }
1410         } else {
1411             self.parse_lit_expr()
1412         }
1413     }
1414
1415     fn parse_lit_expr(&mut self) -> PResult<'a, P<Expr>> {
1416         let lo = self.token.span;
1417         match self.parse_opt_lit() {
1418             Some(literal) => {
1419                 let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal));
1420                 self.maybe_recover_from_bad_qpath(expr)
1421             }
1422             None => self.try_macro_suggestion(),
1423         }
1424     }
1425
1426     fn parse_tuple_parens_expr(&mut self) -> PResult<'a, P<Expr>> {
1427         let lo = self.token.span;
1428         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1429         let (es, trailing_comma) = match self.parse_seq_to_end(
1430             &token::CloseDelim(Delimiter::Parenthesis),
1431             SeqSep::trailing_allowed(token::Comma),
1432             |p| p.parse_expr_catch_underscore(),
1433         ) {
1434             Ok(x) => x,
1435             Err(err) => {
1436                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err)));
1437             }
1438         };
1439         let kind = if es.len() == 1 && !trailing_comma {
1440             // `(e)` is parenthesized `e`.
1441             ExprKind::Paren(es.into_iter().next().unwrap())
1442         } else {
1443             // `(e,)` is a tuple with only one field, `e`.
1444             ExprKind::Tup(es)
1445         };
1446         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1447         self.maybe_recover_from_bad_qpath(expr)
1448     }
1449
1450     fn parse_array_or_repeat_expr(&mut self, close_delim: Delimiter) -> PResult<'a, P<Expr>> {
1451         let lo = self.token.span;
1452         self.bump(); // `[` or other open delim
1453
1454         let close = &token::CloseDelim(close_delim);
1455         let kind = if self.eat(close) {
1456             // Empty vector
1457             ExprKind::Array(Vec::new())
1458         } else {
1459             // Non-empty vector
1460             let first_expr = self.parse_expr()?;
1461             if self.eat(&token::Semi) {
1462                 // Repeating array syntax: `[ 0; 512 ]`
1463                 let count = self.parse_anon_const_expr()?;
1464                 self.expect(close)?;
1465                 ExprKind::Repeat(first_expr, count)
1466             } else if self.eat(&token::Comma) {
1467                 // Vector with two or more elements.
1468                 let sep = SeqSep::trailing_allowed(token::Comma);
1469                 let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
1470                 let mut exprs = vec![first_expr];
1471                 exprs.extend(remaining_exprs);
1472                 ExprKind::Array(exprs)
1473             } else {
1474                 // Vector with one element
1475                 self.expect(close)?;
1476                 ExprKind::Array(vec![first_expr])
1477             }
1478         };
1479         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1480         self.maybe_recover_from_bad_qpath(expr)
1481     }
1482
1483     fn parse_path_start_expr(&mut self) -> PResult<'a, P<Expr>> {
1484         let (qself, path) = if self.eat_lt() {
1485             let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
1486             (Some(qself), path)
1487         } else {
1488             (None, self.parse_path(PathStyle::Expr)?)
1489         };
1490
1491         // `!`, as an operator, is prefix, so we know this isn't that.
1492         let (span, kind) = if self.eat(&token::Not) {
1493             // MACRO INVOCATION expression
1494             if qself.is_some() {
1495                 self.sess.emit_err(MacroInvocationWithQualifiedPath(path.span));
1496             }
1497             let lo = path.span;
1498             let mac = P(MacCall {
1499                 path,
1500                 args: self.parse_mac_args()?,
1501                 prior_type_ascription: self.last_type_ascription,
1502             });
1503             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
1504         } else if self.check(&token::OpenDelim(Delimiter::Brace)) &&
1505             let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path) {
1506                 if qself.is_some() {
1507                     self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
1508                 }
1509                 return expr;
1510         } else {
1511             (path.span, ExprKind::Path(qself, path))
1512         };
1513
1514         let expr = self.mk_expr(span, kind);
1515         self.maybe_recover_from_bad_qpath(expr)
1516     }
1517
1518     /// Parse `'label: $expr`. The label is already parsed.
1519     fn parse_labeled_expr(
1520         &mut self,
1521         label_: Label,
1522         mut consume_colon: bool,
1523     ) -> PResult<'a, P<Expr>> {
1524         let lo = label_.ident.span;
1525         let label = Some(label_);
1526         let ate_colon = self.eat(&token::Colon);
1527         let expr = if self.eat_keyword(kw::While) {
1528             self.parse_while_expr(label, lo)
1529         } else if self.eat_keyword(kw::For) {
1530             self.parse_for_expr(label, lo)
1531         } else if self.eat_keyword(kw::Loop) {
1532             self.parse_loop_expr(label, lo)
1533         } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
1534             || self.token.is_whole_block()
1535         {
1536             self.parse_block_expr(label, lo, BlockCheckMode::Default)
1537         } else if !ate_colon
1538             && self.may_recover()
1539             && (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
1540                 || self.token.is_op())
1541         {
1542             let lit = self.recover_unclosed_char(label_.ident, |self_| {
1543                 self_.sess.create_err(UnexpectedTokenAfterLabel {
1544                     span: self_.token.span,
1545                     remove_label: None,
1546                     enclose_in_block: None,
1547                 })
1548             });
1549             consume_colon = false;
1550             Ok(self.mk_expr(lo, ExprKind::Lit(lit)))
1551         } else if !ate_colon
1552             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
1553         {
1554             // We're probably inside of a `Path<'a>` that needs a turbofish
1555             self.sess.emit_err(UnexpectedTokenAfterLabel {
1556                 span: self.token.span,
1557                 remove_label: None,
1558                 enclose_in_block: None,
1559             });
1560             consume_colon = false;
1561             Ok(self.mk_expr_err(lo))
1562         } else {
1563             let mut err = UnexpectedTokenAfterLabel {
1564                 span: self.token.span,
1565                 remove_label: None,
1566                 enclose_in_block: None,
1567             };
1568
1569             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
1570             let expr = self.parse_expr().map(|expr| {
1571                 let span = expr.span;
1572
1573                 let found_labeled_breaks = {
1574                     struct FindLabeledBreaksVisitor(bool);
1575
1576                     impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
1577                         fn visit_expr_post(&mut self, ex: &'ast Expr) {
1578                             if let ExprKind::Break(Some(_label), _) = ex.kind {
1579                                 self.0 = true;
1580                             }
1581                         }
1582                     }
1583
1584                     let mut vis = FindLabeledBreaksVisitor(false);
1585                     vis.visit_expr(&expr);
1586                     vis.0
1587                 };
1588
1589                 // Suggestion involves adding a (as of time of writing this, unstable) labeled block.
1590                 //
1591                 // If there are no breaks that may use this label, suggest removing the label and
1592                 // recover to the unmodified expression.
1593                 if !found_labeled_breaks {
1594                     err.remove_label = Some(lo.until(span));
1595
1596                     return expr;
1597                 }
1598
1599                 err.enclose_in_block = Some(UnexpectedTokenAfterLabelSugg {
1600                     left: span.shrink_to_lo(),
1601                     right: span.shrink_to_hi(),
1602                 });
1603
1604                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
1605                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
1606                 let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
1607                 self.mk_expr(span, ExprKind::Block(blk, label))
1608             });
1609
1610             self.sess.emit_err(err);
1611             expr
1612         }?;
1613
1614         if !ate_colon && consume_colon {
1615             self.sess.emit_err(RequireColonAfterLabeledExpression {
1616                 span: expr.span,
1617                 label: lo,
1618                 label_end: lo.shrink_to_hi(),
1619             });
1620         }
1621
1622         Ok(expr)
1623     }
1624
1625     /// Emit an error when a char is parsed as a lifetime because of a missing quote
1626     pub(super) fn recover_unclosed_char(
1627         &mut self,
1628         lifetime: Ident,
1629         err: impl FnOnce(&mut Self) -> DiagnosticBuilder<'a, ErrorGuaranteed>,
1630     ) -> ast::Lit {
1631         if let Some(mut diag) =
1632             self.sess.span_diagnostic.steal_diagnostic(lifetime.span, StashKey::LifetimeIsChar)
1633         {
1634             diag.span_suggestion_verbose(
1635                 lifetime.span.shrink_to_hi(),
1636                 "add `'` to close the char literal",
1637                 "'",
1638                 Applicability::MaybeIncorrect,
1639             )
1640             .emit();
1641         } else {
1642             err(self)
1643                 .span_suggestion_verbose(
1644                     lifetime.span.shrink_to_hi(),
1645                     "add `'` to close the char literal",
1646                     "'",
1647                     Applicability::MaybeIncorrect,
1648                 )
1649                 .emit();
1650         }
1651         ast::Lit {
1652             token_lit: token::Lit::new(token::LitKind::Char, lifetime.name, None),
1653             kind: ast::LitKind::Char(lifetime.name.as_str().chars().next().unwrap_or('_')),
1654             span: lifetime.span,
1655         }
1656     }
1657
1658     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
1659     fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
1660         let lo = self.token.span;
1661
1662         self.bump(); // `do`
1663         self.bump(); // `catch`
1664
1665         let span = lo.to(self.prev_token.span);
1666         self.sess.emit_err(DoCatchSyntaxRemoved { span });
1667
1668         self.parse_try_block(lo)
1669     }
1670
1671     /// Parse an expression if the token can begin one.
1672     fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
1673         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
1674     }
1675
1676     /// Parse `"return" expr?`.
1677     fn parse_return_expr(&mut self) -> PResult<'a, P<Expr>> {
1678         let lo = self.prev_token.span;
1679         let kind = ExprKind::Ret(self.parse_expr_opt()?);
1680         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
1681         self.maybe_recover_from_bad_qpath(expr)
1682     }
1683
1684     /// Parse `"do" "yeet" expr?`.
1685     fn parse_yeet_expr(&mut self) -> PResult<'a, P<Expr>> {
1686         let lo = self.token.span;
1687
1688         self.bump(); // `do`
1689         self.bump(); // `yeet`
1690
1691         let kind = ExprKind::Yeet(self.parse_expr_opt()?);
1692
1693         let span = lo.to(self.prev_token.span);
1694         self.sess.gated_spans.gate(sym::yeet_expr, span);
1695         let expr = self.mk_expr(span, kind);
1696         self.maybe_recover_from_bad_qpath(expr)
1697     }
1698
1699     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
1700     /// If the label is followed immediately by a `:` token, the label and `:` are
1701     /// parsed as part of the expression (i.e. a labeled loop). The language team has
1702     /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
1703     /// the break expression of an unlabeled break is a labeled loop (as in
1704     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
1705     /// expression only gets a warning for compatibility reasons; and a labeled break
1706     /// with a labeled loop does not even get a warning because there is no ambiguity.
1707     fn parse_break_expr(&mut self) -> PResult<'a, P<Expr>> {
1708         let lo = self.prev_token.span;
1709         let mut label = self.eat_label();
1710         let kind = if label.is_some() && self.token == token::Colon {
1711             // The value expression can be a labeled loop, see issue #86948, e.g.:
1712             // `loop { break 'label: loop { break 'label 42; }; }`
1713             let lexpr = self.parse_labeled_expr(label.take().unwrap(), true)?;
1714             self.sess.emit_err(LabeledLoopInBreak {
1715                 span: lexpr.span,
1716                 sub: WrapExpressionInParentheses {
1717                     left: lexpr.span.shrink_to_lo(),
1718                     right: lexpr.span.shrink_to_hi(),
1719                 },
1720             });
1721             Some(lexpr)
1722         } else if self.token != token::OpenDelim(Delimiter::Brace)
1723             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
1724         {
1725             let expr = self.parse_expr_opt()?;
1726             if let Some(ref expr) = expr {
1727                 if label.is_some()
1728                     && matches!(
1729                         expr.kind,
1730                         ExprKind::While(_, _, None)
1731                             | ExprKind::ForLoop(_, _, _, None)
1732                             | ExprKind::Loop(_, None)
1733                             | ExprKind::Block(_, None)
1734                     )
1735                 {
1736                     self.sess.buffer_lint_with_diagnostic(
1737                         BREAK_WITH_LABEL_AND_LOOP,
1738                         lo.to(expr.span),
1739                         ast::CRATE_NODE_ID,
1740                         "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
1741                         BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span),
1742                     );
1743                 }
1744             }
1745             expr
1746         } else {
1747             None
1748         };
1749         let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
1750         self.maybe_recover_from_bad_qpath(expr)
1751     }
1752
1753     /// Parse `"yield" expr?`.
1754     fn parse_yield_expr(&mut self) -> PResult<'a, P<Expr>> {
1755         let lo = self.prev_token.span;
1756         let kind = ExprKind::Yield(self.parse_expr_opt()?);
1757         let span = lo.to(self.prev_token.span);
1758         self.sess.gated_spans.gate(sym::generators, span);
1759         let expr = self.mk_expr(span, kind);
1760         self.maybe_recover_from_bad_qpath(expr)
1761     }
1762
1763     /// Returns a string literal if the next token is a string literal.
1764     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
1765     /// and returns `None` if the next token is not literal at all.
1766     pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> {
1767         match self.parse_opt_lit() {
1768             Some(lit) => match lit.kind {
1769                 ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
1770                     style,
1771                     symbol: lit.token_lit.symbol,
1772                     suffix: lit.token_lit.suffix,
1773                     span: lit.span,
1774                     symbol_unescaped,
1775                 }),
1776                 _ => Err(Some(lit)),
1777             },
1778             None => Err(None),
1779         }
1780     }
1781
1782     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
1783         self.parse_opt_lit().ok_or(()).or_else(|()| {
1784             if let token::Interpolated(inner) = &self.token.kind {
1785                 let expr = match inner.as_ref() {
1786                     token::NtExpr(expr) => Some(expr),
1787                     token::NtLiteral(expr) => Some(expr),
1788                     _ => None,
1789                 };
1790                 if let Some(expr) = expr {
1791                     if matches!(expr.kind, ExprKind::Err) {
1792                         let mut err = InvalidInterpolatedExpression { span: self.token.span }
1793                             .into_diagnostic(&self.sess.span_diagnostic);
1794                         err.downgrade_to_delayed_bug();
1795                         return Err(err);
1796                     }
1797                 }
1798             }
1799             let token = self.token.clone();
1800             let err = |self_: &mut Self| {
1801                 let msg = format!("unexpected token: {}", super::token_descr(&token));
1802                 self_.struct_span_err(token.span, &msg)
1803             };
1804             // On an error path, eagerly consider a lifetime to be an unclosed character lit
1805             if self.token.is_lifetime() {
1806                 let lt = self.expect_lifetime();
1807                 Ok(self.recover_unclosed_char(lt.ident, err))
1808             } else {
1809                 Err(err(self))
1810             }
1811         })
1812     }
1813
1814     /// Matches `lit = true | false | token_lit`.
1815     /// Returns `None` if the next token is not a literal.
1816     pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> {
1817         let mut recovered = None;
1818         if self.token == token::Dot {
1819             // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
1820             // dot would follow an optional literal, so we do this unconditionally.
1821             recovered = self.look_ahead(1, |next_token| {
1822                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
1823                     next_token.kind
1824                 {
1825                     if self.token.span.hi() == next_token.span.lo() {
1826                         let s = String::from("0.") + symbol.as_str();
1827                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
1828                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
1829                     }
1830                 }
1831                 None
1832             });
1833             if let Some(token) = &recovered {
1834                 self.bump();
1835                 self.sess.emit_err(FloatLiteralRequiresIntegerPart {
1836                     span: token.span,
1837                     correct: pprust::token_to_string(token).into_owned(),
1838                 });
1839             }
1840         }
1841
1842         let token = recovered.as_ref().unwrap_or(&self.token);
1843         match Lit::from_token(token) {
1844             Ok(lit) => {
1845                 self.bump();
1846                 Some(lit)
1847             }
1848             Err(LitError::NotLiteral) => None,
1849             Err(err) => {
1850                 let span = token.span;
1851                 let token::Literal(lit) = token.kind else {
1852                     unreachable!();
1853                 };
1854                 self.bump();
1855                 self.report_lit_error(err, lit, span);
1856                 // Pack possible quotes and prefixes from the original literal into
1857                 // the error literal's symbol so they can be pretty-printed faithfully.
1858                 let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
1859                 let symbol = Symbol::intern(&suffixless_lit.to_string());
1860                 let lit = token::Lit::new(token::Err, symbol, lit.suffix);
1861                 Some(Lit::from_token_lit(lit, span).unwrap_or_else(|_| unreachable!()))
1862             }
1863         }
1864     }
1865
1866     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
1867         // Checks if `s` looks like i32 or u1234 etc.
1868         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
1869             s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
1870         }
1871
1872         // Try to lowercase the prefix if it's a valid base prefix.
1873         fn fix_base_capitalisation(s: &str) -> Option<String> {
1874             if let Some(stripped) = s.strip_prefix('B') {
1875                 Some(format!("0b{stripped}"))
1876             } else if let Some(stripped) = s.strip_prefix('O') {
1877                 Some(format!("0o{stripped}"))
1878             } else if let Some(stripped) = s.strip_prefix('X') {
1879                 Some(format!("0x{stripped}"))
1880             } else {
1881                 None
1882             }
1883         }
1884
1885         let token::Lit { kind, suffix, .. } = lit;
1886         match err {
1887             // `NotLiteral` is not an error by itself, so we don't report
1888             // it and give the parser opportunity to try something else.
1889             LitError::NotLiteral => {}
1890             // `LexerError` *is* an error, but it was already reported
1891             // by lexer, so here we don't report it the second time.
1892             LitError::LexerError => {}
1893             LitError::InvalidSuffix => {
1894                 if let Some(suffix) = suffix {
1895                     self.sess.emit_err(InvalidLiteralSuffix {
1896                         span,
1897                         kind: format!("{}", kind.descr()),
1898                         suffix,
1899                     });
1900                 }
1901             }
1902             LitError::InvalidIntSuffix => {
1903                 let suf = suffix.expect("suffix error with no suffix");
1904                 let suf = suf.as_str();
1905                 if looks_like_width_suffix(&['i', 'u'], &suf) {
1906                     // If it looks like a width, try to be helpful.
1907                     self.sess.emit_err(InvalidIntLiteralWidth { span, width: suf[1..].into() });
1908                 } else if let Some(fixed) = fix_base_capitalisation(suf) {
1909                     self.sess.emit_err(InvalidNumLiteralBasePrefix { span, fixed });
1910                 } else {
1911                     self.sess.emit_err(InvalidNumLiteralSuffix { span, suffix: suf.to_string() });
1912                 }
1913             }
1914             LitError::InvalidFloatSuffix => {
1915                 let suf = suffix.expect("suffix error with no suffix");
1916                 let suf = suf.as_str();
1917                 if looks_like_width_suffix(&['f'], suf) {
1918                     // If it looks like a width, try to be helpful.
1919                     self.sess
1920                         .emit_err(InvalidFloatLiteralWidth { span, width: suf[1..].to_string() });
1921                 } else {
1922                     self.sess.emit_err(InvalidFloatLiteralSuffix { span, suffix: suf.to_string() });
1923                 }
1924             }
1925             LitError::NonDecimalFloat(base) => {
1926                 match base {
1927                     16 => self.sess.emit_err(HexadecimalFloatLiteralNotSupported { span }),
1928                     8 => self.sess.emit_err(OctalFloatLiteralNotSupported { span }),
1929                     2 => self.sess.emit_err(BinaryFloatLiteralNotSupported { span }),
1930                     _ => unreachable!(),
1931                 };
1932             }
1933             LitError::IntTooLarge => {
1934                 self.sess.emit_err(IntLiteralTooLarge { span });
1935             }
1936         }
1937     }
1938
1939     pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
1940         if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
1941             // #59553: warn instead of reject out of hand to allow the fix to percolate
1942             // through the ecosystem when people fix their macros
1943             self.sess.emit_warning(InvalidLiteralSuffixOnTupleIndex {
1944                 span,
1945                 suffix,
1946                 exception: Some(()),
1947             });
1948         } else {
1949             self.sess.emit_err(InvalidLiteralSuffixOnTupleIndex { span, suffix, exception: None });
1950         }
1951     }
1952
1953     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
1954     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
1955     pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
1956         maybe_whole_expr!(self);
1957
1958         let lo = self.token.span;
1959         let minus_present = self.eat(&token::BinOp(token::Minus));
1960         let lit = self.parse_lit()?;
1961         let expr = self.mk_expr(lit.span, ExprKind::Lit(lit));
1962
1963         if minus_present {
1964             Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
1965         } else {
1966             Ok(expr)
1967         }
1968     }
1969
1970     fn is_array_like_block(&mut self) -> bool {
1971         self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
1972             && self.look_ahead(2, |t| t == &token::Comma)
1973             && self.look_ahead(3, |t| t.can_begin_expr())
1974     }
1975
1976     /// Emits a suggestion if it looks like the user meant an array but
1977     /// accidentally used braces, causing the code to be interpreted as a block
1978     /// expression.
1979     fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
1980         let mut snapshot = self.create_snapshot_for_diagnostic();
1981         match snapshot.parse_array_or_repeat_expr(Delimiter::Brace) {
1982             Ok(arr) => {
1983                 self.sess.emit_err(ArrayBracketsInsteadOfSpaces {
1984                     span: arr.span,
1985                     sub: ArrayBracketsInsteadOfSpacesSugg {
1986                         left: lo,
1987                         right: snapshot.prev_token.span,
1988                     },
1989                 });
1990
1991                 self.restore_snapshot(snapshot);
1992                 Some(self.mk_expr_err(arr.span))
1993             }
1994             Err(e) => {
1995                 e.cancel();
1996                 None
1997             }
1998         }
1999     }
2000
2001     fn suggest_missing_semicolon_before_array(
2002         &self,
2003         prev_span: Span,
2004         open_delim_span: Span,
2005     ) -> PResult<'a, ()> {
2006         if !self.may_recover() {
2007             return Ok(());
2008         }
2009
2010         if self.token.kind == token::Comma {
2011             if !self.sess.source_map().is_multiline(prev_span.until(self.token.span)) {
2012                 return Ok(());
2013             }
2014             let mut snapshot = self.create_snapshot_for_diagnostic();
2015             snapshot.bump();
2016             match snapshot.parse_seq_to_before_end(
2017                 &token::CloseDelim(Delimiter::Bracket),
2018                 SeqSep::trailing_allowed(token::Comma),
2019                 |p| p.parse_expr(),
2020             ) {
2021                 Ok(_)
2022                     // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
2023                     // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
2024                     // This is because the `token.kind` of the close delim is treated as the same as
2025                     // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
2026                     // Therefore, `token.kind` should not be compared here.
2027                     if snapshot
2028                         .span_to_snippet(snapshot.token.span)
2029                         .map_or(false, |snippet| snippet == "]") =>
2030                 {
2031                     return Err(MissingSemicolonBeforeArray {
2032                         open_delim: open_delim_span,
2033                         semicolon: prev_span.shrink_to_hi(),
2034                     }.into_diagnostic(&self.sess.span_diagnostic));
2035                 }
2036                 Ok(_) => (),
2037                 Err(err) => err.cancel(),
2038             }
2039         }
2040         Ok(())
2041     }
2042
2043     /// Parses a block or unsafe block.
2044     pub(super) fn parse_block_expr(
2045         &mut self,
2046         opt_label: Option<Label>,
2047         lo: Span,
2048         blk_mode: BlockCheckMode,
2049     ) -> PResult<'a, P<Expr>> {
2050         if self.may_recover() && self.is_array_like_block() {
2051             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
2052                 return Ok(arr);
2053             }
2054         }
2055
2056         if self.token.is_whole_block() {
2057             self.sess.emit_err(InvalidBlockMacroSegment {
2058                 span: self.token.span,
2059                 context: lo.to(self.token.span),
2060             });
2061         }
2062
2063         let (attrs, blk) = self.parse_block_common(lo, blk_mode)?;
2064         Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
2065     }
2066
2067     /// Parse a block which takes no attributes and has no label
2068     fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
2069         let blk = self.parse_block()?;
2070         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
2071     }
2072
2073     /// Parses a closure expression (e.g., `move |args| expr`).
2074     fn parse_closure_expr(&mut self) -> PResult<'a, P<Expr>> {
2075         let lo = self.token.span;
2076
2077         let binder = if self.check_keyword(kw::For) {
2078             let lo = self.token.span;
2079             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
2080             let span = lo.to(self.prev_token.span);
2081
2082             self.sess.gated_spans.gate(sym::closure_lifetime_binder, span);
2083
2084             ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) }
2085         } else {
2086             ClosureBinder::NotPresent
2087         };
2088
2089         let movability =
2090             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
2091
2092         let asyncness = if self.token.uninterpolated_span().rust_2018() {
2093             self.parse_asyncness()
2094         } else {
2095             Async::No
2096         };
2097
2098         let capture_clause = self.parse_capture_clause()?;
2099         let decl = self.parse_fn_block_decl()?;
2100         let decl_hi = self.prev_token.span;
2101         let mut body = match decl.output {
2102             FnRetTy::Default(_) => {
2103                 let restrictions = self.restrictions - Restrictions::STMT_EXPR;
2104                 self.parse_expr_res(restrictions, None)?
2105             }
2106             _ => {
2107                 // If an explicit return type is given, require a block to appear (RFC 968).
2108                 let body_lo = self.token.span;
2109                 self.parse_block_expr(None, body_lo, BlockCheckMode::Default)?
2110             }
2111         };
2112
2113         if let Async::Yes { span, .. } = asyncness {
2114             // Feature-gate `async ||` closures.
2115             self.sess.gated_spans.gate(sym::async_closure, span);
2116         }
2117
2118         if self.token.kind == TokenKind::Semi
2119             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
2120             // HACK: This is needed so we can detect whether we're inside a macro,
2121             // where regular assumptions about what tokens can follow other tokens
2122             // don't necessarily apply.
2123             && self.may_recover()
2124             // FIXME(Nilstrieb): Remove this check once `may_recover` actually stops recovery
2125             && self.subparser_name.is_none()
2126         {
2127             // It is likely that the closure body is a block but where the
2128             // braces have been removed. We will recover and eat the next
2129             // statements later in the parsing process.
2130             body = self.mk_expr_err(body.span);
2131         }
2132
2133         let body_span = body.span;
2134
2135         let closure = self.mk_expr(
2136             lo.to(body.span),
2137             ExprKind::Closure(
2138                 binder,
2139                 capture_clause,
2140                 asyncness,
2141                 movability,
2142                 decl,
2143                 body,
2144                 lo.to(decl_hi),
2145             ),
2146         );
2147
2148         // Disable recovery for closure body
2149         let spans =
2150             ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
2151         self.current_closure = Some(spans);
2152
2153         Ok(closure)
2154     }
2155
2156     /// Parses an optional `move` prefix to a closure-like construct.
2157     fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
2158         if self.eat_keyword(kw::Move) {
2159             // Check for `move async` and recover
2160             if self.check_keyword(kw::Async) {
2161                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
2162                 Err(AsyncMoveOrderIncorrect { span: move_async_span }
2163                     .into_diagnostic(&self.sess.span_diagnostic))
2164             } else {
2165                 Ok(CaptureBy::Value)
2166             }
2167         } else {
2168             Ok(CaptureBy::Ref)
2169         }
2170     }
2171
2172     /// Parses the `|arg, arg|` header of a closure.
2173     fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
2174         let inputs = if self.eat(&token::OrOr) {
2175             Vec::new()
2176         } else {
2177             self.expect(&token::BinOp(token::Or))?;
2178             let args = self
2179                 .parse_seq_to_before_tokens(
2180                     &[&token::BinOp(token::Or), &token::OrOr],
2181                     SeqSep::trailing_allowed(token::Comma),
2182                     TokenExpectType::NoExpect,
2183                     |p| p.parse_fn_block_param(),
2184                 )?
2185                 .0;
2186             self.expect_or()?;
2187             args
2188         };
2189         let output =
2190             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
2191
2192         Ok(P(FnDecl { inputs, output }))
2193     }
2194
2195     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
2196     fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
2197         let lo = self.token.span;
2198         let attrs = self.parse_outer_attributes()?;
2199         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2200             let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
2201             let ty = if this.eat(&token::Colon) {
2202                 this.parse_ty()?
2203             } else {
2204                 this.mk_ty(this.prev_token.span, TyKind::Infer)
2205             };
2206
2207             Ok((
2208                 Param {
2209                     attrs,
2210                     ty,
2211                     pat,
2212                     span: lo.to(this.prev_token.span),
2213                     id: DUMMY_NODE_ID,
2214                     is_placeholder: false,
2215                 },
2216                 TrailingToken::MaybeComma,
2217             ))
2218         })
2219     }
2220
2221     /// Parses an `if` expression (`if` token already eaten).
2222     fn parse_if_expr(&mut self) -> PResult<'a, P<Expr>> {
2223         let lo = self.prev_token.span;
2224         let cond = self.parse_cond_expr()?;
2225         self.parse_if_after_cond(lo, cond)
2226     }
2227
2228     fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
2229         let cond_span = cond.span;
2230         // Tries to interpret `cond` as either a missing expression if it's a block,
2231         // or as an unfinished expression if it's a binop and the RHS is a block.
2232         // We could probably add more recoveries here too...
2233         let mut recover_block_from_condition = |this: &mut Self| {
2234             let block = match &mut cond.kind {
2235                 ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
2236                     if let ExprKind::Block(_, None) = right.kind => {
2237                         self.sess.emit_err(IfExpressionMissingThenBlock {
2238                             if_span: lo,
2239                             sub: IfExpressionMissingThenBlockSub::UnfinishedCondition(
2240                                 cond_span.shrink_to_lo().to(*binop_span)
2241                             ),
2242                         });
2243                         std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi()))
2244                     },
2245                 ExprKind::Block(_, None) => {
2246                     self.sess.emit_err(IfExpressionMissingCondition {
2247                         if_span: lo.shrink_to_hi(),
2248                         block_span: self.sess.source_map().start_point(cond_span),
2249                     });
2250                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))
2251                 }
2252                 _ => {
2253                     return None;
2254                 }
2255             };
2256             if let ExprKind::Block(block, _) = &block.kind {
2257                 Some(block.clone())
2258             } else {
2259                 unreachable!()
2260             }
2261         };
2262         // Parse then block
2263         let thn = if self.token.is_keyword(kw::Else) {
2264             if let Some(block) = recover_block_from_condition(self) {
2265                 block
2266             } else {
2267                 self.sess.emit_err(IfExpressionMissingThenBlock {
2268                     if_span: lo,
2269                     sub: IfExpressionMissingThenBlockSub::AddThenBlock(cond_span.shrink_to_hi()),
2270                 });
2271                 self.mk_block_err(cond_span.shrink_to_hi())
2272             }
2273         } else {
2274             let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2275             let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
2276                 self.parse_block()?
2277             } else {
2278                 if let Some(block) = recover_block_from_condition(self) {
2279                     block
2280                 } else {
2281                     // Parse block, which will always fail, but we can add a nice note to the error
2282                     self.parse_block().map_err(|mut err| {
2283                         err.span_note(
2284                             cond_span,
2285                             "the `if` expression is missing a block after this condition",
2286                         );
2287                         err
2288                     })?
2289                 }
2290             };
2291             self.error_on_if_block_attrs(lo, false, block.span, &attrs);
2292             block
2293         };
2294         let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None };
2295         Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
2296     }
2297
2298     /// Parses the condition of a `if` or `while` expression.
2299     fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
2300         let cond =
2301             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
2302
2303         if let ExprKind::Let(..) = cond.kind {
2304             // Remove the last feature gating of a `let` expression since it's stable.
2305             self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2306         }
2307
2308         Ok(cond)
2309     }
2310
2311     /// Parses a `let $pat = $expr` pseudo-expression.
2312     fn parse_let_expr(&mut self) -> PResult<'a, P<Expr>> {
2313         // This is a *approximate* heuristic that detects if `let` chains are
2314         // being parsed in the right position. It's approximate because it
2315         // doesn't deny all invalid `let` expressions, just completely wrong usages.
2316         let not_in_chain = !matches!(
2317             self.prev_token.kind,
2318             TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
2319         );
2320         if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
2321             self.sess.emit_err(ExpectedExpressionFoundLet { span: self.token.span });
2322         }
2323
2324         self.bump(); // Eat `let` token
2325         let lo = self.prev_token.span;
2326         let pat = self.parse_pat_allow_top_alt(
2327             None,
2328             RecoverComma::Yes,
2329             RecoverColon::Yes,
2330             CommaRecoveryMode::LikelyTuple,
2331         )?;
2332         if self.token == token::EqEq {
2333             self.sess.emit_err(ExpectedEqForLetExpr {
2334                 span: self.token.span,
2335                 sugg_span: self.token.span,
2336             });
2337             self.bump();
2338         } else {
2339             self.expect(&token::Eq)?;
2340         }
2341         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
2342             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
2343         })?;
2344         let span = lo.to(expr.span);
2345         self.sess.gated_spans.gate(sym::let_chains, span);
2346         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span)))
2347     }
2348
2349     /// Parses an `else { ... }` expression (`else` token already eaten).
2350     fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
2351         let else_span = self.prev_token.span; // `else`
2352         let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
2353         let expr = if self.eat_keyword(kw::If) {
2354             self.parse_if_expr()?
2355         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
2356             self.parse_simple_block()?
2357         } else {
2358             let snapshot = self.create_snapshot_for_diagnostic();
2359             let first_tok = super::token_descr(&self.token);
2360             let first_tok_span = self.token.span;
2361             match self.parse_expr() {
2362                 Ok(cond)
2363                 // If it's not a free-standing expression, and is followed by a block,
2364                 // then it's very likely the condition to an `else if`.
2365                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
2366                         && classify::expr_requires_semi_to_be_stmt(&cond) =>
2367                 {
2368                     self.sess.emit_err(ExpectedElseBlock {
2369                         first_tok_span,
2370                         first_tok,
2371                         else_span,
2372                         condition_start: cond.span.shrink_to_lo(),
2373                     });
2374                     self.parse_if_after_cond(cond.span.shrink_to_lo(), cond)?
2375                 }
2376                 Err(e) => {
2377                     e.cancel();
2378                     self.restore_snapshot(snapshot);
2379                     self.parse_simple_block()?
2380                 },
2381                 Ok(_) => {
2382                     self.restore_snapshot(snapshot);
2383                     self.parse_simple_block()?
2384                 },
2385             }
2386         };
2387         self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
2388         Ok(expr)
2389     }
2390
2391     fn error_on_if_block_attrs(
2392         &self,
2393         ctx_span: Span,
2394         is_ctx_else: bool,
2395         branch_span: Span,
2396         attrs: &[ast::Attribute],
2397     ) {
2398         let (attributes, last) = match attrs {
2399             [] => return,
2400             [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span),
2401         };
2402         let ctx = if is_ctx_else { "else" } else { "if" };
2403         self.sess.emit_err(OuterAttributeNotAllowedOnIfElse {
2404             last,
2405             branch_span,
2406             ctx_span,
2407             ctx: ctx.to_string(),
2408             attributes,
2409         });
2410     }
2411
2412     /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
2413     fn parse_for_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2414         // Record whether we are about to parse `for (`.
2415         // This is used below for recovery in case of `for ( $stuff ) $block`
2416         // in which case we will suggest `for $stuff $block`.
2417         let begin_paren = match self.token.kind {
2418             token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span),
2419             _ => None,
2420         };
2421
2422         let pat = self.parse_pat_allow_top_alt(
2423             None,
2424             RecoverComma::Yes,
2425             RecoverColon::Yes,
2426             CommaRecoveryMode::LikelyTuple,
2427         )?;
2428         if !self.eat_keyword(kw::In) {
2429             self.error_missing_in_for_loop();
2430         }
2431         self.check_for_for_in_in_typo(self.prev_token.span);
2432         let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2433
2434         let pat = self.recover_parens_around_for_head(pat, begin_paren);
2435
2436         let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
2437
2438         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
2439         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2440     }
2441
2442     fn error_missing_in_for_loop(&mut self) {
2443         let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
2444             // Possibly using JS syntax (#75311).
2445             let span = self.token.span;
2446             self.bump();
2447             (span, MissingInInForLoopSub::InNotOf)
2448         } else {
2449             (self.prev_token.span.between(self.token.span), MissingInInForLoopSub::AddIn)
2450         };
2451
2452         self.sess.emit_err(MissingInInForLoop { span, sub: sub(span) });
2453     }
2454
2455     /// Parses a `while` or `while let` expression (`while` token already eaten).
2456     fn parse_while_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2457         let cond = self.parse_cond_expr().map_err(|mut err| {
2458             err.span_label(lo, "while parsing the condition of this `while` expression");
2459             err
2460         })?;
2461         let (attrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
2462             err.span_label(lo, "while parsing the body of this `while` expression");
2463             err.span_label(cond.span, "this `while` condition successfully parsed");
2464             err
2465         })?;
2466         Ok(self.mk_expr_with_attrs(
2467             lo.to(self.prev_token.span),
2468             ExprKind::While(cond, body, opt_label),
2469             attrs,
2470         ))
2471     }
2472
2473     /// Parses `loop { ... }` (`loop` token already eaten).
2474     fn parse_loop_expr(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
2475         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2476         Ok(self.mk_expr_with_attrs(
2477             lo.to(self.prev_token.span),
2478             ExprKind::Loop(body, opt_label),
2479             attrs,
2480         ))
2481     }
2482
2483     pub(crate) fn eat_label(&mut self) -> Option<Label> {
2484         self.token.lifetime().map(|ident| {
2485             self.bump();
2486             Label { ident }
2487         })
2488     }
2489
2490     /// Parses a `match ... { ... }` expression (`match` token already eaten).
2491     fn parse_match_expr(&mut self) -> PResult<'a, P<Expr>> {
2492         let match_span = self.prev_token.span;
2493         let lo = self.prev_token.span;
2494         let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
2495         if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2496             if self.token == token::Semi {
2497                 e.span_suggestion_short(
2498                     match_span,
2499                     "try removing this `match`",
2500                     "",
2501                     Applicability::MaybeIncorrect, // speculative
2502                 );
2503             }
2504             if self.maybe_recover_unexpected_block_label() {
2505                 e.cancel();
2506                 self.bump();
2507             } else {
2508                 return Err(e);
2509             }
2510         }
2511         let attrs = self.parse_inner_attributes()?;
2512
2513         let mut arms: Vec<Arm> = Vec::new();
2514         while self.token != token::CloseDelim(Delimiter::Brace) {
2515             match self.parse_arm() {
2516                 Ok(arm) => arms.push(arm),
2517                 Err(mut e) => {
2518                     // Recover by skipping to the end of the block.
2519                     e.emit();
2520                     self.recover_stmt();
2521                     let span = lo.to(self.token.span);
2522                     if self.token == token::CloseDelim(Delimiter::Brace) {
2523                         self.bump();
2524                     }
2525                     return Ok(self.mk_expr_with_attrs(
2526                         span,
2527                         ExprKind::Match(scrutinee, arms),
2528                         attrs,
2529                     ));
2530                 }
2531             }
2532         }
2533         let hi = self.token.span;
2534         self.bump();
2535         Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs))
2536     }
2537
2538     /// Attempt to recover from match arm body with statements and no surrounding braces.
2539     fn parse_arm_body_missing_braces(
2540         &mut self,
2541         first_expr: &P<Expr>,
2542         arrow_span: Span,
2543     ) -> Option<P<Expr>> {
2544         if self.token.kind != token::Semi {
2545             return None;
2546         }
2547         let start_snapshot = self.create_snapshot_for_diagnostic();
2548         let semi_sp = self.token.span;
2549         self.bump(); // `;`
2550         let mut stmts =
2551             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
2552         let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
2553             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
2554
2555             this.sess.emit_err(MatchArmBodyWithoutBraces {
2556                 statements: span,
2557                 arrow: arrow_span,
2558                 num_statements: stmts.len(),
2559                 sub: if stmts.len() > 1 {
2560                     MatchArmBodyWithoutBracesSugg::AddBraces {
2561                         left: span.shrink_to_lo(),
2562                         right: span.shrink_to_hi(),
2563                     }
2564                 } else {
2565                     MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
2566                 },
2567             });
2568             this.mk_expr_err(span)
2569         };
2570         // We might have either a `,` -> `;` typo, or a block without braces. We need
2571         // a more subtle parsing strategy.
2572         loop {
2573             if self.token.kind == token::CloseDelim(Delimiter::Brace) {
2574                 // We have reached the closing brace of the `match` expression.
2575                 return Some(err(self, stmts));
2576             }
2577             if self.token.kind == token::Comma {
2578                 self.restore_snapshot(start_snapshot);
2579                 return None;
2580             }
2581             let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
2582             match self.parse_pat_no_top_alt(None) {
2583                 Ok(_pat) => {
2584                     if self.token.kind == token::FatArrow {
2585                         // Reached arm end.
2586                         self.restore_snapshot(pre_pat_snapshot);
2587                         return Some(err(self, stmts));
2588                     }
2589                 }
2590                 Err(err) => {
2591                     err.cancel();
2592                 }
2593             }
2594
2595             self.restore_snapshot(pre_pat_snapshot);
2596             match self.parse_stmt_without_recovery(true, ForceCollect::No) {
2597                 // Consume statements for as long as possible.
2598                 Ok(Some(stmt)) => {
2599                     stmts.push(stmt);
2600                 }
2601                 Ok(None) => {
2602                     self.restore_snapshot(start_snapshot);
2603                     break;
2604                 }
2605                 // We couldn't parse either yet another statement missing it's
2606                 // enclosing block nor the next arm's pattern or closing brace.
2607                 Err(stmt_err) => {
2608                     stmt_err.cancel();
2609                     self.restore_snapshot(start_snapshot);
2610                     break;
2611                 }
2612             }
2613         }
2614         None
2615     }
2616
2617     pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
2618         // Used to check the `let_chains` and `if_let_guard` features mostly by scanning
2619         // `&&` tokens.
2620         fn check_let_expr(expr: &Expr) -> (bool, bool) {
2621             match expr.kind {
2622                 ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, ref lhs, ref rhs) => {
2623                     let lhs_rslt = check_let_expr(lhs);
2624                     let rhs_rslt = check_let_expr(rhs);
2625                     (lhs_rslt.0 || rhs_rslt.0, false)
2626                 }
2627                 ExprKind::Let(..) => (true, true),
2628                 _ => (false, true),
2629             }
2630         }
2631         let attrs = self.parse_outer_attributes()?;
2632         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2633             let lo = this.token.span;
2634             let pat = this.parse_pat_allow_top_alt(
2635                 None,
2636                 RecoverComma::Yes,
2637                 RecoverColon::Yes,
2638                 CommaRecoveryMode::EitherTupleOrPipe,
2639             )?;
2640             let guard = if this.eat_keyword(kw::If) {
2641                 let if_span = this.prev_token.span;
2642                 let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
2643                 let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
2644                 if has_let_expr {
2645                     if does_not_have_bin_op {
2646                         // Remove the last feature gating of a `let` expression since it's stable.
2647                         this.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
2648                     }
2649                     let span = if_span.to(cond.span);
2650                     this.sess.gated_spans.gate(sym::if_let_guard, span);
2651                 }
2652                 Some(cond)
2653             } else {
2654                 None
2655             };
2656             let arrow_span = this.token.span;
2657             if let Err(mut err) = this.expect(&token::FatArrow) {
2658                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
2659                 if TokenKind::FatArrow
2660                     .similar_tokens()
2661                     .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
2662                 {
2663                     err.span_suggestion(
2664                         this.token.span,
2665                         "try using a fat arrow here",
2666                         "=>",
2667                         Applicability::MaybeIncorrect,
2668                     );
2669                     err.emit();
2670                     this.bump();
2671                 } else {
2672                     return Err(err);
2673                 }
2674             }
2675             let arm_start_span = this.token.span;
2676
2677             let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
2678                 err.span_label(arrow_span, "while parsing the `match` arm starting here");
2679                 err
2680             })?;
2681
2682             let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
2683                 && this.token != token::CloseDelim(Delimiter::Brace);
2684
2685             let hi = this.prev_token.span;
2686
2687             if require_comma {
2688                 let sm = this.sess.source_map();
2689                 if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) {
2690                     let span = body.span;
2691                     return Ok((
2692                         ast::Arm {
2693                             attrs,
2694                             pat,
2695                             guard,
2696                             body,
2697                             span,
2698                             id: DUMMY_NODE_ID,
2699                             is_placeholder: false,
2700                         },
2701                         TrailingToken::None,
2702                     ));
2703                 }
2704                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
2705                     .or_else(|mut err| {
2706                         if this.token == token::FatArrow {
2707                             if let Ok(expr_lines) = sm.span_to_lines(expr.span)
2708                             && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
2709                             && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
2710                             && expr_lines.lines.len() == 2
2711                             {
2712                                 // We check whether there's any trailing code in the parse span,
2713                                 // if there isn't, we very likely have the following:
2714                                 //
2715                                 // X |     &Y => "y"
2716                                 //   |        --    - missing comma
2717                                 //   |        |
2718                                 //   |        arrow_span
2719                                 // X |     &X => "x"
2720                                 //   |      - ^^ self.token.span
2721                                 //   |      |
2722                                 //   |      parsed until here as `"y" & X`
2723                                 err.span_suggestion_short(
2724                                     arm_start_span.shrink_to_hi(),
2725                                     "missing a comma here to end this `match` arm",
2726                                     ",",
2727                                     Applicability::MachineApplicable,
2728                                 );
2729                                 return Err(err);
2730                             }
2731                         } else {
2732                             // FIXME(compiler-errors): We could also recover `; PAT =>` here
2733
2734                             // Try to parse a following `PAT =>`, if successful
2735                             // then we should recover.
2736                             let mut snapshot = this.create_snapshot_for_diagnostic();
2737                             let pattern_follows = snapshot
2738                                 .parse_pat_allow_top_alt(
2739                                     None,
2740                                     RecoverComma::Yes,
2741                                     RecoverColon::Yes,
2742                                     CommaRecoveryMode::EitherTupleOrPipe,
2743                                 )
2744                                 .map_err(|err| err.cancel())
2745                                 .is_ok();
2746                             if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
2747                                 err.cancel();
2748                                 this.sess.emit_err(MissingCommaAfterMatchArm {
2749                                     span: hi.shrink_to_hi(),
2750                                 });
2751                                 return Ok(true);
2752                             }
2753                         }
2754                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
2755                         Err(err)
2756                     })?;
2757             } else {
2758                 this.eat(&token::Comma);
2759             }
2760
2761             Ok((
2762                 ast::Arm {
2763                     attrs,
2764                     pat,
2765                     guard,
2766                     body: expr,
2767                     span: lo.to(hi),
2768                     id: DUMMY_NODE_ID,
2769                     is_placeholder: false,
2770                 },
2771                 TrailingToken::None,
2772             ))
2773         })
2774     }
2775
2776     /// Parses a `try {...}` expression (`try` token already eaten).
2777     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
2778         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2779         if self.eat_keyword(kw::Catch) {
2780             Err(CatchAfterTry { span: self.prev_token.span }
2781                 .into_diagnostic(&self.sess.span_diagnostic))
2782         } else {
2783             let span = span_lo.to(body.span);
2784             self.sess.gated_spans.gate(sym::try_blocks, span);
2785             Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body), attrs))
2786         }
2787     }
2788
2789     fn is_do_catch_block(&self) -> bool {
2790         self.token.is_keyword(kw::Do)
2791             && self.is_keyword_ahead(1, &[kw::Catch])
2792             && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2793             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
2794     }
2795
2796     fn is_do_yeet(&self) -> bool {
2797         self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
2798     }
2799
2800     fn is_try_block(&self) -> bool {
2801         self.token.is_keyword(kw::Try)
2802             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2803             && self.token.uninterpolated_span().rust_2018()
2804     }
2805
2806     /// Parses an `async move? {...}` expression.
2807     fn parse_async_block(&mut self) -> PResult<'a, P<Expr>> {
2808         let lo = self.token.span;
2809         self.expect_keyword(kw::Async)?;
2810         let capture_clause = self.parse_capture_clause()?;
2811         let (attrs, body) = self.parse_inner_attrs_and_block()?;
2812         let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);
2813         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
2814     }
2815
2816     fn is_async_block(&self) -> bool {
2817         self.token.is_keyword(kw::Async)
2818             && ((
2819                 // `async move {`
2820                 self.is_keyword_ahead(1, &[kw::Move])
2821                     && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
2822             ) || (
2823                 // `async {`
2824                 self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
2825             ))
2826     }
2827
2828     fn is_certainly_not_a_block(&self) -> bool {
2829         self.look_ahead(1, |t| t.is_ident())
2830             && (
2831                 // `{ ident, ` cannot start a block.
2832                 self.look_ahead(2, |t| t == &token::Comma)
2833                     || self.look_ahead(2, |t| t == &token::Colon)
2834                         && (
2835                             // `{ ident: token, ` cannot start a block.
2836                             self.look_ahead(4, |t| t == &token::Comma) ||
2837                 // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`.
2838                 self.look_ahead(3, |t| !t.can_begin_type())
2839                         )
2840             )
2841     }
2842
2843     fn maybe_parse_struct_expr(
2844         &mut self,
2845         qself: Option<&ast::QSelf>,
2846         path: &ast::Path,
2847     ) -> Option<PResult<'a, P<Expr>>> {
2848         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
2849         if struct_allowed || self.is_certainly_not_a_block() {
2850             if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
2851                 return Some(Err(err));
2852             }
2853             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), true);
2854             if let (Ok(expr), false) = (&expr, struct_allowed) {
2855                 // This is a struct literal, but we don't can't accept them here.
2856                 self.sess.emit_err(StructLiteralNotAllowedHere {
2857                     span: expr.span,
2858                     sub: StructLiteralNotAllowedHereSugg {
2859                         left: path.span.shrink_to_lo(),
2860                         right: expr.span.shrink_to_hi(),
2861                     },
2862                 });
2863             }
2864             return Some(expr);
2865         }
2866         None
2867     }
2868
2869     pub(super) fn parse_struct_fields(
2870         &mut self,
2871         pth: ast::Path,
2872         recover: bool,
2873         close_delim: Delimiter,
2874     ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> {
2875         let mut fields = Vec::new();
2876         let mut base = ast::StructRest::None;
2877         let mut recover_async = false;
2878
2879         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
2880             recover_async = true;
2881             e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
2882             e.help_use_latest_edition();
2883         };
2884
2885         while self.token != token::CloseDelim(close_delim) {
2886             if self.eat(&token::DotDot) || self.recover_struct_field_dots(close_delim) {
2887                 let exp_span = self.prev_token.span;
2888                 // We permit `.. }` on the left-hand side of a destructuring assignment.
2889                 if self.check(&token::CloseDelim(close_delim)) {
2890                     base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
2891                     break;
2892                 }
2893                 match self.parse_expr() {
2894                     Ok(e) => base = ast::StructRest::Base(e),
2895                     Err(mut e) if recover => {
2896                         e.emit();
2897                         self.recover_stmt();
2898                     }
2899                     Err(e) => return Err(e),
2900                 }
2901                 self.recover_struct_comma_after_dotdot(exp_span);
2902                 break;
2903             }
2904
2905             let recovery_field = self.find_struct_error_after_field_looking_code();
2906             let parsed_field = match self.parse_expr_field() {
2907                 Ok(f) => Some(f),
2908                 Err(mut e) => {
2909                     if pth == kw::Async {
2910                         async_block_err(&mut e, pth.span);
2911                     } else {
2912                         e.span_label(pth.span, "while parsing this struct");
2913                     }
2914                     e.emit();
2915
2916                     // If the next token is a comma, then try to parse
2917                     // what comes next as additional fields, rather than
2918                     // bailing out until next `}`.
2919                     if self.token != token::Comma {
2920                         self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2921                         if self.token != token::Comma {
2922                             break;
2923                         }
2924                     }
2925                     None
2926                 }
2927             };
2928
2929             let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
2930             // A shorthand field can be turned into a full field with `:`.
2931             // We should point this out.
2932             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
2933
2934             match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
2935                 Ok(_) => {
2936                     if let Some(f) = parsed_field.or(recovery_field) {
2937                         // Only include the field if there's no parse error for the field name.
2938                         fields.push(f);
2939                     }
2940                 }
2941                 Err(mut e) => {
2942                     if pth == kw::Async {
2943                         async_block_err(&mut e, pth.span);
2944                     } else {
2945                         e.span_label(pth.span, "while parsing this struct");
2946                         if let Some(f) = recovery_field {
2947                             fields.push(f);
2948                             e.span_suggestion(
2949                                 self.prev_token.span.shrink_to_hi(),
2950                                 "try adding a comma",
2951                                 ",",
2952                                 Applicability::MachineApplicable,
2953                             );
2954                         } else if is_shorthand
2955                             && (AssocOp::from_token(&self.token).is_some()
2956                                 || matches!(&self.token.kind, token::OpenDelim(_))
2957                                 || self.token.kind == token::Dot)
2958                         {
2959                             // Looks like they tried to write a shorthand, complex expression.
2960                             let ident = parsed_field.expect("is_shorthand implies Some").ident;
2961                             e.span_suggestion(
2962                                 ident.span.shrink_to_lo(),
2963                                 "try naming a field",
2964                                 &format!("{ident}: "),
2965                                 Applicability::HasPlaceholders,
2966                             );
2967                         }
2968                     }
2969                     if !recover {
2970                         return Err(e);
2971                     }
2972                     e.emit();
2973                     self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
2974                     self.eat(&token::Comma);
2975                 }
2976             }
2977         }
2978         Ok((fields, base, recover_async))
2979     }
2980
2981     /// Precondition: already parsed the '{'.
2982     pub(super) fn parse_struct_expr(
2983         &mut self,
2984         qself: Option<ast::QSelf>,
2985         pth: ast::Path,
2986         recover: bool,
2987     ) -> PResult<'a, P<Expr>> {
2988         let lo = pth.span;
2989         let (fields, base, recover_async) =
2990             self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
2991         let span = lo.to(self.token.span);
2992         self.expect(&token::CloseDelim(Delimiter::Brace))?;
2993         let expr = if recover_async {
2994             ExprKind::Err
2995         } else {
2996             ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
2997         };
2998         Ok(self.mk_expr(span, expr))
2999     }
3000
3001     /// Use in case of error after field-looking code: `S { foo: () with a }`.
3002     fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> {
3003         match self.token.ident() {
3004             Some((ident, is_raw))
3005                 if (is_raw || !ident.is_reserved())
3006                     && self.look_ahead(1, |t| *t == token::Colon) =>
3007             {
3008                 Some(ast::ExprField {
3009                     ident,
3010                     span: self.token.span,
3011                     expr: self.mk_expr_err(self.token.span),
3012                     is_shorthand: false,
3013                     attrs: AttrVec::new(),
3014                     id: DUMMY_NODE_ID,
3015                     is_placeholder: false,
3016                 })
3017             }
3018             _ => None,
3019         }
3020     }
3021
3022     fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
3023         if self.token != token::Comma {
3024             return;
3025         }
3026         self.sess.emit_err(CommaAfterBaseStruct {
3027             span: span.to(self.prev_token.span),
3028             comma: self.token.span,
3029         });
3030         self.recover_stmt();
3031     }
3032
3033     fn recover_struct_field_dots(&mut self, close_delim: Delimiter) -> bool {
3034         if !self.look_ahead(1, |t| *t == token::CloseDelim(close_delim))
3035             && self.eat(&token::DotDotDot)
3036         {
3037             // recover from typo of `...`, suggest `..`
3038             let span = self.prev_token.span;
3039             self.sess.emit_err(MissingDotDot { token_span: span, sugg_span: span });
3040             return true;
3041         }
3042         false
3043     }
3044
3045     /// Parses `ident (COLON expr)?`.
3046     fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
3047         let attrs = self.parse_outer_attributes()?;
3048         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3049             let lo = this.token.span;
3050
3051             // Check if a colon exists one ahead. This means we're parsing a fieldname.
3052             let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
3053             let (ident, expr) = if is_shorthand {
3054                 // Mimic `x: x` for the `x` field shorthand.
3055                 let ident = this.parse_ident_common(false)?;
3056                 let path = ast::Path::from_ident(ident);
3057                 (ident, this.mk_expr(ident.span, ExprKind::Path(None, path)))
3058             } else {
3059                 let ident = this.parse_field_name()?;
3060                 this.error_on_eq_field_init(ident);
3061                 this.bump(); // `:`
3062                 (ident, this.parse_expr()?)
3063             };
3064
3065             Ok((
3066                 ast::ExprField {
3067                     ident,
3068                     span: lo.to(expr.span),
3069                     expr,
3070                     is_shorthand,
3071                     attrs,
3072                     id: DUMMY_NODE_ID,
3073                     is_placeholder: false,
3074                 },
3075                 TrailingToken::MaybeComma,
3076             ))
3077         })
3078     }
3079
3080     /// Check for `=`. This means the source incorrectly attempts to
3081     /// initialize a field with an eq rather than a colon.
3082     fn error_on_eq_field_init(&self, field_name: Ident) {
3083         if self.token != token::Eq {
3084             return;
3085         }
3086
3087         self.sess.emit_err(EqFieldInit {
3088             span: self.token.span,
3089             eq: field_name.span.shrink_to_hi().to(self.token.span),
3090         });
3091     }
3092
3093     fn err_dotdotdot_syntax(&self, span: Span) {
3094         self.sess.emit_err(DotDotDot { span });
3095     }
3096
3097     fn err_larrow_operator(&self, span: Span) {
3098         self.sess.emit_err(LeftArrowOperator { span });
3099     }
3100
3101     fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3102         ExprKind::AssignOp(binop, lhs, rhs)
3103     }
3104
3105     fn mk_range(
3106         &mut self,
3107         start: Option<P<Expr>>,
3108         end: Option<P<Expr>>,
3109         limits: RangeLimits,
3110     ) -> ExprKind {
3111         if end.is_none() && limits == RangeLimits::Closed {
3112             self.inclusive_range_with_incorrect_end(self.prev_token.span);
3113             ExprKind::Err
3114         } else {
3115             ExprKind::Range(start, end, limits)
3116         }
3117     }
3118
3119     fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
3120         ExprKind::Unary(unop, expr)
3121     }
3122
3123     fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
3124         ExprKind::Binary(binop, lhs, rhs)
3125     }
3126
3127     fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
3128         ExprKind::Index(expr, idx)
3129     }
3130
3131     fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
3132         ExprKind::Call(f, args)
3133     }
3134
3135     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
3136         let span = lo.to(self.prev_token.span);
3137         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg));
3138         self.recover_from_await_method_call();
3139         await_expr
3140     }
3141
3142     pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
3143         P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
3144     }
3145
3146     pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
3147         P(Expr { kind, span, attrs: AttrVec::new(), id: DUMMY_NODE_ID, tokens: None })
3148     }
3149
3150     pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> {
3151         self.mk_expr(span, ExprKind::Err)
3152     }
3153
3154     /// Create expression span ensuring the span of the parent node
3155     /// is larger than the span of lhs and rhs, including the attributes.
3156     fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span {
3157         lhs.attrs
3158             .iter()
3159             .find(|a| a.style == AttrStyle::Outer)
3160             .map_or(lhs_span, |a| a.span)
3161             .to(rhs_span)
3162     }
3163
3164     fn collect_tokens_for_expr(
3165         &mut self,
3166         attrs: AttrWrapper,
3167         f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
3168     ) -> PResult<'a, P<Expr>> {
3169         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
3170             let res = f(this, attrs)?;
3171             let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
3172                 && this.token.kind == token::Semi
3173             {
3174                 TrailingToken::Semi
3175             } else if this.token.kind == token::Gt {
3176                 TrailingToken::Gt
3177             } else {
3178                 // FIXME - pass this through from the place where we know
3179                 // we need a comma, rather than assuming that `#[attr] expr,`
3180                 // always captures a trailing comma
3181                 TrailingToken::MaybeComma
3182             };
3183             Ok((res, trailing))
3184         })
3185     }
3186 }