diff options
Diffstat (limited to 'compiler/rustc_parse/src/parser/expr.rs')
| -rw-r--r-- | compiler/rustc_parse/src/parser/expr.rs | 3288 |
1 files changed, 3288 insertions, 0 deletions
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs new file mode 100644 index 000000000..0719a0ef0 --- /dev/null +++ b/compiler/rustc_parse/src/parser/expr.rs @@ -0,0 +1,3288 @@ +use super::diagnostics::SnapshotParser; +use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED}; +use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign}; +use super::{ + AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions, + SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken, +}; +use crate::maybe_recover_from_interpolated_ty_qpath; + +use core::mem; +use rustc_ast::ptr::P; +use rustc_ast::token::{self, Delimiter, Token, TokenKind}; +use rustc_ast::tokenstream::Spacing; +use rustc_ast::util::classify; +use rustc_ast::util::literal::LitError; +use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity}; +use rustc_ast::visit::Visitor; +use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID}; +use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind}; +use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits}; +use rustc_ast::{ClosureBinder, StmtKind}; +use rustc_ast_pretty::pprust; +use rustc_data_structures::thin_vec::ThinVec; +use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, PResult}; +use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP; +use rustc_session::lint::BuiltinLintDiagnostics; +use rustc_span::source_map::{self, Span, Spanned}; +use rustc_span::symbol::{kw, sym, Ident, Symbol}; +use rustc_span::{BytePos, Pos}; + +/// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression +/// dropped into the token stream, which happens while parsing the result of +/// macro expansion). Placement of these is not as complex as I feared it would +/// be. The important thing is to make sure that lookahead doesn't balk at +/// `token::Interpolated` tokens. +macro_rules! maybe_whole_expr { + ($p:expr) => { + if let token::Interpolated(nt) = &$p.token.kind { + match &**nt { + token::NtExpr(e) | token::NtLiteral(e) => { + let e = e.clone(); + $p.bump(); + return Ok(e); + } + token::NtPath(path) => { + let path = (**path).clone(); + $p.bump(); + return Ok($p.mk_expr( + $p.prev_token.span, + ExprKind::Path(None, path), + AttrVec::new(), + )); + } + token::NtBlock(block) => { + let block = block.clone(); + $p.bump(); + return Ok($p.mk_expr( + $p.prev_token.span, + ExprKind::Block(block, None), + AttrVec::new(), + )); + } + _ => {} + }; + } + }; +} + +#[derive(Debug)] +pub(super) enum LhsExpr { + NotYetParsed, + AttributesParsed(AttrWrapper), + AlreadyParsed(P<Expr>), +} + +impl From<Option<AttrWrapper>> for LhsExpr { + /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)` + /// and `None` into `LhsExpr::NotYetParsed`. + /// + /// This conversion does not allocate. + fn from(o: Option<AttrWrapper>) -> Self { + if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed } + } +} + +impl From<P<Expr>> for LhsExpr { + /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed(expr)`. + /// + /// This conversion does not allocate. + fn from(expr: P<Expr>) -> Self { + LhsExpr::AlreadyParsed(expr) + } +} + +impl<'a> Parser<'a> { + /// Parses an expression. + #[inline] + pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> { + self.current_closure.take(); + + self.parse_expr_res(Restrictions::empty(), None) + } + + /// Parses an expression, forcing tokens to be collected + pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> { + self.collect_tokens_no_attrs(|this| this.parse_expr()) + } + + pub fn parse_anon_const_expr(&mut self) -> PResult<'a, AnonConst> { + self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value }) + } + + fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> { + match self.parse_expr() { + Ok(expr) => Ok(expr), + Err(mut err) => match self.token.ident() { + Some((Ident { name: kw::Underscore, .. }, false)) + if self.look_ahead(1, |t| t == &token::Comma) => + { + // Special-case handling of `foo(_, _, _)` + err.emit(); + self.bump(); + Ok(self.mk_expr(self.prev_token.span, ExprKind::Err, AttrVec::new())) + } + _ => Err(err), + }, + } + } + + /// Parses a sequence of expressions delimited by parentheses. + fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> { + self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r) + } + + /// Parses an expression, subject to the given restrictions. + #[inline] + pub(super) fn parse_expr_res( + &mut self, + r: Restrictions, + already_parsed_attrs: Option<AttrWrapper>, + ) -> PResult<'a, P<Expr>> { + self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs)) + } + + /// Parses an associative expression. + /// + /// This parses an expression accounting for associativity and precedence of the operators in + /// the expression. + #[inline] + fn parse_assoc_expr( + &mut self, + already_parsed_attrs: Option<AttrWrapper>, + ) -> PResult<'a, P<Expr>> { + self.parse_assoc_expr_with(0, already_parsed_attrs.into()) + } + + /// Parses an associative expression with operators of at least `min_prec` precedence. + pub(super) fn parse_assoc_expr_with( + &mut self, + min_prec: usize, + lhs: LhsExpr, + ) -> PResult<'a, P<Expr>> { + let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs { + expr + } else { + let attrs = match lhs { + LhsExpr::AttributesParsed(attrs) => Some(attrs), + _ => None, + }; + if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) { + return self.parse_prefix_range_expr(attrs); + } else { + self.parse_prefix_expr(attrs)? + } + }; + let last_type_ascription_set = self.last_type_ascription.is_some(); + + if !self.should_continue_as_assoc_expr(&lhs) { + self.last_type_ascription = None; + return Ok(lhs); + } + + self.expected_tokens.push(TokenType::Operator); + while let Some(op) = self.check_assoc_op() { + // Adjust the span for interpolated LHS to point to the `$lhs` token + // and not to what it refers to. + let lhs_span = match self.prev_token.kind { + TokenKind::Interpolated(..) => self.prev_token.span, + _ => lhs.span, + }; + + let cur_op_span = self.token.span; + let restrictions = if op.node.is_assign_like() { + self.restrictions & Restrictions::NO_STRUCT_LITERAL + } else { + self.restrictions + }; + let prec = op.node.precedence(); + if prec < min_prec { + break; + } + // Check for deprecated `...` syntax + if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq { + self.err_dotdotdot_syntax(self.token.span); + } + + if self.token == token::LArrow { + self.err_larrow_operator(self.token.span); + } + + self.bump(); + if op.node.is_comparison() { + if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? { + return Ok(expr); + } + } + + // Look for JS' `===` and `!==` and recover + if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual) + && self.token.kind == token::Eq + && self.prev_token.span.hi() == self.token.span.lo() + { + let sp = op.span.to(self.token.span); + let sugg = match op.node { + AssocOp::Equal => "==", + AssocOp::NotEqual => "!=", + _ => unreachable!(), + }; + self.struct_span_err(sp, &format!("invalid comparison operator `{sugg}=`")) + .span_suggestion_short( + sp, + &format!("`{s}=` is not a valid comparison operator, use `{s}`", s = sugg), + sugg, + Applicability::MachineApplicable, + ) + .emit(); + self.bump(); + } + + // Look for PHP's `<>` and recover + if op.node == AssocOp::Less + && self.token.kind == token::Gt + && self.prev_token.span.hi() == self.token.span.lo() + { + let sp = op.span.to(self.token.span); + self.struct_span_err(sp, "invalid comparison operator `<>`") + .span_suggestion_short( + sp, + "`<>` is not a valid comparison operator, use `!=`", + "!=", + Applicability::MachineApplicable, + ) + .emit(); + self.bump(); + } + + // Look for C++'s `<=>` and recover + if op.node == AssocOp::LessEqual + && self.token.kind == token::Gt + && self.prev_token.span.hi() == self.token.span.lo() + { + let sp = op.span.to(self.token.span); + self.struct_span_err(sp, "invalid comparison operator `<=>`") + .span_label( + sp, + "`<=>` is not a valid comparison operator, use `std::cmp::Ordering`", + ) + .emit(); + self.bump(); + } + + if self.prev_token == token::BinOp(token::Plus) + && self.token == token::BinOp(token::Plus) + && self.prev_token.span.between(self.token.span).is_empty() + { + let op_span = self.prev_token.span.to(self.token.span); + // Eat the second `+` + self.bump(); + lhs = self.recover_from_postfix_increment(lhs, op_span)?; + continue; + } + + let op = op.node; + // Special cases: + if op == AssocOp::As { + lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?; + continue; + } else if op == AssocOp::Colon { + lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?; + continue; + } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq { + // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to + // generalise it to the Fixity::None code. + lhs = self.parse_range_expr(prec, lhs, op, cur_op_span)?; + break; + } + + let fixity = op.fixity(); + let prec_adjustment = match fixity { + Fixity::Right => 0, + Fixity::Left => 1, + // We currently have no non-associative operators that are not handled above by + // the special cases. The code is here only for future convenience. + Fixity::None => 1, + }; + let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| { + this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed) + })?; + + let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span); + lhs = match op { + AssocOp::Add + | AssocOp::Subtract + | AssocOp::Multiply + | AssocOp::Divide + | AssocOp::Modulus + | AssocOp::LAnd + | AssocOp::LOr + | AssocOp::BitXor + | AssocOp::BitAnd + | AssocOp::BitOr + | AssocOp::ShiftLeft + | AssocOp::ShiftRight + | AssocOp::Equal + | AssocOp::Less + | AssocOp::LessEqual + | AssocOp::NotEqual + | AssocOp::Greater + | AssocOp::GreaterEqual => { + let ast_op = op.to_ast_binop().unwrap(); + let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs); + self.mk_expr(span, binary, AttrVec::new()) + } + AssocOp::Assign => { + self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span), AttrVec::new()) + } + AssocOp::AssignOp(k) => { + let aop = match k { + token::Plus => BinOpKind::Add, + token::Minus => BinOpKind::Sub, + token::Star => BinOpKind::Mul, + token::Slash => BinOpKind::Div, + token::Percent => BinOpKind::Rem, + token::Caret => BinOpKind::BitXor, + token::And => BinOpKind::BitAnd, + token::Or => BinOpKind::BitOr, + token::Shl => BinOpKind::Shl, + token::Shr => BinOpKind::Shr, + }; + let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs); + self.mk_expr(span, aopexpr, AttrVec::new()) + } + AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => { + self.span_bug(span, "AssocOp should have been handled by special case") + } + }; + + if let Fixity::None = fixity { + break; + } + } + if last_type_ascription_set { + self.last_type_ascription = None; + } + Ok(lhs) + } + + fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool { + match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) { + // Semi-statement forms are odd: + // See https://github.com/rust-lang/rust/issues/29071 + (true, None) => false, + (false, _) => true, // Continue parsing the expression. + // An exhaustive check is done in the following block, but these are checked first + // because they *are* ambiguous but also reasonable looking incorrect syntax, so we + // want to keep their span info to improve diagnostics in these cases in a later stage. + (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3` + (true, Some(AssocOp::Subtract)) | // `{ 42 } -5` + (true, Some(AssocOp::Add)) // `{ 42 } + 42 + // If the next token is a keyword, then the tokens above *are* unambiguously incorrect: + // `if x { a } else { b } && if y { c } else { d }` + if !self.look_ahead(1, |t| t.is_used_keyword()) => { + // These cases are ambiguous and can't be identified in the parser alone. + let sp = self.sess.source_map().start_point(self.token.span); + self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span); + false + } + (true, Some(AssocOp::LAnd)) | + (true, Some(AssocOp::LOr)) | + (true, Some(AssocOp::BitOr)) => { + // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`. Separated from the + // above due to #74233. + // These cases are ambiguous and can't be identified in the parser alone. + // + // Bitwise AND is left out because guessing intent is hard. We can make + // suggestions based on the assumption that double-refs are rarely intentional, + // and closures are distinct enough that they don't get mixed up with their + // return value. + let sp = self.sess.source_map().start_point(self.token.span); + self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span); + false + } + (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => false, + (true, Some(_)) => { + self.error_found_expr_would_be_stmt(lhs); + true + } + } + } + + /// We've found an expression that would be parsed as a statement, + /// but the next token implies this should be parsed as an expression. + /// For example: `if let Some(x) = x { x } else { 0 } / 2`. + fn error_found_expr_would_be_stmt(&self, lhs: &Expr) { + let mut err = self.struct_span_err( + self.token.span, + &format!("expected expression, found `{}`", pprust::token_to_string(&self.token),), + ); + err.span_label(self.token.span, "expected expression"); + self.sess.expr_parentheses_needed(&mut err, lhs.span); + err.emit(); + } + + /// Possibly translate the current token to an associative operator. + /// The method does not advance the current token. + /// + /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively. + fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> { + let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) { + // When parsing const expressions, stop parsing when encountering `>`. + ( + Some( + AssocOp::ShiftRight + | AssocOp::Greater + | AssocOp::GreaterEqual + | AssocOp::AssignOp(token::BinOpToken::Shr), + ), + _, + ) if self.restrictions.contains(Restrictions::CONST_EXPR) => { + return None; + } + (Some(op), _) => (op, self.token.span), + (None, Some((Ident { name: sym::and, span }, false))) => { + self.error_bad_logical_op("and", "&&", "conjunction"); + (AssocOp::LAnd, span) + } + (None, Some((Ident { name: sym::or, span }, false))) => { + self.error_bad_logical_op("or", "||", "disjunction"); + (AssocOp::LOr, span) + } + _ => return None, + }; + Some(source_map::respan(span, op)) + } + + /// Error on `and` and `or` suggesting `&&` and `||` respectively. + fn error_bad_logical_op(&self, bad: &str, good: &str, english: &str) { + self.struct_span_err(self.token.span, &format!("`{bad}` is not a logical operator")) + .span_suggestion_short( + self.token.span, + &format!("use `{good}` to perform logical {english}"), + good, + Applicability::MachineApplicable, + ) + .note("unlike in e.g., python and PHP, `&&` and `||` are used for logical operators") + .emit(); + } + + /// Checks if this expression is a successfully parsed statement. + fn expr_is_complete(&self, e: &Expr) -> bool { + self.restrictions.contains(Restrictions::STMT_EXPR) + && !classify::expr_requires_semi_to_be_stmt(e) + } + + /// Parses `x..y`, `x..=y`, and `x..`/`x..=`. + /// The other two variants are handled in `parse_prefix_range_expr` below. + fn parse_range_expr( + &mut self, + prec: usize, + lhs: P<Expr>, + op: AssocOp, + cur_op_span: Span, + ) -> PResult<'a, P<Expr>> { + let rhs = if self.is_at_start_of_range_notation_rhs() { + Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?) + } else { + None + }; + let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span); + let span = self.mk_expr_sp(&lhs, lhs.span, rhs_span); + let limits = + if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed }; + let range = self.mk_range(Some(lhs), rhs, limits); + Ok(self.mk_expr(span, range, AttrVec::new())) + } + + fn is_at_start_of_range_notation_rhs(&self) -> bool { + if self.token.can_begin_expr() { + // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`. + if self.token == token::OpenDelim(Delimiter::Brace) { + return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL); + } + true + } else { + false + } + } + + /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`. + fn parse_prefix_range_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> { + // Check for deprecated `...` syntax. + if self.token == token::DotDotDot { + self.err_dotdotdot_syntax(self.token.span); + } + + debug_assert!( + [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind), + "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq", + self.token + ); + + let limits = match self.token.kind { + token::DotDot => RangeLimits::HalfOpen, + _ => RangeLimits::Closed, + }; + let op = AssocOp::from_token(&self.token); + // FIXME: `parse_prefix_range_expr` is called when the current + // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already + // parsed attributes, then trying to parse them here will always fail. + // We should figure out how we want attributes on range expressions to work. + let attrs = self.parse_or_use_outer_attributes(attrs)?; + self.collect_tokens_for_expr(attrs, |this, attrs| { + let lo = this.token.span; + this.bump(); + let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() { + // RHS must be parsed with more associativity than the dots. + this.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed) + .map(|x| (lo.to(x.span), Some(x)))? + } else { + (lo, None) + }; + let range = this.mk_range(None, opt_end, limits); + Ok(this.mk_expr(span, range, attrs.into())) + }) + } + + /// Parses a prefix-unary-operator expr. + fn parse_prefix_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> { + let attrs = self.parse_or_use_outer_attributes(attrs)?; + let lo = self.token.span; + + macro_rules! make_it { + ($this:ident, $attrs:expr, |this, _| $body:expr) => { + $this.collect_tokens_for_expr($attrs, |$this, attrs| { + let (hi, ex) = $body?; + Ok($this.mk_expr(lo.to(hi), ex, attrs.into())) + }) + }; + } + + let this = self; + + // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr() + match this.token.uninterpolate().kind { + token::Not => make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Not)), // `!expr` + token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)), // `~expr` + token::BinOp(token::Minus) => { + make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Neg)) + } // `-expr` + token::BinOp(token::Star) => { + make_it!(this, attrs, |this, _| this.parse_unary_expr(lo, UnOp::Deref)) + } // `*expr` + token::BinOp(token::And) | token::AndAnd => { + make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo)) + } + token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => { + let mut err = this.struct_span_err(lo, "leading `+` is not supported"); + err.span_label(lo, "unexpected `+`"); + + // a block on the LHS might have been intended to be an expression instead + if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) { + this.sess.expr_parentheses_needed(&mut err, *sp); + } else { + err.span_suggestion_verbose( + lo, + "try removing the `+`", + "", + Applicability::MachineApplicable, + ); + } + err.emit(); + + this.bump(); + this.parse_prefix_expr(None) + } // `+expr` + // Recover from `++x`: + token::BinOp(token::Plus) + if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) => + { + let prev_is_semi = this.prev_token == token::Semi; + let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span)); + // Eat both `+`s. + this.bump(); + this.bump(); + + let operand_expr = this.parse_dot_or_call_expr(Default::default())?; + this.recover_from_prefix_increment(operand_expr, pre_span, prev_is_semi) + } + token::Ident(..) if this.token.is_keyword(kw::Box) => { + make_it!(this, attrs, |this, _| this.parse_box_expr(lo)) + } + token::Ident(..) if this.is_mistaken_not_ident_negation() => { + make_it!(this, attrs, |this, _| this.recover_not_expr(lo)) + } + _ => return this.parse_dot_or_call_expr(Some(attrs)), + } + } + + fn parse_prefix_expr_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> { + self.bump(); + let expr = self.parse_prefix_expr(None); + let (span, expr) = self.interpolated_or_expr_span(expr)?; + Ok((lo.to(span), expr)) + } + + fn parse_unary_expr(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> { + let (span, expr) = self.parse_prefix_expr_common(lo)?; + Ok((span, self.mk_unary(op, expr))) + } + + // Recover on `!` suggesting for bitwise negation instead. + fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> { + self.struct_span_err(lo, "`~` cannot be used as a unary operator") + .span_suggestion_short( + lo, + "use `!` to perform bitwise not", + "!", + Applicability::MachineApplicable, + ) + .emit(); + + self.parse_unary_expr(lo, UnOp::Not) + } + + /// Parse `box expr`. + fn parse_box_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> { + let (span, expr) = self.parse_prefix_expr_common(lo)?; + self.sess.gated_spans.gate(sym::box_syntax, span); + Ok((span, ExprKind::Box(expr))) + } + + fn is_mistaken_not_ident_negation(&self) -> bool { + let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind { + // These tokens can start an expression after `!`, but + // can't continue an expression after an ident + token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw), + token::Literal(..) | token::Pound => true, + _ => t.is_whole_expr(), + }; + self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr) + } + + /// Recover on `not expr` in favor of `!expr`. + fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> { + // Emit the error... + let not_token = self.look_ahead(1, |t| t.clone()); + self.struct_span_err( + not_token.span, + &format!("unexpected {} after identifier", super::token_descr(¬_token)), + ) + .span_suggestion_short( + // Span the `not` plus trailing whitespace to avoid + // trailing whitespace after the `!` in our suggestion + self.sess.source_map().span_until_non_whitespace(lo.to(not_token.span)), + "use `!` to perform logical negation", + "!", + Applicability::MachineApplicable, + ) + .emit(); + + // ...and recover! + self.parse_unary_expr(lo, UnOp::Not) + } + + /// Returns the span of expr, if it was not interpolated or the span of the interpolated token. + fn interpolated_or_expr_span( + &self, + expr: PResult<'a, P<Expr>>, + ) -> PResult<'a, (Span, P<Expr>)> { + expr.map(|e| { + ( + match self.prev_token.kind { + TokenKind::Interpolated(..) => self.prev_token.span, + _ => e.span, + }, + e, + ) + }) + } + + fn parse_assoc_op_cast( + &mut self, + lhs: P<Expr>, + lhs_span: Span, + expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind, + ) -> PResult<'a, P<Expr>> { + let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| { + this.mk_expr( + this.mk_expr_sp(&lhs, lhs_span, rhs.span), + expr_kind(lhs, rhs), + AttrVec::new(), + ) + }; + + // Save the state of the parser before parsing type normally, in case there is a + // LessThan comparison after this cast. + let parser_snapshot_before_type = self.clone(); + let cast_expr = match self.parse_as_cast_ty() { + Ok(rhs) => mk_expr(self, lhs, rhs), + Err(type_err) => { + // Rewind to before attempting to parse the type with generics, to recover + // from situations like `x as usize < y` in which we first tried to parse + // `usize < y` as a type with generic arguments. + let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type); + + // Check for typo of `'a: loop { break 'a }` with a missing `'`. + match (&lhs.kind, &self.token.kind) { + ( + // `foo: ` + ExprKind::Path(None, ast::Path { segments, .. }), + TokenKind::Ident(kw::For | kw::Loop | kw::While, false), + ) if segments.len() == 1 => { + let snapshot = self.create_snapshot_for_diagnostic(); + let label = Label { + ident: Ident::from_str_and_span( + &format!("'{}", segments[0].ident), + segments[0].ident.span, + ), + }; + match self.parse_labeled_expr(label, AttrVec::new(), false) { + Ok(expr) => { + type_err.cancel(); + self.struct_span_err(label.ident.span, "malformed loop label") + .span_suggestion( + label.ident.span, + "use the correct loop label format", + label.ident, + Applicability::MachineApplicable, + ) + .emit(); + return Ok(expr); + } + Err(err) => { + err.cancel(); + self.restore_snapshot(snapshot); + } + } + } + _ => {} + } + + match self.parse_path(PathStyle::Expr) { + Ok(path) => { + let (op_noun, op_verb) = match self.token.kind { + token::Lt => ("comparison", "comparing"), + token::BinOp(token::Shl) => ("shift", "shifting"), + _ => { + // We can end up here even without `<` being the next token, for + // example because `parse_ty_no_plus` returns `Err` on keywords, + // but `parse_path` returns `Ok` on them due to error recovery. + // Return original error and parser state. + *self = parser_snapshot_after_type; + return Err(type_err); + } + }; + + // Successfully parsed the type path leaving a `<` yet to parse. + type_err.cancel(); + + // Report non-fatal diagnostics, keep `x as usize` as an expression + // in AST and continue parsing. + let msg = format!( + "`<` is interpreted as a start of generic arguments for `{}`, not a {}", + pprust::path_to_string(&path), + op_noun, + ); + let span_after_type = parser_snapshot_after_type.token.span; + let expr = + mk_expr(self, lhs, self.mk_ty(path.span, TyKind::Path(None, path))); + + self.struct_span_err(self.token.span, &msg) + .span_label( + self.look_ahead(1, |t| t.span).to(span_after_type), + "interpreted as generic arguments", + ) + .span_label(self.token.span, format!("not interpreted as {op_noun}")) + .multipart_suggestion( + &format!("try {op_verb} the cast value"), + vec![ + (expr.span.shrink_to_lo(), "(".to_string()), + (expr.span.shrink_to_hi(), ")".to_string()), + ], + Applicability::MachineApplicable, + ) + .emit(); + + expr + } + Err(path_err) => { + // Couldn't parse as a path, return original error and parser state. + path_err.cancel(); + *self = parser_snapshot_after_type; + return Err(type_err); + } + } + } + }; + + self.parse_and_disallow_postfix_after_cast(cast_expr) + } + + /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast, + /// then emits an error and returns the newly parsed tree. + /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`. + fn parse_and_disallow_postfix_after_cast( + &mut self, + cast_expr: P<Expr>, + ) -> PResult<'a, P<Expr>> { + let span = cast_expr.span; + let (cast_kind, maybe_ascription_span) = + if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind { + ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi()))) + } else { + ("cast", None) + }; + + // Save the memory location of expr before parsing any following postfix operators. + // This will be compared with the memory location of the output expression. + // If they different we can assume we parsed another expression because the existing expression is not reallocated. + let addr_before = &*cast_expr as *const _ as usize; + let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?; + let changed = addr_before != &*with_postfix as *const _ as usize; + + // Check if an illegal postfix operator has been added after the cast. + // If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator. + if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) || changed { + let msg = format!( + "{cast_kind} cannot be followed by {}", + match with_postfix.kind { + ExprKind::Index(_, _) => "indexing", + ExprKind::Try(_) => "`?`", + ExprKind::Field(_, _) => "a field access", + ExprKind::MethodCall(_, _, _) => "a method call", + ExprKind::Call(_, _) => "a function call", + ExprKind::Await(_) => "`.await`", + ExprKind::Err => return Ok(with_postfix), + _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"), + } + ); + let mut err = self.struct_span_err(span, &msg); + + let suggest_parens = |err: &mut DiagnosticBuilder<'_, _>| { + let suggestions = vec![ + (span.shrink_to_lo(), "(".to_string()), + (span.shrink_to_hi(), ")".to_string()), + ]; + err.multipart_suggestion( + "try surrounding the expression in parentheses", + suggestions, + Applicability::MachineApplicable, + ); + }; + + // If type ascription is "likely an error", the user will already be getting a useful + // help message, and doesn't need a second. + if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) { + self.maybe_annotate_with_ascription(&mut err, false); + } else if let Some(ascription_span) = maybe_ascription_span { + let is_nightly = self.sess.unstable_features.is_nightly_build(); + if is_nightly { + suggest_parens(&mut err); + } + err.span_suggestion( + ascription_span, + &format!( + "{}remove the type ascription", + if is_nightly { "alternatively, " } else { "" } + ), + "", + if is_nightly { + Applicability::MaybeIncorrect + } else { + Applicability::MachineApplicable + }, + ); + } else { + suggest_parens(&mut err); + } + err.emit(); + }; + Ok(with_postfix) + } + + fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> { + let maybe_path = self.could_ascription_be_path(&lhs.kind); + self.last_type_ascription = Some((self.prev_token.span, maybe_path)); + let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?; + self.sess.gated_spans.gate(sym::type_ascription, lhs.span); + Ok(lhs) + } + + /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`. + fn parse_borrow_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> { + self.expect_and()?; + let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon); + let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below. + let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo); + let expr = self.parse_prefix_expr(None); + let (hi, expr) = self.interpolated_or_expr_span(expr)?; + let span = lo.to(hi); + if let Some(lt) = lifetime { + self.error_remove_borrow_lifetime(span, lt.ident.span); + } + Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr))) + } + + fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) { + self.struct_span_err(span, "borrow expressions cannot be annotated with lifetimes") + .span_label(lt_span, "annotated with lifetime here") + .span_suggestion( + lt_span, + "remove the lifetime annotation", + "", + Applicability::MachineApplicable, + ) + .emit(); + } + + /// Parse `mut?` or `raw [ const | mut ]`. + fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) { + if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) { + // `raw [ const | mut ]`. + let found_raw = self.eat_keyword(kw::Raw); + assert!(found_raw); + let mutability = self.parse_const_or_mut().unwrap(); + self.sess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span)); + (ast::BorrowKind::Raw, mutability) + } else { + // `mut?` + (ast::BorrowKind::Ref, self.parse_mutability()) + } + } + + /// Parses `a.b` or `a(13)` or `a[4]` or just `a`. + fn parse_dot_or_call_expr(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> { + let attrs = self.parse_or_use_outer_attributes(attrs)?; + self.collect_tokens_for_expr(attrs, |this, attrs| { + let base = this.parse_bottom_expr(); + let (span, base) = this.interpolated_or_expr_span(base)?; + this.parse_dot_or_call_expr_with(base, span, attrs) + }) + } + + pub(super) fn parse_dot_or_call_expr_with( + &mut self, + e0: P<Expr>, + lo: Span, + mut attrs: Vec<ast::Attribute>, + ) -> PResult<'a, P<Expr>> { + // Stitch the list of outer attributes onto the return value. + // A little bit ugly, but the best way given the current code + // structure + self.parse_dot_or_call_expr_with_(e0, lo).map(|expr| { + expr.map(|mut expr| { + attrs.extend::<Vec<_>>(expr.attrs.into()); + expr.attrs = attrs.into(); + expr + }) + }) + } + + fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> { + loop { + let has_question = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) { + // we are using noexpect here because we don't expect a `?` directly after a `return` + // which could be suggested otherwise + self.eat_noexpect(&token::Question) + } else { + self.eat(&token::Question) + }; + if has_question { + // `expr?` + e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e), AttrVec::new()); + continue; + } + let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, false) { + // we are using noexpect here because we don't expect a `.` directly after a `return` + // which could be suggested otherwise + self.eat_noexpect(&token::Dot) + } else { + self.eat(&token::Dot) + }; + if has_dot { + // expr.f + e = self.parse_dot_suffix_expr(lo, e)?; + continue; + } + if self.expr_is_complete(&e) { + return Ok(e); + } + e = match self.token.kind { + token::OpenDelim(Delimiter::Parenthesis) => self.parse_fn_call_expr(lo, e), + token::OpenDelim(Delimiter::Bracket) => self.parse_index_expr(lo, e)?, + _ => return Ok(e), + } + } + } + + fn look_ahead_type_ascription_as_field(&mut self) -> bool { + self.look_ahead(1, |t| t.is_ident()) + && self.look_ahead(2, |t| t == &token::Colon) + && self.look_ahead(3, |t| t.can_begin_expr()) + } + + fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> { + match self.token.uninterpolate().kind { + token::Ident(..) => self.parse_dot_suffix(base, lo), + token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => { + Ok(self.parse_tuple_field_access_expr(lo, base, symbol, suffix, None)) + } + token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => { + Ok(self.parse_tuple_field_access_expr_float(lo, base, symbol, suffix)) + } + _ => { + self.error_unexpected_after_dot(); + Ok(base) + } + } + } + + fn error_unexpected_after_dot(&self) { + // FIXME Could factor this out into non_fatal_unexpected or something. + let actual = pprust::token_to_string(&self.token); + self.struct_span_err(self.token.span, &format!("unexpected token: `{actual}`")).emit(); + } + + // We need an identifier or integer, but the next token is a float. + // Break the float into components to extract the identifier or integer. + // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2 + // parts unless those parts are processed immediately. `TokenCursor` should either + // support pushing "future tokens" (would be also helpful to `break_and_eat`), or + // we should break everything including floats into more basic proc-macro style + // tokens in the lexer (probably preferable). + fn parse_tuple_field_access_expr_float( + &mut self, + lo: Span, + base: P<Expr>, + float: Symbol, + suffix: Option<Symbol>, + ) -> P<Expr> { + #[derive(Debug)] + enum FloatComponent { + IdentLike(String), + Punct(char), + } + use FloatComponent::*; + + let float_str = float.as_str(); + let mut components = Vec::new(); + let mut ident_like = String::new(); + for c in float_str.chars() { + if c == '_' || c.is_ascii_alphanumeric() { + ident_like.push(c); + } else if matches!(c, '.' | '+' | '-') { + if !ident_like.is_empty() { + components.push(IdentLike(mem::take(&mut ident_like))); + } + components.push(Punct(c)); + } else { + panic!("unexpected character in a float token: {:?}", c) + } + } + if !ident_like.is_empty() { + components.push(IdentLike(ident_like)); + } + + // With proc macros the span can refer to anything, the source may be too short, + // or too long, or non-ASCII. It only makes sense to break our span into components + // if its underlying text is identical to our float literal. + let span = self.token.span; + let can_take_span_apart = + || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref(); + + match &*components { + // 1e2 + [IdentLike(i)] => { + self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None) + } + // 1. + [IdentLike(i), Punct('.')] => { + let (ident_span, dot_span) = if can_take_span_apart() { + let (span, ident_len) = (span.data(), BytePos::from_usize(i.len())); + let ident_span = span.with_hi(span.lo + ident_len); + let dot_span = span.with_lo(span.lo + ident_len); + (ident_span, dot_span) + } else { + (span, span) + }; + assert!(suffix.is_none()); + let symbol = Symbol::intern(&i); + self.token = Token::new(token::Ident(symbol, false), ident_span); + let next_token = (Token::new(token::Dot, dot_span), self.token_spacing); + self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token)) + } + // 1.2 | 1.2e3 + [IdentLike(i1), Punct('.'), IdentLike(i2)] => { + let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() { + let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len())); + let ident1_span = span.with_hi(span.lo + ident1_len); + let dot_span = span + .with_lo(span.lo + ident1_len) + .with_hi(span.lo + ident1_len + BytePos(1)); + let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1)); + (ident1_span, dot_span, ident2_span) + } else { + (span, span, span) + }; + let symbol1 = Symbol::intern(&i1); + self.token = Token::new(token::Ident(symbol1, false), ident1_span); + // This needs to be `Spacing::Alone` to prevent regressions. + // See issue #76399 and PR #76285 for more details + let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone); + let base1 = + self.parse_tuple_field_access_expr(lo, base, symbol1, None, Some(next_token1)); + let symbol2 = Symbol::intern(&i2); + let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span); + self.bump_with((next_token2, self.token_spacing)); // `.` + self.parse_tuple_field_access_expr(lo, base1, symbol2, suffix, None) + } + // 1e+ | 1e- (recovered) + [IdentLike(_), Punct('+' | '-')] | + // 1e+2 | 1e-2 + [IdentLike(_), Punct('+' | '-'), IdentLike(_)] | + // 1.2e+ | 1.2e- + [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] | + // 1.2e+3 | 1.2e-3 + [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => { + // See the FIXME about `TokenCursor` above. + self.error_unexpected_after_dot(); + base + } + _ => panic!("unexpected components in a float token: {:?}", components), + } + } + + fn parse_tuple_field_access_expr( + &mut self, + lo: Span, + base: P<Expr>, + field: Symbol, + suffix: Option<Symbol>, + next_token: Option<(Token, Spacing)>, + ) -> P<Expr> { + match next_token { + Some(next_token) => self.bump_with(next_token), + None => self.bump(), + } + let span = self.prev_token.span; + let field = ExprKind::Field(base, Ident::new(field, span)); + self.expect_no_suffix(span, "a tuple index", suffix); + self.mk_expr(lo.to(span), field, AttrVec::new()) + } + + /// Parse a function call expression, `expr(...)`. + fn parse_fn_call_expr(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> { + let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) + && self.look_ahead_type_ascription_as_field() + { + Some((self.create_snapshot_for_diagnostic(), fun.kind.clone())) + } else { + None + }; + let open_paren = self.token.span; + + let mut seq = self.parse_paren_expr_seq().map(|args| { + self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new()) + }); + if let Some(expr) = + self.maybe_recover_struct_lit_bad_delims(lo, open_paren, &mut seq, snapshot) + { + return expr; + } + self.recover_seq_parse_error(Delimiter::Parenthesis, lo, seq) + } + + /// If we encounter a parser state that looks like the user has written a `struct` literal with + /// parentheses instead of braces, recover the parser state and provide suggestions. + #[instrument(skip(self, seq, snapshot), level = "trace")] + fn maybe_recover_struct_lit_bad_delims( + &mut self, + lo: Span, + open_paren: Span, + seq: &mut PResult<'a, P<Expr>>, + snapshot: Option<(SnapshotParser<'a>, ExprKind)>, + ) -> Option<P<Expr>> { + match (seq.as_mut(), snapshot) { + (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => { + let name = pprust::path_to_string(&path); + snapshot.bump(); // `(` + match snapshot.parse_struct_fields(path, false, Delimiter::Parenthesis) { + Ok((fields, ..)) + if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) => + { + // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest + // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`. + self.restore_snapshot(snapshot); + let close_paren = self.prev_token.span; + let span = lo.to(self.prev_token.span); + if !fields.is_empty() { + let replacement_err = self.struct_span_err( + span, + "invalid `struct` delimiters or `fn` call arguments", + ); + mem::replace(err, replacement_err).cancel(); + + err.multipart_suggestion( + &format!("if `{name}` is a struct, use braces as delimiters"), + vec![ + (open_paren, " { ".to_string()), + (close_paren, " }".to_string()), + ], + Applicability::MaybeIncorrect, + ); + err.multipart_suggestion( + &format!("if `{name}` is a function, use the arguments directly"), + fields + .into_iter() + .map(|field| (field.span.until(field.expr.span), String::new())) + .collect(), + Applicability::MaybeIncorrect, + ); + err.emit(); + } else { + err.emit(); + } + return Some(self.mk_expr_err(span)); + } + Ok(_) => {} + Err(mut err) => { + err.emit(); + } + } + } + _ => {} + } + None + } + + /// Parse an indexing expression `expr[...]`. + fn parse_index_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> { + self.bump(); // `[` + let index = self.parse_expr()?; + self.expect(&token::CloseDelim(Delimiter::Bracket))?; + Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_index(base, index), AttrVec::new())) + } + + /// Assuming we have just parsed `.`, continue parsing into an expression. + fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> { + if self.token.uninterpolated_span().rust_2018() && self.eat_keyword(kw::Await) { + return Ok(self.mk_await_expr(self_arg, lo)); + } + + let fn_span_lo = self.token.span; + let mut segment = self.parse_path_segment(PathStyle::Expr, None)?; + self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(Delimiter::Parenthesis)]); + self.check_turbofish_missing_angle_brackets(&mut segment); + + if self.check(&token::OpenDelim(Delimiter::Parenthesis)) { + // Method call `expr.f()` + let mut args = self.parse_paren_expr_seq()?; + args.insert(0, self_arg); + + let fn_span = fn_span_lo.to(self.prev_token.span); + let span = lo.to(self.prev_token.span); + Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new())) + } else { + // Field access `expr.f` + if let Some(args) = segment.args { + self.struct_span_err( + args.span(), + "field expressions cannot have generic arguments", + ) + .emit(); + } + + let span = lo.to(self.prev_token.span); + Ok(self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), AttrVec::new())) + } + } + + /// At the bottom (top?) of the precedence hierarchy, + /// Parses things like parenthesized exprs, macros, `return`, etc. + /// + /// N.B., this does not parse outer attributes, and is private because it only works + /// correctly if called from `parse_dot_or_call_expr()`. + fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> { + maybe_recover_from_interpolated_ty_qpath!(self, true); + maybe_whole_expr!(self); + + // Outer attributes are already parsed and will be + // added to the return value after the fact. + // + // Therefore, prevent sub-parser from parsing + // attributes by giving them an empty "already-parsed" list. + let attrs = AttrVec::new(); + + // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`. + let lo = self.token.span; + if let token::Literal(_) = self.token.kind { + // This match arm is a special-case of the `_` match arm below and + // could be removed without changing functionality, but it's faster + // to have it here, especially for programs with large constants. + self.parse_lit_expr(attrs) + } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) { + self.parse_tuple_parens_expr(attrs) + } else if self.check(&token::OpenDelim(Delimiter::Brace)) { + self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs) + } else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) { + self.parse_closure_expr(attrs).map_err(|mut err| { + // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }` + // then suggest parens around the lhs. + if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) { + self.sess.expr_parentheses_needed(&mut err, *sp); + } + err + }) + } else if self.check(&token::OpenDelim(Delimiter::Bracket)) { + self.parse_array_or_repeat_expr(attrs, Delimiter::Bracket) + } else if self.check_path() { + self.parse_path_start_expr(attrs) + } else if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) { + self.parse_closure_expr(attrs) + } else if self.eat_keyword(kw::If) { + self.parse_if_expr(attrs) + } else if self.check_keyword(kw::For) { + if self.choose_generics_over_qpath(1) { + self.parse_closure_expr(attrs) + } else { + assert!(self.eat_keyword(kw::For)); + self.parse_for_expr(None, self.prev_token.span, attrs) + } + } else if self.eat_keyword(kw::While) { + self.parse_while_expr(None, self.prev_token.span, attrs) + } else if let Some(label) = self.eat_label() { + self.parse_labeled_expr(label, attrs, true) + } else if self.eat_keyword(kw::Loop) { + let sp = self.prev_token.span; + self.parse_loop_expr(None, self.prev_token.span, attrs).map_err(|mut err| { + err.span_label(sp, "while parsing this `loop` expression"); + err + }) + } else if self.eat_keyword(kw::Continue) { + let kind = ExprKind::Continue(self.eat_label()); + Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs)) + } else if self.eat_keyword(kw::Match) { + let match_sp = self.prev_token.span; + self.parse_match_expr(attrs).map_err(|mut err| { + err.span_label(match_sp, "while parsing this `match` expression"); + err + }) + } else if self.eat_keyword(kw::Unsafe) { + let sp = self.prev_token.span; + self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs) + .map_err(|mut err| { + err.span_label(sp, "while parsing this `unsafe` expression"); + err + }) + } else if self.check_inline_const(0) { + self.parse_const_block(lo.to(self.token.span), false) + } else if self.is_do_catch_block() { + self.recover_do_catch(attrs) + } else if self.is_try_block() { + self.expect_keyword(kw::Try)?; + self.parse_try_block(lo, attrs) + } else if self.eat_keyword(kw::Return) { + self.parse_return_expr(attrs) + } else if self.eat_keyword(kw::Break) { + self.parse_break_expr(attrs) + } else if self.eat_keyword(kw::Yield) { + self.parse_yield_expr(attrs) + } else if self.is_do_yeet() { + self.parse_yeet_expr(attrs) + } else if self.check_keyword(kw::Let) { + self.parse_let_expr(attrs) + } else if self.eat_keyword(kw::Underscore) { + Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs)) + } else if !self.unclosed_delims.is_empty() && self.check(&token::Semi) { + // Don't complain about bare semicolons after unclosed braces + // recovery in order to keep the error count down. Fixing the + // delimiters will possibly also fix the bare semicolon found in + // expression context. For example, silence the following error: + // + // error: expected expression, found `;` + // --> file.rs:2:13 + // | + // 2 | foo(bar(; + // | ^ expected expression + self.bump(); + Ok(self.mk_expr_err(self.token.span)) + } else if self.token.uninterpolated_span().rust_2018() { + // `Span::rust_2018()` is somewhat expensive; don't get it repeatedly. + if self.check_keyword(kw::Async) { + if self.is_async_block() { + // Check for `async {` and `async move {`. + self.parse_async_block(attrs) + } else { + self.parse_closure_expr(attrs) + } + } else if self.eat_keyword(kw::Await) { + self.recover_incorrect_await_syntax(lo, self.prev_token.span, attrs) + } else { + self.parse_lit_expr(attrs) + } + } else { + self.parse_lit_expr(attrs) + } + } + + fn parse_lit_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + match self.parse_opt_lit() { + Some(literal) => { + let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(literal), attrs); + self.maybe_recover_from_bad_qpath(expr) + } + None => self.try_macro_suggestion(), + } + } + + fn parse_tuple_parens_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + self.expect(&token::OpenDelim(Delimiter::Parenthesis))?; + let (es, trailing_comma) = match self.parse_seq_to_end( + &token::CloseDelim(Delimiter::Parenthesis), + SeqSep::trailing_allowed(token::Comma), + |p| p.parse_expr_catch_underscore(), + ) { + Ok(x) => x, + Err(err) => { + return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, Err(err))); + } + }; + let kind = if es.len() == 1 && !trailing_comma { + // `(e)` is parenthesized `e`. + ExprKind::Paren(es.into_iter().next().unwrap()) + } else { + // `(e,)` is a tuple with only one field, `e`. + ExprKind::Tup(es) + }; + let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + fn parse_array_or_repeat_expr( + &mut self, + attrs: AttrVec, + close_delim: Delimiter, + ) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + self.bump(); // `[` or other open delim + + let close = &token::CloseDelim(close_delim); + let kind = if self.eat(close) { + // Empty vector + ExprKind::Array(Vec::new()) + } else { + // Non-empty vector + let first_expr = self.parse_expr()?; + if self.eat(&token::Semi) { + // Repeating array syntax: `[ 0; 512 ]` + let count = self.parse_anon_const_expr()?; + self.expect(close)?; + ExprKind::Repeat(first_expr, count) + } else if self.eat(&token::Comma) { + // Vector with two or more elements. + let sep = SeqSep::trailing_allowed(token::Comma); + let (remaining_exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?; + let mut exprs = vec![first_expr]; + exprs.extend(remaining_exprs); + ExprKind::Array(exprs) + } else { + // Vector with one element + self.expect(close)?; + ExprKind::Array(vec![first_expr]) + } + }; + let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let (qself, path) = if self.eat_lt() { + let (qself, path) = self.parse_qpath(PathStyle::Expr)?; + (Some(qself), path) + } else { + (None, self.parse_path(PathStyle::Expr)?) + }; + let lo = path.span; + + // `!`, as an operator, is prefix, so we know this isn't that. + let (hi, kind) = if self.eat(&token::Not) { + // MACRO INVOCATION expression + if qself.is_some() { + self.struct_span_err(path.span, "macros cannot use qualified paths").emit(); + } + let mac = MacCall { + path, + args: self.parse_mac_args()?, + prior_type_ascription: self.last_type_ascription, + }; + (self.prev_token.span, ExprKind::MacCall(mac)) + } else if self.check(&token::OpenDelim(Delimiter::Brace)) { + if let Some(expr) = self.maybe_parse_struct_expr(qself.as_ref(), &path, &attrs) { + if qself.is_some() { + self.sess.gated_spans.gate(sym::more_qualified_paths, path.span); + } + return expr; + } else { + (path.span, ExprKind::Path(qself, path)) + } + } else { + (path.span, ExprKind::Path(qself, path)) + }; + + let expr = self.mk_expr(lo.to(hi), kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + /// Parse `'label: $expr`. The label is already parsed. + fn parse_labeled_expr( + &mut self, + label: Label, + attrs: AttrVec, + mut consume_colon: bool, + ) -> PResult<'a, P<Expr>> { + let lo = label.ident.span; + let label = Some(label); + let ate_colon = self.eat(&token::Colon); + let expr = if self.eat_keyword(kw::While) { + self.parse_while_expr(label, lo, attrs) + } else if self.eat_keyword(kw::For) { + self.parse_for_expr(label, lo, attrs) + } else if self.eat_keyword(kw::Loop) { + self.parse_loop_expr(label, lo, attrs) + } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace)) + || self.token.is_whole_block() + { + self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs) + } else if !ate_colon + && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt)) + { + // We're probably inside of a `Path<'a>` that needs a turbofish + let msg = "expected `while`, `for`, `loop` or `{` after a label"; + self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit(); + consume_colon = false; + Ok(self.mk_expr_err(lo)) + } else { + let msg = "expected `while`, `for`, `loop` or `{` after a label"; + + let mut err = self.struct_span_err(self.token.span, msg); + err.span_label(self.token.span, msg); + + // Continue as an expression in an effort to recover on `'label: non_block_expr`. + let expr = self.parse_expr().map(|expr| { + let span = expr.span; + + let found_labeled_breaks = { + struct FindLabeledBreaksVisitor(bool); + + impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor { + fn visit_expr_post(&mut self, ex: &'ast Expr) { + if let ExprKind::Break(Some(_label), _) = ex.kind { + self.0 = true; + } + } + } + + let mut vis = FindLabeledBreaksVisitor(false); + vis.visit_expr(&expr); + vis.0 + }; + + // Suggestion involves adding a (as of time of writing this, unstable) labeled block. + // + // If there are no breaks that may use this label, suggest removing the label and + // recover to the unmodified expression. + if !found_labeled_breaks { + let msg = "consider removing the label"; + err.span_suggestion_verbose( + lo.until(span), + msg, + "", + Applicability::MachineApplicable, + ); + + return expr; + } + + let sugg_msg = "consider enclosing expression in a block"; + let suggestions = vec![ + (span.shrink_to_lo(), "{ ".to_owned()), + (span.shrink_to_hi(), " }".to_owned()), + ]; + + err.multipart_suggestion_verbose( + sugg_msg, + suggestions, + Applicability::MachineApplicable, + ); + + // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to supress future errors about `break 'label`. + let stmt = self.mk_stmt(span, StmtKind::Expr(expr)); + let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span); + self.mk_expr(span, ExprKind::Block(blk, label), ThinVec::new()) + }); + + err.emit(); + expr + }?; + + if !ate_colon && consume_colon { + self.error_labeled_expr_must_be_followed_by_colon(lo, expr.span); + } + + Ok(expr) + } + + fn error_labeled_expr_must_be_followed_by_colon(&self, lo: Span, span: Span) { + self.struct_span_err(span, "labeled expression must be followed by `:`") + .span_label(lo, "the label") + .span_suggestion_short( + lo.shrink_to_hi(), + "add `:` after the label", + ": ", + Applicability::MachineApplicable, + ) + .note("labels are used before loops and blocks, allowing e.g., `break 'label` to them") + .emit(); + } + + /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead. + fn recover_do_catch(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + + self.bump(); // `do` + self.bump(); // `catch` + + let span_dc = lo.to(self.prev_token.span); + self.struct_span_err(span_dc, "found removed `do catch` syntax") + .span_suggestion( + span_dc, + "replace with the new syntax", + "try", + Applicability::MachineApplicable, + ) + .note("following RFC #2388, the new non-placeholder syntax is `try`") + .emit(); + + self.parse_try_block(lo, attrs) + } + + /// Parse an expression if the token can begin one. + fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> { + Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None }) + } + + /// Parse `"return" expr?`. + fn parse_return_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let kind = ExprKind::Ret(self.parse_expr_opt()?); + let expr = self.mk_expr(lo.to(self.prev_token.span), kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + /// Parse `"do" "yeet" expr?`. + fn parse_yeet_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + + self.bump(); // `do` + self.bump(); // `yeet` + + let kind = ExprKind::Yeet(self.parse_expr_opt()?); + + let span = lo.to(self.prev_token.span); + self.sess.gated_spans.gate(sym::yeet_expr, span); + let expr = self.mk_expr(span, kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten. + /// If the label is followed immediately by a `:` token, the label and `:` are + /// parsed as part of the expression (i.e. a labeled loop). The language team has + /// decided in #87026 to require parentheses as a visual aid to avoid confusion if + /// the break expression of an unlabeled break is a labeled loop (as in + /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value + /// expression only gets a warning for compatibility reasons; and a labeled break + /// with a labeled loop does not even get a warning because there is no ambiguity. + fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let mut label = self.eat_label(); + let kind = if label.is_some() && self.token == token::Colon { + // The value expression can be a labeled loop, see issue #86948, e.g.: + // `loop { break 'label: loop { break 'label 42; }; }` + let lexpr = self.parse_labeled_expr(label.take().unwrap(), AttrVec::new(), true)?; + self.struct_span_err( + lexpr.span, + "parentheses are required around this expression to avoid confusion with a labeled break expression", + ) + .multipart_suggestion( + "wrap the expression in parentheses", + vec![ + (lexpr.span.shrink_to_lo(), "(".to_string()), + (lexpr.span.shrink_to_hi(), ")".to_string()), + ], + Applicability::MachineApplicable, + ) + .emit(); + Some(lexpr) + } else if self.token != token::OpenDelim(Delimiter::Brace) + || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL) + { + let expr = self.parse_expr_opt()?; + if let Some(ref expr) = expr { + if label.is_some() + && matches!( + expr.kind, + ExprKind::While(_, _, None) + | ExprKind::ForLoop(_, _, _, None) + | ExprKind::Loop(_, None) + | ExprKind::Block(_, None) + ) + { + self.sess.buffer_lint_with_diagnostic( + BREAK_WITH_LABEL_AND_LOOP, + lo.to(expr.span), + ast::CRATE_NODE_ID, + "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression", + BuiltinLintDiagnostics::BreakWithLabelAndLoop(expr.span), + ); + } + } + expr + } else { + None + }; + let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind), attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + /// Parse `"yield" expr?`. + fn parse_yield_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let kind = ExprKind::Yield(self.parse_expr_opt()?); + let span = lo.to(self.prev_token.span); + self.sess.gated_spans.gate(sym::generators, span); + let expr = self.mk_expr(span, kind, attrs); + self.maybe_recover_from_bad_qpath(expr) + } + + /// Returns a string literal if the next token is a string literal. + /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind, + /// and returns `None` if the next token is not literal at all. + pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<Lit>> { + match self.parse_opt_lit() { + Some(lit) => match lit.kind { + ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit { + style, + symbol: lit.token.symbol, + suffix: lit.token.suffix, + span: lit.span, + symbol_unescaped, + }), + _ => Err(Some(lit)), + }, + None => Err(None), + } + } + + pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> { + self.parse_opt_lit().ok_or_else(|| { + if let token::Interpolated(inner) = &self.token.kind { + let expr = match inner.as_ref() { + token::NtExpr(expr) => Some(expr), + token::NtLiteral(expr) => Some(expr), + _ => None, + }; + if let Some(expr) = expr { + if matches!(expr.kind, ExprKind::Err) { + let mut err = self + .diagnostic() + .struct_span_err(self.token.span, "invalid interpolated expression"); + err.downgrade_to_delayed_bug(); + return err; + } + } + } + let msg = format!("unexpected token: {}", super::token_descr(&self.token)); + self.struct_span_err(self.token.span, &msg) + }) + } + + /// Matches `lit = true | false | token_lit`. + /// Returns `None` if the next token is not a literal. + pub(super) fn parse_opt_lit(&mut self) -> Option<Lit> { + let mut recovered = None; + if self.token == token::Dot { + // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where + // dot would follow an optional literal, so we do this unconditionally. + recovered = self.look_ahead(1, |next_token| { + if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = + next_token.kind + { + if self.token.span.hi() == next_token.span.lo() { + let s = String::from("0.") + symbol.as_str(); + let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix); + return Some(Token::new(kind, self.token.span.to(next_token.span))); + } + } + None + }); + if let Some(token) = &recovered { + self.bump(); + self.error_float_lits_must_have_int_part(&token); + } + } + + let token = recovered.as_ref().unwrap_or(&self.token); + match Lit::from_token(token) { + Ok(lit) => { + self.bump(); + Some(lit) + } + Err(LitError::NotLiteral) => None, + Err(err) => { + let span = token.span; + let token::Literal(lit) = token.kind else { + unreachable!(); + }; + self.bump(); + self.report_lit_error(err, lit, span); + // Pack possible quotes and prefixes from the original literal into + // the error literal's symbol so they can be pretty-printed faithfully. + let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None); + let symbol = Symbol::intern(&suffixless_lit.to_string()); + let lit = token::Lit::new(token::Err, symbol, lit.suffix); + Some(Lit::from_lit_token(lit, span).unwrap_or_else(|_| unreachable!())) + } + } + } + + fn error_float_lits_must_have_int_part(&self, token: &Token) { + self.struct_span_err(token.span, "float literals must have an integer part") + .span_suggestion( + token.span, + "must have an integer part", + pprust::token_to_string(token), + Applicability::MachineApplicable, + ) + .emit(); + } + + fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) { + // Checks if `s` looks like i32 or u1234 etc. + fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool { + s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit()) + } + + // Try to lowercase the prefix if it's a valid base prefix. + fn fix_base_capitalisation(s: &str) -> Option<String> { + if let Some(stripped) = s.strip_prefix('B') { + Some(format!("0b{stripped}")) + } else if let Some(stripped) = s.strip_prefix('O') { + Some(format!("0o{stripped}")) + } else if let Some(stripped) = s.strip_prefix('X') { + Some(format!("0x{stripped}")) + } else { + None + } + } + + let token::Lit { kind, suffix, .. } = lit; + match err { + // `NotLiteral` is not an error by itself, so we don't report + // it and give the parser opportunity to try something else. + LitError::NotLiteral => {} + // `LexerError` *is* an error, but it was already reported + // by lexer, so here we don't report it the second time. + LitError::LexerError => {} + LitError::InvalidSuffix => { + self.expect_no_suffix( + span, + &format!("{} {} literal", kind.article(), kind.descr()), + suffix, + ); + } + LitError::InvalidIntSuffix => { + let suf = suffix.expect("suffix error with no suffix"); + let suf = suf.as_str(); + if looks_like_width_suffix(&['i', 'u'], &suf) { + // If it looks like a width, try to be helpful. + let msg = format!("invalid width `{}` for integer literal", &suf[1..]); + self.struct_span_err(span, &msg) + .help("valid widths are 8, 16, 32, 64 and 128") + .emit(); + } else if let Some(fixed) = fix_base_capitalisation(suf) { + let msg = "invalid base prefix for number literal"; + + self.struct_span_err(span, msg) + .note("base prefixes (`0xff`, `0b1010`, `0o755`) are lowercase") + .span_suggestion( + span, + "try making the prefix lowercase", + fixed, + Applicability::MaybeIncorrect, + ) + .emit(); + } else { + let msg = format!("invalid suffix `{suf}` for number literal"); + self.struct_span_err(span, &msg) + .span_label(span, format!("invalid suffix `{suf}`")) + .help("the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)") + .emit(); + } + } + LitError::InvalidFloatSuffix => { + let suf = suffix.expect("suffix error with no suffix"); + let suf = suf.as_str(); + if looks_like_width_suffix(&['f'], suf) { + // If it looks like a width, try to be helpful. + let msg = format!("invalid width `{}` for float literal", &suf[1..]); + self.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit(); + } else { + let msg = format!("invalid suffix `{suf}` for float literal"); + self.struct_span_err(span, &msg) + .span_label(span, format!("invalid suffix `{suf}`")) + .help("valid suffixes are `f32` and `f64`") + .emit(); + } + } + LitError::NonDecimalFloat(base) => { + let descr = match base { + 16 => "hexadecimal", + 8 => "octal", + 2 => "binary", + _ => unreachable!(), + }; + self.struct_span_err(span, &format!("{descr} float literal is not supported")) + .span_label(span, "not supported") + .emit(); + } + LitError::IntTooLarge => { + self.struct_span_err(span, "integer literal is too large").emit(); + } + } + } + + pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) { + if let Some(suf) = suffix { + let mut err = if kind == "a tuple index" + && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf) + { + // #59553: warn instead of reject out of hand to allow the fix to percolate + // through the ecosystem when people fix their macros + let mut err = self + .sess + .span_diagnostic + .struct_span_warn(sp, &format!("suffixes on {kind} are invalid")); + err.note(&format!( + "`{}` is *temporarily* accepted on tuple index fields as it was \ + incorrectly accepted on stable for a few releases", + suf, + )); + err.help( + "on proc macros, you'll want to use `syn::Index::from` or \ + `proc_macro::Literal::*_unsuffixed` for code that will desugar \ + to tuple field access", + ); + err.note( + "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \ + for more information", + ); + err + } else { + self.struct_span_err(sp, &format!("suffixes on {kind} are invalid")) + .forget_guarantee() + }; + err.span_label(sp, format!("invalid suffix `{suf}`")); + err.emit(); + } + } + + /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`). + /// Keep this in sync with `Token::can_begin_literal_maybe_minus`. + pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> { + maybe_whole_expr!(self); + + let lo = self.token.span; + let minus_present = self.eat(&token::BinOp(token::Minus)); + let lit = self.parse_lit()?; + let expr = self.mk_expr(lit.span, ExprKind::Lit(lit), AttrVec::new()); + + if minus_present { + Ok(self.mk_expr( + lo.to(self.prev_token.span), + self.mk_unary(UnOp::Neg, expr), + AttrVec::new(), + )) + } else { + Ok(expr) + } + } + + fn is_array_like_block(&mut self) -> bool { + self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_))) + && self.look_ahead(2, |t| t == &token::Comma) + && self.look_ahead(3, |t| t.can_begin_expr()) + } + + /// Emits a suggestion if it looks like the user meant an array but + /// accidentally used braces, causing the code to be interpreted as a block + /// expression. + fn maybe_suggest_brackets_instead_of_braces( + &mut self, + lo: Span, + attrs: AttrVec, + ) -> Option<P<Expr>> { + let mut snapshot = self.create_snapshot_for_diagnostic(); + match snapshot.parse_array_or_repeat_expr(attrs, Delimiter::Brace) { + Ok(arr) => { + let hi = snapshot.prev_token.span; + self.struct_span_err(arr.span, "this is a block expression, not an array") + .multipart_suggestion( + "to make an array, use square brackets instead of curly braces", + vec![(lo, "[".to_owned()), (hi, "]".to_owned())], + Applicability::MaybeIncorrect, + ) + .emit(); + + self.restore_snapshot(snapshot); + Some(self.mk_expr_err(arr.span)) + } + Err(e) => { + e.cancel(); + None + } + } + } + + /// Parses a block or unsafe block. + pub(super) fn parse_block_expr( + &mut self, + opt_label: Option<Label>, + lo: Span, + blk_mode: BlockCheckMode, + mut attrs: AttrVec, + ) -> PResult<'a, P<Expr>> { + if self.is_array_like_block() { + if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo, attrs.clone()) { + return Ok(arr); + } + } + + if let Some(label) = opt_label { + self.sess.gated_spans.gate(sym::label_break_value, label.ident.span); + } + + if self.token.is_whole_block() { + self.struct_span_err(self.token.span, "cannot use a `block` macro fragment here") + .span_label(lo.to(self.token.span), "the `block` fragment is within this context") + .emit(); + } + + let (inner_attrs, blk) = self.parse_block_common(lo, blk_mode)?; + attrs.extend(inner_attrs); + Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs)) + } + + /// Parse a block which takes no attributes and has no label + fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> { + let blk = self.parse_block()?; + Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())) + } + + /// Parses a closure expression (e.g., `move |args| expr`). + fn parse_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + + let binder = if self.check_keyword(kw::For) { + let lo = self.token.span; + let lifetime_defs = self.parse_late_bound_lifetime_defs()?; + let span = lo.to(self.prev_token.span); + + self.sess.gated_spans.gate(sym::closure_lifetime_binder, span); + + ClosureBinder::For { span, generic_params: P::from_vec(lifetime_defs) } + } else { + ClosureBinder::NotPresent + }; + + let movability = + if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable }; + + let asyncness = if self.token.uninterpolated_span().rust_2018() { + self.parse_asyncness() + } else { + Async::No + }; + + let capture_clause = self.parse_capture_clause()?; + let decl = self.parse_fn_block_decl()?; + let decl_hi = self.prev_token.span; + let mut body = match decl.output { + FnRetTy::Default(_) => { + let restrictions = self.restrictions - Restrictions::STMT_EXPR; + self.parse_expr_res(restrictions, None)? + } + _ => { + // If an explicit return type is given, require a block to appear (RFC 968). + let body_lo = self.token.span; + self.parse_block_expr(None, body_lo, BlockCheckMode::Default, AttrVec::new())? + } + }; + + if let Async::Yes { span, .. } = asyncness { + // Feature-gate `async ||` closures. + self.sess.gated_spans.gate(sym::async_closure, span); + } + + if self.token.kind == TokenKind::Semi + && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _))) + { + // It is likely that the closure body is a block but where the + // braces have been removed. We will recover and eat the next + // statements later in the parsing process. + body = self.mk_expr_err(body.span); + } + + let body_span = body.span; + + let closure = self.mk_expr( + lo.to(body.span), + ExprKind::Closure( + binder, + capture_clause, + asyncness, + movability, + decl, + body, + lo.to(decl_hi), + ), + attrs, + ); + + // Disable recovery for closure body + let spans = + ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span }; + self.current_closure = Some(spans); + + Ok(closure) + } + + /// Parses an optional `move` prefix to a closure-like construct. + fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> { + if self.eat_keyword(kw::Move) { + // Check for `move async` and recover + if self.check_keyword(kw::Async) { + let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo); + Err(self.incorrect_move_async_order_found(move_async_span)) + } else { + Ok(CaptureBy::Value) + } + } else { + Ok(CaptureBy::Ref) + } + } + + /// Parses the `|arg, arg|` header of a closure. + fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> { + let inputs = if self.eat(&token::OrOr) { + Vec::new() + } else { + self.expect(&token::BinOp(token::Or))?; + let args = self + .parse_seq_to_before_tokens( + &[&token::BinOp(token::Or), &token::OrOr], + SeqSep::trailing_allowed(token::Comma), + TokenExpectType::NoExpect, + |p| p.parse_fn_block_param(), + )? + .0; + self.expect_or()?; + args + }; + let output = + self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?; + + Ok(P(FnDecl { inputs, output })) + } + + /// Parses a parameter in a closure header (e.g., `|arg, arg|`). + fn parse_fn_block_param(&mut self) -> PResult<'a, Param> { + let lo = self.token.span; + let attrs = self.parse_outer_attributes()?; + self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| { + let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?; + let ty = if this.eat(&token::Colon) { + this.parse_ty()? + } else { + this.mk_ty(this.prev_token.span, TyKind::Infer) + }; + + Ok(( + Param { + attrs: attrs.into(), + ty, + pat, + span: lo.to(this.token.span), + id: DUMMY_NODE_ID, + is_placeholder: false, + }, + TrailingToken::MaybeComma, + )) + }) + } + + /// Parses an `if` expression (`if` token already eaten). + fn parse_if_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let cond = self.parse_cond_expr()?; + + self.parse_if_after_cond(attrs, lo, cond) + } + + fn parse_if_after_cond( + &mut self, + attrs: AttrVec, + lo: Span, + mut cond: P<Expr>, + ) -> PResult<'a, P<Expr>> { + let cond_span = cond.span; + // Tries to interpret `cond` as either a missing expression if it's a block, + // or as an unfinished expression if it's a binop and the RHS is a block. + // We could probably add more recoveries here too... + let mut recover_block_from_condition = |this: &mut Self| { + let block = match &mut cond.kind { + ExprKind::Binary(Spanned { span: binop_span, .. }, _, right) + if let ExprKind::Block(_, None) = right.kind => { + this.error_missing_if_then_block(lo, cond_span.shrink_to_lo().to(*binop_span), true).emit(); + std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi())) + }, + ExprKind::Block(_, None) => { + this.error_missing_if_cond(lo, cond_span).emit(); + std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi())) + } + _ => { + return None; + } + }; + if let ExprKind::Block(block, _) = &block.kind { + Some(block.clone()) + } else { + unreachable!() + } + }; + // Parse then block + let thn = if self.token.is_keyword(kw::Else) { + if let Some(block) = recover_block_from_condition(self) { + block + } else { + self.error_missing_if_then_block(lo, cond_span, false).emit(); + self.mk_block_err(cond_span.shrink_to_hi()) + } + } else { + let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery. + let block = if self.check(&token::OpenDelim(Delimiter::Brace)) { + self.parse_block()? + } else { + if let Some(block) = recover_block_from_condition(self) { + block + } else { + // Parse block, which will always fail, but we can add a nice note to the error + self.parse_block().map_err(|mut err| { + err.span_note( + cond_span, + "the `if` expression is missing a block after this condition", + ); + err + })? + } + }; + self.error_on_if_block_attrs(lo, false, block.span, &attrs); + block + }; + let els = if self.eat_keyword(kw::Else) { Some(self.parse_else_expr()?) } else { None }; + Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els), attrs)) + } + + fn error_missing_if_then_block( + &self, + if_span: Span, + cond_span: Span, + is_unfinished: bool, + ) -> DiagnosticBuilder<'a, ErrorGuaranteed> { + let mut err = self.struct_span_err( + if_span, + "this `if` expression is missing a block after the condition", + ); + if is_unfinished { + err.span_help(cond_span, "this binary operation is possibly unfinished"); + } else { + err.span_help(cond_span.shrink_to_hi(), "add a block here"); + } + err + } + + fn error_missing_if_cond( + &self, + lo: Span, + span: Span, + ) -> DiagnosticBuilder<'a, ErrorGuaranteed> { + let next_span = self.sess.source_map().next_point(lo); + let mut err = self.struct_span_err(next_span, "missing condition for `if` expression"); + err.span_label(next_span, "expected condition here"); + err.span_label( + self.sess.source_map().start_point(span), + "if this block is the condition of the `if` expression, then it must be followed by another block" + ); + err + } + + /// Parses the condition of a `if` or `while` expression. + fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> { + let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?; + + if let ExprKind::Let(..) = cond.kind { + // Remove the last feature gating of a `let` expression since it's stable. + self.sess.gated_spans.ungate_last(sym::let_chains, cond.span); + } + + Ok(cond) + } + + /// Parses a `let $pat = $expr` pseudo-expression. + fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + // This is a *approximate* heuristic that detects if `let` chains are + // being parsed in the right position. It's approximate because it + // doesn't deny all invalid `let` expressions, just completely wrong usages. + let not_in_chain = !matches!( + self.prev_token.kind, + TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _) + ); + if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain { + self.struct_span_err(self.token.span, "expected expression, found `let` statement") + .emit(); + } + + self.bump(); // Eat `let` token + let lo = self.prev_token.span; + let pat = self.parse_pat_allow_top_alt( + None, + RecoverComma::Yes, + RecoverColon::Yes, + CommaRecoveryMode::LikelyTuple, + )?; + self.expect(&token::Eq)?; + let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| { + this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into()) + })?; + let span = lo.to(expr.span); + self.sess.gated_spans.gate(sym::let_chains, span); + Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span), attrs)) + } + + /// Parses an `else { ... }` expression (`else` token already eaten). + fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> { + let else_span = self.prev_token.span; // `else` + let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery. + let expr = if self.eat_keyword(kw::If) { + self.parse_if_expr(AttrVec::new())? + } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) { + self.parse_simple_block()? + } else { + let snapshot = self.create_snapshot_for_diagnostic(); + let first_tok = super::token_descr(&self.token); + let first_tok_span = self.token.span; + match self.parse_expr() { + Ok(cond) + // If it's not a free-standing expression, and is followed by a block, + // then it's very likely the condition to an `else if`. + if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) + && classify::expr_requires_semi_to_be_stmt(&cond) => + { + self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}")) + .span_label(else_span, "expected an `if` or a block after this `else`") + .span_suggestion( + cond.span.shrink_to_lo(), + "add an `if` if this is the condition of a chained `else if` statement", + "if ", + Applicability::MaybeIncorrect, + ) + .emit(); + self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)? + } + Err(e) => { + e.cancel(); + self.restore_snapshot(snapshot); + self.parse_simple_block()? + }, + Ok(_) => { + self.restore_snapshot(snapshot); + self.parse_simple_block()? + }, + } + }; + self.error_on_if_block_attrs(else_span, true, expr.span, &attrs); + Ok(expr) + } + + fn error_on_if_block_attrs( + &self, + ctx_span: Span, + is_ctx_else: bool, + branch_span: Span, + attrs: &[ast::Attribute], + ) { + let (span, last) = match attrs { + [] => return, + [x0 @ xn] | [x0, .., xn] => (x0.span.to(xn.span), xn.span), + }; + let ctx = if is_ctx_else { "else" } else { "if" }; + self.struct_span_err(last, "outer attributes are not allowed on `if` and `else` branches") + .span_label(branch_span, "the attributes are attached to this branch") + .span_label(ctx_span, format!("the branch belongs to this `{ctx}`")) + .span_suggestion(span, "remove the attributes", "", Applicability::MachineApplicable) + .emit(); + } + + /// Parses `for <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten). + fn parse_for_expr( + &mut self, + opt_label: Option<Label>, + lo: Span, + mut attrs: AttrVec, + ) -> PResult<'a, P<Expr>> { + // Record whether we are about to parse `for (`. + // This is used below for recovery in case of `for ( $stuff ) $block` + // in which case we will suggest `for $stuff $block`. + let begin_paren = match self.token.kind { + token::OpenDelim(Delimiter::Parenthesis) => Some(self.token.span), + _ => None, + }; + + let pat = self.parse_pat_allow_top_alt( + None, + RecoverComma::Yes, + RecoverColon::Yes, + CommaRecoveryMode::LikelyTuple, + )?; + if !self.eat_keyword(kw::In) { + self.error_missing_in_for_loop(); + } + self.check_for_for_in_in_typo(self.prev_token.span); + let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?; + + let pat = self.recover_parens_around_for_head(pat, begin_paren); + + let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?; + attrs.extend(iattrs); + + let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label); + Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs)) + } + + fn error_missing_in_for_loop(&mut self) { + let (span, msg, sugg) = if self.token.is_ident_named(sym::of) { + // Possibly using JS syntax (#75311). + let span = self.token.span; + self.bump(); + (span, "try using `in` here instead", "in") + } else { + (self.prev_token.span.between(self.token.span), "try adding `in` here", " in ") + }; + self.struct_span_err(span, "missing `in` in `for` loop") + .span_suggestion_short( + span, + msg, + sugg, + // Has been misleading, at least in the past (closed Issue #48492). + Applicability::MaybeIncorrect, + ) + .emit(); + } + + /// Parses a `while` or `while let` expression (`while` token already eaten). + fn parse_while_expr( + &mut self, + opt_label: Option<Label>, + lo: Span, + mut attrs: AttrVec, + ) -> PResult<'a, P<Expr>> { + let cond = self.parse_cond_expr().map_err(|mut err| { + err.span_label(lo, "while parsing the condition of this `while` expression"); + err + })?; + let (iattrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| { + err.span_label(lo, "while parsing the body of this `while` expression"); + err.span_label(cond.span, "this `while` condition successfully parsed"); + err + })?; + attrs.extend(iattrs); + Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::While(cond, body, opt_label), attrs)) + } + + /// Parses `loop { ... }` (`loop` token already eaten). + fn parse_loop_expr( + &mut self, + opt_label: Option<Label>, + lo: Span, + mut attrs: AttrVec, + ) -> PResult<'a, P<Expr>> { + let (iattrs, body) = self.parse_inner_attrs_and_block()?; + attrs.extend(iattrs); + Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::Loop(body, opt_label), attrs)) + } + + pub(crate) fn eat_label(&mut self) -> Option<Label> { + self.token.lifetime().map(|ident| { + self.bump(); + Label { ident } + }) + } + + /// Parses a `match ... { ... }` expression (`match` token already eaten). + fn parse_match_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> { + let match_span = self.prev_token.span; + let lo = self.prev_token.span; + let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?; + if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) { + if self.token == token::Semi { + e.span_suggestion_short( + match_span, + "try removing this `match`", + "", + Applicability::MaybeIncorrect, // speculative + ); + } + if self.maybe_recover_unexpected_block_label() { + e.cancel(); + self.bump(); + } else { + return Err(e); + } + } + attrs.extend(self.parse_inner_attributes()?); + + let mut arms: Vec<Arm> = Vec::new(); + while self.token != token::CloseDelim(Delimiter::Brace) { + match self.parse_arm() { + Ok(arm) => arms.push(arm), + Err(mut e) => { + // Recover by skipping to the end of the block. + e.emit(); + self.recover_stmt(); + let span = lo.to(self.token.span); + if self.token == token::CloseDelim(Delimiter::Brace) { + self.bump(); + } + return Ok(self.mk_expr(span, ExprKind::Match(scrutinee, arms), attrs)); + } + } + } + let hi = self.token.span; + self.bump(); + Ok(self.mk_expr(lo.to(hi), ExprKind::Match(scrutinee, arms), attrs)) + } + + /// Attempt to recover from match arm body with statements and no surrounding braces. + fn parse_arm_body_missing_braces( + &mut self, + first_expr: &P<Expr>, + arrow_span: Span, + ) -> Option<P<Expr>> { + if self.token.kind != token::Semi { + return None; + } + let start_snapshot = self.create_snapshot_for_diagnostic(); + let semi_sp = self.token.span; + self.bump(); // `;` + let mut stmts = + vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))]; + let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| { + let span = stmts[0].span.to(stmts[stmts.len() - 1].span); + let mut err = this.struct_span_err(span, "`match` arm body without braces"); + let (these, s, are) = + if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") }; + err.span_label( + span, + &format!( + "{these} statement{s} {are} not surrounded by a body", + these = these, + s = s, + are = are + ), + ); + err.span_label(arrow_span, "while parsing the `match` arm starting here"); + if stmts.len() > 1 { + err.multipart_suggestion( + &format!("surround the statement{s} with a body"), + vec![ + (span.shrink_to_lo(), "{ ".to_string()), + (span.shrink_to_hi(), " }".to_string()), + ], + Applicability::MachineApplicable, + ); + } else { + err.span_suggestion( + semi_sp, + "use a comma to end a `match` arm expression", + ",", + Applicability::MachineApplicable, + ); + } + err.emit(); + this.mk_expr_err(span) + }; + // We might have either a `,` -> `;` typo, or a block without braces. We need + // a more subtle parsing strategy. + loop { + if self.token.kind == token::CloseDelim(Delimiter::Brace) { + // We have reached the closing brace of the `match` expression. + return Some(err(self, stmts)); + } + if self.token.kind == token::Comma { + self.restore_snapshot(start_snapshot); + return None; + } + let pre_pat_snapshot = self.create_snapshot_for_diagnostic(); + match self.parse_pat_no_top_alt(None) { + Ok(_pat) => { + if self.token.kind == token::FatArrow { + // Reached arm end. + self.restore_snapshot(pre_pat_snapshot); + return Some(err(self, stmts)); + } + } + Err(err) => { + err.cancel(); + } + } + + self.restore_snapshot(pre_pat_snapshot); + match self.parse_stmt_without_recovery(true, ForceCollect::No) { + // Consume statements for as long as possible. + Ok(Some(stmt)) => { + stmts.push(stmt); + } + Ok(None) => { + self.restore_snapshot(start_snapshot); + break; + } + // We couldn't parse either yet another statement missing it's + // enclosing block nor the next arm's pattern or closing brace. + Err(stmt_err) => { + stmt_err.cancel(); + self.restore_snapshot(start_snapshot); + break; + } + } + } + None + } + + pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> { + // Used to check the `let_chains` and `if_let_guard` features mostly by scaning + // `&&` tokens. + fn check_let_expr(expr: &Expr) -> (bool, bool) { + match expr.kind { + ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, ref lhs, ref rhs) => { + let lhs_rslt = check_let_expr(lhs); + let rhs_rslt = check_let_expr(rhs); + (lhs_rslt.0 || rhs_rslt.0, false) + } + ExprKind::Let(..) => (true, true), + _ => (false, true), + } + } + let attrs = self.parse_outer_attributes()?; + self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| { + let lo = this.token.span; + let pat = this.parse_pat_allow_top_alt( + None, + RecoverComma::Yes, + RecoverColon::Yes, + CommaRecoveryMode::EitherTupleOrPipe, + )?; + let guard = if this.eat_keyword(kw::If) { + let if_span = this.prev_token.span; + let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?; + let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond); + if has_let_expr { + if does_not_have_bin_op { + // Remove the last feature gating of a `let` expression since it's stable. + this.sess.gated_spans.ungate_last(sym::let_chains, cond.span); + } + let span = if_span.to(cond.span); + this.sess.gated_spans.gate(sym::if_let_guard, span); + } + Some(cond) + } else { + None + }; + let arrow_span = this.token.span; + if let Err(mut err) = this.expect(&token::FatArrow) { + // We might have a `=>` -> `=` or `->` typo (issue #89396). + if TokenKind::FatArrow + .similar_tokens() + .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind)) + { + err.span_suggestion( + this.token.span, + "try using a fat arrow here", + "=>", + Applicability::MaybeIncorrect, + ); + err.emit(); + this.bump(); + } else { + return Err(err); + } + } + let arm_start_span = this.token.span; + + let expr = this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| { + err.span_label(arrow_span, "while parsing the `match` arm starting here"); + err + })?; + + let require_comma = classify::expr_requires_semi_to_be_stmt(&expr) + && this.token != token::CloseDelim(Delimiter::Brace); + + let hi = this.prev_token.span; + + if require_comma { + let sm = this.sess.source_map(); + if let Some(body) = this.parse_arm_body_missing_braces(&expr, arrow_span) { + let span = body.span; + return Ok(( + ast::Arm { + attrs: attrs.into(), + pat, + guard, + body, + span, + id: DUMMY_NODE_ID, + is_placeholder: false, + }, + TrailingToken::None, + )); + } + this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)]) + .or_else(|mut err| { + if this.token == token::FatArrow { + if let Ok(expr_lines) = sm.span_to_lines(expr.span) + && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span) + && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col + && expr_lines.lines.len() == 2 + { + // We check whether there's any trailing code in the parse span, + // if there isn't, we very likely have the following: + // + // X | &Y => "y" + // | -- - missing comma + // | | + // | arrow_span + // X | &X => "x" + // | - ^^ self.token.span + // | | + // | parsed until here as `"y" & X` + err.span_suggestion_short( + arm_start_span.shrink_to_hi(), + "missing a comma here to end this `match` arm", + ",", + Applicability::MachineApplicable, + ); + return Err(err); + } + } else { + // FIXME(compiler-errors): We could also recover `; PAT =>` here + + // Try to parse a following `PAT =>`, if successful + // then we should recover. + let mut snapshot = this.create_snapshot_for_diagnostic(); + let pattern_follows = snapshot + .parse_pat_allow_top_alt( + None, + RecoverComma::Yes, + RecoverColon::Yes, + CommaRecoveryMode::EitherTupleOrPipe, + ) + .map_err(|err| err.cancel()) + .is_ok(); + if pattern_follows && snapshot.check(&TokenKind::FatArrow) { + err.cancel(); + this.struct_span_err( + hi.shrink_to_hi(), + "expected `,` following `match` arm", + ) + .span_suggestion( + hi.shrink_to_hi(), + "missing a comma here to end this `match` arm", + ",", + Applicability::MachineApplicable, + ) + .emit(); + return Ok(true); + } + } + err.span_label(arrow_span, "while parsing the `match` arm starting here"); + Err(err) + })?; + } else { + this.eat(&token::Comma); + } + + Ok(( + ast::Arm { + attrs: attrs.into(), + pat, + guard, + body: expr, + span: lo.to(hi), + id: DUMMY_NODE_ID, + is_placeholder: false, + }, + TrailingToken::None, + )) + }) + } + + /// Parses a `try {...}` expression (`try` token already eaten). + fn parse_try_block(&mut self, span_lo: Span, mut attrs: AttrVec) -> PResult<'a, P<Expr>> { + let (iattrs, body) = self.parse_inner_attrs_and_block()?; + attrs.extend(iattrs); + if self.eat_keyword(kw::Catch) { + let mut error = self.struct_span_err( + self.prev_token.span, + "keyword `catch` cannot follow a `try` block", + ); + error.help("try using `match` on the result of the `try` block instead"); + error.emit(); + Err(error) + } else { + let span = span_lo.to(body.span); + self.sess.gated_spans.gate(sym::try_blocks, span); + Ok(self.mk_expr(span, ExprKind::TryBlock(body), attrs)) + } + } + + fn is_do_catch_block(&self) -> bool { + self.token.is_keyword(kw::Do) + && self.is_keyword_ahead(1, &[kw::Catch]) + && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace)) + && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL) + } + + fn is_do_yeet(&self) -> bool { + self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet]) + } + + fn is_try_block(&self) -> bool { + self.token.is_keyword(kw::Try) + && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace)) + && self.token.uninterpolated_span().rust_2018() + } + + /// Parses an `async move? {...}` expression. + fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + self.expect_keyword(kw::Async)?; + let capture_clause = self.parse_capture_clause()?; + let (iattrs, body) = self.parse_inner_attrs_and_block()?; + attrs.extend(iattrs); + let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body); + Ok(self.mk_expr(lo.to(self.prev_token.span), kind, attrs)) + } + + fn is_async_block(&self) -> bool { + self.token.is_keyword(kw::Async) + && (( + // `async move {` + self.is_keyword_ahead(1, &[kw::Move]) + && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace)) + ) || ( + // `async {` + self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace)) + )) + } + + fn is_certainly_not_a_block(&self) -> bool { + self.look_ahead(1, |t| t.is_ident()) + && ( + // `{ ident, ` cannot start a block. + self.look_ahead(2, |t| t == &token::Comma) + || self.look_ahead(2, |t| t == &token::Colon) + && ( + // `{ ident: token, ` cannot start a block. + self.look_ahead(4, |t| t == &token::Comma) || + // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`. + self.look_ahead(3, |t| !t.can_begin_type()) + ) + ) + } + + fn maybe_parse_struct_expr( + &mut self, + qself: Option<&ast::QSelf>, + path: &ast::Path, + attrs: &AttrVec, + ) -> Option<PResult<'a, P<Expr>>> { + let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL); + if struct_allowed || self.is_certainly_not_a_block() { + if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) { + return Some(Err(err)); + } + let expr = self.parse_struct_expr(qself.cloned(), path.clone(), attrs.clone(), true); + if let (Ok(expr), false) = (&expr, struct_allowed) { + // This is a struct literal, but we don't can't accept them here. + self.error_struct_lit_not_allowed_here(path.span, expr.span); + } + return Some(expr); + } + None + } + + fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) { + self.struct_span_err(sp, "struct literals are not allowed here") + .multipart_suggestion( + "surround the struct literal with parentheses", + vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())], + Applicability::MachineApplicable, + ) + .emit(); + } + + pub(super) fn parse_struct_fields( + &mut self, + pth: ast::Path, + recover: bool, + close_delim: Delimiter, + ) -> PResult<'a, (Vec<ExprField>, ast::StructRest, bool)> { + let mut fields = Vec::new(); + let mut base = ast::StructRest::None; + let mut recover_async = false; + + let mut async_block_err = |e: &mut Diagnostic, span: Span| { + recover_async = true; + e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later"); + e.help_use_latest_edition(); + }; + + while self.token != token::CloseDelim(close_delim) { + if self.eat(&token::DotDot) { + let exp_span = self.prev_token.span; + // We permit `.. }` on the left-hand side of a destructuring assignment. + if self.check(&token::CloseDelim(close_delim)) { + base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi()); + break; + } + match self.parse_expr() { + Ok(e) => base = ast::StructRest::Base(e), + Err(mut e) if recover => { + e.emit(); + self.recover_stmt(); + } + Err(e) => return Err(e), + } + self.recover_struct_comma_after_dotdot(exp_span); + break; + } + + let recovery_field = self.find_struct_error_after_field_looking_code(); + let parsed_field = match self.parse_expr_field() { + Ok(f) => Some(f), + Err(mut e) => { + if pth == kw::Async { + async_block_err(&mut e, pth.span); + } else { + e.span_label(pth.span, "while parsing this struct"); + } + e.emit(); + + // If the next token is a comma, then try to parse + // what comes next as additional fields, rather than + // bailing out until next `}`. + if self.token != token::Comma { + self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore); + if self.token != token::Comma { + break; + } + } + None + } + }; + + let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand); + // A shorthand field can be turned into a full field with `:`. + // We should point this out. + self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon)); + + match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) { + Ok(_) => { + if let Some(f) = parsed_field.or(recovery_field) { + // Only include the field if there's no parse error for the field name. + fields.push(f); + } + } + Err(mut e) => { + if pth == kw::Async { + async_block_err(&mut e, pth.span); + } else { + e.span_label(pth.span, "while parsing this struct"); + if let Some(f) = recovery_field { + fields.push(f); + e.span_suggestion( + self.prev_token.span.shrink_to_hi(), + "try adding a comma", + ",", + Applicability::MachineApplicable, + ); + } else if is_shorthand + && (AssocOp::from_token(&self.token).is_some() + || matches!(&self.token.kind, token::OpenDelim(_)) + || self.token.kind == token::Dot) + { + // Looks like they tried to write a shorthand, complex expression. + let ident = parsed_field.expect("is_shorthand implies Some").ident; + e.span_suggestion( + ident.span.shrink_to_lo(), + "try naming a field", + &format!("{ident}: "), + Applicability::HasPlaceholders, + ); + } + } + if !recover { + return Err(e); + } + e.emit(); + self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore); + self.eat(&token::Comma); + } + } + } + Ok((fields, base, recover_async)) + } + + /// Precondition: already parsed the '{'. + pub(super) fn parse_struct_expr( + &mut self, + qself: Option<ast::QSelf>, + pth: ast::Path, + attrs: AttrVec, + recover: bool, + ) -> PResult<'a, P<Expr>> { + let lo = pth.span; + let (fields, base, recover_async) = + self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?; + let span = lo.to(self.token.span); + self.expect(&token::CloseDelim(Delimiter::Brace))?; + let expr = if recover_async { + ExprKind::Err + } else { + ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base })) + }; + Ok(self.mk_expr(span, expr, attrs)) + } + + /// Use in case of error after field-looking code: `S { foo: () with a }`. + fn find_struct_error_after_field_looking_code(&self) -> Option<ExprField> { + match self.token.ident() { + Some((ident, is_raw)) + if (is_raw || !ident.is_reserved()) + && self.look_ahead(1, |t| *t == token::Colon) => + { + Some(ast::ExprField { + ident, + span: self.token.span, + expr: self.mk_expr_err(self.token.span), + is_shorthand: false, + attrs: AttrVec::new(), + id: DUMMY_NODE_ID, + is_placeholder: false, + }) + } + _ => None, + } + } + + fn recover_struct_comma_after_dotdot(&mut self, span: Span) { + if self.token != token::Comma { + return; + } + self.struct_span_err( + span.to(self.prev_token.span), + "cannot use a comma after the base struct", + ) + .span_suggestion_short( + self.token.span, + "remove this comma", + "", + Applicability::MachineApplicable, + ) + .note("the base struct must always be the last field") + .emit(); + self.recover_stmt(); + } + + /// Parses `ident (COLON expr)?`. + fn parse_expr_field(&mut self) -> PResult<'a, ExprField> { + let attrs = self.parse_outer_attributes()?; + self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| { + let lo = this.token.span; + + // Check if a colon exists one ahead. This means we're parsing a fieldname. + let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq); + let (ident, expr) = if is_shorthand { + // Mimic `x: x` for the `x` field shorthand. + let ident = this.parse_ident_common(false)?; + let path = ast::Path::from_ident(ident); + (ident, this.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new())) + } else { + let ident = this.parse_field_name()?; + this.error_on_eq_field_init(ident); + this.bump(); // `:` + (ident, this.parse_expr()?) + }; + + Ok(( + ast::ExprField { + ident, + span: lo.to(expr.span), + expr, + is_shorthand, + attrs: attrs.into(), + id: DUMMY_NODE_ID, + is_placeholder: false, + }, + TrailingToken::MaybeComma, + )) + }) + } + + /// Check for `=`. This means the source incorrectly attempts to + /// initialize a field with an eq rather than a colon. + fn error_on_eq_field_init(&self, field_name: Ident) { + if self.token != token::Eq { + return; + } + + self.struct_span_err(self.token.span, "expected `:`, found `=`") + .span_suggestion( + field_name.span.shrink_to_hi().to(self.token.span), + "replace equals symbol with a colon", + ":", + Applicability::MachineApplicable, + ) + .emit(); + } + + fn err_dotdotdot_syntax(&self, span: Span) { + self.struct_span_err(span, "unexpected token: `...`") + .span_suggestion( + span, + "use `..` for an exclusive range", + "..", + Applicability::MaybeIncorrect, + ) + .span_suggestion( + span, + "or `..=` for an inclusive range", + "..=", + Applicability::MaybeIncorrect, + ) + .emit(); + } + + fn err_larrow_operator(&self, span: Span) { + self.struct_span_err(span, "unexpected token: `<-`") + .span_suggestion( + span, + "if you meant to write a comparison against a negative value, add a \ + space in between `<` and `-`", + "< -", + Applicability::MaybeIncorrect, + ) + .emit(); + } + + fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind { + ExprKind::AssignOp(binop, lhs, rhs) + } + + fn mk_range( + &mut self, + start: Option<P<Expr>>, + end: Option<P<Expr>>, + limits: RangeLimits, + ) -> ExprKind { + if end.is_none() && limits == RangeLimits::Closed { + self.inclusive_range_with_incorrect_end(self.prev_token.span); + ExprKind::Err + } else { + ExprKind::Range(start, end, limits) + } + } + + fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind { + ExprKind::Unary(unop, expr) + } + + fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind { + ExprKind::Binary(binop, lhs, rhs) + } + + fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind { + ExprKind::Index(expr, idx) + } + + fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind { + ExprKind::Call(f, args) + } + + fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> { + let span = lo.to(self.prev_token.span); + let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), AttrVec::new()); + self.recover_from_await_method_call(); + await_expr + } + + pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> { + P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None }) + } + + pub(super) fn mk_expr_err(&self, span: Span) -> P<Expr> { + self.mk_expr(span, ExprKind::Err, AttrVec::new()) + } + + /// Create expression span ensuring the span of the parent node + /// is larger than the span of lhs and rhs, including the attributes. + fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) -> Span { + lhs.attrs + .iter() + .find(|a| a.style == AttrStyle::Outer) + .map_or(lhs_span, |a| a.span) + .to(rhs_span) + } + + fn collect_tokens_for_expr( + &mut self, + attrs: AttrWrapper, + f: impl FnOnce(&mut Self, Vec<ast::Attribute>) -> PResult<'a, P<Expr>>, + ) -> PResult<'a, P<Expr>> { + self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| { + let res = f(this, attrs)?; + let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR) + && this.token.kind == token::Semi + { + TrailingToken::Semi + } else { + // FIXME - pass this through from the place where we know + // we need a comma, rather than assuming that `#[attr] expr,` + // always captures a trailing comma + TrailingToken::MaybeComma + }; + Ok((res, trailing)) + }) + } +} |