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Diffstat (limited to 'compiler/rustc_parse/src/parser/expr.rs')
| -rw-r--r-- | compiler/rustc_parse/src/parser/expr.rs | 2293 |
1 files changed, 2293 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 00000000000..f022c628fe2 --- /dev/null +++ b/compiler/rustc_parse/src/parser/expr.rs @@ -0,0 +1,2293 @@ +use super::pat::{GateOr, PARAM_EXPECTED}; +use super::ty::{AllowPlus, RecoverQPath}; +use super::{BlockMode, Parser, PathStyle, Restrictions, TokenType}; +use super::{SemiColonMode, SeqSep, TokenExpectType}; +use crate::maybe_recover_from_interpolated_ty_qpath; + +use rustc_ast::ptr::P; +use rustc_ast::token::{self, Token, TokenKind}; +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::{self as ast, AttrStyle, AttrVec, CaptureBy, Field, 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_pretty::pprust; +use rustc_errors::{Applicability, DiagnosticBuilder, PResult}; +use rustc_span::source_map::{self, Span, Spanned}; +use rustc_span::symbol::{kw, sym, Ident, Symbol}; +use std::mem; +use tracing::debug; + +/// 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.token.span, + ExprKind::Path(None, path), + AttrVec::new(), + )); + } + token::NtBlock(block) => { + let block = block.clone(); + $p.bump(); + return Ok($p.mk_expr( + $p.token.span, + ExprKind::Block(block, None), + AttrVec::new(), + )); + } + _ => {} + }; + } + }; +} + +#[derive(Debug)] +pub(super) enum LhsExpr { + NotYetParsed, + AttributesParsed(AttrVec), + AlreadyParsed(P<Expr>), +} + +impl From<Option<AttrVec>> for LhsExpr { + /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)` + /// and `None` into `LhsExpr::NotYetParsed`. + /// + /// This conversion does not allocate. + fn from(o: Option<AttrVec>) -> 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.parse_expr_res(Restrictions::empty(), None) + } + + pub(super) 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<AttrVec>, + ) -> 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<AttrVec>) -> 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); + } + } + + if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual) + && self.token.kind == token::Eq + && self.prev_token.span.hi() == self.token.span.lo() + { + // Look for JS' `===` and `!==` and recover 😇 + 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.to_string(), + Applicability::MachineApplicable, + ) + .emit(); + self.bump(); + } + + 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) + })?; + + // Make sure that the span of the parent node is larger than the span of lhs and rhs, + // including the attributes. + let lhs_span = + lhs.attrs.iter().find(|a| a.style == AttrStyle::Outer).map_or(lhs_span, |a| a.span); + let span = lhs_span.to(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)) => { + // `{ 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. + 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, Some(pprust::expr_to_string(&lhs))); + 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()) { + (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!("`{}` is not a logical operator", bad)) + .span_suggestion_short( + self.token.span, + &format!("use `{}` to perform logical {}", good, english), + good.to_string(), + 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 = lhs.span.to(rhs_span); + let limits = + if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed }; + Ok(self.mk_expr(span, self.mk_range(Some(lhs), rhs, limits)?, 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(token::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<AttrVec>) -> 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); + let attrs = self.parse_or_use_outer_attributes(attrs)?; + let lo = self.token.span; + self.bump(); + let (span, opt_end) = if self.is_at_start_of_range_notation_rhs() { + // RHS must be parsed with more associativity than the dots. + self.parse_assoc_expr_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed) + .map(|x| (lo.to(x.span), Some(x)))? + } else { + (lo, None) + }; + Ok(self.mk_expr(span, self.mk_range(None, opt_end, limits)?, attrs)) + } + + /// Parses a prefix-unary-operator expr. + fn parse_prefix_expr(&mut self, attrs: Option<AttrVec>) -> PResult<'a, P<Expr>> { + let attrs = self.parse_or_use_outer_attributes(attrs)?; + self.maybe_collect_tokens(!attrs.is_empty(), |this| { + let lo = this.token.span; + // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr() + let (hi, ex) = match this.token.uninterpolate().kind { + token::Not => this.parse_unary_expr(lo, UnOp::Not), // `!expr` + token::Tilde => this.recover_tilde_expr(lo), // `~expr` + token::BinOp(token::Minus) => this.parse_unary_expr(lo, UnOp::Neg), // `-expr` + token::BinOp(token::Star) => this.parse_unary_expr(lo, UnOp::Deref), // `*expr` + token::BinOp(token::And) | token::AndAnd => this.parse_borrow_expr(lo), + token::Ident(..) if this.token.is_keyword(kw::Box) => this.parse_box_expr(lo), + token::Ident(..) if this.is_mistaken_not_ident_negation() => { + this.recover_not_expr(lo) + } + _ => return this.parse_dot_or_call_expr(Some(attrs)), + }?; + Ok(this.mk_expr(lo.to(hi), ex, 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", + "!".to_owned(), + 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", + "!".to_owned(), + 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, rhs: P<Ty>| { + this.mk_expr(lhs_span.to(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_ty_no_plus() { + Ok(rhs) => mk_expr(self, rhs), + Err(mut 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); + + 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, self.mk_ty(path.span, TyKind::Path(None, path))); + + let expr_str = self + .span_to_snippet(expr.span) + .unwrap_or_else(|_| pprust::expr_to_string(&expr)); + + 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)) + .span_suggestion( + expr.span, + &format!("try {} the cast value", op_verb), + format!("({})", expr_str), + Applicability::MachineApplicable, + ) + .emit(); + + expr + } + Err(mut 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>> { + // 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 span = cast_expr.span; + 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!( + "casts 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); + // 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 { + 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, + ); + } + 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", + String::new(), + 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<AttrVec>) -> PResult<'a, P<Expr>> { + let attrs = self.parse_or_use_outer_attributes(attrs)?; + let base = self.parse_bottom_expr(); + let (span, base) = self.interpolated_or_expr_span(base)?; + self.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: AttrVec, + ) -> 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; + expr + }) + }) + } + + fn parse_dot_or_call_expr_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> { + loop { + if self.eat(&token::Question) { + // `expr?` + e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e), AttrVec::new()); + continue; + } + if self.eat(&token::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(token::Paren) => self.parse_fn_call_expr(lo, e), + token::OpenDelim(token::Bracket) => self.parse_index_expr(lo, e)?, + _ => return Ok(e), + } + } + } + + 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 and 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 mut components = Vec::new(); + let mut ident_like = String::new(); + for c in float.as_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)); + } + + // FIXME: Make the span more precise. + let span = self.token.span; + match &*components { + // 1e2 + [IdentLike(i)] => { + self.parse_tuple_field_access_expr(lo, base, Symbol::intern(&i), suffix, None) + } + // 1. + [IdentLike(i), Punct('.')] => { + assert!(suffix.is_none()); + let symbol = Symbol::intern(&i); + self.token = Token::new(token::Ident(symbol, false), span); + let next_token = Token::new(token::Dot, span); + self.parse_tuple_field_access_expr(lo, base, symbol, None, Some(next_token)) + } + // 1.2 | 1.2e3 + [IdentLike(i1), Punct('.'), IdentLike(i2)] => { + let symbol1 = Symbol::intern(&i1); + self.token = Token::new(token::Ident(symbol1, false), span); + let next_token1 = Token::new(token::Dot, span); + 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), span); + self.bump_with(next_token2); // `.` + 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+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>, + ) -> 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 seq = self.parse_paren_expr_seq().map(|args| { + self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args), AttrVec::new()) + }); + self.recover_seq_parse_error(token::Paren, lo, seq) + } + + /// 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(token::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 self.mk_await_expr(self_arg, lo); + } + + let fn_span_lo = self.token.span; + let mut segment = self.parse_path_segment(PathStyle::Expr)?; + self.check_trailing_angle_brackets(&segment, &[&token::OpenDelim(token::Paren)]); + self.check_turbofish_missing_angle_brackets(&mut segment); + + if self.check(&token::OpenDelim(token::Paren)) { + // 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 a 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(token::Paren)) { + self.parse_tuple_parens_expr(attrs) + } else if self.check(&token::OpenDelim(token::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) + } else if self.check(&token::OpenDelim(token::Bracket)) { + self.parse_array_or_repeat_expr(attrs) + } else if self.eat_lt() { + let (qself, path) = self.parse_qpath(PathStyle::Expr)?; + Ok(self.mk_expr(lo.to(path.span), ExprKind::Path(Some(qself), path), attrs)) + } 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) { + // NOTE(Centril, eddyb): DO NOT REMOVE! Beyond providing parser recovery, + // this is an insurance policy in case we allow qpaths in (tuple-)struct patterns. + // When `for <Foo as Bar>::Proj in $expr $block` is wanted, + // you can disambiguate in favor of a pattern with `(...)`. + self.recover_quantified_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) + } else if self.eat_keyword(kw::Loop) { + self.parse_loop_expr(None, self.prev_token.span, attrs) + } 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) { + self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs) + } 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.eat_keyword(kw::Let) { + self.parse_let_expr(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 maybe_collect_tokens( + &mut self, + has_outer_attrs: bool, + f: impl FnOnce(&mut Self) -> PResult<'a, P<Expr>>, + ) -> PResult<'a, P<Expr>> { + if has_outer_attrs { + let (mut expr, tokens) = self.collect_tokens(f)?; + debug!("maybe_collect_tokens: Collected tokens for {:?} (tokens {:?}", expr, tokens); + expr.tokens = Some(tokens); + Ok(expr) + } else { + f(self) + } + } + + 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, true) + } + None => self.try_macro_suggestion(), + } + } + + fn parse_tuple_parens_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + self.expect(&token::OpenDelim(token::Paren))?; + attrs.extend(self.parse_inner_attributes()?); // `(#![foo] a, b, ...)` is OK. + let (es, trailing_comma) = match self.parse_seq_to_end( + &token::CloseDelim(token::Paren), + SeqSep::trailing_allowed(token::Comma), + |p| p.parse_expr_catch_underscore(), + ) { + Ok(x) => x, + Err(err) => return Ok(self.recover_seq_parse_error(token::Paren, 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, true) + } + + fn parse_array_or_repeat_expr(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + self.bump(); // `[` + + attrs.extend(self.parse_inner_attributes()?); + + let close = &token::CloseDelim(token::Bracket); + 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, true) + } + + fn parse_path_start_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let path = 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 + 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(token::Brace)) { + if let Some(expr) = self.maybe_parse_struct_expr(&path, &attrs) { + return expr; + } else { + (path.span, ExprKind::Path(None, path)) + } + } else { + (path.span, ExprKind::Path(None, path)) + }; + + let expr = self.mk_expr(lo.to(hi), kind, attrs); + self.maybe_recover_from_bad_qpath(expr, true) + } + + /// Parse `'label: $expr`. The label is already parsed. + fn parse_labeled_expr(&mut self, label: Label, attrs: AttrVec) -> 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(&token::OpenDelim(token::Brace)) || self.token.is_whole_block() { + self.parse_block_expr(label, lo, BlockCheckMode::Default, attrs) + } else { + 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(); + // Continue as an expression in an effort to recover on `'label: non_block_expr`. + self.parse_expr() + }?; + + if !ate_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", + ": ".to_string(), + 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".to_string(), + 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, true) + } + + /// Parse `"('label ":")? break expr?`. + fn parse_break_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let label = self.eat_label(); + let kind = if self.token != token::OpenDelim(token::Brace) + || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL) + { + self.parse_expr_opt()? + } 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, true) + } + + /// 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, true) + } + + /// 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(|| { + 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 lit = match token.kind { + token::Literal(lit) => lit, + _ => 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()) + } + + 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").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 { + let msg = format!("invalid suffix `{}` for integer literal", suf); + self.struct_span_err(span, &msg) + .span_label(span, format!("invalid suffix `{}`", suf)) + .help("the suffix must be one of the integral types (`u32`, `isize`, etc)") + .emit(); + } + } + LitError::InvalidFloatSuffix => { + let suf = suffix.expect("suffix error with no suffix").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 `{}` for float literal", suf); + 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!("{} float literal is not supported", descr)) + .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 {} are invalid", kind)); + 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 {} are invalid", kind)) + }; + 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(super) 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) + } + } + + /// 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 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)) + } + + /// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`. + fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.token.span; + let _ = self.parse_late_bound_lifetime_defs()?; + let span_for = lo.to(self.prev_token.span); + let closure = self.parse_closure_expr(attrs)?; + + self.struct_span_err(span_for, "cannot introduce explicit parameters for a closure") + .span_label(closure.span, "the parameters are attached to this closure") + .span_suggestion( + span_for, + "remove the parameters", + String::new(), + Applicability::MachineApplicable, + ) + .emit(); + + Ok(self.mk_expr_err(lo.to(closure.span))) + } + + /// 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 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 + }; + if let Async::Yes { span, .. } = asyncness { + // Feature-gate `async ||` closures. + self.sess.gated_spans.gate(sym::async_closure, span); + } + + let capture_clause = self.parse_capture_clause(); + let decl = self.parse_fn_block_decl()?; + let decl_hi = self.prev_token.span; + let 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())? + } + }; + + Ok(self.mk_expr( + lo.to(body.span), + ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)), + attrs, + )) + } + + /// Parses an optional `move` prefix to a closure-like construct. + fn parse_capture_clause(&mut self) -> CaptureBy { + if self.eat_keyword(kw::Move) { CaptureBy::Value } else { 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)?; + + 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()?; + let pat = self.parse_pat(PARAM_EXPECTED)?; + let ty = if self.eat(&token::Colon) { + self.parse_ty()? + } else { + self.mk_ty(self.prev_token.span, TyKind::Infer) + }; + Ok(Param { + attrs: attrs.into(), + ty, + pat, + span: lo.to(self.token.span), + id: DUMMY_NODE_ID, + is_placeholder: false, + }) + } + + /// 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()?; + + // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then + // verify that the last statement is either an implicit return (no `;`) or an explicit + // return. This won't catch blocks with an explicit `return`, but that would be caught by + // the dead code lint. + let thn = if self.eat_keyword(kw::Else) || !cond.returns() { + self.error_missing_if_cond(lo, cond.span) + } else { + let attrs = self.parse_outer_attributes()?; // For recovery. + let not_block = self.token != token::OpenDelim(token::Brace); + let block = self.parse_block().map_err(|mut err| { + if not_block { + err.span_label(lo, "this `if` expression has a condition, but no block"); + if let ExprKind::Binary(_, _, ref right) = cond.kind { + if let ExprKind::Block(_, _) = right.kind { + err.help("maybe you forgot the right operand of the 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_cond(&self, lo: Span, span: Span) -> P<ast::Block> { + let sp = self.sess.source_map().next_point(lo); + self.struct_span_err(sp, "missing condition for `if` expression") + .span_label(sp, "expected if condition here") + .emit(); + self.mk_block_err(span) + } + + /// 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, 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. + /// The `let` token has already been eaten. + fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> { + let lo = self.prev_token.span; + let pat = self.parse_top_pat(GateOr::No)?; + self.expect(&token::Eq)?; + let expr = self.with_res(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), attrs)) + } + + /// Parses an `else { ... }` expression (`else` token already eaten). + fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> { + let ctx_span = self.prev_token.span; // `else` + let attrs = self.parse_outer_attributes()?; // For recovery. + let expr = if self.eat_keyword(kw::If) { + self.parse_if_expr(AttrVec::new())? + } else { + let blk = self.parse_block()?; + self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()) + }; + self.error_on_if_block_attrs(ctx_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", + String::new(), + 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(token::Paren) => Some(self.token.span), + _ => None, + }; + + let pat = self.parse_top_pat(GateOr::Yes)?; + 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, &expr, 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.into(), + // 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()?; + let (iattrs, body) = self.parse_inner_attrs_and_block()?; + 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)) + } + + 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(token::Brace)) { + if self.token == token::Semi { + e.span_suggestion_short( + match_span, + "try removing this `match`", + String::new(), + Applicability::MaybeIncorrect, // speculative + ); + } + return Err(e); + } + attrs.extend(self.parse_inner_attributes()?); + + let mut arms: Vec<Arm> = Vec::new(); + while self.token != token::CloseDelim(token::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(token::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)) + } + + pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> { + let attrs = self.parse_outer_attributes()?; + let lo = self.token.span; + let pat = self.parse_top_pat(GateOr::No)?; + let guard = if self.eat_keyword(kw::If) { + let if_span = self.prev_token.span; + let cond = self.parse_expr()?; + 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); + let span = if_span.to(cond.span); + self.sess.gated_spans.gate(sym::if_let_guard, span); + } + Some(cond) + } else { + None + }; + let arrow_span = self.token.span; + self.expect(&token::FatArrow)?; + let arm_start_span = self.token.span; + + let expr = self.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) + && self.token != token::CloseDelim(token::Brace); + + let hi = self.prev_token.span; + + if require_comma { + let sm = self.sess.source_map(); + self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]).map_err( + |mut err| { + match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) { + (Ok(ref expr_lines), Ok(ref arm_start_lines)) + if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col + && expr_lines.lines.len() == 2 + && self.token == token::FatArrow => + { + // 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", + ",".to_owned(), + Applicability::MachineApplicable, + ); + } + _ => { + err.span_label( + arrow_span, + "while parsing the `match` arm starting here", + ); + } + } + err + }, + )?; + } else { + self.eat(&token::Comma); + } + + Ok(ast::Arm { + attrs, + pat, + guard, + body: expr, + span: lo.to(hi), + id: DUMMY_NODE_ID, + is_placeholder: false, + }) + } + + /// 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(token::Brace)) + && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL) + } + + fn is_try_block(&self) -> bool { + self.token.is_keyword(kw::Try) + && self.look_ahead(1, |t| *t == token::OpenDelim(token::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(token::Brace)) + ) || ( + // `async {` + self.look_ahead(1, |t| *t == token::OpenDelim(token::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, + 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() { + // This is a struct literal, but we don't can't accept them here. + let expr = self.parse_struct_expr(path.clone(), attrs.clone()); + if let (Ok(expr), false) = (&expr, struct_allowed) { + 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_expr( + &mut self, + pth: ast::Path, + mut attrs: AttrVec, + ) -> PResult<'a, P<Expr>> { + self.bump(); + let mut fields = Vec::new(); + let mut base = None; + let mut recover_async = false; + + attrs.extend(self.parse_inner_attributes()?); + + let mut async_block_err = |e: &mut DiagnosticBuilder<'_>, span: Span| { + recover_async = true; + e.span_label(span, "`async` blocks are only allowed in the 2018 edition"); + e.help("set `edition = \"2018\"` in `Cargo.toml`"); + e.note("for more on editions, read https://doc.rust-lang.org/edition-guide"); + }; + + while self.token != token::CloseDelim(token::Brace) { + if self.eat(&token::DotDot) { + let exp_span = self.prev_token.span; + match self.parse_expr() { + Ok(e) => base = Some(e), + Err(mut e) => { + e.emit(); + self.recover_stmt(); + } + } + 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_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 + } + }; + + match self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)]) { + 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", + ",".into(), + Applicability::MachineApplicable, + ); + } + } + e.emit(); + self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore); + self.eat(&token::Comma); + } + } + } + + let span = pth.span.to(self.token.span); + self.expect(&token::CloseDelim(token::Brace))?; + let expr = if recover_async { ExprKind::Err } else { ExprKind::Struct(pth, fields, 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<Field> { + match self.token.ident() { + Some((ident, is_raw)) + if (is_raw || !ident.is_reserved()) + && self.look_ahead(1, |t| *t == token::Colon) => + { + Some(ast::Field { + 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", + String::new(), + Applicability::MachineApplicable, + ) + .note("the base struct must always be the last field") + .emit(); + self.recover_stmt(); + } + + /// Parses `ident (COLON expr)?`. + fn parse_field(&mut self) -> PResult<'a, Field> { + let attrs = self.parse_outer_attributes()?.into(); + let lo = self.token.span; + + // Check if a colon exists one ahead. This means we're parsing a fieldname. + let is_shorthand = !self.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 = self.parse_ident_common(false)?; + let path = ast::Path::from_ident(ident); + (ident, self.mk_expr(ident.span, ExprKind::Path(None, path), AttrVec::new())) + } else { + let ident = self.parse_field_name()?; + self.error_on_eq_field_init(ident); + self.bump(); // `:` + (ident, self.parse_expr()?) + }; + Ok(ast::Field { + ident, + span: lo.to(expr.span), + expr, + is_shorthand, + attrs, + id: DUMMY_NODE_ID, + is_placeholder: false, + }) + } + + /// 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", + ":".to_string(), + 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", + "..".to_owned(), + Applicability::MaybeIncorrect, + ) + .span_suggestion( + span, + "or `..=` for an inclusive range", + "..=".to_owned(), + 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 `-`", + "< -".to_string(), + 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( + &self, + start: Option<P<Expr>>, + end: Option<P<Expr>>, + limits: RangeLimits, + ) -> PResult<'a, ExprKind> { + if end.is_none() && limits == RangeLimits::Closed { + self.error_inclusive_range_with_no_end(self.prev_token.span); + Ok(ExprKind::Err) + } else { + Ok(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) -> PResult<'a, 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(); + Ok(await_expr) + } + + 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()) + } +} |