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rust/rust/f9ddd9fdbb2b0df76216dfafebc843e46e7ebd08/./compiler/rustc_parse/src/parser/expr.rs
blob: 35c271cb70204a118334560ca60c92a8c90304f9 [file]
// ignore-tidy-filelength
use core::mem;
use core::ops::{Bound, ControlFlow};
use ast::mut_visit::{self, MutVisitor};
use ast::token::IdentIsRaw;
use ast::{CoroutineKind, ForLoopKind, GenBlockKind, MatchKind, Pat, Path, PathSegment, Recovered};
use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, Token, TokenKind};
use rustc_ast::tokenstream::TokenTree;
use rustc_ast::util::case::Case;
use rustc_ast::util::classify;
use rustc_ast::util::parser::{AssocOp, ExprPrecedence, Fixity, prec_let_scrutinee_needs_par};
use rustc_ast::visit::{Visitor, walk_expr};
use rustc_ast::{
self as ast, AnonConst, Arm, AssignOp, AssignOpKind, AttrStyle, AttrVec, BinOp, BinOpKind,
BlockCheckMode, CaptureBy, ClosureBinder, DUMMY_NODE_ID, Expr, ExprField, ExprKind, FnDecl,
FnRetTy, Guard, Label, MacCall, MetaItemLit, MgcaDisambiguation, Movability, Param,
RangeLimits, StmtKind, Ty, TyKind, UnOp, UnsafeBinderCastKind, YieldKind,
};
use rustc_ast_pretty::pprust;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::{Applicability, Diag, PResult, StashKey, Subdiagnostic};
use rustc_literal_escaper::unescape_char;
use rustc_session::errors::{ExprParenthesesNeeded, report_lit_error};
use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
use rustc_span::edition::Edition;
use rustc_span::{BytePos, ErrorGuaranteed, Ident, Pos, Span, Spanned, Symbol, kw, respan, sym};
use thin_vec::{ThinVec, thin_vec};
use tracing::instrument;
use super::diagnostics::SnapshotParser;
use super::pat::{CommaRecoveryMode, Expected, RecoverColon, RecoverComma};
use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
use super::{
AttrWrapper, BlockMode, ClosureSpans, ExpTokenPair, ForceCollect, Parser, PathStyle,
Restrictions, SemiColonMode, SeqSep, TokenType, Trailing, UsePreAttrPos,
};
use crate::{errors, exp, maybe_recover_from_interpolated_ty_qpath};
#[derive(Debug)]
pub(super) enum DestructuredFloat {
/// 1e2
Single(Symbol, Span),
/// 1.
TrailingDot(Symbol, Span, Span),
/// 1.2 | 1.2e3
MiddleDot(Symbol, Span, Span, Symbol, Span),
/// Invalid
Error,
}
impl<'a> Parser<'a> {
/// Parses an expression.
#[inline]
pub fn parse_expr(&mut self) -> PResult<'a, Box<Expr>> {
self.current_closure.take();
let attrs = self.parse_outer_attributes()?;
self.parse_expr_res(Restrictions::empty(), attrs).map(|res| res.0)
}
/// Parses an expression, forcing tokens to be collected.
pub fn parse_expr_force_collect(&mut self) -> PResult<'a, Box<Expr>> {
self.current_closure.take();
// If the expression is associative (e.g. `1 + 2`), then any preceding
// outer attribute actually belongs to the first inner sub-expression.
// In which case we must use the pre-attr pos to include the attribute
// in the collected tokens for the outer expression.
let pre_attr_pos = self.collect_pos();
let attrs = self.parse_outer_attributes()?;
self.collect_tokens(
Some(pre_attr_pos),
AttrWrapper::empty(),
ForceCollect::Yes,
|this, _empty_attrs| {
let (expr, is_assoc) = this.parse_expr_res(Restrictions::empty(), attrs)?;
let use_pre_attr_pos =
if is_assoc { UsePreAttrPos::Yes } else { UsePreAttrPos::No };
Ok((expr, Trailing::No, use_pre_attr_pos))
},
)
}
pub fn parse_expr_anon_const(
&mut self,
mgca_disambiguation: impl FnOnce(&Self, &Expr) -> MgcaDisambiguation,
) -> PResult<'a, AnonConst> {
self.parse_expr().map(|value| AnonConst {
id: DUMMY_NODE_ID,
mgca_disambiguation: mgca_disambiguation(self, &value),
value,
})
}
fn parse_expr_catch_underscore(
&mut self,
restrictions: Restrictions,
) -> PResult<'a, Box<Expr>> {
let attrs = self.parse_outer_attributes()?;
match self.parse_expr_res(restrictions, attrs) {
Ok((expr, _)) => Ok(expr),
Err(err) => match self.token.ident() {
Some((Ident { name: kw::Underscore, .. }, IdentIsRaw::No))
if self.may_recover() && self.look_ahead(1, |t| t == &token::Comma) =>
{
// Special-case handling of `foo(_, _, _)`
let guar = err.emit();
self.bump();
Ok(self.mk_expr(self.prev_token.span, ExprKind::Err(guar)))
}
_ => Err(err),
},
}
}
/// Parses a sequence of expressions delimited by parentheses.
fn parse_expr_paren_seq(&mut self) -> PResult<'a, ThinVec<Box<Expr>>> {
self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore(Restrictions::empty()))
.map(|(r, _)| r)
}
/// Parses an expression, subject to the given restrictions.
#[inline]
pub(super) fn parse_expr_res(
&mut self,
r: Restrictions,
attrs: AttrWrapper,
) -> PResult<'a, (Box<Expr>, bool)> {
self.with_res(r, |this| this.parse_expr_assoc_with(Bound::Unbounded, attrs))
}
/// Parses an associative expression with operators of at least `min_prec` precedence.
/// The `bool` in the return value indicates if it was an assoc expr, i.e. with an operator
/// followed by a subexpression (e.g. `1 + 2`).
pub(super) fn parse_expr_assoc_with(
&mut self,
min_prec: Bound<ExprPrecedence>,
attrs: AttrWrapper,
) -> PResult<'a, (Box<Expr>, bool)> {
let lhs = if self.token.is_range_separator() {
return self.parse_expr_prefix_range(attrs).map(|res| (res, false));
} else {
self.parse_expr_prefix(attrs)?
};
self.parse_expr_assoc_rest_with(min_prec, false, lhs)
}
/// Parses the rest of an associative expression (i.e. the part after the lhs) with operators
/// of at least `min_prec` precedence. The `bool` in the return value indicates if something
/// was actually parsed.
pub(super) fn parse_expr_assoc_rest_with(
&mut self,
min_prec: Bound<ExprPrecedence>,
starts_stmt: bool,
mut lhs: Box<Expr>,
) -> PResult<'a, (Box<Expr>, bool)> {
let mut parsed_something = false;
if !self.should_continue_as_assoc_expr(&lhs) {
return Ok((lhs, parsed_something));
}
self.expected_token_types.insert(TokenType::Operator);
while let Some(op) = self.check_assoc_op() {
let lhs_span = self.interpolated_or_expr_span(&lhs);
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 match min_prec {
Bound::Included(min_prec) => prec < min_prec,
Bound::Excluded(min_prec) => prec <= min_prec,
Bound::Unbounded => false,
} {
break;
}
// Check for deprecated `...` syntax
if self.token == token::DotDotDot && op.node == AssocOp::Range(RangeLimits::Closed) {
self.err_dotdotdot_syntax(self.token.span);
}
if self.token == token::LArrow {
self.err_larrow_operator(self.token.span);
}
parsed_something = true;
self.bump();
if op.node.is_comparison() {
if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
return Ok((expr, parsed_something));
}
}
// Look for JS' `===` and `!==` and recover
if let AssocOp::Binary(bop @ BinOpKind::Eq | bop @ BinOpKind::Ne) = op.node
&& self.token == token::Eq
&& self.prev_token.span.hi() == self.token.span.lo()
{
let sp = op.span.to(self.token.span);
let sugg = bop.as_str().into();
let invalid = format!("{sugg}=");
self.dcx().emit_err(errors::InvalidComparisonOperator {
span: sp,
invalid: invalid.clone(),
sub: errors::InvalidComparisonOperatorSub::Correctable {
span: sp,
invalid,
correct: sugg,
},
});
self.bump();
}
// Look for PHP's `<>` and recover
if op.node == AssocOp::Binary(BinOpKind::Lt)
&& self.token == token::Gt
&& self.prev_token.span.hi() == self.token.span.lo()
{
let sp = op.span.to(self.token.span);
self.dcx().emit_err(errors::InvalidComparisonOperator {
span: sp,
invalid: "<>".into(),
sub: errors::InvalidComparisonOperatorSub::Correctable {
span: sp,
invalid: "<>".into(),
correct: "!=".into(),
},
});
self.bump();
}
// Look for C++'s `<=>` and recover
if op.node == AssocOp::Binary(BinOpKind::Le)
&& self.token == token::Gt
&& self.prev_token.span.hi() == self.token.span.lo()
{
let sp = op.span.to(self.token.span);
self.dcx().emit_err(errors::InvalidComparisonOperator {
span: sp,
invalid: "<=>".into(),
sub: errors::InvalidComparisonOperatorSub::Spaceship(sp),
});
self.bump();
}
if self.prev_token == token::Plus
&& self.token == 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, starts_stmt)?;
continue;
}
if self.prev_token == token::Minus
&& self.token == token::Minus
&& self.prev_token.span.between(self.token.span).is_empty()
&& !self.look_ahead(1, |tok| tok.can_begin_expr())
{
let op_span = self.prev_token.span.to(self.token.span);
// Eat the second `-`
self.bump();
lhs = self.recover_from_postfix_decrement(lhs, op_span, starts_stmt)?;
continue;
}
let op_span = op.span;
let op = op.node;
// Special cases:
if op == AssocOp::Cast {
lhs = self.parse_assoc_op_cast(lhs, lhs_span, op_span, ExprKind::Cast)?;
continue;
} else if let AssocOp::Range(limits) = op {
// 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_expr_range(prec, lhs, limits, cur_op_span)?;
break;
}
let min_prec = match op.fixity() {
Fixity::Right => Bound::Included(prec),
Fixity::Left | Fixity::None => Bound::Excluded(prec),
};
let (rhs, _) = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
let attrs = this.parse_outer_attributes()?;
this.parse_expr_assoc_with(min_prec, attrs)
})?;
let span = self.mk_expr_sp(&lhs, lhs_span, op_span, rhs.span);
lhs = match op {
AssocOp::Binary(ast_op) => {
let binary = self.mk_binary(respan(cur_op_span, ast_op), lhs, rhs);
self.mk_expr(span, binary)
}
AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span)),
AssocOp::AssignOp(aop) => {
let aopexpr = self.mk_assign_op(respan(cur_op_span, aop), lhs, rhs);
self.mk_expr(span, aopexpr)
}
AssocOp::Cast | AssocOp::Range(_) => {
self.dcx().span_bug(span, "AssocOp should have been handled by special case")
}
};
}
Ok((lhs, parsed_something))
}
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::Binary(
BinOpKind::Mul | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
BinOpKind::Sub | // `{ 42 } -5`
BinOpKind::Add | // `{ 42 } + 42` (unary plus)
BinOpKind::And | // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
BinOpKind::Or | // `{ 42 } || 42` ("logical or" or closure)
BinOpKind::BitOr // `{ 42 } | 42` or `{ 42 } |x| 42`
))) => {
// 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.psess.source_map().start_point(self.token.span);
self.psess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
false
}
(true, Some(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) {
self.dcx().emit_err(errors::FoundExprWouldBeStmt {
span: self.token.span,
token: pprust::token_to_string(&self.token),
suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
});
}
/// 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.
pub(super) 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::Binary(BinOpKind::Shr | BinOpKind::Gt | BinOpKind::Ge)
| AssocOp::AssignOp(AssignOpKind::ShrAssign),
),
_,
) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
return None;
}
// When recovering patterns as expressions, stop parsing when encountering an
// assignment `=`, an alternative `|`, or a range `..`.
(
Some(
AssocOp::Assign
| AssocOp::AssignOp(_)
| AssocOp::Binary(BinOpKind::BitOr)
| AssocOp::Range(_),
),
_,
) if self.restrictions.contains(Restrictions::IS_PAT) => {
return None;
}
(Some(op), _) => (op, self.token.span),
(None, Some((Ident { name: sym::and, span }, IdentIsRaw::No)))
if self.may_recover() =>
{
self.dcx().emit_err(errors::InvalidLogicalOperator {
span: self.token.span,
incorrect: "and".into(),
sub: errors::InvalidLogicalOperatorSub::Conjunction(self.token.span),
});
(AssocOp::Binary(BinOpKind::And), span)
}
(None, Some((Ident { name: sym::or, span }, IdentIsRaw::No))) if self.may_recover() => {
self.dcx().emit_err(errors::InvalidLogicalOperator {
span: self.token.span,
incorrect: "or".into(),
sub: errors::InvalidLogicalOperatorSub::Disjunction(self.token.span),
});
(AssocOp::Binary(BinOpKind::Or), span)
}
_ => return None,
};
Some(respan(span, op))
}
/// 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_is_complete(e)
}
/// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
/// The other two variants are handled in `parse_prefix_range_expr` below.
fn parse_expr_range(
&mut self,
prec: ExprPrecedence,
lhs: Box<Expr>,
limits: RangeLimits,
cur_op_span: Span,
) -> PResult<'a, Box<Expr>> {
let rhs = if self.is_at_start_of_range_notation_rhs() {
let maybe_lt = self.token;
let attrs = self.parse_outer_attributes()?;
Some(
self.parse_expr_assoc_with(Bound::Excluded(prec), attrs)
.map_err(|err| self.maybe_err_dotdotlt_syntax(maybe_lt, err))?
.0,
)
} 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, cur_op_span, rhs_span);
let range = self.mk_range(Some(lhs), rhs, limits);
Ok(self.mk_expr(span, range))
}
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::OpenBrace {
return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
}
true
} else {
false
}
}
/// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
fn parse_expr_prefix_range(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
if !attrs.is_empty() {
let err = errors::DotDotRangeAttribute { span: self.token.span };
self.dcx().emit_err(err);
}
// Check for deprecated `...` syntax.
if self.token == token::DotDotDot {
self.err_dotdotdot_syntax(self.token.span);
}
debug_assert!(
self.token.is_range_separator(),
"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_outer_attributes()?;
self.collect_tokens_for_expr(attrs, |this, attrs| {
let lo = this.token.span;
let maybe_lt = this.look_ahead(1, |t| t.clone());
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.
let attrs = this.parse_outer_attributes()?;
this.parse_expr_assoc_with(Bound::Excluded(op.unwrap().precedence()), attrs)
.map(|(x, _)| (lo.to(x.span), Some(x)))
.map_err(|err| this.maybe_err_dotdotlt_syntax(maybe_lt, err))?
} else {
(lo, None)
};
let range = this.mk_range(None, opt_end, limits);
Ok(this.mk_expr_with_attrs(span, range, attrs))
})
}
/// Parses a prefix-unary-operator expr.
fn parse_expr_prefix(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
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_with_attrs(lo.to(hi), ex, attrs))
})
};
}
let this = self;
// Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
match this.token.uninterpolate().kind {
// `!expr`
token::Bang => make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Not)),
// `~expr`
token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)),
// `-expr`
token::Minus => {
make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Neg))
}
// `*expr`
token::Star => {
make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Deref))
}
// `&expr` and `&&expr`
token::And | token::AndAnd => {
make_it!(this, attrs, |this, _| this.parse_expr_borrow(lo))
}
// `+lit`
token::Plus if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
let mut err = errors::LeadingPlusNotSupported {
span: lo,
remove_plus: None,
add_parentheses: None,
};
// a block on the LHS might have been intended to be an expression instead
if let Some(sp) = this.psess.ambiguous_block_expr_parse.borrow().get(&lo) {
err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
} else {
err.remove_plus = Some(lo);
}
this.dcx().emit_err(err);
this.bump();
let attrs = this.parse_outer_attributes()?;
this.parse_expr_prefix(attrs)
}
// Recover from `++x`:
token::Plus if this.look_ahead(1, |t| *t == token::Plus) => {
let starts_stmt =
this.prev_token == token::Semi || this.prev_token == token::CloseBrace;
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_expr_dot_or_call(attrs)?;
this.recover_from_prefix_increment(operand_expr, pre_span, starts_stmt)
}
token::Ident(..) if this.token.is_keyword(kw::Box) => {
make_it!(this, attrs, |this, _| this.parse_expr_box(lo))
}
token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
}
_ => return this.parse_expr_dot_or_call(attrs),
}
}
fn parse_expr_prefix_common(&mut self, lo: Span) -> PResult<'a, (Span, Box<Expr>)> {
self.bump();
let attrs = self.parse_outer_attributes()?;
let expr = if self.token.is_range_separator() {
self.parse_expr_prefix_range(attrs)
} else {
self.parse_expr_prefix(attrs)
}?;
let span = self.interpolated_or_expr_span(&expr);
Ok((lo.to(span), expr))
}
fn parse_expr_unary(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
let (span, expr) = self.parse_expr_prefix_common(lo)?;
Ok((span, self.mk_unary(op, expr)))
}
/// Recover on `~expr` in favor of `!expr`.
fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
self.dcx().emit_err(errors::TildeAsUnaryOperator(lo));
self.parse_expr_unary(lo, UnOp::Not)
}
/// Parse `box expr` - this syntax has been removed, but we still parse this
/// for now to provide a more useful error
fn parse_expr_box(&mut self, box_kw: Span) -> PResult<'a, (Span, ExprKind)> {
let (span, expr) = self.parse_expr_prefix_common(box_kw)?;
// Make a multipart suggestion instead of `span_to_snippet` in case source isn't available
let box_kw_and_lo = box_kw.until(self.interpolated_or_expr_span(&expr));
let hi = span.shrink_to_hi();
let sugg = errors::AddBoxNew { box_kw_and_lo, hi };
let guar = self.dcx().emit_err(errors::BoxSyntaxRemoved { span, sugg });
Ok((span, ExprKind::Err(guar)))
}
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_metavar_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)> {
let negated_token = self.look_ahead(1, |t| *t);
let sub_diag = if negated_token.is_numeric_lit() {
errors::NotAsNegationOperatorSub::SuggestNotBitwise
} else if negated_token.is_bool_lit() {
errors::NotAsNegationOperatorSub::SuggestNotLogical
} else {
errors::NotAsNegationOperatorSub::SuggestNotDefault
};
self.dcx().emit_err(errors::NotAsNegationOperator {
negated: negated_token.span,
negated_desc: super::token_descr(&negated_token),
// Span the `not` plus trailing whitespace to avoid
// trailing whitespace after the `!` in our suggestion
sub: sub_diag(
self.psess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
),
});
self.parse_expr_unary(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: &Expr) -> Span {
match self.prev_token.kind {
token::NtIdent(..) | token::NtLifetime(..) => self.prev_token.span,
token::CloseInvisible(InvisibleOrigin::MetaVar(_)) => {
// `expr.span` is the interpolated span, because invisible open
// and close delims both get marked with the same span, one
// that covers the entire thing between them. (See
// `rustc_expand::mbe::transcribe::transcribe`.)
self.prev_token.span
}
_ => expr.span,
}
}
fn parse_assoc_op_cast(
&mut self,
lhs: Box<Expr>,
lhs_span: Span,
op_span: Span,
expr_kind: fn(Box<Expr>, Box<Ty>) -> ExprKind,
) -> PResult<'a, Box<Expr>> {
let mk_expr = |this: &mut Self, lhs: Box<Expr>, rhs: Box<Ty>| {
this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, op_span, rhs.span), expr_kind(lhs, rhs))
};
// 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) => {
if !self.may_recover() {
return 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, .. }),
token::Ident(kw::For | kw::Loop | kw::While, IdentIsRaw::No),
) if let [segment] = segments.as_slice() => {
let snapshot = self.create_snapshot_for_diagnostic();
let label = Label {
ident: Ident::from_str_and_span(
&format!("'{}", segment.ident),
segment.ident.span,
),
};
match self.parse_expr_labeled(label, false) {
Ok(expr) => {
type_err.cancel();
self.dcx().emit_err(errors::MalformedLoopLabel {
span: label.ident.span,
suggestion: label.ident.span.shrink_to_lo(),
});
return Ok(expr);
}
Err(err) => {
err.cancel();
self.restore_snapshot(snapshot);
}
}
}
_ => {}
}
match self.parse_path(PathStyle::Expr) {
Ok(path) => {
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.clone())),
);
let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
match self.token.kind {
token::Lt => {
self.dcx().emit_err(errors::ComparisonInterpretedAsGeneric {
comparison: self.token.span,
r#type: pprust::path_to_string(&path),
args: args_span,
suggestion: errors::ComparisonInterpretedAsGenericSugg {
left: expr.span.shrink_to_lo(),
right: expr.span.shrink_to_hi(),
},
})
}
token::Shl => self.dcx().emit_err(errors::ShiftInterpretedAsGeneric {
shift: self.token.span,
r#type: pprust::path_to_string(&path),
args: args_span,
suggestion: errors::ShiftInterpretedAsGenericSugg {
left: expr.span.shrink_to_lo(),
right: expr.span.shrink_to_hi(),
},
}),
_ => {
// 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();
// Keep `x as usize` as an expression in AST and continue parsing.
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);
}
}
}
};
// Try to parse a postfix operator such as `.`, `?`, or index (`[]`)
// after a cast. If one is present, emit an error then return a valid
// parse tree; For something like `&x as T[0]` will be as if it was
// written `((&x) as T)[0]`.
let span = cast_expr.span;
let with_postfix = self.parse_expr_dot_or_call_with(AttrVec::new(), cast_expr, span)?;
// Check if an illegal postfix operator has been added after the cast.
// If the resulting expression is not a cast, it is an illegal postfix operator.
if !matches!(with_postfix.kind, ExprKind::Cast(_, _)) {
let msg = format!(
"cast 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::Use(_, _) => "`.use`",
ExprKind::Yield(YieldKind::Postfix(_)) => "`.yield`",
ExprKind::Match(_, _, MatchKind::Postfix) => "a postfix match",
ExprKind::Err(_) => return Ok(with_postfix),
_ => unreachable!(
"did not expect {:?} as an illegal postfix operator following cast",
with_postfix.kind
),
}
);
let mut err = self.dcx().struct_span_err(span, msg);
let suggest_parens = |err: &mut Diag<'_>| {
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,
);
};
suggest_parens(&mut err);
err.emit();
};
Ok(with_postfix)
}
/// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
fn parse_expr_borrow(&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();
let attrs = self.parse_outer_attributes()?;
let expr = if self.token.is_range_separator() {
self.parse_expr_prefix_range(attrs)
} else {
self.parse_expr_prefix(attrs)
}?;
let hi = 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.until(expr.span));
}
// Add expected tokens if we parsed `&raw` as an expression.
// This will make sure we see "expected `const`, `mut`", and
// guides recovery in case we write `&raw expr`.
if borrow_kind == ast::BorrowKind::Ref
&& mutbl == ast::Mutability::Not
&& matches!(&expr.kind, ExprKind::Path(None, p) if *p == kw::Raw)
{
self.expected_token_types.insert(TokenType::KwMut);
self.expected_token_types.insert(TokenType::KwConst);
}
Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
}
fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
self.dcx().emit_err(errors::LifetimeInBorrowExpression { span, lifetime_span: lt_span });
}
/// Parse `mut?` or `[ raw | pin ] [ const | mut ]`.
fn parse_borrow_modifiers(&mut self) -> (ast::BorrowKind, ast::Mutability) {
if self.check_keyword(exp!(Raw)) && self.look_ahead(1, Token::is_mutability) {
// `raw [ const | mut ]`.
let found_raw = self.eat_keyword(exp!(Raw));
assert!(found_raw);
let mutability = self.parse_mut_or_const().unwrap();
(ast::BorrowKind::Raw, mutability)
} else {
match self.parse_pin_and_mut() {
// `mut?`
(ast::Pinnedness::Not, mutbl) => (ast::BorrowKind::Ref, mutbl),
// `pin [ const | mut ]`.
// `pin` has been gated in `self.parse_pin_and_mut()` so we don't
// need to gate it here.
(ast::Pinnedness::Pinned, mutbl) => (ast::BorrowKind::Pin, mutbl),
}
}
}
/// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
fn parse_expr_dot_or_call(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
self.collect_tokens_for_expr(attrs, |this, attrs| {
let base = this.parse_expr_bottom()?;
let span = this.interpolated_or_expr_span(&base);
this.parse_expr_dot_or_call_with(attrs, base, span)
})
}
pub(super) fn parse_expr_dot_or_call_with(
&mut self,
mut attrs: ast::AttrVec,
mut e: Box<Expr>,
lo: Span,
) -> PResult<'a, Box<Expr>> {
let mut res = ensure_sufficient_stack(|| {
loop {
let has_question =
if self.prev_token == TokenKind::Ident(kw::Return, IdentIsRaw::No) {
// 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(exp!(Question))
};
if has_question {
// `expr?`
e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
continue;
}
let has_dot = if self.prev_token == TokenKind::Ident(kw::Return, IdentIsRaw::No) {
// 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 if self.token == TokenKind::RArrow && self.may_recover() {
// Recovery for `expr->suffix`.
self.bump();
let span = self.prev_token.span;
self.dcx().emit_err(errors::ExprRArrowCall { span });
true
} else {
self.eat(exp!(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::OpenParen => self.parse_expr_fn_call(lo, e),
token::OpenBracket => self.parse_expr_index(lo, e)?,
_ => return Ok(e),
}
}
});
// Stitch the list of outer attributes onto the return value. A little
// bit ugly, but the best way given the current code structure.
if !attrs.is_empty()
&& let Ok(expr) = &mut res
{
mem::swap(&mut expr.attrs, &mut attrs);
expr.attrs.extend(attrs)
}
res
}
pub(super) fn parse_dot_suffix_expr(
&mut self,
lo: Span,
base: Box<Expr>,
) -> PResult<'a, Box<Expr>> {
// At this point we've consumed something like `expr.` and `self.token` holds the token
// after the dot.
match self.token.uninterpolate().kind {
token::Ident(..) => self.parse_dot_suffix(base, lo),
token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
let ident_span = self.token.span;
self.bump();
Ok(self.mk_expr_tuple_field_access(lo, ident_span, base, symbol, suffix))
}
token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
Ok(match self.break_up_float(symbol, self.token.span) {
// 1e2
DestructuredFloat::Single(sym, _sp) => {
// `foo.1e2`: a single complete dot access, fully consumed. We end up with
// the `1e2` token in `self.prev_token` and the following token in
// `self.token`.
let ident_span = self.token.span;
self.bump();
self.mk_expr_tuple_field_access(lo, ident_span, base, sym, suffix)
}
// 1.
DestructuredFloat::TrailingDot(sym, ident_span, dot_span) => {
// `foo.1.`: a single complete dot access and the start of another.
// We end up with the `sym` (`1`) token in `self.prev_token` and a dot in
// `self.token`.
assert!(suffix.is_none());
self.token = Token::new(token::Ident(sym, IdentIsRaw::No), ident_span);
self.bump_with((Token::new(token::Dot, dot_span), self.token_spacing));
self.mk_expr_tuple_field_access(lo, ident_span, base, sym, None)
}
// 1.2 | 1.2e3
DestructuredFloat::MiddleDot(
sym1,
ident1_span,
_dot_span,
sym2,
ident2_span,
) => {
// `foo.1.2` (or `foo.1.2e3`): two complete dot accesses. We end up with
// the `sym2` (`2` or `2e3`) token in `self.prev_token` and the following
// token in `self.token`.
let next_token2 =
Token::new(token::Ident(sym2, IdentIsRaw::No), ident2_span);
self.bump_with((next_token2, self.token_spacing));
self.bump();
let base1 =
self.mk_expr_tuple_field_access(lo, ident1_span, base, sym1, None);
self.mk_expr_tuple_field_access(lo, ident2_span, base1, sym2, suffix)
}
DestructuredFloat::Error => base,
})
}
_ => {
self.error_unexpected_after_dot();
Ok(base)
}
}
}
fn error_unexpected_after_dot(&self) {
let actual = super::token_descr(&self.token);
let span = self.token.span;
let sm = self.psess.source_map();
let (span, actual) = match (&self.token.kind, self.subparser_name) {
(token::Eof, Some(_)) if let Ok(snippet) = sm.span_to_snippet(sm.next_point(span)) => {
(span.shrink_to_hi(), format!("`{}`", snippet))
}
(token::CloseInvisible(InvisibleOrigin::MetaVar(_)), _) => {
// No need to report an error. This case will only occur when parsing a pasted
// metavariable, and we should have emitted an error when parsing the macro call in
// the first place. E.g. in this code:
// ```
// macro_rules! m { ($e:expr) => { $e }; }
//
// fn main() {
// let f = 1;
// m!(f.);
// }
// ```
// we'll get an error "unexpected token: `)` when parsing the `m!(f.)`, so we don't
// want to issue a second error when parsing the expansion `«f.»` (where `«`/`»`
// represent the invisible delimiters).
self.dcx().span_delayed_bug(span, "bad dot expr in metavariable");
return;
}
_ => (span, actual),
};
self.dcx().emit_err(errors::UnexpectedTokenAfterDot { span, actual });
}
/// We need an identifier or integer, but the next token is a float.
/// Break the float into components to extract the identifier or integer.
///
/// See also [`TokenKind::break_two_token_op`] which does similar splitting of `>>` into `>`.
//
// 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).
pub(super) fn break_up_float(&self, float: Symbol, span: Span) -> DestructuredFloat {
#[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 can_take_span_apart =
|| self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
match &*components {
// 1e2
[IdentLike(i)] => {
DestructuredFloat::Single(Symbol::intern(i), span)
}
// 1.
[IdentLike(left), Punct('.')] => {
let (left_span, dot_span) = if can_take_span_apart() {
let left_span = span.with_hi(span.lo() + BytePos::from_usize(left.len()));
let dot_span = span.with_lo(left_span.hi());
(left_span, dot_span)
} else {
(span, span)
};
let left = Symbol::intern(left);
DestructuredFloat::TrailingDot(left, left_span, dot_span)
}
// 1.2 | 1.2e3
[IdentLike(left), Punct('.'), IdentLike(right)] => {
let (left_span, dot_span, right_span) = if can_take_span_apart() {
let left_span = span.with_hi(span.lo() + BytePos::from_usize(left.len()));
let dot_span = span.with_lo(left_span.hi()).with_hi(left_span.hi() + BytePos(1));
let right_span = span.with_lo(dot_span.hi());
(left_span, dot_span, right_span)
} else {
(span, span, span)
};
let left = Symbol::intern(left);
let right = Symbol::intern(right);
DestructuredFloat::MiddleDot(left, left_span, dot_span, right, right_span)
}
// 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();
DestructuredFloat::Error
}
_ => panic!("unexpected components in a float token: {components:?}"),
}
}
/// Parse the field access used in offset_of, matched by `$(e:expr)+`.
/// Currently returns a list of idents. However, it should be possible in
/// future to also do array indices, which might be arbitrary expressions.
pub(crate) fn parse_floating_field_access(&mut self) -> PResult<'a, Vec<Ident>> {
let mut fields = Vec::new();
let mut trailing_dot = None;
loop {
// This is expected to use a metavariable $(args:expr)+, but the builtin syntax
// could be called directly. Calling `parse_expr` allows this function to only
// consider `Expr`s.
let expr = self.parse_expr()?;
let mut current = &expr;
let start_idx = fields.len();
loop {
match current.kind {
ExprKind::Field(ref left, right) => {
// Field access is read right-to-left.
fields.insert(start_idx, right);
trailing_dot = None;
current = left;
}
// Parse this both to give helpful error messages and to
// verify it can be done with this parser setup.
ExprKind::Index(ref left, ref _right, span) => {
self.dcx().emit_err(errors::ArrayIndexInOffsetOf(span));
current = left;
}
ExprKind::Lit(token::Lit {
kind: token::Float | token::Integer,
symbol,
suffix,
}) => {
if let Some(suffix) = suffix {
self.dcx().emit_err(errors::InvalidLiteralSuffixOnTupleIndex {
span: current.span,
suffix,
});
}
match self.break_up_float(symbol, current.span) {
// 1e2
DestructuredFloat::Single(sym, sp) => {
trailing_dot = None;
fields.insert(start_idx, Ident::new(sym, sp));
}
// 1.
DestructuredFloat::TrailingDot(sym, sym_span, dot_span) => {
assert!(suffix.is_none());
trailing_dot = Some(dot_span);
fields.insert(start_idx, Ident::new(sym, sym_span));
}
// 1.2 | 1.2e3
DestructuredFloat::MiddleDot(
symbol1,
span1,
_dot_span,
symbol2,
span2,
) => {
trailing_dot = None;
fields.insert(start_idx, Ident::new(symbol2, span2));
fields.insert(start_idx, Ident::new(symbol1, span1));
}
DestructuredFloat::Error => {
trailing_dot = None;
fields.insert(start_idx, Ident::new(symbol, self.prev_token.span));
}
}
break;
}
ExprKind::Path(None, Path { ref segments, .. }) => {
match &segments[..] {
[PathSegment { ident, args: None, .. }] => {
trailing_dot = None;
fields.insert(start_idx, *ident)
}
_ => {
self.dcx().emit_err(errors::InvalidOffsetOf(current.span));
break;
}
}
break;
}
_ => {
self.dcx().emit_err(errors::InvalidOffsetOf(current.span));
break;
}
}
}
if self.token.kind.close_delim().is_some() || self.token.kind == token::Comma {
break;
} else if trailing_dot.is_none() {
// This loop should only repeat if there is a trailing dot.
self.dcx().emit_err(errors::InvalidOffsetOf(self.token.span));
break;
}
}
if let Some(dot) = trailing_dot {
self.dcx().emit_err(errors::InvalidOffsetOf(dot));
}
Ok(fields.into_iter().collect())
}
fn mk_expr_tuple_field_access(
&self,
lo: Span,
ident_span: Span,
base: Box<Expr>,
field: Symbol,
suffix: Option<Symbol>,
) -> Box<Expr> {
if let Some(suffix) = suffix {
self.dcx()
.emit_err(errors::InvalidLiteralSuffixOnTupleIndex { span: ident_span, suffix });
}
self.mk_expr(lo.to(ident_span), ExprKind::Field(base, Ident::new(field, ident_span)))
}
/// Parse a function call expression, `expr(...)`.
fn parse_expr_fn_call(&mut self, lo: Span, fun: Box<Expr>) -> Box<Expr> {
let snapshot = if self.token == token::OpenParen {
Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
} else {
None
};
let open_paren = self.token.span;
let seq = self
.parse_expr_paren_seq()
.map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
match self.maybe_recover_struct_lit_bad_delims(lo, open_paren, seq, snapshot) {
Ok(expr) => expr,
Err(err) => self.recover_seq_parse_error(exp!(OpenParen), exp!(CloseParen), lo, err),
}
}
/// 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: PResult<'a, Box<Expr>>,
snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
) -> PResult<'a, Box<Expr>> {
match (self.may_recover(), seq, snapshot) {
(true, Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
snapshot.bump(); // `(`
match snapshot.parse_struct_fields(path.clone(), false, exp!(CloseParen)) {
Ok((fields, ..)) if snapshot.eat(exp!(CloseParen)) => {
// 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(close_paren);
// filter shorthand fields
let fields: Vec<_> =
fields.into_iter().filter(|field| !field.is_shorthand).collect();
let guar = if !fields.is_empty() &&
// `token.kind` should not be compared here.
// This is because the `snapshot.token.kind` is treated as the same as
// that of the open delim in `TokenTreesReader::parse_token_tree`, even
// if they are different.
self.span_to_snippet(close_paren).is_ok_and(|snippet| snippet == ")")
{
err.cancel();
let type_str = pprust::path_to_string(&path);
self.dcx()
.create_err(errors::ParenthesesWithStructFields {
span,
braces_for_struct: errors::BracesForStructLiteral {
first: open_paren,
second: close_paren,
r#type: type_str.clone(),
},
no_fields_for_fn: errors::NoFieldsForFnCall {
r#type: type_str,
fields: fields
.into_iter()
.map(|field| field.span.until(field.expr.span))
.collect(),
},
})
.emit()
} else {
err.emit()
};
Ok(self.mk_expr_err(span, guar))
}
Ok(_) => Err(err),
Err(err2) => {
err2.cancel();
Err(err)
}
}
}
(_, seq, _) => seq,
}
}
/// Parse an indexing expression `expr[...]`.
fn parse_expr_index(&mut self, lo: Span, base: Box<Expr>) -> PResult<'a, Box<Expr>> {
let prev_span = self.prev_token.span;
let open_delim_span = self.token.span;
self.bump(); // `[`
let index = self.parse_expr()?;
self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
self.expect(exp!(CloseBracket))?;
Ok(self.mk_expr(
lo.to(self.prev_token.span),
self.mk_index(base, index, open_delim_span.to(self.prev_token.span)),
))
}
/// Assuming we have just parsed `.`, continue parsing into an expression.
fn parse_dot_suffix(&mut self, self_arg: Box<Expr>, lo: Span) -> PResult<'a, Box<Expr>> {
if self.token_uninterpolated_span().at_least_rust_2018() && self.eat_keyword(exp!(Await)) {
return Ok(self.mk_await_expr(self_arg, lo));
}
if self.eat_keyword(exp!(Use)) {
let use_span = self.prev_token.span;
self.psess.gated_spans.gate(sym::ergonomic_clones, use_span);
return Ok(self.mk_use_expr(self_arg, lo));
}
// Post-fix match
if self.eat_keyword(exp!(Match)) {
let match_span = self.prev_token.span;
self.psess.gated_spans.gate(sym::postfix_match, match_span);
return self.parse_match_block(lo, match_span, self_arg, MatchKind::Postfix);
}
// Parse a postfix `yield`.
if self.eat_keyword(exp!(Yield)) {
let yield_span = self.prev_token.span;
self.psess.gated_spans.gate(sym::yield_expr, yield_span);
return Ok(
self.mk_expr(lo.to(yield_span), ExprKind::Yield(YieldKind::Postfix(self_arg)))
);
}
let fn_span_lo = self.token.span;
let mut seg = self.parse_path_segment(PathStyle::Expr, None)?;
self.check_trailing_angle_brackets(&seg, &[exp!(OpenParen)]);
self.check_turbofish_missing_angle_brackets(&mut seg);
if self.check(exp!(OpenParen)) {
// Method call `expr.f()`
let args = self.parse_expr_paren_seq()?;
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(Box::new(ast::MethodCall {
seg,
receiver: self_arg,
args,
span: fn_span,
})),
))
} else {
// Field access `expr.f`
let span = lo.to(self.prev_token.span);
if let Some(args) = seg.args {
// See `StashKey::GenericInFieldExpr` for more info on why we stash this.
self.dcx()
.create_err(errors::FieldExpressionWithGeneric(args.span()))
.stash(seg.ident.span, StashKey::GenericInFieldExpr);
}
Ok(self.mk_expr(span, ExprKind::Field(self_arg, seg.ident)))
}
}
/// 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_expr_dot_or_call`.
fn parse_expr_bottom(&mut self) -> PResult<'a, Box<Expr>> {
maybe_recover_from_interpolated_ty_qpath!(self, true);
let span = self.token.span;
if let Some(expr) = self.eat_metavar_seq_with_matcher(
|mv_kind| matches!(mv_kind, MetaVarKind::Expr { .. }),
|this| {
// Force collection (as opposed to just `parse_expr`) is required to avoid the
// attribute duplication seen in #138478.
let expr = this.parse_expr_force_collect();
// FIXME(nnethercote) Sometimes with expressions we get a trailing comma, possibly
// related to the FIXME in `collect_tokens_for_expr`. Examples are the multi-line
// `assert_eq!` calls involving arguments annotated with `#[rustfmt::skip]` in
// `compiler/rustc_index/src/bit_set/tests.rs`.
if this.token.kind == token::Comma {
this.bump();
}
expr
},
) {
return Ok(expr);
} else if let Some(lit) =
self.eat_metavar_seq(MetaVarKind::Literal, |this| this.parse_literal_maybe_minus())
{
return Ok(lit);
} else if let Some(block) =
self.eat_metavar_seq(MetaVarKind::Block, |this| this.parse_block())
{
return Ok(self.mk_expr(span, ExprKind::Block(block, None)));
} else if let Some(path) =
self.eat_metavar_seq(MetaVarKind::Path, |this| this.parse_path(PathStyle::Type))
{
return Ok(self.mk_expr(span, ExprKind::Path(None, path)));
}
// Outer attributes are already parsed and will be
// added to the return value after the fact.
let restrictions = self.restrictions;
self.with_res(restrictions - Restrictions::ALLOW_LET, |this| {
// Note: adding new syntax here? Don't forget to adjust `TokenKind::can_begin_expr()`.
let lo = this.token.span;
if let token::Literal(_) = this.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.
this.parse_expr_lit()
} else if this.check(exp!(OpenParen)) {
this.parse_expr_tuple_parens(restrictions)
} else if this.check(exp!(OpenBrace)) {
if let Some(expr) = this.maybe_recover_bad_struct_literal_path(false)? {
return Ok(expr);
}
this.parse_expr_block(None, lo, BlockCheckMode::Default)
} else if this.check(exp!(Or)) || this.check(exp!(OrOr)) {
this.parse_expr_closure().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) = this.psess.ambiguous_block_expr_parse.borrow().get(&lo) {
err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
}
err
})
} else if this.check(exp!(OpenBracket)) {
this.parse_expr_array_or_repeat(exp!(CloseBracket))
} else if this.is_builtin() {
this.parse_expr_builtin()
} else if this.check_path() {
this.parse_expr_path_start()
} else if this.check_keyword(exp!(Move))
|| this.check_keyword(exp!(Use))
|| this.check_keyword(exp!(Static))
|| this.check_const_closure()
{
this.parse_expr_closure()
} else if this.eat_keyword(exp!(If)) {
this.parse_expr_if()
} else if this.check_keyword(exp!(For)) {
if this.choose_generics_over_qpath(1) {
this.parse_expr_closure()
} else {
assert!(this.eat_keyword(exp!(For)));
this.parse_expr_for(None, lo)
}
} else if this.eat_keyword(exp!(While)) {
this.parse_expr_while(None, lo)
} else if let Some(label) = this.eat_label() {
this.parse_expr_labeled(label, true)
} else if this.eat_keyword(exp!(Loop)) {
this.parse_expr_loop(None, lo).map_err(|mut err| {
err.span_label(lo, "while parsing this `loop` expression");
err
})
} else if this.eat_keyword(exp!(Match)) {
this.parse_expr_match().map_err(|mut err| {
err.span_label(lo, "while parsing this `match` expression");
err
})
} else if this.eat_keyword(exp!(Unsafe)) {
this.parse_expr_block(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
|mut err| {
err.span_label(lo, "while parsing this `unsafe` expression");
err
},
)
} else if this.check_inline_const(0) {
this.parse_const_block(lo, false)
} else if this.may_recover() && this.is_do_catch_block() {
this.recover_do_catch()
} else if this.is_try_block() {
this.expect_keyword(exp!(Try))?;
this.parse_try_block(lo)
} else if this.eat_keyword(exp!(Return)) {
this.parse_expr_return()
} else if this.eat_keyword(exp!(Continue)) {
this.parse_expr_continue(lo)
} else if this.eat_keyword(exp!(Break)) {
this.parse_expr_break()
} else if this.eat_keyword(exp!(Yield)) {
this.parse_expr_yield()
} else if this.is_do_yeet() {
this.parse_expr_yeet()
} else if this.eat_keyword(exp!(Become)) {
this.parse_expr_become()
} else if this.check_keyword(exp!(Let)) {
this.parse_expr_let(restrictions)
} else if this.eat_keyword(exp!(Underscore)) {
if let Some(expr) = this.maybe_recover_bad_struct_literal_path(true)? {
return Ok(expr);
}
Ok(this.mk_expr(this.prev_token.span, ExprKind::Underscore))
} else if this.token_uninterpolated_span().at_least_rust_2018() {
// `Span::at_least_rust_2018()` is somewhat expensive; don't get it repeatedly.
let at_async = this.check_keyword(exp!(Async));
// check for `gen {}` and `gen move {}`
// or `async gen {}` and `async gen move {}`
// FIXME: (async) gen closures aren't yet parsed.
// FIXME(gen_blocks): Parse `gen async` and suggest swap
if this.token_uninterpolated_span().at_least_rust_2024()
&& this.is_gen_block(kw::Gen, at_async as usize)
{
this.parse_gen_block()
// Check for `async {` and `async move {`,
} else if this.is_gen_block(kw::Async, 0) {
this.parse_gen_block()
} else if at_async {
this.parse_expr_closure()
} else if this.eat_keyword_noexpect(kw::Await) {
this.recover_incorrect_await_syntax(lo)
} else {
this.parse_expr_lit()
}
} else {
this.parse_expr_lit()
}
})
}
fn parse_expr_lit(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
match self.parse_opt_token_lit() {
Some((token_lit, _)) => {
let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(token_lit));
self.maybe_recover_from_bad_qpath(expr)
}
None => self.try_macro_suggestion(),
}
}
fn parse_expr_tuple_parens(&mut self, restrictions: Restrictions) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
self.expect(exp!(OpenParen))?;
let (es, trailing_comma) = match self.parse_seq_to_end(
exp!(CloseParen),
SeqSep::trailing_allowed(exp!(Comma)),
|p| p.parse_expr_catch_underscore(restrictions.intersection(Restrictions::ALLOW_LET)),
) {
Ok(x) => x,
Err(err) => {
return Ok(self.recover_seq_parse_error(
exp!(OpenParen),
exp!(CloseParen),
lo,
err,
));
}
};
let kind = if es.len() == 1 && matches!(trailing_comma, Trailing::No) {
// `(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);
self.maybe_recover_from_bad_qpath(expr)
}
fn parse_expr_array_or_repeat(&mut self, close: ExpTokenPair) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
self.bump(); // `[` or other open delim
let kind = if self.eat(close) {
// Empty vector
ExprKind::Array(ThinVec::new())
} else {
// Non-empty vector
let first_expr = self.parse_expr()?;
if self.eat(exp!(Semi)) {
// Repeating array syntax: `[ 0; 512 ]`
let count = self.parse_expr_anon_const(|_, _| MgcaDisambiguation::Direct)?;
self.expect(close)?;
ExprKind::Repeat(first_expr, count)
} else if self.eat(exp!(Comma)) {
// Vector with two or more elements.
let sep = SeqSep::trailing_allowed(exp!(Comma));
let (mut exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
exprs.insert(0, first_expr);
ExprKind::Array(exprs)
} else {
// Vector with one element
self.expect(close)?;
ExprKind::Array(thin_vec![first_expr])
}
};
let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
self.maybe_recover_from_bad_qpath(expr)
}
fn parse_expr_path_start(&mut self) -> PResult<'a, Box<Expr>> {
let maybe_eq_tok = self.prev_token;
let (qself, path) = if self.eat_lt() {
let lt_span = self.prev_token.span;
let (qself, path) = self.parse_qpath(PathStyle::Expr).map_err(|mut err| {
// Suggests using '<=' if there is an error parsing qpath when the previous token
// is an '=' token. Only emits suggestion if the '<' token and '=' token are
// directly adjacent (i.e. '=<')
if maybe_eq_tok == TokenKind::Eq && maybe_eq_tok.span.hi() == lt_span.lo() {
let eq_lt = maybe_eq_tok.span.to(lt_span);
err.span_suggestion(eq_lt, "did you mean", "<=", Applicability::Unspecified);
}
err
})?;
(Some(qself), path)
} else {
(None, self.parse_path(PathStyle::Expr)?)
};
// `!`, as an operator, is prefix, so we know this isn't that.
let (span, kind) = if self.eat(exp!(Bang)) {
// MACRO INVOCATION expression
if qself.is_some() {
self.dcx().emit_err(errors::MacroInvocationWithQualifiedPath(path.span));
}
let lo = path.span;
let mac = Box::new(MacCall { path, args: self.parse_delim_args()? });
(lo.to(self.prev_token.span), ExprKind::MacCall(mac))
} else if self.check(exp!(OpenBrace))
&& let Some(expr) = self.maybe_parse_struct_expr(&qself, &path)
{
if qself.is_some() {
self.psess.gated_spans.gate(sym::more_qualified_paths, path.span);
}
return expr;
} else {
(path.span, ExprKind::Path(qself, path))
};
let expr = self.mk_expr(span, kind);
self.maybe_recover_from_bad_qpath(expr)
}
/// Parse `'label: $expr`. The label is already parsed.
pub(super) fn parse_expr_labeled(
&mut self,
label_: Label,
mut consume_colon: bool,
) -> PResult<'a, Box<Expr>> {
let lo = label_.ident.span;
let label = Some(label_);
let ate_colon = self.eat(exp!(Colon));
let tok_sp = self.token.span;
let expr = if self.eat_keyword(exp!(While)) {
self.parse_expr_while(label, lo)
} else if self.eat_keyword(exp!(For)) {
self.parse_expr_for(label, lo)
} else if self.eat_keyword(exp!(Loop)) {
self.parse_expr_loop(label, lo)
} else if self.check_noexpect(&token::OpenBrace) || self.token.is_metavar_block() {
self.parse_expr_block(label, lo, BlockCheckMode::Default)
} else if !ate_colon
&& self.may_recover()
&& (self.token.kind.close_delim().is_some() || self.token.is_punct())
&& could_be_unclosed_char_literal(label_.ident)
{
let (lit, _) =
self.recover_unclosed_char(label_.ident, Parser::mk_token_lit_char, |self_| {
self_.dcx().create_err(errors::UnexpectedTokenAfterLabel {
span: self_.token.span,
remove_label: None,
enclose_in_block: None,
})
});
consume_colon = false;
Ok(self.mk_expr(lo, ExprKind::Lit(lit)))
} 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 guar = self.dcx().emit_err(errors::UnexpectedTokenAfterLabel {
span: self.token.span,
remove_label: None,
enclose_in_block: None,
});
consume_colon = false;
Ok(self.mk_expr_err(lo, guar))
} else {
let mut err = errors::UnexpectedTokenAfterLabel {
span: self.token.span,
remove_label: None,
enclose_in_block: None,
};
// 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;
impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
type Result = ControlFlow<()>;
fn visit_expr(&mut self, ex: &'ast Expr) -> ControlFlow<()> {
if let ExprKind::Break(Some(_label), _) = ex.kind {
ControlFlow::Break(())
} else {
walk_expr(self, ex)
}
}
}
FindLabeledBreaksVisitor.visit_expr(&expr).is_break()
};
// Suggestion involves adding a 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 {
err.remove_label = Some(lo.until(span));
return expr;
}
err.enclose_in_block = Some(errors::UnexpectedTokenAfterLabelSugg {
left: span.shrink_to_lo(),
right: span.shrink_to_hi(),
});
// Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
let blk = self.mk_block(thin_vec![stmt], BlockCheckMode::Default, span);
self.mk_expr(span, ExprKind::Block(blk, label))
});
self.dcx().emit_err(err);
expr
}?;
if !ate_colon && consume_colon {
self.dcx().emit_err(errors::RequireColonAfterLabeledExpression {
span: expr.span,
label: lo,
label_end: lo.between(tok_sp),
});
}
Ok(expr)
}
/// Emit an error when a char is parsed as a lifetime or label because of a missing quote.
pub(super) fn recover_unclosed_char<L>(
&self,
ident: Ident,
mk_lit_char: impl FnOnce(Symbol, Span) -> L,
err: impl FnOnce(&Self) -> Diag<'a>,
) -> L {
assert!(could_be_unclosed_char_literal(ident));
self.dcx()
.try_steal_modify_and_emit_err(ident.span, StashKey::LifetimeIsChar, |err| {
err.span_suggestion_verbose(
ident.span.shrink_to_hi(),
"add `'` to close the char literal",
"'",
Applicability::MaybeIncorrect,
);
})
.unwrap_or_else(|| {
err(self)
.with_span_suggestion_verbose(
ident.span.shrink_to_hi(),
"add `'` to close the char literal",
"'",
Applicability::MaybeIncorrect,
)
.emit()
});
let name = ident.without_first_quote().name;
mk_lit_char(name, ident.span)
}
/// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
fn recover_do_catch(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
self.bump(); // `do`
self.bump(); // `catch`
let span = lo.to(self.prev_token.span);
self.dcx().emit_err(errors::DoCatchSyntaxRemoved { span });
self.parse_try_block(lo)
}
/// Parse an expression if the token can begin one.
fn parse_expr_opt(&mut self) -> PResult<'a, Option<Box<Expr>>> {
Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
}
/// Parse `"return" expr?`.
fn parse_expr_return(&mut self) -> PResult<'a, Box<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);
self.maybe_recover_from_bad_qpath(expr)
}
/// Parse `"do" "yeet" expr?`.
fn parse_expr_yeet(&mut self) -> PResult<'a, Box<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.psess.gated_spans.gate(sym::yeet_expr, span);
let expr = self.mk_expr(span, kind);
self.maybe_recover_from_bad_qpath(expr)
}
/// Parse `"become" expr`, with `"become"` token already eaten.
fn parse_expr_become(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.prev_token.span;
let kind = ExprKind::Become(self.parse_expr()?);
let span = lo.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::explicit_tail_calls, span);
let expr = self.mk_expr(span, kind);
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_expr_break(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.prev_token.span;
let mut label = self.eat_label();
let kind = if self.token == token::Colon
&& let Some(label) = label.take()
{
// The value expression can be a labeled loop, see issue #86948, e.g.:
// `loop { break 'label: loop { break 'label 42; }; }`
let lexpr = self.parse_expr_labeled(label, true)?;
self.dcx().emit_err(errors::LabeledLoopInBreak {
span: lexpr.span,
sub: errors::WrapInParentheses::Expression {
left: lexpr.span.shrink_to_lo(),
right: lexpr.span.shrink_to_hi(),
},
});
Some(lexpr)
} else if self.token != token::OpenBrace
|| !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
{
let mut expr = self.parse_expr_opt()?;
if let Some(expr) = &mut expr {
if label.is_some()
&& match &expr.kind {
ExprKind::While(_, _, None)
| ExprKind::ForLoop { label: None, .. }
| ExprKind::Loop(_, None, _) => true,
ExprKind::Block(block, None) => {
matches!(block.rules, BlockCheckMode::Default)
}
_ => false,
}
{
let span = expr.span;
self.psess.buffer_lint(
BREAK_WITH_LABEL_AND_LOOP,
lo.to(expr.span),
ast::CRATE_NODE_ID,
errors::BreakWithLabelAndLoop {
sub: errors::BreakWithLabelAndLoopSub {
left: span.shrink_to_lo(),
right: span.shrink_to_hi(),
},
},
);
}
// Recover `break label aaaaa`
if self.may_recover()
&& let ExprKind::Path(None, p) = &expr.kind
&& let [segment] = &*p.segments
&& let &ast::PathSegment { ident, args: None, .. } = segment
&& let Some(next) = self.parse_expr_opt()?
{
label = Some(self.recover_ident_into_label(ident));
*expr = next;
}
}
expr
} else {
None
};
let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
self.maybe_recover_from_bad_qpath(expr)
}
/// Parse `"continue" label?`.
fn parse_expr_continue(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
let mut label = self.eat_label();
// Recover `continue label` -> `continue 'label`
if self.may_recover()
&& label.is_none()
&& let Some((ident, _)) = self.token.ident()
{
self.bump();
label = Some(self.recover_ident_into_label(ident));
}
let kind = ExprKind::Continue(label);
Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
}
/// Parse `"yield" expr?`.
fn parse_expr_yield(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.prev_token.span;
let kind = ExprKind::Yield(YieldKind::Prefix(self.parse_expr_opt()?));
let span = lo.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::yield_expr, span);
let expr = self.mk_expr(span, kind);
self.maybe_recover_from_bad_qpath(expr)
}
/// Parse `builtin # ident(args,*)`.
fn parse_expr_builtin(&mut self) -> PResult<'a, Box<Expr>> {
self.parse_builtin(|this, lo, ident| {
Ok(match ident.name {
sym::offset_of => Some(this.parse_expr_offset_of(lo)?),
sym::type_ascribe => Some(this.parse_expr_type_ascribe(lo)?),
sym::wrap_binder => {
Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Wrap)?)
}
sym::unwrap_binder => {
Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Unwrap)?)
}
_ => None,
})
})
}
pub(crate) fn parse_builtin<T>(
&mut self,
parse: impl FnOnce(&mut Parser<'a>, Span, Ident) -> PResult<'a, Option<T>>,
) -> PResult<'a, T> {
let lo = self.token.span;
self.bump(); // `builtin`
self.bump(); // `#`
let Some((ident, IdentIsRaw::No)) = self.token.ident() else {
let err = self.dcx().create_err(errors::ExpectedBuiltinIdent { span: self.token.span });
return Err(err);
};
self.psess.gated_spans.gate(sym::builtin_syntax, ident.span);
self.bump();
self.expect(exp!(OpenParen))?;
let ret = if let Some(res) = parse(self, lo, ident)? {
Ok(res)
} else {
let err = self.dcx().create_err(errors::UnknownBuiltinConstruct {
span: lo.to(ident.span),
name: ident,
});
return Err(err);
};
self.expect(exp!(CloseParen))?;
ret
}
/// Built-in macro for `offset_of!` expressions.
pub(crate) fn parse_expr_offset_of(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
let container = self.parse_ty()?;
self.expect(exp!(Comma))?;
let fields = self.parse_floating_field_access()?;
let trailing_comma = self.eat_noexpect(&TokenKind::Comma);
if let Err(mut e) = self.expect_one_of(&[], &[exp!(CloseParen)]) {
if trailing_comma {
e.note("unexpected third argument to offset_of");
} else {
e.note("offset_of expects dot-separated field and variant names");
}
e.emit();
}
// Eat tokens until the macro call ends.
if self.may_recover() {
while !self.token.kind.is_close_delim_or_eof() {
self.bump();
}
}
let span = lo.to(self.token.span);
Ok(self.mk_expr(span, ExprKind::OffsetOf(container, fields)))
}
/// Built-in macro for type ascription expressions.
pub(crate) fn parse_expr_type_ascribe(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
let expr = self.parse_expr()?;
self.expect(exp!(Comma))?;
let ty = self.parse_ty()?;
let span = lo.to(self.token.span);
Ok(self.mk_expr(span, ExprKind::Type(expr, ty)))
}
pub(crate) fn parse_expr_unsafe_binder_cast(
&mut self,
lo: Span,
kind: UnsafeBinderCastKind,
) -> PResult<'a, Box<Expr>> {
let expr = self.parse_expr()?;
let ty = if self.eat(exp!(Comma)) { Some(self.parse_ty()?) } else { None };
let span = lo.to(self.token.span);
Ok(self.mk_expr(span, ExprKind::UnsafeBinderCast(kind, expr, ty)))
}
/// 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<MetaItemLit>> {
match self.parse_opt_meta_item_lit() {
Some(lit) => match lit.kind {
ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
style,
symbol: lit.symbol,
suffix: lit.suffix,
span: lit.span,
symbol_unescaped,
}),
_ => Err(Some(lit)),
},
None => Err(None),
}
}
pub(crate) fn mk_token_lit_char(name: Symbol, span: Span) -> (token::Lit, Span) {
(token::Lit { symbol: name, suffix: None, kind: token::Char }, span)
}
fn mk_meta_item_lit_char(name: Symbol, span: Span) -> MetaItemLit {
ast::MetaItemLit {
symbol: name,
suffix: None,
kind: ast::LitKind::Char(name.as_str().chars().next().unwrap_or('_')),
span,
}
}
fn handle_missing_lit<L>(
&mut self,
mk_lit_char: impl FnOnce(Symbol, Span) -> L,
) -> PResult<'a, L> {
let token = self.token;
let err = |self_: &Self| {
let msg = format!("unexpected token: {}", super::token_descr(&token));
self_.dcx().struct_span_err(token.span, msg)
};
// On an error path, eagerly consider a lifetime to be an unclosed character lit, if that
// makes sense.
if let Some((ident, IdentIsRaw::No)) = self.token.lifetime()
&& could_be_unclosed_char_literal(ident)
{
let lt = self.expect_lifetime();
Ok(self.recover_unclosed_char(lt.ident, mk_lit_char, err))
} else {
Err(err(self))
}
}
pub(super) fn parse_token_lit(&mut self) -> PResult<'a, (token::Lit, Span)> {
self.parse_opt_token_lit()
.ok_or(())
.or_else(|()| self.handle_missing_lit(Parser::mk_token_lit_char))
}
pub(super) fn parse_meta_item_lit(&mut self) -> PResult<'a, MetaItemLit> {
self.parse_opt_meta_item_lit()
.ok_or(())
.or_else(|()| self.handle_missing_lit(Parser::mk_meta_item_lit_char))
}
fn recover_after_dot(&mut self) {
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.
let recovered = self.look_ahead(1, |next_token| {
// If it's an integer that looks like a float, then recover as such.
//
// We will never encounter the exponent part of a floating
// point literal here, since there's no use of the exponent
// syntax that also constitutes a valid integer, so we need
// not check for that.
if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
next_token.kind
&& suffix.is_none_or(|s| s == sym::f32 || s == sym::f64)
&& symbol.as_str().chars().all(|c| c.is_numeric() || c == '_')
&& 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);
Some(Token::new(kind, self.token.span.to(next_token.span)))
} else {
None
}
});
if let Some(recovered) = recovered {
self.dcx().emit_err(errors::FloatLiteralRequiresIntegerPart {
span: recovered.span,
suggestion: recovered.span.shrink_to_lo(),
});
self.bump();
self.token = recovered;
}
}
}
/// Keep this in sync with `Token::can_begin_literal_maybe_minus` and
/// `Lit::from_token` (excluding unary negation).
pub fn eat_token_lit(&mut self) -> Option<token::Lit> {
let check_expr = |expr: Box<Expr>| {
if let ast::ExprKind::Lit(token_lit) = expr.kind {
Some(token_lit)
} else if let ast::ExprKind::Unary(UnOp::Neg, inner) = &expr.kind
&& let ast::Expr { kind: ast::ExprKind::Lit(_), .. } = **inner
{
None
} else {
panic!("unexpected reparsed expr/literal: {:?}", expr.kind);
}
};
match self.token.uninterpolate().kind {
token::Ident(name, IdentIsRaw::No) if name.is_bool_lit() => {
self.bump();
Some(token::Lit::new(token::Bool, name, None))
}
token::Literal(token_lit) => {
self.bump();
Some(token_lit)
}
token::OpenInvisible(InvisibleOrigin::MetaVar(MetaVarKind::Literal)) => {
let lit = self
.eat_metavar_seq(MetaVarKind::Literal, |this| this.parse_literal_maybe_minus())
.expect("metavar seq literal");
check_expr(lit)
}
token::OpenInvisible(InvisibleOrigin::MetaVar(
mv_kind @ MetaVarKind::Expr { can_begin_literal_maybe_minus: true, .. },
)) => {
let expr = self
.eat_metavar_seq(mv_kind, |this| this.parse_expr())
.expect("metavar seq expr");
check_expr(expr)
}
_ => None,
}
}
/// Matches `lit = true | false | token_lit`.
/// Returns `None` if the next token is not a literal.
fn parse_opt_token_lit(&mut self) -> Option<(token::Lit, Span)> {
self.recover_after_dot();
let span = self.token.span;
self.eat_token_lit().map(|token_lit| (token_lit, span))
}
/// Matches `lit = true | false | token_lit`.
/// Returns `None` if the next token is not a literal.
fn parse_opt_meta_item_lit(&mut self) -> Option<MetaItemLit> {
self.recover_after_dot();
let span = self.token.span;
let uninterpolated_span = self.token_uninterpolated_span();
self.eat_token_lit().map(|token_lit| {
match MetaItemLit::from_token_lit(token_lit, span) {
Ok(lit) => lit,
Err(err) => {
let guar = report_lit_error(&self.psess, err, token_lit, uninterpolated_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(token_lit.kind, token_lit.symbol, None);
let symbol = Symbol::intern(&suffixless_lit.to_string());
let token_lit = token::Lit::new(token::Err(guar), symbol, token_lit.suffix);
MetaItemLit::from_token_lit(token_lit, uninterpolated_span).unwrap()
}
}
})
}
/// 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, Box<Expr>> {
if let Some(expr) = self.eat_metavar_seq_with_matcher(
|mv_kind| matches!(mv_kind, MetaVarKind::Expr { .. }),
|this| {
// FIXME(nnethercote) The `expr` case should only match if
// `e` is an `ExprKind::Lit` or an `ExprKind::Unary` containing
// an `UnOp::Neg` and an `ExprKind::Lit`, like how
// `can_begin_literal_maybe_minus` works. But this method has
// been over-accepting for a long time, and to make that change
// here requires also changing some `parse_literal_maybe_minus`
// call sites to accept additional expression kinds. E.g.
// `ExprKind::Path` must be accepted when parsing range
// patterns. That requires some care. So for now, we continue
// being less strict here than we should be.
this.parse_expr()
},
) {
return Ok(expr);
} else if let Some(lit) =
self.eat_metavar_seq(MetaVarKind::Literal, |this| this.parse_literal_maybe_minus())
{
return Ok(lit);
}
let lo = self.token.span;
let minus_present = self.eat(exp!(Minus));
let (token_lit, span) = self.parse_token_lit()?;
let expr = self.mk_expr(span, ExprKind::Lit(token_lit));
if minus_present {
Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
} else {
Ok(expr)
}
}
fn is_array_like_block(&mut self) -> bool {
self.token.kind == TokenKind::OpenBrace
&& 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) -> Option<Box<Expr>> {
let mut snapshot = self.create_snapshot_for_diagnostic();
match snapshot.parse_expr_array_or_repeat(exp!(CloseBrace)) {
Ok(arr) => {
let guar = self.dcx().emit_err(errors::ArrayBracketsInsteadOfBraces {
span: arr.span,
sub: errors::ArrayBracketsInsteadOfBracesSugg {
left: lo,
right: snapshot.prev_token.span,
},
});
self.restore_snapshot(snapshot);
Some(self.mk_expr_err(arr.span, guar))
}
Err(e) => {
e.cancel();
None
}
}
}
fn suggest_missing_semicolon_before_array(
&self,
prev_span: Span,
open_delim_span: Span,
) -> PResult<'a, ()> {
if !self.may_recover() {
return Ok(());
}
if self.token == token::Comma {
if !self.psess.source_map().is_multiline(prev_span.until(self.token.span)) {
return Ok(());
}
let mut snapshot = self.create_snapshot_for_diagnostic();
snapshot.bump();
match snapshot.parse_seq_to_before_end(
exp!(CloseBracket),
SeqSep::trailing_allowed(exp!(Comma)),
|p| p.parse_expr(),
) {
Ok(_)
// When the close delim is `)`, `token.kind` is expected to be `token::CloseParen`,
// but the actual `token.kind` is `token::CloseBracket`.
// This is because the `token.kind` of the close delim is treated as the same as
// that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
// Therefore, `token.kind` should not be compared here.
if snapshot
.span_to_snippet(snapshot.token.span)
.is_ok_and(|snippet| snippet == "]") =>
{
return Err(self.dcx().create_err(errors::MissingSemicolonBeforeArray {
open_delim: open_delim_span,
semicolon: prev_span.shrink_to_hi(),
}));
}
Ok(_) => (),
Err(err) => err.cancel(),
}
}
Ok(())
}
/// Parses a block or unsafe block.
pub(super) fn parse_expr_block(
&mut self,
opt_label: Option<Label>,
lo: Span,
blk_mode: BlockCheckMode,
) -> PResult<'a, Box<Expr>> {
if self.may_recover() && self.is_array_like_block() {
if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
return Ok(arr);
}
}
if self.token.is_metavar_block() {
self.dcx().emit_err(errors::InvalidBlockMacroSegment {
span: self.token.span,
context: lo.to(self.token.span),
wrap: errors::WrapInExplicitBlock {
lo: self.token.span.shrink_to_lo(),
hi: self.token.span.shrink_to_hi(),
},
});
}
let (attrs, blk) = self.parse_block_common(lo, blk_mode, None)?;
Ok(self.mk_expr_with_attrs(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, Box<Expr>> {
let blk = self.parse_block()?;
Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
}
/// Parses a closure expression (e.g., `move |args| expr`).
fn parse_expr_closure(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
let before = self.prev_token;
let binder = if self.check_keyword(exp!(For)) {
let lo = self.token.span;
let (bound_vars, _) = self.parse_higher_ranked_binder()?;
let span = lo.to(self.prev_token.span);
self.psess.gated_spans.gate(sym::closure_lifetime_binder, span);
ClosureBinder::For { span, generic_params: bound_vars }
} else {
ClosureBinder::NotPresent
};
let constness = self.parse_closure_constness();
let movability = if self.eat_keyword(exp!(Static)) {
self.psess.gated_spans.gate(sym::coroutines, self.prev_token.span);
Movability::Static
} else {
Movability::Movable
};
let coroutine_kind = if self.token_uninterpolated_span().at_least_rust_2018() {
self.parse_coroutine_kind(Case::Sensitive)
} else {
None
};
if let ClosureBinder::NotPresent = binder
&& coroutine_kind.is_some()
{
// coroutine closures and generators can have the same qualifiers, so we might end up
// in here if there is a missing `|` but also no `{`. Adjust the expectations in that case.
self.expected_token_types.insert(TokenType::OpenBrace);
}
let capture_clause = self.parse_capture_clause()?;
let (fn_decl, fn_arg_span) = self.parse_fn_block_decl()?;
let decl_hi = self.prev_token.span;
let mut body = match &fn_decl.output {
// No return type.
FnRetTy::Default(_) => {
let restrictions =
self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET;
let prev = self.prev_token;
let token = self.token;
let attrs = self.parse_outer_attributes()?;
match self.parse_expr_res(restrictions, attrs) {
Ok((expr, _)) => expr,
Err(err) => self.recover_closure_body(err, before, prev, token, lo, decl_hi)?,
}
}
// Explicit return type (`->`) needs block `-> T { }`.
FnRetTy::Ty(ty) => self.parse_closure_block_body(ty.span)?,
};
match coroutine_kind {
Some(CoroutineKind::Async { .. }) => {}
Some(CoroutineKind::Gen { span, .. }) | Some(CoroutineKind::AsyncGen { span, .. }) => {
// Feature-gate `gen ||` and `async gen ||` closures.
// FIXME(gen_blocks): This perhaps should be a different gate.
self.psess.gated_spans.gate(sym::gen_blocks, span);
}
None => {}
}
if self.token == TokenKind::Semi
&& let Some(last) = self.token_cursor.stack.last()
&& let Some(TokenTree::Delimited(_, _, Delimiter::Parenthesis, _)) = last.curr()
&& self.may_recover()
{
// 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,
self.dcx().span_delayed_bug(body.span, "recovered a closure body as a block"),
);
}
let body_span = body.span;
let closure = self.mk_expr(
lo.to(body.span),
ExprKind::Closure(Box::new(ast::Closure {
binder,
capture_clause,
constness,
coroutine_kind,
movability,
fn_decl,
body,
fn_decl_span: lo.to(decl_hi),
fn_arg_span,
})),
);
// 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)
}
/// If an explicit return type is given, require a block to appear (RFC 968).
fn parse_closure_block_body(&mut self, ret_span: Span) -> PResult<'a, Box<Expr>> {
if self.may_recover()
&& self.token.can_begin_expr()
&& self.token.kind != TokenKind::OpenBrace
&& !self.token.is_metavar_block()
{
let snapshot = self.create_snapshot_for_diagnostic();
let restrictions =
self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET;
let tok = self.token.clone();
match self.parse_expr_res(restrictions, AttrWrapper::empty()) {
Ok((expr, _)) => {
let descr = super::token_descr(&tok);
let mut diag = self
.dcx()
.struct_span_err(tok.span, format!("expected `{{`, found {descr}"));
diag.span_label(
ret_span,
"explicit return type requires closure body to be enclosed in braces",
);
diag.multipart_suggestion(
"wrap the expression in curly braces",
vec![
(expr.span.shrink_to_lo(), "{ ".to_string()),
(expr.span.shrink_to_hi(), " }".to_string()),
],
Applicability::MachineApplicable,
);
diag.emit();
return Ok(expr);
}
Err(diag) => {
diag.cancel();
self.restore_snapshot(snapshot);
}
}
}
let body_lo = self.token.span;
self.parse_expr_block(None, body_lo, BlockCheckMode::Default)
}
/// Parses an optional `move` or `use` prefix to a closure-like construct.
fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
if self.eat_keyword(exp!(Move)) {
let move_kw_span = self.prev_token.span;
// Check for `move async` and recover
if self.check_keyword(exp!(Async)) {
let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
Err(self
.dcx()
.create_err(errors::AsyncMoveOrderIncorrect { span: move_async_span }))
} else {
Ok(CaptureBy::Value { move_kw: move_kw_span })
}
} else if self.eat_keyword(exp!(Use)) {
let use_kw_span = self.prev_token.span;
self.psess.gated_spans.gate(sym::ergonomic_clones, use_kw_span);
// Check for `use async` and recover
if self.check_keyword(exp!(Async)) {
let use_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
Err(self.dcx().create_err(errors::AsyncUseOrderIncorrect { span: use_async_span }))
} else {
Ok(CaptureBy::Use { use_kw: use_kw_span })
}
} else {
Ok(CaptureBy::Ref)
}
}
/// Parses the `|arg, arg|` header of a closure.
fn parse_fn_block_decl(&mut self) -> PResult<'a, (Box<FnDecl>, Span)> {
let arg_start = self.token.span.lo();
let inputs = if self.eat(exp!(OrOr)) {
ThinVec::new()
} else {
self.expect(exp!(Or))?;
let args = self
.parse_seq_to_before_tokens(
&[exp!(Or)],
&[&token::OrOr],
SeqSep::trailing_allowed(exp!(Comma)),
|p| p.parse_fn_block_param(),
)?
.0;
self.expect_or()?;
args
};
let arg_span = self.prev_token.span.with_lo(arg_start);
let output =
self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
Ok((Box::new(FnDecl { inputs, output }), arg_span))
}
/// 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(None, attrs, ForceCollect::No, |this, attrs| {
let pat = Box::new(this.parse_pat_no_top_alt(Some(Expected::ParameterName), None)?);
let ty = if this.eat(exp!(Colon)) {
this.parse_ty()?
} else {
this.mk_ty(pat.span, TyKind::Infer)
};
Ok((
Param {
attrs,
ty,
pat,
span: lo.to(this.prev_token.span),
id: DUMMY_NODE_ID,
is_placeholder: false,
},
Trailing::from(this.token == token::Comma),
UsePreAttrPos::No,
))
})
}
/// Parses an `if` expression (`if` token already eaten).
fn parse_expr_if(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.prev_token.span;
// Scoping code checks the top level edition of the `if`; let's match it here.
// The `CondChecker` also checks the edition of the `let` itself, just to make sure.
let let_chains_policy = LetChainsPolicy::EditionDependent { current_edition: lo.edition() };
let cond = self.parse_expr_cond(let_chains_policy)?;
self.parse_if_after_cond(lo, cond)
}
fn parse_if_after_cond(&mut self, lo: Span, mut cond: Box<Expr>) -> PResult<'a, Box<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 =>
{
let guar = this.dcx().emit_err(errors::IfExpressionMissingThenBlock {
if_span: lo,
missing_then_block_sub:
errors::IfExpressionMissingThenBlockSub::UnfinishedCondition(
cond_span.shrink_to_lo().to(*binop_span),
),
let_else_sub: None,
});
std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi(), guar))
}
ExprKind::Block(_, None) => {
let guar = this.dcx().emit_err(errors::IfExpressionMissingCondition {
if_span: lo.with_neighbor(cond.span).shrink_to_hi(),
block_span: self.psess.source_map().start_point(cond_span),
});
std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi(), guar))
}
_ => {
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 {
let let_else_sub = matches!(cond.kind, ExprKind::Let(..))
.then(|| errors::IfExpressionLetSomeSub { if_span: lo.until(cond_span) });
let guar = self.dcx().emit_err(errors::IfExpressionMissingThenBlock {
if_span: lo,
missing_then_block_sub: errors::IfExpressionMissingThenBlockSub::AddThenBlock(
cond_span.shrink_to_hi(),
),
let_else_sub,
});
self.mk_block_err(cond_span.shrink_to_hi(), guar)
}
} else {
let attrs = self.parse_outer_attributes()?; // For recovery.
let maybe_fatarrow = self.token;
let block = if self.check(exp!(OpenBrace)) {
self.parse_block()?
} else if let Some(block) = recover_block_from_condition(self) {
block
} else {
self.error_on_extra_if(&cond)?;
// Parse block, which will always fail, but we can add a nice note to the error
self.parse_block().map_err(|mut err| {
if self.prev_token == token::Semi
&& self.token == token::AndAnd
&& let maybe_let = self.look_ahead(1, |t| t.clone())
&& maybe_let.is_keyword(kw::Let)
{
err.span_suggestion(
self.prev_token.span,
"consider removing this semicolon to parse the `let` as part of the same chain",
"",
Applicability::MachineApplicable,
).span_note(
self.token.span.to(maybe_let.span),
"you likely meant to continue parsing the let-chain starting here",
);
} else {
// Look for usages of '=>' where '>=' might be intended
if maybe_fatarrow == token::FatArrow {
err.span_suggestion(
maybe_fatarrow.span,
"you might have meant to write a \"greater than or equal to\" comparison",
">=",
Applicability::MaybeIncorrect,
);
}
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(exp!(Else)) { Some(self.parse_expr_else()?) } else { None };
Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
}
/// Parses the condition of a `if` or `while` expression.
///
/// The specified `edition` in `let_chains_policy` should be that of the whole `if` construct,
/// i.e. the same span we use to later decide whether the drop behaviour should be that of
/// edition `..=2021` or that of `2024..`.
// Public to use it for custom `if` expressions in rustfmt forks like https://github.com/tucant/rustfmt
pub fn parse_expr_cond(
&mut self,
let_chains_policy: LetChainsPolicy,
) -> PResult<'a, Box<Expr>> {
let attrs = self.parse_outer_attributes()?;
let (mut cond, _) =
self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, attrs)?;
let mut checker = CondChecker::new(self, let_chains_policy);
checker.visit_expr(&mut cond);
Ok(if let Some(guar) = checker.found_incorrect_let_chain {
self.mk_expr_err(cond.span, guar)
} else {
cond
})
}
/// Parses a `let $pat = $expr` pseudo-expression.
fn parse_expr_let(&mut self, restrictions: Restrictions) -> PResult<'a, Box<Expr>> {
let recovered: Recovered = if !restrictions.contains(Restrictions::ALLOW_LET) {
let err = errors::ExpectedExpressionFoundLet {
span: self.token.span,
reason: errors::ForbiddenLetReason::OtherForbidden,
missing_let: None,
comparison: None,
};
if self.prev_token == token::Or {
// This was part of a closure, the that part of the parser recover.
return Err(self.dcx().create_err(err));
} else {
Recovered::Yes(self.dcx().emit_err(err))
}
} else {
Recovered::No
};
self.bump(); // Eat `let` token
let lo = self.prev_token.span;
let pat = self.parse_pat_no_top_guard(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::LikelyTuple,
)?;
if self.token == token::EqEq {
self.dcx().emit_err(errors::ExpectedEqForLetExpr {
span: self.token.span,
sugg_span: self.token.span,
});
self.bump();
} else {
self.expect(exp!(Eq))?;
}
let attrs = self.parse_outer_attributes()?;
let (expr, _) =
self.parse_expr_assoc_with(Bound::Excluded(prec_let_scrutinee_needs_par()), attrs)?;
let span = lo.to(expr.span);
Ok(self.mk_expr(span, ExprKind::Let(Box::new(pat), expr, span, recovered)))
}
/// Parses an `else { ... }` expression (`else` token already eaten).
fn parse_expr_else(&mut self) -> PResult<'a, Box<Expr>> {
let else_span = self.prev_token.span; // `else`
let attrs = self.parse_outer_attributes()?; // For recovery.
let expr = if self.eat_keyword(exp!(If)) {
ensure_sufficient_stack(|| self.parse_expr_if())?
} else if self.check(exp!(OpenBrace)) {
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)
// Try to guess the difference between a "condition-like" vs
// "statement-like" expression.
//
// We are seeing the following code, in which $cond is neither
// ExprKind::Block nor ExprKind::If (the 2 cases wherein this
// would be valid syntax).
//
// if ... {
// } else $cond
//
// If $cond is "condition-like" such as ExprKind::Binary, we
// want to suggest inserting `if`.
//
// if ... {
// } else if a == b {
// ^^
// }
//
// We account for macro calls that were meant as conditions as well.
//
// if ... {
// } else if macro! { foo bar } {
// ^^
// }
//
// If $cond is "statement-like" such as ExprKind::While then we
// want to suggest wrapping in braces.
//
// if ... {
// } else {
// ^
// while true {}
// }
// ^
if self.check(exp!(OpenBrace))
&& (classify::expr_requires_semi_to_be_stmt(&cond)
|| matches!(cond.kind, ExprKind::MacCall(..)))
=>
{
self.dcx().emit_err(errors::ExpectedElseBlock {
first_tok_span,
first_tok,
else_span,
condition_start: cond.span.shrink_to_lo(),
});
self.parse_if_after_cond(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: AttrWrapper,
) {
if !attrs.is_empty()
&& let [x0 @ xn] | [x0, .., xn] = &*attrs.take_for_recovery(self.psess)
{
let attributes = x0.span.until(branch_span);
let last = xn.span;
let ctx = if is_ctx_else { "else" } else { "if" };
self.dcx().emit_err(errors::OuterAttributeNotAllowedOnIfElse {
last,
branch_span,
ctx_span,
ctx: ctx.to_string(),
attributes,
});
}
}
fn error_on_extra_if(&mut self, cond: &Box<Expr>) -> PResult<'a, ()> {
if let ExprKind::Binary(Spanned { span: binop_span, node: binop }, _, right) = &cond.kind
&& let BinOpKind::And = binop
&& let ExprKind::If(cond, ..) = &right.kind
{
Err(self.dcx().create_err(errors::UnexpectedIfWithIf(
binop_span.shrink_to_hi().to(cond.span.shrink_to_lo()),
)))
} else {
Ok(())
}
}
// Public to use it for custom `for` expressions in rustfmt forks like https://github.com/tucant/rustfmt
pub fn parse_for_head(&mut self) -> PResult<'a, (Pat, Box<Expr>)> {
let begin_paren = if self.token == token::OpenParen {
// 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 $block`.
let start_span = self.token.span;
let left = self.prev_token.span.between(self.look_ahead(1, |t| t.span));
Some((start_span, left))
} else {
None
};
// Try to parse the pattern `for ($PAT) in $EXPR`.
let pat = match (
self.parse_pat_allow_top_guard(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::LikelyTuple,
),
begin_paren,
) {
(Ok(pat), _) => pat, // Happy path.
(Err(err), Some((start_span, left))) if self.eat_keyword(exp!(In)) => {
// We know for sure we have seen `for ($SOMETHING in`. In the happy path this would
// happen right before the return of this method.
let attrs = self.parse_outer_attributes()?;
let (expr, _) = match self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs) {
Ok(expr) => expr,
Err(expr_err) => {
// We don't know what followed the `in`, so cancel and bubble up the
// original error.
expr_err.cancel();
return Err(err);
}
};
return if self.token == token::CloseParen {
// We know for sure we have seen `for ($SOMETHING in $EXPR)`, so we recover the
// parser state and emit a targeted suggestion.
let span = vec![start_span, self.token.span];
let right = self.prev_token.span.between(self.look_ahead(1, |t| t.span));
self.bump(); // )
err.cancel();
self.dcx().emit_err(errors::ParenthesesInForHead {
span,
// With e.g. `for (x) in y)` this would replace `(x) in y)`
// with `x) in y)` which is syntactically invalid.
// However, this is prevented before we get here.
sugg: errors::ParenthesesInForHeadSugg { left, right },
});
Ok((self.mk_pat(start_span.to(right), ast::PatKind::Wild), expr))
} else {
Err(err) // Some other error, bubble up.
};
}
(Err(err), _) => return Err(err), // Some other error, bubble up.
};
if !self.eat_keyword(exp!(In)) {
self.error_missing_in_for_loop();
}
self.check_for_for_in_in_typo(self.prev_token.span);
let attrs = self.parse_outer_attributes()?;
let (expr, _) = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
Ok((pat, expr))
}
/// Parses `for await? <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
fn parse_expr_for(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
let is_await =
self.token_uninterpolated_span().at_least_rust_2018() && self.eat_keyword(exp!(Await));
if is_await {
self.psess.gated_spans.gate(sym::async_for_loop, self.prev_token.span);
}
let kind = if is_await { ForLoopKind::ForAwait } else { ForLoopKind::For };
let (pat, expr) = self.parse_for_head()?;
let pat = Box::new(pat);
// Recover from missing expression in `for` loop
if matches!(expr.kind, ExprKind::Block(..))
&& self.token.kind != token::OpenBrace
&& self.may_recover()
{
let guar = self
.dcx()
.emit_err(errors::MissingExpressionInForLoop { span: expr.span.shrink_to_lo() });
let err_expr = self.mk_expr(expr.span, ExprKind::Err(guar));
let block = self.mk_block(thin_vec![], BlockCheckMode::Default, self.prev_token.span);
return Ok(self.mk_expr(
lo.to(self.prev_token.span),
ExprKind::ForLoop { pat, iter: err_expr, body: block, label: opt_label, kind },
));
}
let (attrs, loop_block) = self.parse_inner_attrs_and_block(
// Only suggest moving erroneous block label to the loop header
// if there is not already a label there
opt_label.is_none().then_some(lo),
)?;
let kind = ExprKind::ForLoop { pat, iter: expr, body: loop_block, label: opt_label, kind };
self.recover_loop_else("for", lo)?;
Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
}
/// Recovers from an `else` clause after a loop (`for...else`, `while...else`)
fn recover_loop_else(&mut self, loop_kind: &'static str, loop_kw: Span) -> PResult<'a, ()> {
if self.token.is_keyword(kw::Else) && self.may_recover() {
let else_span = self.token.span;
self.bump();
let else_clause = self.parse_expr_else()?;
self.dcx().emit_err(errors::LoopElseNotSupported {
span: else_span.to(else_clause.span),
loop_kind,
loop_kw,
});
}
Ok(())
}
fn error_missing_in_for_loop(&mut self) {
let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
// Possibly using JS syntax (#75311).
let span = self.token.span;
self.bump();
(span, errors::MissingInInForLoopSub::InNotOf)
} else if self.eat(exp!(Eq)) {
(self.prev_token.span, errors::MissingInInForLoopSub::InNotEq)
} else {
(self.prev_token.span.between(self.token.span), errors::MissingInInForLoopSub::AddIn)
};
self.dcx().emit_err(errors::MissingInInForLoop { span, sub: sub(span) });
}
/// Parses a `while` or `while let` expression (`while` token already eaten).
fn parse_expr_while(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
let policy = LetChainsPolicy::EditionDependent { current_edition: lo.edition() };
let cond = self.parse_expr_cond(policy).map_err(|mut err| {
err.span_label(lo, "while parsing the condition of this `while` expression");
err
})?;
let (attrs, body) = self
.parse_inner_attrs_and_block(
// Only suggest moving erroneous block label to the loop header
// if there is not already a label there
opt_label.is_none().then_some(lo),
)
.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
})?;
self.recover_loop_else("while", lo)?;
Ok(self.mk_expr_with_attrs(
lo.to(self.prev_token.span),
ExprKind::While(cond, body, opt_label),
attrs,
))
}
/// Parses `loop { ... }` (`loop` token already eaten).
fn parse_expr_loop(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
let loop_span = self.prev_token.span;
let (attrs, body) = self.parse_inner_attrs_and_block(
// Only suggest moving erroneous block label to the loop header
// if there is not already a label there
opt_label.is_none().then_some(lo),
)?;
self.recover_loop_else("loop", lo)?;
Ok(self.mk_expr_with_attrs(
lo.to(self.prev_token.span),
ExprKind::Loop(body, opt_label, loop_span),
attrs,
))
}
pub(crate) fn eat_label(&mut self) -> Option<Label> {
if let Some((ident, is_raw)) = self.token.lifetime() {
// Disallow `'fn`, but with a better error message than `expect_lifetime`.
if is_raw == IdentIsRaw::No && ident.without_first_quote().is_reserved() {
self.dcx().emit_err(errors::KeywordLabel { span: ident.span });
}
self.bump();
Some(Label { ident })
} else {
None
}
}
/// Parses a `match ... { ... }` expression (`match` token already eaten).
fn parse_expr_match(&mut self) -> PResult<'a, Box<Expr>> {
let match_span = self.prev_token.span;
let attrs = self.parse_outer_attributes()?;
let (scrutinee, _) = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
self.parse_match_block(match_span, match_span, scrutinee, MatchKind::Prefix)
}
/// Parses the block of a `match expr { ... }` or a `expr.match { ... }`
/// expression. This is after the match token and scrutinee are eaten
fn parse_match_block(
&mut self,
lo: Span,
match_span: Span,
scrutinee: Box<Expr>,
match_kind: MatchKind,
) -> PResult<'a, Box<Expr>> {
if let Err(mut e) = self.expect(exp!(OpenBrace)) {
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(None) {
e.cancel();
self.bump();
} else {
return Err(e);
}
}
let attrs = self.parse_inner_attributes()?;
let mut arms = ThinVec::new();
while self.token != token::CloseBrace {
match self.parse_arm() {
Ok(arm) => arms.push(arm),
Err(e) => {
// Recover by skipping to the end of the block.
let guar = e.emit();
self.recover_stmt();
let span = lo.to(self.token.span);
if self.token == token::CloseBrace {
self.bump();
}
// Always push at least one arm to make the match non-empty
arms.push(Arm {
attrs: Default::default(),
pat: Box::new(self.mk_pat(span, ast::PatKind::Err(guar))),
guard: None,
body: Some(self.mk_expr_err(span, guar)),
span,
id: DUMMY_NODE_ID,
is_placeholder: false,
});
return Ok(self.mk_expr_with_attrs(
span,
ExprKind::Match(scrutinee, arms, match_kind),
attrs,
));
}
}
}
let hi = self.token.span;
self.bump();
Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms, match_kind), attrs))
}
/// Attempt to recover from match arm body with statements and no surrounding braces.
fn parse_arm_body_missing_braces(
&mut self,
first_expr: &Box<Expr>,
arrow_span: Span,
) -> Option<(Span, ErrorGuaranteed)> {
if self.token != 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: &Parser<'_>, stmts: Vec<ast::Stmt>| {
let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
let guar = this.dcx().emit_err(errors::MatchArmBodyWithoutBraces {
statements: span,
arrow: arrow_span,
num_statements: stmts.len(),
sub: if stmts.len() > 1 {
errors::MatchArmBodyWithoutBracesSugg::AddBraces {
left: span.shrink_to_lo(),
right: span.shrink_to_hi(),
num_statements: stmts.len(),
}
} else {
errors::MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
},
});
(span, guar)
};
// We might have either a `,` -> `;` typo, or a block without braces. We need
// a more subtle parsing strategy.
loop {
if self.token == token::CloseBrace {
// We have reached the closing brace of the `match` expression.
return Some(err(self, stmts));
}
if self.token == 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, None) {
Ok(_pat) => {
if self.token == 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, false) {
// 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> {
let attrs = self.parse_outer_attributes()?;
self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
let lo = this.token.span;
let (pat, guard) = this.parse_match_arm_pat_and_guard()?;
let pat = Box::new(pat);
let span_before_body = this.prev_token.span;
let arm_body;
let is_fat_arrow = this.check(exp!(FatArrow));
let is_almost_fat_arrow =
TokenKind::FatArrow.similar_tokens().contains(&this.token.kind);
// this avoids the compiler saying that a `,` or `}` was expected even though
// the pattern isn't a never pattern (and thus an arm body is required)
let armless = (!is_fat_arrow && !is_almost_fat_arrow && pat.could_be_never_pattern())
|| matches!(this.token.kind, token::Comma | token::CloseBrace);
let mut result = if armless {
// A pattern without a body, allowed for never patterns.
arm_body = None;
let span = lo.to(this.prev_token.span);
this.expect_one_of(&[exp!(Comma)], &[exp!(CloseBrace)]).map(|x| {
// Don't gate twice
if !pat.contains_never_pattern() {
this.psess.gated_spans.gate(sym::never_patterns, span);
}
x
})
} else {
if let Err(mut err) = this.expect(exp!(FatArrow)) {
// We might have a `=>` -> `=` or `->` typo (issue #89396).
if is_almost_fat_arrow {
err.span_suggestion(
this.token.span,
"use a fat arrow to start a match arm",
"=>",
Applicability::MachineApplicable,
);
if matches!(
(&this.prev_token.kind, &this.token.kind),
(token::DotDotEq, token::Gt)
) {
// `error_inclusive_range_match_arrow` handles cases like `0..=> {}`,
// so we suppress the error here
err.delay_as_bug();
} else {
err.emit();
}
this.bump();
} else {
return Err(err);
}
}
let arrow_span = this.prev_token.span;
let arm_start_span = this.token.span;
let attrs = this.parse_outer_attributes()?;
let (expr, _) =
this.parse_expr_res(Restrictions::STMT_EXPR, attrs).map_err(|mut err| {
err.span_label(arrow_span, "while parsing the `match` arm starting here");
err
})?;
let require_comma =
!classify::expr_is_complete(&expr) && this.token != token::CloseBrace;
if !require_comma {
arm_body = Some(expr);
// Eat a comma if it exists, though.
let _ = this.eat(exp!(Comma));
Ok(Recovered::No)
} else if let Some((span, guar)) =
this.parse_arm_body_missing_braces(&expr, arrow_span)
{
let body = this.mk_expr_err(span, guar);
arm_body = Some(body);
Ok(Recovered::Yes(guar))
} else {
let expr_span = expr.span;
arm_body = Some(expr);
this.expect_one_of(&[exp!(Comma)], &[exp!(CloseBrace)]).map_err(|mut err| {
if this.token == token::FatArrow {
let sm = this.psess.source_map();
if let Ok(expr_lines) = sm.span_to_lines(expr_span)
&& let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
&& expr_lines.lines.len() == 2
{
if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col {
// 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,
);
} else if arm_start_lines.lines[0].end_col + rustc_span::CharPos(1)
== expr_lines.lines[0].end_col
{
// similar to the above, but we may typo a `.` or `/` at the end of the line
let comma_span = arm_start_span
.shrink_to_hi()
.with_hi(arm_start_span.hi() + rustc_span::BytePos(1));
if let Ok(res) = sm.span_to_snippet(comma_span)
&& (res == "." || res == "/")
{
err.span_suggestion_short(
comma_span,
"you might have meant to write a `,` to end this `match` arm",
",",
Applicability::MachineApplicable,
);
}
}
}
} else {
err.span_label(
arrow_span,
"while parsing the `match` arm starting here",
);
}
err
})
}
};
let hi_span = arm_body.as_ref().map_or(span_before_body, |body| body.span);
let arm_span = lo.to(hi_span);
// We want to recover:
// X | Some(_) => foo()
// | - missing comma
// X | None => "x"
// | ^^^^ self.token.span
// as well as:
// X | Some(!)
// | - missing comma
// X | None => "x"
// | ^^^^ self.token.span
// But we musn't recover
// X | pat[0] => {}
// | ^ self.token.span
let recover_missing_comma = arm_body.is_some() || pat.could_be_never_pattern();
if recover_missing_comma {
result = result.or_else(|err| {
// 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_no_top_guard(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::EitherTupleOrPipe,
)
.map_err(|err| err.cancel())
.is_ok();
if pattern_follows && snapshot.check(exp!(FatArrow)) {
err.cancel();
let guar = this.dcx().emit_err(errors::MissingCommaAfterMatchArm {
span: arm_span.shrink_to_hi(),
});
return Ok(Recovered::Yes(guar));
}
Err(err)
});
}
result?;
Ok((
ast::Arm {
attrs,
pat,
guard,
body: arm_body,
span: arm_span,
id: DUMMY_NODE_ID,
is_placeholder: false,
},
Trailing::No,
UsePreAttrPos::No,
))
})
}
pub(crate) fn eat_metavar_guard(&mut self) -> Option<Box<Guard>> {
self.eat_metavar_seq(MetaVarKind::Guard, |this| {
this.expect_match_arm_guard(ForceCollect::Yes)
})
}
fn parse_match_arm_guard(&mut self) -> PResult<'a, Option<Box<Guard>>> {
if let Some(guard) = self.eat_metavar_guard() {
return Ok(Some(guard));
}
if !self.eat_keyword(exp!(If)) {
// No match arm guard present.
return Ok(None);
}
self.expect_match_arm_guard_cond(ForceCollect::No).map(Some)
}
pub(crate) fn expect_match_arm_guard(
&mut self,
force_collect: ForceCollect,
) -> PResult<'a, Box<Guard>> {
if let Some(guard) = self.eat_metavar_guard() {
return Ok(guard);
}
self.expect_keyword(exp!(If))?;
self.expect_match_arm_guard_cond(force_collect)
}
fn expect_match_arm_guard_cond(
&mut self,
force_collect: ForceCollect,
) -> PResult<'a, Box<Guard>> {
let leading_if_span = self.prev_token.span;
let mut cond = self.parse_match_guard_condition(force_collect)?;
let cond_span = cond.span;
CondChecker::new(self, LetChainsPolicy::AlwaysAllowed).visit_expr(&mut cond);
let guard = Guard { cond: *cond, span_with_leading_if: leading_if_span.to(cond_span) };
Ok(Box::new(guard))
}
fn parse_match_arm_pat_and_guard(&mut self) -> PResult<'a, (Pat, Option<Box<Guard>>)> {
if self.token == token::OpenParen {
let left = self.token.span;
let pat = self.parse_pat_no_top_guard(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::EitherTupleOrPipe,
)?;
if let ast::PatKind::Paren(subpat) = &pat.kind
&& let ast::PatKind::Guard(..) = &subpat.kind
{
// Detect and recover from `($pat if $cond) => $arm`.
// FIXME(guard_patterns): convert this to a normal guard instead
let span = pat.span;
let ast::PatKind::Paren(subpat) = pat.kind else { unreachable!() };
let ast::PatKind::Guard(_, mut guard) = subpat.kind else { unreachable!() };
self.psess.gated_spans.ungate_last(sym::guard_patterns, guard.span());
let mut checker = CondChecker::new(self, LetChainsPolicy::AlwaysAllowed);
checker.visit_expr(&mut guard.cond);
let right = self.prev_token.span;
self.dcx().emit_err(errors::ParenthesesInMatchPat {
span: vec![left, right],
sugg: errors::ParenthesesInMatchPatSugg { left, right },
});
if let Some(guar) = checker.found_incorrect_let_chain {
guard.cond = *self.mk_expr_err(guard.span(), guar);
}
Ok((self.mk_pat(span, ast::PatKind::Wild), Some(guard)))
} else {
Ok((pat, self.parse_match_arm_guard()?))
}
} else {
// Regular parser flow:
let pat = self.parse_pat_no_top_guard(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::EitherTupleOrPipe,
)?;
Ok((pat, self.parse_match_arm_guard()?))
}
}
fn parse_match_guard_condition(
&mut self,
force_collect: ForceCollect,
) -> PResult<'a, Box<Expr>> {
let attrs = self.parse_outer_attributes()?;
let expr = self.collect_tokens(
None,
AttrWrapper::empty(),
force_collect,
|this, _empty_attrs| {
match this
.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, attrs)
{
Ok((expr, _)) => Ok((expr, Trailing::No, UsePreAttrPos::No)),
Err(mut err) => {
if this.prev_token == token::OpenBrace {
let sugg_sp = this.prev_token.span.shrink_to_lo();
// Consume everything within the braces, let's avoid further parse
// errors.
this.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
let msg =
"you might have meant to start a match arm after the match guard";
if this.eat(exp!(CloseBrace)) {
let applicability = if this.token != token::FatArrow {
// We have high confidence that we indeed didn't have a struct
// literal in the match guard, but rather we had some operation
// that ended in a path, immediately followed by a block that was
// meant to be the match arm.
Applicability::MachineApplicable
} else {
Applicability::MaybeIncorrect
};
err.span_suggestion_verbose(sugg_sp, msg, "=> ", applicability);
}
}
Err(err)
}
}
},
)?;
Ok(expr)
}
pub(crate) fn is_builtin(&self) -> bool {
self.token.is_keyword(kw::Builtin) && self.look_ahead(1, |t| *t == token::Pound)
}
/// Parses a `try {...}` or `try bikeshed Ty {...}` expression (`try` token already eaten).
fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, Box<Expr>> {
let annotation =
if self.eat_keyword(exp!(Bikeshed)) { Some(self.parse_ty()?) } else { None };
let (attrs, body) = self.parse_inner_attrs_and_block(None)?;
if self.eat_keyword(exp!(Catch)) {
Err(self.dcx().create_err(errors::CatchAfterTry { span: self.prev_token.span }))
} else {
let span = span_lo.to(body.span);
let gate_sym =
if annotation.is_none() { sym::try_blocks } else { sym::try_blocks_heterogeneous };
self.psess.gated_spans.gate(gate_sym, span);
Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body, annotation), 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::OpenBrace || t.is_metavar_block())
&& !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::OpenBrace
|| t.is_metavar_block()
|| t.kind == TokenKind::Ident(sym::bikeshed, IdentIsRaw::No)
})
&& self.token_uninterpolated_span().at_least_rust_2018()
}
/// Parses an `async move? {...}` or `gen move? {...}` expression.
fn parse_gen_block(&mut self) -> PResult<'a, Box<Expr>> {
let lo = self.token.span;
let kind = if self.eat_keyword(exp!(Async)) {
if self.eat_keyword(exp!(Gen)) { GenBlockKind::AsyncGen } else { GenBlockKind::Async }
} else {
assert!(self.eat_keyword(exp!(Gen)));
GenBlockKind::Gen
};
match kind {
GenBlockKind::Async => {
// `async` blocks are stable
}
GenBlockKind::Gen | GenBlockKind::AsyncGen => {
self.psess.gated_spans.gate(sym::gen_blocks, lo.to(self.prev_token.span));
}
}
let capture_clause = self.parse_capture_clause()?;
let decl_span = lo.to(self.prev_token.span);
let (attrs, body) = self.parse_inner_attrs_and_block(None)?;
let kind = ExprKind::Gen(capture_clause, body, kind, decl_span);
Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
}
fn is_gen_block(&self, kw: Symbol, lookahead: usize) -> bool {
self.is_keyword_ahead(lookahead, &[kw])
&& ((
// `async move {`
self.is_keyword_ahead(lookahead + 1, &[kw::Move, kw::Use])
&& self.look_ahead(lookahead + 2, |t| {
*t == token::OpenBrace || t.is_metavar_block()
})
) || (
// `async {`
self.look_ahead(lookahead + 1, |t| *t == token::OpenBrace || t.is_metavar_block())
))
}
pub(super) fn is_async_gen_block(&self) -> bool {
self.token.is_keyword(kw::Async) && self.is_gen_block(kw::Gen, 1)
}
fn is_likely_struct_lit(&self) -> bool {
// `{ ident, ` and `{ ident: ` cannot start a block.
self.look_ahead(1, |t| t.is_ident())
&& self.look_ahead(2, |t| t == &token::Comma || t == &token::Colon)
}
fn maybe_parse_struct_expr(
&mut self,
qself: &Option<Box<ast::QSelf>>,
path: &ast::Path,
) -> Option<PResult<'a, Box<Expr>>> {
let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
match (struct_allowed, self.is_likely_struct_lit()) {
// A struct literal isn't expected and one is pretty much assured not to be present. The
// only situation that isn't detected is when a struct with a single field was attempted
// in a place where a struct literal wasn't expected, but regular parser errors apply.
// Happy path.
(false, false) => None,
(true, _) => {
// A struct is accepted here, try to parse it and rely on `parse_expr_struct` for
// any kind of recovery. Happy path.
if let Err(err) = self.expect(exp!(OpenBrace)) {
return Some(Err(err));
}
Some(self.parse_expr_struct(qself.clone(), path.clone(), true))
}
(false, true) => {
// We have something like `match foo { bar,` or `match foo { bar:`, which means the
// user might have meant to write a struct literal as part of the `match`
// discriminant. This is done purely for error recovery.
let snapshot = self.create_snapshot_for_diagnostic();
if let Err(err) = self.expect(exp!(OpenBrace)) {
return Some(Err(err));
}
match self.parse_expr_struct(qself.clone(), path.clone(), false) {
Ok(expr) => {
// This is a struct literal, but we don't accept them here.
self.dcx().emit_err(errors::StructLiteralNotAllowedHere {
span: expr.span,
sub: errors::StructLiteralNotAllowedHereSugg {
left: path.span.shrink_to_lo(),
right: expr.span.shrink_to_hi(),
},
});
Some(Ok(expr))
}
Err(err) => {
// We couldn't parse a valid struct, rollback and let the parser emit an
// error elsewhere.
err.cancel();
self.restore_snapshot(snapshot);
None
}
}
}
}
}
fn maybe_recover_bad_struct_literal_path(
&mut self,
is_underscore_entry_point: bool,
) -> PResult<'a, Option<Box<Expr>>> {
if self.may_recover()
&& self.check_noexpect(&token::OpenBrace)
&& (!self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
&& self.is_likely_struct_lit())
{
let span = if is_underscore_entry_point {
self.prev_token.span
} else {
self.token.span.shrink_to_lo()
};
self.bump(); // {
let expr = self.parse_expr_struct(
None,
Path::from_ident(Ident::new(kw::Underscore, span)),
false,
)?;
let guar = if is_underscore_entry_point {
self.dcx().create_err(errors::StructLiteralPlaceholderPath { span }).emit()
} else {
self.dcx()
.create_err(errors::StructLiteralWithoutPathLate {
span: expr.span,
suggestion_span: expr.span.shrink_to_lo(),
})
.emit()
};
Ok(Some(self.mk_expr_err(expr.span, guar)))
} else {
Ok(None)
}
}
pub(super) fn parse_struct_fields(
&mut self,
pth: ast::Path,
recover: bool,
close: ExpTokenPair,
) -> PResult<
'a,
(
ThinVec<ExprField>,
ast::StructRest,
Option<ErrorGuaranteed>, /* async blocks are forbidden in Rust 2015 */
),
> {
let mut fields = ThinVec::new();
let mut base = ast::StructRest::None;
let mut recovered_async = None;
let in_if_guard = self.restrictions.contains(Restrictions::IN_IF_GUARD);
let async_block_err = |e: &mut Diag<'_>, span: Span| {
errors::AsyncBlockIn2015 { span }.add_to_diag(e);
errors::HelpUseLatestEdition::new().add_to_diag(e);
};
while self.token != close.tok {
if self.eat(exp!(DotDot)) || self.recover_struct_field_dots(&close.tok) {
let exp_span = self.prev_token.span;
// We permit `.. }` on the left-hand side of a destructuring assignment.
if self.check(close) {
base = ast::StructRest::Rest(self.prev_token.span);
break;
}
match self.parse_expr() {
Ok(e) => base = ast::StructRest::Base(e),
Err(e) if recover => {
e.emit();
self.recover_stmt();
}
Err(e) => return Err(e),
}
self.recover_struct_comma_after_dotdot(exp_span);
break;
}
// Peek the field's ident before parsing its expr in order to emit better diagnostics.
let peek = self
.token
.ident()
.filter(|(ident, is_raw)| {
(!ident.is_reserved() || matches!(is_raw, IdentIsRaw::Yes))
&& self.look_ahead(1, |tok| *tok == token::Colon)
})
.map(|(ident, _)| ident);
// We still want a field even if its expr didn't parse.
let field_ident = |this: &Self, guar: ErrorGuaranteed| {
peek.map(|ident| {
let span = ident.span;
ExprField {
ident,
span,
expr: this.mk_expr_err(span, guar),
is_shorthand: false,
attrs: AttrVec::new(),
id: DUMMY_NODE_ID,
is_placeholder: false,
}
})
};
let parsed_field = match self.parse_expr_field() {
Ok(f) => Ok(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((ident, _)) = self.token.ident()
&& !self.token.is_reserved_ident()
&& self.look_ahead(1, |t| {
AssocOp::from_token(t).is_some()
|| matches!(
t.kind,
token::OpenParen | token::OpenBracket | token::OpenBrace
)
|| *t == token::Dot
})
{
// Looks like they tried to write a shorthand, complex expression,
// E.g.: `n + m`, `f(a)`, `a[i]`, `S { x: 3 }`, or `x.y`.
e.span_suggestion_verbose(
self.token.span.shrink_to_lo(),
"try naming a field",
&format!("{ident}: ",),
Applicability::MaybeIncorrect,
);
}
if in_if_guard && close.token_type == TokenType::CloseBrace {
return Err(e);
}
if !recover {
return Err(e);
}
let guar = e.emit();
if pth == kw::Async {
recovered_async = Some(guar);
}
// If we encountered an error which we are recovering from, treat the struct
// as if it has a `..` in it, because we don’t know what fields the user
// might have *intended* it to have.
//
// This assignment will be overwritten if we actually parse a `..` later.
//
// (Note that this code is duplicated between here and below in comma parsing.
base = ast::StructRest::NoneWithError(guar);
// 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;
}
}
Err(guar)
}
};
let is_shorthand = parsed_field.as_ref().is_ok_and(|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::Colon);
match self.expect_one_of(&[exp!(Comma)], &[close]) {
Ok(_) => {
if let Ok(f) = parsed_field.or_else(|guar| field_ident(self, guar).ok_or(guar))
{
// 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 peek.is_some() {
e.span_suggestion(
self.prev_token.span.shrink_to_hi(),
"try adding a comma",
",",
Applicability::MachineApplicable,
);
}
}
if !recover {
return Err(e);
}
let guar = e.emit();
if pth == kw::Async {
recovered_async = Some(guar);
} else if let Some(f) = field_ident(self, guar) {
fields.push(f);
}
// See comment above on this same assignment inside of field parsing.
base = ast::StructRest::NoneWithError(guar);
self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
let _ = self.eat(exp!(Comma));
}
}
}
Ok((fields, base, recovered_async))
}
/// Precondition: already parsed the '{'.
pub(super) fn parse_expr_struct(
&mut self,
qself: Option<Box<ast::QSelf>>,
pth: ast::Path,
recover: bool,
) -> PResult<'a, Box<Expr>> {
let lo = pth.span;
let (fields, base, recovered_async) =
self.parse_struct_fields(pth.clone(), recover, exp!(CloseBrace))?;
let span = lo.to(self.token.span);
self.expect(exp!(CloseBrace))?;
let expr = if let Some(guar) = recovered_async {
ExprKind::Err(guar)
} else {
ExprKind::Struct(Box::new(ast::StructExpr { qself, path: pth, fields, rest: base }))
};
Ok(self.mk_expr(span, expr))
}
fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
if self.token != token::Comma {
return;
}
self.dcx().emit_err(errors::CommaAfterBaseStruct {
span: span.to(self.prev_token.span),
comma: self.token.span,
});
self.recover_stmt();
}
fn recover_struct_field_dots(&mut self, close: &TokenKind) -> bool {
if !self.look_ahead(1, |t| t == close) && self.eat(exp!(DotDotDot)) {
// recover from typo of `...`, suggest `..`
let span = self.prev_token.span;
self.dcx().emit_err(errors::MissingDotDot { token_span: span, sugg_span: span });
return true;
}
false
}
/// Converts an ident into 'label and emits an "expected a label, found an identifier" error.
fn recover_ident_into_label(&mut self, ident: Ident) -> Label {
// Convert `label` -> `'label`,
// so that nameres doesn't complain about non-existing label
let label = format!("'{}", ident.name);
let ident = Ident::new(Symbol::intern(&label), ident.span);
self.dcx().emit_err(errors::ExpectedLabelFoundIdent {
span: ident.span,
start: ident.span.shrink_to_lo(),
});
Label { ident }
}
/// Parses `ident (COLON expr)?`.
fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
let attrs = self.parse_outer_attributes()?;
self.recover_vcs_conflict_marker();
self.collect_tokens(None, 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);
// Proactively check whether parsing the field will be incorrect.
let is_wrong = this.token.is_non_reserved_ident()
&& !this.look_ahead(1, |t| {
t == &token::Colon
|| t == &token::Eq
|| t == &token::Comma
|| t == &token::CloseBrace
|| t == &token::CloseParen
});
if is_wrong {
return Err(this.dcx().create_err(errors::ExpectedStructField {
span: this.look_ahead(1, |t| t.span),
ident_span: this.token.span,
token: pprust::token_to_string(&this.look_ahead(1, |t| *t)),
}));
}
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)))
} 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,
id: DUMMY_NODE_ID,
is_placeholder: false,
},
Trailing::from(this.token == token::Comma),
UsePreAttrPos::No,
))
})
}
/// 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.dcx().emit_err(errors::EqFieldInit {
span: self.token.span,
eq: field_name.span.shrink_to_hi().to(self.token.span),
});
}
fn err_dotdotdot_syntax(&self, span: Span) {
self.dcx().emit_err(errors::DotDotDot { span });
}
fn err_larrow_operator(&self, span: Span) {
self.dcx().emit_err(errors::LeftArrowOperator { span });
}
fn mk_assign_op(&self, assign_op: AssignOp, lhs: Box<Expr>, rhs: Box<Expr>) -> ExprKind {
ExprKind::AssignOp(assign_op, lhs, rhs)
}
fn mk_range(
&mut self,
start: Option<Box<Expr>>,
end: Option<Box<Expr>>,
limits: RangeLimits,
) -> ExprKind {
if end.is_none() && limits == RangeLimits::Closed {
let guar = self.inclusive_range_with_incorrect_end();
ExprKind::Err(guar)
} else {
ExprKind::Range(start, end, limits)
}
}
fn mk_unary(&self, unop: UnOp, expr: Box<Expr>) -> ExprKind {
ExprKind::Unary(unop, expr)
}
fn mk_binary(&self, binop: BinOp, lhs: Box<Expr>, rhs: Box<Expr>) -> ExprKind {
ExprKind::Binary(binop, lhs, rhs)
}
fn mk_index(&self, expr: Box<Expr>, idx: Box<Expr>, brackets_span: Span) -> ExprKind {
ExprKind::Index(expr, idx, brackets_span)
}
fn mk_call(&self, f: Box<Expr>, args: ThinVec<Box<Expr>>) -> ExprKind {
ExprKind::Call(f, args)
}
fn mk_await_expr(&mut self, self_arg: Box<Expr>, lo: Span) -> Box<Expr> {
let span = lo.to(self.prev_token.span);
let await_expr = self.mk_expr(span, ExprKind::Await(self_arg, self.prev_token.span));
self.recover_from_await_method_call();
await_expr
}
fn mk_use_expr(&mut self, self_arg: Box<Expr>, lo: Span) -> Box<Expr> {
let span = lo.to(self.prev_token.span);
let use_expr = self.mk_expr(span, ExprKind::Use(self_arg, self.prev_token.span));
self.recover_from_use();
use_expr
}
pub(crate) fn mk_expr_with_attrs(
&self,
span: Span,
kind: ExprKind,
attrs: AttrVec,
) -> Box<Expr> {
Box::new(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
}
pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> Box<Expr> {
self.mk_expr_with_attrs(span, kind, AttrVec::new())
}
pub(super) fn mk_expr_err(&self, span: Span, guar: ErrorGuaranteed) -> Box<Expr> {
self.mk_expr(span, ExprKind::Err(guar))
}
pub(crate) fn mk_unit_expr(&self, span: Span) -> Box<Expr> {
self.mk_expr(span, ExprKind::Tup(Default::default()))
}
pub(crate) fn mk_closure_expr(&self, span: Span, body: Box<Expr>) -> Box<Expr> {
self.mk_expr(
span,
ast::ExprKind::Closure(Box::new(ast::Closure {
binder: rustc_ast::ClosureBinder::NotPresent,
constness: rustc_ast::Const::No,
movability: rustc_ast::Movability::Movable,
capture_clause: rustc_ast::CaptureBy::Ref,
coroutine_kind: None,
fn_decl: Box::new(rustc_ast::FnDecl {
inputs: Default::default(),
output: rustc_ast::FnRetTy::Default(span),
}),
fn_arg_span: span,
fn_decl_span: span,
body,
})),
)
}
/// 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: &Box<Expr>, lhs_span: Span, op_span: Span, rhs_span: Span) -> Span {
lhs.attrs
.iter()
.find(|a| a.style == AttrStyle::Outer)
.map_or(lhs_span, |a| a.span)
.to(op_span)
.to(rhs_span)
}
fn collect_tokens_for_expr(
&mut self,
attrs: AttrWrapper,
f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, Box<Expr>>,
) -> PResult<'a, Box<Expr>> {
self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
let res = f(this, attrs)?;
let trailing = Trailing::from(
this.restrictions.contains(Restrictions::STMT_EXPR)
&& this.token == token::Semi
// FIXME: pass an additional condition through from the place
// where we know we need a comma, rather than assuming that
// `#[attr] expr,` always captures a trailing comma.
|| this.token == token::Comma,
);
Ok((res, trailing, UsePreAttrPos::No))
})
}
}
/// Could this lifetime/label be an unclosed char literal? For example, `'a`
/// could be, but `'abc` could not.
pub(crate) fn could_be_unclosed_char_literal(ident: Ident) -> bool {
ident.name.as_str().starts_with('\'')
&& unescape_char(ident.without_first_quote().name.as_str()).is_ok()
}
/// Whether let chains are allowed on all editions, or it's edition dependent (allowed only on
/// 2024 and later). In case of edition dependence, specify the currently present edition.
pub enum LetChainsPolicy {
AlwaysAllowed,
EditionDependent { current_edition: Edition },
}
/// Visitor to check for invalid use of `ExprKind::Let` that can't
/// easily be caught in parsing. For example:
///
/// ```rust,ignore (example)
/// // Only know that the let isn't allowed once the `||` token is reached
/// if let Some(x) = y || true {}
/// // Only know that the let isn't allowed once the second `=` token is reached.
/// if let Some(x) = y && z = 1 {}
/// ```
struct CondChecker<'a> {
parser: &'a Parser<'a>,
let_chains_policy: LetChainsPolicy,
depth: u32,
forbid_let_reason: Option<errors::ForbiddenLetReason>,
missing_let: Option<errors::MaybeMissingLet>,
comparison: Option<errors::MaybeComparison>,
found_incorrect_let_chain: Option<ErrorGuaranteed>,
}
impl<'a> CondChecker<'a> {
fn new(parser: &'a Parser<'a>, let_chains_policy: LetChainsPolicy) -> Self {
CondChecker {
parser,
forbid_let_reason: None,
missing_let: None,
comparison: None,
let_chains_policy,
found_incorrect_let_chain: None,
depth: 0,
}
}
}
impl MutVisitor for CondChecker<'_> {
fn visit_expr(&mut self, e: &mut Expr) {
self.depth += 1;
let span = e.span;
match e.kind {
ExprKind::Let(_, _, _, ref mut recovered @ Recovered::No) => {
if let Some(reason) = self.forbid_let_reason {
let error = match reason {
errors::ForbiddenLetReason::NotSupportedOr(or_span) => {
self.parser.dcx().emit_err(errors::OrInLetChain { span: or_span })
}
_ => {
let guar =
self.parser.dcx().emit_err(errors::ExpectedExpressionFoundLet {
span,
reason,
missing_let: self.missing_let,
comparison: self.comparison,
});
if let Some(_) = self.missing_let {
self.found_incorrect_let_chain = Some(guar);
}
guar
}
};
*recovered = Recovered::Yes(error);
} else if self.depth > 1 {
// Top level `let` is always allowed; only gate chains
match self.let_chains_policy {
LetChainsPolicy::AlwaysAllowed => (),
LetChainsPolicy::EditionDependent { current_edition } => {
if !current_edition.at_least_rust_2024() || !span.at_least_rust_2024() {
self.parser.dcx().emit_err(errors::LetChainPre2024 { span });
}
}
}
}
}
ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, _, _) => {
mut_visit::walk_expr(self, e);
}
ExprKind::Binary(Spanned { node: BinOpKind::Or, span: or_span }, _, _)
if let None | Some(errors::ForbiddenLetReason::NotSupportedOr(_)) =
self.forbid_let_reason =>
{
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(errors::ForbiddenLetReason::NotSupportedOr(or_span));
mut_visit::walk_expr(self, e);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Paren(ref inner)
if let None | Some(errors::ForbiddenLetReason::NotSupportedParentheses(_)) =
self.forbid_let_reason =>
{
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason =
Some(errors::ForbiddenLetReason::NotSupportedParentheses(inner.span));
mut_visit::walk_expr(self, e);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Assign(ref lhs, ref rhs, span) => {
if let ExprKind::Call(_, _) = &lhs.kind {
fn get_path_from_rhs(e: &Expr) -> Option<(u32, &Path)> {
fn inner(e: &Expr, depth: u32) -> Option<(u32, &Path)> {
match &e.kind {
ExprKind::Binary(_, lhs, _) => inner(lhs, depth + 1),
ExprKind::Path(_, path) => Some((depth, path)),
_ => None,
}
}
inner(e, 0)
}
if let Some((depth, path)) = get_path_from_rhs(rhs) {
// For cases like if Some(_) = x && let Some(_) = y && let Some(_) = z
// This return let Some(_) = y expression
fn find_let_some(expr: &Expr) -> Option<&Expr> {
match &expr.kind {
ExprKind::Let(..) => Some(expr),
ExprKind::Binary(op, lhs, rhs) if op.node == BinOpKind::And => {
find_let_some(lhs).or_else(|| find_let_some(rhs))
}
_ => None,
}
}
let expr_span = lhs.span.to(path.span);
if let Some(later_rhs) = find_let_some(rhs)
&& depth > 0
{
let guar = self.parser.dcx().emit_err(errors::LetChainMissingLet {
span: lhs.span,
label_span: expr_span,
rhs_span: later_rhs.span,
sug_span: lhs.span.shrink_to_lo(),
});
self.found_incorrect_let_chain = Some(guar);
}
}
}
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(errors::ForbiddenLetReason::OtherForbidden);
let missing_let = self.missing_let;
if let ExprKind::Binary(_, _, rhs) = &lhs.kind
&& let ExprKind::Path(_, _)
| ExprKind::Struct(_)
| ExprKind::Call(_, _)
| ExprKind::Array(_) = rhs.kind
{
self.missing_let =
Some(errors::MaybeMissingLet { span: rhs.span.shrink_to_lo() });
}
let comparison = self.comparison;
self.comparison = Some(errors::MaybeComparison { span: span.shrink_to_hi() });
mut_visit::walk_expr(self, e);
self.forbid_let_reason = forbid_let_reason;
self.missing_let = missing_let;
self.comparison = comparison;
}
ExprKind::Unary(_, _)
| ExprKind::Await(_, _)
| ExprKind::Use(_, _)
| ExprKind::AssignOp(_, _, _)
| ExprKind::Range(_, _, _)
| ExprKind::Try(_)
| ExprKind::AddrOf(_, _, _)
| ExprKind::Binary(_, _, _)
| ExprKind::Field(_, _)
| ExprKind::Index(_, _, _)
| ExprKind::Call(_, _)
| ExprKind::MethodCall(_)
| ExprKind::Tup(_)
| ExprKind::Paren(_) => {
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(errors::ForbiddenLetReason::OtherForbidden);
mut_visit::walk_expr(self, e);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Cast(ref mut op, _)
| ExprKind::Type(ref mut op, _)
| ExprKind::UnsafeBinderCast(_, ref mut op, _) => {
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(errors::ForbiddenLetReason::OtherForbidden);
self.visit_expr(op);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Let(_, _, _, Recovered::Yes(_))
| ExprKind::Array(_)
| ExprKind::ConstBlock(_)
| ExprKind::Lit(_)
| ExprKind::If(_, _, _)
| ExprKind::While(_, _, _)
| ExprKind::ForLoop { .. }
| ExprKind::Loop(_, _, _)
| ExprKind::Match(_, _, _)
| ExprKind::Closure(_)
| ExprKind::Block(_, _)
| ExprKind::Gen(_, _, _, _)
| ExprKind::TryBlock(_, _)
| ExprKind::Underscore
| ExprKind::Path(_, _)
| ExprKind::Break(_, _)
| ExprKind::Continue(_)
| ExprKind::Ret(_)
| ExprKind::InlineAsm(_)
| ExprKind::OffsetOf(_, _)
| ExprKind::MacCall(_)
| ExprKind::Struct(_)
| ExprKind::Repeat(_, _)
| ExprKind::Yield(_)
| ExprKind::Yeet(_)
| ExprKind::Become(_)
| ExprKind::IncludedBytes(_)
| ExprKind::FormatArgs(_)
| ExprKind::Err(_)
| ExprKind::Dummy => {
// These would forbid any let expressions they contain already.
}
}
self.depth -= 1;
}
}