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use crate::method::MethodCallee;
use crate::{has_expected_num_generic_args, FnCtxt, PlaceOp};
use rustc_ast as ast;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_hir_analysis::autoderef::Autoderef;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::InferOk;
use rustc_middle::ty::adjustment::{Adjust, Adjustment, OverloadedDeref, PointerCoercion};
use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Type-check `*oprnd_expr` with `oprnd_expr` type-checked already.
pub(super) fn lookup_derefing(
&self,
expr: &hir::Expr<'_>,
oprnd_expr: &'tcx hir::Expr<'tcx>,
oprnd_ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
if let Some(mt) = oprnd_ty.builtin_deref(true) {
return Some(mt.ty);
}
let ok = self.try_overloaded_deref(expr.span, oprnd_ty)?;
let method = self.register_infer_ok_obligations(ok);
if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
self.apply_adjustments(
oprnd_expr,
vec![Adjustment {
kind: Adjust::Borrow(AutoBorrow::Ref(*region, AutoBorrowMutability::Not)),
target: method.sig.inputs()[0],
}],
);
} else {
span_bug!(expr.span, "input to deref is not a ref?");
}
let ty = self.make_overloaded_place_return_type(method).ty;
self.write_method_call(expr.hir_id, method);
Some(ty)
}
/// Type-check `*base_expr[index_expr]` with `base_expr` and `index_expr` type-checked already.
pub(super) fn lookup_indexing(
&self,
expr: &hir::Expr<'_>,
base_expr: &'tcx hir::Expr<'tcx>,
base_ty: Ty<'tcx>,
index_expr: &'tcx hir::Expr<'tcx>,
idx_ty: Ty<'tcx>,
) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
// FIXME(#18741) -- this is almost but not quite the same as the
// autoderef that normal method probing does. They could likely be
// consolidated.
let mut autoderef = self.autoderef(base_expr.span, base_ty);
let mut result = None;
while result.is_none() && autoderef.next().is_some() {
result = self.try_index_step(expr, base_expr, &autoderef, idx_ty, index_expr);
}
self.register_predicates(autoderef.into_obligations());
result
}
fn negative_index(
&self,
ty: Ty<'tcx>,
span: Span,
base_expr: &hir::Expr<'_>,
) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
let ty = self.resolve_vars_if_possible(ty);
let mut err = self.tcx.sess.struct_span_err(
span,
format!("negative integers cannot be used to index on a `{ty}`"),
);
err.span_label(span, format!("cannot use a negative integer for indexing on `{ty}`"));
if let (hir::ExprKind::Path(..), Ok(snippet)) =
(&base_expr.kind, self.tcx.sess.source_map().span_to_snippet(base_expr.span))
{
// `foo[-1]` to `foo[foo.len() - 1]`
err.span_suggestion_verbose(
span.shrink_to_lo(),
format!(
"to access an element starting from the end of the `{ty}`, compute the index",
),
format!("{snippet}.len() "),
Applicability::MachineApplicable,
);
}
let reported = err.emit();
Some((Ty::new_error(self.tcx, reported), Ty::new_error(self.tcx, reported)))
}
/// To type-check `base_expr[index_expr]`, we progressively autoderef
/// (and otherwise adjust) `base_expr`, looking for a type which either
/// supports builtin indexing or overloaded indexing.
/// This loop implements one step in that search; the autoderef loop
/// is implemented by `lookup_indexing`.
fn try_index_step(
&self,
expr: &hir::Expr<'_>,
base_expr: &hir::Expr<'_>,
autoderef: &Autoderef<'a, 'tcx>,
index_ty: Ty<'tcx>,
index_expr: &hir::Expr<'_>,
) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
let adjusted_ty =
self.structurally_resolve_type(autoderef.span(), autoderef.final_ty(false));
debug!(
"try_index_step(expr={:?}, base_expr={:?}, adjusted_ty={:?}, \
index_ty={:?})",
expr, base_expr, adjusted_ty, index_ty
);
if let hir::ExprKind::Unary(
hir::UnOp::Neg,
hir::Expr {
kind: hir::ExprKind::Lit(hir::Lit { node: ast::LitKind::Int(..), .. }),
..
},
) = index_expr.kind
{
match adjusted_ty.kind() {
ty::Adt(def, _) if self.tcx.is_diagnostic_item(sym::Vec, def.did()) => {
return self.negative_index(adjusted_ty, index_expr.span, base_expr);
}
ty::Slice(_) | ty::Array(_, _) => {
return self.negative_index(adjusted_ty, index_expr.span, base_expr);
}
_ => {}
}
}
for unsize in [false, true] {
let mut self_ty = adjusted_ty;
if unsize {
// We only unsize arrays here.
if let ty::Array(element_ty, _) = adjusted_ty.kind() {
self_ty = Ty::new_slice(self.tcx, *element_ty);
} else {
continue;
}
}
// If some lookup succeeds, write callee into table and extract index/element
// type from the method signature.
// If some lookup succeeded, install method in table
let input_ty = self.next_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::AutoDeref,
span: base_expr.span,
});
let method =
self.try_overloaded_place_op(expr.span, self_ty, &[input_ty], PlaceOp::Index);
if let Some(result) = method {
debug!("try_index_step: success, using overloaded indexing");
let method = self.register_infer_ok_obligations(result);
let mut adjustments = self.adjust_steps(autoderef);
if let ty::Ref(region, _, hir::Mutability::Not) = method.sig.inputs()[0].kind() {
adjustments.push(Adjustment {
kind: Adjust::Borrow(AutoBorrow::Ref(*region, AutoBorrowMutability::Not)),
target: Ty::new_ref(
self.tcx,
*region,
ty::TypeAndMut { mutbl: hir::Mutability::Not, ty: adjusted_ty },
),
});
} else {
span_bug!(expr.span, "input to index is not a ref?");
}
if unsize {
adjustments.push(Adjustment {
kind: Adjust::Pointer(PointerCoercion::Unsize),
target: method.sig.inputs()[0],
});
}
self.apply_adjustments(base_expr, adjustments);
self.write_method_call(expr.hir_id, method);
return Some((input_ty, self.make_overloaded_place_return_type(method).ty));
}
}
None
}
/// Try to resolve an overloaded place op. We only deal with the immutable
/// variant here (Deref/Index). In some contexts we would need the mutable
/// variant (DerefMut/IndexMut); those would be later converted by
/// `convert_place_derefs_to_mutable`.
pub(super) fn try_overloaded_place_op(
&self,
span: Span,
base_ty: Ty<'tcx>,
arg_tys: &[Ty<'tcx>],
op: PlaceOp,
) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
debug!("try_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
let (Some(imm_tr), imm_op) = (match op {
PlaceOp::Deref => (self.tcx.lang_items().deref_trait(), sym::deref),
PlaceOp::Index => (self.tcx.lang_items().index_trait(), sym::index),
}) else {
// Bail if `Deref` or `Index` isn't defined.
return None;
};
// If the lang item was declared incorrectly, stop here so that we don't
// run into an ICE (#83893). The error is reported where the lang item is
// declared.
if !has_expected_num_generic_args(
self.tcx,
imm_tr,
match op {
PlaceOp::Deref => 0,
PlaceOp::Index => 1,
},
) {
return None;
}
self.lookup_method_in_trait(
self.misc(span),
Ident::with_dummy_span(imm_op),
imm_tr,
base_ty,
Some(arg_tys),
)
}
fn try_mutable_overloaded_place_op(
&self,
span: Span,
base_ty: Ty<'tcx>,
arg_tys: &[Ty<'tcx>],
op: PlaceOp,
) -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
debug!("try_mutable_overloaded_place_op({:?},{:?},{:?})", span, base_ty, op);
let (Some(mut_tr), mut_op) = (match op {
PlaceOp::Deref => (self.tcx.lang_items().deref_mut_trait(), sym::deref_mut),
PlaceOp::Index => (self.tcx.lang_items().index_mut_trait(), sym::index_mut),
}) else {
// Bail if `DerefMut` or `IndexMut` isn't defined.
return None;
};
// If the lang item was declared incorrectly, stop here so that we don't
// run into an ICE (#83893). The error is reported where the lang item is
// declared.
if !has_expected_num_generic_args(
self.tcx,
mut_tr,
match op {
PlaceOp::Deref => 0,
PlaceOp::Index => 1,
},
) {
return None;
}
self.lookup_method_in_trait(
self.misc(span),
Ident::with_dummy_span(mut_op),
mut_tr,
base_ty,
Some(arg_tys),
)
}
/// Convert auto-derefs, indices, etc of an expression from `Deref` and `Index`
/// into `DerefMut` and `IndexMut` respectively.
///
/// This is a second pass of typechecking derefs/indices. We need this because we do not
/// always know whether a place needs to be mutable or not in the first pass.
/// This happens whether there is an implicit mutable reborrow, e.g. when the type
/// is used as the receiver of a method call.
pub fn convert_place_derefs_to_mutable(&self, expr: &hir::Expr<'_>) {
// Gather up expressions we want to munge.
let mut exprs = vec![expr];
while let hir::ExprKind::Field(ref expr, _)
| hir::ExprKind::Index(ref expr, _, _)
| hir::ExprKind::Unary(hir::UnOp::Deref, ref expr) = exprs.last().unwrap().kind
{
exprs.push(expr);
}
debug!("convert_place_derefs_to_mutable: exprs={:?}", exprs);
// Fix up autoderefs and derefs.
let mut inside_union = false;
for (i, &expr) in exprs.iter().rev().enumerate() {
debug!("convert_place_derefs_to_mutable: i={} expr={:?}", i, expr);
let mut source = self.node_ty(expr.hir_id);
if matches!(expr.kind, hir::ExprKind::Unary(hir::UnOp::Deref, _)) {
// Clear previous flag; after a pointer indirection it does not apply any more.
inside_union = false;
}
if source.is_union() {
inside_union = true;
}
// Fix up the autoderefs. Autorefs can only occur immediately preceding
// overloaded place ops, and will be fixed by them in order to get
// the correct region.
// Do not mutate adjustments in place, but rather take them,
// and replace them after mutating them, to avoid having the
// typeck results borrowed during (`deref_mut`) method resolution.
let previous_adjustments =
self.typeck_results.borrow_mut().adjustments_mut().remove(expr.hir_id);
if let Some(mut adjustments) = previous_adjustments {
for adjustment in &mut adjustments {
if let Adjust::Deref(Some(ref mut deref)) = adjustment.kind
&& let Some(ok) = self.try_mutable_overloaded_place_op(
expr.span,
source,
&[],
PlaceOp::Deref,
)
{
let method = self.register_infer_ok_obligations(ok);
if let ty::Ref(region, _, mutbl) = *method.sig.output().kind() {
*deref = OverloadedDeref { region, mutbl, span: deref.span };
}
// If this is a union field, also throw an error for `DerefMut` of `ManuallyDrop` (see RFC 2514).
// This helps avoid accidental drops.
if inside_union
&& source.ty_adt_def().is_some_and(|adt| adt.is_manually_drop())
{
let mut err = self.tcx.sess.struct_span_err(
expr.span,
"not automatically applying `DerefMut` on `ManuallyDrop` union field",
);
err.help(
"writing to this reference calls the destructor for the old value",
);
err.help("add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor");
err.emit();
}
}
source = adjustment.target;
}
self.typeck_results.borrow_mut().adjustments_mut().insert(expr.hir_id, adjustments);
}
match expr.kind {
hir::ExprKind::Index(base_expr, ..) => {
self.convert_place_op_to_mutable(PlaceOp::Index, expr, base_expr);
}
hir::ExprKind::Unary(hir::UnOp::Deref, base_expr) => {
self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr);
}
_ => {}
}
}
}
fn convert_place_op_to_mutable(
&self,
op: PlaceOp,
expr: &hir::Expr<'_>,
base_expr: &hir::Expr<'_>,
) {
debug!("convert_place_op_to_mutable({:?}, {:?}, {:?})", op, expr, base_expr);
if !self.typeck_results.borrow().is_method_call(expr) {
debug!("convert_place_op_to_mutable - builtin, nothing to do");
return;
}
// Need to deref because overloaded place ops take self by-reference.
let base_ty = self
.typeck_results
.borrow()
.expr_ty_adjusted(base_expr)
.builtin_deref(false)
.expect("place op takes something that is not a ref")
.ty;
let arg_ty = match op {
PlaceOp::Deref => None,
PlaceOp::Index => {
// We would need to recover the `T` used when we resolve `<_ as Index<T>>::index`
// in try_index_step. This is the subst at index 1.
//
// Note: we should *not* use `expr_ty` of index_expr here because autoderef
// during coercions can cause type of index_expr to differ from `T` (#72002).
// We also could not use `expr_ty_adjusted` of index_expr because reborrowing
// during coercions can also cause type of index_expr to differ from `T`,
// which can potentially cause regionck failure (#74933).
Some(self.typeck_results.borrow().node_args(expr.hir_id).type_at(1))
}
};
let arg_tys = arg_ty.as_slice();
let method = self.try_mutable_overloaded_place_op(expr.span, base_ty, arg_tys, op);
let method = match method {
Some(ok) => self.register_infer_ok_obligations(ok),
// Couldn't find the mutable variant of the place op, keep the
// current, immutable version.
None => return,
};
debug!("convert_place_op_to_mutable: method={:?}", method);
self.write_method_call(expr.hir_id, method);
let ty::Ref(region, _, hir::Mutability::Mut) = method.sig.inputs()[0].kind() else {
span_bug!(expr.span, "input to mutable place op is not a mut ref?");
};
// Convert the autoref in the base expr to mutable with the correct
// region and mutability.
let base_expr_ty = self.node_ty(base_expr.hir_id);
if let Some(adjustments) =
self.typeck_results.borrow_mut().adjustments_mut().get_mut(base_expr.hir_id)
{
let mut source = base_expr_ty;
for adjustment in &mut adjustments[..] {
if let Adjust::Borrow(AutoBorrow::Ref(..)) = adjustment.kind {
debug!("convert_place_op_to_mutable: converting autoref {:?}", adjustment);
let mutbl = AutoBorrowMutability::Mut {
// Deref/indexing can be desugared to a method call,
// so maybe we could use two-phase here.
// See the documentation of AllowTwoPhase for why that's
// not the case today.
allow_two_phase_borrow: AllowTwoPhase::No,
};
adjustment.kind = Adjust::Borrow(AutoBorrow::Ref(*region, mutbl));
adjustment.target = Ty::new_ref(
self.tcx,
*region,
ty::TypeAndMut { ty: source, mutbl: mutbl.into() },
);
}
source = adjustment.target;
}
// If we have an autoref followed by unsizing at the end, fix the unsize target.
if let [
..,
Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
Adjustment { kind: Adjust::Pointer(PointerCoercion::Unsize), ref mut target },
] = adjustments[..]
{
*target = method.sig.inputs()[0];
}
}
}
}