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Fix regionck failure when converting Index to IndexMut

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This commit is contained in:
Gary Guo 2020-07-30 21:14:15 +01:00 • committed by Mark Rousskov
parent 32c481e156
commit b4e552b1c8
1 changed files with 24 additions and 13 deletions
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37
src/librustc_typeck/check/place_op.rs
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@ -9,6 +9,7 @@ use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
use rustc_trait_selection::autoderef::Autoderef;
use std::slice;
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Type-check `*oprnd_expr` with `oprnd_expr` type-checked already.
@ -245,19 +246,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
match expr.kind {
hir::ExprKind::Index(ref base_expr, ref index_expr) => {
// We need to get the final type in case dereferences were needed for the trait
// to apply (#72002).
let index_expr_ty = self.tables.borrow().expr_ty_adjusted(index_expr);
self.convert_place_op_to_mutable(
PlaceOp::Index,
expr,
base_expr,
&[index_expr_ty],
);
hir::ExprKind::Index(ref base_expr, ..) => {
self.convert_place_op_to_mutable(PlaceOp::Index, expr, base_expr);
}
hir::ExprKind::Unary(hir::UnOp::UnDeref, ref base_expr) => {
self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr, &[]);
self.convert_place_op_to_mutable(PlaceOp::Deref, expr, base_expr);
}
_ => {}
}
@ -269,9 +262,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
op: PlaceOp,
expr: &hir::Expr<'_>,
base_expr: &hir::Expr<'_>,
arg_tys: &[Ty<'tcx>],
) {
debug!("convert_place_op_to_mutable({:?}, {:?}, {:?}, {:?})", op, expr, base_expr, arg_tys);
debug!("convert_place_op_to_mutable({:?}, {:?}, {:?})", op, expr, base_expr);
if !self.tables.borrow().is_method_call(expr) {
debug!("convert_place_op_to_mutable - builtin, nothing to do");
return;
@ -286,6 +278,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.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.tables.borrow().node_substs(expr.hir_id).type_at(1))
}
};
let arg_tys = match arg_ty {
None => &[],
Some(ref ty) => slice::from_ref(ty),
};
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),