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Rollup merge of #103386 - compiler-errors:no-coerceunsized-to-dynstar, r=eholk

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Don't allow `CoerceUnsized` into `dyn*` (except for trait upcasting)

This makes sure we don't accidentally allow coercions like `Box<T>` -> `Box<dyn* Trait>`, or in the case of this ICE, `&T` to `&dyn* Trait`. These coercions don't make sense, at least not via the `CoerceUnsized` trait.

Fixes #102172
Fixes #102429
This commit is contained in:
Matthias Krüger 2022-11-18 14:13:35 +01:00 • committed by GitHub
commit 741f3cf383
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5 changed files with 53 additions and 5 deletions
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8
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@ -912,7 +912,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let mut nested = vec![];
match (source.kind(), target.kind()) {
// Trait+Kx+'a -> Trait+Ky+'b (auto traits and lifetime subtyping).
(&ty::Dynamic(ref data_a, r_a, ty::Dyn), &ty::Dynamic(ref data_b, r_b, ty::Dyn)) => {
(&ty::Dynamic(ref data_a, r_a, dyn_a), &ty::Dynamic(ref data_b, r_b, dyn_b))
if dyn_a == dyn_b =>
{
// See `assemble_candidates_for_unsizing` for more info.
// We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
let iter = data_a
@ -931,7 +933,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
.map(ty::Binder::dummy),
);
let existential_predicates = tcx.mk_poly_existential_predicates(iter);
let source_trait = tcx.mk_dynamic(existential_predicates, r_b, ty::Dyn);
let source_trait = tcx.mk_dynamic(existential_predicates, r_b, dyn_a);
// Require that the traits involved in this upcast are **equal**;
// only the **lifetime bound** is changed.
@ -1140,7 +1142,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}));
}
_ => bug!(),
_ => bug!("source: {source}, target: {target}"),
};
Ok(ImplSourceBuiltinData { nested })