8000 Don't allow `CoerceUnsized` into `dyn*` (except for trait upcasting) by compiler-errors · Pull Request #103386 · rust-lang/rust · GitHub
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Don't allow CoerceUnsized into dyn* (except for trait upcasting) #103386

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Merged
merged 3 commits into from
Nov 18, 2022
Merged

Don't allow CoerceUnsized into dyn* (except for trait upcasting) #103386

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0af211a
Don't allow implement CoerceUnsized into dyn-star
compiler-errors Oct 22, 2022
6e6c49e
Don't CoerceUnsized dyn* to dyn*
compiler-errors Nov 10, 2022
4f978db
Unbreak upcasting
compiler-errors Nov 10, 2022
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Unbreak upcasting
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@compiler-errors
compiler-errors committed Nov 10, 2022
commit 4f978dbaf91e7029792dd1f7e14a851ee040aabb
4 changes: 3 additions & 1 deletion compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -779,7 +779,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {

match (source.kind(), target.kind()) {
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
(&ty::Dynamic(ref data_a, _, ty::Dyn), &ty::Dynamic(ref data_b, _, ty::Dyn)) => {
(&ty::Dynamic(ref data_a, _, dyn_a), &ty::Dynamic(ref data_b, _, dyn_b))
if dyn_a == dyn_b =>
{
// Upcast coercions permit several things:
//
// 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`
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6 changes: 4 additions & 2 deletions compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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Expand Up @@ -919,7 +919,9 @@ 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
Expand All @@ -938,7 +940,7 @@ 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.
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