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Disable dyn* upcasting

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This commit is contained in:
Michael Goulet 2022-11-19 04:48:01 +00:00
parent 70f8737b2f
commit c620a972f3
7 changed files with 75 additions and 35 deletions
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38
compiler/rustc_hir_typeck/src/coercion.rs
View File

@ -755,20 +755,9 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
if let ty::Dynamic(a_data, _, _) = a.kind()
&& let ty::Dynamic(b_data, _, _) = b.kind()
&& a_data.principal_def_id() == b_data.principal_def_id()
{
if a_data.principal_def_id() == b_data.principal_def_id() {
return self.unify_and(a, b, |_| vec![]);
} else if !self.tcx().features().trait_upcasting {
let mut err = feature_err(
&self.tcx.sess.parse_sess,
sym::trait_upcasting,
self.cause.span,
&format!(
"cannot cast `{a}` to `{b}`, trait upcasting coercion is experimental"
),
);
err.emit();
}
return self.unify_and(a, b, |_| vec![]);
}
// Check the obligations of the cast -- for example, when casting
@ -796,19 +785,16 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
])
.collect();
// Enforce that the type is `usize`/pointer-sized. For now, only those
// can be coerced to `dyn*`, except for `dyn* -> dyn*` upcasts.
if !a.is_dyn_star() {
obligations.push(Obligation::new(
self.tcx,
self.cause.clone(),
self.param_env,
ty::Binder::dummy(
self.tcx.at(self.cause.span).mk_trait_ref(hir::LangItem::PointerSized, [a]),
)
.to_poly_trait_predicate(),
));
}
// Enforce that the type is `usize`/pointer-sized.
obligations.push(Obligation::new(
self.tcx,
self.cause.clone(),
self.param_env,
ty::Binder::dummy(
self.tcx.at(self.cause.span).mk_trait_ref(hir::LangItem::PointerSized, [a]),
)
.to_poly_trait_predicate(),
));
Ok(InferOk {
value: (vec![Adjustment { kind: Adjust::DynStar, target: b }], b),

4
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
View File

@ -776,9 +776,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
match (source.kind(), target.kind()) {
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
(&ty::Dynamic(ref data_a, _, dyn_a), &ty::Dynamic(ref data_b, _, dyn_b))
if dyn_a == dyn_b =>
{
(&ty::Dynamic(ref data_a, _, ty::Dyn), &ty::Dynamic(ref data_b, _, ty::Dyn)) => {
// Upcast coercions permit several things:
//
// 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`

9
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View File

@ -803,9 +803,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let upcast_trait_ref;
match (source.kind(), target.kind()) {
// TraitA+Kx+'a -> TraitB+Ky+'b (trait upcasting coercion).
(&ty::Dynamic(ref data_a, r_a, repr_a), &ty::Dynamic(ref data_b, r_b, repr_b))
if repr_a == repr_b =>
{
(
&ty::Dynamic(ref data_a, r_a, repr_a @ ty::Dyn),
&ty::Dynamic(ref data_b, r_b, ty::Dyn),
) => {
// See `assemble_candidates_for_unsizing` for more info.
// We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
let principal_a = data_a.principal().unwrap();
@ -831,7 +832,7 @@ 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, repr_b);
let source_trait = tcx.mk_dynamic(existential_predicates, r_b, repr_a);
// Require that the traits involved in this upcast are **equal**;
// only the **lifetime bound** is changed.

13
src/test/ui/dyn-star/no-unsize-coerce-dyn-trait.rs Normal file
View File

@ -0,0 +1,13 @@
#![feature(dyn_star, trait_upcasting)]
//~^ WARN the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
trait A: B {}
trait B {}
impl A for usize {}
impl B for usize {}
fn main() {
let x: Box<dyn* A> = Box::new(1usize as dyn* A);
let y: Box<dyn* B> = x;
//~^ ERROR mismatched types
}

23
src/test/ui/dyn-star/no-unsize-coerce-dyn-trait.stderr Normal file
View File

@ -0,0 +1,23 @@
warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/no-unsize-coerce-dyn-trait.rs:1:12
|
LL | #![feature(dyn_star, trait_upcasting)]
| ^^^^^^^^
|
= note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
= note: `#[warn(incomplete_features)]` on by default
error[E0308]: mismatched types
--> $DIR/no-unsize-coerce-dyn-trait.rs:11:26
|
LL | let y: Box<dyn* B> = x;
| ----------- ^ expected trait `B`, found trait `A`
| |
| expected due to this
|
= note: expected struct `Box<dyn* B>`
found struct `Box<dyn* A>`
error: aborting due to previous error; 1 warning emitted
For more information about this error, try `rustc --explain E0308`.

3
src/test/ui/dyn-star/upcast.rs
View File

@ -1,7 +1,6 @@
// run-pass
// known-bug: unknown
#![feature(dyn_star, trait_upcasting)]
#![allow(incomplete_features)]
trait Foo: Bar {
fn hello(&self);

20
src/test/ui/dyn-star/upcast.stderr Normal file
View File

@ -0,0 +1,20 @@
warning: the feature `dyn_star` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/upcast.rs:3:12
|
LL | #![feature(dyn_star, trait_upcasting)]
| ^^^^^^^^
|
= note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
= note: `#[warn(incomplete_features)]` on by default
error[E0277]: `dyn* Foo` needs to be a pointer-sized type
--> $DIR/upcast.rs:30:23
|
LL | let w: dyn* Bar = w;
| ^ `dyn* Foo` needs to be a pointer-sized type
|
= help: the trait `PointerSized` is not implemented for `dyn* Foo`
error: aborting due to previous error; 1 warning emitted
For more information about this error, try `rustc --explain E0277`.