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Rollup merge of #113741 - compiler-errors:rpitit-projects-to-missing-opaque, r=spastorino

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Don't install default projection bound for return-position `impl Trait` in trait methods with no body

This ensures that we never try to project to an opaque type in a trait method that has no body to infer its hidden type, which means we never later call `type_of` on that opaque. This is because opaque types try to reveal their hidden type when proving auto traits.

I thought about this a lot, and I think this is a fix that's less likely to introduce other strange downstream ICEs than #113461.

Fixes #113434

r? `@spastorino`
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Jubilee 2023-07-30 17:50:48 -07:00 committed by GitHub
commit 126d809287
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4 changed files with 30 additions and 8 deletions
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8
compiler/rustc_metadata/src/rmeta/encoder.rs
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@ -1144,13 +1144,7 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
let assoc_item = tcx.associated_item(def_id);
match assoc_item.container {
ty::AssocItemContainer::ImplContainer => true,
// Always encode RPITITs, since we need to be able to project
// from an RPITIT associated item to an opaque when installing
// the default projection predicates in default trait methods
// with RPITITs.
ty::AssocItemContainer::TraitContainer => {
assoc_item.defaultness(tcx).has_value() || assoc_item.is_impl_trait_in_trait()
}
ty::AssocItemContainer::TraitContainer => assoc_item.defaultness(tcx).has_value(),
}
}
DefKind::TyParam => {

4
compiler/rustc_ty_utils/src/ty.rs
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@ -129,7 +129,9 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
// sure that this will succeed without errors anyway.
if tcx.def_kind(def_id) == DefKind::AssocFn
&& tcx.associated_item(def_id).container == ty::AssocItemContainer::TraitContainer
&& let assoc_item = tcx.associated_item(def_id)
&& assoc_item.container == ty::AssocItemContainer::TraitContainer
&& assoc_item.defaultness(tcx).has_value()
{
let sig = tcx.fn_sig(def_id).instantiate_identity();
// We accounted for the binder of the fn sig, so skip the binder.

10
tests/ui/impl-trait/in-trait/check-wf-on-non-defaulted-rpitit.rs Normal file
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@ -0,0 +1,10 @@
#![feature(return_position_impl_trait_in_trait)]
struct Wrapper<G: Send>(G);
trait Foo {
fn bar() -> Wrapper<impl Sized>;
//~^ ERROR `impl Sized` cannot be sent between threads safely
}
fn main() {}

16
tests/ui/impl-trait/in-trait/check-wf-on-non-defaulted-rpitit.stderr Normal file
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@ -0,0 +1,16 @@
error[E0277]: `impl Sized` cannot be sent between threads safely
--> $DIR/check-wf-on-non-defaulted-rpitit.rs:6:17
|
LL | fn bar() -> Wrapper<impl Sized>;
| ^^^^^^^^^^^^^^^^^^^ `impl Sized` cannot be sent between threads safely
|
= help: the trait `Send` is not implemented for `impl Sized`
note: required by a bound in `Wrapper`
--> $DIR/check-wf-on-non-defaulted-rpitit.rs:3:19
|
LL | struct Wrapper<G: Send>(G);
| ^^^^ required by this bound in `Wrapper`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.