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Rollup merge of #133768 - compiler-errors:gate, r=lcnr,jackh726

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Remove `generic_associated_types_extended` feature gate

This PR retires nightly support for the `generic_associated_types_extended` feature. This feature hasn't received much attention in the last two years or so, and I believe the feature still remains both unsound and ICEy to use. I think that if we were to redesign and reimplement it, we'd want to first figure out how to implement it soundly, but in the mean time I'd prefer to clean this up.

r? ``@lcnr`` cc ``@jackh726`` who added this feature gate I think
This commit is contained in:
Matthias Krüger 2024-12-03 21:55:28 +01:00 committed by GitHub
commit 12519a6acd
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GPG Key ID: B5690EEEBB952194
24 changed files with 300 additions and 124 deletions
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7
compiler/rustc_feature/src/removed.rs
View File

@ -119,6 +119,13 @@ declare_features! (
(removed, generator_clone, "1.65.0", Some(95360), Some("renamed to `coroutine_clone`")),
/// Allows defining generators.
(removed, generators, "1.21.0", Some(43122), Some("renamed to `coroutines`")),
/// An extension to the `generic_associated_types` feature, allowing incomplete features.
(removed, generic_associated_types_extended, "CURRENT_RUSTC_VERSION", Some(95451),
Some(
"feature needs overhaul and reimplementation pending \
better implied higher-ranked implied bounds support"
)
),
/// Allows `impl Trait` in bindings (`let`, `const`, `static`).
(removed, impl_trait_in_bindings, "1.55.0", Some(63065),
Some("the implementation was not maintainable, the feature may get reintroduced once the current refactorings are done")),

2
compiler/rustc_feature/src/unstable.rs
View File

@ -497,8 +497,6 @@ declare_features! (
(unstable, gen_blocks, "1.75.0", Some(117078)),
/// Infer generic args for both consts and types.
(unstable, generic_arg_infer, "1.55.0", Some(85077)),
/// An extension to the `generic_associated_types` feature, allowing incomplete features.
(incomplete, generic_associated_types_extended, "1.61.0", Some(95451)),
/// Allows non-trivial generic constants which have to have wfness manually propagated to callers
(incomplete, generic_const_exprs, "1.56.0", Some(76560)),
/// Allows generic parameters and where-clauses on free & associated const items.

5
compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
View File

@ -329,10 +329,7 @@ pub fn dyn_compatibility_violations_for_assoc_item(
.collect(),
// Associated types can only be dyn-compatible if they have `Self: Sized` bounds.
ty::AssocKind::Type => {
if !tcx.features().generic_associated_types_extended()
&& !tcx.generics_of(item.def_id).is_own_empty()
&& !item.is_impl_trait_in_trait()
{
if !tcx.generics_of(item.def_id).is_own_empty() && !item.is_impl_trait_in_trait() {
vec![DynCompatibilityViolation::GAT(item.name, item.ident(tcx).span)]
} else {
// We will permit associated types if they are explicitly mentioned in the trait object.

26
compiler/rustc_trait_selection/src/traits/project.rs
View File

@ -14,7 +14,7 @@ use rustc_middle::traits::select::OverflowError;
use rustc_middle::traits::{BuiltinImplSource, ImplSource, ImplSourceUserDefinedData};
use rustc_middle::ty::fast_reject::DeepRejectCtxt;
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable, TypeVisitableExt};
use rustc_middle::ty::visit::TypeVisitableExt;
use rustc_middle::ty::{self, Term, Ty, TyCtxt, TypingMode, Upcast};
use rustc_middle::{bug, span_bug};
use rustc_span::symbol::sym;
@ -179,35 +179,11 @@ pub(super) fn poly_project_and_unify_term<'cx, 'tcx>(
) -> ProjectAndUnifyResult<'tcx> {
let infcx = selcx.infcx;
let r = infcx.commit_if_ok(|_snapshot| {
let old_universe = infcx.universe();
let placeholder_predicate = infcx.enter_forall_and_leak_universe(obligation.predicate);
let new_universe = infcx.universe();
let placeholder_obligation = obligation.with(infcx.tcx, placeholder_predicate);
match project_and_unify_term(selcx, &placeholder_obligation) {
ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
ProjectAndUnifyResult::Holds(obligations)
if old_universe != new_universe
&& selcx.tcx().features().generic_associated_types_extended() =>
{
// If the `generic_associated_types_extended` feature is active, then we ignore any
// obligations references lifetimes from any universe greater than or equal to the
// universe just created. Otherwise, we can end up with something like `for<'a> I: 'a`,
// which isn't quite what we want. Ideally, we want either an implied
// `for<'a where I: 'a> I: 'a` or we want to "lazily" check these hold when we
// instantiate concrete regions. There is design work to be done here; until then,
// however, this allows experimenting potential GAT features without running into
// well-formedness issues.
let new_obligations = obligations
.into_iter()
.filter(|obligation| {
let mut visitor = MaxUniverse::new();
obligation.predicate.visit_with(&mut visitor);
visitor.max_universe() < new_universe
})
.collect();
Ok(ProjectAndUnifyResult::Holds(new_obligations))
}
other => Ok(other),
}
});

2
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View File

@ -626,7 +626,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
for assoc_type in assoc_types {
let defs: &ty::Generics = tcx.generics_of(assoc_type);
if !defs.own_params.is_empty() && !tcx.features().generic_associated_types_extended() {
if !defs.own_params.is_empty() {
tcx.dcx().span_delayed_bug(
obligation.cause.span,
"GATs in trait object shouldn't have been considered",

13
tests/crashes/131538.rs
View File

@ -1,13 +0,0 @@
//@ known-bug: #131538
#![feature(generic_associated_types_extended)]
#![feature(trivial_bounds)]
trait HealthCheck {
async fn check<const N: usize>();
}
fn do_health_check_par()
where
HealthCheck: HealthCheck,
{
}

4
tests/ui/feature-gates/feature-gate-generic_associated_types_extended.rs
View File

@ -1,4 +0,0 @@
// This feature doesn't *currently* fire on any specific code; it's just a
// behavior change. Future changes might.
#[rustc_error] //~ the
fn main() {}

12
tests/ui/feature-gates/feature-gate-generic_associated_types_extended.stderr
View File

@ -1,12 +0,0 @@
error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
--> $DIR/feature-gate-generic_associated_types_extended.rs:3:1
|
LL | #[rustc_error]
| ^^^^^^^^^^^^^^
|
= help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0658`.

9
tests/ui/generic-associated-types/extended/lending_iterator.rs
View File

@ -1,9 +1,4 @@
//@ revisions: base extended
//@[base] check-fail
//@[extended] check-pass
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
//@ known-bug: #133805
pub trait FromLendingIterator<A>: Sized {
fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
@ -11,7 +6,6 @@ pub trait FromLendingIterator<A>: Sized {
impl<A> FromLendingIterator<A> for Vec<A> {
fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) -> Self {
//[base]~^ impl has stricter
let mut v = vec![];
while let Some(item) = iter.next() {
v.push(item);
@ -32,7 +26,6 @@ pub trait LendingIterator {
Self: for<'q> LendingIterator<Item<'q> = A>,
{
<B as FromLendingIterator<A>>::from_iter(self)
//[base]~^ ERROR: does not live long enough
}
}

4
tests/ui/generic-associated-types/extended/lending_iterator.base.stderr → tests/ui/generic-associated-types/extended/lending_iterator.stderr
View File

@ -1,5 +1,5 @@
error[E0276]: impl has stricter requirements than trait
--> $DIR/lending_iterator.rs:13:45
--> $DIR/lending_iterator.rs:8:45
|
LL | fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
| ------------------------------------------------------------------------ definition of `from_iter` from trait
@ -8,7 +8,7 @@ LL | fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) ->
| ^^^^^^^^^^^^ impl has extra requirement `I: 'x`
error: `Self` does not live long enough
--> $DIR/lending_iterator.rs:34:9
--> $DIR/lending_iterator.rs:28:9
|
LL | <B as FromLendingIterator<A>>::from_iter(self)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

8
tests/ui/generic-associated-types/extended/lending_iterator_2.rs
View File

@ -1,9 +1,4 @@
//@ revisions: base extended
//@[base] check-fail
//@[extended] check-pass
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
//@ known-bug: #133805
pub trait FromLendingIterator<A>: Sized {
fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
@ -11,7 +6,6 @@ pub trait FromLendingIterator<A>: Sized {
impl<A> FromLendingIterator<A> for Vec<A> {
fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) -> Self {
//[base]~^ impl has stricter
let mut v = vec![];
while let Some(item) = iter.next() {
v.push(item);

2
tests/ui/generic-associated-types/extended/lending_iterator_2.base.stderr → tests/ui/generic-associated-types/extended/lending_iterator_2.stderr
View File

@ -1,5 +1,5 @@
error[E0276]: impl has stricter requirements than trait
--> $DIR/lending_iterator_2.rs:13:45
--> $DIR/lending_iterator_2.rs:8:45
|
LL | fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
| ------------------------------------------------------------------------ definition of `from_iter` from trait

12
tests/ui/generic-associated-types/gat-in-trait-path.rs
View File

@ -1,10 +1,6 @@
//@ revisions: base extended
//@[base] check-fail
//@[extended] check-pass
//@ check-fail
#![feature(associated_type_defaults)]
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
trait Foo {
type A<'a> where Self: 'a;
@ -24,12 +20,12 @@ impl<T> Foo for Fooer<T> {
}
fn f(_arg : Box<dyn for<'a> Foo<A<'a> = &'a ()>>) {}
//[base]~^ the trait `Foo` cannot be made into an object
//~^ the trait `Foo` cannot be made into an object
fn main() {
let foo = Fooer(5);
f(Box::new(foo));
//[base]~^ the trait `Foo` cannot be made into an object
//[base]~| the trait `Foo` cannot be made into an object
//~^ the trait `Foo` cannot be made into an object
//~| the trait `Foo` cannot be made into an object
}

58
tests/ui/generic-associated-types/gat-in-trait-path.stderr Normal file
View File

@ -0,0 +1,58 @@
error[E0038]: the trait `Foo` cannot be made into an object
--> $DIR/gat-in-trait-path.rs:22:17
|
LL | fn f(_arg : Box<dyn for<'a> Foo<A<'a> = &'a ()>>) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Foo` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/gat-in-trait-path.rs:6:10
|
LL | trait Foo {
| --- this trait cannot be made into an object...
LL | type A<'a> where Self: 'a;
| ^ ...because it contains the generic associated type `A`
= help: consider moving `A` to another trait
= help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
Fooy
Fooer<T>
error[E0038]: the trait `Foo` cannot be made into an object
--> $DIR/gat-in-trait-path.rs:28:5
|
LL | f(Box::new(foo));
| ^^^^^^^^^^^^^ `Foo` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/gat-in-trait-path.rs:6:10
|
LL | trait Foo {
| --- this trait cannot be made into an object...
LL | type A<'a> where Self: 'a;
| ^ ...because it contains the generic associated type `A`
= help: consider moving `A` to another trait
= help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
Fooy
Fooer<T>
error[E0038]: the trait `Foo` cannot be made into an object
--> $DIR/gat-in-trait-path.rs:28:5
|
LL | f(Box::new(foo));
| ^^^^^^^^^^^^^ `Foo` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/gat-in-trait-path.rs:6:10
|
LL | trait Foo {
| --- this trait cannot be made into an object...
LL | type A<'a> where Self: 'a;
| ^ ...because it contains the generic associated type `A`
= help: consider moving `A` to another trait
= help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
Fooy
Fooer<T>
= note: required for the cast from `Box<Fooer<{integer}>>` to `Box<(dyn Foo<A<'a> = &'a ()> + 'static)>`
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0038`.

9
tests/ui/generic-associated-types/issue-67510-pass.rs
View File

@ -1,15 +1,10 @@
//@ revisions: base extended
//@[base] check-fail
//@[extended] check-pass
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
//@ check-fail
trait X {
type Y<'a>;
}
fn _func1<'a>(_x: Box<dyn X<Y<'a>=&'a ()>>) {}
//[base]~^ ERROR the trait `X` cannot be made into an object
//~^ ERROR the trait `X` cannot be made into an object
fn main() {}

18
tests/ui/generic-associated-types/issue-67510-pass.stderr Normal file
View File

@ -0,0 +1,18 @@
error[E0038]: the trait `X` cannot be made into an object
--> $DIR/issue-67510-pass.rs:7:23
|
LL | fn _func1<'a>(_x: Box<dyn X<Y<'a>=&'a ()>>) {}
| ^^^^^^^^^^^^^^^^^^^ `X` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-67510-pass.rs:4:10
|
LL | trait X {
| - this trait cannot be made into an object...
LL | type Y<'a>;
| ^ ...because it contains the generic associated type `Y`
= help: consider moving `Y` to another trait
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0038`.

9
tests/ui/generic-associated-types/issue-76535.rs
View File

@ -1,8 +1,3 @@
//@ revisions: base extended
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
pub trait SubTrait {}
pub trait SuperTrait {
@ -38,6 +33,6 @@ impl SuperTrait for SuperStruct {
fn main() {
let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
//~^ ERROR missing generics for associated type
//[base]~^^ ERROR the trait
//[base]~| ERROR the trait
//~^^ ERROR the trait
//~| ERROR the trait
}

55
tests/ui/generic-associated-types/issue-76535.stderr Normal file
View File

@ -0,0 +1,55 @@
error[E0107]: missing generics for associated type `SuperTrait::SubType`
--> $DIR/issue-76535.rs:34:33
|
LL | let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
| ^^^^^^^ expected 1 lifetime argument
|
note: associated type defined here, with 1 lifetime parameter: `'a`
--> $DIR/issue-76535.rs:4:10
|
LL | type SubType<'a>: SubTrait where Self: 'a;
| ^^^^^^^ --
help: add missing lifetime argument
|
LL | let sub: Box<dyn SuperTrait<SubType<'a> = SubStruct>> = Box::new(SuperStruct::new(0));
| ++++
error[E0038]: the trait `SuperTrait` cannot be made into an object
--> $DIR/issue-76535.rs:34:14
|
LL | let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-76535.rs:4:10
|
LL | pub trait SuperTrait {
| ---------- this trait cannot be made into an object...
LL | type SubType<'a>: SubTrait where Self: 'a;
| ^^^^^^^ ...because it contains the generic associated type `SubType`
= help: consider moving `SubType` to another trait
= help: only type `SuperStruct` is seen to implement the trait in this crate, consider using it directly instead
= note: `SuperTrait` can be implemented in other crates; if you want to support your users passing their own types here, you can't refer to a specific type
error[E0038]: the trait `SuperTrait` cannot be made into an object
--> $DIR/issue-76535.rs:34:57
|
LL | let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-76535.rs:4:10
|
LL | pub trait SuperTrait {
| ---------- this trait cannot be made into an object...
LL | type SubType<'a>: SubTrait where Self: 'a;
| ^^^^^^^ ...because it contains the generic associated type `SubType`
= help: consider moving `SubType` to another trait
= help: only type `SuperStruct` is seen to implement the trait in this crate, consider using it directly instead
= note: `SuperTrait` can be implemented in other crates; if you want to support your users passing their own types here, you can't refer to a specific type
= note: required for the cast from `Box<SuperStruct>` to `Box<dyn SuperTrait<SubType<'_> = SubStruct<'_>>>`
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0038, E0107.
For more information about an error, try `rustc --explain E0038`.

7
tests/ui/generic-associated-types/issue-78671.rs
View File

@ -1,15 +1,10 @@
//@ revisions: base extended
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
trait CollectionFamily {
type Member<T>;
}
fn floatify() {
Box::new(Family) as &dyn CollectionFamily<Member=usize>
//~^ ERROR: missing generics for associated type
//[base]~^^ ERROR: the trait `CollectionFamily` cannot be made into an object
//~| ERROR: the trait `CollectionFamily` cannot be made into an object
}
struct Family;

35
tests/ui/generic-associated-types/issue-78671.stderr Normal file
View File

@ -0,0 +1,35 @@
error[E0107]: missing generics for associated type `CollectionFamily::Member`
--> $DIR/issue-78671.rs:5:47
|
LL | Box::new(Family) as &dyn CollectionFamily<Member=usize>
| ^^^^^^ expected 1 generic argument
|
note: associated type defined here, with 1 generic parameter: `T`
--> $DIR/issue-78671.rs:2:10
|
LL | type Member<T>;
| ^^^^^^ -
help: add missing generic argument
|
LL | Box::new(Family) as &dyn CollectionFamily<Member<T>=usize>
| +++
error[E0038]: the trait `CollectionFamily` cannot be made into an object
--> $DIR/issue-78671.rs:5:25
|
LL | Box::new(Family) as &dyn CollectionFamily<Member=usize>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `CollectionFamily` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-78671.rs:2:10
|
LL | trait CollectionFamily {
| ---------------- this trait cannot be made into an object...
LL | type Member<T>;
| ^^^^^^ ...because it contains the generic associated type `Member`
= help: consider moving `Member` to another trait
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0038, E0107.
For more information about an error, try `rustc --explain E0038`.

10
tests/ui/generic-associated-types/issue-79422.rs
View File

@ -1,8 +1,3 @@
//@ revisions: base extended
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
trait RefCont<'a, T> {
fn t(&'a self) -> &'a T;
}
@ -42,9 +37,8 @@ impl<K, V: Default> MapLike<K, V> for Source {
fn main() {
let m = Box::new(std::collections::BTreeMap::<u8, u8>::new())
//[base]~^ ERROR the trait
//[extended]~^^ type mismatch
//~^ ERROR the trait
as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
//~^ ERROR missing generics for associated type
//[base]~^^ ERROR the trait
//~| ERROR the trait
}

57
tests/ui/generic-associated-types/issue-79422.stderr Normal file
View File

@ -0,0 +1,57 @@
error[E0107]: missing generics for associated type `MapLike::VRefCont`
--> $DIR/issue-79422.rs:41:36
|
LL | as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
| ^^^^^^^^ expected 1 lifetime argument
|
note: associated type defined here, with 1 lifetime parameter: `'a`
--> $DIR/issue-79422.rs:18:10
|
LL | type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
| ^^^^^^^^ --
help: add missing lifetime argument
|
LL | as Box<dyn MapLike<u8, u8, VRefCont<'a> = dyn RefCont<'_, u8>>>;
| ++++
error[E0038]: the trait `MapLike` cannot be made into an object
--> $DIR/issue-79422.rs:41:12
|
LL | as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-79422.rs:18:10
|
LL | trait MapLike<K, V> {
| ------- this trait cannot be made into an object...
LL | type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
| ^^^^^^^^ ...because it contains the generic associated type `VRefCont`
= help: consider moving `VRefCont` to another trait
= help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `MapLike` for this new enum and using it instead:
std::collections::BTreeMap<K, V>
Source
error[E0038]: the trait `MapLike` cannot be made into an object
--> $DIR/issue-79422.rs:39:13
|
LL | let m = Box::new(std::collections::BTreeMap::<u8, u8>::new())
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/issue-79422.rs:18:10
|
LL | trait MapLike<K, V> {
| ------- this trait cannot be made into an object...
LL | type VRefCont<'a>: RefCont<'a, V> where Self: 'a;
| ^^^^^^^^ ...because it contains the generic associated type `VRefCont`
= help: consider moving `VRefCont` to another trait
= help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `MapLike` for this new enum and using it instead:
std::collections::BTreeMap<K, V>
Source
= note: required for the cast from `Box<BTreeMap<u8, u8>>` to `Box<dyn MapLike<u8, u8, VRefCont<'_> = (dyn RefCont<'_, u8> + 'static)>>`
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0038, E0107.
For more information about an error, try `rustc --explain E0038`.

12
tests/ui/generic-associated-types/trait-objects.rs
View File

@ -1,8 +1,3 @@
//@ revisions: base extended
#![cfg_attr(extended, feature(generic_associated_types_extended))]
#![cfg_attr(extended, allow(incomplete_features))]
trait StreamingIterator {
type Item<'a> where Self: 'a;
fn size_hint(&self) -> (usize, Option<usize>);
@ -11,11 +6,10 @@ trait StreamingIterator {
}
fn min_size(x: &mut dyn for<'a> StreamingIterator<Item<'a> = &'a i32>) -> usize {
//[base]~^ the trait `StreamingIterator` cannot be made into an object
//~^ the trait `StreamingIterator` cannot be made into an object
x.size_hint().0
//[extended]~^ borrowed data escapes
//[base]~^^ the trait `StreamingIterator` cannot be made into an object
//[base]~| the trait `StreamingIterator` cannot be made into an object
//~^ the trait `StreamingIterator` cannot be made into an object
//~| the trait `StreamingIterator` cannot be made into an object
}
fn main() {}

48
tests/ui/generic-associated-types/trait-objects.stderr Normal file
View File

@ -0,0 +1,48 @@
error[E0038]: the trait `StreamingIterator` cannot be made into an object
--> $DIR/trait-objects.rs:8:21
|
LL | fn min_size(x: &mut dyn for<'a> StreamingIterator<Item<'a> = &'a i32>) -> usize {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `StreamingIterator` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/trait-objects.rs:2:10
|
LL | trait StreamingIterator {
| ----------------- this trait cannot be made into an object...
LL | type Item<'a> where Self: 'a;
| ^^^^ ...because it contains the generic associated type `Item`
= help: consider moving `Item` to another trait
error[E0038]: the trait `StreamingIterator` cannot be made into an object
--> $DIR/trait-objects.rs:10:7
|
LL | x.size_hint().0
| ^^^^^^^^^ `StreamingIterator` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/trait-objects.rs:2:10
|
LL | trait StreamingIterator {
| ----------------- this trait cannot be made into an object...
LL | type Item<'a> where Self: 'a;
| ^^^^ ...because it contains the generic associated type `Item`
= help: consider moving `Item` to another trait
error[E0038]: the trait `StreamingIterator` cannot be made into an object
--> $DIR/trait-objects.rs:10:5
|
LL | x.size_hint().0
| ^^^^^^^^^^^^^ `StreamingIterator` cannot be made into an object
|
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
--> $DIR/trait-objects.rs:2:10
|
LL | trait StreamingIterator {
| ----------------- this trait cannot be made into an object...
LL | type Item<'a> where Self: 'a;
| ^^^^ ...because it contains the generic associated type `Item`
= help: consider moving `Item` to another trait
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0038`.