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split up #[rustc_deny_explicit_impl] attribute

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This commit splits the `#[rustc_deny_explicit_impl(implement_via_object = ...)]` attribute
into two attributes `#[rustc_deny_explicit_impl]` and `#[rustc_do_not_implement_via_object]`.

This allows us to have special traits that can have user-defined impls but do not have the
automatic trait impl for trait objects (`impl Trait for dyn Trait`).
This commit is contained in:
Lukas Markeffsky 2024-12-20 16:57:14 +01:00
parent 8a1f8039a7
commit 42c00cb647
13 changed files with 152 additions and 91 deletions
Download patch file Download diff file Expand all files Collapse all files

11
compiler/rustc_feature/src/builtin_attrs.rs
View file

@ -912,11 +912,20 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
rustc_attr!(
rustc_deny_explicit_impl,
AttributeType::Normal,
template!(List: "implement_via_object = (true|false)"),
template!(Word),
ErrorFollowing,
EncodeCrossCrate::No,
"#[rustc_deny_explicit_impl] enforces that a trait can have no user-provided impls"
),
rustc_attr!(
rustc_do_not_implement_via_object,
AttributeType::Normal,
template!(Word),
ErrorFollowing,
EncodeCrossCrate::No,
"#[rustc_do_not_implement_via_object] opts out of the automatic trait impl for trait objects \
(`impl Trait for dyn Trait`)"
),
rustc_attr!(
rustc_has_incoherent_inherent_impls, AttributeType::Normal, template!(Word),
ErrorFollowing, EncodeCrossCrate::Yes,

4
compiler/rustc_hir_analysis/src/coherence/mod.rs
View file

@ -206,7 +206,9 @@ fn check_object_overlap<'tcx>(
// so this is valid.
} else {
let mut supertrait_def_ids = tcx.supertrait_def_ids(component_def_id);
if supertrait_def_ids.any(|d| d == trait_def_id) {
if supertrait_def_ids
.any(|d| d == trait_def_id && tcx.trait_def(d).implement_via_object)
{
let span = tcx.def_span(impl_def_id);
return Err(struct_span_code_err!(
tcx.dcx(),

45
compiler/rustc_hir_analysis/src/collect.rs
View file

@ -1261,49 +1261,8 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
no_dups.then_some(list)
});
let mut deny_explicit_impl = false;
let mut implement_via_object = true;
if let Some(attr) = tcx.get_attr(def_id, sym::rustc_deny_explicit_impl) {
deny_explicit_impl = true;
let mut seen_attr = false;
for meta in attr.meta_item_list().iter().flatten() {
if let Some(meta) = meta.meta_item()
&& meta.name_or_empty() == sym::implement_via_object
&& let Some(lit) = meta.name_value_literal()
{
if seen_attr {
tcx.dcx().span_err(meta.span, "duplicated `implement_via_object` meta item");
}
seen_attr = true;
match lit.symbol {
kw::True => {
implement_via_object = true;
}
kw::False => {
implement_via_object = false;
}
_ => {
tcx.dcx().span_err(
meta.span,
format!(
"unknown literal passed to `implement_via_object` attribute: {}",
lit.symbol
),
);
}
}
} else {
tcx.dcx().span_err(
meta.span(),
format!("unknown meta item passed to `rustc_deny_explicit_impl` {meta:?}"),
);
}
}
if !seen_attr {
tcx.dcx().span_err(attr.span, "missing `implement_via_object` meta item");
}
}
let deny_explicit_impl = tcx.has_attr(def_id, sym::rustc_deny_explicit_impl);
let implement_via_object = !tcx.has_attr(def_id, sym::rustc_do_not_implement_via_object);
ty::TraitDef {
def_id: def_id.to_def_id(),

4
compiler/rustc_middle/src/ty/trait_def.rs
View file

@ -70,12 +70,12 @@ pub struct TraitDef {
/// Whether to add a builtin `dyn Trait: Trait` implementation.
/// This is enabled for all traits except ones marked with
/// `#[rustc_deny_explicit_impl(implement_via_object = false)]`.
/// `#[rustc_do_not_implement_via_object]`.
pub implement_via_object: bool,
/// Whether a trait is fully built-in, and any implementation is disallowed.
/// This only applies to built-in traits, and is marked via
/// `#[rustc_deny_explicit_impl(implement_via_object = ...)]`.
/// `#[rustc_deny_explicit_impl]`.
pub deny_explicit_impl: bool,
}

1
compiler/rustc_passes/src/check_attr.rs
View file

@ -186,6 +186,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
[sym::rustc_coinductive, ..]
| [sym::rustc_must_implement_one_of, ..]
| [sym::rustc_deny_explicit_impl, ..]
| [sym::rustc_do_not_implement_via_object, ..]
| [sym::const_trait, ..] => self.check_must_be_applied_to_trait(attr, span, target),
[sym::collapse_debuginfo, ..] => self.check_collapse_debuginfo(attr, span, target),
[sym::must_not_suspend, ..] => self.check_must_not_suspend(attr, span, target),

1
compiler/rustc_span/src/symbol.rs
View file

@ -1717,6 +1717,7 @@ symbols! {
rustc_diagnostic_macros,
rustc_dirty,
rustc_do_not_const_check,
rustc_do_not_implement_via_object,
rustc_doc_primitive,
rustc_driver,
rustc_dummy,

4
library/core/src/future/async_drop.rs
View file

@ -133,7 +133,9 @@ pub trait AsyncDrop {
}
#[lang = "async_destruct"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
trait AsyncDestruct {
type AsyncDestructor: Future<Output = ()>;
}

24
library/core/src/marker.rs
View file

@ -141,7 +141,9 @@ unsafe impl<T: Sync + ?Sized> Send for &T {}
)]
#[fundamental] // for Default, for example, which requires that `[T]: !Default` be evaluatable
#[rustc_specialization_trait]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
#[rustc_coinductive]
pub trait Sized {
// Empty.
@ -181,7 +183,9 @@ pub trait Sized {
/// [^1]: Formerly known as *object safe*.
#[unstable(feature = "unsize", issue = "18598")]
#[lang = "unsize"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
pub trait Unsize<T: ?Sized> {
// Empty.
}
@ -815,7 +819,9 @@ impl<T: ?Sized> StructuralPartialEq for PhantomData<T> {}
reason = "this trait is unlikely to ever be stabilized, use `mem::discriminant` instead"
)]
#[lang = "discriminant_kind"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
pub trait DiscriminantKind {
/// The type of the discriminant, which must satisfy the trait
/// bounds required by `mem::Discriminant`.
@ -956,7 +962,9 @@ marker_impls! {
#[unstable(feature = "const_destruct", issue = "133214")]
#[lang = "destruct"]
#[rustc_on_unimplemented(message = "can't drop `{Self}`", append_const_msg)]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
#[cfg_attr(not(bootstrap), const_trait)]
pub trait Destruct {}
@ -967,7 +975,9 @@ pub trait Destruct {}
#[unstable(feature = "tuple_trait", issue = "none")]
#[lang = "tuple_trait"]
#[diagnostic::on_unimplemented(message = "`{Self}` is not a tuple")]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
pub trait Tuple {}
/// A marker for pointer-like types.
@ -1068,7 +1078,9 @@ marker_impls! {
reason = "internal trait for implementing various traits for all function pointers"
)]
#[lang = "fn_ptr_trait"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
pub trait FnPtr: Copy + Clone {
/// Returns the address of the function pointer.
#[lang = "fn_ptr_addr"]

4
library/core/src/mem/transmutability.rs
View file

@ -84,7 +84,9 @@ use crate::marker::{ConstParamTy_, UnsizedConstParamTy};
/// `usize` is stable, but not portable.
#[unstable(feature = "transmutability", issue = "99571")]
#[lang = "transmute_trait"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
#[rustc_coinductive]
pub unsafe trait TransmuteFrom<Src, const ASSUME: Assume = { Assume::NOTHING }>
where

4
library/core/src/ptr/metadata.rs
View file

@ -53,7 +53,9 @@ use crate::ptr::NonNull;
///
/// [`to_raw_parts`]: *const::to_raw_parts
#[lang = "pointee_trait"]
#[rustc_deny_explicit_impl(implement_via_object = false)]
#[cfg_attr(bootstrap, rustc_deny_explicit_impl(implement_via_object = false))]
#[cfg_attr(not(bootstrap), rustc_deny_explicit_impl)]
#[cfg_attr(not(bootstrap), rustc_do_not_implement_via_object)]
pub trait Pointee {
/// The type for metadata in pointers and references to `Self`.
#[lang = "metadata_type"]

50
tests/ui/traits/deny-builtin-object-impl.current.stderr
View file

@ -1,20 +1,44 @@
error[E0277]: the trait bound `dyn NotObject: NotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:19:23
error[E0322]: explicit impls for the `NotImplYesObject` trait are not permitted
--> $DIR/deny-builtin-object-impl.rs:20:1
|
LL | test_not_object::<dyn NotObject>();
| ^^^^^^^^^^^^^ the trait `NotObject` is not implemented for `dyn NotObject`
LL | impl NotImplYesObject for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `NotImplYesObject` not allowed
error[E0277]: the trait bound `dyn NotImplNotObject: NotImplNotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:37:32
|
LL | test_not_impl_not_object::<dyn NotImplNotObject>();
| ^^^^^^^^^^^^^^^^^^^^ the trait `NotImplNotObject` is not implemented for `dyn NotImplNotObject`
|
help: this trait has no implementations, consider adding one
--> $DIR/deny-builtin-object-impl.rs:11:1
--> $DIR/deny-builtin-object-impl.rs:12:1
|
LL | trait NotObject {}
| ^^^^^^^^^^^^^^^
note: required by a bound in `test_not_object`
--> $DIR/deny-builtin-object-impl.rs:15:23
LL | trait NotImplNotObject {}
| ^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `test_not_impl_not_object`
--> $DIR/deny-builtin-object-impl.rs:28:32
|
LL | fn test_not_object<T: NotObject + ?Sized>() {}
| ^^^^^^^^^ required by this bound in `test_not_object`
LL | fn test_not_impl_not_object<T: NotImplNotObject + ?Sized>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `test_not_impl_not_object`
error: aborting due to 1 previous error
error[E0277]: the trait bound `dyn YesImplNotObject: YesImplNotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:40:32
|
LL | test_yes_impl_not_object::<dyn YesImplNotObject>();
| ^^^^^^^^^^^^^^^^^^^^ the trait `YesImplNotObject` is not implemented for `dyn YesImplNotObject`
|
help: this trait has no implementations, consider adding one
--> $DIR/deny-builtin-object-impl.rs:15:1
|
LL | trait YesImplNotObject {}
| ^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `test_yes_impl_not_object`
--> $DIR/deny-builtin-object-impl.rs:30:32
|
LL | fn test_yes_impl_not_object<T: YesImplNotObject + ?Sized>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `test_yes_impl_not_object`
For more information about this error, try `rustc --explain E0277`.
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0277, E0322.
For more information about an error, try `rustc --explain E0277`.

50
tests/ui/traits/deny-builtin-object-impl.next.stderr
View file

@ -1,20 +1,44 @@
error[E0277]: the trait bound `dyn NotObject: NotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:19:23
error[E0322]: explicit impls for the `NotImplYesObject` trait are not permitted
--> $DIR/deny-builtin-object-impl.rs:20:1
|
LL | test_not_object::<dyn NotObject>();
| ^^^^^^^^^^^^^ the trait `NotObject` is not implemented for `dyn NotObject`
LL | impl NotImplYesObject for () {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `NotImplYesObject` not allowed
error[E0277]: the trait bound `dyn NotImplNotObject: NotImplNotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:37:32
|
LL | test_not_impl_not_object::<dyn NotImplNotObject>();
| ^^^^^^^^^^^^^^^^^^^^ the trait `NotImplNotObject` is not implemented for `dyn NotImplNotObject`
|
help: this trait has no implementations, consider adding one
--> $DIR/deny-builtin-object-impl.rs:11:1
--> $DIR/deny-builtin-object-impl.rs:12:1
|
LL | trait NotObject {}
| ^^^^^^^^^^^^^^^
note: required by a bound in `test_not_object`
--> $DIR/deny-builtin-object-impl.rs:15:23
LL | trait NotImplNotObject {}
| ^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `test_not_impl_not_object`
--> $DIR/deny-builtin-object-impl.rs:28:32
|
LL | fn test_not_object<T: NotObject + ?Sized>() {}
| ^^^^^^^^^ required by this bound in `test_not_object`
LL | fn test_not_impl_not_object<T: NotImplNotObject + ?Sized>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `test_not_impl_not_object`
error: aborting due to 1 previous error
error[E0277]: the trait bound `dyn YesImplNotObject: YesImplNotObject` is not satisfied
--> $DIR/deny-builtin-object-impl.rs:40:32
|
LL | test_yes_impl_not_object::<dyn YesImplNotObject>();
| ^^^^^^^^^^^^^^^^^^^^ the trait `YesImplNotObject` is not implemented for `dyn YesImplNotObject`
|
help: this trait has no implementations, consider adding one
--> $DIR/deny-builtin-object-impl.rs:15:1
|
LL | trait YesImplNotObject {}
| ^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `test_yes_impl_not_object`
--> $DIR/deny-builtin-object-impl.rs:30:32
|
LL | fn test_yes_impl_not_object<T: YesImplNotObject + ?Sized>() {}
| ^^^^^^^^^^^^^^^^ required by this bound in `test_yes_impl_not_object`
For more information about this error, try `rustc --explain E0277`.
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0277, E0322.
For more information about an error, try `rustc --explain E0277`.

41
tests/ui/traits/deny-builtin-object-impl.rs
View file

@ -4,18 +4,41 @@
#![feature(rustc_attrs)]
#[rustc_deny_explicit_impl(implement_via_object = true)]
trait YesObject {}
#[rustc_deny_explicit_impl]
trait NotImplYesObject {}
#[rustc_deny_explicit_impl(implement_via_object = false)]
trait NotObject {}
#[rustc_deny_explicit_impl]
#[rustc_do_not_implement_via_object]
trait NotImplNotObject {}
fn test_yes_object<T: YesObject + ?Sized>() {}
#[rustc_do_not_implement_via_object]
trait YesImplNotObject {}
fn test_not_object<T: NotObject + ?Sized>() {}
#[rustc_do_not_implement_via_object]
trait YesImplNotObject2 {}
impl NotImplYesObject for () {}
//~^ ERROR explicit impls for the `NotImplYesObject` trait are not permitted
// If there is no automatic impl then we can add a manual impl:
impl YesImplNotObject2 for dyn YesImplNotObject2 {}
fn test_not_impl_yes_object<T: NotImplYesObject + ?Sized>() {}
fn test_not_impl_not_object<T: NotImplNotObject + ?Sized>() {}
fn test_yes_impl_not_object<T: YesImplNotObject + ?Sized>() {}
fn test_yes_impl_not_object2<T: YesImplNotObject2 + ?Sized>() {}
fn main() {
test_yes_object::<dyn YesObject>();
test_not_object::<dyn NotObject>();
//~^ ERROR the trait bound `dyn NotObject: NotObject` is not satisfied
test_not_impl_yes_object::<dyn NotImplYesObject>();
test_not_impl_not_object::<dyn NotImplNotObject>();
//~^ ERROR the trait bound `dyn NotImplNotObject: NotImplNotObject` is not satisfied
test_yes_impl_not_object::<dyn YesImplNotObject>();
//~^ ERROR the trait bound `dyn YesImplNotObject: YesImplNotObject` is not satisfied
test_yes_impl_not_object2::<dyn YesImplNotObject2>();
}