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require trait impls to have matching const stabilities as the traits
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8 files changed

+200
-17
lines changed

8 files changed

+200
-17
lines changed

‎compiler/rustc_const_eval/src/check_consts/mod.rs

+5
Original file line numberDiff line numberDiff line change
@@ -92,6 +92,11 @@ pub fn rustc_allow_const_fn_unstable(
9292
/// world into two functions: those that are safe to expose on stable (and hence may not use
9393
/// unstable features, not even recursively), and those that are not.
9494
pub fn is_fn_or_trait_safe_to_expose_on_stable(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
95+
// A default body in a `#[const_trait]` is const-stable when the trait is const-stable.
96+
if tcx.is_const_default_method(def_id) {
97+
return is_fn_or_trait_safe_to_expose_on_stable(tcx, tcx.parent(def_id));
98+
}
99+
95100
match tcx.lookup_const_stability(def_id) {
96101
None => {
97102
// In a `staged_api` crate, we do enforce recursive const stability for all unmarked

‎compiler/rustc_passes/messages.ftl

+6
Original file line numberDiff line numberDiff line change
@@ -732,6 +732,12 @@ passes_target_feature_on_statement =
732732
.warn = {-passes_previously_accepted}
733733
.label = {passes_should_be_applied_to_fn.label}
734734
735+
passes_trait_impl_const_stability_mismatch = const stability on the impl does not match the const stability on the trait
736+
passes_trait_impl_const_stability_mismatch_impl_stable = this impl is (implicitly) stable...
737+
passes_trait_impl_const_stability_mismatch_impl_unstable = this impl is unstable...
738+
passes_trait_impl_const_stability_mismatch_trait_stable = ...but the trait is stable
739+
passes_trait_impl_const_stability_mismatch_trait_unstable = ...but the trait is unstable
740+
735741
passes_trait_impl_const_stable =
736742
trait implementations cannot be const stable yet
737743
.note = see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information

‎compiler/rustc_passes/src/errors.rs

+39
Original file line numberDiff line numberDiff line change
@@ -1588,6 +1588,45 @@ pub(crate) struct TraitImplConstStable {
15881588
pub span: Span,
15891589
}
15901590

1591+
#[derive(Diagnostic)]
1592+
#[diag(passes_trait_impl_const_stability_mismatch)]
1593+
pub(crate) struct TraitImplConstStabilityMismatch {
1594+
#[primary_span]
1595+
pub span: Span,
1596+
#[subdiagnostic]
1597+
pub impl_stability: ImplConstStability,
1598+
#[subdiagnostic]
1599+
pub trait_stability: TraitConstStability,
1600+
}
1601+
1602+
#[derive(Subdiagnostic)]
1603+
pub(crate) enum TraitConstStability {
1604+
#[note(passes_trait_impl_const_stability_mismatch_trait_stable)]
1605+
Stable {
1606+
#[primary_span]
1607+
span: Span,
1608+
},
1609+
#[note(passes_trait_impl_const_stability_mismatch_trait_unstable)]
1610+
Unstable {
1611+
#[primary_span]
1612+
span: Span,
1613+
},
1614+
}
1615+
1616+
#[derive(Subdiagnostic)]
1617+
pub(crate) enum ImplConstStability {
1618+
#[note(passes_trait_impl_const_stability_mismatch_impl_stable)]
1619+
Stable {
1620+
#[primary_span]
1621+
span: Span,
1622+
},
1623+
#[note(passes_trait_impl_const_stability_mismatch_impl_unstable)]
1624+
Unstable {
1625+
#[primary_span]
1626+
span: Span,
1627+
},
1628+
}
1629+
15911630
#[derive(Diagnostic)]
15921631
#[diag(passes_unknown_feature, code = E0635)]
15931632
pub(crate) struct UnknownFeature {

‎compiler/rustc_passes/src/stability.rs

+46-16
Original file line numberDiff line numberDiff line change
@@ -301,7 +301,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
301301
let mut const_stab = const_stab.map(|(stab, _span)| stab);
302302

303303
// If this is a const fn but not annotated with stability markers, see if we can inherit regular stability.
304-
if fn_sig.is_some_and(|s| s.header.is_const()) && const_stab.is_none() &&
304+
if fn_sig.is_some_and(|s| s.header.is_const()) && const_stab.is_none() &&
305305
// We only ever inherit unstable features.
306306
let Some(inherit_regular_stab) =
307307
final_stab.filter(|s| s.is_unstable())
@@ -816,24 +816,54 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
816816
}
817817
}
818818

819-
// `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
820-
// needs to have an error emitted.
821-
if features.const_trait_impl()
822-
&& self.tcx.is_const_trait_impl(item.owner_id.to_def_id())
823-
&& const_stab.is_some_and(|(stab, _)| stab.is_const_stable())
824-
{
825-
self.tcx.dcx().emit_err(errors::TraitImplConstStable { span: item.span });
819+
if features.const_trait_impl() && hir::Constness::Const == *constness {
820+
let stable_or_implied_stable = match const_stab {
821+
None => true,
822+
Some((stab, _)) if stab.is_const_stable() => {
823+
// `#![feature(const_trait_impl)]` is unstable, so any impl declared stable
824+
// needs to have an error emitted.
825+
// Note: Remove this error once `const_trait_impl` is stabilized
826+
self.tcx
827+
.dcx()
828+
.emit_err(errors::TraitImplConstStable { span: item.span });
829+
true
830+
}
831+
Some(_) => false,
832+
};
833+
834+
if let Some(trait_id) = t.trait_def_id()
835+
&& let Some(const_stab) = self.tcx.lookup_const_stability(trait_id)
836+
{
837+
// the const stability of a trait impl must match the const stability on the trait.
838+
if const_stab.is_const_stable() != stable_or_implied_stable {
839+
let trait_span = self.tcx.def_ident_span(trait_id).unwrap();
840+
841+
let impl_stability = if stable_or_implied_stable {
842+
errors::ImplConstStability::Stable { span: item.span }
843+
} else {
844+
errors::ImplConstStability::Unstable { span: item.span }
845+
};
846+
let trait_stability = if const_stab.is_const_stable() {
847+
errors::TraitConstStability::Stable { span: trait_span }
848+
} else {
849+
errors::TraitConstStability::Unstable { span: trait_span }
850+
};
851+
852+
self.tcx.dcx().emit_err(errors::TraitImplConstStabilityMismatch {
853+
span: item.span,
854+
impl_stability,
855+
trait_stability,
856+
});
857+
}
858+
}
826859
}
827860
}
828861

829-
match constness {
830-
rustc_hir::Constness::Const => {
831-
if let Some(def_id) = t.trait_def_id() {
832-
// FIXME(const_trait_impl): Improve the span here.
833-
self.tcx.check_const_stability(def_id, t.path.span, t.path.span);
834-
}
835-
}
836-
rustc_hir::Constness::NotConst => {}
862+
if let hir::Constness::Const = constness
863+
&& let Some(def_id) = t.trait_def_id()
864+
{
865+
// FIXME(const_trait_impl): Improve the span here.
866+
self.tcx.check_const_stability(def_id, t.path.span, t.path.span);
837867
}
838868

839869
for impl_item_ref in *items {

‎library/core/src/ops/arith.rs

+1
Original file line numberDiff line numberDiff line change
@@ -96,6 +96,7 @@ pub trait Add<Rhs = Self> {
9696
macro_rules! add_impl {
9797
($($t:ty)*) => ($(
9898
#[stable(feature = "rust1", since = "1.0.0")]
99+
#[rustc_const_unstable(feature = "const_ops", issue = "90080")]
99100
impl const Add for $t {
100101
type Output = $t;
101102

‎library/core/src/ops/deref.rs

+3
Original file line numberDiff line numberDiff line change
@@ -150,6 +150,7 @@ pub trait Deref {
150150
}
151151

152152
#[stable(feature = "rust1", since = "1.0.0")]
153+
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
153154
impl<T: ?Sized> const Deref for &T {
154155
type Target = T;
155156

@@ -163,6 +164,7 @@ impl<T: ?Sized> const Deref for &T {
163164
impl<T: ?Sized> !DerefMut for &T {}
164165

165166
#[stable(feature = "rust1", since = "1.0.0")]
167+
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
166168
impl<T: ?Sized> const Deref for &mut T {
167169
type Target = T;
168170

@@ -273,6 +275,7 @@ pub trait DerefMut: ~const Deref {
273275
}
274276

275277
#[stable(feature = "rust1", since = "1.0.0")]
278+
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
276279
impl<T: ?Sized> const DerefMut for &mut T {
277280
fn deref_mut(&mut self) -> &mut T {
278281
*self

‎tests/ui/traits/const-traits/staged-api.rs

+32
Original file line numberDiff line numberDiff line change
@@ -85,4 +85,36 @@ const fn implicitly_stable_const_context() {
8585
//~^ ERROR cannot use `#[feature(const_trait_impl)]`
8686
}
8787

88+
// check that const stability of impls and traits must match
89+
#[const_trait]
90+
#[rustc_const_unstable(feature = "beef", issue = "none")]
91+
trait U {}
92+
93+
#[const_trait]
94+
#[rustc_const_stable(since = "0.0.0", feature = "beef2")]
95+
trait S {}
96+
97+
// implied stable
98+
impl const U for u8 {}
99+
//~^ const stability on the impl does not match the const stability on the trait
100+
101+
#[rustc_const_stable(since = "0.0.0", feature = "beef2")]
102+
impl const U for u16 {}
103+
//~^ const stability on the impl does not match the const stability on the trait
104+
//~| trait implementations cannot be const stable yet
105+
106+
#[rustc_const_unstable(feature = "beef", issue = "none")]
107+
impl const U for u32 {}
108+
109+
// implied stable
110+
impl const S for u8 {}
111+
112+
#[rustc_const_stable(since = "0.0.0", feature = "beef2")]
113+
impl const S for u16 {}
114+
//~^ trait implementations cannot be const stable yet
115+
116+
#[rustc_const_unstable(feature = "beef", issue = "none")]
117+
impl const S for u32 {}
118+
//~^ const stability on the impl does not match the const stability on the trait
119+
88120
fn main() {}

‎tests/ui/traits/const-traits/staged-api.stderr

+68-1
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,70 @@
1+
error: const stability on the impl does not match the const stability on the trait
2+
--> $DIR/staged-api.rs:98:1
3+
|
4+
LL | impl const U for u8 {}
5+
| ^^^^^^^^^^^^^^^^^^^^^^
6+
|
7+
note: this impl is (implicitly) stable..
8+
--> $DIR/staged-api.rs:98:1
9+
|
10+
LL | impl const U for u8 {}
11+
| ^^^^^^^^^^^^^^^^^^^^^^
12+
note: ..but the trait is unstable
13+
--> $DIR/staged-api.rs:91:7
14+
|
15+
LL | trait U {}
16+
| ^
17+
18+
error: trait implementations cannot be const stable yet
19+
--> $DIR/staged-api.rs:102:1
20+
|
21+
LL | impl const U for u16 {}
22+
| ^^^^^^^^^^^^^^^^^^^^^^^
23+
|
24+
= note: see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information
25+
26+
error: const stability on the impl does not match the const stability on the trait
27+
--> $DIR/staged-api.rs:102:1
28+
|
29+
LL | impl const U for u16 {}
30+
| ^^^^^^^^^^^^^^^^^^^^^^^
31+
|
32+
note: this impl is (implicitly) stable..
33+
--> $DIR/staged-api.rs:102:1
34+
|
35+
LL | impl const U for u16 {}
36+
| ^^^^^^^^^^^^^^^^^^^^^^^
37+
note: ..but the trait is unstable
38+
--> $DIR/staged-api.rs:91:7
39+
|
40+
LL | trait U {}
41+
| ^
42+
43+
error: trait implementations cannot be const stable yet
44+
--> $DIR/staged-api.rs:113:1
45+
|
46+
LL | impl const S for u16 {}
47+
| ^^^^^^^^^^^^^^^^^^^^^^^
48+
|
49+
= note: see issue #67792 <https://github.com/rust-lang/rust/issues/67792> for more information
50+
51+
error: const stability on the impl does not match the const stability on the trait
52+
--> $DIR/staged-api.rs:117:1
53+
|
54+
LL | impl const S for u32 {}
55+
| ^^^^^^^^^^^^^^^^^^^^^^^
56+
|
57+
note: this impl is unstable..
58+
--> $DIR/staged-api.rs:117:1
59+
|
60+
LL | impl const S for u32 {}
61+
| ^^^^^^^^^^^^^^^^^^^^^^^
62+
note: ..but the trait is stable
63+
--> $DIR/staged-api.rs:95:7
64+
|
65+
LL | trait S {}
66+
| ^
67+
168
error: const function that might be (indirectly) exposed to stable cannot use `#[feature(const_trait_impl)]`
269
--> $DIR/staged-api.rs:38:5
370
|
@@ -323,5 +390,5 @@ LL + #[rustc_allow_const_fn_unstable(const_trait_impl)]
323390
LL | const fn implicitly_stable_const_context() {
324391
|
325392

326-
error: aborting due to 19 previous errors
393+
error: aborting due to 24 previous errors
327394

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