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Infer all anonymous lifetimes in assoc consts as 'static #156508

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b2dfdd2
Turn elided_lifetimes_in_associated_constant FCW into a hard error
oli-obk May 12, 2026
7ebcdfd
Infer all anonymous lifetimes in (assoc) consts as `'static`
oli-obk May 26, 2026
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43 changes: 0 additions & 43 deletions compiler/rustc_lint_defs/src/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,6 @@ declare_lint_pass! {
DEPRECATED_WHERE_CLAUSE_LOCATION,
DUPLICATE_FEATURES,
DUPLICATE_MACRO_ATTRIBUTES,
ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
ELIDED_LIFETIMES_IN_PATHS,
EXPLICIT_BUILTIN_CFGS_IN_FLAGS,
EXPORTED_PRIVATE_DEPENDENCIES,
Expand Down Expand Up @@ -4809,48 +4808,6 @@ declare_lint! {
"impl trait in impl method signature does not match trait method signature",
}

declare_lint! {
/// The `elided_lifetimes_in_associated_constant` lint detects elided lifetimes
/// in associated constants when there are other lifetimes in scope. This was
/// accidentally supported, and this lint was later relaxed to allow eliding
/// lifetimes to `'static` when there are no lifetimes in scope.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(elided_lifetimes_in_associated_constant)]
///
/// struct Foo<'a>(&'a ());
///
/// impl<'a> Foo<'a> {
/// const STR: &str = "hello, world";
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Previous version of Rust
///
/// Implicit static-in-const behavior was decided [against] for associated
/// constants because of ambiguity. This, however, regressed and the compiler
/// erroneously treats elided lifetimes in associated constants as lifetime
/// parameters on the impl.
///
/// This is a [future-incompatible] lint to transition this to a
/// hard error in the future.
///
/// [against]: https://github.com/rust-lang/rust/issues/38831
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
Deny,
"elided lifetimes cannot be used in associated constants in impls",
@future_incompatible = FutureIncompatibleInfo {
reason: fcw!(FutureReleaseError #115010),
};
}

declare_lint! {
/// The `private_macro_use` lint detects private macros that are imported
/// with `#[macro_use]`.
Expand Down
22 changes: 0 additions & 22 deletions compiler/rustc_resolve/src/errors.rs
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Expand Up @@ -1661,28 +1661,6 @@ pub(crate) struct UnusedQualifications {
pub removal_span: Span,
}

#[derive(Diagnostic)]
#[diag(
"{$elided ->
[true] `&` without an explicit lifetime name cannot be used here
*[false] `'_` cannot be used here
}"
)]
pub(crate) struct AssociatedConstElidedLifetime {
#[suggestion(
"use the `'static` lifetime",
style = "verbose",
code = "{code}",
applicability = "machine-applicable"
)]
pub span: Span,

pub code: &'static str,
pub elided: bool,
#[note("cannot automatically infer `'static` because of other lifetimes in scope")]
pub lifetimes_in_scope: MultiSpan,
}

#[derive(Diagnostic)]
#[diag("lifetime parameter `{$ident}` only used once")]
pub(crate) struct SingleUseLifetime {
Expand Down
153 changes: 38 additions & 115 deletions compiler/rustc_resolve/src/late.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -342,11 +342,6 @@ enum LifetimeRibKind {
/// error on default object bounds (e.g., `Box<dyn Foo>`).
AnonymousReportError,

/// Resolves elided lifetimes to `'static` if there are no other lifetimes in scope,
/// otherwise give a warning that the previous behavior of introducing a new early-bound
/// lifetime is a bug and will be removed (if `emit_lint` is enabled).
StaticIfNoLifetimeInScope { lint_id: NodeId, emit_lint: bool },

/// Signal we cannot find which should be the anonymous lifetime.
ElisionFailure,

Expand Down Expand Up @@ -1373,7 +1368,6 @@ impl<'ast, 'ra, 'tcx> Visitor<'ast> for LateResolutionVisitor<'_, 'ast, 'ra, 'tc
}
LifetimeRibKind::AnonymousCreateParameter { .. }
| LifetimeRibKind::AnonymousReportError
| LifetimeRibKind::StaticIfNoLifetimeInScope { .. }
| LifetimeRibKind::ImplTrait
| LifetimeRibKind::Elided(_)
| LifetimeRibKind::ElisionFailure
Expand Down Expand Up @@ -1779,7 +1773,6 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
// lifetime would be illegal.
LifetimeRibKind::Item
| LifetimeRibKind::AnonymousReportError
| LifetimeRibKind::StaticIfNoLifetimeInScope { .. }
| LifetimeRibKind::ElisionFailure => Some(LifetimeUseSet::Many),
// An anonymous lifetime is legal here, and bound to the right
// place, go ahead.
Expand Down Expand Up @@ -1843,8 +1836,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
| LifetimeRibKind::Generics { .. }
| LifetimeRibKind::ElisionFailure
| LifetimeRibKind::AnonymousReportError
| LifetimeRibKind::ImplTrait
| LifetimeRibKind::StaticIfNoLifetimeInScope { .. } => {}
| LifetimeRibKind::ImplTrait => {}
}
}

Expand Down Expand Up @@ -1883,48 +1875,6 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
self.record_lifetime_use(lifetime.id, res, elision_candidate);
return;
}
LifetimeRibKind::StaticIfNoLifetimeInScope { lint_id: node_id, emit_lint } => {
let mut lifetimes_in_scope = vec![];
for rib in self.lifetime_ribs[..i].iter().rev() {
lifetimes_in_scope.extend(rib.bindings.iter().map(|(ident, _)| ident.span));
// Consider any anonymous lifetimes, too
if let LifetimeRibKind::AnonymousCreateParameter { binder, .. } = rib.kind
&& let Some(extra) = self.r.extra_lifetime_params_map.get(&binder)
{
lifetimes_in_scope.extend(extra.iter().map(|(ident, _, _)| ident.span));
}
if let LifetimeRibKind::Item = rib.kind {
break;
}
}
if lifetimes_in_scope.is_empty() {
self.record_lifetime_use(
lifetime.id,
LifetimeRes::Static,
elision_candidate,
);
return;
} else if emit_lint {
let lt_span = if elided {
lifetime.ident.span.shrink_to_hi()
} else {
lifetime.ident.span
};
let code = if elided { "'static " } else { "'static" };

self.r.lint_buffer.buffer_lint(
lint::builtin::ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
node_id,
lifetime.ident.span,
crate::errors::AssociatedConstElidedLifetime {
elided,
code,
span: lt_span,
lifetimes_in_scope: lifetimes_in_scope.into(),
},
);
}
}
LifetimeRibKind::AnonymousReportError => {
let guar = if elided {
let suggestion = self.lifetime_ribs[i..].iter().rev().find_map(|rib| {
Expand Down Expand Up @@ -2274,8 +2224,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
//
// impl Foo for std::cell::Ref<u32> // note lack of '_
// async fn foo(_: std::cell::Ref<u32>) { ... }
LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. }
| LifetimeRibKind::StaticIfNoLifetimeInScope { .. } => {
LifetimeRibKind::AnonymousCreateParameter { report_in_path: true, .. } => {
let sess = self.r.tcx.sess;
let subdiag = elided_lifetime_in_path_suggestion(
sess.source_map(),
Expand Down Expand Up @@ -3348,10 +3297,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
generics.span,
|this| {
this.with_lifetime_rib(
LifetimeRibKind::StaticIfNoLifetimeInScope {
lint_id: item.id,
emit_lint: false,
},
LifetimeRibKind::Elided(LifetimeRes::Static),
|this| {
this.visit_generics(generics);
if rhs_kind.is_type_const()
Expand Down Expand Up @@ -3567,67 +3513,44 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
generics.span,
|this| {
this.with_lifetime_rib(
// Until these are a hard error, we need to create them within the
// correct binder, Otherwise the lifetimes of this assoc const think
// they are lifetimes of the trait.
LifetimeRibKind::AnonymousCreateParameter {
binder: item.id,
report_in_path: true,
},
LifetimeRibKind::Elided(LifetimeRes::Static),
|this| {
this.with_lifetime_rib(
LifetimeRibKind::StaticIfNoLifetimeInScope {
lint_id: item.id,
// In impls, it's not a hard error yet due to backcompat.
emit_lint: true,
},
|this| {
// If this is a trait impl, ensure the const
// exists in trait
this.check_trait_item(
item.id,
*ident,
*ident,
&item.kind,
ValueNS,
item.span,
seen_trait_items,
|i, s, c| ConstNotMemberOfTrait(i, s, c),
);
// If this is a trait impl, ensure the const
// exists in trait
this.check_trait_item(
item.id,
*ident,
*ident,
&item.kind,
ValueNS,
item.span,
seen_trait_items,
|i, s, c| ConstNotMemberOfTrait(i, s, c),
);

this.visit_generics(generics);
if rhs_kind.is_type_const()
&& !this
.r
.tcx
.features()
.generic_const_parameter_types()
{
this.with_rib(TypeNS, RibKind::ConstParamTy, |this| {
this.with_rib(
ValueNS,
RibKind::ConstParamTy,
|this| {
this.with_lifetime_rib(
LifetimeRibKind::ConstParamTy,
|this| this.visit_ty(ty),
)
},
)
});
} else {
this.visit_ty(ty);
}
// We allow arbitrary const expressions inside of associated consts,
// even if they are potentially not const evaluatable.
//
// Type parameters can already be used and as associated consts are
// not used as part of the type system, this is far less surprising.
this.resolve_const_item_rhs(rhs_kind, None);
},
)
this.visit_generics(generics);
if rhs_kind.is_type_const()
&& !this.r.tcx.features().generic_const_parameter_types()
{
this.with_rib(TypeNS, RibKind::ConstParamTy, |this| {
this.with_rib(ValueNS, RibKind::ConstParamTy, |this| {
this.with_lifetime_rib(
LifetimeRibKind::ConstParamTy,
|this| this.visit_ty(ty),
)
})
});
} else {
this.visit_ty(ty);
}
// We allow arbitrary const expressions inside of associated consts,
// even if they are potentially not const evaluatable.
//
// Type parameters can already be used and as associated consts are
// not used as part of the type system, this is far less surprising.
this.resolve_const_item_rhs(rhs_kind, None);
},
);
)
},
);
self.resolve_define_opaques(define_opaque);
Expand Down
8 changes: 0 additions & 8 deletions src/tools/rust-analyzer/crates/ide-db/src/generated/lints.rs
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Expand Up @@ -383,13 +383,6 @@ pub const DEFAULT_LINTS: &[Lint] = &[
warn_since: None,
deny_since: None,
},
Lint {
label: "elided_lifetimes_in_associated_constant",
description: r##"elided lifetimes cannot be used in associated constants in impls"##,
default_severity: Severity::Error,
warn_since: None,
deny_since: None,
},
Lint {
label: "elided_lifetimes_in_paths",
description: r##"hidden lifetime parameters in types are deprecated"##,
Expand Down Expand Up @@ -1851,7 +1844,6 @@ pub const DEFAULT_LINT_GROUPS: &[LintGroup] = &[
"coherence_leak_check",
"conflicting_repr_hints",
"const_evaluatable_unchecked",
"elided_lifetimes_in_associated_constant",
"float_literal_f32_fallback",
"forbidden_lint_groups",
"ill_formed_attribute_input",
Expand Down
6 changes: 1 addition & 5 deletions tests/ui/consts/assoc-const-elided-lifetime.rs
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@@ -1,4 +1,4 @@
#![deny(elided_lifetimes_in_associated_constant)]
//@ check-pass

use std::marker::PhantomData;

Expand All @@ -8,12 +8,8 @@ struct Foo<'a> {

impl<'a> Foo<'a> {
const FOO: Foo<'_> = Foo { x: PhantomData::<&()> };
//~^ ERROR `'_` cannot be used here
//~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!

const BAR: &() = &();
//~^ ERROR `&` without an explicit lifetime name cannot be used here
//~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
}

fn main() {}
44 changes: 0 additions & 44 deletions tests/ui/consts/assoc-const-elided-lifetime.stderr
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