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Explicitly deny elided lifetimes in associated consts #114716

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73 changes: 38 additions & 35 deletions compiler/rustc_resolve/src/late.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2727,19 +2727,21 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
kind: LifetimeBinderKind::ConstItem,
},
|this| {
this.visit_generics(generics);
this.visit_ty(ty);

// Only impose the restrictions of `ConstRibKind` for an
// actual constant expression in a provided default.
if let Some(expr) = expr {
// 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_body(expr, None);
}
this.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
this.visit_generics(generics);
this.visit_ty(ty);

// Only impose the restrictions of `ConstRibKind` for an
// actual constant expression in a provided default.
if let Some(expr) = expr {
// 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_body(expr, None);
}
});
},
);
}
Expand Down Expand Up @@ -2898,7 +2900,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
match &item.kind {
AssocItemKind::Const(box ast::ConstItem { generics, ty, expr, .. }) => {
debug!("resolve_implementation AssocItemKind::Const");

self.with_generic_param_rib(
&generics.params,
RibKind::AssocItem,
Expand All @@ -2908,28 +2909,30 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
kind: LifetimeBinderKind::ConstItem,
},
|this| {
// If this is a trait impl, ensure the const
// exists in trait
this.check_trait_item(
item.id,
item.ident,
&item.kind,
ValueNS,
item.span,
seen_trait_items,
|i, s, c| ConstNotMemberOfTrait(i, s, c),
);
this.with_lifetime_rib(LifetimeRibKind::AnonymousReportError, |this| {
// If this is a trait impl, ensure the const
// exists in trait
this.check_trait_item(
item.id,
item.ident,
&item.kind,
ValueNS,
item.span,
seen_trait_items,
|i, s, c| ConstNotMemberOfTrait(i, s, c),
);

this.visit_generics(generics);
this.visit_ty(ty);
if let Some(expr) = expr {
// 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_body(expr, None);
}
this.visit_generics(generics);
this.visit_ty(ty);
if let Some(expr) = expr {
// 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_body(expr, None);
}
});
},
);
}
Expand Down
1 change: 1 addition & 0 deletions tests/ui/associated-consts/infer-placeholder-in-non-suggestable-pos.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ trait Trait {
impl Trait for () {
const ASSOC: &dyn Fn(_) = 1i32;
//~^ ERROR the placeholder `_` is not allowed within types on item signatures for associated constants
//~| ERROR `&` without an explicit lifetime name cannot be used here
}

fn main() {}
11 changes: 9 additions & 2 deletions tests/ui/associated-consts/infer-placeholder-in-non-suggestable-pos.stderr
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Original file line number Diff line number Diff line change
@@ -1,9 +1,16 @@
error[E0637]: `&` without an explicit lifetime name cannot be used here
--> $DIR/infer-placeholder-in-non-suggestable-pos.rs:6:18
|
LL | const ASSOC: &dyn Fn(_) = 1i32;
| ^ explicit lifetime name needed here

error[E0121]: the placeholder `_` is not allowed within types on item signatures for associated constants
--> $DIR/infer-placeholder-in-non-suggestable-pos.rs:6:26
|
LL | const ASSOC: &dyn Fn(_) = 1i32;
| ^ not allowed in type signatures

error: aborting due to previous error
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0121`.
Some errors have detailed explanations: E0121, E0637.
For more information about an error, try `rustc --explain E0121`.
12 changes: 12 additions & 0 deletions tests/ui/consts/assoc-const-elided-lifetime.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
use std::marker::PhantomData;

struct Foo<'a> {
x: PhantomData<&'a ()>,
}

impl<'a> Foo<'a> {
const FOO: Foo<'_> = Foo { x: PhantomData::<&'a ()> };
//~^ ERROR `'_` cannot be used here
}

fn main() {}
9 changes: 9 additions & 0 deletions tests/ui/consts/assoc-const-elided-lifetime.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
error[E0637]: `'_` cannot be used here
--> $DIR/assoc-const-elided-lifetime.rs:8:20
|
LL | const FOO: Foo<'_> = Foo { x: PhantomData::<&'a ()> };
| ^^ `'_` is a reserved lifetime name

error: aborting due to previous error

For more information about this error, try `rustc --explain E0637`.
25 changes: 6 additions & 19 deletions tests/ui/suggestions/missing-lifetime-in-assoc-const-type.default.stderr
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Original file line number Diff line number Diff line change
@@ -1,14 +1,8 @@
error[E0106]: missing lifetime specifier
error[E0637]: `&` without an explicit lifetime name cannot be used here
--> $DIR/missing-lifetime-in-assoc-const-type.rs:6:14
|
LL | const A: &str = "";
| ^ expected named lifetime parameter
|
help: consider introducing a named lifetime parameter
|
LL ~ trait ZstAssert<'a>: Sized {
LL ~ const A: &'a str = "";
|
| ^ explicit lifetime name needed here

error[E0106]: missing lifetime specifier
--> $DIR/missing-lifetime-in-assoc-const-type.rs:7:14
Expand All @@ -23,19 +17,11 @@ LL | const A: &str = "";
LL ~ const B: S<'a> = S { s: &() };
|

error[E0106]: missing lifetime specifier
error[E0637]: `'_` cannot be used here
--> $DIR/missing-lifetime-in-assoc-const-type.rs:8:15
|
LL | const C: &'_ str = "";
| ^^ expected named lifetime parameter
|
help: consider introducing a named lifetime parameter
|
LL ~ trait ZstAssert<'a>: Sized {
LL | const A: &str = "";
LL | const B: S = S { s: &() };
LL ~ const C: &'a str = "";
|
| ^^ `'_` is a reserved lifetime name

error[E0106]: missing lifetime specifiers
--> $DIR/missing-lifetime-in-assoc-const-type.rs:9:14
Expand All @@ -54,4 +40,5 @@ LL ~ const D: T<'a, 'a> = T { a: &(), b: &() };

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0106`.
Some errors have detailed explanations: E0106, E0637.
For more information about an error, try `rustc --explain E0106`.
21 changes: 6 additions & 15 deletions tests/ui/suggestions/missing-lifetime-in-assoc-const-type.generic_const_items.stderr
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Original file line number Diff line number Diff line change
@@ -1,13 +1,8 @@
error[E0106]: missing lifetime specifier
error[E0637]: `&` without an explicit lifetime name cannot be used here
--> $DIR/missing-lifetime-in-assoc-const-type.rs:6:14
|
LL | const A: &str = "";
| ^ expected named lifetime parameter
|
help: consider introducing a named lifetime parameter
|
LL | const A<'a>: &'a str = "";
| ++++ ++
| ^ explicit lifetime name needed here

error[E0106]: missing lifetime specifier
--> $DIR/missing-lifetime-in-assoc-const-type.rs:7:14
Expand All @@ -20,16 +15,11 @@ help: consider introducing a named lifetime parameter
LL | const B<'a>: S<'a> = S { s: &() };
| ++++ ++++

error[E0106]: missing lifetime specifier
error[E0637]: `'_` cannot be used here
--> $DIR/missing-lifetime-in-assoc-const-type.rs:8:15
|
LL | const C: &'_ str = "";
| ^^ expected named lifetime parameter
|
help: consider introducing a named lifetime parameter
|
LL | const C<'a>: &'a str = "";
| ++++ ~~
Comment on lines -27 to -32
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I guess I could probably recover this suggestion by inverting the order of the lifetime ribs... Doesn't seem particularly useful, though.

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@fmease fmease Aug 10, 2023 •
edited
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If we end up deciding on dropping these suggestion diagnostics (personally I'm fine either way, I also don't know how useful they are, mainly they're consistent with other diagnostics), then you can get rid of the revisions of this test as well as LifetimeBinderKind::ConstItem (replace it with Item) in late/diagnostics.rs and error handling code related to it since it will become unreachable.

| ^^ `'_` is a reserved lifetime name

error[E0106]: missing lifetime specifiers
--> $DIR/missing-lifetime-in-assoc-const-type.rs:9:14
Expand All @@ -44,4 +34,5 @@ LL | const D<'a>: T<'a, 'a> = T { a: &(), b: &() };

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0106`.
Some errors have detailed explanations: E0106, E0637.
For more information about an error, try `rustc --explain E0106`.
4 changes: 2 additions & 2 deletions tests/ui/suggestions/missing-lifetime-in-assoc-const-type.rs
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Expand Up @@ -3,9 +3,9 @@
#![cfg_attr(generic_const_items, feature(generic_const_items), allow(incomplete_features))]

trait ZstAssert: Sized {
const A: &str = ""; //~ ERROR missing lifetime specifier
const A: &str = ""; //~ ERROR `&` without an explicit lifetime name cannot be used here
const B: S = S { s: &() }; //~ ERROR missing lifetime specifier
const C: &'_ str = ""; //~ ERROR missing lifetime specifier
const C: &'_ str = ""; //~ ERROR `'_` cannot be used here
const D: T = T { a: &(), b: &() }; //~ ERROR missing lifetime specifier
}

Expand Down