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lcnrlcnr
committedFeb 27, 2024
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‎tests/ui/type-alias-impl-trait/wf-check-definition-site.rs

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//
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// `Opaque<'a> = Static<&'a str>`, vs
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// `Opaque<'a> = Static<&'static str>`.
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//
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// The hidden type of the opaque ends up as `Static<'?0 str>`. When
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// computing member constraints we end up choosing `'a` for `?0` unless
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// `?0` is already required to outlive `'a`. We achieve this by checking
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// that `Static<'?0 str>` is well-formed.
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#![feature(type_alias_impl_trait)]
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struct Static<T: 'static>(T);

‎tests/ui/type-alias-impl-trait/wf-nested.rs

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// Well-formedness of nested opaque types, i.e. `impl Sized` in
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// `type Outer = impl Trait<Assoc = impl Sized>`.
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// See the comments below.
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//
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//@ revisions: pass pass_sound fail
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//@ [pass] check-fail
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//@ [pass_sound] check-fail
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//@ [fail] check-fail
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// `type Outer = impl Trait<Assoc = impl Sized>`. We check that
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// the nested type is well-formed, even though this would also
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// be implied by the item bounds of the opaque being
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// well-formed. See the comments below.
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#![feature(type_alias_impl_trait)]
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struct IsStatic<T: 'static>(T);
@@ -23,46 +19,26 @@ impl<T> Trait<&'static T> for () {
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type Out = IsStatic<T>;
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}
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// The hidden type for `impl Sized` is `IsStatic<T>`, which requires `T: 'static`.
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// We know it is well-formed because it can *only* be referenced as a projection:
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// <OuterOpaque<T> as Trait<&'static T>>::Out`.
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// So any instantiation of the type already requires proving `T: 'static`.
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#[cfg(pass)]
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mod pass {
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use super::*;
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type OuterOpaque<T> = impl Trait<&'static T, Out = impl Sized>;
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fn define<T>() -> OuterOpaque<T> {}
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//[pass]~^ ERROR `T` may not live long enough
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fn define_rpit<T>() -> impl Trait<&'static T, Out = impl Sized> {}
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//[pass]~^ ERROR the parameter type `T` may not live long enough
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}
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// Test the soundness of `pass` - We should require `T: 'static` at the use site.
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#[cfg(pass_sound)]
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mod pass_sound {
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use super::*;
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type OuterOpaque<T> = impl Trait<&'static T, Out = impl Sized>;
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fn define<T>() -> OuterOpaque<T> {}
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//[pass_sound]~^ ERROR `T` may not live long enough
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fn test<T>() {
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let outer = define::<T>();
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let _ = outer.get();
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//[pass_sound]~^ ERROR `T` may not live long enough
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//[pass_sound]~| ERROR `T` may not live long enough
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}
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}
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// Similar to `pass` but here `impl Sized` can be referenced directly as
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// InnerOpaque<T>, so we require an explicit bound `T: 'static`.
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#[cfg(fail)]
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mod fail {
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use super::*;
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type InnerOpaque<T> = impl Sized;
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type OuterOpaque<T> = impl Trait<&'static T, Out = InnerOpaque<T>>;
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fn define<T>() -> OuterOpaque<T> {}
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//[fail]~^ ERROR the parameter type `T` may not live long enough
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}
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// We could theoretically allow this (and previously did), as even
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// though the nested opaque is not well-formed, it can only be
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// used by normalizing the projection
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// <OuterOpaque1<T> as Trait<&'static T>>::Out
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// Assuming that we check that this projection is well-formed, the wf
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// of the nested opaque is implied.
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type OuterOpaque1<T> = impl Trait<&'static T, Out = impl Sized>;
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fn define<T>() -> OuterOpaque1<T> {}
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//~^ ERROR `T` may not live long enough
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fn define_rpit<T>() -> impl Trait<&'static T, Out = impl Sized> {}
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//~^ ERROR the parameter type `T` may not live long enough
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// Similar to `define` but here `impl Sized` can be referenced directly as
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// InnerOpaque<T>, so the `'static` bound is definitely required for
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// soundness.
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type InnerOpaque<T> = impl Sized;
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type OuterOpaque2<T> = impl Trait<&'static T, Out = InnerOpaque<T>>;
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fn define_nested_rpit<T>() -> OuterOpaque2<T> {}
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//~^ ERROR the parameter type `T` may not live long enough
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fn main() {}

‎tests/ui/type-alias-impl-trait/wf-nested.stderr

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error[E0310]: the parameter type `T` may not live long enough
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--> $DIR/wf-nested.rs:30:35
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|
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LL | fn define<T>() -> OuterOpaque1<T> {}
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| ^^
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| |
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| the parameter type `T` must be valid for the static lifetime...
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| ...so that the type `T` will meet its required lifetime bounds
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|
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help: consider adding an explicit lifetime bound
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|
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LL | fn define<T: 'static>() -> OuterOpaque1<T> {}
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| +++++++++
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error[E0310]: the parameter type `T` may not live long enough
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--> $DIR/wf-nested.rs:33:65
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|
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LL | fn define_rpit<T>() -> impl Trait<&'static T, Out = impl Sized> {}
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| ^^
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| |
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| the parameter type `T` must be valid for the static lifetime...
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| ...so that the type `T` will meet its required lifetime bounds
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|
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help: consider adding an explicit lifetime bound
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|
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LL | fn define_rpit<T: 'static>() -> impl Trait<&'static T, Out = impl Sized> {}
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| +++++++++
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error[E0310]: the parameter type `T` may not live long enough
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--> $DIR/wf-nested.rs:41:47
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|
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LL | fn define_nested_rpit<T>() -> OuterOpaque2<T> {}
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| ^^
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| |
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| the parameter type `T` must be valid for the static lifetime...
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| ...so that the type `T` will meet its required lifetime bounds
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|
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help: consider adding an explicit lifetime bound
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|
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LL | fn define_nested_rpit<T: 'static>() -> OuterOpaque2<T> {}
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| +++++++++
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error: aborting due to 3 previous errors
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For more information about this error, try `rustc --explain E0310`.

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