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Rollup merge of #152688 - fmease:implied-preds-default-bounds, r=jackh726
Trait aliases: Also imply default trait bounds on type params other than `Self` Trait aliases already correctly imply default trait bounds on `Self` type params. However, due to an oversight, they didn't do that for normal type params. Fixes #152687.
2 parents 2a0b534 + 9d627dd commit 7e40efc

5 files changed

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‎compiler/rustc_hir_analysis/src/collect/predicates_of.rs‎

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@@ -979,6 +979,32 @@ impl<'tcx> ItemCtxt<'tcx> {
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) -> Vec<(ty::Clause<'tcx>, Span)> {
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let mut bounds = Vec::new();
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if let PredicateFilter::All = filter {
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for param in hir_generics.params {
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match param.kind {
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hir::GenericParamKind::Type { .. } => {
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let param_ty = self.lowerer().lower_ty_param(param.hir_id);
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self.lowerer().add_implicit_sizedness_bounds(
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&mut bounds,
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param_ty,
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&[],
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ImpliedBoundsContext::TyParam(param.def_id, hir_generics.predicates),
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param.span,
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);
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self.lowerer().add_default_traits(
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&mut bounds,
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param_ty,
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&[],
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ImpliedBoundsContext::TyParam(param.def_id, hir_generics.predicates),
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param.span,
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);
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}
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hir::GenericParamKind::Lifetime { .. }
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| hir::GenericParamKind::Const { .. } => {}
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}
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}
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}
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for predicate in hir_generics.predicates {
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let hir_id = predicate.hir_id;
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let hir::WherePredicateKind::BoundPredicate(predicate) = predicate.kind else {

‎tests/ui/traits/alias/default-trait-bounds.fail.stderr‎

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error[E0277]: the size for values of type `str` cannot be known at compilation time
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--> $DIR/default-trait-bounds.rs:26:34
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|
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LL | #[cfg(fail)] fn a1_fail() { a1::<str>; }
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| ^^^ doesn't have a size known at compile-time
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|
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= help: the trait `Sized` is not implemented for `str`
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= note: required for `()` to implement `A1<str>`
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note: required by a bound in `a1`
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--> $DIR/default-trait-bounds.rs:25:30
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|
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LL | fn a1<T: ?Sized>() where (): A1<T> { ensure_is_sized::<T>; }
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| ^^^^^ required by this bound in `a1`
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error[E0277]: the size for values of type `ExternTy` cannot be known
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--> $DIR/default-trait-bounds.rs:49:34
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|
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LL | #[cfg(fail)] fn b1_fail() { b1::<ExternTy>; }
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| ^^^^^^^^ doesn't have a known size
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|
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= help: the nightly-only, unstable trait `MetaSized` is not implemented for `ExternTy`
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= note: required for `()` to implement `B1<ExternTy>`
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note: required by a bound in `b1`
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--> $DIR/default-trait-bounds.rs:47:36
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|
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LL | fn b1<T: PointeeSized>() where (): B1<T> { ensure_is_meta_sized::<T>(); }
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| ^^^^^ required by this bound in `b1`
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error[E0277]: the trait bound `ExternTy: C1` is not satisfied
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--> $DIR/default-trait-bounds.rs:65:34
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|
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LL | #[cfg(fail)] fn c1_fail() { c1::<ExternTy>; }
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| ^^^^^^^^ the nightly-only, unstable trait `MetaSized` is not implemented for `ExternTy`
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|
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= note: required for `ExternTy` to implement `C1`
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note: required by a bound in `c1`
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--> $DIR/default-trait-bounds.rs:63:35
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|
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LL | fn c1<T: PointeeSized>() where T: C1 { ensure_is_meta_sized::<T>; }
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| ^^ required by this bound in `c1`
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error: aborting due to 3 previous errors
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For more information about this error, try `rustc --explain E0277`.

‎tests/ui/traits/alias/default-trait-bounds.rs‎

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// Check that trait alias bounds also imply default trait bounds to ensure that
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// default and user-written bounds behave the same wrt. trait solving.
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//
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// Previously, we would only imply default trait bounds on
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// *`Self`* type params, not on regular type params however.
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// issue: <https://github.com/rust-lang/rust/issues/152687>
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//
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//@ revisions: pass fail
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//@[pass] check-pass
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#![feature(trait_alias)]
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#![feature(sized_hierarchy, extern_types)] // only used for the `MetaSized` test cases
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//------------------------- `Sized`
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trait A0<T: Sized> =; // has a user-written `T: Sized` boun
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// `(): A0<T>` requires+implies `T: Sized`
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fn a0<T: ?Sized>() where (): A0<T> { ensure_is_sized::<T>; }
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trait A1<T> =; // has a default `T: Sized` bound
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// `(): A1<T>` requires+implies `T: Sized`
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fn a1<T: ?Sized>() where (): A1<T> { ensure_is_sized::<T>; }
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#[cfg(fail)] fn a1_fail() { a1::<str>; }
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//[fail]~^ ERROR the size for values of type `str` cannot be known at compilation time
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fn ensure_is_sized<T: Sized>() {}
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//------------------------- `MetaSized`
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use std::marker::{MetaSized, PointeeSized};
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unsafe extern "C" { type ExternTy; }
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trait B0<T: MetaSized> =; // has a user-written `T: MetaSized` bounds
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// `(): B0<T>` requires+implies `T: MetaSized`
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fn b0<T: PointeeSized>() where (): B0<T> { ensure_is_meta_sized::<T>(); }
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trait B1<T: ?Sized> =; // has a default `T: MetaSized` bound
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// `(): B1<T>` requires+implies `T: MetaSized`
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fn b1<T: PointeeSized>() where (): B1<T> { ensure_is_meta_sized::<T>(); }
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#[cfg(fail)] fn b1_fail() { b1::<ExternTy>; }
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//[fail]~^ ERROR the size for values of type `ExternTy` cannot be known
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// For completeness, let's also check default trait bounds on `Self`.
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trait C0 = MetaSized; // has a user-written `Self: MetaSized` bound
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// `T: C0` requires+implies `T: MetaSized`
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fn c0<T: PointeeSized>() where T: C0 { ensure_is_meta_sized::<T>; }
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trait C1 =; // has a default `Self: MetaSized` bound
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// `T: C1` requires+implies `T: MetaSized`
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fn c1<T: PointeeSized>() where T: C1 { ensure_is_meta_sized::<T>; }
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#[cfg(fail)] fn c1_fail() { c1::<ExternTy>; }
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//[fail]~^ ERROR the trait bound `ExternTy: C1` is not satisfied
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fn ensure_is_meta_sized<T: MetaSized>() {}
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fn main() {}

‎tests/ui/traits/alias/more-default-trait-bounds.fail.stderr‎

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error[E0277]: the trait bound `Unmarked: Mark` is not satisfied
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--> $DIR/more-default-trait-bounds.rs:27:34
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|
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LL | #[cfg(fail)] fn a1_fail() { a1::<Unmarked>; }
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| ^^^^^^^^ unsatisfied trait bound
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|
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help: the trait `Mark` is not implemented for `Unmarked`
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--> $DIR/more-default-trait-bounds.rs:47:1
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|
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LL | enum Unmarked {}
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| ^^^^^^^^^^^^^
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= note: required for `()` to implement `A1<Unmarked>`
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note: required by a bound in `a1`
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--> $DIR/more-default-trait-bounds.rs:25:29
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|
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LL | fn a1<T: ?Mark>() where (): A1<T> { ensure_has_mark::<T>; }
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| ^^^^^ required by this bound in `a1`
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error[E0277]: the trait bound `Unmarked: B1` is not satisfied
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--> $DIR/more-default-trait-bounds.rs:41:34
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|
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LL | #[cfg(fail)] fn b1_fail() { b1::<Unmarked>; }
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| ^^^^^^^^ unsatisfied trait bound
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|
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help: the trait `Mark` is not implemented for `Unmarked`
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--> $DIR/more-default-trait-bounds.rs:47:1
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|
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LL | enum Unmarked {}
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| ^^^^^^^^^^^^^
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= note: required for `Unmarked` to implement `B1`
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note: required by a bound in `b1`
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--> $DIR/more-default-trait-bounds.rs:39:28
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|
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LL | fn b1<T: ?Mark>() where T: B1 { ensure_has_mark::<T>; }
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| ^^ required by this bound in `b1`
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0277`.

‎tests/ui/traits/alias/more-default-trait-bounds.rs‎

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// Check that trait alias bounds also imply default trait bounds to ensure_has_mark that
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// default and user-written bounds behave the same wrt. trait solving.
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//
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// Previously, we would only imply default trait bounds on
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// *`Self`* type params, not on regular type params however.
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// issue: <https://github.com/rust-lang/rust/issues/152687>
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//
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//@ revisions: pass fail
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//@ compile-flags: -Zexperimental-default-bounds
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//@[pass] check-pass
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#![feature(trait_alias, more_maybe_bounds, lang_items, auto_traits, negative_impls)]
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#[lang = "default_trait1"]
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auto trait Mark {}
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trait A0<T: Mark> = ?Mark; // has a user-written `T: Mark` bound
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fn a0<T: ?Mark>() where (): A0<T> { ensure_has_mark::<T>; }
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trait A1<T> = ?Mark; // has a default `T: Mark` bound
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fn a1<T: ?Mark>() where (): A1<T> { ensure_has_mark::<T>; }
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#[cfg(fail)] fn a1_fail() { a1::<Unmarked>; }
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//[fail]~^ ERROR the trait bound `Unmarked: Mark` is not satisfied
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// For completeness, let's also check default trait bounds on `Self`.
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trait B0 = Mark; // has a user-written `Self: Mark` bound
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fn b0<T: ?Mark>() where T: B0 { ensure_has_mark::<T>; }
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trait B1 =; // has a default `Self: Mark` bound
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fn b1<T: ?Mark>() where T: B1 { ensure_has_mark::<T>; }
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#[cfg(fail)] fn b1_fail() { b1::<Unmarked>; }
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//[fail]~^ ERROR the trait bound `Unmarked: B1` is not satisfied
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fn ensure_has_mark<T: Mark>() {}
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enum Unmarked {}
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impl !Mark for Unmarked {}
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fn main() {}

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