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Enforce Sized return types on Fn* bounds
In a `fn() -> Out` bound, enforce `Out: Sized` to avoid unsoundness. Fix rust-lang#82633.
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3 files changed

+195
-0
lines changed

3 files changed

+195
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lines changed

‎compiler/rustc_trait_selection/src/traits/select/confirmation.rs

+24
Original file line numberDiff line numberDiff line change
@@ -529,6 +529,30 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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obligation.predicate.to_poly_trait_ref(),
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trait_ref,
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)?);
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let lang_items = self.tcx().lang_items();
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if [lang_items.fn_once_trait(), lang_items.fn_trait(), lang_items.fn_mut_trait()]
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.contains(&Some(obligation.predicate.def_id()))
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{
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// Do not allow `foo::<fn() -> A>();` for `A: !Sized` (#82633)
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let fn_sig = obligation.predicate.self_ty().skip_binder().fn_sig(self.tcx());
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let ty = fn_sig.output().skip_binder();
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let trait_ref = ty::TraitRef {
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def_id: lang_items.sized_trait().unwrap(),
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substs: self.tcx().mk_substs_trait(ty, &[]),
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};
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if !matches!(ty.kind(), ty::Projection(_) | ty::Opaque(..)) {
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let pred = crate::traits::util::predicate_for_trait_ref(
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self.tcx(),
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obligation.cause.clone(),
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obligation.param_env,
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trait_ref,
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obligation.recursion_depth,
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);
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obligations.push(pred);
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}
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}
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Ok(ImplSourceFnPointerData { fn_ty: self_ty, nested: obligations })
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}
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‎src/test/ui/closures/closure-return-type-must-be-sized.rs

+72
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,72 @@
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#![feature(unboxed_closures)]
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trait A {
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fn a() where Self: Sized;
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}
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mod a {
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use A;
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pub fn foo<F: FnOnce<()>>() where F::Output: A {
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F::Output::a()
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}
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pub fn bar<F: FnOnce() -> R, R: ?Sized>() {}
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pub fn baz<F: FnOnce<()>>() where F::Output: A, F::Output: Sized {
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F::Output::a()
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}
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}
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mod b {
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use A;
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pub fn foo<F: Fn<()>>() where F::Output: A {
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F::Output::a()
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}
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pub fn bar<F: Fn() -> R, R: ?Sized>() {}
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pub fn baz<F: Fn<()>>() where F::Output: A, F::Output: Sized {
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F::Output::a()
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}
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}
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mod c {
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use A;
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pub fn foo<F: FnMut<()>>() where F::Output: A {
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F::Output::a()
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}
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pub fn bar<F: FnMut() -> R, R: ?Sized>() {}
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pub fn baz<F: FnMut<()>>() where F::Output: A, F::Output: Sized {
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F::Output::a()
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}
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}
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impl A for Box<dyn A> {
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fn a() {}
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}
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fn main() {
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a::foo::<fn() -> dyn A>(); //~ERROR E0277
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a::bar::<fn() -> dyn A, _>(); //~ERROR E0277
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a::baz::<fn() -> dyn A>(); //~ERROR E0277
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a::foo::<fn() -> Box<dyn A>>(); // ok
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a::bar::<fn() -> Box<dyn A>, _>(); // ok
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a::baz::<fn() -> Box<dyn A>>(); // ok
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b::foo::<fn() -> dyn A>(); //~ERROR E0277
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b::bar::<fn() -> dyn A, _>(); //~ERROR E0277
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b::baz::<fn() -> dyn A>(); //~ERROR E0277
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b::foo::<fn() -> Box<dyn A>>(); // ok
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b::bar::<fn() -> Box<dyn A>, _>(); // ok
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b::baz::<fn() -> Box<dyn A>>(); // ok
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c::foo::<fn() -> dyn A>(); //~ERROR E0277
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c::bar::<fn() -> dyn A, _>(); //~ERROR E0277
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c::baz::<fn() -> dyn A>(); //~ERROR E0277
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c::foo::<fn() -> Box<dyn A>>(); // ok
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c::bar::<fn() -> Box<dyn A>, _>(); // ok
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c::baz::<fn() -> Box<dyn A>>(); // ok
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}

‎src/test/ui/closures/closure-return-type-must-be-sized.stderr

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@@ -0,0 +1,99 @@
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:54:5
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|
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LL | a::foo::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:55:5
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|
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LL | pub fn bar<F: FnOnce() -> R, R: ?Sized>() {}
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| ------------- required by this bound in `a::bar`
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...
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LL | a::bar::<fn() -> dyn A, _>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:56:5
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|
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LL | pub fn baz<F: FnOnce<()>>() where F::Output: A, F::Output: Sized {
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| ----- required by this bound in `a::baz`
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...
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LL | a::baz::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:60:5
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|
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LL | pub fn foo<F: Fn<()>>() where F::Output: A {
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| ------ required by this bound in `b::foo`
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...
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LL | b::foo::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:61:5
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|
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LL | pub fn bar<F: Fn() -> R, R: ?Sized>() {}
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| --------- required by this bound in `b::bar`
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...
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LL | b::bar::<fn() -> dyn A, _>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:62:5
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|
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LL | pub fn baz<F: Fn<()>>() where F::Output: A, F::Output: Sized {
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| ----- required by this bound in `b::baz`
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...
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LL | b::baz::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:66:5
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|
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LL | pub fn foo<F: FnMut<()>>() where F::Output: A {
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| --------- required by this bound in `c::foo`
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...
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LL | c::foo::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:67:5
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|
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LL | pub fn bar<F: FnMut() -> R, R: ?Sized>() {}
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| ------------ required by this bound in `c::bar`
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...
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LL | c::bar::<fn() -> dyn A, _>();
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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 `(dyn A + 'static)`
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error[E0277]: the size for values of type `(dyn A + 'static)` cannot be known at compilation time
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--> $DIR/closure-return-type-must-be-sized.rs:68:5
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|
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LL | pub fn baz<F: FnMut<()>>() where F::Output: A, F::Output: Sized {
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| ----- required by this bound in `c::baz`
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...
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LL | c::baz::<fn() -> dyn A>();
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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 `(dyn A + 'static)`
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error: aborting due to 9 previous errors
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For more information about this error, try `rustc --explain E0277`.

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