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Fix debug assertion in typeck #72714

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Jul 21, 2020
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2 changes: 1 addition & 1 deletion src/librustc_typeck/collect.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1927,7 +1927,7 @@ fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicat
let re_root_empty = tcx.lifetimes.re_root_empty;
let predicate = ty::OutlivesPredicate(ty, re_root_empty);
predicates.push((
ty::PredicateKind::TypeOutlives(ty::Binder::dummy(predicate))
ty::PredicateKind::TypeOutlives(ty::Binder::bind(predicate))
.to_predicate(tcx),
span,
));
Expand Down
18 changes: 18 additions & 0 deletions src/test/ui/traits/issue-72410.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
// Regression test for #72410, this should be used with debug assertion enabled.

// should be fine
pub trait Foo {
fn map()
where
Self: Sized,
for<'a> &'a mut [u8]: ;
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We should have a test for a type that is not WF, which this PR would allow compiling, but we'd never want to.

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Should we separate that test in an another file? And I'm not sure what kind of test case is appropriate.

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Perhaps something like

trait Foo<'a> { }

fn map()
    where for<'a> &'a mut [dyn Foo<'a>]

which I think ought to fail because dyn Foo<'a>: Sized doesn't hold

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you could add it in the same file I suppose

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Thanks Niko! Added it.

}

// should fail
pub trait Bar {
fn map()
where for<'a> &'a mut [dyn Bar]: ;
//~^ ERROR: the trait `Bar` cannot be made into an object
}

fn main() {}
18 changes: 18 additions & 0 deletions src/test/ui/traits/issue-72410.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
error[E0038]: the trait `Bar` cannot be made into an object
--> $DIR/issue-72410.rs:14:19
|
LL | pub trait Bar {
| --- this trait cannot be made into an object...
LL | fn map()
| --- ...because associated function `map` has no `self` parameter
LL | where for<'a> &'a mut [dyn Bar]: ;
| ^^^^^^^^^^^^^^^^^ the trait `Bar` cannot be made into an object
|
help: consider turning `map` into a method by giving it a `&self` argument or constraining it so it does not apply to trait objects
|
LL | where for<'a> &'a mut [dyn Bar]:, Self: Sized ;
| ^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0038`.