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Fix stack overflow with recursive associated types #122366

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Mar 12, 2024
Merged

Fix stack overflow with recursive associated types #122366

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4 changes: 4 additions & 0 deletions compiler/rustc_ty_utils/src/opaque_types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,10 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
continue;
}

if !self.seen.insert(assoc.def_id.expect_local()) {
return;
}
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one thought: if we first encounter <Self as Trait>::Gat<u32> which normalizes to <u32 as Trait>::Atpit and then later encounter <Self as Trait>::Gat<Self>, which normalizes to <Self as Trait>::Atpit, this change causes us to not define Atpit anymore, does it?

While it seems fine to not support that for now, I would like to have an open issue/test for that

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oof right, we had this issue with structs before -.- I knew why I didn't want this check. Maybe I should move the recursion check even later


let impl_args = alias_ty.args.rebase_onto(
self.tcx,
impl_trait_ref.def_id,
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14 changes: 14 additions & 0 deletions tests/ui/impl-trait/associated-type-cycle.rs
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@@ -0,0 +1,14 @@
trait Foo {
type Bar;
fn foo(self) -> Self::Bar;
}

impl Foo for Box<dyn Foo> {
//~^ ERROR: the value of the associated type `Bar` in `Foo` must be specified
type Bar = <Self as Foo>::Bar;
fn foo(self) -> <Self as Foo>::Bar {
(*self).foo()
}
}

fn main() {}
12 changes: 12 additions & 0 deletions tests/ui/impl-trait/associated-type-cycle.stderr
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@@ -0,0 +1,12 @@
error[E0191]: the value of the associated type `Bar` in `Foo` must be specified
--> $DIR/associated-type-cycle.rs:6:22
|
LL | type Bar;
| -------- `Bar` defined here
...
LL | impl Foo for Box<dyn Foo> {
| ^^^ help: specify the associated type: `Foo<Bar = Type>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0191`.
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