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Gracefully handle non-WF alias in assemble_alias_bound_candidates_recur
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compiler-errors committed Feb 10, 2024
1 parent 6cc4843 commit 5461fd4
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Showing 3 changed files with 42 additions and 2 deletions.
8 changes: 6 additions & 2 deletions compiler/rustc_trait_selection/src/solve/assembly/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ use rustc_middle::ty::fast_reject::{SimplifiedType, TreatParams};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{fast_reject, TypeFoldable};
use rustc_middle::ty::{ToPredicate, TypeVisitableExt};
use rustc_span::ErrorGuaranteed;
use rustc_span::{ErrorGuaranteed, DUMMY_SP};
use std::fmt::Debug;

pub(super) mod structural_traits;
Expand Down Expand Up @@ -612,7 +612,11 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {

ty::Alias(kind @ (ty::Projection | ty::Opaque), alias_ty) => (kind, alias_ty),
ty::Alias(ty::Inherent | ty::Weak, _) => {
unreachable!("Weak and Inherent aliases should have been normalized away already")
self.tcx().sess.dcx().span_delayed_bug(
DUMMY_SP,
format!("could not normalize {self_ty}, it is not WF"),
);
return;
}
};

Expand Down
19 changes: 19 additions & 0 deletions tests/ui/impl-trait/in-trait/alias-bounds-when-not-wf.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
// compile-flags: -Znext-solver

#![feature(lazy_type_alias)]
//~^ WARN the feature `lazy_type_alias` is incomplete

trait Foo {}

type A<T: Foo> = T;

struct W<T>(T);

// For `W<A<usize>>` to be WF, `A<usize>: Sized` must hold. However, when assembling
// alias bounds for `A<usize>`, we try to normalize it, but it doesn't hold because
// `usize: Foo` doesn't hold. Therefore we ICE, because we don't expect to still
// encounter weak types in `assemble_alias_bound_candidates_recur`.
fn hello(_: W<A<usize>>) {}
//~^ ERROR the type `W<A<usize>>` is not well-formed

fn main() {}
17 changes: 17 additions & 0 deletions tests/ui/impl-trait/in-trait/alias-bounds-when-not-wf.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
warning: the feature `lazy_type_alias` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/alias-bounds-when-not-wf.rs:3:12
|
LL | #![feature(lazy_type_alias)]
| ^^^^^^^^^^^^^^^
|
= note: see issue #112792 <https://github.com/rust-lang/rust/issues/112792> for more information
= note: `#[warn(incomplete_features)]` on by default

error: the type `W<A<usize>>` is not well-formed
--> $DIR/alias-bounds-when-not-wf.rs:16:13
|
LL | fn hello(_: W<A<usize>>) {}
| ^^^^^^^^^^^

error: aborting due to 1 previous error; 1 warning emitted

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