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Rollup merge of rust-lang#115559 - lcnr:implied-bounds-unconstrained,…
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… r=aliemjay

implied bounds: do not ICE on unconstrained region vars

fixes rust-lang#112832

see tests/ui/implied-bounds/implied-bounds-unconstrained-2.rs for a minimal example showing why this is necessary.

r? types

cc `@compiler-errors` `@aliemjay` https://rust-lang.zulipchat.com/#narrow/stream/144729-t-types/topic/assoc.20type.20bound.20in.20super.20trait
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Dylan-DPC authored Sep 5, 2023
2 parents 4c0332b + 98fa0c9 commit dcc4b5c
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Showing 3 changed files with 53 additions and 9 deletions.
14 changes: 5 additions & 9 deletions compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
Original file line number Diff line number Diff line change
Expand Up @@ -57,16 +57,12 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
let ty = OpportunisticRegionResolver::new(self).fold_ty(ty);

// We do not expect existential variables in implied bounds.
// We may however encounter unconstrained lifetime variables in invalid
// code. See #110161 for context.
// We may however encounter unconstrained lifetime variables
// in very rare cases.
//
// See `ui/implied-bounds/implied-bounds-unconstrained-2.rs` for
// an example.
assert!(!ty.has_non_region_infer());
if ty.has_infer() {
self.tcx.sess.delay_span_bug(
self.tcx.def_span(body_id),
"skipped implied_outlives_bounds due to unconstrained lifetimes",
);
return vec![];
}

let mut canonical_var_values = OriginalQueryValues::default();
let canonical_ty =
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28 changes: 28 additions & 0 deletions tests/ui/implied-bounds/implied-bounds-unconstrained-1.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
// check-pass

// Regression test for #112832.
pub trait QueryDb {
type Db;
}

pub struct QueryTable<Q, DB> {
db: DB,
storage: Q,
}

// We normalize `<Q as QueryDb>::Db` to `<Q as AsyncQueryFunction<'d>>::SendDb`
// using the where-bound. 'd is an unconstrained region variable which previously
// triggered an assert.
impl<Q> QueryTable<Q, <Q as QueryDb>::Db> where Q: for<'d> AsyncQueryFunction<'d> {}

pub trait AsyncQueryFunction<'d>: QueryDb<Db = <Self as AsyncQueryFunction<'d>>::SendDb> {
type SendDb: 'd;
}

pub trait QueryStorageOpsAsync<Q>
where
Q: for<'d> AsyncQueryFunction<'d>,
{
}

fn main() {}
20 changes: 20 additions & 0 deletions tests/ui/implied-bounds/implied-bounds-unconstrained-2.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
// check-pass

// Another minimized regression test for #112832.
trait Trait {
type Assoc;
}

trait Sub<'a>: Trait<Assoc = <Self as Sub<'a>>::SubAssoc> {
type SubAssoc;
}

// By using the where-clause we normalize `<T as Trait>::Assoc` to
// `<T as Sub<'a>>::SubAssoc` where `'a` is an unconstrained region
// variable.
fn foo<T>(x: <T as Trait>::Assoc)
where
for<'a> T: Sub<'a>,
{}

fn main() {}

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