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Merge #11878

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11878: fix: Paper over GAT panic r=flodiebold a=flodiebold

TIL that Chalk expects the arguments to a generic associated type to come *before* the ones for the parent trait, not *after* as we have been doing with all other nested generics. Fixing this requires a larger refactoring, so for now this just papers over the problem by completely ignoring parameters of associated types.

Fixes #11769.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>
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bors[bot] 2022-04-02 12:41:14 +00:00 committed by GitHub
commit 5fe366c649
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19
crates/hir_ty/src/tests/regression.rs
View file

@ -1497,3 +1497,22 @@ fn regression_11688_3() {
"#,
);
}
#[test]
fn gat_crash() {
cov_mark::check!(ignore_gats);
check_no_mismatches(
r#"
trait ATrait {}
trait Crash {
type Member<const N: usize>: ATrait;
fn new<const N: usize>() -> Self::Member<N>;
}
fn test<T: Crash>() {
T::new();
}
"#,
);
}

9
crates/hir_ty/src/utils.rs
View file

@ -175,6 +175,15 @@ pub(super) fn associated_type_by_name_including_super_traits(
pub(crate) fn generics(db: &dyn DefDatabase, def: GenericDefId) -> Generics {
let parent_generics = parent_generic_def(db, def).map(|def| Box::new(generics(db, def)));
if parent_generics.is_some() && matches!(def, GenericDefId::TypeAliasId(_)) {
// XXX: treat generic associated types as not existing to avoid crashes (#)
//
// Chalk expects the inner associated type's parameters to come
// *before*, not after the trait's generics as we've always done it.
// Adapting to this requires a larger refactoring
cov_mark::hit!(ignore_gats);
return Generics { def, params: Interned::new(Default::default()), parent_generics };
}
Generics { def, params: db.generic_params(def), parent_generics }
}