fix: Cycle handlers for `HirDatabase::infer, const_param_ty_with_diagnostics

crates/hir-ty/src/db.rs

@@ -31,6 +31,7 @@ use crate::{
 #[query_group::query_group]
 pub trait HirDatabase: DefDatabase + std::fmt::Debug {
     #[salsa::invoke(crate::infer::infer_query)]
+    #[salsa::cycle(cycle_result = crate::infer::infer_cycle_result)]
     fn infer(&self, def: DefWithBodyId) -> Arc<InferenceResult>;
 
     // region:mir
@@ -132,6 +133,7 @@ pub trait HirDatabase: DefDatabase + std::fmt::Debug {
 
     // FIXME: Make this a non-interned query.
     #[salsa::invoke_interned(crate::lower::const_param_ty_with_diagnostics_query)]
+    #[salsa::cycle(cycle_result = crate::lower::const_param_ty_with_diagnostics_cycle_result)]
     fn const_param_ty_with_diagnostics(&self, def: ConstParamId) -> (Ty, Diagnostics);
 
     #[salsa::invoke(crate::lower::const_param_ty_query)]

crates/hir-ty/src/infer.rs

@@ -135,6 +135,10 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer
     Arc::new(ctx.resolve_all())
 }
 
+pub(crate) fn infer_cycle_result(_: &dyn HirDatabase, _: DefWithBodyId) -> Arc<InferenceResult> {
+    Arc::new(InferenceResult { has_errors: true, ..Default::default() })
+}
+
 /// Fully normalize all the types found within `ty` in context of `owner` body definition.
 ///
 /// This is appropriate to use only after type-check: it assumes
@@ -558,6 +562,9 @@ impl InferenceResult {
             ExprOrPatId::PatId(id) => self.type_of_pat.get(id),
         }
     }
+    pub fn is_erroneous(&self) -> bool {
+        self.has_errors && self.type_of_expr.iter().count() == 0
+    }
 }
 
 impl Index<ExprId> for InferenceResult {

crates/hir-ty/src/lower.rs

@@ -1604,6 +1604,14 @@ pub(crate) fn impl_self_ty_with_diagnostics_query(
     )
 }
 
+pub(crate) fn impl_self_ty_with_diagnostics_cycle_result(
+    db: &dyn HirDatabase,
+    impl_id: ImplId,
+) -> (Binders<Ty>, Diagnostics) {
+    let generics = generics(db, impl_id.into());
+    (make_binders(db, &generics, TyKind::Error.intern(Interner)), None)
+}
+
 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
     db.const_param_ty_with_diagnostics(def).0
 }
@@ -1633,12 +1641,12 @@ pub(crate) fn const_param_ty_with_diagnostics_query(
     (ty, create_diagnostics(ctx.diagnostics))
 }
 
-pub(crate) fn impl_self_ty_with_diagnostics_cycle_result(
-    db: &dyn HirDatabase,
-    impl_id: ImplId,
-) -> (Binders<Ty>, Diagnostics) {
-    let generics = generics(db, impl_id.into());
-    (make_binders(db, &generics, TyKind::Error.intern(Interner)), None)
+pub(crate) fn const_param_ty_with_diagnostics_cycle_result(
+    _: &dyn HirDatabase,
+    _: crate::db::HirDatabaseData,
+    _: ConstParamId,
+) -> (Ty, Diagnostics) {
+    (TyKind::Error.intern(Interner), None)
 }
 
 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {

crates/hir-ty/src/mir/lower.rs

@@ -2182,7 +2182,7 @@ pub fn lower_to_mir(
     // need to take this input explicitly.
     root_expr: ExprId,
 ) -> Result<MirBody> {
-    if infer.type_mismatches().next().is_some() {
+    if infer.type_mismatches().next().is_some() || infer.is_erroneous() {
         return Err(MirLowerError::HasErrors);
     }
     let mut ctx = MirLowerCtx::new(db, owner, body, infer);

crates/hir-ty/src/tests/regression.rs

@@ -2301,3 +2301,51 @@ trait Foo {
         "#]],
     );
 }
+
+#[test]
+fn no_panic_on_recursive_const() {
+    check_infer(
+        r#"
+struct Foo<const N: usize> {}
+impl<const N: Foo<N>> Foo<N> {
+    fn foo(self) {}
+}
+
+fn test() {
+    let _ = N;
+}
+"#,
+        expect![[r#"
+            72..76 'self': Foo<N>
+            78..80 '{}': ()
+            94..112 '{     ...= N; }': ()
+            104..105 '_': {unknown}
+            108..109 'N': {unknown}
+        "#]],
+    );
+
+    check_infer(
+        r#"
+struct Foo<const N: usize>;
+const N: Foo<N> = Foo;
+
+impl<const N: usize> Foo<N> {
+    fn foo(self) -> usize {
+        N
+    }
+}
+
+fn test() {
+    let _ = N;
+}
+"#,
+        expect![[r#"
+            93..97 'self': Foo<N>
+            108..125 '{     ...     }': usize
+            118..119 'N': usize
+            139..157 '{     ...= N; }': ()
+            149..150 '_': Foo<_>
+            153..154 'N': Foo<_>
+        "#]],
+    );
+}