Raise diagnostic on impl inference cycle. (#4367)

crates/cairo-lang-semantic/src/db.rs

@@ -458,6 +458,7 @@ pub trait SemanticGroup:
     // ==============
     /// Returns candidate [ImplDefId]s for a specific trait lookup constraint.
     #[salsa::invoke(items::imp::module_impl_ids_for_trait_filter)]
+    #[salsa::cycle(items::imp::module_impl_ids_for_trait_filter_cycle)]
     fn module_impl_ids_for_trait_filter(
         &self,
         module_id: ModuleId,
@@ -497,6 +498,7 @@ pub trait SemanticGroup:
     fn impl_def_resolver_data(&self, impl_def_id: ImplDefId) -> Maybe<Arc<ResolverData>>;
     /// Returns the concrete trait that is implemented by the impl.
     #[salsa::invoke(items::imp::impl_def_concrete_trait)]
+    #[salsa::cycle(items::imp::impl_def_concrete_trait_cycle)]
     fn impl_def_concrete_trait(&self, impl_def_id: ImplDefId) -> Maybe<ConcreteTraitId>;
     /// Returns the attributes attached to the impl.
     #[salsa::invoke(items::imp::impl_def_attributes)]

crates/cairo-lang-semantic/src/diagnostic.rs

@@ -135,7 +135,9 @@ impl DiagnosticEntry for SemanticDiagnostic {
                 "Cycle detected while resolving 'impls alias' items.".into()
             }
             SemanticDiagnosticKind::ImplRequirementCycle => {
-                "Cycle detected while resolving generic param.".into()
+                "Cycle detected while resolving generic param. Try specifying the generic impl \
+                 parameter explicitly to break the cycle."
+                    .into()
             }
             SemanticDiagnosticKind::MissingMember { member_name } => {
                 format!(r#"Missing member "{member_name}"."#)

crates/cairo-lang-semantic/src/expr/test_data/generics

@@ -433,3 +433,37 @@ error: Trait not found.
  --> lib.cairo:1:16
 fn bar<impl X: unknown>() {}
                ^*****^
+
+//! > ==========================================================================
+
+//! > Test impl infernce cycle
+
+//! > test_runner_name
+test_function_diagnostics(expect_diagnostics: true)
+
+//! > function
+trait Introspect<T> {
+}
+
+#[derive(Drop)]
+struct Generic<T, +Introspect<T>> {
+    value: T,
+}
+
+fn foo() {
+    let generic = Generic { value: 123 };
+}
+
+impl GenericStructIntrospect<T, impl IntrospectTImp: Introspect<T>> of Introspect<Generic<T>> {}
+impl Felt252Introspect of Introspect<felt252> {}
+
+//! > function_name
+foo
+
+//! > module_code
+
+//! > expected_diagnostics
+error: Cycle detected while resolving generic param. Try specifying the generic impl parameter explicitly to break the cycle.
+ --> lib.cairo:13:72
+impl GenericStructIntrospect<T, impl IntrospectTImp: Introspect<T>> of Introspect<Generic<T>> {}
+                                                                       ^********************^

crates/cairo-lang-semantic/src/items/imp.rs

@@ -253,6 +253,17 @@ pub fn impl_def_concrete_trait(
     db.priv_impl_declaration_data(impl_def_id)?.concrete_trait
 }
 
+/// Cycle handling for [crate::db::SemanticGroup::impl_def_concrete_trait].
+pub fn impl_def_concrete_trait_cycle(
+    _db: &dyn SemanticGroup,
+    _cycle: &[String],
+    _impl_def_id: &ImplDefId,
+) -> Maybe<ConcreteTraitId> {
+    // The diagnostics will be reported from the calling function, specifically from
+    // `priv_impl_declaration_data_inner`.
+    Err(skip_diagnostic())
+}
+
 /// Query implementation of [crate::db::SemanticGroup::impl_def_attributes].
 pub fn impl_def_attributes(
     db: &dyn SemanticGroup,
@@ -364,10 +375,10 @@ pub fn priv_impl_declaration_data_inner(
             .and_then(|concrete_item| {
                 try_extract_matches!(concrete_item, ResolvedConcreteItem::Trait)
             })
+            .ok_or_else(|| diagnostics.report(&trait_path_syntax, NotATrait))
     } else {
-        None
-    }
-    .ok_or_else(|| diagnostics.report(&trait_path_syntax, NotATrait));
+        Err(diagnostics.report(&trait_path_syntax, ImplRequirementCycle))
+    };
 
     // Check fully resolved.
     if let Some((stable_ptr, inference_err)) = resolver.inference().finalize() {
@@ -719,7 +730,9 @@ pub fn module_impl_ids_for_trait_filter(
         if trait_id != trait_filter.trait_id {
             continue;
         }
-        let Ok(concrete_trait_id) = uninferred_impl.concrete_trait(db) else { continue };
+        let Ok(concrete_trait_id) = uninferred_impl.concrete_trait(db) else {
+            continue;
+        };
         if let Ok(true) = concrete_trait_fits_trait_filter(db, concrete_trait_id, &trait_filter) {
             res.push(uninferred_impl);
         }
@@ -728,6 +741,18 @@ pub fn module_impl_ids_for_trait_filter(
     Ok(res)
 }
 
+/// Cycle handeling for [crate::db::SemanticGroup::module_impl_ids_for_trait_filter].
+pub fn module_impl_ids_for_trait_filter_cycle(
+    _db: &dyn SemanticGroup,
+    _cycle: &[String],
+    _module_id: &ModuleId,
+    _trait_filter: &TraitFilter,
+) -> Maybe<Vec<UninferredImpl>> {
+    // The diagnostics will be reported from the calling function, specifically from
+    // `priv_impl_declaration_data_inner`.
+    Err(skip_diagnostic())
+}
+
 /// Checks whether an [ImplDefId] passes a [TraitFilter].
 fn concrete_trait_fits_trait_filter(
     db: &dyn SemanticGroup,

crates/cairo-lang-semantic/src/items/tests/module

@@ -69,7 +69,7 @@ error: The name `abc` is defined multiple times.
 impl abc of abc;
      ^*^
 
-error: Not a trait.
+error: Cycle detected while resolving generic param. Try specifying the generic impl parameter explicitly to break the cycle.
  --> lib.cairo:22:13
 impl abc of abc;
             ^*^

crates/cairo-lang-semantic/src/items/tests/trait

@@ -141,7 +141,7 @@ error: Return type of impl function `MyImpl2::no_ret_ty` is incompatible with `M
     fn no_ret_ty(ref a: u128) {
                               ^
 
-error: Not a trait.
+error: Cycle detected while resolving generic param. Try specifying the generic impl parameter explicitly to break the cycle.
  --> lib.cairo:34:13
 impl abc of abc;
             ^*^
@@ -619,3 +619,45 @@ error: The number of parameters in the impl function `MyImpl::foo` is incompatib
  --> lib.cairo:7:14
    fn foo<S>(a: felt252, b: S, c: felt252) {}
              ^**************************^
+
+//! > ==========================================================================
+
+//! > Test impl of an impl instead of trait.
+
+//! > test_runner_name
+test_function_diagnostics(expect_diagnostics: true)
+
+//! > function
+fn bla() {
+}
+
+//! > function_name
+bla
+
+//! > module_code
+trait t1 {}
+impl imp1 of t1 {}
+impl imp2 of imp1 {}
+impl imp3 of imp3 {}
+mod inner {
+   trait t_inner {}
+   impl imp of t_inner {}
+}
+use inner::imp as inner_imp;
+impl imp4 of inner_imp {}
+
+//! > expected_diagnostics
+error: Not a trait.
+ --> lib.cairo:3:14
+impl imp2 of imp1 {}
+             ^**^
+
+error: Cycle detected while resolving generic param. Try specifying the generic impl parameter explicitly to break the cycle.
+ --> lib.cairo:4:14
+impl imp3 of imp3 {}
+             ^**^
+
+error: Not a trait.
+ --> lib.cairo:10:14
+impl imp4 of inner_imp {}
+             ^*******^