fix: double alias in path (#6855)

compiler/noirc_frontend/src/elaborator/path_resolution.rs

@@ -9,7 +9,7 @@ use crate::hir::resolution::visibility::item_in_module_is_visible;
 
 use crate::locations::ReferencesTracker;
 use crate::node_interner::{FuncId, GlobalId, StructId, TraitId, TypeAliasId};
-use crate::Type;
+use crate::{Shared, Type, TypeAlias};
 
 use super::types::SELF_TYPE_NAME;
 use super::Elaborator;
@@ -218,18 +218,8 @@ impl<'context> Elaborator<'context> {
                 ),
                 ModuleDefId::TypeAliasId(id) => {
                     let type_alias = self.interner.get_type_alias(id);
-                    let type_alias = type_alias.borrow();
-
-                    let module_id = match &type_alias.typ {
-                        Type::Struct(struct_id, _generics) => struct_id.borrow().id.module_id(),
-                        Type::Error => {
-                            return Err(PathResolutionError::Unresolved(last_ident.clone()));
-                        }
-                        _ => {
-                            // For now we only allow type aliases that point to structs.
-                            // The more general case is captured here: https://github.com/noir-lang/noir/issues/6398
-                            panic!("Type alias in path not pointing to struct not yet supported")
-                        }
+                    let Some(module_id) = get_type_alias_module_def_id(&type_alias) else {
+                        return Err(PathResolutionError::Unresolved(last_ident.clone()));
                     };
 
                     (
@@ -345,3 +335,18 @@ fn merge_intermediate_path_resolution_item_with_module_def_id(
         },
     }
 }
+
+fn get_type_alias_module_def_id(type_alias: &Shared<TypeAlias>) -> Option<ModuleId> {
+    let type_alias = type_alias.borrow();
+
+    match &type_alias.typ {
+        Type::Struct(struct_id, _generics) => Some(struct_id.borrow().id.module_id()),
+        Type::Alias(type_alias, _generics) => get_type_alias_module_def_id(type_alias),
+        Type::Error => None,
+        _ => {
+            // For now we only allow type aliases that point to structs.
+            // The more general case is captured here: https://github.com/noir-lang/noir/issues/6398
+            panic!("Type alias in path not pointing to struct not yet supported")
+        }
+    }
+}

compiler/noirc_frontend/src/elaborator/patterns.rs

@@ -604,17 +604,11 @@ impl<'context> Elaborator<'context> {
                     alias_generics
                 };
 
-                // Now instantiate the underlying struct with those generics, the struct might
+                // Now instantiate the underlying struct or alias with those generics, the struct might
                 // have more generics than those in the alias, like in this example:
                 //
                 // type Alias<T> = Struct<T, i32>;
-                let typ = type_alias.get_type(&generics);
-                let Type::Struct(_, generics) = typ else {
-                    // See https://github.com/noir-lang/noir/issues/6398
-                    panic!("Expected type alias to point to struct")
-                };
-
-                generics
+                get_type_alias_generics(&type_alias, &generics)
             }
             PathResolutionItem::TraitFunction(trait_id, Some(generics), _func_id) => {
                 let trait_ = self.interner.get_trait(trait_id);
@@ -880,3 +874,14 @@ impl<'context> Elaborator<'context> {
         (id, typ)
     }
 }
+
+fn get_type_alias_generics(type_alias: &TypeAlias, generics: &[Type]) -> Vec<Type> {
+    let typ = type_alias.get_type(generics);
+    match typ {
+        Type::Struct(_, generics) => generics,
+        Type::Alias(type_alias, generics) => {
+            get_type_alias_generics(&type_alias.borrow(), &generics)
+        }
+        _ => panic!("Expected type alias to point to struct or alias"),
+    }
+}

compiler/noirc_frontend/src/tests/aliases.rs

@@ -47,3 +47,31 @@ fn alias_in_let_pattern() {
     "#;
     assert_no_errors(src);
 }
+
+#[test]
+fn double_alias_in_path() {
+    let src = r#"
+    struct Foo {}
+
+    impl Foo {
+        fn new() -> Self {
+            Self {}
+        }
+    }
+
+    type FooAlias1 = Foo;
+    type FooAlias2 = FooAlias1;
+
+    fn main() { 
+        let _ = FooAlias2::new();
+    }
+    "#;
+    assert_no_errors(src);
+}
+
+#[test]
+fn double_generic_alias_in_path() {
+    let src = r#"
+    "#;
+    assert_no_errors(src);
+}

test_programs/compile_success_empty/double_generic_alias_in_path/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "double_generic_alias_in_path"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.32.0"
+
+[dependencies]

test_programs/compile_success_empty/double_generic_alias_in_path/src/main.nr

@@ -0,0 +1,14 @@
+struct Foo<T> {}
+
+impl<T> Foo<T> {
+    fn new() -> Self {
+        Self {}
+    }
+}
+
+type FooAlias1 = Foo<i32>;
+type FooAlias2 = FooAlias1;
+
+fn main() {
+    let _ = FooAlias2::new();
+}