some tests and fixes

frame/support/procedural/src/storage_alias.rs

@@ -597,9 +597,8 @@ fn generate_storage_instance(
 	let storage_name_str = storage_name.to_string();
 
 	let counter_code = is_counted_map.then(|| {
-
 		let counter_name = Ident::new(&counter_prefix(&name.to_string()), Span::call_site());
-		let counter_storage_name_str = "counter_".to_owned() + &storage_name_str;
+		let counter_storage_name_str = counter_prefix(&storage_name_str);
 
 		quote! {
 			#visibility struct #counter_name< #impl_generics >(
@@ -616,8 +615,10 @@ fn generate_storage_instance(
 				const STORAGE_PREFIX: &'static str = #counter_storage_name_str;
 			}
 
-			impl<#impl_generics> #crate_::storage::types::CountedStorageMapInstance for #name< #impl_generics > {
-				type CounterPrefix = #counter_name;
+			impl<#impl_generics> #crate_::storage::types::CountedStorageMapInstance
+				for #name< #type_generics > #where_clause
+			{
+				type CounterPrefix = #counter_name < #type_generics >;
 			}
 		}
 	});

frame/support/test/tests/pallet.rs

@@ -1906,14 +1906,26 @@ fn assert_type_all_pallets_without_system_reversed_is_correct() {
 
 #[test]
 fn test_storage_alias() {
+	use frame_support::Twox64Concat;
+
 	#[frame_support::storage_alias]
 	type Value<T: pallet::Config>
 	where
 		<T as frame_system::Config>::AccountId: From<SomeType1> + SomeAssociation1,
 	= StorageValue<pallet::Pallet<T>, u32, ValueQuery>;
 
+	#[frame_support::storage_alias]
+	type SomeCountedStorageMap<T: pallet2::Config>
+	where
+		<T as frame_system::Config>::AccountId: From<SomeType1> + SomeAssociation1,
+	= CountedStorageMap<pallet2::Pallet<T>, Twox64Concat, u8, u32>;
+
 	TestExternalities::default().execute_with(|| {
 		pallet::Value::<Runtime>::put(10);
 		assert_eq!(10, Value::<Runtime>::get());
+
+		pallet2::SomeCountedStorageMap::<Runtime>::insert(10, 100);
+		assert_eq!(Some(100), SomeCountedStorageMap::<Runtime>::get(10));
+		assert_eq!(1, SomeCountedStorageMap::<Runtime>::count());
 	})
 }