Allow other pallets to check asset ids.

frame/assets/src/impl_fungibles.rs

@@ -283,3 +283,12 @@ impl<T: Config<I>, I: 'static> fungibles::roles::Inspect<<T as SystemConfig>::Ac
 		Asset::<T, I>::get(asset).map(|x| x.freezer)
 	}
 }
+
+impl<T: Config<I>, I: 'static> fungibles::InspectEnumerable<T::AccountId> for Pallet<T, I> {
+	/// Returns an iterator of the assets in existence.
+	///
+	/// NOTE: iterating this list invokes a storage read per item.
+	fn asset_ids() -> Box<dyn Iterator<Item = Self::AssetId>> {
+		Box::new(Asset::<T, I>::iter_keys())
+	}
+}

frame/assets/src/tests.rs

@@ -19,10 +19,19 @@
 
 use super::*;
 use crate::{mock::*, Error};
-use frame_support::{assert_noop, assert_ok, traits::Currency};
+use frame_support::{
+	assert_noop, assert_ok,
+	traits::{fungibles::InspectEnumerable, Currency},
+};
 use pallet_balances::Error as BalancesError;
 use sp_runtime::{traits::ConvertInto, TokenError};
 
+fn asset_ids() -> Vec<u32> {
+	let mut s: Vec<_> = Assets::asset_ids().collect();
+	s.sort();
+	s
+}
+
 #[test]
 fn basic_minting_should_work() {
 	new_test_ext().execute_with(|| {
@@ -31,6 +40,7 @@ fn basic_minting_should_work() {
 		assert_eq!(Assets::balance(0, 1), 100);
 		assert_ok!(Assets::mint(RuntimeOrigin::signed(1), 0, 2, 100));
 		assert_eq!(Assets::balance(0, 2), 100);
+		assert_eq!(asset_ids(), vec![0, 999]);
 	});
 }
 
@@ -48,6 +58,7 @@ fn minting_too_many_insufficient_assets_fails() {
 		Balances::make_free_balance_be(&2, 1);
 		assert_ok!(Assets::transfer(RuntimeOrigin::signed(1), 0, 2, 100));
 		assert_ok!(Assets::mint(RuntimeOrigin::signed(1), 2, 1, 100));
+		assert_eq!(asset_ids(), vec![0, 1, 2, 999]);
 	});
 }
 
@@ -137,6 +148,7 @@ fn refunding_calls_died_hook() {
 
 		assert_eq!(Asset::<Test>::get(0).unwrap().accounts, 0);
 		assert_eq!(hooks(), vec![Hook::Died(0, 1)]);
+		assert_eq!(asset_ids(), vec![0, 999]);
 	});
 }
 
@@ -162,6 +174,7 @@ fn approval_lifecycle_works() {
 		assert_eq!(Assets::balance(0, 1), 60);
 		assert_eq!(Assets::balance(0, 3), 40);
 		assert_eq!(Balances::reserved_balance(&1), 0);
+		assert_eq!(asset_ids(), vec![0, 999]);
 	});
 }
 
@@ -352,12 +365,14 @@ fn destroy_with_bad_witness_should_not_work() {
 		assert_ok!(Assets::force_create(RuntimeOrigin::root(), 0, 1, true, 1));
 		let mut w = Asset::<Test>::get(0).unwrap().destroy_witness();
 		assert_ok!(Assets::mint(RuntimeOrigin::signed(1), 0, 10, 100));
+		assert_eq!(asset_ids(), vec![0, 999]);
 		// witness too low
 		assert_noop!(Assets::destroy(RuntimeOrigin::signed(1), 0, w), Error::<Test>::BadWitness);
 		// witness too high is okay though
 		w.accounts += 2;
 		w.sufficients += 2;
 		assert_ok!(Assets::destroy(RuntimeOrigin::signed(1), 0, w));
+		assert_eq!(asset_ids(), vec![999]);
 	});
 }
 
@@ -371,10 +386,12 @@ fn destroy_should_refund_approvals() {
 		assert_ok!(Assets::approve_transfer(RuntimeOrigin::signed(1), 0, 3, 50));
 		assert_ok!(Assets::approve_transfer(RuntimeOrigin::signed(1), 0, 4, 50));
 		assert_eq!(Balances::reserved_balance(&1), 3);
+		assert_eq!(asset_ids(), vec![0, 999]);
 
 		let w = Asset::<Test>::get(0).unwrap().destroy_witness();
 		assert_ok!(Assets::destroy(RuntimeOrigin::signed(1), 0, w));
 		assert_eq!(Balances::reserved_balance(&1), 0);
+		assert_eq!(asset_ids(), vec![999]);
 
 		// all approvals are removed
 		assert!(Approvals::<Test>::iter().count().is_zero())
@@ -406,6 +423,7 @@ fn non_providing_should_work() {
 		Balances::make_free_balance_be(&2, 100);
 		assert_ok!(Assets::transfer(RuntimeOrigin::signed(0), 0, 1, 25));
 		assert_ok!(Assets::force_transfer(RuntimeOrigin::signed(1), 0, 0, 2, 25));
+		assert_eq!(asset_ids(), vec![0, 999]);
 	});
 }
 
@@ -498,6 +516,7 @@ fn transferring_enough_to_kill_source_when_keep_alive_should_fail() {
 		assert_eq!(Assets::balance(0, 1), 10);
 		assert_eq!(Assets::balance(0, 2), 90);
 		assert!(hooks().is_empty());
+		assert_eq!(asset_ids(), vec![0, 999]);
 	});
 }
 
@@ -582,6 +601,7 @@ fn transfer_owner_should_work() {
 		Balances::make_free_balance_be(&1, 100);
 		Balances::make_free_balance_be(&2, 100);
 		assert_ok!(Assets::create(RuntimeOrigin::signed(1), 0, 1, 1));
+		assert_eq!(asset_ids(), vec![0, 999]);
 
 		assert_eq!(Balances::reserved_balance(&1), 1);
 
@@ -1012,7 +1032,7 @@ fn balance_conversion_should_work() {
 		assert_ok!(Assets::force_create(RuntimeOrigin::root(), id, 1, true, 10));
 		let not_sufficient = 23;
 		assert_ok!(Assets::force_create(RuntimeOrigin::root(), not_sufficient, 1, false, 10));
-
+		assert_eq!(asset_ids(), vec![23, 42, 999]);
 		assert_eq!(
 			BalanceToAssetBalance::<Balances, Test, ConvertInto>::to_asset_balance(100, 1234),
 			Err(ConversionError::AssetMissing)
@@ -1035,7 +1055,7 @@ fn balance_conversion_should_work() {
 #[test]
 fn assets_from_genesis_should_exist() {
 	new_test_ext().execute_with(|| {
-		assert!(Asset::<Test>::contains_key(999));
+		assert_eq!(asset_ids(), vec![999]);
 		assert!(Metadata::<Test>::contains_key(999));
 		assert_eq!(Assets::balance(999, 1), 100);
 		assert_eq!(Assets::total_supply(999), 100);

frame/support/src/traits/tokens/fungibles.rs

@@ -27,6 +27,8 @@ use sp_std::vec::Vec;
 
 pub mod approvals;
 mod balanced;
+pub mod enumerable;
+pub use enumerable::InspectEnumerable;
 pub mod metadata;
 pub use balanced::{Balanced, Unbalanced};
 mod imbalance;

frame/support/src/traits/tokens/fungibles/enumerable.rs

@@ -0,0 +1,25 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2019-2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::traits::fungibles::Inspect;
+use sp_std::boxed::Box;
+
+/// Interface for enumerating assets in existence or owned by a given account.
+pub trait InspectEnumerable<AccountId>: Inspect<AccountId> {
+	/// Returns an iterator of the collections in existence.
+	fn asset_ids() -> Box<dyn Iterator<Item = Self::AssetId>>;
+}