feat: add check in default claim to manage collisions

pallets/unified-accounts/src/lib.rs

@@ -241,6 +241,12 @@ impl<T: Config> Pallet<T> {
         );
         // get the default evm address
         let evm_address = T::DefaultAccountMapping::into_h160(account_id.clone());
+        // make sure default address is not already mapped, this should not
+        // happen but for sanity check.
+        ensure!(
+            !NativeToEvm::<T>::contains_key(&evm_address),
+            Error::<T>::AlreadyMapped
+        );
         // create double mappings for the pair with default evm address
         Self::add_mappings(account_id, evm_address.clone());
         Ok(evm_address)

pallets/unified-accounts/src/tests.rs

@@ -222,6 +222,24 @@ fn account_default_claim_works() {
     });
 }
 
+#[test]
+fn account_default_claim_should_not_work_if_collision() {
+    ExtBuilder::default().build().execute_with(|| {
+        let bob_default_h160 = <UnifiedAccounts as UnifiedAddressMapper<_>>::to_default_h160(&BOB);
+
+        // connect alice native with bob's default address
+        // in real world possibilty of this happening is minuscule
+        UnifiedAccounts::add_mappings(ALICE, bob_default_h160);
+
+        // bob try claiming default h160 address, it should fail since alice already
+        // has mapping in place with it.
+        assert_noop!(
+            UnifiedAccounts::claim_default_evm_address(RuntimeOrigin::signed(BOB)),
+            Error::<TestRuntime>::AlreadyMapped
+        );
+    });
+}
+
 #[test]
 fn replay_attack_should_not_be_possible() {
     ExtBuilder::default().build().execute_with(|| {