ERC-721: Clear approval in burn()

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix the `StorageVec` type by excluding the `len_cached` field from its type info - [#2052](https://github.com/paritytech/ink/pull/2052)
 - Fix panic in `approve_for` in the ERC-721 example - [#2092](https://github.com/paritytech/ink/pull/2092)
 - ERC-721: `transfer_token_from` now ensures the token owner is correct - [#2093](https://github.com/paritytech/ink/pull/2093)
+- ERC-721: `burn()` clears token approval - [#2099](https://github.com/paritytech/ink/pull/2099)
 
 ## Version 5.0.0-rc
 

integration-tests/erc721/lib.rs

@@ -226,6 +226,7 @@ mod erc721 {
                 .ok_or(Error::CannotFetchValue)?;
             owned_tokens_count.insert(caller, &count);
             token_owner.remove(id);
+            self.clear_approval(id);
 
             self.env().emit_event(Transfer {
                 from: Some(caller),
@@ -635,6 +636,31 @@ mod erc721 {
             assert_eq!(erc721.burn(1), Err(Error::NotOwner));
         }
 
+        #[ink::test]
+        fn burn_clears_approval() {
+            let accounts =
+                ink::env::test::default_accounts::<ink::env::DefaultEnvironment>();
+            // Create a new contract instance.
+            let mut erc721 = Erc721::new();
+            // Create token Id 1 for Alice
+            assert_eq!(erc721.mint(1), Ok(()));
+            // Alice gives approval to Bob to transfer token Id 1
+            assert_eq!(erc721.approve(accounts.bob, 1), Ok(()));
+            // Alice burns token
+            assert_eq!(erc721.burn(1), Ok(()));
+            // Set caller to Frank
+            set_caller(accounts.frank);
+            // Frank mints token Id 1
+            assert_eq!(erc721.mint(1), Ok(()));
+            // Set caller to Bob
+            set_caller(accounts.bob);
+            // Bob tries to transfer token Id 1 from Frank to himself
+            assert_eq!(
+                erc721.transfer_from(accounts.frank, accounts.bob, 1),
+                Err(Error::NotApproved)
+            );
+        }
+
         #[ink::test]
         fn transfer_from_fails_not_owner() {
             let accounts =