Add ability to unset minter in UpdateMinter message.

CHANGELOG.md

@@ -4,6 +4,10 @@
 
 [Full Changelog](https://github.com/CosmWasm/cw-plus/compare/v0.13.4...HEAD)
 
+**Merged pull requests:**
+
+- Add ability to unset minter in UpdateMinter message. [\#748](https://github.com/CosmWasm/cw-plus/pull/748) ([ezekiiel](https://github.com/ezekiiel)) 
+
 ## [v0.13.4](https://github.com/CosmWasm/cw-plus/tree/v0.13.4) (2022-06-02)
 
 [Full Changelog](https://github.com/CosmWasm/cw-plus/compare/v0.13.3...v0.13.4)

contracts/cw20-base/src/contract.rs

@@ -393,7 +393,7 @@ pub fn execute_update_minter(
     deps: DepsMut,
     _env: Env,
     info: MessageInfo,
-    new_minter: String,
+    new_minter: Option<String>,
 ) -> Result<Response, ContractError> {
     let mut config = TOKEN_INFO
         .may_load(deps.storage)?
@@ -404,18 +404,27 @@ pub fn execute_update_minter(
         return Err(ContractError::Unauthorized {});
     }
 
-    let minter = deps.api.addr_validate(&new_minter)?;
-    let minter_data = MinterData {
-        minter,
-        cap: mint.cap,
-    };
-    config.mint = Some(minter_data);
+    let minter_data = new_minter
+        .map(|new_minter| deps.api.addr_validate(&new_minter))
+        .transpose()?
+        .map(|minter| MinterData {
+            minter,
+            cap: mint.cap,
+        });
+
+    config.mint = minter_data;
 
     TOKEN_INFO.save(deps.storage, &config)?;
 
     Ok(Response::default()
         .add_attribute("action", "update_minter")
-        .add_attribute("new_minter", new_minter))
+        .add_attribute(
+            "new_minter",
+            config
+                .mint
+                .map(|m| m.minter.into_string())
+                .unwrap_or_else(|| "None".to_string()),
+        ))
 }
 
 pub fn execute_update_marketing(
@@ -927,7 +936,7 @@ mod tests {
 
         let new_minter = "new_minter";
         let msg = ExecuteMsg::UpdateMinter {
-            new_minter: new_minter.to_string(),
+            new_minter: Some(new_minter.to_string()),
         };
 
         let info = mock_info(&minter, &[]);
@@ -956,7 +965,7 @@ mod tests {
         );
 
         let msg = ExecuteMsg::UpdateMinter {
-            new_minter: String::from("new_minter"),
+            new_minter: Some("new_minter".to_string()),
         };
 
         let info = mock_info("not the minter", &[]);
@@ -965,6 +974,43 @@ mod tests {
         assert_eq!(err, ContractError::Unauthorized {});
     }
 
+    #[test]
+    fn unset_minter() {
+        let mut deps = mock_dependencies();
+        let minter = String::from("minter");
+        let cap = None;
+        do_instantiate_with_minter(
+            deps.as_mut(),
+            &String::from("genesis"),
+            Uint128::new(1234),
+            &minter,
+            cap,
+        );
+
+        let msg = ExecuteMsg::UpdateMinter { new_minter: None };
+
+        let info = mock_info(&minter, &[]);
+        let env = mock_env();
+        let res = execute(deps.as_mut(), env.clone(), info, msg);
+        assert!(res.is_ok());
+        let query_minter_msg = QueryMsg::Minter {};
+        let res = query(deps.as_ref(), env, query_minter_msg);
+        let mint: Option<MinterResponse> = from_binary(&res.unwrap()).unwrap();
+
+        // Check that mint information was removed.
+        assert_eq!(mint, None);
+
+        // Check that old minter can no longer mint.
+        let msg = ExecuteMsg::Mint {
+            recipient: String::from("lucky"),
+            amount: Uint128::new(222),
+        };
+        let info = mock_info("minter", &[]);
+        let env = mock_env();
+        let err = execute(deps.as_mut(), env, info, msg).unwrap_err();
+        assert_eq!(err, ContractError::Unauthorized {});
+    }
+
     #[test]
     fn no_one_mints_if_minter_unset() {
         let mut deps = mock_dependencies();

packages/cw20/README.md

@@ -128,6 +128,11 @@ minter address and handle updating the ACL there.
 this will create `amount` new tokens (updating total supply) and
 add them to the balance of `recipient`, as long as it does not exceed the cap.
 
+`UpdateMinter { new_minter: Option<String> }` - Callable only by the
+current minter. If `new_minter` is `Some(address)` the minter is set
+to the specified address, otherwise the minter is removed and no
+future minters may be set. 
+
 ### Queries
 
 `Minter{}` - Returns who and how much can be minted. Return type is

packages/cw20/src/msg.rs

@@ -55,8 +55,10 @@ pub enum Cw20ExecuteMsg {
     /// Only with the "mintable" extension. If authorized, creates amount new tokens
     /// and adds to the recipient balance.
     Mint { recipient: String, amount: Uint128 },
-    /// Only with the "mintable" extension. The current minter may set a new minter.
-    UpdateMinter { new_minter: String },
+    /// Only with the "mintable" extension. The current minter may set
+    /// a new minter. Setting the minter to None will remove the
+    /// token's minter forever.
+    UpdateMinter { new_minter: Option<String> },
     /// Only with the "marketing" extension. If authorized, updates marketing metadata.
     /// Setting None/null for any of these will leave it unchanged.
     /// Setting Some("") will clear this field on the contract storage