Handle setting a working set item to None twice

Without this, setting an item to None that did not already exist failed,
because the kv delete operation did not find the referenced key.

This also checks that the index is not 0, which is not allowed as the
working set is 1-indexed.

taskchampion/src/storage/kv.rs

@@ -308,7 +308,7 @@ impl<'t> StorageTxn for Txn<'t> {
             Err(e) => return Err(e.into()),
         };
 
-        if index >= next_index {
+        if index < 1 || index >= next_index {
             anyhow::bail!("Index {} is not in the working set", index);
         }
 
@@ -319,7 +319,11 @@ impl<'t> StorageTxn for Txn<'t> {
                 Msgpack::to_value_buf(uuid)?,
             )?;
         } else {
-            kvtxn.del(working_set_bucket, index.into())?;
+            match kvtxn.del(working_set_bucket, index.into()) {
+                Ok(_) => {}
+                Err(Error::NotFound) => {}
+                Err(e) => return Err(e.into()),
+            };
         }
 
         Ok(())
@@ -650,6 +654,82 @@ mod test {
         Ok(())
     }
 
+    #[test]
+    fn set_working_set_item() -> anyhow::Result<()> {
+        let tmp_dir = TempDir::new()?;
+        let mut storage = KvStorage::new(&tmp_dir.path())?;
+        let uuid1 = Uuid::new_v4();
+        let uuid2 = Uuid::new_v4();
+
+        {
+            let mut txn = storage.txn()?;
+            txn.add_to_working_set(uuid1)?;
+            txn.add_to_working_set(uuid2)?;
+            txn.commit()?;
+        }
+
+        {
+            let mut txn = storage.txn()?;
+            txn.set_working_set_item(1, Some(uuid2))?;
+            txn.set_working_set_item(2, None)?;
+            txn.commit()?;
+        }
+
+        {
+            let mut txn = storage.txn()?;
+            let ws = txn.get_working_set()?;
+            assert_eq!(ws, vec![None, Some(uuid2), None]);
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn set_working_set_item_nonexistent() -> anyhow::Result<()> {
+        let tmp_dir = TempDir::new()?;
+        let mut storage = KvStorage::new(&tmp_dir.path())?;
+        let uuid1 = Uuid::new_v4();
+
+        {
+            let mut txn = storage.txn()?;
+            txn.add_to_working_set(uuid1)?;
+            txn.commit()?;
+        }
+
+        {
+            let mut txn = storage.txn()?;
+            txn.set_working_set_item(1, None)?;
+            txn.commit()?;
+        }
+
+        {
+            let mut txn = storage.txn()?;
+            // set it to None again, to check idempotency
+            txn.set_working_set_item(1, None)?;
+            txn.commit()?;
+        }
+
+        {
+            let mut txn = storage.txn()?;
+            let ws = txn.get_working_set()?;
+            assert_eq!(ws, vec![None, None]);
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn set_working_set_item_zero() -> anyhow::Result<()> {
+        let tmp_dir = TempDir::new()?;
+        let mut storage = KvStorage::new(&tmp_dir.path())?;
+        let uuid1 = Uuid::new_v4();
+
+        let mut txn = storage.txn()?;
+        assert!(txn.set_working_set_item(0, Some(uuid1)).is_err());
+
+        Ok(())
+    }
+
     #[test]
     fn clear_working_set() -> anyhow::Result<()> {
         let tmp_dir = TempDir::new()?;