Lint check for accessing stateSnapshot in MutateState

[sockeqwe]

Accessing the stateSnapshot parameter inside a MutateState block should be forbidden by a lint Rule.

fun onActionXDoFoo(action: ActionX, stateSnapshot: State) {
   ....
   return MutateState {
       stateSnapshot.copy( ... ) // Accessing must be forbidden because lambda parameter state must be used instead
   }
}

[gabrielittner]

This might be a bit easier now that the snapshot is a property on State since you can search for usages of that specifically instead of an arbitrary parameter. I think one other issue that this check should cover is that the object returned in the lambda is created inside the lambda, which will also reduce the risk of creating it based on an outdated snapshot.

fun onActionXDoFoo(action: ActionX, stateSnapshot: State) {
   ....
   val newState =  stateSnapshot.copy( ... )
   return MutateState { 
       newState // Returning newState must be forbidden because it was created outside the lambda where we can't check whether the snapshot was used to create it
   }
}

In summary:

• state.snapshot should never be accessed inside the lambda
• the returned object has to be created inside the lambda