Store: is metaReducers signature correct?

[GiuseppePiscopo]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request

What is the current behavior?

In StoreModule.forRoot(), in its StoreConfig<T,V> parameter, its metaReducers property is typed as an (optional) array of ActionReducer<T,V>.

But then in meta reducers docs provided example (which is correct, I think), does not adhere to that type:

function debug(reducer) {
  return function(state, action) {
    // ... log things ...
    return reducer(state, action);
  }
}

which is like (adding fictional generic types):

function debug(reducer: ActionReducer<T,V>): 
  (red: ActionReducer<T,V>) => ActionReducer<T,V> {

  return function wrapperReducer(state: T, action: V): ActionReducer<T,V> {
    // ... log things ...
    return reducer(state, action);
  }

}

Infact, being a meta-reducer, debug is not a reducer itself: is a function taking a reducer and giving another (transformed, wrapped, decorated ...) reducer.

So it seems to me that metaReducers cannot be an array of ActionReducer<T,V>. As a matter of fact, when I add (non generic) types to my debug function, code does not compile because of metareducers issue with types:

[...]
Types of property 'metaReducers' are incompatible. [...]
Type '(reducer: ActionReducer<PublicAppState, Action>) => ActionReducer<PublicAppState, Action>' is not assignable to type 'ActionReducer<PublicAppState, Action>'.

Expected behavior:

metaReducers property should be typed as an (optional) array of reducer-transformers, each item like: (red: ActionReducer<T,V>) => ActionReducer<T,V>

Minimal reproduction of the problem with instructions:

Version of affected browser(s),operating system(s), npm, node and ngrx:

Other information: