Ref: https://github.com/reactjs/rfcs/pull/147#issuecomment-623740218

React version: 0.0.0-experimental-e5d06e34b

## Steps To Reproduce

1. createMutableSource that contains functions
2. getSnapshot returns one of the functions

Link to code example:

https://codesandbox.io/s/jovial-dew-1eg4t?file=/src/App.js

## The current behavior

If getSnapshot returns a function, it will run the function in render. This results in various errors.

My workaround: return an object wrapping a function, and destruct on caller.

> For now, you can work around this by returning a function that returns your function

I don't know how this works as workaround.

## The expected behavior

It would be nice if returning a function just works.

Note: this is not a rare use case in my library https://github.com/dai-shi/use-context-selector
because we often pass `[state, setState]` in a context value.
workInProgress.effectTag &= ~(PassiveEffect | UpdateEffect);
  if (current.expirationTime <= expirationTime) {
    current.expirationTime = NoWork;
  }
}
export function resetHooksAfterThrow(): void {
  
  
  ReactCurrentDispatcher.current = ContextOnlyDispatcher;
  if (didScheduleRenderPhaseUpdate) {
    
    
    
    
    
    
    
    
    let hook: Hook | null = currentlyRenderingFiber.memoizedState;
    while (hook !== null) {
      const queue = hook.queue;
      if (queue !== null) {
        queue.pending = null;
      }
      hook = hook.next;
    }
    didScheduleRenderPhaseUpdate = false;
  }
  renderExpirationTime = NoWork;
  currentlyRenderingFiber = (null: any);