Unfortunately type can be changed by any change:

class A {
  def foo = goo
 
  def goo = 1 //change it to "" and type of 'foo' will be changed
} 

I'm sure it's possible to handle dependencies and to do smarter caching, but I'm also sure that it's too complex to do it now.

Current plugin state of this problem is that everything will be much faster if you type code inside '{}', which cannot change anything outside this scope, for example:

class A {
  def foo: Int = {
    //everything will be faster during typing just here
  } 
}

Best regards,

Alexander Podkhalyuzin.