I have encountered in some grammar books that you can never have the future tense in the sub-ordinate clause when the main clause is also in the future tense. It seems to hold in conditional clauses and time clauses (those that contain when, if etc).
Based on that, the sentence "What will be will be" has always stuck out in my mind as an abberation.
So my question is, is this an actual rule? That is, should the above sentence be rewritten in some way to make it grammatically sound?
For example by replacing what will be by what is to be or what is going to be or something in that line.
Another such example: I will decide what I will do