Why must it be A or B here? There's a third option C, which is simply this: the PHB defines what each action is. They are specific rules that apply to the action they are defining alone, and not general rules that apply to the whole game.
And yet your case relies on 'rules'
that are not rules that
you choose to apply to one Action-the Attack action-but not to the others. You don't even realise that you're doing this!
I really think that this is where you've gone off the rails and it's forcing you to make conclusions that are not supported by the words in the PHB.
Wait!
I was going to say that to
you!
I apologize in advance as this post will likely be long
I don't mind if a post is long, as long as it is interesting. Yours is interesting. Incorrect, but interesting.
but I will make one more attempt to explain why it doesn't have to be A or B as you defined them here. I'm going to start with some basic assumptions, in particular that in order for you to actually be able to do something during combat, there must be a rule that says you can do that thing...
...and no rule that says you
can't do that thing, agreed.
Like the rules say you
can take your bonus action whenever you want in your turn, and
no rule saying you
can't take it
during an action.
Similarly, I'm going to assume that the simplest outcome for a given rule is the correct one, as this helps to ensure that turns in combat are generally quick and easy (as apparently this was one of the goals of the 5E combat system, unlike previous editions).
A tempting assumption, but unfounded. This cannot be relied upon in any way.
Some people have argued that spells like Sanctuary or Shield imply that the Attack action or actions in general must work in a certain way, but this is not correct: the spells provide exceptions to the rules governing those actions, and apply to those spells only.
While I agree that specific spells do not count as general rules in and of themselves, it is the case that the wording of some spells reveal how some general rules work.
This is the foundation on which we build everything else, and it sets up the precedent that there is an order to the individual elements of your turn. That is, there are clearly-defined portions of your turn "before your action" and "after your action". This suggests that the elements of your turn are played and resolved sequentially, and that order matters.
Why do I suggest that discrete elements must be resolved sequentially and that order matters? The answer is simple: there might be a reaction waiting to happen, with a trigger of any individual element on your turn.
What you've done here, with many correct examples, is draw the wrong conclusion.
Yes, the elements must be discrete, and must be in a definite order, and must be resolved sequentially. I agree.
But, no, Actions In Combat are not necessarily discrete elements themselves!
With Extra Attack for example, it's not the Attack
action that is a single discrete element, it's
each individual attack which is a discrete element!
Yes, you must have each 5 feet of movement, each attack, each shield bash, each opportunity attack, in a definite order and resolved sequentially. Even if two discrete elements
occur simultaneously, the rules require us to
resolve them sequentially.
But no, the Attack
action, with Extra Attack, is
not a discrete element in and of itself! I really think that
this is where
you've gone off the rails and it's forcing you to make conclusions that are not supported by the words in the PHB.
We've already determined that there are well-defined periods of time on your turn that are "before your action" and "after your action", based on the movement rules.
Agreed. And there are
also periods of time on your turn that are "during your action", when you have Extra Attack. The passage you quote regards a single attack, which IS a discrete element, so there is no 'during' in that case for that paragraph to mention.
But that paragraph is
not a rule that forbids you from doing anything
between elements that
are discrete, nor addresses how Extra Attack
changes the situation, because although there is no 'during' when there is only one element, there IS a 'during' when you have two or more discrete elements in one Action In Combat.
So, when can I use the Shield Master bonus action on the turn I described above?
1) At the start of my turn, my menu of available options is "move, action". I have not taken the Attack action, so I do not have access to the bonus action shove yet.
2) I use some of my movement, and my menu of available options is still "move, action" because I have movement left.
3) I take the Attack action, and choose to take the bonus action shield shove so generated (because this is the point where the condition "take the Attack action" is true) at the same time. My menu becomes "move, weapon attack, shield shove" because there's an explicit rule that lets me take my bonus action whenever I want.
FIFY.
Again, my turn is constructed of elements that are explicitly allowed by rules in the PHB. At no point do I have to guess or infer something, I'm using the actual words in the PHB. These elements must be played and resolved in order.
The rules say I
can take the Attack action, they say I
can take a bonus action shield shove if I take the Attack action on my turn, the rules say I
can take my bonus action whenever I want as soon as I have it, and if the relationship between this Action and this bonus action is one of 'cause and effect', then I
can let them coincide, and because they coincide then I
can choose the order in which those individual elements are resolved.
I have limited myself only to those things the rules say I
can do, and I have nowhere done anything the rules say I
can't do!