You can also check once you know the action is not taken, which is when another action is taken instead or the turn ends without it being taken.
Show me that rule.
Before that, you won’t know whether the action will be taken or not, but it’s still alright to shove a creature at that time.
Show me that rule, too.
You just won’t know whether the shove used the Attack action or a bonus action until after you’ve checked.
And this is just blatantly false. You know the moment you use something whether it's an action or a bonus action. The ability you use tells you straight out. Despite your claims, there is no Shrodinger's action in 5e.
Edit: Actually, what Crawford said is that there’s no action-declaration phase in 5E combat. You still have to declare actions to play the game because actually attacking the people you’re playing with is not okay.
This is just sophistry. You don't declare that you are going to use an action in the game at some point during the turn. I'll go Yoda on you. Use or use not, there is no declare.
You don’t have that quite right. The idea is that if you shove a creature and are prevented from making any more attacks after that, even if you’re a shield master, you still only took the Attack action and didn’t use a bonus action. The rules that allow this are the Attack action, the rules for making attacks, and the rules for shoving a creature.
This is not possible by RAW. The Rules as Written tell you what type of action you are taking in the instant you take it. The moment the PC takes a shove, it is either the action or the bonus action. Either you take it as a Bonus Action, in which case the trigger already has to have happened, or you take it as part of your Attack action, in which case you must say that as soon as you take it. There is no limbo state that the shove waits in to see what it will become.
Edit: I left out Reactions since they are not a part of this discussion. I added it in, because many people here have problems with context and/or will seize on the omission as an evasion.
I’m trying to take your post seriously, but I have a hard time believing you don’t honestly see the many glaring differences between declaring that you shove a creature without first attacking it (which is something you can do) and declaring your nonmagical weapon is magic without a spell first being cast on it (which is something you can’t do). Have a nice day.
1. Magic Weapon: Is this contingent on something occurring later in the round? Yes.
1. Shove: Is this contingent on something occurring later in the round? Yes.
2. Magic weapon: Am I using the ability before the trigger happens? Yes.
2. Shove. Are you using the ability before the trigger happens? Yes.
3. Is my wizard being knocked out before the trigger occurs? Yes.
3. Is your fighter being knocked out before the trigger occurs? Yes.
4. Am I then re-writing reality so that the trigger never needed to happen and an action was taken to provide the effect? Yes.
4. Are you then re-writing reality so that the trigger never needed to happen and an action was taken to provide the effect? Yes.
I'm not seeing any difference in the steps taken between the two. The reasoning for both examples is the same. That one is an action and the other a bonus action is not relevant. Both can be taken at any point during the turn. If you are having problems with my wizard example, you really should take a closer look at what you are claiming.