Consider an Eldritch Knight fighter that has a bonded thrown weapon. Once the Knight gets Extra Attack, can they throw the weapon, use a bonus action to retrieve it, and then throw it again? Or does that mess too much with the action order?
In case the Knight can't do this and doesn't have more thrown weapons, can they just throw one and then attack with a melee weapon?
The rules for bonus actions state:
You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.
Therefore, nothing prevents a character from using their bonus actions during another action, such as an attack action.
The Eldritch Knight's weapon bond feature states:
Once you have bonded a weapon to yourself, you can’t be disarmed of that weapon unless you are incapacitated. If it is on the same plane of existence, you can summon that weapon as a bonus action on your turn, causing it to teleport instantly to your hand.
Therefore, since the Eldritch Knight's weapon bond doesn't require any special timing or conditions, other than the weapon remaining on the same plane, and the teleportation effect is instantaneous, they can use their bonus action during their attack action to summon their weapon back to them.
As per RAW:
Weapon Bond
At 3rd level, you learn a ritual that creates a magical bond between yourself and one weapon. You perform the ritual over the course of 1 hour, which can be done during a short rest. The weapon must be within your reach throughout the ritual, at the conclusion of which you touch the weapon and forge the bond.
Once you have bonded a weapon to yourself, you can’t be disarmed of that weapon unless you are incapacitated. If it is on the same plane of existence, you can summon that weapon as a bonus action on your turn, causing it to teleport instantly to your hand.
You can have up to two bonded weapons, but can summon only one at a time with your bonus action. If you attempt to bond with a third weapon, you must break the bond with one of the other two.
So when you get the Extra Attack Feature, you can indeed throw the weapon, resummon it using your bonus action, and then throw it again. However on your next turn you would have to burn your bonus action to summon the weapon because you willingly threw it (which is not being disarmed).
Bonus actions are covered under PHB pg. 189:
Bonus Actions
Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action. The Cunning Action feature, for example, allows a rogue to take a bonus action. You can take a bonus action only when a special ability, spell, or other feature of the game states that you can do something as a bonus action. You otherwise don’t have a bonus action to take.
You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.
You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.
The only prerequisite for you to summon your weapon as a bonus action is that it is the weapon covered under your weapon bond. So yes, you can throw, summon, then throw again.
Attack actions are listed on PHB pg. 193 and cover all the different kinds of attacks you can take on your turn. Ranged attacks are one of the types covered, so you're good to go.
