5e rules designer Jeremy Crawford stated the following in a tweet about the dragon's breath spell:
Dragon's breath has two sets of targets: the creature you give the breath weapon to and the creatures in the area of effect created by the spell.
Imagine that there are 3 creatures in a fight: a wizard, the wizard's ally, and an enemy. The enemy is able to impose the charmed condition on the wizard. While charmed, can the wizard cast dragon's breath on their ally?
Since there are only three creatures, the charmed wizard should've realized that giving dragon's breath to their ally would enable them to use it against the charmer. It is akin to: "Hey, I can't beat this guy! Here, have a bat - go and beat him for me!"
Since being charmed forbids you from casting a harmful spell targeting the charmer, does it mean that being a potential secondary target for the dragon's breath spell prevents the charmed spellcaster from casting dragon's breath while charmed?
Can the charmed spellcaster cast dragon's breath in this situation?