The Shillelagh cantrip says that your attacks become magical, but the green-flame blade cantrip (SCAG, p. 143) says it works with a melee attack.
As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails.
Does the fact that my staff's attacks become magical stop green-flame blade from working?
Best Answer
The green-flame blade spell works just the same with a shillelagh-ed weapon.
The green-flame blade spell (SCAG, p. 143) states:
Here we see that it only requires "a weapon" not a "non-magical weapon". Similarly, its material component requirement is simply "a weapon". Thus we can conclude that it works with a magical weapon, but let's look at shillelagh just in case:
All this does is allow you to change the ability modifier added to melee attack and damage rolls, change the weapon die, and make the weapon magical. None of these would make the booming blade spell invalid as the weapon is still a weapon.
Note that both of these spells only affect "melee attacks" made with the weapon (in fact, making a ranged attack with a shillelagh-ed weapon will end shillelagh completely).