Is the `\summon` command broken?

Question

Based on this video. I tried to make this kind of rocket launcher for my mini game.

I Used this command:

/execute @e[type=Snowball] ~ ~ ~ /summon Fireball ~ ~ ~ {Motion:[0.0,0.0,0.0],direction:[0.0,0.0­,0.0]}

but I got:

unable to summon object.

I used the 15w51b snapshot. I think I also tested this a while back in 1.8 but i can't remember if it worked

Answer 1

No.

I just did some testing in 1.8.9, as well as the 1.9 snapshots 15w51b and 16w03a. Fireball (and SmallFireball) require you to specify the direction tag (the Motion tag is not needed!), see the invalid "bug" MC-86011. In 1.8.9, a Fireball without direction will simply vanish immediately. In the snapshots/1.9, the direction tag is more strict: It needs to exist, and needs to contain exactly 3 doubles. Otherwise, you'll will get a message saying "Unable to summon".

In any case, if a direction tag is correctly specified, the object will be summoned.

Now the problem you are having is that there is a strange hidden character in your direction tag, which can be seen when you copy-paste the command into Minecraft (SE doesn't show it at all):

This character causes Minecraft to think the second entry of the tag is a string rather than a double, and Minecraft promptly throws it out. Your direction tag now has only 2 entries and is therefore invalid, which causes your problems. You can copy-paste this command instead:

/execute @e[type=Snowball] ~ ~ ~ /summon Fireball ~ ~ ~ {direction:[0.0,0.0,0.0]}

^{Thanks to @Skylinerw for explaining the technical details.}