The spell description says that the caster can make a melee attack against a creature within 5 feet of the weapon. This would indicate that the weapon has not YET hit the target until the roll is successfully made - which, if you could simply manifest it within someone's chest or head or neck, would be a successful hit without a roll.
There's two types of players who make this kind of suggestion, and depending on which kind of player you're dealing with, you'll come at it differently. This is really the important part, since this question nearly always means you're going to get MORE questions along the same lines, and it's really about matching expectations of what this game is about.
The clever, creative player
"That's a clever idea! Unfortunately, that's not how this spell works.
You should look at the spell list and look for clever ways to use
spells, because it's pretty fun when you find some way to show us what
a determined (wizard/sorcerer/etc) can do!"
The clever, creative player is looking to find fun ways to use magic and their skills to find fun answers to problems. These players are fun to play with, if they don't spend too much time trying to find 1001 answers to any given problem ("You know you can just OPEN the door, right?").
The annoying cheap trick player
The annoying cheap trick player is always asking questions or trying to find ways to instantly win every problem. They're not looking for clever ways, they're looking for lazy loopholes that involve actively and willfully ignoring clear and obvious readings of the rules. I haven't yet met one of these players who decides to stop, but you can at least give them a chance:
"Ok, this is the fifth time this session you've asked a question like
this. This isn't even a clever solution, this is just asking to throw
away common sense readings of the rules so you can instantly win a
situation. I know there's a level of wish fulfillment in roleplaying,
but if you can't deal with challenge or conflict, I'm not really sure
this is the game for you. Do you want to play the game with us? We'd
love for you to play with us, but you seem very intent on playing some
If they decide they're still wanting to play rhetorical games, you should let them go and not play with them. They're not interested in playing the game with you, even though they'll always have excuses about how they "just happened" to "misread" or be "confused" about the rules in ways that no reasonable person could be, over and over.