What happends in Texas Holdem when a player does not have enough chips to match a raise?

Question

What happends in Texas Holdem when a player does not have enough chips to match a raise?

Answer 1

The player is all in, unless they fold, and then a side pot is started for other players that are still betting.

Answer 2

The Player Goes all in

Answer 3

That player goes all in and any other players involved in the pot start a side pot just for them.