In the CARES Act that just passed (text here), section 2201 provides the recovery rebate tax credit for 2020, with section (f) providing advance refunds (the check). It says that the advance refund amount will be determined based on the amount of credit you would have gotten if it were applied to your 2019 tax return, or (in subsection (f)(5)), if you haven't filed a 2019 tax return by the time they make the determination, your 2018 tax return, or, if you didn't file that, based on amounts from your SSA-1099 or RRB-1099. However, SSA-1099 and RRB-1099 are Social Security or Railroad Retirement benefit statements, which you would only have if you had one of those retirement benefits.
So what if you are someone who did not (and does not by the time they make the determination) file 2018 or 2019 tax returns (e.g. because your income is below the threshold for being required to file), and you are not getting Social Security benefits? Does that mean that you won't get the check (advance refund) and will have to claim the credit on your 2020 tax return? Or can they figure out your income from other sources and still give you the check?