At the switch the black wire is connected to the new switch. At the light fixture box the black wire is spliced with the black wire running to the switch.

Rose Gold Wire Cage Pendant Light Plug In Light Fixture With Onoff Switch 1light
Wiring a light fixture to a switch. Grab your light fixture and twist the fixtures ground wire in with the other ground wires and secure them with a wire connector or wire nut. Two wire cable runs from the combo to the light fixture and the switch output is connected to the black wire running to the fixture hot terminal. More about wiring a switch. The wiring would need to include a neutral wire to satisfy nec code requirements. Back at the source the neutral wire is spliced to the white wire running to the light and to a pigtail connecting back to the receptacle neutral terminal. How to wire an additional light to an existing light switch.
Installing electrical wiring from a switch for a light switch for a project like this electrical wiring is typically installed from the ceiling box to the wall switch location as you have stated. If youre only connecting a single light fixture to a switch youll have one live cable with a black white and bare ground wire in the fixture box. At the light it connects to the neutral terminal. The source neutral wire is spliced to the neutral on the receptacle half of the combo device and to the white cable wire running to the light. Connect the black wire to the black wire on the light the white wire to the white one on the light and the bare one to the ground wire or the ground screw. Take the white wire that is coming from the circuit the original line and the white wire from the fixture twist them together and tighten a wire nut over them.
You can wire the new wall light fixture into the existing light and have a single switch control both lights. Since the existing light is already connected to the switch and you are not adding a light switch most of the wiring you need will be present in the wall or ceiling.