https://en.wikipedia.org/wiki/Kunming%E2%80%93Singapore_rail...
Despite the name it's actually a series of different routes, and while all of them still have gaps, the Boten-Vientiane link connecting China to Thailand (and hence Singapore) via Laos is scheduled to open in late 2021:
https://en.wikipedia.org/wiki/Vientiane%E2%80%93Boten_railwa...
Although the corresponding line on the Chinese side also needs to open (ETA 2022):