I just tried setting up a dev environment with the latest Forge (1.12.2-14.23.0.2545), I'm using IntelliJ IDEA 2017.2.5.
I tried following the instructions, but when I try to change the "Use classpath of module" field, there's only two options: no module or simply the name of the directory I'm in, no option that ends in _main.
When I try to run the MC Client with these default options, the example mod doesn't get compiled and can't be found by Forge.