I've been trying to install forge for Minecraft version 1.12.2. I noticed the problem after running the official Forge installer, and the Forge version did not appear in the Minecraft Launcher.
I have successfully installed Forge for other versions, so when this one didn't work, I looked in the version files to compare.
The 1.12.2 version file has a .json but no .jar like the others. I looked for and attempted several different solutions. I started with a clean install of Minecraft, the .jar file still didn't appear after running the installer, so I attempted to manually install the Forge Universal for 1.12.2, and when I did, the version appeared in the Minecraft launcher, but the game failed to launch.
Perhaps I incorrectly installed Forge Universal. Regardless, I still believe the 1.12.2 installer is broken, as it does not install all of the files needed to run the game.