The build fails while giving this error, i am using IntelliJ IDEA

com.intellij.openapi.externalSystem.model.ExternalSystemException: Could not find minecraftBin.jar (net.minecraft:minecraftBin:1.12.2).
Searched in the following locations:
https://files.minecraftforge.net/maven/net/minecraft/minecraftBin/1.12.2/minecraftBin-1.12.2.jar

Could not find minecraftBin.jar (net.minecraft:minecraftBin:1.12.2).
Searched in the following locations:
https://files.minecraftforge.net/maven/net/minecraft/minecraftBin/1.12.2/minecraftBin-1.12.2.jar

Possible solution:

• Declare repository providing the artifact, see the documentation at https://docs.gradle.org/current/userguide/declaring_repositories.html

the build.gradle file is the same as the original

This seems to be back working. Forge seem to have fixed their maven.

this is a known issue, forge did something to their maven and it's a bit hardcoded in forgegradle2. hopefully there will either be a switch to ForgeGradle3 for 1.12 fix or switch to someone who's patched it.

for example:
maven { url 'https://jitpack.io' }
and
classpath 'com.github.SizableShrimp:ForgeGradle:FG_2.3-SNAPSHOT'