To reproduce, take a similar buildscript as the one in Forge's 1.13-pre branch at the moment, and replace the line pipeline = 'joined' with pipeline = 'server'.
Then, running gradlew setup gives the following error:
Could not find a step of type net.minecraftforge.gradle.mcp.function.DownloadVersionJSONFunction
To reproduce, take a similar buildscript as the one in Forge's 1.13-pre branch at the moment, and replace the line
pipeline = 'joined'
withpipeline = 'server'
. Then, runninggradlew setup
gives the following error:This is due to https://github.com/MinecraftForge/ForgeGradle/blob/FG_3.0/src/mcp/java/net/minecraftforge/gradle/mcp/function/AbstractDownloadMCFunction.java#L21 assuming that the pipeline contains a function to download version json, which the server pipeline is currently missing.