ImpactInstaller is an installer program for Impact based on LiteLoaderInstaller which, in turn, was origionally built upon the Minecraft Forge Installer.
ImpactInstaller uses the Gradle build automation
system. It is designed to be built alongside the LiteLoader project, and
requires that the upstream artefact is specified using the upstreamJar project
property. The property will be evaluated with x being substituted for the
target project object, so for example you may use:
gradle -P-PupstreamJar='"${x.projectDir}/../LiteLoader/build/libs/liteloader-${x.mcversion}-SNAPSHOT-release.jar"'