build gradle with git and gradle window setup

build.gradle

apply plugin: 'idea'

idea {
  project {
    jdkName "1.8"
    languageLevel "1.8"
    ipr {
      withXml { provider ->
        def node = provider.asNode()
        node.component.find { it.'@name' == 'VcsDirectoryMappings' }?.mapping[0].'@vcs' = 'Git'
        node.append(new XmlParser().parseText('''
<component name="GradleSettings">
    <option name="linkedExternalProjectsSettings">
      <GradleProjectSettings>
        <option name="distributionType" value="DEFAULT_WRAPPED" />
        <option name="externalProjectPath" value="$PROJECT_DIR$" />
        <option name="useAutoImport" value="true" />
      </GradleProjectSettings>
    </option>
</component>
'''))
      }
    }
  }
}

Naturally, I would never recommend setting jdkName on an OSS project as that can vary from one machine to another.

You can set languageLevel = "JDK_1_8" safely, I think.