Run Groovy Project Without Compilation Using Gradle
To be honest it is automatically compiled by Gradle. All changes made into "buildSrc/src/main/groovy" are automatically compiled during startup.
Key feature of Gradle is how nicely it manages "buildSrc" directory.
Here is sample project https://bitbucket.org/bugs_/samples/src/default/RunGroovyProjectWithoutCompilationUsingGradle/