Build cache

class CustomTask extends DefaultTask {
  @InputDirectory
  File sourceDirectory

  @OutputFile
  File outputFile

  // ...
}

class CustomTask extends DefaultTask {

  @PathSensitive(PathSensitivity.RELATIVE)
  @InputDirectory
  File sourceDirectory

  // ...
}

@CacheableTask
class ConcatenateTask extends DefaultTask {
  @PathSensitive(PathSensitivity.NONE)
  @InputFiles FileCollection sourceFiles
  @OutputFile File outputFile

  @TaskAction
  void concatenate() {
    outputFile.createNewFile()
    sourceFiles.each {
      outputFile << it.text + '\n'
    }
  }
}

@CacheableTask
class ConcatenateTask extends DefaultTask {
  @PathSensitive(PathSensitivity.NONE)
  @InputFiles FileCollection sourceFiles
  @OutputFile File outputFile

  @TaskAction
  void concatenate() {
    outputFile.createNewFile()
    sourceFiles.sort().each {
      outputFile << it.text + '\n'
    }
  }
}