third_party/allwpilib_2019/hal/simjni.gradle

def athenaSimJniOutputDir = file("$buildDir/generated/cpp")
def athenaSimJniOutputFile = file("$athenaSimJniOutputDir/simjni.cpp")

task generateAthenaSimFiles() {
    Set dirs = [];

    def createdTask = it
    outputs.file athenaSimJniOutputFile

    model {
        components {
            it.all { component ->
                if (component in getJniSpecClass()) {
                    component.binaries.all { binary ->
                        if (binary.targetPlatform.architecture.name == 'athena') {
                            binary.tasks.withType(CppCompile) {
                                it.dependsOn createdTask
                            }
                            component.jniHeaderLocations.each {
                                dependsOn it.key
                                createdTask.inputs.dir it.value
                                dirs << it.value
                            }
                        }
                    }
                }
            }
        }
    }

    doLast {
        def symbolList = []
        dirs.each {
            def tree = fileTree(dir: it)
            tree.each { file ->
                if (!file.name.contains('edu_wpi_first_hal_sim_mockdata_')) {
                    return
                }
                boolean reading = false
                String currentLine = ''
                file.eachLine { line ->
                    if (line.trim()) {
                        if (line.contains(';') && reading) {
                            currentLine += line.trim()
                            reading = false
                            symbolList << currentLine
                            currentLine = ''
                        }
                        if (line.startsWith("JNIEXPORT ") && line.contains('JNICALL')) {
                            if (line.contains(';')) {
                                symbolList << line
                                currentLine = ''
                                reading = false
                            } else {
                                reading = true
                                currentLine += line.trim()
                            }

                        }
                    }
                }
            }
        }
        athenaSimJniOutputDir.mkdirs()
        athenaSimJniOutputFile.withWriter { out ->
            out.println '#include <jni.h>'
            out.println '''
static JavaVM* jvm = nullptr;

namespace sim {
jint SimOnLoad(JavaVM* vm, void* reserved) {
  jvm = vm;

  JNIEnv *env;
  if (vm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6) != JNI_OK)
    return JNI_ERR;

  return JNI_VERSION_1_6;
}

void SimOnUnload(JavaVM * vm, void* reserved) {
  JNIEnv *env;
  if (vm->GetEnv(reinterpret_cast<void **>(&env), JNI_VERSION_1_6) != JNI_OK)
    return;
  jvm = nullptr;
}
}

static void ThrowSimException(JNIEnv* env) {

}
'''
            out.println 'extern "C" {'
            symbolList.each {
                def symbol = it.replace('JNIEnv *', 'JNIEnv * env')
                if (symbol.contains('JNIEXPORT void')) {
                    symbol = symbol.replace(';', ''' {
  ThrowSimException(env);
}''')
                } else {
                    symbol = symbol.replace(';', ''' {
  ThrowSimException(env);
  return 0;
}''')
                }
                out.println symbol
            }
            out.println '}'
        }
    }
}