fail the build if no init scripts are available

Author: Denis Zhdanov

src/main/kotlin/tech/harmonysoft/oss/gradle/dist/BuildCustomGradleDistributionTask.kt

@@ -371,11 +371,21 @@ abstract class BuildCustomGradleDistributionTask @Inject constructor(
         )
         .use { zipFileSystem ->
             config.initScriptsSourceDir.get().asFile.let { initScriptsSourceDir ->
+                val includeRootDir = distribution?.let {
+                    File(initScriptsSourceDir, it)
+                } ?: initScriptsSourceDir
+                val initScripts = includeRootDir.listFiles()?.filter {
+                    it.name.endsWith(".gradle") || it.name.endsWith(".gradle.kts")
+                } ?: emptyList()
+                if (initScripts.isEmpty()) {
+                    throw IllegalStateException(
+                        "can not generate custom distribution ${zip.name} - there must be at least one file to "
+                        + "include into its init.d, but directory ${initScriptsSourceDir.canonicalPath} is empty"
+                    )
+                }
                 addToZip(
                     zip = zipFileSystem,
-                    includeRootDir = distribution?.let {
-                        File(initScriptsSourceDir, it)
-                    } ?: initScriptsSourceDir,
+                    includeRootDir = includeRootDir,
                     gradleVersion = gradleVersion,
                     pathsToExcludeFromContentExpansion = pathsToExcludeFromContentExpansion,
                     replacements = replacements

src/test/kotlin/tech/harmonysoft/oss/gradle/dist/CustomGradleDistributionPluginTest.kt

@@ -446,8 +446,8 @@ class CustomGradleDistributionPluginTest {
     private fun prepareGradleDistributionZip(projectRootDir: File) {
         val downloadDir = File(projectRootDir, "build/gradle-download")
         Files.createDirectories(downloadDir.toPath())
-        listOf("bin", "all").forEach {
-            val zip = File(downloadDir, "gradle-${GRADLE_VERSION}-${it}.zip")
+        for (type in DISTRIBUTION_TYPES) {
+            val zip = File(downloadDir, "gradle-${GRADLE_VERSION}-${type}.zip")
             createGradleDistributionZip(zip)
         }
     }
@@ -593,8 +593,8 @@ class CustomGradleDistributionPluginTest {
         const val GRADLE_VERSION = "8.3"
         const val PROJECT_NAME = "my-project"
         const val PROJECT_VERSION = "1.0"
-        const val DEFAULT_DISTRIBUTION_TYPE = "bin"
         const val BUILT_DISTS_DIR = "build/gradle-dist"
+        val DISTRIBUTION_TYPES = setOf("bin", "all")
 
         @field:TempDir(cleanup = CleanupMode.ON_SUCCESS)
         lateinit var TESTS_ARTIFACTS_ROOT_DIR: Path