GenerateProtoBuf: support java_multiple_files mode

generators/tests/org/jetbrains/kotlin/generators/protobuf/GenerateProtoBuf.kt

@@ -66,7 +66,7 @@ val PROTO_PATHS: List<ProtoPath> = listOf(
 private val EXT_OPTIONS_PROTO_PATH = ProtoPath("core/metadata/src/ext_options.proto")
 private val PROTOBUF_PROTO_PATHS = listOf("./", "core/metadata/src")
 
-fun main(args: Array<String>) {
+fun main() {
     try {
         checkVersion()
 
@@ -80,12 +80,10 @@ fun main(args: Array<String>) {
 
         println()
         println("Do not forget to run GenerateProtoBufCompare")
-    }
-    catch (e: Throwable) {
+    } catch (e: Throwable) {
         e.printStackTrace()
         throw e
-    }
-    finally {
+    } finally {
         // Workaround for JVM hanging: IDEA's process handler creates thread pool
         exitProcess(0)
     }
@@ -128,17 +126,34 @@ private fun renamePackages(protoPath: String, outPath: String) {
     val className = protoFileContents.findValue("option java_outer_classname = \"(\\w+)\";".toRegex())
         ?: error("No java_outer_classname option found in $protoPath")
 
-    val javaFile = File(outPath, "${packageName.replace('.', '/')}/$className.java")
+    val javaMultipleFiles = protoFileContents.findValue("option java_multiple_files = (\\w+);".toRegex()) == "true"
+
+    if (javaMultipleFiles) {
+        val packageDirectory = File(outPath, packageName.replace('.', '/'))
+        if (!packageDirectory.exists() || !packageDirectory.isDirectory) {
+            throw AssertionError("$protoPath, java_multiple_files mode: '$packageDirectory' doesn't exist or is not a directory")
+        }
+        val javaFiles = packageDirectory.listFiles { f: File -> f.extension == "java" }
+            ?: throw AssertionError("$protoPath, java_multiple_files mode: Can't list directory contents of '$packageDirectory'")
+        for (javaFile in javaFiles) {
+            renamePackagesInSingleFile(javaFile)
+        }
+    } else {
+        renamePackagesInSingleFile(File(outPath, "${packageName.replace('.', '/')}/$className.java"))
+    }
+}
+
+private fun renamePackagesInSingleFile(javaFile: File) {
     if (!javaFile.exists()) {
         throw AssertionError("File does not exist: $javaFile")
     }
 
     javaFile.writeText(
-            javaFile.readLines().map { line ->
+        javaFile.readLines().joinToString(LineSeparator.getSystemLineSeparator().separatorString) { line ->
             line.replace("com.google.protobuf", "org.jetbrains.kotlin.protobuf")
                 // Memory footprint optimizations: do not allocate too big bytes buffers that effectively remain unused
                 .replace("              unknownFieldsOutput);", "              unknownFieldsOutput, 1);")
-            }.joinToString(LineSeparator.getSystemLineSeparator().separatorString)
+        }
     )
 }
 
@@ -156,8 +171,10 @@ private fun modifyAndExecProtoc(protoPath: ProtoPath) {
 
 private fun modifyForDebug(protoPath: ProtoPath): String {
     var text = File(protoPath.file).readText()
-            .replace("option java_outer_classname = \"${protoPath.className}\"",
-                     "option java_outer_classname = \"${protoPath.debugClassName}\"") // give different name for class
+        .replace(
+            "option java_outer_classname = \"${protoPath.className}\"",
+            "option java_outer_classname = \"${protoPath.debugClassName}\""
+        ) // give different name for class
         .replace("option optimize_for = LITE_RUNTIME;", "") // using default instead
     (listOf(EXT_OPTIONS_PROTO_PATH) + PROTO_PATHS).forEach {
         val file = it.file