Add single_file and preamble.

Fixes #67

compiler-plugin/src/main/scala/com/trueaccord/scalapb/compiler/DescriptorPimps.scala

@@ -400,7 +400,6 @@ trait DescriptorPimps {
 
   def baseName(fileName: String) =
     fileName.split("/").last.replaceAll(raw"[.]proto$$|[.]protodevel", "")
-
 }
 
 object Helper {

compiler-plugin/src/main/scala/com/trueaccord/scalapb/compiler/ProtobufGenerator.scala

@@ -8,6 +8,9 @@ import scala.collection.JavaConversions._
 
 case class GeneratorParams(javaConversions: Boolean = false, flatPackage: Boolean = false, grpc: Boolean = false)
 
+// Exceptions that are caught and passed upstreams as errors.
+case class GeneratorException(message: String) extends Exception(message)
+
 class ProtobufGenerator(val params: GeneratorParams) extends DescriptorPimps {
   def printEnum(e: EnumDescriptor, printer: FunctionalPrinter): FunctionalPrinter = {
     val name = e.nameSymbol
@@ -887,6 +890,9 @@ class ProtobufGenerator(val params: GeneratorParams) extends DescriptorPimps {
   }
 
   def scalaFileHeader(file: FileDescriptor): FunctionalPrinter = {
+    if (file.scalaOptions.getPreambleList.nonEmpty && !file.scalaOptions.getSingleFile) {
+      throw new GeneratorException(s"${file.getName}: single_file must be true when a preamble is provided.")
+    }
     new FunctionalPrinter().addM(
       s"""// Generated by the Scala Plugin for the Protocol Buffer Compiler.
          |// Do not edit!
@@ -900,6 +906,8 @@ class ProtobufGenerator(val params: GeneratorParams) extends DescriptorPimps {
       case (i, printer) => printer.add(s"import $i")
     }
     .add("")
+    .seq(file.scalaOptions.getPreambleList)
+    .when(file.scalaOptions.getPreambleList.nonEmpty)(_.add(""))
   }
 
   def generateFileDescriptor(file: FileDescriptor)(fp: FunctionalPrinter): FunctionalPrinter = {
@@ -960,8 +968,24 @@ class ProtobufGenerator(val params: GeneratorParams) extends DescriptorPimps {
     }
   }
 
-  def generateScalaFilesForFileDescriptor(file: FileDescriptor): Seq[CodeGeneratorResponse.File] = {
-    val serviceFiles = if(params.grpc) {
+  def generateSingleScalaFileForFileDescriptor(file: FileDescriptor): Seq[CodeGeneratorResponse.File] = {
+    val code = 
+      scalaFileHeader(file)
+      .print(file.getEnumTypes)(printEnum)
+      .print(file.getMessageTypes)(printMessage)
+      .add(s"object ${file.fileDescriptorObjectName} {")
+      .indent
+      .call(generateFileDescriptor(file))
+      .outdent
+      .add("}").result()
+    val b = CodeGeneratorResponse.File.newBuilder()
+    b.setName(file.scalaPackageName.replace('.', '/') + "/" + file.fileDescriptorObjectName + ".scala")
+    b.setContent(code)
+    generateServiceFiles(file) :+ b.build
+  }
+
+  def generateServiceFiles(file: FileDescriptor): Seq[CodeGeneratorResponse.File] = {
+    if(params.grpc) {
       file.getServices.map { service =>
         val p = new GrpcServicePrinter(service, params)
         val code = p.printService(FunctionalPrinter()).result()
@@ -971,6 +995,10 @@ class ProtobufGenerator(val params: GeneratorParams) extends DescriptorPimps {
         b.build
       }
     } else Nil
+  }
+
+  def generateMultipleScalaFilesForFileDescriptor(file: FileDescriptor): Seq[CodeGeneratorResponse.File] = {
+    val serviceFiles = generateServiceFiles(file)
 
     val enumFiles = for {
       enum <- file.getEnumTypes
@@ -1026,18 +1054,27 @@ object ProtobufGenerator {
     val b = CodeGeneratorResponse.newBuilder
     parseParameters(request.getParameter) match {
       case Right(params) =>
-        val generator = new ProtobufGenerator(params)
-        val filesByName: Map[String, FileDescriptor] =
-          request.getProtoFileList.foldLeft[Map[String, FileDescriptor]](Map.empty) {
-            case (acc, fp) =>
-              val deps = fp.getDependencyList.map(acc)
-              acc + (fp.getName -> FileDescriptor.buildFrom(fp, deps.toArray))
+        try {
+          val generator = new ProtobufGenerator(params)
+          import generator.FileDescriptorPimp
+          val filesByName: Map[String, FileDescriptor] =
+            request.getProtoFileList.foldLeft[Map[String, FileDescriptor]](Map.empty) {
+              case (acc, fp) =>
+                val deps = fp.getDependencyList.map(acc)
+                acc + (fp.getName -> FileDescriptor.buildFrom(fp, deps.toArray))
+            }
+          request.getFileToGenerateList.foreach {
+            name =>
+              val file = filesByName(name)
+              val responseFiles = 
+                if (file.scalaOptions.getSingleFile) 
+                  generator.generateSingleScalaFileForFileDescriptor(file)
+                else generator.generateMultipleScalaFilesForFileDescriptor(file)
+              b.addAllFile(responseFiles)
           }
-        request.getFileToGenerateList.foreach {
-          name =>
-            val file = filesByName(name)
-            val responseFiles = generator.generateScalaFilesForFileDescriptor(file)
-            b.addAllFile(responseFiles)
+        } catch {
+          case e: GeneratorException =>
+            b.setError(e.message)
         }
       case Left(error) =>
         b.setError(error)

e2e/src/main/protobuf/sealed_trait.proto

@@ -0,0 +1,33 @@
+syntax = "proto2";
+
+package com.trueaccord.proto.e2e;
+
+import "scalapb/scalapb.proto";
+
+// Demonstrates a sealed trait and two messages extending it.
+
+option (scalapb.options) = {
+  // All classes that extend a sealed trait need to be in the same Scala
+  // file, so we set single_file to true.
+  single_file: true
+
+  // Generate the base trait.
+  preamble: [
+    "sealed trait MyBaseTrait {",
+    "  def getFoo: Int",
+    "  def getBar: String",
+    "}"
+  ];
+};
+
+message Type1 {
+  option (scalapb.message).extends = "MyBaseTrait";
+  optional int32 foo = 1;
+  optional string bar = 2;
+}
+
+message Type2 {
+  option (scalapb.message).extends = "MyBaseTrait";
+  optional int32 foo = 1;
+  optional string bar = 2;
+}

proptest/src/test/scala/GeneratedCodeSpec.scala

@@ -86,8 +86,8 @@ class GeneratedCodeSpec extends PropSpec with GeneratorDrivenPropertyChecks with
               javaParse(scalaAscii) should be(javaProto)
               javaParse(scalaUnicodeAscii) should be(javaProto)
 
-              val jsonRep = com.trueaccord.scalapb.json.JsonFormat.toJson(scalaProto)
-              com.trueaccord.scalapb.json.JsonFormat.fromJson(jsonRep)(companion.asInstanceOf[GeneratedMessageCompanion[T] forSome {type T <: GeneratedMessage with ScalaPBMessage[T] }]) should be(scalaProto)
+              val jsonRep = com.trueaccord.scalapb.json.JsonFormat.toJsonString(scalaProto)
+              com.trueaccord.scalapb.json.JsonFormat.fromJsonString(jsonRep)(companion.asInstanceOf[GeneratedMessageCompanion[T] forSome {type T <: GeneratedMessage with ScalaPBMessage[T] }]) should be(scalaProto)
 
             } catch {
               case e: Exception =>

proptest/src/test/scala/GraphGen.scala

@@ -130,12 +130,14 @@ object GraphGen {
   def genScalaOptions(state: State): Gen[(Option[ScalaPbOptions], State)] = for {
     (scalaPackageName, state) <- GenUtils.listWithStatefulGen(state, minSize = 1, maxSize = 4)(_.generateName)
     flatPackage <- Gen.oneOf(true, false)
+    singleFile <- Gen.oneOf(true, false)
   } yield {
     val b = ScalaPbOptions.newBuilder
     if (scalaPackageName.nonEmpty) {
       b.setPackageName(scalaPackageName.mkString("."))
     }
     b.setFlatPackage(flatPackage)
+     .setSingleFile(singleFile)
     (Some(b.build), state)
   }
 

protobuf/scalapb/scalapb.proto

@@ -19,6 +19,14 @@ message ScalaPbOptions {
   // Adds the following imports at the top of the file (this is meant
   // to provide implicit TypeMappers)
   repeated string import = 3;
+
+  // If true, all messages and enums (but not services) will be written
+  // to a single Scala file.
+  optional bool single_file = 5;
+
+  // Text to add to the generated scala file.  This can be used only
+  // when single_file is true.
+  repeated string preamble = 4;
 }
 
 extend google.protobuf.FileOptions {