Split codegen into two libraries:

1) a codegen library that can be used as a protoc plugin without SBT
2) an SBT compiler plugin that registers the plugin from (1)

Author: rafikk

build.sbt

@@ -24,14 +24,23 @@ lazy val commonSettings = List(
 )
 
 lazy val codegen = (project in file("codegen"))
+  .settings(
+    commonSettings,
+    name := "twinagle-codegen",
+    crossScalaVersions := Seq(scala212, scala213, scala3LTS),
+    libraryDependencies += "com.thesamet.scalapb" %% "compilerplugin" % scalapb.compiler.Version.scalapbVersion,
+    publishLocal                                  := publishLocal.dependsOn(runtime / publishLocal).value,
+  )
+
+lazy val plugin = (project in file("plugin"))
   .enablePlugins(SbtPlugin, BuildInfoPlugin)
+  .dependsOn(codegen)
   .settings(
     commonSettings,
     name := "twinagle-scalapb-plugin",
     addSbtPlugin("com.thesamet" % "sbt-protoc" % "1.0.7"),
-    libraryDependencies += "com.thesamet.scalapb" %% "compilerplugin" % scalapb.compiler.Version.scalapbVersion,
     buildInfoKeys                                 := Seq[BuildInfoKey](version, scalaBinaryVersion),
-    buildInfoPackage                              := "com.soundcloud.twinagle.codegen",
+    buildInfoPackage                              := "com.soundcloud.twinagle.plugin",
     buildInfoUsePackageAsPath                     := true,
     publishLocal                                  := publishLocal.dependsOn(runtime / publishLocal).value,
     scriptedLaunchOpts ++= Seq("-Xmx1024M", "-Dplugin.version=" + version.value),
@@ -77,7 +86,7 @@ lazy val runtime = (project in file("runtime")).settings(
 )
 
 lazy val root = (project in file("."))
-  .aggregate(runtime, codegen)
+  .aggregate(runtime, codegen, plugin)
   .settings(
     name := "twinagle-root",
     resolvers += Resolver.typesafeIvyRepo("releases"),

codegen/src/main/scala/com/soundcloud/twinagle/codegen/ServerClientCodeGenerator.scala

@@ -4,32 +4,16 @@ import com.google.protobuf.Descriptors._
 import com.google.protobuf.ExtensionRegistry
 import com.google.protobuf.compiler.PluginProtos
 import com.google.protobuf.compiler.PluginProtos.CodeGeneratorResponse
-import protocbridge.Artifact
 import protocgen.{CodeGenApp, CodeGenRequest, CodeGenResponse}
 import scalapb.compiler.{DescriptorImplicits, FunctionalPrinter, ProtobufGenerator}
 
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
-object ServerClientCodeGenerator extends CodeGenApp {
+trait ServerClientCodeGenerator extends CodeGenApp {
   override def registerExtensions(registry: ExtensionRegistry): Unit = {
     scalapb.options.Scalapb.registerAllExtensions(registry)
   }
 
-  override def suggestedDependencies: Seq[protocbridge.Artifact] = Seq(
-    Artifact(
-      "com.soundcloud",
-      "twinagle-runtime",
-      BuildInfo.version,
-      crossVersion = true
-    ),
-    Artifact(
-      "com.thesamet.scalapb",
-      "scalapb-runtime",
-      scalapb.compiler.Version.scalapbVersion,
-      crossVersion = true
-    )
-  )
-
   def process(request: CodeGenRequest): CodeGenResponse =
     ProtobufGenerator.parseParameters(request.parameter) match {
       case Right(params) =>
@@ -54,7 +38,7 @@ object ServerClientCodeGenerator extends CodeGenApp {
       file: FileDescriptor,
       di: DescriptorImplicits
   ): Seq[PluginProtos.CodeGeneratorResponse.File] = {
-    file.getServices.asScala.map { service =>
+    file.getServices.asScala.toSeq.map { service =>
       val p = new TwinagleServicePrinter(service, di)
 
       import di.{ExtendedFileDescriptor, ExtendedServiceDescriptor}
@@ -68,3 +52,5 @@ object ServerClientCodeGenerator extends CodeGenApp {
   }
 
 }
+
+object StandaloneServerClientCodeGenerator extends ServerClientCodeGenerator {}

codegen/README.md plugin/README.md

@@ -0,0 +1,23 @@
+package com.soundcloud.twinagle.plugin
+
+import com.soundcloud.twinagle.codegen.ServerClientCodeGenerator
+import protocbridge.Artifact
+
+object SbtServerClientCodeGenerator extends ServerClientCodeGenerator {
+
+  override def suggestedDependencies: Seq[Artifact] = Seq(
+    Artifact(
+      "com.soundcloud",
+      "twinagle-runtime",
+      BuildInfo.version,
+      crossVersion = true
+    ),
+    Artifact(
+      "com.thesamet.scalapb",
+      "scalapb-runtime",
+      scalapb.compiler.Version.scalapbVersion,
+      crossVersion = true
+    )
+  )
+
+}

plugin/src/main/scala/com/soundcloud/twinagle/plugin/SbtServerClientCodeGenerator.scala

@@ -1,4 +1,4 @@
-package com.soundcloud.twinagle.codegen
+package com.soundcloud.twinagle.plugin
 
 import protocbridge.{JvmGenerator, Target}
 import sbt._
@@ -33,7 +33,7 @@ object Twinagle extends AutoPlugin {
         (Compile / sourceManaged).value / "twinagle-protobuf"
       ),
       Target(
-        JvmGenerator("scala-twinagle", ServerClientCodeGenerator),
+        JvmGenerator("scala-twinagle", SbtServerClientCodeGenerator),
         (Compile / sourceManaged).value / "twinagle-services",
         scalapb.gen(scalapbCodeGeneratorOptions.value)._2
       )