Support external trait providers

Author: kubukoz

sbtPlugin/src/main/scala/org/polyvariant/smithytraitcodegen/SmithyTraitCodegen.scala

@@ -38,12 +38,13 @@ object SmithyTraitCodegen {
     targetDir: os.Path,
     smithySourcesDir: PathRef,
     dependencies: List[PathRef],
+    externalProviders: List[String],
   )
 
   object Args {
 
     // format: off
-    private type ArgsDeconstructed = String :*: String :*: os.Path :*: PathRef :*: List[PathRef] :*: LNil
+    private type ArgsDeconstructed = String :*: String :*: os.Path :*: PathRef :*: List[PathRef] :*: List[String] :*: LNil
     // format: on
 
     private implicit val pathFormat: JsonFormat[os.Path] = BasicJsonProtocol
@@ -56,6 +57,7 @@ object SmithyTraitCodegen {
           ("targetDir", args.targetDir) :*:
           ("smithySourcesDir", args.smithySourcesDir) :*:
           ("dependencies", args.dependencies) :*:
+          ("externalProviders", args.externalProviders) :*:
           LNil
       },
       {
@@ -64,13 +66,15 @@ object SmithyTraitCodegen {
             (_, targetDir) :*:
             (_, smithySourcesDir) :*:
             (_, dependencies) :*:
+            (_, externalProviders) :*:
             LNil =>
           Args(
             javaPackage = javaPackage,
             smithyNamespace = smithyNamespace,
             targetDir = targetDir,
             smithySourcesDir = smithySourcesDir,
             dependencies = dependencies,
+            externalProviders = externalProviders,
           )
       },
     )
@@ -141,6 +145,15 @@ object SmithyTraitCodegen {
     if (os.exists(genDir / "META-INF"))
       os.move(genDir / "META-INF", metaDir / "META-INF")
 
+    os
+      .walk(metaDir, includeTarget = true)
+      .filter(os.isFile)
+      .foreach { p =>
+        if (p.toIO.name == "software.amazon.smithy.model.traits.TraitService") {
+          args.externalProviders.foreach(provider => os.write.append(p, provider))
+        }
+      }
+
     Output(metaDir = metaDir.toIO, javaDir = genDir.toIO)
   }
 

sbtPlugin/src/main/scala/org/polyvariant/smithytraitcodegen/SmithyTraitCodegenPlugin.scala

@@ -47,13 +47,18 @@ object SmithyTraitCodegenPlugin extends AutoPlugin {
       "The directory where the generated Java sources and resources will be placed"
     )
 
+    val smithyTraitCodegenExternalProviders = settingKey[List[String]](
+      "External trait provideres"
+    )
+
   }
 
   import autoImport.*
 
   override def projectSettings: Seq[Setting[?]] = Seq(
     smithyTraitCodegenSourceDirectory := (Compile / resourceDirectory).value / "META-INF" / "smithy",
     smithyTraitCodegenTargetDirectory := (Compile / target).value,
+    smithyTraitCodegenExternalProviders := Nil,
     Keys.generateSmithyTraits := Def.task {
       import sbt.util.CacheImplicits.*
       val s = (Compile / streams).value
@@ -77,6 +82,7 @@ object SmithyTraitCodegenPlugin extends AutoPlugin {
         targetDir = os.Path(smithyTraitCodegenTargetDirectory.value),
         smithySourcesDir = PathRef(smithyTraitCodegenSourceDirectory.value),
         dependencies = jars.map(PathRef(_)).toList,
+        externalProviders = smithyTraitCodegenExternalProviders.value,
       )
       val cachedCodegen =
         Tracked.inputChanged[SmithyTraitCodegen.Args, SmithyTraitCodegen.Output](