Support gradle incremental processing in code gen (#824)

* Support gradle incremental processing in code gen

This adds support for incremental compilation in gradle via incap helper and marking the code gen as `ISOLATING`.

Depends on a newer version of KotlinPoet that has https://github.com/square/kotlinpoet/pull/647

Resolves #589

* Opportunistically update to auto-service 1.0-rc5

Supports incremental compilation and moves annotations to a separate artifact

* 1.2.0 final!

* Mark compiler embeddales as test only

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/AdapterGenerator.kt

@@ -52,6 +52,7 @@ internal class AdapterGenerator(
 
   private val nameAllocator = NameAllocator()
   private val adapterName = "${className.simpleNames.joinToString(separator = "_")}JsonAdapter"
+  private val originalElement = target.element
   private val originalTypeName = target.element.asType().asTypeName()
 
   private val moshiParam = ParameterSpec.builder(
@@ -97,6 +98,7 @@ internal class AdapterGenerator(
 
   private fun generateType(generatedOption: TypeElement?): TypeSpec {
     val result = TypeSpec.classBuilder(adapterName)
+        .addOriginatingElement(originalElement)
 
     generatedOption?.let {
       result.addAnnotation(AnnotationSpec.builder(it.asClassName())

kotlin/codegen/src/main/java/com/squareup/moshi/kotlin/codegen/JsonClassCodegenProcessor.kt

@@ -16,12 +16,12 @@
 package com.squareup.moshi.kotlin.codegen
 
 import com.google.auto.service.AutoService
-import com.squareup.kotlinpoet.TypeSpec
 import com.squareup.moshi.JsonClass
 import me.eugeniomarletti.kotlin.metadata.KotlinMetadataUtils
 import me.eugeniomarletti.kotlin.metadata.declaresDefaultValue
 import me.eugeniomarletti.kotlin.processing.KotlinAbstractProcessor
-import java.io.File
+import net.ltgt.gradle.incap.IncrementalAnnotationProcessor
+import net.ltgt.gradle.incap.IncrementalAnnotationProcessorType.ISOLATING
 import javax.annotation.processing.ProcessingEnvironment
 import javax.annotation.processing.Processor
 import javax.annotation.processing.RoundEnvironment
@@ -42,6 +42,7 @@ import javax.tools.Diagnostic.Kind.ERROR
  * If you don't want this though, you can use the runtime [JsonClass] factory implementation.
  */
 @AutoService(Processor::class)
+@IncrementalAnnotationProcessor(ISOLATING)
 class JsonClassCodegenProcessor : KotlinAbstractProcessor(), KotlinMetadataUtils {
 
   companion object {
@@ -86,7 +87,8 @@ class JsonClassCodegenProcessor : KotlinAbstractProcessor(), KotlinMetadataUtils
       val jsonClass = type.getAnnotation(annotation)
       if (jsonClass.generateAdapter) {
         val generator = adapterGenerator(type) ?: continue
-        generator.generateAndWrite(generatedType)
+        generator.generateFile(generatedType)
+            .writeTo(filer)
       }
     }
 
@@ -123,18 +125,4 @@ class JsonClassCodegenProcessor : KotlinAbstractProcessor(), KotlinMetadataUtils
 
     return AdapterGenerator(type, sortedProperties)
   }
-
-  private fun AdapterGenerator.generateAndWrite(generatedOption: TypeElement?) {
-    val fileSpec = generateFile(generatedOption)
-    val adapterName = fileSpec.members.filterIsInstance<TypeSpec>().first().name!!
-    val outputDir = generatedDir ?: mavenGeneratedDir(adapterName)
-    fileSpec.writeTo(outputDir)
-  }
-
-  private fun mavenGeneratedDir(adapterName: String): File {
-    // Hack since the maven plugin doesn't supply `kapt.kotlin.generated` option
-    // Bug filed at https://youtrack.jetbrains.com/issue/KT-22783
-    val file = filer.createSourceFile(adapterName).toUri().let(::File)
-    return file.parentFile.also { file.delete() }
-  }
 }