Kapt: support incremental compilation in Gradle (KT-13500)

Kapt will process sources on each step of incremental compilation.
(cherry picked from commit 4cb2127)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/Kapt2KotlinGradleSubplugin.kt

@@ -78,19 +78,24 @@ class Kapt2KotlinGradleSubplugin : KotlinGradleSubplugin {
                 kaptClasspath.addAll(kapt2Configuration.resolve())
             }
         }
-
-        val generatedFilesDir = if (variantData != null) {
+        
+        val sourceSetName = if (variantData != null) {
             for (provider in (variantData as BaseVariantData<*>).sourceProviders) {
                 handleSourceSet((provider as AndroidSourceSet).name)
             }
 
-            getKaptGeneratedDir(project, variantData.name).apply { variantData.addJavaSourceFoldersToModel(this) }
+            variantData.name
         }
         else {
             if (javaSourceSet == null) error("Java source set should not be null")
 
             handleSourceSet(javaSourceSet.name)
-            getKaptGeneratedDir(project, javaSourceSet.name)
+            javaSourceSet.name
+        }
+
+        val generatedFilesDir = getKaptGeneratedDir(project, sourceSetName)
+        if (variantData != null) {
+            (variantData as BaseVariantData<*>).addJavaSourceFoldersToModel(generatedFilesDir)
         }
 
         // Skip annotation processing in kotlinc if no kapt dependencies were provided
@@ -117,6 +122,9 @@ class Kapt2KotlinGradleSubplugin : KotlinGradleSubplugin {
             pluginOptions += SubpluginOption("verbose", "true")
         }
         
+        val incrementalCompilationDataFile = File(project.buildDir, "tmp/kapt2/$sourceSetName/incrementalData.txt")
+        pluginOptions += SubpluginOption("incrementalData", incrementalCompilationDataFile.absolutePath)
+        
         return pluginOptions
     }
 

libraries/tools/kotlin-gradle-plugin/src/test/kotlin/org/jetbrains/kotlin/gradle/Kapt2IT.kt

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.gradle
 
+import org.jetbrains.kotlin.gradle.util.getFileByName
 import org.junit.Test
 import java.io.File
 import java.io.FileFilter
@@ -63,6 +64,31 @@ class Kapt2IT: BaseGradleIT() {
         }
     }
 
+    @Test
+    fun testSimpleWithIC() {
+        val options = defaultBuildOptions().copy(incremental = true)
+        val project = Project("simple", GRADLE_VERSION, directoryPrefix = "kapt2")
+
+        project.build("build", options = options) {
+            assertSuccessful()
+            assertKaptSuccessful()
+            assertContains(":compileKotlin")
+            assertContains(":compileJava")
+        }
+
+        val files = listOf("InternalDummy.kt", "test.kt")
+        kotlin.repeat(2) { i ->
+            project.projectDir.getFileByName(files[i]).appendText(" ")
+
+            project.build("build", options = options) {
+                assertSuccessful()
+                assertKaptSuccessful()
+                assertContains(":compileKotlin")
+                assertContains(":compileJava")
+            }
+        }
+    }
+
     @Test
     fun testInheritedAnnotations() {
         Project("inheritedAnnotations", GRADLE_VERSION, directoryPrefix = "kapt2").build("build") {