Avoid iterating jar inputs in inspectClassesForKotlinIC task

Jar's inputs can contain zipTrees in case of fat jars,
which can cause slow build
(Gradle unpacks them into temporary dir; that can be slow)

    #KT-24956 fixed

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

@@ -387,6 +387,7 @@ internal abstract class AbstractKotlinPlugin(
             return
         }
         val inspectTask = project.tasks.create("inspectClassesForKotlinIC", InspectClassesForMultiModuleIC::class.java)
+        inspectTask.sourceSetName = SourceSet.MAIN_SOURCE_SET_NAME
         inspectTask.jarTask = jarTask
         inspectTask.dependsOn(classesTask)
         jarTask.dependsOn(inspectTask)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/tasks/InspectClassesForMultiModuleIC.kt

@@ -7,9 +7,9 @@ package org.jetbrains.kotlin.gradle.tasks
 
 import org.gradle.api.DefaultTask
 import org.gradle.api.file.FileCollection
+import org.gradle.api.plugins.JavaPluginConvention
 import org.gradle.api.tasks.*
 import org.gradle.jvm.tasks.Jar
-import org.jetbrains.kotlin.gradle.utils.inputsCompatible
 import org.jetbrains.kotlin.gradle.utils.isClassFile
 import java.io.File
 
@@ -17,6 +17,9 @@ internal open class InspectClassesForMultiModuleIC : DefaultTask() {
     @get:Internal
     lateinit var jarTask: Jar
 
+    @get:Input
+    lateinit var sourceSetName: String
+
     @Suppress("MemberVisibilityCanBePrivate")
     @get:OutputFile
     internal val classesListFile: File
@@ -25,7 +28,9 @@ internal open class InspectClassesForMultiModuleIC : DefaultTask() {
     @Suppress("MemberVisibilityCanBePrivate")
     @get:InputFiles
     internal val classFiles: FileCollection
-        get() = jarTask.inputsCompatible.files.filter { it.isClassFile() }
+        get() = project.convention.findPlugin(JavaPluginConvention::class.java)?.let {
+            it.sourceSets.findByName(sourceSetName)?.output?.asFileTree?.filter { it.isClassFile() }
+        } ?: project.files()
 
     @get:Input
     internal val archivePath: String
@@ -34,8 +39,7 @@ internal open class InspectClassesForMultiModuleIC : DefaultTask() {
     @TaskAction
     fun run() {
         classesListFile.parentFile.mkdirs()
-        val paths = classFiles.map { it.canonicalPath }.sorted()
-        val text = paths.joinToString(File.pathSeparator)
+        val text = classFiles.map { it.absolutePath }.sorted().joinToString(File.pathSeparator)
         classesListFile.writeText(text)
     }