[Gradle, JS] Non-nullable properties in KotlinWebpack with delegate

#KT-37582 fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/KotlinBrowserJsIr.kt

@@ -169,7 +169,7 @@ open class KotlinBrowserJsIr @Inject constructor(target: KotlinJsIrTarget) :
                     compilation.developmentLinkTask.map { it.outputFile }
                 ).get()
                 it.description = "build webpack ${kind.name.toLowerCase()} bundle"
-                it.destinationDirectory = distribution.directory
+                it._destinationDirectory = distribution.directory
 
                 commonWebpackConfigurations.forEach { configure ->
                     it.configure()

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/subtargets/KotlinBrowserJs.kt

@@ -195,7 +195,7 @@ open class KotlinBrowserJs @Inject constructor(target: KotlinJsTarget) :
 
                 it.compilation = compilation
                 it.description = "build webpack ${kind.name.toLowerCase()} bundle"
-                it.destinationDirectory = distribution.directory
+                it._destinationDirectory = distribution.directory
 
                 when (kind) {
                     BuildVariantKind.PRODUCTION -> {

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpack.kt

@@ -23,6 +23,8 @@ import org.jetbrains.kotlin.gradle.targets.js.npm.npmProject
 import org.jetbrains.kotlin.gradle.targets.js.webpack.KotlinWebpackConfig.Mode
 import org.jetbrains.kotlin.gradle.testing.internal.reportsDir
 import org.jetbrains.kotlin.gradle.utils.injected
+import org.jetbrains.kotlin.gradle.utils.property
+import org.jetbrains.kotlin.gradle.utils.provider
 import java.io.File
 import javax.inject.Inject
 
@@ -51,14 +53,17 @@ open class KotlinWebpack : DefaultTask(), RequiresNpmDependencies {
     @Input
     var mode: Mode = Mode.DEVELOPMENT
 
+    private var _entry: File? = null
+
     @get:PathSensitive(PathSensitivity.ABSOLUTE)
     @get:InputFile
-    var entry: File? = null
-        get() = field ?: compilation.compileKotlinTask.outputFile
+    var entry: File by property(::_entry) {
+        compilation.compileKotlinTask.outputFile
+    }
 
     init {
         onlyIf {
-            entry!!.exists()
+            entry.exists()
         }
     }
 
@@ -84,22 +89,29 @@ open class KotlinWebpack : DefaultTask(), RequiresNpmDependencies {
     @get:Internal
     @Deprecated("use destinationDirectory instead", ReplaceWith("destinationDirectory"))
     val outputPath: File
-        get() = destinationDirectory!!
+        get() = destinationDirectory
 
     private val baseConventions: BasePluginConvention?
         get() = project.convention.plugins["base"] as BasePluginConvention?
 
     @get:Internal
-    var destinationDirectory: File? = null
-        get() = field ?: project.buildDir.resolve(baseConventions!!.distsDirName)
+    internal var _destinationDirectory: File? = null
 
     @get:Internal
-    var outputFileName: String? = null
-        get() = field ?: (baseConventions?.archivesBaseName + ".js")
+    val destinationDirectory: File by provider(::_destinationDirectory) {
+        project.buildDir.resolve(baseConventions!!.distsDirName)
+    }
+
+    private var _outputFileName: String? = null
+
+    @get:Internal
+    var outputFileName: String by property(::_outputFileName) {
+        baseConventions?.archivesBaseName + ".js"
+    }
 
     @get:OutputFile
     open val outputFile: File
-        get() = destinationDirectory!!.resolve(outputFileName!!)
+        get() = destinationDirectory.resolve(outputFileName)
 
     open val configDirectory: File?
         @Optional @InputDirectory get() = project.projectDir.resolve("webpack.config.d").takeIf { it.isDirectory }
@@ -108,7 +120,7 @@ open class KotlinWebpack : DefaultTask(), RequiresNpmDependencies {
     var report: Boolean = false
 
     open val reportDir: File
-        @OutputDirectory get() = project.reportsDir.resolve("webpack").resolve(entry!!.nameWithoutExtension)
+        @OutputDirectory get() = project.reportsDir.resolve("webpack").resolve(entry.nameWithoutExtension)
 
     open val evaluatedConfigFile: File
         @OutputFile get() = reportDir.resolve("webpack.config.evaluated.js")

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

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.utils
+
+import kotlin.reflect.KMutableProperty
+import kotlin.reflect.KProperty
+
+open class ProviderDelegate<out T : Any>(
+    protected open val backing: KProperty<T?>,
+    private val defaultValueProvider: () -> T
+) {
+    operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
+        return backing.getter.call() ?: defaultValueProvider()
+    }
+}
+
+class PropertyDelegate<T : Any>(
+    override val backing: KMutableProperty<T?>,
+    defaultValueProvider: () -> T
+) : ProviderDelegate<T>(backing, defaultValueProvider) {
+    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
+        backing.setter.call(value)
+    }
+}
+
+fun <T : Any> provider(
+    backing: KProperty<T?>,
+    defaultValueProvider: () -> T
+): ProviderDelegate<T> = ProviderDelegate(backing, defaultValueProvider)
+
+fun <T : Any> property(
+    backing: KMutableProperty<T?>,
+    defaultValueProvider: () -> T
+): PropertyDelegate<T> = PropertyDelegate(backing, defaultValueProvider)