Move conditional task caching setup into the task constructors;

Add 'kotlin.caching.enabled' flag to switch the caching for all tasks;
Rename and change semantics of cache support checks: make two instead
    of one, `isBuildCacheSupported` and `isBuildCacheEnabledForKotlin`;
Remove FileOptionKind entries that are redundant at the moment;
Improvements in BuildCacheIT.kt and other refactoring  suggestions from
    the review
    https://upsource.jetbrains.com/kotlin/review/KOTLIN-CR-1647

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/BuildCacheIT.kt

@@ -16,12 +16,9 @@
 
 package org.jetbrains.kotlin.gradle
 
-import org.jetbrains.kotlin.gradle.util.checkBytecodeContains
 import org.jetbrains.kotlin.gradle.util.modify
 import org.junit.Test
 import java.io.File
-import java.nio.file.Files
-import kotlin.test.assertEquals
 
 class BuildCacheIT : BaseGradleIT() {
     override fun defaultBuildOptions(): BuildOptions =
@@ -32,7 +29,7 @@ class BuildCacheIT : BaseGradleIT() {
     }
 
     @Test
-    fun noCacheWithGradlePre43() = with(Project("simpleProject", "4.2")) {
+    fun testNoCacheWithGradlePre43() = with(Project("simpleProject", "4.2")) {
         // Check that even with the build cache enabled, the Kotlin tasks are not cacheable with Gradle < 4.3:
         val optionsWithCache = defaultBuildOptions().copy(withBuildCache = true)
 
@@ -47,6 +44,21 @@ class BuildCacheIT : BaseGradleIT() {
         }
     }
 
+    @Test
+    fun testKotlinCachingEnabledFlag() = with(Project("simpleProject", GRADLE_VERSION)) {
+        prepareLocalBuildCache()
+
+        build("assemble") {
+            assertSuccessful()
+            assertContains("Packing task ':compileKotlin'")
+        }
+
+        build("clean", "assemble", "-Dkotlin.caching.enabled=false") {
+            assertSuccessful()
+            assertNotContains(":compileKotlin FROM-CACHE")
+        }
+    }
+
     @Test
     fun testCacheHitAfterClean() = with(Project("simpleProject", GRADLE_VERSION)) {
         prepareLocalBuildCache()
@@ -99,20 +111,9 @@ class BuildCacheIT : BaseGradleIT() {
     }
 
     @Test
-    fun testCorrectBuildAfterCacheHit() = with(Project("simpleProject", GRADLE_VERSION)) {
+    fun testCorrectBuildAfterCacheHit() = with(Project("buildCacheSimple", GRADLE_VERSION)) {
         prepareLocalBuildCache()
 
-        val fooKt = File(projectDir, "src/main/kotlin/foo/foo.kt").apply {
-            parentFile.mkdirs()
-            writeText("package foo; fun foo(i: Int): Int = 1")
-        }
-
-        // bar.kt references foo.kt; we expect it to recompile during the first build after a cache hit.
-        File(projectDir, "src/main/kotlin/bar/bar.kt").apply {
-            parentFile.mkdirs()
-            writeText("package bar; import foo.*; fun bar() = foo(1)")
-        }
-
         // First build, should be stored into the build cache:
         build("assemble") {
             assertSuccessful()
@@ -125,13 +126,11 @@ class BuildCacheIT : BaseGradleIT() {
             assertContains(":compileKotlin FROM-CACHE")
         }
 
-        // Change the return type Int to String, so that bar.kt should be recompiled, and check that:
-        fooKt.modify { it.replace("Int = 1", "String = \"abc\"") }
+        // Change the return type of foo() from Int to String in foo.kt, and check that fooUsage.kt is recompiled as well:
+        File(projectDir, "src/main/kotlin/foo.kt").modify { it.replace("Int = 1", "String = \"abc\"") }
         build("assemble") {
             assertSuccessful()
-            checkBytecodeContains(
-                    File(projectDir, "build/classes/kotlin/main/bar/BarKt.class"),
-                    "INVOKESTATIC foo/FooKt.foo (I)Ljava/lang/String;")
+            assertCompiledKotlinSources(relativize(allKotlinFiles))
         }
     }
 
@@ -166,7 +165,7 @@ class BuildCacheIT : BaseGradleIT() {
     }
 }
 
-fun BaseGradleIT.Project.prepareLocalBuildCache(directory: File = Files.createTempDirectory("GradleTestBuildCache").toFile()): File {
+fun BaseGradleIT.Project.prepareLocalBuildCache(directory: File = File(projectDir.parentFile, "buildCache").apply { mkdir() }): File {
     if (!projectDir.exists()) {
         setupWorkingDir()
     }

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/buildCacheSimple/build.gradle

@@ -0,0 +1,21 @@
+buildscript {
+    repositories {
+        mavenLocal()
+        mavenCentral()
+    }
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
+apply plugin: "kotlin"
+apply plugin: 'java'
+
+repositories {
+    mavenLocal()
+    mavenCentral()
+}
+
+dependencies {
+    compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/buildCacheSimple/src/main/kotlin/foo.kt

@@ -0,0 +1,3 @@
+package foo
+
+fun foo(i: Int): Int = 1

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/buildCacheSimple/src/main/kotlin/fooUsage.kt

@@ -0,0 +1,5 @@
+package bar
+
+import foo.*
+
+fun bar() = foo(1)