Gradle: set default values of languageVersion and apiVersion to null

Before the change, Gradle always explicitly set language and api
version to the latest version, preventing the compiler
from inferencing the arguments.

     #KT-18047 fixed

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/DefaultValues.kt

@@ -29,7 +29,7 @@ open class DefaultValues(val defaultValue: String, val possibleValues: List<Stri
     object StringNullDefault : DefaultValues("null")
 
     object LanguageVersions : DefaultValues(
-            "\"" + LanguageVersion.LATEST_STABLE.versionString + "\"",
+            "null",
             LanguageVersion.values().map { "\"${it.description}\"" }
     )
 

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

@@ -492,4 +492,53 @@ class KotlinGradleIT: BaseGradleIT() {
             assertSuccessful()
         }
     }
+
+    @Test
+    fun testLanguageVersionApiVersionExplicit() {
+        val project = Project("kotlinProject", "3.3")
+        project.setupWorkingDir()
+
+        val buildGradle = File(project.projectDir, "build.gradle")
+        val buildGradleContentCopy = buildGradle.readText()
+
+        fun updateBuildGradle(langVersion: String, apiVersion: String) {
+            buildGradle.writeText(
+                    """
+                $buildGradleContentCopy
+
+                compileKotlin {
+                    kotlinOptions {
+                        languageVersion = '$langVersion'
+                        apiVersion = '$apiVersion'
+                    }
+                }
+            """.trimIndent())
+        }
+
+        assert(buildGradleContentCopy.indexOf("languageVersion") < 0) { "build.gradle should not contain 'languageVersion'" }
+        assert(buildGradleContentCopy.indexOf("apiVersion") < 0) { "build.gradle should not contain 'apiVersion'" }
+
+        // check the arguments are not passed by default (they are inferred by the compiler)
+        project.build("clean", "compileKotlin") {
+            assertSuccessful()
+            assertNotContains("-language-version")
+            assertNotContains("-api-version")
+            assertNoWarnings()
+        }
+
+        // check the arguments are always passed if specified explicitly
+        updateBuildGradle("1.0", "1.0")
+        project.build("clean", "compileKotlin") {
+            assertSuccessful()
+            assertContains("-language-version 1.0")
+            assertContains("-api-version 1.0")
+        }
+
+        updateBuildGradle("1.1", "1.1")
+        project.build("clean", "compileKotlin") {
+            assertSuccessful()
+            assertContains("-language-version 1.1")
+            assertContains("-api-version 1.1")
+        }
+    }
 }

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

@@ -7,16 +7,16 @@ interface KotlinCommonOptions {
     /**
      * Allow to use declarations only from the specified version of bundled libraries
      * Possible values: "1.0", "1.1", "1.2 (EXPERIMENTAL)"
-     * Default value: "1.1"
+     * Default value: null
      */
-     var apiVersion: kotlin.String
+     var apiVersion: kotlin.String?
 
     /**
      * Provide source compatibility with specified language version
      * Possible values: "1.0", "1.1", "1.2 (EXPERIMENTAL)"
-     * Default value: "1.1"
+     * Default value: null
      */
-     var languageVersion: kotlin.String
+     var languageVersion: kotlin.String?
 
     /**
      * Generate no warnings

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

@@ -4,14 +4,14 @@ package org.jetbrains.kotlin.gradle.dsl
 
 internal abstract class KotlinJsOptionsBase : org.jetbrains.kotlin.gradle.dsl.KotlinJsOptions {
 
-    private var apiVersionField: kotlin.String? = null
-    override var apiVersion: kotlin.String
-        get() = apiVersionField ?: "1.1"
+    private var apiVersionField: kotlin.String?? = null
+    override var apiVersion: kotlin.String?
+        get() = apiVersionField ?: null
         set(value) { apiVersionField = value }
 
-    private var languageVersionField: kotlin.String? = null
-    override var languageVersion: kotlin.String
-        get() = languageVersionField ?: "1.1"
+    private var languageVersionField: kotlin.String?? = null
+    override var languageVersion: kotlin.String?
+        get() = languageVersionField ?: null
         set(value) { languageVersionField = value }
 
     private var suppressWarningsField: kotlin.Boolean? = null
@@ -87,8 +87,8 @@ internal abstract class KotlinJsOptionsBase : org.jetbrains.kotlin.gradle.dsl.Ko
 }
 
 internal fun org.jetbrains.kotlin.cli.common.arguments.K2JSCompilerArguments.fillDefaultValues() {
-    apiVersion = "1.1"
-    languageVersion = "1.1"
+    apiVersion = null
+    languageVersion = null
     suppressWarnings = false
     verbose = false
     friendModulesDisabled = false

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

@@ -4,14 +4,14 @@ package org.jetbrains.kotlin.gradle.dsl
 
 internal abstract class KotlinJvmOptionsBase : org.jetbrains.kotlin.gradle.dsl.KotlinJvmOptions {
 
-    private var apiVersionField: kotlin.String? = null
-    override var apiVersion: kotlin.String
-        get() = apiVersionField ?: "1.1"
+    private var apiVersionField: kotlin.String?? = null
+    override var apiVersion: kotlin.String?
+        get() = apiVersionField ?: null
         set(value) { apiVersionField = value }
 
-    private var languageVersionField: kotlin.String? = null
-    override var languageVersion: kotlin.String
-        get() = languageVersionField ?: "1.1"
+    private var languageVersionField: kotlin.String?? = null
+    override var languageVersion: kotlin.String?
+        get() = languageVersionField ?: null
         set(value) { languageVersionField = value }
 
     private var suppressWarningsField: kotlin.Boolean? = null
@@ -75,8 +75,8 @@ internal abstract class KotlinJvmOptionsBase : org.jetbrains.kotlin.gradle.dsl.K
 }
 
 internal fun org.jetbrains.kotlin.cli.common.arguments.K2JVMCompilerArguments.fillDefaultValues() {
-    apiVersion = "1.1"
-    languageVersion = "1.1"
+    apiVersion = null
+    languageVersion = null
     suppressWarnings = false
     verbose = false
     includeRuntime = false