Kotlin Facet: Fix language/API version initialization

#KT-21180 Fixed

idea/idea-gradle/tests/org/jetbrains/kotlin/idea/codeInsight/gradle/GradleFacetImportTest.kt

@@ -29,6 +29,7 @@ import com.intellij.openapi.util.text.StringUtil
 import org.jetbrains.kotlin.cli.common.arguments.K2JSCompilerArguments
 import org.jetbrains.kotlin.cli.common.arguments.K2JVMCompilerArguments
 import org.jetbrains.kotlin.config.*
+import org.jetbrains.kotlin.idea.compiler.configuration.KotlinCommonCompilerArgumentsHolder
 import org.jetbrains.kotlin.idea.configuration.ConfigureKotlinStatus
 import org.jetbrains.kotlin.idea.configuration.ModuleSourceRootMap
 import org.jetbrains.kotlin.idea.configuration.allConfigurators
@@ -1618,6 +1619,43 @@ compileTestKotlin {
         assertAllModulesConfigured()
     }
 
+    @Test
+    fun testIgnoreProjectLanguageAndAPIVersion() {
+        KotlinCommonCompilerArgumentsHolder.getInstance(myProject).update {
+            languageVersion = "1.0"
+            apiVersion = "1.0"
+        }
+
+        createProjectSubFile("build.gradle", """
+            buildscript {
+                repositories {
+                    mavenCentral()
+                    maven {
+                        url 'http://dl.bintray.com/kotlin/kotlin-eap-1.1'
+                    }
+                }
+
+                dependencies {
+                    classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.1.0")
+                }
+            }
+
+            apply plugin: 'kotlin'
+
+            dependencies {
+                compile "org.jetbrains.kotlin:kotlin-stdlib:1.1.0"
+            }
+        """)
+        importProject()
+
+        with (facetSettings) {
+            Assert.assertEquals("1.1", languageLevel!!.versionString)
+            Assert.assertEquals("1.1", apiLevel!!.versionString)
+        }
+
+        assertAllModulesConfigured()
+    }
+
     private fun assertAllModulesConfigured() {
         runReadAction {
             for (moduleGroup in ModuleSourceRootMap(myProject).groupByBaseModules(myProject.allModules())) {

idea/src/org/jetbrains/kotlin/idea/facet/facetUtils.kt

@@ -68,6 +68,9 @@ fun KotlinFacetSettings.initializeIfNeeded(
 ) {
     val project = module.project
 
+    val shouldInferLanguageLevel = languageLevel == null
+    val shouldInferAPILevel = apiLevel == null
+
     if (compilerSettings == null) {
         compilerSettings = KotlinCompilerSettings.getInstance(project).settings
     }
@@ -82,12 +85,12 @@ fun KotlinFacetSettings.initializeIfNeeded(
         }
     }
 
-    if (languageLevel == null) {
+    if (shouldInferLanguageLevel) {
         languageLevel = (if (useProjectSettings) LanguageVersion.fromVersionString(commonArguments.languageVersion) else null)
                         ?: getDefaultLanguageLevel(module, languageVersion)
     }
 
-    if (apiLevel == null) {
+    if (shouldInferAPILevel) {
         apiLevel = if (useProjectSettings) {
             LanguageVersion.fromVersionString(commonArguments.apiVersion) ?: languageLevel
         }