Kotlin Facet: Configure facet automatically on Maven project import

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.config
 
 import com.intellij.openapi.module.Module
+import com.intellij.util.text.VersionComparatorUtil
 import org.jetbrains.kotlin.config.LanguageVersion.KOTLIN_1_1
 import org.jetbrains.kotlin.utils.DescriptionAware
 
@@ -59,6 +60,9 @@ enum class LanguageVersion(val versionString: String) : DescriptionAware {
         @JvmStatic
         fun fromVersionString(str: String) = values().find { it.versionString == str }
 
+        @JvmStatic
+        fun fromFullVersionString(str: String) = str.split(".", "-").let { if (it.size >= 2) fromVersionString("${it[0]}.${it[1]}") else null }
+
         @JvmField
         val LATEST = values().last()
     }

idea/idea-maven/src/org/jetbrains/kotlin/idea/maven/KotlinMavenImporter.kt

@@ -33,6 +33,12 @@ import org.jetbrains.idea.maven.model.MavenPlugin
 import org.jetbrains.idea.maven.project.*
 import org.jetbrains.jps.model.java.JavaSourceRootType
 import org.jetbrains.jps.model.module.JpsModuleSourceRootType
+import org.jetbrains.kotlin.config.LanguageVersion
+import org.jetbrains.kotlin.config.TargetPlatformKind
+import org.jetbrains.kotlin.idea.facet.getOrCreateFacet
+import org.jetbrains.kotlin.idea.facet.initializeIfNeeded
+import org.jetbrains.kotlin.idea.facet.mavenLibraryId
+import org.jetbrains.kotlin.idea.maven.configuration.KotlinMavenConfigurator
 import java.io.File
 import java.util.*
 
@@ -79,6 +85,27 @@ class KotlinMavenImporter : MavenImporter(KotlinPluginGroupId, KotlinPluginArtif
                 MavenProjectsManager.getInstance(module.project).scheduleArtifactsDownloading(listOf(mavenProject), toBeDownloaded, true, false, AsyncResult())
             }
         }
+
+        configureFacet(mavenProject, modifiableModelsProvider, module)
+    }
+
+    private fun configureFacet(mavenProject: MavenProject, modifiableModelsProvider: IdeModifiableModelsProvider, module: Module) {
+        val compilerVersion = mavenProject.findPlugin(KotlinMavenConfigurator.GROUP_ID, KotlinMavenConfigurator.MAVEN_PLUGIN_ID)?.version ?: return
+        val artifacts = mavenProject.dependencyArtifactIndex.data[KotlinPluginGroupId]?.values?.flatMap { it.filter { it.isResolved } }
+        val expectedLibraryIds = TargetPlatformKind.ALL_PLATFORMS.map { it.mavenLibraryId }
+        val stdlibArtifact = artifacts?.firstOrNull { it.artifactId in expectedLibraryIds }
+
+        val facet = module.getOrCreateFacet(modifiableModelsProvider)
+        with(facet.configuration.settings.versionInfo) {
+            targetPlatformKind = null
+            apiLevel = null
+            facet.configuration.settings.initializeIfNeeded(module, modifiableModelsProvider.getModifiableRootModel(module))
+            languageLevel = LanguageVersion.fromFullVersionString(compilerVersion)
+            // Both apiLevel and languageLevel should be initialized in the lines above
+            if (apiLevel!! > languageLevel!!) {
+                apiLevel = languageLevel
+            }
+        }
     }
 
     // TODO in theory it should work like this but it doesn't as it couldn't unmark source roots that are not roots anymore.

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

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.idea.facet
 
+import com.intellij.openapi.externalSystem.service.project.IdeModifiableModelsProvider
 import com.intellij.openapi.module.Module
 import com.intellij.openapi.projectRoots.JavaSdk
 import com.intellij.openapi.projectRoots.JavaSdkVersion
@@ -98,7 +99,7 @@ internal fun getLibraryLanguageLevel(
     return getDefaultLanguageLevel(module, minVersion)
 }
 
-internal fun KotlinFacetSettings.initializeIfNeeded(module: Module, rootModel: ModuleRootModel?) {
+fun KotlinFacetSettings.initializeIfNeeded(module: Module, rootModel: ModuleRootModel?) {
     val project = module.project
 
     with(versionInfo) {
@@ -135,3 +136,13 @@ val TargetPlatformKind<*>.mavenLibraryId: String
         is TargetPlatformKind.Jvm -> MAVEN_STDLIB_ID
         is TargetPlatformKind.JavaScript -> MAVEN_JS_STDLIB_ID
     }
+
+fun Module.getOrCreateFacet(modelsProvider: IdeModifiableModelsProvider): KotlinFacet {
+    val facetModel = modelsProvider.getModifiableFacetModel(this)
+
+    facetModel.findFacet(KotlinFacetType.TYPE_ID, KotlinFacetType.INSTANCE.defaultFacetName)?.let { return it }
+
+    val facet = with(KotlinFacetType.INSTANCE) { createFacet(this@getOrCreateFacet, defaultFacetName, createDefaultConfiguration(), null) }
+    facetModel.addFacet(facet)
+    return facet
+}