Export filename extension from KotlinScriptDefinition, register...

extensions after loading definitions

compiler/psi/src/org/jetbrains/kotlin/script/KotlinScriptDefinition.kt

@@ -45,6 +45,9 @@ open class KotlinScriptDefinition(open val template: KClass<out Any>) : UserData
     open fun getScriptName(script: KtScript): Name =
         NameUtils.getScriptNameForFile(script.containingKtFile.name)
 
+    open val fileExtension: String
+        get() = "kts"
+
     open val dependencyResolver: DependenciesResolver get() = DependenciesResolver.NoDependencies
 
     open val acceptedAnnotations: List<KClass<out Annotation>> get() = emptyList()

compiler/psi/src/org/jetbrains/kotlin/script/KotlinScriptDefinitionProvider.kt

@@ -34,6 +34,8 @@ interface ScriptDefinitionProvider {
     fun isScript(fileName: String): Boolean
     fun getDefaultScriptDefinition(): KotlinScriptDefinition
 
+    fun getKnownFilenameExtensions(): Sequence<String>
+
     companion object {
         fun getInstance(project: Project): ScriptDefinitionProvider =
             ServiceManager.getService(project, ScriptDefinitionProvider::class.java)
@@ -94,6 +96,10 @@ abstract class LazyScriptDefinitionProvider : ScriptDefinitionProvider {
 
     override fun isScript(fileName: String) = findScriptDefinition(fileName) != null
 
+    override fun getKnownFilenameExtensions(): Sequence<String> = lock.read {
+        cachedDefinitions?.map { it.fileExtension } ?: emptySequence()
+    }
+
     companion object {
         // TODO: find a common place for storing kotlin-related extensions and reuse values from it everywhere
         protected val nonScriptFilenameSuffixes = arrayOf(".${KotlinFileType.EXTENSION}", ".${JavaFileType.DEFAULT_EXTENSION}")