FIR IDE: add type parameters support to completion

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/HighLevelApiLookupElementFactory.kt

@@ -28,12 +28,14 @@ internal class HighLevelApiLookupElementFactory {
     private val classLookupElementFactory = ClassLookupElementFactory()
     private val variableLookupElementFactory = VariableLookupElementFactory()
     private val functionLookupElementFactory = FunctionLookupElementFactory()
+    private val typeParameterLookupElementFactory = TypeParameterLookupElementFactory()
 
     fun createLookupElement(symbol: KtNamedSymbol): LookupElement {
         val elementBuilder = when (symbol) {
             is KtFunctionSymbol -> functionLookupElementFactory.createLookup(symbol)
             is KtVariableLikeSymbol -> variableLookupElementFactory.createLookup(symbol)
             is KtClassLikeSymbol -> classLookupElementFactory.createLookup(symbol)
+            is KtTypeParameterSymbol -> typeParameterLookupElementFactory.createLookup(symbol)
             else -> throw IllegalArgumentException("Cannot create a lookup element for $symbol")
         }
 
@@ -54,6 +56,12 @@ private class ClassLookupElementFactory {
     }
 }
 
+private class TypeParameterLookupElementFactory {
+    fun createLookup(symbol: KtTypeParameterSymbol): LookupElementBuilder {
+        return LookupElementBuilder.create(UniqueLookupObject(), symbol.name.asString())
+    }
+}
+
 private class VariableLookupElementFactory {
     fun createLookup(symbol: KtVariableLikeSymbol): LookupElementBuilder {
         return LookupElementBuilder.create(UniqueLookupObject(), symbol.name.asString())

idea/idea-fir/src/org/jetbrains/kotlin/idea/completion/KotlinFirCompletionContributor.kt

@@ -136,7 +136,7 @@ private object KotlinAvailableScopesCompletionContributor {
 
                 extensionNonMembers.forEach(::addToCompletion)
 
-                val availableClasses = implicitScopes.getClassClassLikeSymbols()
+                val availableClasses = implicitScopes.getClassifierSymbols()
                 availableClasses.forEach(::addToCompletion)
             }
         }