Complete statement for class declaration: add '()' to supertype

#KT-31668 Fixed

idea/src/org/jetbrains/kotlin/idea/editor/fixers/KotlinClassBodyFixer.kt

@@ -19,8 +19,12 @@ package org.jetbrains.kotlin.idea.editor.fixers
 import com.intellij.lang.SmartEnterProcessorWithFixers
 import com.intellij.openapi.editor.Editor
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.idea.caches.resolve.allowResolveInDispatchThread
 import org.jetbrains.kotlin.idea.editor.KotlinSmartEnterHandler
+import org.jetbrains.kotlin.idea.references.mainReference
+import org.jetbrains.kotlin.psi.KtClass
 import org.jetbrains.kotlin.psi.KtClassOrObject
+import org.jetbrains.kotlin.psi.KtSuperTypeCallEntry
 import org.jetbrains.kotlin.psi.psiUtil.endOffset
 import org.jetbrains.kotlin.psi.psiUtil.getPrevSiblingIgnoringWhitespaceAndComments
 
@@ -28,7 +32,7 @@ class KotlinClassBodyFixer : SmartEnterProcessorWithFixers.Fixer<KotlinSmartEnte
     override fun apply(editor: Editor, processor: KotlinSmartEnterHandler, psiElement: PsiElement) {
         if (psiElement !is KtClassOrObject) return
 
-        val body = psiElement.getBody()
+        val body = psiElement.body
         if (!body?.text.isNullOrBlank()) return
 
         var endOffset = psiElement.range.end
@@ -39,6 +43,17 @@ class KotlinClassBodyFixer : SmartEnterProcessorWithFixers.Fixer<KotlinSmartEnte
             }
         }
 
+        val notInitializedSuperType = allowResolveInDispatchThread {
+            psiElement.superTypeListEntries.firstOrNull {
+                if (it is KtSuperTypeCallEntry) return@firstOrNull false
+                (it.typeAsUserType?.referenceExpression?.mainReference?.resolve() as? KtClass)?.isInterface() != true
+            }            
+        }
+        if (notInitializedSuperType != null) {
+            editor.document.insertString(notInitializedSuperType.endOffset, "()")
+            endOffset += 2
+        }
+
         editor.caretModel.moveToOffset(endOffset - 1)
 
         // Insert '\n' to force a multiline body, otherwise there will be an empty body on one line and a caret on the next one.

idea/tests/org/jetbrains/kotlin/idea/codeInsight/smartEnter/SmartEnterTest.kt

@@ -1399,6 +1399,66 @@ class SmartEnterTest : KotlinLightCodeInsightFixtureTestCase() {
             """
     )
 
+    fun testClassBodyHasInitializedSuperType() = doFileTest(
+        """
+            open class A
+            class B : A()<caret>
+        """
+        ,
+        """
+            open class A
+            class B : A() {
+                <caret>
+            }
+        """
+    )
+
+    fun testClassBodyHasNotInitializedSuperType() = doFileTest(
+        """
+            open class A
+            class B : A<caret>
+        """
+        ,
+        """
+            open class A
+            class B : A() {
+                <caret>
+            }
+        """
+    )
+
+    fun testClassBodyHasNotInitializedSuperType2() = doFileTest(
+        """
+            sealed class A(val s: String)
+            class B : A<caret>
+        """
+        ,
+        """
+            sealed class A(val s: String)
+            class B : A() {
+                <caret>
+            }
+        """
+    )
+
+    fun testClassBodyHasNotInitializedSuperType3() = doFileTest(
+        """
+            interface I
+            interface J
+            abstract class A
+            class B : I, A, J<caret>
+        """
+        ,
+        """
+            interface I
+            interface J
+            abstract class A
+            class B : I, A(), J {
+                <caret>
+            }
+        """
+    )
+
     fun testEmptyLine() = doFileTest(
         """fun foo() {}
 <caret>""",