Use of substringBefore/After

idea/src/org/jetbrains/kotlin/idea/completion/CompletionSession.kt

@@ -286,8 +286,7 @@ class BasicCompletionSession(configuration: CompletionSessionConfiguration,
                 addReferenceVariants(kindFilter, runtimeReceiverType = false)
             }
 
-            val ampIndex = prefix.indexOf("@")
-            val keywordsPrefix = if (ampIndex < 0) prefix else prefix.substring(0, ampIndex) // if there is '@' in the prefix - use shorter prefix to not loose 'this' etc
+            val keywordsPrefix = prefix.substringBefore('@') // if there is '@' in the prefix - use shorter prefix to not loose 'this' etc
             KeywordCompletion.complete(expression ?: parameters.getPosition(), keywordsPrefix) { lookupElement ->
                 val keyword = lookupElement.getLookupString()
                 when (keyword) {

idea/src/org/jetbrains/kotlin/idea/completion/LookupElementFactory.kt

@@ -110,8 +110,7 @@ public class LookupElementFactory(
         }
 
         val qualifiedName = psiClass.getQualifiedName()!!
-        val dotIndex = qualifiedName.lastIndexOf('.')
-        val packageName = if (dotIndex <= 0) "<root>" else qualifiedName.substring(0, dotIndex)
+        val packageName = qualifiedName.substringBeforeLast('.', "<root>")
         element = element.appendTailText(" ($packageName)", true)
 
         if (psiClass.isDeprecated()) {