Simplify FirDelegationInInterfaceChecker

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDelegationInInterfaceChecker.kt

@@ -5,13 +5,10 @@
 
 package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 
-import com.intellij.lang.LighterASTNode
-import com.intellij.util.diff.FlyweightCapableTreeStructure
 import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.fir.FirSourceElement
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.fir.analysis.checkers.getChildren
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.FirClass
@@ -23,23 +20,11 @@ object FirDelegationInInterfaceChecker : FirMemberDeclarationChecker() {
             return
         }
 
-        declaration.source?.findSuperTypeDelegation()?.let {
-            reporter.report(declaration.superTypeRefs.getOrNull(it)?.source)
-        }
-    }
-
-    private fun FirSourceElement.findSuperTypeDelegation(): Int =
-        lighterASTNode.findSuperTypeDelegation(treeStructure)
-
-    private fun LighterASTNode.findSuperTypeDelegation(tree: FlyweightCapableTreeStructure<LighterASTNode>): Int {
-        val children = getChildren(tree)
-        return if (children.isNotEmpty()) {
-            children.find { it?.tokenType == KtNodeTypes.SUPER_TYPE_LIST }
-                ?.getChildren(tree)
-                ?.indexOfFirst { it?.tokenType == KtNodeTypes.DELEGATED_SUPER_TYPE_ENTRY }
-                ?: -1
-        } else {
-            -1
+        for (superTypeRef in declaration.superTypeRefs) {
+            val source = superTypeRef.source ?: continue
+            if (source.treeStructure.getParent(source.lighterASTNode)?.tokenType == KtNodeTypes.DELEGATED_SUPER_TYPE_ENTRY) {
+                reporter.report(source)
+            }
         }
     }