Minor. Extract KtElement::isMainFunction in the IDE context

idea/src/org/jetbrains/kotlin/idea/highlighter/KotlinRunLineMarkerContributor.kt

@@ -20,10 +20,8 @@ import com.intellij.execution.lineMarker.ExecutorAction
 import com.intellij.execution.lineMarker.RunLineMarkerContributor
 import com.intellij.icons.AllIcons
 import com.intellij.psi.PsiElement
-import org.jetbrains.kotlin.idea.MainFunctionDetector
-import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
+import org.jetbrains.kotlin.idea.isMainFunction
 import org.jetbrains.kotlin.idea.platform.tooling
-import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.project.platform
 import org.jetbrains.kotlin.idea.util.module
 import org.jetbrains.kotlin.psi.KtNamedFunction
@@ -34,11 +32,7 @@ class KotlinRunLineMarkerContributor : RunLineMarkerContributor() {
 
         if (function.nameIdentifier != element) return null
 
-        val detector = MainFunctionDetector(function.languageVersionSettings) { someFunction ->
-            someFunction.resolveToDescriptorIfAny()
-        }
-
-        if (detector.isMain(function)) {
+        if (function.isMainFunction()) {
             val platform = function.containingKtFile.module?.platform ?: return null
             if (!platform.kind.tooling.acceptsAsEntryPoint(function)) return null
 

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedReceiverParameterInspection.kt

@@ -25,11 +25,10 @@ import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor
 import org.jetbrains.kotlin.idea.KotlinBundle
-import org.jetbrains.kotlin.idea.MainFunctionDetector
 import org.jetbrains.kotlin.idea.caches.resolve.analyzeWithContent
 import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
 import org.jetbrains.kotlin.idea.core.isOverridable
-import org.jetbrains.kotlin.idea.project.languageVersionSettings
+import org.jetbrains.kotlin.idea.isMainFunction
 import org.jetbrains.kotlin.idea.refactoring.changeSignature.KotlinChangeSignatureConfiguration
 import org.jetbrains.kotlin.idea.refactoring.changeSignature.KotlinMethodDescriptor
 import org.jetbrains.kotlin.idea.refactoring.changeSignature.modify
@@ -78,9 +77,7 @@ class UnusedReceiverParameterInspection : AbstractKotlinInspection() {
 
                 val callable = callableDeclaration.descriptor ?: return
 
-                val mainFunctionDetector =
-                    MainFunctionDetector(callableDeclaration.languageVersionSettings) { it.resolveToDescriptorIfAny() }
-                if (mainFunctionDetector.isMain(callable)) return
+                if (callableDeclaration.isMainFunction(callable)) return
 
                 val containingDeclaration = callable.containingDeclaration
                 if (containingDeclaration != null && containingDeclaration == receiverTypeDeclaration) {

idea/src/org/jetbrains/kotlin/idea/mainDetectorUtil.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea
+
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
+import org.jetbrains.kotlin.idea.project.languageVersionSettings
+import org.jetbrains.kotlin.psi.KtElement
+import org.jetbrains.kotlin.psi.KtNamedFunction
+
+fun KtElement.isMainFunction(computedDescriptor: DeclarationDescriptor? = null): Boolean {
+    if (this !is KtNamedFunction) return false
+    val mainFunctionDetector = MainFunctionDetector(languageVersionSettings) { it.resolveToDescriptorIfAny() }
+
+    if (computedDescriptor != null) return mainFunctionDetector.isMain(computedDescriptor)
+
+    return mainFunctionDetector.isMain(this)
+}