Report warning on unused entities that can be renamed to _

Currently it's all about lambda parameters/destructuring entries

 #KT-14347 In Progress

compiler/frontend/src/org/jetbrains/kotlin/cfg/ControlFlowInformationProvider.kt

@@ -578,6 +578,7 @@ class ControlFlowInformationProvider private constructor(
                         }
                         else if (element is KtParameter) {
                             val owner = element.parent?.parent
+                            if (element.isSingleUnderscore) return@traverse
                             when (owner) {
                                 is KtPrimaryConstructor -> if (!element.hasValOrVar()) {
                                     val containingClass = owner.getContainingClassOrObject()
@@ -590,7 +591,6 @@ class ControlFlowInformationProvider private constructor(
                                 is KtFunction -> {
                                     val mainFunctionDetector = MainFunctionDetector(trace.bindingContext)
                                     val isMain = owner is KtNamedFunction && mainFunctionDetector.isMain(owner)
-                                    if (owner is KtFunctionLiteral) return@traverse
                                     val functionDescriptor =
                                             trace.get(BindingContext.DECLARATION_TO_DESCRIPTOR, owner) as? FunctionDescriptor
                                             ?: throw AssertionError(owner.text)

compiler/frontend/src/org/jetbrains/kotlin/psi/KtPsiUtil.java

@@ -42,7 +42,6 @@ import org.jetbrains.kotlin.parsing.KotlinExpressionParsing;
 import org.jetbrains.kotlin.psi.psiUtil.KtPsiUtilKt;
 import org.jetbrains.kotlin.resolve.StatementFilter;
 import org.jetbrains.kotlin.resolve.StatementFilterKt;
-import org.jetbrains.kotlin.types.expressions.OperatorConventions;
 
 import java.util.Collection;
 import java.util.HashSet;
@@ -280,9 +279,8 @@ public class KtPsiUtil {
         if (!(declaration instanceof KtVariableDeclaration)) return false;
         if (declaration instanceof KtProperty) return true;
         assert declaration instanceof KtDestructuringDeclarationEntry;
-        KtDestructuringDeclaration parentDeclaration = (KtDestructuringDeclaration) declaration.getParent();
-        List<KtDestructuringDeclarationEntry> entries = parentDeclaration.getEntries();
-        return entries.size() > 1 && entries.get(entries.size() - 1) == declaration;
+        // We can always replace destructuring entry with _
+        return true;
     }
 
     @Nullable