KT-16828: use _ when appropriate in destructure intention

idea/src/org/jetbrains/kotlin/idea/intentions/DestructureIntention.kt

@@ -68,8 +68,15 @@ class DestructureIntention : SelfTargetingRangeIntention<KtDeclaration>(
                 excludedDeclarations = usagesToRemove.map { listOfNotNull(it.declarationToDrop) }.flatten()
         )
         val names = ArrayList<String>()
+        val underscoreSupported = element.languageVersionSettings.supportsFeature(LanguageFeature.SingleUnderscoreForParameterName)
         usagesToRemove.forEach { (descriptor, usagesToReplace, variableToDrop, name) ->
-            val suggestedName = name ?: KotlinNameSuggester.suggestNameByName(descriptor.name.asString(), validator)
+            val suggestedName =
+                    if (usagesToReplace.isEmpty() && variableToDrop == null && underscoreSupported) {
+                        "_"
+                    }
+                    else {
+                        name ?: KotlinNameSuggester.suggestNameByName(descriptor.name.asString(), validator)
+                    }
             variableToDrop?.delete()
             usagesToReplace.forEach {
                 it.replace(factory.createExpression(suggestedName))

idea/testData/intentions/destructuringInLambda/inspectionData/expected.xml

@@ -63,4 +63,12 @@
         <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Use destructuring declaration</problem_class>
         <description>Use destructuring declaration</description>
     </problem>
+    <problem>
+        <file>mapIndexedLast.kt</file>
+        <line>5</line>
+        <module>light_idea_test_case</module>
+        <entry_point TYPE="file" FQNAME="temp:///src/mapIndexedLast.kt" />
+        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Use destructuring declaration</problem_class>
+        <description>Use destructuring declaration</description>
+    </problem>
 </problems>

idea/testData/intentions/destructuringInLambda/last.kt.after

@@ -3,7 +3,7 @@
 data class My(val first: String, val second: Int)
 
 fun foo(list: List<My>) {
-    list.forEach { (first, second) ->
+    list.forEach { (_, second) ->
         println(second)
     }
 }

idea/testData/intentions/destructuringInLambda/mapIndexedLast.kt

@@ -0,0 +1,5 @@
+// WITH_RUNTIME
+
+data class Package(val name: String, val version: String, val source: String, val id: String)
+
+val pkgs = listOf<Package>().mapIndexed { i, <caret>p -> p.id to i }.toMap()

idea/testData/intentions/destructuringInLambda/mapIndexedLast.kt.after

@@ -0,0 +1,5 @@
+// WITH_RUNTIME
+
+data class Package(val name: String, val version: String, val source: String, val id: String)
+
+val pkgs = listOf<Package>().mapIndexed { i, (_, _, _, id) -> id to i }.toMap()

idea/testData/intentions/iterationOverMap/DataClassLast.kt.after

@@ -3,7 +3,7 @@
 data class My(val first: String, val second: Int)
 
 fun foo(list: List<My>) {
-    for ((first, second) in list) {
+    for ((_, second) in list) {
         println(second)
     }
 }

idea/testData/intentions/iterationOverMap/DataClassNotAllPropertiesUsed.kt.after

@@ -2,7 +2,7 @@
 
 fun main(args: Array<String>) {
     val list = listOf(MyClass(1, 2, 3, 4))
-    for ((a, b, c) in list) {
+    for ((a, _, c) in list) {
         println("$a$c")
     }
 }

idea/testData/intentions/iterationOverMap/ValueOnly.kt.after

@@ -2,7 +2,7 @@
 
 fun main(args: Array<String>) {
     val map = hashMapOf(1 to 1)
-    for ((key, value) in map) {
+    for ((_, value) in map) {
         println(value)
     }
 }

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -7645,6 +7645,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("mapIndexedLast.kt")
+        public void testMapIndexedLast() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/destructuringInLambda/mapIndexedLast.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("noIt.kt")
         public void testNoIt() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/destructuringInLambda/noIt.kt");