KT-5717 "Replace 'when' with 'if'" loses a comment

#KT-5717 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/branchedTransformations/intentions/WhenToIfIntention.kt

@@ -21,7 +21,10 @@ import com.intellij.openapi.editor.Editor
 import com.intellij.openapi.util.TextRange
 import org.jetbrains.kotlin.idea.intentions.SelfTargetingRangeIntention
 import org.jetbrains.kotlin.idea.intentions.branchedTransformations.combineWhenConditions
-import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.idea.util.CommentSaver
+import org.jetbrains.kotlin.psi.KtPsiFactory
+import org.jetbrains.kotlin.psi.KtWhenExpression
+import org.jetbrains.kotlin.psi.buildExpression
 
 class WhenToIfIntention : SelfTargetingRangeIntention<KtWhenExpression>(KtWhenExpression::class.java, "Replace 'when' with 'if'"), LowPriorityAction {
     override fun applicabilityRange(element: KtWhenExpression): TextRange? {
@@ -33,6 +36,8 @@ class WhenToIfIntention : SelfTargetingRangeIntention<KtWhenExpression>(KtWhenEx
     }
 
     override fun applyTo(element: KtWhenExpression, editor: Editor?) {
+        val commentSaver = CommentSaver(element)
+
         val factory = KtPsiFactory(element)
         val ifExpression = factory.buildExpression {
             val entries = element.entries
@@ -57,6 +62,7 @@ class WhenToIfIntention : SelfTargetingRangeIntention<KtWhenExpression>(KtWhenEx
             }
         }
 
-        element.replace(ifExpression)
+        val result = element.replace(ifExpression)
+        commentSaver.restore(result)
     }
 }

idea/testData/intentions/branched/ifWhen/whenToIf/comment.kt

@@ -0,0 +1,8 @@
+fun foo(b: Boolean) {
+    <caret>when {
+        // comment 1
+        b -> 1 // comment 2
+
+        else -> 2
+    }
+}

idea/testData/intentions/branched/ifWhen/whenToIf/comment.kt.after

@@ -0,0 +1,5 @@
+fun foo(b: Boolean) {
+    if (// comment 1
+    b) 1 // comment 2
+    else 2
+}

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

@@ -1564,6 +1564,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                     KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/testData/intentions/branched/ifWhen/whenToIf"), Pattern.compile("^([\\w\\-_]+)\\.kt$"), true);
                 }
 
+                @TestMetadata("comment.kt")
+                public void testComment() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/whenToIf/comment.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("whenWithDotQualifiedExpression.kt")
                 public void testWhenWithDotQualifiedExpression() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/whenToIf/whenWithDotQualifiedExpression.kt");