If to when: more accurate comment handling #KT-12649 Fixed

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

@@ -89,9 +89,11 @@ class IfToWhenIntention : SelfTargetingRangeIntention<KtIfExpression>(KtIfExpres
 
     override fun applyTo(element: KtIfExpression, editor: Editor?) {
         val siblings = element.siblings()
-        val commentSaver = CommentSaver(PsiChildRange(element, siblings.last()), saveLineBreaks = true)
+        val elementCommentSaver = CommentSaver(element)
+        val fullCommentSaver = CommentSaver(PsiChildRange(element, siblings.last()), saveLineBreaks = true)
 
         val toDelete = ArrayList<PsiElement>()
+        var applyFullCommentSaver = true
         var whenExpression = KtPsiFactory(element).buildExpression {
             appendFixedText("when {\n")
 
@@ -134,8 +136,8 @@ class IfToWhenIntention : SelfTargetingRangeIntention<KtIfExpression>(KtIfExpres
                     currentIfExpression = currentElseBranch
                 }
                 else {
-                    toDelete.addAll(baseIfExpressionForSyntheticBranch.siblingsUpTo(currentElseBranch))
                     appendElseBlock(currentElseBranch)
+                    applyFullCommentSaver = false
                     break
                 }
             }
@@ -149,7 +151,7 @@ class IfToWhenIntention : SelfTargetingRangeIntention<KtIfExpression>(KtIfExpres
         }
 
         val result = element.replace(whenExpression)
-        commentSaver.restore(result)
+        (if (applyFullCommentSaver) fullCommentSaver else elementCommentSaver).restore(result)
         toDelete.forEach {
             it.delete()
         }

idea/testData/intentions/branched/ifWhen/ifToWhen/ifElseSwallowReturnComment.kt.after

@@ -1,6 +1,6 @@
 fun foo(arg: Int): Int {
     when (arg) {
         0 -> return 0 // 1
-        else -> return -1 // 2
+        else -> return -1
-    }
+    } // 2
 }

idea/testData/intentions/branched/ifWhen/ifToWhen/ifElseSwallowTail.kt

@@ -0,0 +1,16 @@
+fun toInt(s: Number): Int {
+    <caret>if (s is Int) {
+        foo()
+    }
+    else {
+        return -1
+    }
+
+    // code below will be lost!
+    bar()
+    // before return
+    return s
+}
+
+fun foo() {}
+fun bar() {}

idea/testData/intentions/branched/ifWhen/ifToWhen/ifElseSwallowTail.kt.after

@@ -0,0 +1,14 @@
+fun toInt(s: Number): Int {
+    when (s) {
+        is Int -> foo()
+        else -> return -1
+    }
+
+    // code below will be lost!
+    bar()
+    // before return
+    return s
+}
+
+fun foo() {}
+fun bar() {}

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

@@ -1576,6 +1576,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("ifElseSwallowTail.kt")
+                public void testIfElseSwallowTail() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/ifToWhen/ifElseSwallowTail.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("ifWithEqualityTests.kt")
                 public void testIfWithEqualityTests() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/ifToWhen/ifWithEqualityTests.kt");