Fixed KT-7755 Convert to expression body kills comment

#KT-7755

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

@@ -22,17 +22,15 @@ import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.analyzer.analyzeInContext
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
-import org.jetbrains.kotlin.descriptors.DeclarationDescriptorWithVisibility
 import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptor
+import org.jetbrains.kotlin.idea.core.CommentSaver
 import org.jetbrains.kotlin.lexer.JetTokens
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.endOffset
 import org.jetbrains.kotlin.psi.psiUtil.startOffset
 import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.bindingContextUtil.isUsedAsStatement
 import org.jetbrains.kotlin.types.typeUtil.isSubtypeOf
-import kotlin.platform.platformName
 
 public class ConvertToExpressionBodyIntention : JetSelfTargetingOffsetIndependentIntention<JetDeclarationWithBody>(
         javaClass(), "Convert to expression body", firstElementOfTypeOnly = true
@@ -73,8 +71,13 @@ public class ConvertToExpressionBodyIntention : JetSelfTargetingOffsetIndependen
         val omitType = declaration.hasDeclaredReturnType() && declaration is JetCallableDeclaration && canOmitType(declaration, value)
 
         val body = declaration.getBodyExpression()!!
+
+        val commentSaver = CommentSaver(body)
+
         declaration.addBefore(JetPsiFactory(declaration).createEQ(), body)
-        body.replace(value)
+        val newBody = body.replace(value)
+
+        commentSaver.restoreComments(newBody)
 
         if (omitType) {
             onFinish(declaration as JetCallableDeclaration)

idea/testData/intentions/convertToExpressionBody/keepComments/1.kt

@@ -0,0 +1,3 @@
+fun getText(): String {
+    <caret>return "xxx" //TODO
+}

idea/testData/intentions/convertToExpressionBody/keepComments/1.kt.after

@@ -0,0 +1 @@
+fun getText()<selection>: String</selection> = "xxx" //TODO

idea/testData/intentions/convertToExpressionBody/keepComments/2.kt

@@ -0,0 +1,4 @@
+fun getText(): String {
+    // let's return xxx
+    <caret>return "xxx" //TODO
+}

idea/testData/intentions/convertToExpressionBody/keepComments/2.kt.after

@@ -0,0 +1,2 @@
+fun getText()<selection>: String</selection> = // let's return xxx
+        "xxx" //TODO

idea/testData/intentions/convertToExpressionBody/keepComments/3.kt

@@ -0,0 +1,3 @@
+fun getText(): String { // let's return xxx
+    <caret>return "xxx"
+}

idea/testData/intentions/convertToExpressionBody/keepComments/3.kt.after

@@ -0,0 +1,2 @@
+fun getText()<selection>: String</selection> = // let's return xxx
+        "xxx"

idea/testData/intentions/convertToExpressionBody/keepComments/4.kt

@@ -0,0 +1,4 @@
+fun getText(): String {
+    /* let's return xxx */
+    <caret>return "xxx" /* TODO */
+}

idea/testData/intentions/convertToExpressionBody/keepComments/4.kt.after

@@ -0,0 +1,2 @@
+fun getText(): String = /* let's return xxx */
+        "xxx" /* TODO */

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

@@ -3876,6 +3876,39 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/while.kt");
             doTest(fileName);
         }
+
+        @TestMetadata("idea/testData/intentions/convertToExpressionBody/keepComments")
+        @TestDataPath("$PROJECT_ROOT")
+        @RunWith(JUnit3RunnerWithInners.class)
+        public static class KeepComments extends AbstractIntentionTest {
+            @TestMetadata("1.kt")
+            public void test1() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/keepComments/1.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("2.kt")
+            public void test2() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/keepComments/2.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("3.kt")
+            public void test3() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/keepComments/3.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("4.kt")
+            public void test4() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/intentions/convertToExpressionBody/keepComments/4.kt");
+                doTest(fileName);
+            }
+
+            public void testAllFilesPresentInKeepComments() throws Exception {
+                JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/testData/intentions/convertToExpressionBody/keepComments"), Pattern.compile("^(.+)\\.kt$"), true);
+            }
+        }
     }
 
     @TestMetadata("idea/testData/intentions/convertToForEachFunctionCall")