preserve comments while converting from lambda to method ref (IDEA-156734)

java/java-analysis-impl/src/com/intellij/codeInspection/LambdaCanBeMethodReferenceInspection.java

@@ -30,10 +30,12 @@ import com.intellij.psi.util.*;
 import com.intellij.refactoring.util.RefactoringChangeUtil;
 import com.intellij.util.ArrayUtil;
 import com.intellij.util.IncorrectOperationException;
+import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.Nls;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.Collection;
 import java.util.Map;
 
 /**
@@ -492,6 +494,10 @@ public class LambdaCanBeMethodReferenceInspection extends BaseJavaBatchLocalInsp
       if (functionalInterfaceType == null || !functionalInterfaceType.isValid()) return;
       final PsiType denotableFunctionalInterfaceType = RefactoringChangeUtil.getTypeByExpression(lambdaExpression);
       if (denotableFunctionalInterfaceType == null) return;
+
+      Collection<PsiComment> comments = ContainerUtil.map(PsiTreeUtil.findChildrenOfType(lambdaExpression, PsiComment.class),
+                                                          (comment) -> (PsiComment)comment.copy());
+
       final String methodRefText = createMethodReferenceText(element, functionalInterfaceType,
                                                              lambdaExpression.getParameterList().getParameters());
 
@@ -508,6 +514,14 @@ public class LambdaCanBeMethodReferenceInspection extends BaseJavaBatchLocalInsp
           cast.getOperand().replace(replace);
           replace = replace.replace(cast);
         }
+
+        PsiElement anchor = PsiTreeUtil.getParentOfType(replace, PsiStatement.class);
+        if (anchor == null) {
+          anchor = replace;
+        }
+        for (PsiComment comment : comments) {
+          anchor.getParent().addBefore(comment, anchor);
+        }
         JavaCodeStyleManager.getInstance(project).shortenClassReferences(replace);
       }
     }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/lambda2methodReference/afterComments.java

@@ -0,0 +1,10 @@
+// "Replace lambda with method reference" "true"
+class Example {
+  public void m() {
+  }
+
+  {
+      //my comments here
+      Runnable r = this::m
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/lambda2methodReference/beforeComments.java

@@ -0,0 +1,12 @@
+// "Replace lambda with method reference" "true"
+class Example {
+  public void m() {
+  }
+
+  {
+    Runnable r = () -> {
+      //my comments here
+      m<caret>();
+    }
+  }
+}