Move: Keep original file package name when moving top-level declarations to separate file (provided it's not ambiguous)

#KT-10950 Fixed

ChangeLog.md

@@ -40,6 +40,7 @@ Issues fixed:
 - [KT-11482](https://youtrack.jetbrains.com/issue/KT-11482) Fixed exception in "Move to companion object" intention
 - [KT-11483](https://youtrack.jetbrains.com/issue/KT-11483) Pass implicit receiver as argument when moving member function to companion object
 - [KT-11512](https://youtrack.jetbrains.com/issue/KT-11512) Allow choosing any source root in "Move file to directory" intention
+- [KT-10950](https://youtrack.jetbrains.com/issue/KT-10950) Keep original file package name when moving top-level declarations to separate file (provided it's not ambiguous)
 
 #### Debugger
 

idea/src/org/jetbrains/kotlin/idea/refactoring/jetRefactoringUtil.kt

@@ -95,8 +95,11 @@ import java.lang.annotation.Retention
 import java.util.*
 import javax.swing.Icon
 
-fun getOrCreateKotlinFile(fileName: String, targetDir: PsiDirectory): KtFile? =
-        (targetDir.findFile(fileName) ?: createKotlinFile(fileName, targetDir)) as? KtFile
+@JvmOverloads
+fun getOrCreateKotlinFile(fileName: String,
+                          targetDir: PsiDirectory,
+                          packageName: String? = targetDir.getPackage()?.qualifiedName): KtFile? =
+        (targetDir.findFile(fileName) ?: createKotlinFile(fileName, targetDir, packageName)) as? KtFile
 
 fun createKotlinFile(fileName: String,
                      targetDir: PsiDirectory,

idea/src/org/jetbrains/kotlin/idea/refactoring/move/moveDeclarations/ui/MoveKotlinTopLevelDeclarationsDialog.java

@@ -586,19 +586,34 @@ public class MoveKotlinTopLevelDeclarationsDialog extends RefactoringDialog {
             return null;
         }
 
-        PsiPackage psiPackage = JavaDirectoryService.getInstance().getPackage(psiDirectory);
-        if (psiPackage == null) {
-            setErrorText("Could not find package corresponding to " + targetDir.getPath());
-            return null;
+        Set<FqName> sourcePackageFqNames = CollectionsKt.mapTo(
+                sourceFiles,
+                new LinkedHashSet<FqName>(),
+                new Function1<KtFile, FqName>() {
+                    @Override
+                    public FqName invoke(KtFile file) {
+                        return file.getPackageFqName();
+                    }
+                }
+        );
+        FqName targetPackageFqName = CollectionsKt.singleOrNull(sourcePackageFqNames);
+        if (targetPackageFqName == null) {
+            PsiPackage psiPackage = JavaDirectoryService.getInstance().getPackage(psiDirectory);
+            if (psiPackage == null) {
+                setErrorText("Could not find package corresponding to " + targetDir.getPath());
+                return null;
+            }
+            targetPackageFqName = new FqName(psiPackage.getQualifiedName());
         }
 
+        final String finalTargetPackageFqName = targetPackageFqName.asString();
         return new KotlinMoveTargetForDeferredFile(
-                new FqName(psiPackage.getQualifiedName()),
+                targetPackageFqName,
                 psiDirectory,
                 new Function1<KtFile, KtFile>() {
                     @Override
                     public KtFile invoke(@NotNull KtFile originalFile) {
-                        return JetRefactoringUtilKt.getOrCreateKotlinFile(targetFile.getName(), psiDirectory);
+                        return JetRefactoringUtilKt.getOrCreateKotlinFile(targetFile.getName(), psiDirectory, finalTargetPackageFqName);
                     }
                 }
         );