Move to Companion Object: Warn if companion object already contains function with the same signature

#KT-13877 Fixed

ChangeLog.md

@@ -115,6 +115,7 @@ These artifacts include extensions for the types available in the latter JDKs, s
 - [`KT-13874`](https://youtrack.jetbrains.com/issue/KT-13874) Move to Companion: Fix AssertionError on running refactoring from Conflicts View
 - [`KT-13883`](https://youtrack.jetbrains.com/issue/KT-13883) Move to Companion Object: Fix exception when applied to class
 - [`KT-13876`](https://youtrack.jetbrains.com/issue/KT-13876) Move to Companion Object: Forbid for functions/properties referencing type parameters of the containing class
+- [`KT-13877`](https://youtrack.jetbrains.com/issue/KT-13877) Move to Companion Object: Warn if companion object already contains function with the same signature
 
 ##### New features
 

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

@@ -34,11 +34,13 @@ import com.intellij.usageView.UsageInfo
 import com.intellij.util.SmartList
 import com.intellij.util.containers.MultiMap
 import org.jetbrains.kotlin.asJava.toLightClass
+import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.ClassDescriptorWithResolutionScopes
 import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptor
+import org.jetbrains.kotlin.idea.codeInsight.DescriptorToSourceUtilsIde
 import org.jetbrains.kotlin.idea.core.*
 import org.jetbrains.kotlin.idea.refactoring.checkConflictsInteractively
 import org.jetbrains.kotlin.idea.refactoring.move.OuterInstanceReferenceUsageInfo
@@ -64,6 +66,7 @@ import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
 import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 import org.jetbrains.kotlin.resolve.scopes.receivers.ExpressionReceiver
 import org.jetbrains.kotlin.resolve.scopes.receivers.ImplicitReceiver
+import org.jetbrains.kotlin.util.findCallableMemberBySignature
 
 class MoveMemberToCompanionObjectIntention : SelfTargetingRangeIntention<KtNamedDeclaration>(KtNamedDeclaration::class.java,
                                                                                              "Move to companion object") {
@@ -248,6 +251,8 @@ class MoveMemberToCompanionObjectIntention : SelfTargetingRangeIntention<KtNamed
     override fun applyTo(element: KtNamedDeclaration, editor: Editor?) {
         val project = element.project
 
+        val containingClass = element.containingClassOrObject as KtClass
+
         if (element is KtClassOrObject) {
             val nameSuggestions = if (traverseOuterInstanceReferences(element, true)) getNameSuggestionsForOuterInstance(element) else emptyList()
             val outerInstanceName = nameSuggestions.firstOrNull()
@@ -258,7 +263,7 @@ class MoveMemberToCompanionObjectIntention : SelfTargetingRangeIntention<KtNamed
                 }
             }
             val moveDescriptor = MoveDeclarationsDescriptor(listOf(element),
-                                                            KotlinMoveTargetForCompanion(element.containingClassOrObject!! as KtClass),
+                                                            KotlinMoveTargetForCompanion(containingClass),
                                                             MoveDeclarationsDelegate.NestedClass(null, outerInstanceName),
                                                             moveCallback = MoveCallback { runTemplateForInstanceParam(movedClass!!, nameSuggestions, editor) })
             MoveKotlinDeclarationsProcessor(project, moveDescriptor, mover).run()
@@ -271,7 +276,7 @@ class MoveMemberToCompanionObjectIntention : SelfTargetingRangeIntention<KtNamed
             return CommonRefactoringUtil.showErrorHint(project, editor, "$description is overridden by declaration(s) in a subclass", text, null)
         }
 
-        if (hasTypeParameterReferences(element.containingClassOrObject!!, element)) {
+        if (hasTypeParameterReferences(containingClass, element)) {
             return CommonRefactoringUtil.showErrorHint(project, editor, "$description references type parameters of the containing class", text, null)
         }
 
@@ -279,6 +284,16 @@ class MoveMemberToCompanionObjectIntention : SelfTargetingRangeIntention<KtNamed
         val outerInstanceUsages = SmartList<UsageInfo>()
         val conflicts = MultiMap<PsiElement, String>()
 
+        containingClass.getCompanionObjects().firstOrNull()?.let { companion ->
+            val companionDescriptor = companion.resolveToDescriptor() as ClassDescriptor
+            val callableDescriptor = element.resolveToDescriptor() as CallableMemberDescriptor
+            companionDescriptor.findCallableMemberBySignature(callableDescriptor)?.let {
+                DescriptorToSourceUtilsIde.getAnyDeclaration(project, it)
+            }?.let {
+                conflicts.putValue(it, "Companion object already contains ${RefactoringUIUtil.getDescription(it, false)}")
+            }
+        }
+
         val outerInstanceReferences = collectOuterInstanceReferences(element)
         if (outerInstanceReferences.isNotEmpty()) {
             if (element is KtProperty) {

idea/testData/intentions/moveToCompanion/redeclarationConflict.kt

@@ -0,0 +1,7 @@
+// SHOULD_FAIL_WITH: Companion object already contains function f1(Int)
+class Test9{
+    fun <caret>f1(n: Int){}
+    companion object{
+        fun f1(n: Int){}
+    }
+}

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

@@ -9133,6 +9133,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("redeclarationConflict.kt")
+        public void testRedeclarationConflict() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/moveToCompanion/redeclarationConflict.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("topLevelFunction.kt")
         public void testTopLevelFunction() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/moveToCompanion/topLevelFunction.kt");