Rename: Allow deleting name of companion object

#KT-20178 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/references/KtSimpleNameReference.kt

@@ -28,10 +28,7 @@ import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.caches.resolve.resolveImportReference
 import org.jetbrains.kotlin.idea.codeInsight.shorten.addDelayedImportRequest
 import org.jetbrains.kotlin.idea.codeInsight.shorten.addToShorteningWaitSet
-import org.jetbrains.kotlin.idea.core.ShortenReferences
-import org.jetbrains.kotlin.idea.core.copied
-import org.jetbrains.kotlin.idea.core.quoteIfNeeded
-import org.jetbrains.kotlin.idea.core.replaced
+import org.jetbrains.kotlin.idea.core.*
 import org.jetbrains.kotlin.idea.intentions.OperatorToFunctionIntention
 import org.jetbrains.kotlin.idea.refactoring.fqName.getKotlinFqName
 import org.jetbrains.kotlin.lexer.KtToken
@@ -39,6 +36,7 @@ import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.load.java.descriptors.JavaPropertyDescriptor
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.name.SpecialNames
 import org.jetbrains.kotlin.name.isOneSegmentFQN
 import org.jetbrains.kotlin.plugin.references.SimpleNameReferenceExtension
 import org.jetbrains.kotlin.psi.*
@@ -108,6 +106,20 @@ class KtSimpleNameReference(expression: KtSimpleNameExpression) : KtSimpleRefere
         if (!canRename()) throw IncorrectOperationException()
         if (newElementName == null) return expression
 
+        if (newElementName.unquote() == "") {
+            val qualifiedElement = expression.getQualifiedElement()
+            return when (qualifiedElement) {
+                is KtQualifiedExpression -> {
+                    expression.replace(qualifiedElement.receiverExpression)
+                    qualifiedElement.replaced(qualifiedElement.selectorExpression!!)
+                }
+                is KtUserType -> {
+                    expression.replaced(KtPsiFactory(expression).createSimpleName(SpecialNames.DEFAULT_NAME_FOR_COMPANION_OBJECT.asString()))
+                }
+                else -> expression
+            }
+        }
+
         // Do not rename if the reference corresponds to synthesized component function
         val expressionText = expression.text
         if (expressionText != null && Name.isValidIdentifier(expressionText)) {

idea/src/org/jetbrains/kotlin/idea/refactoring/rename/KotlinMemberInplaceRenameHandler.kt

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.idea.refactoring.rename
 
+import com.intellij.lang.Language
 import com.intellij.openapi.editor.Editor
 import com.intellij.psi.*
 import com.intellij.refactoring.RefactoringActionHandler
@@ -24,6 +25,7 @@ import com.intellij.refactoring.rename.inplace.MemberInplaceRenamer
 import com.intellij.refactoring.rename.inplace.VariableInplaceRenamer
 import org.jetbrains.kotlin.idea.core.unquote
 import org.jetbrains.kotlin.psi.KtNamedDeclaration
+import org.jetbrains.kotlin.psi.KtObjectDeclaration
 import org.jetbrains.kotlin.psi.KtPrimaryConstructor
 
 class KotlinMemberInplaceRenameHandler : MemberInplaceRenameHandler() {
@@ -34,6 +36,11 @@ class KotlinMemberInplaceRenameHandler : MemberInplaceRenameHandler() {
         currentName: String,
         oldName: String
     ) : MemberInplaceRenamer(elementToRename, substitutedElement, editor, currentName, oldName) {
+        override fun isIdentifier(newName: String?, language: Language?): Boolean {
+            if (newName == "" && (variable as? KtObjectDeclaration)?.isCompanion() == true) return true
+            return super.isIdentifier(newName, language)
+        }
+
         override fun acceptReference(reference: PsiReference): Boolean {
             val refElement = reference.element
             val textRange = reference.rangeInElement

idea/testData/refactoring/rename/inplace/EraseCompanionName.kt

@@ -0,0 +1,16 @@
+class Foo {
+    companion object <caret>Bar {
+        fun bar(n: Int) {}
+        operator fun invoke(n: Int) {}
+        operator fun get(n: Int) {}
+    }
+}
+
+fun test() {
+    val x = 1
+    Foo.Bar.bar(123)
+    Foo.Bar(123)
+    Foo.Bar[123]
+    val y: Foo.Bar
+    val z: Foo.Bar?
+}

idea/testData/refactoring/rename/inplace/EraseCompanionName.kt.after

@@ -0,0 +1,16 @@
+class Foo {
+    companion object {
+        fun bar(n: Int) {}
+        operator fun invoke(n: Int) {}
+        operator fun get(n: Int) {}
+    }
+}
+
+fun test() {
+    val x = 1
+    Foo.bar(123)
+    Foo(123)
+    Foo[123]
+    val y: Foo.Companion
+    val z: Foo.Companion?
+}

idea/tests/org/jetbrains/kotlin/idea/refactoring/InplaceRenameTest.kt

@@ -151,6 +151,10 @@ class InplaceRenameTest : LightPlatformCodeInsightTestCase() {
         doTestMemberInplaceRename("x")
     }
 
+    fun testEraseCompanionName() {
+        doTestMemberInplaceRename("")
+    }
+
     private fun doTestImplicitLambdaParameter(newName: String) {
         configureByFile(getTestName(false) + ".kt")