Intentions: Implement "Convert sealed class to enum" intention

#KT-14245 Fixed

idea/src/META-INF/plugin.xml

@@ -1401,6 +1401,11 @@
       <category>Kotlin</category>
     </intentionAction>
 
+    <intentionAction>
+      <className>org.jetbrains.kotlin.idea.intentions.ConvertSealedClassToEnumIntention</className>
+      <category>Kotlin</category>
+    </intentionAction>
+
     <localInspection implementationClass="org.jetbrains.kotlin.idea.intentions.ObjectLiteralToLambdaInspection"
                      displayName="Object literal can be converted to lambda"
                      groupName="Kotlin"

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

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.idea.intentions
+
+import com.intellij.openapi.editor.Editor
+import com.intellij.openapi.util.TextRange
+import com.intellij.psi.ElementDescriptionUtil
+import com.intellij.psi.codeStyle.CodeStyleManager
+import com.intellij.refactoring.util.CommonRefactoringUtil
+import com.intellij.refactoring.util.RefactoringDescriptionLocation
+import org.jetbrains.kotlin.asJava.unwrapped
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptor
+import org.jetbrains.kotlin.idea.refactoring.runSynchronouslyWithProgress
+import org.jetbrains.kotlin.idea.search.declarationsSearch.HierarchySearchRequest
+import org.jetbrains.kotlin.idea.search.declarationsSearch.searchInheritors
+import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.KtClass
+import org.jetbrains.kotlin.psi.KtObjectDeclaration
+import org.jetbrains.kotlin.psi.KtPsiFactory
+import org.jetbrains.kotlin.psi.KtSuperTypeCallEntry
+import org.jetbrains.kotlin.psi.psiUtil.containingClassOrObject
+import org.jetbrains.kotlin.psi.psiUtil.endOffset
+import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.resolve.descriptorUtil.getSuperClassNotAny
+
+class ConvertSealedClassToEnumIntention : SelfTargetingRangeIntention<KtClass>(KtClass::class.java, "Convert to enum class") {
+    override fun applicabilityRange(element: KtClass): TextRange? {
+        val nameIdentifier = element.nameIdentifier ?: return null
+        val sealedKeyword = element.modifierList?.getModifier(KtTokens.SEALED_KEYWORD) ?: return null
+
+        val classDescriptor = element.resolveToDescriptor() as ClassDescriptor
+        if (classDescriptor.getSuperClassNotAny() != null) return null
+
+        return TextRange(sealedKeyword.startOffset, nameIdentifier.endOffset)
+    }
+
+    override fun applyTo(element: KtClass, editor: Editor?) {
+        val project = element.project
+
+        val subclasses = project.runSynchronouslyWithProgress("Searching inheritors...", true) {
+            HierarchySearchRequest(element, element.useScope, false).searchInheritors().mapNotNull { it.unwrapped }
+        } ?: return
+
+        val inconvertibleSubclasses = subclasses.filter {
+            it !is KtObjectDeclaration || it.containingClassOrObject != element || it.getSuperTypeListEntries().size != 1
+        }
+        if (inconvertibleSubclasses.isNotEmpty()) {
+            val message = buildString {
+                append("All inheritors must be nested objects of the class itself and may not inherit from other classes or interfaces.\n")
+                append("Following problems are found:\n")
+                inconvertibleSubclasses.joinTo(this) { ElementDescriptionUtil.getElementDescription(it, RefactoringDescriptionLocation.WITHOUT_PARENT) }
+            }
+            return CommonRefactoringUtil.showErrorHint(project, editor, message, text, null)
+        }
+
+        val needSemicolon = element.declarations.size > subclasses.size
+
+        val psiFactory = KtPsiFactory(element)
+
+        val comma = psiFactory.createComma()
+        val semicolon = psiFactory.createSemicolon()
+
+        val constructorCallNeeded = element.hasExplicitPrimaryConstructor() || element.getSecondaryConstructors().isNotEmpty()
+        val entriesToAdd = subclasses.mapIndexed { i, subclass ->
+            subclass as KtObjectDeclaration
+
+            val entryText = buildString {
+                append(subclass.name)
+                if (constructorCallNeeded) {
+                    append((subclass.getSuperTypeListEntries().firstOrNull() as? KtSuperTypeCallEntry)?.valueArgumentList?.text ?: "()")
+                }
+            }
+            val entry = psiFactory.createEnumEntry(entryText)
+
+            subclass.getBody()?.let { body -> entry.add(body) }
+
+            if (i < subclasses.lastIndex) {
+                entry.add(comma)
+            }
+            else if (needSemicolon) {
+                entry.add(semicolon)
+            }
+
+            entry
+        }
+
+        subclasses.forEach { it.delete() }
+
+        element.removeModifier(KtTokens.SEALED_KEYWORD)
+        element.addModifier(KtTokens.ENUM_KEYWORD)
+
+        if (entriesToAdd.isNotEmpty()) {
+            val firstEntry = entriesToAdd
+                    .reversed()
+                    .map { element.addDeclarationBefore(it, null) }
+                    .last()
+            // TODO: Add formatter rule
+            firstEntry.parent.addBefore(psiFactory.createNewLine(), firstEntry)
+        }
+        else if (needSemicolon) {
+            element.declarations.firstOrNull()?.let { anchor ->
+                val delimiter = anchor.parent.addBefore(semicolon, anchor)
+                CodeStyleManager.getInstance(project).reformat(delimiter)
+            }
+        }
+    }
+}