Intentions: Implement "Convert sealed class to enum" intention

#KT-14245 Fixed

idea/testData/intentions/convertSealedClassToEnum/.intention

@@ -0,0 +1 @@
+org.jetbrains.kotlin.idea.intentions.ConvertSealedClassToEnumIntention

idea/testData/intentions/convertSealedClassToEnum/dropDefaultConstructorCall.kt

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+sealed class <caret>MyClass {
+    object FOO : MyClass()
+}

idea/testData/intentions/convertSealedClassToEnum/dropDefaultConstructorCall.kt.after

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+enum class <caret>MyClass {
+    FOO
+}

idea/testData/intentions/convertSealedClassToEnum/inheritorsWithMultipleSupertypes.kt

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+// SHOULD_FAIL_WITH: All inheritors must be nested objects of the class itself and may not inherit from other classes or interfaces. Following problems are found: object <b><code>A</code></b>
+
+interface I
+
+sealed class <caret>X {
+    object A : X(), I
+    object B : X()
+}

idea/testData/intentions/convertSealedClassToEnum/instancesAndMembers.kt

@@ -0,0 +1,23 @@
+// WITH_RUNTIME
+
+sealed class <caret>MyClass(val s: String = "") {
+    fun foo() {
+
+    }
+
+    object FOO : MyClass("FOO")
+    object BAR : MyClass("BAR")
+    object DEFAULT : MyClass()
+}
+
+fun test(e: MyClass) {
+    if (e == MyClass.BAR) {
+        println()
+    }
+
+    val n = when (e) {
+        MyClass.BAR -> 1
+        MyClass.FOO -> 2
+        MyClass.DEFAULT -> 0
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/instancesAndMembers.kt.after

@@ -0,0 +1,22 @@
+// WITH_RUNTIME
+
+enum class <caret>MyClass(val s: String = "") {
+    FOO("FOO"), BAR("BAR"), DEFAULT();
+
+    fun foo() {
+
+    }
+
+}
+
+fun test(e: MyClass) {
+    if (e == MyClass.BAR) {
+        println()
+    }
+
+    val n = when (e) {
+        MyClass.BAR -> 1
+        MyClass.FOO -> 2
+        MyClass.DEFAULT -> 0
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/instancesOnly.kt

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+// WITH_RUNTIME
+
+sealed class <caret>MyClass(val s: String = "") {
+    object FOO : MyClass("FOO")
+    object BAR : MyClass("BAR")
+    object DEFAULT : MyClass()
+}
+
+fun test(e: MyClass) {
+    if (e == MyClass.BAR) {
+        println()
+    }
+
+    val n = when (e) {
+        MyClass.BAR -> 1
+        MyClass.FOO -> 2
+        MyClass.DEFAULT -> 0
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/instancesOnly.kt.after

@@ -0,0 +1,17 @@
+// WITH_RUNTIME
+
+enum class <caret>MyClass(val s: String = "") {
+    FOO("FOO"), BAR("BAR"), DEFAULT()
+}
+
+fun test(e: MyClass) {
+    if (e == MyClass.BAR) {
+        println()
+    }
+
+    val n = when (e) {
+        MyClass.BAR -> 1
+        MyClass.FOO -> 2
+        MyClass.DEFAULT -> 0
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/membersOnly.kt

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+sealed class <caret>MyEnum(val s: String = "") {
+    fun foo() {
+
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/membersOnly.kt.after

@@ -0,0 +1,7 @@
+enum class MyEnum(val s: String = "") {
+     ;
+
+    fun foo() {
+
+    }
+}

idea/testData/intentions/convertSealedClassToEnum/nonNestedInheritors.kt

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+// SHOULD_FAIL_WITH: All inheritors must be nested objects of the class itself and may not inherit from other classes or interfaces. Following problems are found: object <b><code>B</code></b>
+
+sealed class <caret>X {
+    object A : X()
+}
+
+object B : X()

idea/testData/intentions/convertSealedClassToEnum/notSealedClass.kt

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+// IS_APPLICABLE: false
+
+class <caret>X {
+
+}

idea/testData/intentions/convertSealedClassToEnum/outOfRange.kt

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+// IS_APPLICABLE: false
+
+<caret>private sealed class X {
+
+}

idea/testData/intentions/convertSealedClassToEnum/withNonObjectInheritors.kt

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+// SHOULD_FAIL_WITH: All inheritors must be nested objects of the class itself and may not inherit from other classes or interfaces. Following problems are found: class <b><code>A</code></b>, class <b><code>B</code></b>
+
+sealed class <caret>X {
+    class A : X()
+}
+
+class B : X()

idea/testData/intentions/convertSealedClassToEnum/withSuperclass.kt

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+// IS_APPLICABLE: false
+
+open class C
+
+sealed class <caret>X : C() {
+
+}