Support expect enum class without a body. (#263)

Summary:
Currently the parser breaks when encountering these in mutliplatform
projects.

Note that `kotlinc` also supports empty enum definitions.

Pull Request resolved: #263

Reviewed By: davidtorosyan

Differential Revision: D33103316

Pulled By: hick209

fbshipit-source-id: 5fb27fc5f10b8c9d063318f2685467e84947cb85

core/src/main/java/com/facebook/ktfmt/format/KotlinInputAstVisitor.kt

@@ -1312,6 +1312,9 @@ class KotlinInputAstVisitor(
   /** Example `{ RED, GREEN; fun foo() { ... } }` for an enum class */
   private fun visitEnumBody(enumClass: KtClass) {
     val body = enumClass.body
+    if (body == null) {
+      return
+    }
     builder.token("{", Doc.Token.RealOrImaginary.REAL, blockIndent, Optional.of(blockIndent))
     builder.open(ZERO)
     builder.block(blockIndent) {

core/src/test/java/com/facebook/ktfmt/format/FormatterTest.kt

@@ -3441,6 +3441,12 @@ class FormatterTest {
       |}
       |""".trimMargin())
 
+  @Test
+  fun `expect enum class`() =
+      assertFormatted("""
+      |expect enum class ExpectedEnum
+      |""".trimMargin())
+
   @Test
   fun `enum without trailing comma`() =
       assertFormatted(