Support subject variable in specialized code generators for 'when'

compiler/testData/codegen/box/when/whenSubjectVariable/whenByNullableEnum.kt

@@ -0,0 +1,44 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+// WITH_RUNTIME
+// IGNORE_BACKEND: JS
+
+import kotlin.test.assertEquals
+
+enum class Season {
+    WINTER,
+    SPRING,
+    SUMMER,
+    AUTUMN
+}
+
+fun foo1(x : Season?) : String {
+    when(val xx = x) {
+        Season.AUTUMN, Season.SPRING -> return "autumn_or_spring $xx";
+        Season.SUMMER, null -> return "summer_or_null $xx"
+    }
+
+    return "other"
+}
+
+fun foo2(x : Season?) : String {
+    when(val xx = x) {
+        Season.AUTUMN, Season.SPRING -> return "autumn_or_spring $xx";
+        Season.SUMMER -> return "summer"
+    }
+
+    return "other"
+}
+
+fun box() : String {
+    assertEquals("autumn_or_spring AUTUMN", foo1(Season.AUTUMN))
+    assertEquals("autumn_or_spring SPRING", foo1(Season.SPRING))
+    assertEquals("summer_or_null SUMMER", foo1(Season.SUMMER))
+    assertEquals("summer_or_null null", foo1(null))
+
+    assertEquals("autumn_or_spring AUTUMN", foo2(Season.AUTUMN))
+    assertEquals("autumn_or_spring SPRING", foo2(Season.SPRING))
+    assertEquals("summer", foo2(Season.SUMMER))
+    assertEquals("other", foo2(null))
+
+    return "OK"
+}