Recursion depth in CommonSupertypes is bounded by maxDepth + 3

compiler/testData/diagnostics/tests/generics/recursive.kt

@@ -0,0 +1,11 @@
+// !DIAGNOSTICS: -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE -UNUSED_VALUE
+
+trait Rec<T>
+class A : Rec<A>
+class B : Rec<B>
+
+fun test(a: A, b: B, c: Boolean) {
+    var ab = if (c) a else b
+    ab = a
+    ab = b
+}