Sealed class hierarchies are now correctly processed in when (by checking possible smart casts to nested sealed classes) #KT-10648 Fixed

(cherry picked from commit 2eaaf9c)

compiler/testData/diagnostics/tests/sealed/NestedSealed.kt

@@ -0,0 +1,45 @@
+// See KT-10648: Exhaustiveness check does not work with nested sealed hierarchy
+sealed class Base {
+    sealed class A : Base() {
+        class A1 : A()
+        class A2 : A()
+    }
+    sealed class B : Base() {
+        class B1 : B()
+        class B2 : B()
+    }
+}
+
+fun foo(b: Base) = when (b) {
+    is Base.A -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.A.A1 -> 1
+        is Base.A.A2 -> 2
+    }
+    is Base.B -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.B.B1 -> 3
+        is Base.B.B2 -> 4
+    }
+}
+
+fun bar(b: Base?) = if (b == null) 0 else when (<!DEBUG_INFO_SMARTCAST!>b<!>) {
+    is Base.A -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.A.A1 -> 1
+        is Base.A.A2 -> 2
+    }
+    is Base.B -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.B.B1 -> 3
+        is Base.B.B2 -> 4
+    }
+}
+
+fun gav(b: Base?) = when (b) {
+    null -> 0
+    is Base.A -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.A.A1 -> 1
+        is Base.A.A2 -> 2
+    }
+    is Base.B -> when(<!DEBUG_INFO_SMARTCAST!>b<!>) {
+        is Base.B.B1 -> 3
+        is Base.B.B2 -> 4
+    }
+}