FE: add one more test related to KT-56511 with the relevant feature ON

compiler/testData/diagnostics/tests/smartCasts/smartCastOnAlienPropertyFromInvisibleClass.diag.txt

@@ -1,10 +1,10 @@
 // -- Module: <m1> --
 
 // -- Module: <m2> --
-/B.kt:13:13: warning: smart cast to 'String' is deprecated, because 'x' is a property declared in base class from different module inherited in non-public API class
+/B.kt:14:13: warning: smart cast to 'String' is deprecated, because 'x' is a property declared in base class from different module inherited in non-public API class
             x.length
             ^
-/B.kt:22:9: warning: smart cast to 'String' is deprecated, because 'i.x' is a property declared in base class from different module inherited in non-public API class
+/B.kt:23:9: warning: smart cast to 'String' is deprecated, because 'i.x' is a property declared in base class from different module inherited in non-public API class
         i.x.length
         ^
 

compiler/testData/diagnostics/tests/smartCasts/smartCastOnAlienPropertyFromInvisibleClass.fir.kt

@@ -1,3 +1,4 @@
+// !LANGUAGE: -ProhibitSmartcastsOnPropertyFromAlienBaseClassInheritedInInvisibleClass
 // RENDER_DIAGNOSTICS_FULL_TEXT
 // MODULE: m1
 // FILE: A.kt
@@ -19,6 +20,6 @@ internal class Internal : Base("456")
 
 internal fun bar(i: Internal) {
     if (i.x is String) {
-        i.x.length
+        <!SMARTCAST_IMPOSSIBLE!>i.x<!>.length
     }
 }

compiler/testData/diagnostics/tests/smartCasts/smartCastOnAlienPropertyFromInvisibleClass.kt

@@ -1,3 +1,4 @@
+// !LANGUAGE: -ProhibitSmartcastsOnPropertyFromAlienBaseClassInheritedInInvisibleClass
 // RENDER_DIAGNOSTICS_FULL_TEXT
 // MODULE: m1
 // FILE: A.kt

compiler/testData/diagnostics/tests/smartCasts/smartCastOnAlienPropertyFromInvisibleClassForbidden.kt

@@ -0,0 +1,25 @@
+// FIR_IDENTICAL
+// !LANGUAGE: +ProhibitSmartcastsOnPropertyFromAlienBaseClassInheritedInInvisibleClass
+// MODULE: m1
+// FILE: A.kt
+
+open class Base(val x: Any)
+
+// MODULE: m2(m1)
+// FILE: B.kt
+
+private class Derived : Base("123") {
+    fun foo() {
+        if (x is String) {
+            <!SMARTCAST_IMPOSSIBLE!>x<!>.length
+        }
+    }
+}
+
+internal class Internal : Base("456")
+
+internal fun bar(i: Internal) {
+    if (i.x is String) {
+        <!SMARTCAST_IMPOSSIBLE!>i.x<!>.length
+    }
+}