Accurate representation of smart casts on complex expressions

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

@@ -0,0 +1,20 @@
+// Smart casts on complex expressions
+fun baz(s: String?): Int {
+    if (s == null) return 0
+    return <!DEBUG_INFO_SMARTCAST!>when(<!DEBUG_INFO_SMARTCAST!>s<!>) {
+        "abc" -> s
+        else -> "xyz"
+    }<!>.length
+}
+
+var ss: String? = null
+
+fun bar(): Int {
+    if (ss == null) return 0
+    // ss cannot be smart casted, so an error here
+    return when(ss) {
+        "abc" -> ss
+        else -> "xyz"
+    }<!UNSAFE_CALL!>.<!>length
+}
+