Data flow values for Elvis / parenthesized expressions, smart casts on them

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

@@ -0,0 +1,37 @@
+fun foo(s: Any?): String {
+    val t = when {
+        // To resolve: String U Nothing? = String?
+        s is String -> s
+        else -> null
+    } ?: ""
+    // Ideally we should have smart cast to String here
+    return <!TYPE_MISMATCH!>t<!>
+}
+
+fun bar(s: Any?): String {
+    // To resolve: String U Nothing? = String?
+    val t = (if (s == null) {
+        null
+    }
+    else {
+        val u: Any? = null
+        if (u !is String) return ""
+        u
+    }) ?: "xyz"
+    // Ideally we should have smart cast to String here
+    return <!TYPE_MISMATCH!>t<!>
+}
+
+fun baz(s: String?, r: String?): String {
+    val t = r ?: when {
+        s != null -> s
+        else -> ""
+    }
+    return <!DEBUG_INFO_SMARTCAST!>t<!>
+}
+
+fun withNull(s: String?): String {
+    val t = s ?: null
+    // Error: nullable
+    return <!TYPE_MISMATCH!>t<!>
+}