More correct handling of possible type set during assignment #KT-8229 Fixed

compiler/testData/diagnostics/tests/smartCasts/variables/assignmentConversion.kt

@@ -0,0 +1,35 @@
+fun foo(x: String) = x
+
+fun test1() {
+    var c: Any? = "XXX"
+    if (c !is String) return
+
+    val newC: String? = "YYY"
+    if (newC != null) {
+        c = newC
+    }
+    foo(<!DEBUG_INFO_SMARTCAST!>c<!>)
+}
+
+fun test2() {
+    var c: Any? = "XXX"
+    if (c !is String) return
+
+    val newC: String? = "YYY"
+    if (newC is String) {
+        c = newC
+    }
+    foo(<!DEBUG_INFO_SMARTCAST!>c<!>)
+}
+
+fun test3() {
+    var c: Any? = "XXX"
+    if (c !is String) return
+
+    val newC: String? = "YYY"
+    if (newC == null) return
+    c = newC
+
+    foo(<!DEBUG_INFO_SMARTCAST!>c<!>)
+}
+

compiler/testData/diagnostics/tests/smartCasts/variables/assignmentConversion.txt

@@ -0,0 +1,6 @@
+package
+
+public fun foo(/*0*/ x: kotlin.String): kotlin.String
+public fun test1(): kotlin.Unit
+public fun test2(): kotlin.Unit
+public fun test3(): kotlin.Unit