Don't register safe cast type info for unstable values

Important: to be removed in 1.3
So #KT-20752 Fixed

compiler/testData/diagnostics/tests/smartCasts/castchecks/impossible.kt

@@ -0,0 +1,25 @@
+// !LANGUAGE: +SafeCastCheckBoundSmartCasts
+// See KT-20752
+
+class Unstable {
+    val first: String? get() = null
+}
+
+class StringList {
+    fun remove(s: String) = s
+}
+
+fun StringList.remove(s: String?) = s ?: ""
+
+fun foo(list: StringList, arg: Unstable) {
+    list.remove(arg.first)
+    if (arg.first <!USELESS_CAST!>as? String<!> != null) {
+        // Ideally should have smart cast impossible here
+        list.remove(arg.first)
+    }
+    val s = arg.first <!USELESS_CAST!>as? String<!>
+    if (s != null) {
+        // Ideally should have smart cast impossible here
+        list.remove(arg.first)
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/castchecks/impossible.txt

@@ -0,0 +1,20 @@
+package
+
+public fun foo(/*0*/ list: StringList, /*1*/ arg: Unstable): kotlin.Unit
+public fun StringList.remove(/*0*/ s: kotlin.String?): kotlin.String
+
+public final class StringList {
+    public constructor StringList()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun remove(/*0*/ s: kotlin.String): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Unstable {
+    public constructor Unstable()
+    public final val first: kotlin.String?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/smartCasts/elvis/impossible.kt

@@ -0,0 +1,40 @@
+// !LANGUAGE: +BooleanElvisBoundSmartCasts
+// See KT-20752
+
+class Unstable {
+    val first: String? get() = null
+}
+
+class StringList {
+    fun remove(s: String) = s
+}
+
+fun StringList.remove(s: String?) = s ?: ""
+
+fun String.isEmpty() = this == ""
+
+fun foo(list: StringList, arg: Unstable) {
+    list.remove(arg.first)
+    if (arg.first?.isEmpty() ?: false) {
+        // Ideally should have smart cast impossible here
+        list.remove(<!SMARTCAST_IMPOSSIBLE!>arg.first<!>)
+    }
+}
+
+class UnstableBoolean {
+    val first: Boolean? get() = null
+}
+
+class BooleanList {
+    fun remove(b: Boolean) = b
+}
+
+fun BooleanList.remove(b: Boolean?) = b ?: false
+
+fun bar(list: BooleanList, arg: UnstableBoolean) {
+    list.remove(arg.first)
+    if (arg.first ?: false) {
+        // Ideally should have smart cast impossible here
+        list.remove(<!SMARTCAST_IMPOSSIBLE!>arg.first<!>)
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/elvis/impossible.txt

@@ -0,0 +1,39 @@
+package
+
+public fun bar(/*0*/ list: BooleanList, /*1*/ arg: UnstableBoolean): kotlin.Unit
+public fun foo(/*0*/ list: StringList, /*1*/ arg: Unstable): kotlin.Unit
+public fun kotlin.String.isEmpty(): kotlin.Boolean
+public fun BooleanList.remove(/*0*/ b: kotlin.Boolean?): kotlin.Boolean
+public fun StringList.remove(/*0*/ s: kotlin.String?): kotlin.String
+
+public final class BooleanList {
+    public constructor BooleanList()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun remove(/*0*/ b: kotlin.Boolean): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class StringList {
+    public constructor StringList()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun remove(/*0*/ s: kotlin.String): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Unstable {
+    public constructor Unstable()
+    public final val first: kotlin.String?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class UnstableBoolean {
+    public constructor UnstableBoolean()
+    public final val first: kotlin.Boolean?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}