Don't register safe cast type info for unstable values

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

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/smartcasts/DelegatingDataFlowInfo.kt

@@ -96,9 +96,12 @@ internal class DelegatingDataFlowInfo private constructor(
             nullability: Nullability,
             languageVersionSettings: LanguageVersionSettings,
             typeInfo: SetMultimap<DataFlowValue, KotlinType>? = null,
-            affectReceiver: Boolean = true
+            affectReceiver: Boolean = true,
+            recordUnstable: Boolean = true
     ): Boolean {
-        map.put(value, nullability)
+        if (value.isStable || recordUnstable) {
+            map.put(value, nullability)
+        }
 
         val identifierInfo = value.identifierInfo
         if (affectReceiver && !nullability.canBeNull() &&
@@ -108,7 +111,8 @@ internal class DelegatingDataFlowInfo private constructor(
                     val receiverType = identifierInfo.receiverType
                     if (identifierInfo.safe && receiverType != null) {
                         val receiverValue = DataFlowValue(identifierInfo.receiverInfo, receiverType)
-                        putNullabilityAndTypeInfo(map, receiverValue, nullability, languageVersionSettings, typeInfo)
+                        putNullabilityAndTypeInfo(map, receiverValue, nullability,
+                                                  languageVersionSettings, typeInfo, recordUnstable = recordUnstable)
                     }
                 }
                 is IdentifierInfo.SafeCast -> {
@@ -118,12 +122,16 @@ internal class DelegatingDataFlowInfo private constructor(
                         languageVersionSettings.supportsFeature(LanguageFeature.SafeCastCheckBoundSmartCasts)) {
 
                         val subjectValue = DataFlowValue(identifierInfo.subjectInfo, subjectType)
-                        putNullabilityAndTypeInfo(map, subjectValue, nullability, languageVersionSettings, typeInfo)
+                        putNullabilityAndTypeInfo(map, subjectValue, nullability,
-                        typeInfo?.put(subjectValue, targetType)
+                                                  languageVersionSettings, typeInfo, recordUnstable = false)
+                        if (subjectValue.isStable) {
+                            typeInfo?.put(subjectValue, targetType)
+                        }
                     }
                 }
                 is IdentifierInfo.Variable -> identifierInfo.bound?.let {
-                    putNullabilityAndTypeInfo(map, it, nullability, languageVersionSettings, typeInfo)
+                    putNullabilityAndTypeInfo(map, it, nullability,
+                                              languageVersionSettings, typeInfo, recordUnstable = recordUnstable)
                 }
             }
         }

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
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -20910,6 +20910,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("impossible.kt")
+                public void testImpossible() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/castchecks/impossible.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("insideCall.kt")
                 public void testInsideCall() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/castchecks/insideCall.kt");
@@ -20942,6 +20948,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/elvis/basicOn.kt");
                     doTest(fileName);
                 }
+
+                @TestMetadata("impossible.kt")
+                public void testImpossible() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/elvis/impossible.kt");
+                    doTest(fileName);
+                }
             }
 
             @TestMetadata("compiler/testData/diagnostics/tests/smartCasts/inference")

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -20910,6 +20910,12 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     doTest(fileName);
                 }
 
+                @TestMetadata("impossible.kt")
+                public void testImpossible() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/castchecks/impossible.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("insideCall.kt")
                 public void testInsideCall() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/castchecks/insideCall.kt");
@@ -20942,6 +20948,12 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/elvis/basicOn.kt");
                     doTest(fileName);
                 }
+
+                @TestMetadata("impossible.kt")
+                public void testImpossible() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/elvis/impossible.kt");
+                    doTest(fileName);
+                }
             }
 
             @TestMetadata("compiler/testData/diagnostics/tests/smartCasts/inference")