More precise type handling for equality #KT-2311 Fixed

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

@@ -19,8 +19,10 @@ package org.jetbrains.kotlin.resolve.calls.smartcasts;
 import com.google.common.collect.*;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns;
 import org.jetbrains.kotlin.types.KotlinType;
 import org.jetbrains.kotlin.types.TypeUtils;
+import org.jetbrains.kotlin.types.typeUtil.TypeUtilsKt;
 
 import java.util.HashSet;
 import java.util.LinkedHashSet;
@@ -216,6 +218,15 @@ import static org.jetbrains.kotlin.resolve.calls.smartcasts.Nullability.NOT_NULL
         SetMultimap<DataFlowValue, KotlinType> newTypeInfo = newTypeInfo();
         newTypeInfo.putAll(a, collectTypesFromMeAndParents(b));
         newTypeInfo.putAll(b, collectTypesFromMeAndParents(a));
+        if (!a.getType().equals(b.getType())) {
+            // To avoid smart casts to Nothing or Nothing? and recording base types of own type
+            if (!KotlinBuiltIns.isNothingOrNullableNothing(b.getType()) && !TypeUtilsKt.isSubtypeOf(a.getType(), b.getType())) {
+                newTypeInfo.put(a, b.getType());
+            }
+            if (!KotlinBuiltIns.isNothingOrNullableNothing(a.getType()) && !TypeUtilsKt.isSubtypeOf(b.getType(), a.getType())) {
+                newTypeInfo.put(b, a.getType());
+            }
+        }
         changed |= !newTypeInfo.isEmpty();
 
         return !changed

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

@@ -0,0 +1,17 @@
+open class VeryBase
+
+open class Base : VeryBase()
+
+class Derived : Base() {
+    fun original(): VeryBase = this
+}
+
+class Another : Base()
+
+fun foo(d: Derived, a: Another?): Base? {
+    // d is compared with d.original(): VeryBase but should retain its own type
+    if (d.original() != d) return null
+    // ad should be of type Base, not VeryBase
+    val ad = a ?: d
+    return ad
+}

compiler/testData/diagnostics/tests/smartCasts/typeDegradation.txt

@@ -0,0 +1,32 @@
+package
+
+public fun foo(/*0*/ d: Derived, /*1*/ a: Another?): Base?
+
+public final class Another : Base {
+    public constructor Another()
+    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 open class Base : VeryBase {
+    public constructor Base()
+    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 Derived : Base {
+    public constructor Derived()
+    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 original(): VeryBase
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public open class VeryBase {
+    public constructor VeryBase()
+    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/typeInComparison.kt

@@ -0,0 +1,8 @@
+fun foo(): Int {
+    val x: Any? = null
+    val y = 2
+    if (x == y) {
+        return <!DEBUG_INFO_SMARTCAST!>x<!> + y
+    }
+    return y
+}

compiler/testData/diagnostics/tests/smartCasts/typeInComparison.txt

@@ -0,0 +1,3 @@
+package
+
+public fun foo(): kotlin.Int

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

@@ -14643,6 +14643,18 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("typeDegradation.kt")
+            public void testTypeDegradation() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/typeDegradation.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("typeInComparison.kt")
+            public void testTypeInComparison() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/typeInComparison.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("varChangedInInitializer.kt")
             public void testVarChangedInInitializer() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/varChangedInInitializer.kt");