Update 'this' extension receiver when there's a smart cast

If 'this' (implicit or explicit) was used as an extension receiver,
and the corresponding call required a smart-cast,
this information was effectively lost in "old" resolution & inference,
but is required by "old" JVM BE to generate proper CHECKCASTs.

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CandidateResolver.kt

@@ -566,6 +566,9 @@ class CandidateResolver(
                 if (isDispatchReceiver) {
                     candidateCall.setSmartCastDispatchReceiverType(smartCastResult.resultType)
                 }
+                else {
+                    candidateCall.updateExtensionReceiverWithSmartCastIfNeeded(smartCastResult.resultType)
+                }
                 if (!smartCastResult.isCorrect) {
                     // Error about unstable smart cast reported within checkAndRecordPossibleCast
                     return UNSTABLE_SMARTCAST_FOR_RECEIVER_ERROR

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/MutableResolvedCall.java

@@ -67,4 +67,6 @@ public interface MutableResolvedCall<D extends CallableDescriptor> extends Resol
     boolean hasInferredReturnType();
 
     void setSmartCastDispatchReceiverType(@NotNull KotlinType smartCastDispatchReceiverType);
+
+    void updateExtensionReceiverWithSmartCastIfNeeded(@NotNull KotlinType smartCastExtensionReceiverType);
 }

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/model/ResolvedCallImpl.java

@@ -33,6 +33,8 @@ import org.jetbrains.kotlin.resolve.calls.results.ResolutionStatus;
 import org.jetbrains.kotlin.resolve.calls.tasks.ExplicitReceiverKind;
 import org.jetbrains.kotlin.resolve.calls.tasks.ResolutionCandidate;
 import org.jetbrains.kotlin.resolve.calls.tasks.TracingStrategy;
+import org.jetbrains.kotlin.resolve.scopes.receivers.CastImplicitClassReceiver;
+import org.jetbrains.kotlin.resolve.scopes.receivers.ImplicitClassReceiver;
 import org.jetbrains.kotlin.resolve.scopes.receivers.ReceiverValue;
 import org.jetbrains.kotlin.types.KotlinType;
 import org.jetbrains.kotlin.types.TypeProjection;
@@ -60,7 +62,7 @@ public class ResolvedCallImpl<D extends CallableDescriptor> implements MutableRe
     private final D candidateDescriptor;
     private D resultingDescriptor; // Probably substituted
     private final ReceiverValue dispatchReceiver; // receiver object of a method
-    private final ReceiverValue extensionReceiver; // receiver of an extension function
+    private ReceiverValue extensionReceiver; // receiver of an extension function
     private final ExplicitReceiverKind explicitReceiverKind;
     private final TypeSubstitutor knownTypeParametersSubstitutor;
 
@@ -378,4 +380,14 @@ public class ResolvedCallImpl<D extends CallableDescriptor> implements MutableRe
     public KotlinType getSmartCastDispatchReceiverType() {
         return smartCastDispatchReceiverType;
     }
+
+    @Override
+    public void updateExtensionReceiverWithSmartCastIfNeeded(@NotNull KotlinType smartCastExtensionReceiverType) {
+        if (extensionReceiver instanceof ImplicitClassReceiver) {
+            extensionReceiver = new CastImplicitClassReceiver(
+                    ((ImplicitClassReceiver) extensionReceiver).getClassDescriptor(),
+                    smartCastExtensionReceiverType
+            );
+        }
+    }
 }

compiler/testData/codegen/box/smartCasts/kt19058.kt

@@ -0,0 +1,19 @@
+// TARGET_BACKEND: JVM
+// FILE: Test.kt
+open class KFoo {
+    fun foo(): String {
+        if (this is KFooBar) return bar
+        throw AssertionError()
+    }
+}
+
+class KFooBar : KFoo(), JBar
+
+fun box(): String = KFooBar().foo()
+
+// FILE: JBar.java
+public interface JBar {
+    default String getBar() {
+        return "OK";
+    }
+}

compiler/testData/codegen/box/smartCasts/kt19100.kt

@@ -0,0 +1,12 @@
+open class KFoo {
+    fun foo(): String {
+        if (this is KFooQux) return qux
+        throw AssertionError()
+    }
+}
+
+class KFooQux : KFoo()
+
+val KFooQux.qux get() = "OK"
+
+fun box() = KFooQux().foo()

compiler/tests-ir-jvm/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -17600,6 +17600,18 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             doTest(fileName);
         }
 
+        @TestMetadata("kt19058.kt")
+        public void testKt19058() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19058.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt19100.kt")
+        public void testKt19100() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19100.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lambdaArgumentWithoutType.kt")
         public void testLambdaArgumentWithoutType() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/lambdaArgumentWithoutType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -17600,6 +17600,18 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("kt19058.kt")
+        public void testKt19058() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19058.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt19100.kt")
+        public void testKt19100() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19100.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lambdaArgumentWithoutType.kt")
         public void testLambdaArgumentWithoutType() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/lambdaArgumentWithoutType.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -17600,6 +17600,18 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             doTest(fileName);
         }
 
+        @TestMetadata("kt19058.kt")
+        public void testKt19058() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19058.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt19100.kt")
+        public void testKt19100() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19100.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lambdaArgumentWithoutType.kt")
         public void testLambdaArgumentWithoutType() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/lambdaArgumentWithoutType.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -21506,6 +21506,12 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             doTest(fileName);
         }
 
+        @TestMetadata("kt19100.kt")
+        public void testKt19100() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19100.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lambdaArgumentWithoutType.kt")
         public void testLambdaArgumentWithoutType() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/lambdaArgumentWithoutType.kt");