[FE 1.0] Properly handle intersection types in check if cast possible or not

^KT-47685 Fixed

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -3837,6 +3837,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/cast/kt15161.kt");
             }
 
+            @Test
+            @TestMetadata("kt47685.kt")
+            public void testKt47685() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/kt47685.kt");
+            }
+
             @Test
             @TestMetadata("kt614.kt")
             public void testKt614() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java

@@ -3837,6 +3837,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/cast/kt15161.kt");
             }
 
+            @Test
+            @TestMetadata("kt47685.kt")
+            public void testKt47685() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/kt47685.kt");
+            }
+
             @Test
             @TestMetadata("kt614.kt")
             public void testKt614() throws Exception {

compiler/frontend/src/org/jetbrains/kotlin/types/CastDiagnosticsUtil.kt

@@ -43,6 +43,10 @@ object CastDiagnosticsUtil {
         rhsType: KotlinType,
         platformToKotlinClassMapper: PlatformToKotlinClassMapper
     ): Boolean {
+        val typeConstructor = lhsType.constructor
+        if (typeConstructor is IntersectionTypeConstructor) {
+            return typeConstructor.supertypes.any { isCastPossible(it, rhsType, platformToKotlinClassMapper) }
+        }
         val rhsNullable = TypeUtils.isNullableType(rhsType)
         val lhsNullable = TypeUtils.isNullableType(lhsType)
         if (KotlinBuiltIns.isNothing(lhsType)) return true

compiler/testData/diagnostics/tests/cast/kt47685.fir.kt

@@ -0,0 +1,29 @@
+// KT-47685
+interface KtFunction {
+    fun foo() {}
+}
+
+abstract class ASTDelegatePsiElement {
+    fun bar() {}
+}
+
+class KtNamedFunction : ASTDelegatePsiElement(), KtFunction {
+    fun baz() {}
+}
+class KtFunctionLiteral : ASTDelegatePsiElement(), KtFunction
+
+fun test_1(namedFunction: KtNamedFunction, functionLiteral: KtFunctionLiteral, cond: Boolean) {
+    val function = when (cond) {
+        true -> namedFunction
+        false -> functionLiteral
+    }
+    // approve that foo has type (ASTDelegatePsiElement & KtFunction)
+    function.foo()
+    function.bar()
+
+    if (function is KtNamedFunction) {
+        function.baz()
+    }
+
+    val myNamedFunction = function as KtNamedFunction
+}

compiler/testData/diagnostics/tests/cast/kt47685.kt

@@ -0,0 +1,29 @@
+// KT-47685
+interface KtFunction {
+    fun foo() {}
+}
+
+abstract class ASTDelegatePsiElement {
+    fun bar() {}
+}
+
+class KtNamedFunction : ASTDelegatePsiElement(), KtFunction {
+    fun baz() {}
+}
+class KtFunctionLiteral : ASTDelegatePsiElement(), KtFunction
+
+fun test_1(namedFunction: KtNamedFunction, functionLiteral: KtFunctionLiteral, cond: Boolean) {
+    val function = when (cond) {
+        true -> namedFunction
+        false -> functionLiteral
+    }
+    // approve that foo has type (ASTDelegatePsiElement & KtFunction)
+    function.foo()
+    function.bar()
+
+    if (function is KtNamedFunction) {
+        <!DEBUG_INFO_SMARTCAST!>function<!>.baz()
+    }
+
+    val myNamedFunction = function as KtNamedFunction
+}

compiler/testData/diagnostics/tests/cast/kt47685.txt

@@ -0,0 +1,37 @@
+package
+
+public fun test_1(/*0*/ namedFunction: KtNamedFunction, /*1*/ functionLiteral: KtFunctionLiteral, /*2*/ cond: kotlin.Boolean): kotlin.Unit
+
+public abstract class ASTDelegatePsiElement {
+    public constructor ASTDelegatePsiElement()
+    public final fun bar(): kotlin.Unit
+    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 interface KtFunction {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class KtFunctionLiteral : ASTDelegatePsiElement, KtFunction {
+    public constructor KtFunctionLiteral()
+    public final override /*1*/ /*fake_override*/ fun bar(): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun foo(): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class KtNamedFunction : ASTDelegatePsiElement, KtFunction {
+    public constructor KtNamedFunction()
+    public final override /*1*/ /*fake_override*/ fun bar(): kotlin.Unit
+    public final fun baz(): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun foo(): kotlin.Unit
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -3843,6 +3843,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/cast/kt15161.kt");
             }
 
+            @Test
+            @TestMetadata("kt47685.kt")
+            public void testKt47685() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/kt47685.kt");
+            }
+
             @Test
             @TestMetadata("kt614.kt")
             public void testKt614() throws Exception {

idea/idea-frontend-fir/idea-fir-low-level-api/tests/org/jetbrains/kotlin/idea/fir/low/level/api/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -3837,6 +3837,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/cast/kt15161.kt");
             }
 
+            @Test
+            @TestMetadata("kt47685.kt")
+            public void testKt47685() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/cast/kt47685.kt");
+            }
+
             @Test
             @TestMetadata("kt614.kt")
             public void testKt614() throws Exception {