JVM IR: fix isMarkedNullable for nullability-flexible types

Since nullability-flexible types in IR are represented by an annotation
on an IrSimpleType, not a special instance, the common implementation of
`KotlinTypeMarker.isMarkedNullable` in `TypeSystemContext` doesn't work.

This method is used for example to generate `typeOf` in JVM IR, in
`TypeSystemCommonBackendContext.generateTypeOf`, and this issue led to a
difference in behavior of `typeOf` for nullability-flexible types.

 #KT-44726 Fixed

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -35417,6 +35417,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                 runTest("compiler/testData/codegen/box/reflection/typeOf/classes.kt");
             }
 
+            @Test
+            @TestMetadata("flexibleType.kt")
+            public void testFlexibleType() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/typeOf/flexibleType.kt");
+            }
+
             @Test
             @TestMetadata("inlineClasses.kt")
             public void testInlineClasses() throws Exception {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt

@@ -77,6 +77,9 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
 
     override fun SimpleTypeMarker.isMarkedNullable(): Boolean = (this as IrSimpleType).hasQuestionMark
 
+    override fun KotlinTypeMarker.isMarkedNullable(): Boolean =
+        this is IrSimpleType && !isWithFlexibleNullability() && hasQuestionMark
+
     override fun SimpleTypeMarker.withNullability(nullable: Boolean): SimpleTypeMarker {
         val simpleType = this as IrSimpleType
         return if (simpleType.hasQuestionMark == nullable) simpleType

compiler/testData/codegen/box/reflection/typeOf/flexibleType.kt

@@ -0,0 +1,27 @@
+// !USE_EXPERIMENTAL: kotlin.ExperimentalStdlibApi
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
+// WITH_REFLECT
+// FILE: box.kt
+
+package test
+
+import kotlin.reflect.*
+
+fun box(): String {
+    val v = returnTypeOf { J.get() }.toString()
+    if (v != "J") return "Fail: $v"
+
+    return "OK"
+}
+
+inline fun <reified T: Any> returnTypeOf(block: () -> T) =
+    typeOf<T>()
+
+// FILE: J.java
+
+public class J {
+    public static J get() {
+        return null;
+    }
+}

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

@@ -35417,6 +35417,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/reflection/typeOf/classes.kt");
             }
 
+            @Test
+            @TestMetadata("flexibleType.kt")
+            public void testFlexibleType() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/typeOf/flexibleType.kt");
+            }
+
             @Test
             @TestMetadata("inlineClasses.kt")
             public void testInlineClasses() throws Exception {

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

@@ -35417,6 +35417,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/reflection/typeOf/classes.kt");
             }
 
+            @Test
+            @TestMetadata("flexibleType.kt")
+            public void testFlexibleType() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/typeOf/flexibleType.kt");
+            }
+
             @Test
             @TestMetadata("inlineClasses.kt")
             public void testInlineClasses() throws Exception {

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

@@ -28146,6 +28146,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/reflection/typeOf/classes.kt");
             }
 
+            @TestMetadata("flexibleType.kt")
+            public void testFlexibleType() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/typeOf/flexibleType.kt");
+            }
+
             @TestMetadata("inlineClasses.kt")
             public void testInlineClasses() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/typeOf/inlineClasses.kt");