[FIR] fix subtyping for nullable captured types.

The issue is the type checker doesn't consider P? a subtype of
CapturedType<in P>?, whereas P a subtype of CapturedType<in P>?. In
AbstractTypeCheckerContext::checkSubtypeForSpecialCases, it checks if
P? is a subtype of the lower type of the captured type, which is
P, and returns false.

This fix uses nullable version of the lower type when the captured
type is marked nullable. To check if P? is a subtype of Captured<in
P>?, we check the LHS, P?, against the nullable lower type of RHS,
P?.

^KT-42825 Fixed

compiler/fir/fir2ir/tests/org/jetbrains/kotlin/codegen/ir/FirBlackBoxCodegenTestGenerated.java

@@ -16041,6 +16041,11 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                 runTest("compiler/testData/codegen/box/javaInterop/generics/javaNestedSamInterface.kt");
             }
 
+            @TestMetadata("kt42825.kt")
+            public void testKt42825() throws Exception {
+                runTest("compiler/testData/codegen/box/javaInterop/generics/kt42825.kt");
+            }
+
             @TestMetadata("propertyVarianceConflict.kt")
             public void testPropertyVarianceConflict() throws Exception {
                 runTest("compiler/testData/codegen/box/javaInterop/generics/propertyVarianceConflict.kt");

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

@@ -39,6 +39,13 @@ open class IrTypeCheckerContext(override val irBuiltIns: IrBuiltIns) : IrTypeSys
     ): AbstractTypeCheckerContext = IrTypeCheckerContext(irBuiltIns)
 
     override fun KotlinTypeMarker.isUninferredParameter(): Boolean = false
+    override fun KotlinTypeMarker.withNullability(nullable: Boolean): KotlinTypeMarker {
+        if (this.isSimpleType()) {
+            return this.asSimpleType()!!.withNullability(nullable)
+        } else {
+            error("withNullability for non-simple types is not supported in IR")
+        }
+    }
 
     override fun captureFromExpression(type: KotlinTypeMarker): KotlinTypeMarker? =
         error("Captured type is unsupported in IR")

compiler/testData/codegen/box/javaInterop/generics/kt42825.kt

@@ -0,0 +1,23 @@
+// FILE: Processor.java
+
+public interface Processor<T> {
+    boolean process(T t);
+}
+
+// FILE: test.kt
+
+interface PsiModifierListOwner
+interface KtClassOrObject {
+    fun toLightClass(): PsiModifierListOwner?
+}
+
+fun execute(declaration: Any, consumer: Processor<in PsiModifierListOwner>) {
+    when (declaration) {
+        is KtClassOrObject -> {
+            val lightClass = declaration.toLightClass()
+            consumer.process(lightClass)
+        }
+    }
+}
+
+fun box(): String = "OK"

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

@@ -17441,6 +17441,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/javaInterop/generics/javaNestedSamInterface.kt");
             }
 
+            @TestMetadata("kt42825.kt")
+            public void testKt42825() throws Exception {
+                runTest("compiler/testData/codegen/box/javaInterop/generics/kt42825.kt");
+            }
+
             @TestMetadata("propertyVarianceConflict.kt")
             public void testPropertyVarianceConflict() throws Exception {
                 runTest("compiler/testData/codegen/box/javaInterop/generics/propertyVarianceConflict.kt");

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

@@ -17441,6 +17441,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/javaInterop/generics/javaNestedSamInterface.kt");
             }
 
+            @TestMetadata("kt42825.kt")
+            public void testKt42825() throws Exception {
+                runTest("compiler/testData/codegen/box/javaInterop/generics/kt42825.kt");
+            }
+
             @TestMetadata("propertyVarianceConflict.kt")
             public void testPropertyVarianceConflict() throws Exception {
                 runTest("compiler/testData/codegen/box/javaInterop/generics/propertyVarianceConflict.kt");

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

@@ -16041,6 +16041,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/javaInterop/generics/javaNestedSamInterface.kt");
             }
 
+            @TestMetadata("kt42825.kt")
+            public void testKt42825() throws Exception {
+                runTest("compiler/testData/codegen/box/javaInterop/generics/kt42825.kt");
+            }
+
             @TestMetadata("propertyVarianceConflict.kt")
             public void testPropertyVarianceConflict() throws Exception {
                 runTest("compiler/testData/codegen/box/javaInterop/generics/propertyVarianceConflict.kt");