JVM_IR: flexible nullability as annotation

We carry information about flexible nullability of IrType as an
annotation, so there is no need to look at its underlying KotlinType.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmGeneratorExtensions.kt

@@ -5,14 +5,22 @@
 
 package org.jetbrains.kotlin.backend.jvm
 
+import org.jetbrains.kotlin.backend.common.ir.createImplicitParameterDeclarationWithWrappedDescriptor
 import org.jetbrains.kotlin.backend.common.ir.createParameterDeclarations
+import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.codegen.SamType
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.annotations.FilteredAnnotations
+import org.jetbrains.kotlin.ir.builders.declarations.addConstructor
 import org.jetbrains.kotlin.ir.builders.declarations.buildClass
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrFactory
+import org.jetbrains.kotlin.ir.declarations.impl.IrExternalPackageFragmentImpl
+import org.jetbrains.kotlin.ir.declarations.impl.IrFactoryImpl
+import org.jetbrains.kotlin.ir.symbols.impl.DescriptorlessExternalPackageFragmentSymbol
+import org.jetbrains.kotlin.ir.util.constructors
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames
 import org.jetbrains.kotlin.load.java.descriptors.JavaCallableMemberDescriptor
 import org.jetbrains.kotlin.load.java.descriptors.JavaClassDescriptor
@@ -20,6 +28,7 @@ import org.jetbrains.kotlin.load.java.descriptors.getParentJavaStaticClassScope
 import org.jetbrains.kotlin.load.java.sam.JavaSingleAbstractMethodUtils
 import org.jetbrains.kotlin.load.java.typeEnhancement.hasEnhancedNullability
 import org.jetbrains.kotlin.load.kotlin.JvmPackagePartSource
+import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi2ir.generators.GeneratorExtensions
 import org.jetbrains.kotlin.resolve.jvm.JvmClassName
 import org.jetbrains.kotlin.resolve.jvm.annotations.hasJvmFieldAnnotation
@@ -95,4 +104,25 @@ class JvmGeneratorExtensions(private val generateFacades: Boolean = true) : Gene
 
     override fun getParentClassStaticScope(descriptor: ClassDescriptor): MemberScope? =
         descriptor.getParentJavaStaticClassScope()
+
+    private val annotationPackage =
+        IrExternalPackageFragmentImpl(DescriptorlessExternalPackageFragmentSymbol(), KotlinBuiltIns.ANNOTATION_PACKAGE_FQ_NAME)
+
+    private val flexibleNullabilityAnnotationClass = IrFactoryImpl.buildClass {
+        kind = ClassKind.ANNOTATION_CLASS
+        name = FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME.shortName()
+    }.apply {
+        createImplicitParameterDeclarationWithWrappedDescriptor()
+        parent = annotationPackage
+        addConstructor {
+            isPrimary = true
+        }
+    }
+
+    override val flexibleNullabilityAnnotationConstructor: IrConstructor? = flexibleNullabilityAnnotationClass.constructors.single()
+
+    companion object {
+        val FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME =
+            KotlinBuiltIns.ANNOTATION_PACKAGE_FQ_NAME.child(Name.identifier("FlexibleNullability"))
+    }
 }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/AnnotationCodegen.kt

@@ -20,6 +20,7 @@ import org.jetbrains.annotations.NotNull
 import org.jetbrains.annotations.Nullable
 import org.jetbrains.kotlin.backend.common.ir.ir2string
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.backend.jvm.JvmGeneratorExtensions
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.codegen.AsmUtil
@@ -39,7 +40,6 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.checkers.ExpectedActualDeclarationChecker
 import org.jetbrains.kotlin.types.TypeSystemCommonBackendContext
-import org.jetbrains.kotlin.types.isNullabilityFlexible
 import org.jetbrains.kotlin.types.model.KotlinTypeMarker
 import org.jetbrains.org.objectweb.asm.AnnotationVisitor
 import org.jetbrains.org.objectweb.asm.Type
@@ -158,7 +158,7 @@ abstract class AnnotationCodegen(
         }
 
         // A flexible type whose lower bound in not-null and upper bound is nullable, should not be annotated
-        if (type.toKotlinType().isNullabilityFlexible()) {
+        if (type.isNullabilityFlexible()) {
             return
         }
 
@@ -185,6 +185,9 @@ abstract class AnnotationCodegen(
         val retentionPolicy = getRetentionPolicy(annotationClass)
         if (retentionPolicy == RetentionPolicy.SOURCE) return null
 
+        // FlexibleNullability is an internal annotation, used only inside the compiler
+        if (annotationClass.fqNameWhenAvailable == JvmGeneratorExtensions.FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME) return null
+
         // We do not generate annotations whose classes are optional (annotated with `@OptionalExpectation`) because if an annotation entry
         // is resolved to the expected declaration, this means that annotation has no actual class, and thus should not be generated.
         // (Otherwise we would've resolved the entry to the actual annotation class.)
@@ -376,6 +379,9 @@ private fun IrClass.getAnnotationRetention(): KotlinRetention? {
     return KotlinRetention.valueOf(retentionArgumentValue.name.asString())
 }
 
+private fun IrType.isNullabilityFlexible(): Boolean =
+    hasAnnotation(JvmGeneratorExtensions.FLEXIBLE_NULLABILITY_ANNOTATION_FQ_NAME)
+
 // To be generalized to IrMemberAccessExpression as soon as properties get symbols.
 private fun IrConstructorCall.getValueArgument(name: Name): IrExpression? {
     val index = symbol.owner.valueParameters.find { it.name == name }?.index ?: return null

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/StubGeneratorExtensions.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.ir.util
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrFactory
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
@@ -31,6 +32,9 @@ open class StubGeneratorExtensions {
         companion object Instance : EnhancedNullability()
     }
 
+    open val flexibleNullabilityAnnotationConstructor: IrConstructor?
+        get() = null
+
     companion object {
         @JvmField
         val EMPTY = StubGeneratorExtensions()

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/TypeTranslator.kt

@@ -14,8 +14,10 @@ import org.jetbrains.kotlin.descriptors.TypeAliasDescriptor
 import org.jetbrains.kotlin.descriptors.TypeParameterDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
+import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.declarations.IrTypeParametersContainer
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
+import org.jetbrains.kotlin.ir.expressions.impl.IrConstructorCallImpl
 import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.IrTypeAbbreviation
@@ -127,6 +129,15 @@ class TypeTranslator(
                 else ->
                     throw AssertionError("Unexpected type descriptor $ktTypeDescriptor :: ${ktTypeDescriptor::class}")
             }
+            if (flexibleApproximatedType.isNullabilityFlexible())
+                extensions.flexibleNullabilityAnnotationConstructor?.let { flexibleTypeAnnotationConstructor ->
+                    annotations += IrConstructorCallImpl(
+                        UNDEFINED_OFFSET, UNDEFINED_OFFSET,
+                        flexibleTypeAnnotationConstructor.constructedClassType,
+                        flexibleTypeAnnotationConstructor.symbol,
+                        0, 0, 0
+                    )
+                }
         }.buildTypeProjection()
     }
 

core/descriptors/src/org/jetbrains/kotlin/builtins/KotlinBuiltIns.java

@@ -43,7 +43,7 @@ import static org.jetbrains.kotlin.utils.CollectionsKt.newHashSetWithExpectedSiz
 public abstract class KotlinBuiltIns {
     public static final Name BUILT_INS_PACKAGE_NAME = Name.identifier("kotlin");
     public static final FqName BUILT_INS_PACKAGE_FQ_NAME = FqName.topLevel(BUILT_INS_PACKAGE_NAME);
-    private static final FqName ANNOTATION_PACKAGE_FQ_NAME = BUILT_INS_PACKAGE_FQ_NAME.child(Name.identifier("annotation"));
+    public static final FqName ANNOTATION_PACKAGE_FQ_NAME = BUILT_INS_PACKAGE_FQ_NAME.child(Name.identifier("annotation"));
     public static final FqName COLLECTIONS_PACKAGE_FQ_NAME = BUILT_INS_PACKAGE_FQ_NAME.child(Name.identifier("collections"));
     public static final FqName RANGES_PACKAGE_FQ_NAME = BUILT_INS_PACKAGE_FQ_NAME.child(Name.identifier("ranges"));
     public static final FqName TEXT_PACKAGE_FQ_NAME = BUILT_INS_PACKAGE_FQ_NAME.child(Name.identifier("text"));