[K/N] keep internal members in header klibs

This is also the behavior of jvm-abi-gen and desired to support
friend modules.
^KT-65442

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/serializationUtil.kt

@@ -6,12 +6,10 @@
 package org.jetbrains.kotlin.fir.serialization
 
 import org.jetbrains.kotlin.builtins.functions.FunctionTypeKind
+import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.FirAnnotationContainer
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.declarations.FirClass
-import org.jetbrains.kotlin.fir.declarations.FirDeclaration
-import org.jetbrains.kotlin.fir.declarations.FirMemberDeclaration
-import org.jetbrains.kotlin.fir.declarations.nonSourceAnnotations
+import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.isExpect
 import org.jetbrains.kotlin.fir.declarations.utils.isInterface
 import org.jetbrains.kotlin.fir.declarations.utils.visibility
@@ -60,9 +58,11 @@ fun FirMemberDeclaration.isNotExpectOrShouldBeSerialized(actualizedExpectDeclara
 }
 
 fun FirMemberDeclaration.isNotPrivateOrShouldBeSerialized(produceHeaderKlib: Boolean): Boolean {
-    return !produceHeaderKlib || visibility.isPublicAPI
+    return !produceHeaderKlib || visibility.isPublicAPI || visibility == Visibilities.Internal
             // Always keep private interfaces as they can be part of public type hierarchies.
-            || (this as? FirClass)?.isInterface == true
+            // We also keep private type aliases as they leak into public signatures (KT-17229).
+            // TODO: stop preserving private type aliases once KT-17229 is fixed.
+            || (this as? FirClass)?.isInterface == true || this is FirTypeAlias
 }
 
 fun <

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.backend.common.serialization.encodings.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrSimpleTypeNullability
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.DescriptorVisibilities.INTERNAL
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrFileEntry
 import org.jetbrains.kotlin.ir.declarations.*
@@ -1107,9 +1108,9 @@ open class IrFileSerializer(
             .setBase(serializeIrDeclarationBase(property, PropertyFlags.encode(property)))
             .setName(serializeName(property.name))
 
-        property.backingField?.let { proto.backingField = serializeIrField(it) }
-        property.getter?.let { proto.getter = serializeIrFunction(it) }
-        property.setter?.let { proto.setter = serializeIrFunction(it) }
+        property.backingField?.takeUnless { skipIfPrivate(it) }?.let { proto.backingField = serializeIrField(it) }
+        property.getter?.takeUnless { skipIfPrivate(it) }?.let { proto.getter = serializeIrFunction(it) }
+        property.setter?.takeUnless { skipIfPrivate(it) }?.let { proto.setter = serializeIrFunction(it) }
 
         return proto.build()
     }
@@ -1269,9 +1270,9 @@ open class IrFileSerializer(
     open fun backendSpecificMetadata(irFile: IrFile): FileBackendSpecificMetadata? = null
 
     private fun skipIfPrivate(declaration: IrDeclaration) =
-        skipPrivateApi && (declaration as? IrDeclarationWithVisibility)?.visibility?.isPublicAPI != true
-                // Always keep private interfaces as they can be part of public type hierarchies.
-                && (declaration as? IrClass)?.isInterface != true
+        skipPrivateApi && (declaration as? IrDeclarationWithVisibility)?.let { !it.visibility.isPublicAPI && it.visibility != INTERNAL } == true
+                // Always keep private interfaces and type aliases as they can be part of public type hierarchies.
+                && (declaration as? IrClass)?.isInterface != true && declaration !is IrTypeAlias
 
     open fun memberNeedsSerialization(member: IrDeclaration): Boolean {
         val parent = member.parent

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/metadata/KlibMetadataSerializer.kt

@@ -113,9 +113,10 @@ abstract class KlibMetadataSerializer(
 
     private fun Sequence<DeclarationDescriptor>.filterPrivate(): Sequence<DeclarationDescriptor> =
         if (produceHeaderKlib) {
-            // We keep all interfaces since publicly accessible classes can inherit from private interfaces.
             this.filter {
-                it is ClassDescriptor && it.kind.isInterface || it is DeclarationDescriptorWithVisibility && it.effectiveVisibility().publicApi
+                val isPublicOrInternal = it is DeclarationDescriptorWithVisibility
+                        && (it.visibility.isPublicAPI || it.visibility.delegate == Visibilities.Internal)
+                it is ClassDescriptor && it.kind.isInterface || isPublicOrInternal
             }
         } else this
 

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/metadata/KlibMetadataSerializerExtension.kt

@@ -42,7 +42,7 @@ class KlibMetadataSerializerExtension(
                         DescriptorUtils.getAllDescriptors(classDescriptor.defaultType.memberScope)
                             .filterIsInstance<CallableMemberDescriptor>()
                             .filter { it.kind != CallableMemberDescriptor.Kind.FAKE_OVERRIDE }
-                            .filter { it.visibility.isPublicAPI || classDescriptor.isInlineClass() }
+                            .filter { it.visibility.isPublicAPI || it.visibility.delegate == Visibilities.Internal || classDescriptor.isInlineClass() }
                     )
             }
         else super.customClassMembersProducer

native/native.tests/testData/klib/header-klibs/comparison/classPrivateMembers/sameAbi/A.kt

@@ -4,8 +4,8 @@ class A {
     val publicVal = 0
     fun publicMethod() = 0
 
-    internal val internalVal = 42
-    internal fun internalMethod() = 42
+    internal val internalVal = 0
+    internal fun internalMethod() = 0
 
     protected val protectedVal = 0
     protected fun protectedMethod() = 0

native/native.tests/testData/klib/header-klibs/comparison/privateInterface/base/test.kt

@@ -1,7 +1,7 @@
 package test
 
 private interface A {
-    fun foo() = 0
+    fun foo(): Int { if (true) return 1 else return 0 }
     fun bar(): String
 }
 

native/native.tests/testData/klib/header-klibs/comparison/privateInterface/sameAbi/test.kt

@@ -1,7 +1,7 @@
 package test
 
 private interface A {
-    fun foo() = 42
+    fun foo(): Int { if (true) return 0 else return 1 }
     fun bar(): String
 }
 

native/native.tests/testData/klib/header-klibs/comparison/syntheticAccessors/base/test.kt

@@ -4,4 +4,4 @@ private val x = 1
 
 object A { fun f() = x }
 
-val y = 2
+val y = (0..20).random()

native/native.tests/testData/klib/header-klibs/comparison/syntheticAccessors/sameAbi/test.kt

@@ -2,4 +2,4 @@ package test
 
 object A { fun f() = 1 }
 
-val y = 2
+val y = (30..50).random()

native/native.tests/testData/klib/header-klibs/comparison/topLevelPrivateMembers/base/utils.kt

@@ -1,12 +1,7 @@
 package test
 
-val publicVal = 0
-const val publicConst = 0
-fun publicFun() = 0
-
-internal val internalVal = 0
-internal const val internalConst = 0
-internal fun internalFun() = 0
+val publicVal = (0..10).random()
+fun publicFun() = (0..10).random()
 
 private val privateVal = 0
 private const val privateConst = 0

native/native.tests/testData/klib/header-klibs/comparison/topLevelPrivateMembers/sameAbi/utils.kt

@@ -1,9 +1,4 @@
 package test
 
-val publicVal = 0
-const val publicConst = 0
-fun publicFun() = 0
-
-internal val internalVal = 0
-internal const val internalConst = 0
-internal fun internalFun() = 0
+val publicVal = (0..20).random()
+fun publicFun() = (0..20).random()