Support for split-packages in Kotlin Native

See JetBrains/kotlin-native#2034

konan/library-reader/src/org/jetbrains/kotlin/konan/library/KonanLibrary.kt

@@ -44,7 +44,8 @@ interface KonanLibrary {
 
     val dataFlowGraph: ByteArray?
     val moduleHeaderData: KonanProtoBuf.LinkDataLibrary
-    fun packageMetadata(packageFqName: String): KonanProtoBuf.LinkDataPackageFragment
+    fun packageMetadataPartCount(fqName: String): Int
+    fun packageMetadata(packageFqName: String, partIndex: Int): KonanProtoBuf.LinkDataPackageFragment
 }
 
 val KonanLibrary.uniqueName

konan/library-reader/src/org/jetbrains/kotlin/konan/library/KonanLibraryLayout.kt

@@ -35,11 +35,11 @@ interface KonanLibraryLayout {
     val moduleHeaderFile get() = File(linkdataDir, KLIB_MODULE_METADATA_FILE_NAME)
     val dataFlowGraphFile get() = File(linkdataDir, "module_data_flow_graph")
 
-    fun packageFragmentFile(packageFqName: String) =
-        File(
-            linkdataDir,
-            if (packageFqName == "") "root_package.$KLIB_METADATA_FILE_EXTENSION" else "package_$packageFqName.$KLIB_METADATA_FILE_EXTENSION"
-        )
+    fun packageFragmentsDir(packageFqName: String) =
+        File(linkdataDir, if (packageFqName == "") "root_package" else "package_$packageFqName")
+
+    fun packageFragmentFile(packageFqName: String, partIndex: Int) =
+        File(packageFragmentsDir(packageFqName), "$partIndex$KLIB_METADATA_FILE_EXTENSION_WITH_DOT")
 }
 
 sealed class KonanLibrarySource {

konan/library-reader/src/org/jetbrains/kotlin/konan/library/KonanMetadataReader.kt

@@ -9,5 +9,9 @@ import org.jetbrains.kotlin.metadata.konan.KonanProtoBuf
 
 interface MetadataReader {
     fun loadSerializedModule(libraryLayout: KonanLibraryLayout): KonanProtoBuf.LinkDataLibrary
-    fun loadSerializedPackageFragment(libraryLayout: KonanLibraryLayout, packageFqName: String): KonanProtoBuf.LinkDataPackageFragment
+    fun loadSerializedPackageFragment(
+        libraryLayout: KonanLibraryLayout,
+        packageFqName: String,
+        partIndex: Int
+    ): KonanProtoBuf.LinkDataPackageFragment
 }

konan/library-reader/src/org/jetbrains/kotlin/konan/library/impl/DefaultMetadataReaderImpl.kt

@@ -18,7 +18,10 @@ object DefaultMetadataReaderImpl : MetadataReader {
 
     override fun loadSerializedPackageFragment(
         libraryLayout: KonanLibraryLayout,
-        packageFqName: String
+        packageFqName: String,
+        partIndex: Int
     ): KonanProtoBuf.LinkDataPackageFragment =
-        parsePackageFragment(libraryLayout.packageFragmentFile(packageFqName).readBytes())
+        parsePackageFragment(
+            libraryLayout.packageFragmentFile(packageFqName, partIndex).readBytes()
+        )
 }

konan/library-reader/src/org/jetbrains/kotlin/konan/library/impl/KonanLibraryImpl.kt

@@ -6,10 +6,7 @@
 package org.jetbrains.kotlin.konan.library.impl
 
 import org.jetbrains.kotlin.konan.file.File
-import org.jetbrains.kotlin.konan.library.KLIB_PROPERTY_ABI_VERSION
-import org.jetbrains.kotlin.konan.library.KLIB_PROPERTY_LINKED_OPTS
-import org.jetbrains.kotlin.konan.library.KonanLibrary
-import org.jetbrains.kotlin.konan.library.MetadataReader
+import org.jetbrains.kotlin.konan.library.*
 import org.jetbrains.kotlin.konan.properties.Properties
 import org.jetbrains.kotlin.konan.properties.loadProperties
 import org.jetbrains.kotlin.konan.properties.propertyList
@@ -65,7 +62,10 @@ internal class KonanLibraryImpl(
 
     override val moduleHeaderData: KonanProtoBuf.LinkDataLibrary by lazy { layout.inPlace { metadataReader.loadSerializedModule(it) } }
 
-    override fun packageMetadata(packageFqName: String) = layout.inPlace { metadataReader.loadSerializedPackageFragment(it, packageFqName) }
+    override fun packageMetadata(packageFqName: String, partIndex: Int) = layout.inPlace { metadataReader.loadSerializedPackageFragment(it, packageFqName, partIndex) }
+
+    override fun packageMetadataPartCount(fqName: String): Int =
+        layout.inPlace { it.packageFragmentsDir(fqName).listFiles.count { file -> file.extension == KLIB_METADATA_FILE_EXTENSION } }
 
     override fun toString() = "$libraryName[default=$isDefault]"
 }

konan/library-reader/src/org/jetbrains/kotlin/serialization/konan/KonanPackageFragment.kt

@@ -24,7 +24,8 @@ class KonanPackageFragment(
     private val library: KonanLibrary,
     private val packageAccessedHandler: PackageAccessedHandler?,
     storageManager: StorageManager,
-    module: ModuleDescriptor
+    module: ModuleDescriptor,
+    partIndex: Int
 ) : DeserializedPackageFragment(fqName, storageManager, module) {
 
     lateinit var components: DeserializationComponents
@@ -35,7 +36,7 @@ class KonanPackageFragment(
 
     // The proto field is lazy so that we can load only needed
     // packages from the library.
-    private val protoForNames: KonanProtoBuf.LinkDataPackageFragment by lazy { library.packageMetadata(fqName.asString()) }
+    private val protoForNames: KonanProtoBuf.LinkDataPackageFragment by lazy { library.packageMetadata(fqName.asString(), partIndex) }
 
     val proto: KonanProtoBuf.LinkDataPackageFragment
         get() = protoForNames.also { packageAccessedHandler?.markPackageAccessed(fqName) }

konan/library-reader/src/org/jetbrains/kotlin/serialization/konan/impl/KonanDeserializedPackageFragmentsFactoryImpl.kt

@@ -36,8 +36,12 @@ internal object KonanDeserializedPackageFragmentsFactoryImpl : KonanDeserialized
         moduleDescriptor: ModuleDescriptor,
         packageAccessedHandler: PackageAccessedHandler?,
         storageManager: StorageManager
-    ) = packageFragmentNames.map {
-        KonanPackageFragment(FqName(it), library, packageAccessedHandler, storageManager, moduleDescriptor)
+    ) = packageFragmentNames.flatMap {
+        val fqName = FqName(it)
+        val count = library.packageMetadataPartCount(fqName.asString())
+        List(count) { partIndex ->
+            KonanPackageFragment(fqName, library, packageAccessedHandler, storageManager, moduleDescriptor, partIndex)
+        }
     }
 
     override fun createSyntheticPackageFragments(