Support common metadata in kotlinx-metadata

KotlinCommonMetadata can be used to inspect .kotlin_builtins and
.kotlin_metadata files. It's in an internal package for now, but might
be published once the API is finalized.

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/builtins/BuiltInsPackageFragmentImpl.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.builtins.BuiltInsPackageFragment
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.builtins.BuiltInsBinaryVersion
+import org.jetbrains.kotlin.metadata.builtins.readBuiltinsPackageFragment
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.serialization.deserialization.DeserializedPackageFragmentImpl
@@ -33,21 +34,15 @@ class BuiltInsPackageFragmentImpl private constructor(
             inputStream: InputStream,
             isFallback: Boolean
         ): BuiltInsPackageFragmentImpl {
-            lateinit var version: BuiltInsBinaryVersion
+            val (proto, version) = inputStream.readBuiltinsPackageFragment()
 
-            val proto = inputStream.use { stream ->
-                version = BuiltInsBinaryVersion.readFrom(stream)
-
-                if (!version.isCompatible()) {
-                    // TODO: report a proper diagnostic
-                    throw UnsupportedOperationException(
-                        "Kotlin built-in definition format version is not supported: " +
-                                "expected ${BuiltInsBinaryVersion.INSTANCE}, actual $version. " +
-                                "Please update Kotlin"
-                    )
-                }
-
-                ProtoBuf.PackageFragment.parseFrom(stream, BuiltInSerializerProtocol.extensionRegistry)
+            if (proto == null) {
+                // TODO: report a proper diagnostic
+                throw UnsupportedOperationException(
+                    "Kotlin built-in definition format version is not supported: " +
+                            "expected ${BuiltInsBinaryVersion.INSTANCE}, actual $version. " +
+                            "Please update Kotlin"
+                )
             }
 
             return BuiltInsPackageFragmentImpl(fqName, storageManager, module, proto, version, isFallback)

core/metadata/src/org/jetbrains/kotlin/metadata/builtins/readPackageFragment.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.metadata.builtins
+
+import org.jetbrains.kotlin.metadata.ProtoBuf
+import org.jetbrains.kotlin.protobuf.ExtensionRegistryLite
+import java.io.InputStream
+
+fun InputStream.readBuiltinsPackageFragment(): Pair<ProtoBuf.PackageFragment?, BuiltInsBinaryVersion> =
+    use { stream ->
+        val version = BuiltInsBinaryVersion.readFrom(stream)
+        val proto =
+            if (version.isCompatible()) ProtoBuf.PackageFragment.parseFrom(
+                stream,
+                ExtensionRegistryLite.newInstance().apply(BuiltInsProtoBuf::registerAllExtensions)
+            )
+            else null
+        proto to version
+    }

libraries/kotlinx-metadata/jvm/src/kotlinx/metadata/jvm/impl/JvmMetadataExtensions.kt

@@ -298,7 +298,12 @@ internal class JvmMetadataExtensions : MetadataExtensions {
     override fun createPackageExtension(): KmPackageExtension = JvmPackageExtension()
 
     override fun createModuleFragmentExtensions(): KmModuleFragmentExtension =
-        error("metadata-jvm doesn't have any extensions for module fragment!")
+        object : KmModuleFragmentExtension {
+            override val type: KmExtensionType = KmExtensionType(KmModuleFragmentExtension::class)
+
+            override fun accept(visitor: KmModuleFragmentExtensionVisitor) {
+            }
+        }
 
     override fun createFunctionExtension(): KmFunctionExtension = JvmFunctionExtension()
 

libraries/kotlinx-metadata/src/kotlinx/metadata/internal/common/KotlinCommonMetadata.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlinx.metadata.internal.common
+
+import kotlinx.metadata.KmModuleFragment
+import kotlinx.metadata.KmModuleFragmentVisitor
+import kotlinx.metadata.impl.accept
+import org.jetbrains.kotlin.metadata.ProtoBuf
+import org.jetbrains.kotlin.metadata.builtins.readBuiltinsPackageFragment
+import org.jetbrains.kotlin.metadata.deserialization.NameResolverImpl
+import java.io.ByteArrayInputStream
+
+class KotlinCommonMetadata private constructor(private val proto: ProtoBuf.PackageFragment) {
+    fun toKmModuleFragment(): KmModuleFragment =
+        KmModuleFragment().apply(this::accept)
+
+    class Writer : KmModuleFragmentVisitor() {
+        // TODO
+    }
+
+    fun accept(v: KmModuleFragmentVisitor) {
+        val strings = NameResolverImpl(proto.strings, proto.qualifiedNames)
+        if (proto.hasPackage()) {
+            v.visitPackage()?.let { proto.`package`.accept(it, strings) }
+        }
+        for (klass in proto.class_List) {
+            v.visitClass()?.let { klass.accept(it, strings) }
+        }
+        v.visitEnd()
+    }
+
+    companion object {
+        @JvmStatic
+        fun read(bytes: ByteArray): KotlinCommonMetadata? {
+            val (proto, _) = ByteArrayInputStream(bytes).readBuiltinsPackageFragment()
+            if (proto == null) return null
+
+            return KotlinCommonMetadata(proto)
+        }
+    }
+}