MultifileClassCodegen

- initial implementation
- new Kotlin file kinds + stub builder

compiler/backend/src/org/jetbrains/kotlin/codegen/ClassFileFactory.java

@@ -50,6 +50,7 @@ public class ClassFileFactory implements OutputFileCollection {
     private final GenerationState state;
     private final ClassBuilderFactory builderFactory;
     private final Map<FqName, PackageCodegen> package2codegen = new HashMap<FqName, PackageCodegen>();
+    private final Map<FqName, MultifileClassCodegen> multifileClass2codegen = new HashMap<FqName, MultifileClassCodegen>();
     private final Map<String, OutAndSourceFileList> generators = new LinkedHashMap<String, OutAndSourceFileList>();
 
     private boolean isDone = false;
@@ -189,7 +190,7 @@ public class ClassFileFactory implements OutputFileCollection {
     }
 
     @NotNull
-    public PackageCodegen forFacade(@NotNull FqName facadeFqName, @NotNull Collection<JetFile> files) {
+    public PackageCodegen forFacadeLightClass(@NotNull FqName facadeFqName, @NotNull Collection<JetFile> files) {
         assert !isDone : "Already done!";
         PackageCodegen codegen = package2codegen.get(facadeFqName);
         if (codegen == null) {
@@ -200,6 +201,17 @@ public class ClassFileFactory implements OutputFileCollection {
         return codegen;
     }
 
+    @NotNull
+    public MultifileClassCodegen forMultifileClass(@NotNull FqName facadeFqName, @NotNull Collection<JetFile> files) {
+        assert !isDone : "Already done!";
+        MultifileClassCodegen codegen = multifileClass2codegen.get(facadeFqName);
+        if (codegen == null) {
+            codegen = new MultifileClassCodegen(state, files, facadeFqName);
+            multifileClass2codegen.put(facadeFqName, codegen);
+        }
+        return codegen;
+    }
+
     @NotNull
     private static List<File> toIoFilesIgnoringNonPhysical(@NotNull Collection<? extends PsiFile> psiFiles) {
         List<File> result = Lists.newArrayList();

compiler/backend/src/org/jetbrains/kotlin/codegen/KotlinCodegenFacade.java

@@ -20,6 +20,8 @@ import com.google.common.collect.Sets;
 import com.intellij.util.containers.MultiMap;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.codegen.state.GenerationState;
+import org.jetbrains.kotlin.fileClasses.JvmFileClassInfo;
+import org.jetbrains.kotlin.load.kotlin.PackageClassUtils;
 import org.jetbrains.kotlin.progress.ProgressIndicatorAndCompilationCanceledStatus;
 import org.jetbrains.kotlin.name.FqName;
 import org.jetbrains.kotlin.psi.JetFile;
@@ -62,15 +64,31 @@ public class KotlinCodegenFacade {
         ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
 
         MultiMap<FqName, JetFile> packageFqNameToFiles = new MultiMap<FqName, JetFile>();
+        MultiMap<FqName, JetFile> multifileClassFqNameToFiles = new MultiMap<FqName, JetFile>();
+
         for (JetFile file : state.getFiles()) {
             if (file == null) throw new IllegalArgumentException("A null file given for compilation");
-            packageFqNameToFiles.putValue(file.getPackageFqName(), file);
+            JvmFileClassInfo fileClassInfo = state.getFileClassesProvider().getFileClassInfo(file);
+            if (fileClassInfo.getIsMultifileClass()) {
+                multifileClassFqNameToFiles.putValue(fileClassInfo.getFacadeClassFqName(), file);
+            }
+            else if (state.getPackageFacadesAsMultifileClasses()) {
+                multifileClassFqNameToFiles.putValue(PackageClassUtils.getPackageClassFqName(file.getPackageFqName()), file);
+            }
+            else {
+                packageFqNameToFiles.putValue(file.getPackageFqName(), file);
+            }
         }
 
         Set<FqName> packagesWithObsoleteParts = new HashSet<FqName>(state.getPackagesWithObsoleteParts());
-        for (FqName fqName : Sets.union(packagesWithObsoleteParts, packageFqNameToFiles.keySet())) {
+        for (FqName packageFqName : Sets.union(packagesWithObsoleteParts, packageFqNameToFiles.keySet())) {
             ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
-            generatePackage(state, fqName, packageFqNameToFiles.get(fqName), errorHandler);
+            generatePackage(state, packageFqName, packageFqNameToFiles.get(packageFqName), errorHandler);
+        }
+
+        for (FqName multifileClassFqName : multifileClassFqNameToFiles.keySet()) {
+            ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
+            generateMultifileClass(state, multifileClassFqName, multifileClassFqNameToFiles.get(multifileClassFqName), errorHandler);
         }
 
         ProgressIndicatorAndCompilationCanceledStatus.checkCanceled();
@@ -79,13 +97,23 @@ public class KotlinCodegenFacade {
 
     public static void generatePackage(
             @NotNull GenerationState state,
-            @NotNull FqName fqName,
+            @NotNull FqName packageFqName,
             @NotNull Collection<JetFile> jetFiles,
             @NotNull CompilationErrorHandler errorHandler
     ) {
-        PackageCodegen codegen = state.getFactory().forPackage(fqName, jetFiles);
+        PackageCodegen codegen = state.getFactory().forPackage(packageFqName, jetFiles);
         codegen.generate(errorHandler);
     }
 
+    private static void generateMultifileClass(
+            @NotNull GenerationState state,
+            @NotNull FqName multifileClassFqName,
+            @NotNull Collection<JetFile> files,
+            @NotNull CompilationErrorHandler handler
+    ) {
+        MultifileClassCodegen codegen = state.getFactory().forMultifileClass(multifileClassFqName, files);
+        codegen.generate(handler);
+    }
+
     private KotlinCodegenFacade() {}
 }

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassCodegen.kt

@@ -0,0 +1,272 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen
+
+import com.intellij.openapi.application.ApplicationManager
+import com.intellij.openapi.progress.ProcessCanceledException
+import com.intellij.util.ArrayUtil
+import com.intellij.util.SmartList
+import com.intellij.util.containers.ContainerUtil
+import org.jetbrains.kotlin.codegen.context.CodegenContext
+import org.jetbrains.kotlin.codegen.context.FieldOwnerContext
+import org.jetbrains.kotlin.codegen.state.GenerationState
+import org.jetbrains.kotlin.config.IncrementalCompilation
+import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor
+import org.jetbrains.kotlin.diagnostics.DiagnosticUtils
+import org.jetbrains.kotlin.load.java.JvmAbi
+import org.jetbrains.kotlin.load.java.JvmAnnotationNames
+import org.jetbrains.kotlin.load.kotlin.incremental.IncrementalPackageFragmentProvider
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.progress.ProgressIndicatorAndCompilationCanceledStatus
+import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.MemberComparator
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.MultifileClass
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.MultifileClassPart
+import org.jetbrains.kotlin.serialization.DescriptorSerializer
+import org.jetbrains.kotlin.serialization.PackageData
+import org.jetbrains.kotlin.serialization.SerializationUtil
+import org.jetbrains.kotlin.serialization.deserialization.NameResolver
+import org.jetbrains.kotlin.serialization.jvm.BitEncoding
+import org.jetbrains.org.objectweb.asm.Opcodes
+import java.util.*
+
+
+public class MultifileClassCodegen(
+        private val state: GenerationState,
+        private val files: Collection<JetFile>,
+        private val facadeFqName: FqName
+) {
+    private val facadeClassType = AsmUtil.asmTypeByFqNameWithoutInnerClasses(facadeFqName)
+
+    private val packageFragment = getOnlyPackageFragment(facadeFqName.parent(), files, state.bindingContext)
+
+    private val compiledPackageFragment = getCompiledPackageFragment(facadeFqName.parent(), state)
+
+    // TODO incremental compilation support
+    // TODO previouslyCompiledCallables
+    // We can do this (probably without 'compiledPackageFragment') after modifications to part codegen.
+
+    private val classBuilder = ClassBuilderOnDemand {
+        val filesWithTopLevelCallables = files.filter { hasTopLevelCallables(it) }
+        val sourceFile = filesWithTopLevelCallables.firstOrNull()
+        val actualPackageFragment = packageFragment ?:
+                                    compiledPackageFragment ?:
+                                    throw AssertionError("No package fragment for multifile facade $facadeFqName; files: $files")
+        val declarationOrigin = MultifileClass(actualPackageFragment, facadeFqName)
+        val classBuilder = state.factory.newVisitor(declarationOrigin, facadeClassType, filesWithTopLevelCallables)
+
+        classBuilder.defineClass(sourceFile, Opcodes.V1_6, FACADE_CLASS_ATTRIBUTES,
+                                 facadeClassType.internalName,
+                                 null, "java/lang/Object", ArrayUtil.EMPTY_STRING_ARRAY)
+        sourceFile?.let { classBuilder.visitSource(it.name, null) }
+        classBuilder
+    }
+
+    private fun hasTopLevelCallables(file: JetFile) =
+            file.declarations.any { it is JetNamedFunction || it is JetProperty }
+
+    public fun generate(errorHandler: CompilationErrorHandler) {
+        val bindings = ArrayList<JvmSerializationBindings>(files.size() + 1)
+        val generateCallableMemberTasks = HashMap<CallableMemberDescriptor, () -> Unit>()
+        val partFqNames = arrayListOf<FqName>()
+
+        for (file in files) {
+            ProgressIndicatorAndCompilationCanceledStatus.checkCanceled()
+            try {
+                val partClassBuilder = generatePart(file, generateCallableMemberTasks, partFqNames)
+                if (partClassBuilder != null) {
+                    bindings.add(partClassBuilder.serializationBindings)
+                }
+            }
+            catch (e: ProcessCanceledException) {
+                throw e
+            }
+            catch (e: Throwable) {
+                val vFile = file.virtualFile
+                errorHandler.reportException(e, if (vFile == null) "no file" else vFile.url)
+                DiagnosticUtils.throwIfRunningOnServer(e)
+                if (ApplicationManager.getApplication().isInternal) {
+                    //noinspection CallToPrintStackTrace
+                    e.printStackTrace()
+                }
+            }
+        }
+
+//        generateDelegationsToPreviouslyCompiled(generateCallableMemberTasks)
+
+        if (!generateCallableMemberTasks.isEmpty()) {
+            generateMultifileFacadeClass(generateCallableMemberTasks, bindings, partFqNames)
+        }
+    }
+
+    private fun generateMultifileFacadeClass(
+            tasks: Map<CallableMemberDescriptor, () -> Unit>,
+            bindings: MutableList<JvmSerializationBindings>,
+            partFqNames: List<FqName>
+    ) {
+        MemberCodegen.generateModuleNameField(state, classBuilder)
+
+        for (member in tasks.keySet().sortedWith(MemberComparator.INSTANCE)) {
+            tasks[member]!!()
+        }
+
+        bindings.add(classBuilder.serializationBindings)
+        writeKotlinMultifileFacadeAnnotationIfNeeded(JvmSerializationBindings.union(bindings), partFqNames)
+    }
+
+    public fun generateClassOrObject(classOrObject: JetClassOrObject) {
+        val file = classOrObject.getContainingJetFile()
+        val packagePartType = state.fileClassesProvider.getFileClassType(file)
+        val context = CodegenContext.STATIC.intoPackagePart(packageFragment!!, packagePartType)
+        MemberCodegen.genClassOrObject(context, classOrObject, state, null)
+    }
+
+    private fun generatePart(
+            file: JetFile,
+            generateCallableMemberTasks: MutableMap<CallableMemberDescriptor, () -> Unit>,
+            partFqNames: MutableList<FqName>
+    ): ClassBuilder? {
+        val packageFragment = this.packageFragment ?:
+                              throw AssertionError("File part $file of $facadeFqName: no package fragment")
+
+        var generatePart = false
+        val partClassInfo = state.fileClassesProvider.getFileClassInfo(file)
+        val partType = AsmUtil.asmTypeByFqNameWithoutInnerClasses(partClassInfo.fileClassFqName)
+        val partContext = CodegenContext.STATIC.intoMultifileClassPart(packageFragment, facadeClassType, partType)
+
+        for (declaration in file.declarations) {
+            if (declaration is JetProperty || declaration is JetNamedFunction) {
+                generatePart = true
+            }
+            else if (declaration is JetClassOrObject) {
+                if (state.generateDeclaredClassFilter.shouldGenerateClass(declaration)) {
+                    generateClassOrObject(declaration)
+                }
+            }
+            else if (declaration is JetScript) {
+
+                // SCRIPT: generate script code, should be separate execution branch
+                if (state.generateDeclaredClassFilter.shouldGenerateScript(declaration)) {
+                    ScriptCodegen.createScriptCodegen(declaration, state, partContext).generate()
+                }
+            }
+        }
+
+
+        if (!generatePart || !state.generateDeclaredClassFilter.shouldGeneratePackagePart(file)) return null
+
+        partFqNames.add(partClassInfo.fileClassFqName)
+
+//        val name = partType.internalName
+//        packageParts.parts.add(name.substring(name.lastIndexOf('/') + 1))
+
+        val builder = state.factory.newVisitor(MultifileClassPart(file, packageFragment, facadeFqName), partType, file)
+
+        MultifileClassPartCodegen(builder, file, partType, facadeFqName, partContext, state).generate()
+
+        val facadeContext = CodegenContext.STATIC.intoMultifileClass(packageFragment, facadeClassType, partType)
+        val memberCodegen = createCodegenForPartOfMultifileFacade(facadeContext)
+        for (declaration in file.declarations) {
+            if (declaration is JetNamedFunction || declaration is JetProperty) {
+                val descriptor = state.bindingContext.get(BindingContext.DECLARATION_TO_DESCRIPTOR, declaration)
+                assert(descriptor is CallableMemberDescriptor) { "Expected callable member, was " + descriptor + " for " + declaration.text }
+                generateCallableMemberTasks.put(descriptor as CallableMemberDescriptor,
+                                                { memberCodegen.genFunctionOrProperty(declaration) })
+            }
+        }
+
+        return builder
+    }
+
+    private fun writeKotlinMultifileFacadeAnnotationIfNeeded(bindings: JvmSerializationBindings, partFqNames: List<FqName>) {
+        if (state.classBuilderMode != ClassBuilderMode.FULL) return
+        if (files.any { it.isScript }) return
+
+        val serializer = DescriptorSerializer.createTopLevel(JvmSerializerExtension(bindings, state.typeMapper))
+
+        val packageFragments = arrayListOf<PackageFragmentDescriptor>()
+        ContainerUtil.addIfNotNull(packageFragments, packageFragment)
+        ContainerUtil.addIfNotNull(packageFragments, compiledPackageFragment)
+        val facadeProto = serializer.packageProto(packageFragments, /* skip= */ { true }).build()
+
+        val strings = serializer.stringTable
+        val nameResolver = NameResolver(strings.serializeSimpleNames(), strings.serializeQualifiedNames())
+        val facadeData = PackageData(nameResolver, facadeProto)
+
+        val av = classBuilder.newAnnotation(AsmUtil.asmDescByFqNameWithoutInnerClasses(JvmAnnotationNames.KOTLIN_MULTIFILE_CLASS), true)
+        av.visit(JvmAnnotationNames.ABI_VERSION_FIELD_NAME, JvmAbi.VERSION)
+
+        val shortNames = partFqNames.map { it.shortName().asString() }.sorted()
+        val filePartClassNamesArray = av.visitArray(JvmAnnotationNames.FILE_PART_CLASS_NAMES_FIELD_NAME)
+        for (shortName in shortNames) {
+            filePartClassNamesArray.visit(null, shortName)
+        }
+        filePartClassNamesArray.visitEnd()
+
+        val dataArray = av.visitArray(JvmAnnotationNames.DATA_FIELD_NAME)
+        for (string in BitEncoding.encodeBytes(SerializationUtil.serializePackageData(facadeData))) {
+            dataArray.visit(null, string)
+        }
+        dataArray.visitEnd()
+
+        av.visitEnd()
+    }
+
+    private fun createCodegenForPartOfMultifileFacade(facadeContext: FieldOwnerContext<DeclarationDescriptor>): MemberCodegen<JetFile> =
+            object : MemberCodegen<JetFile>(state, null, facadeContext, null, classBuilder) {
+                override fun generateDeclaration() = throw UnsupportedOperationException()
+                override fun generateBody() = throw UnsupportedOperationException()
+                override fun generateKotlinAnnotation() = throw UnsupportedOperationException()
+            }
+
+    public fun done() {
+        classBuilder.done()
+    }
+
+    companion object {
+        private val FACADE_CLASS_ATTRIBUTES = Opcodes.ACC_PUBLIC or Opcodes.ACC_FINAL
+
+        private fun getOnlyPackageFragment(packageFqName: FqName, files: Collection<JetFile>, bindingContext: BindingContext): PackageFragmentDescriptor? {
+            val fragments = SmartList<PackageFragmentDescriptor>()
+            for (file in files) {
+                val fragment = bindingContext.get(BindingContext.FILE_TO_PACKAGE_FRAGMENT, file)
+                assert(fragment != null) { "package fragment is null for " + file + "\n" + file.text }
+
+                assert(packageFqName == fragment!!.fqName) { "expected package fq name: " + packageFqName + ", actual: " + fragment.fqName }
+
+                if (!fragments.contains(fragment)) {
+                    fragments.add(fragment)
+                }
+            }
+            if (fragments.size() > 1) {
+                throw IllegalStateException("More than one package fragment, files: $files | fragments: $fragments")
+            }
+            return fragments.firstOrNull()
+        }
+
+        private fun getCompiledPackageFragment(packageFqName: FqName, state: GenerationState): PackageFragmentDescriptor? =
+                if (!IncrementalCompilation.ENABLED) null
+                else state.module.getPackage(packageFqName).fragments.firstOrNull { fragment ->
+                    fragment is IncrementalPackageFragmentProvider.IncrementalPackageFragment &&
+                    fragment.moduleId == state.moduleId
+                }
+    }
+
+}

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassPartCodegen.kt

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen
+
+import com.intellij.util.ArrayUtil
+import org.jetbrains.kotlin.codegen.context.FieldOwnerContext
+import org.jetbrains.kotlin.codegen.state.GenerationState
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.load.java.JvmAbi
+import org.jetbrains.kotlin.load.java.JvmAnnotationNames
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.psi.JetFile
+import org.jetbrains.kotlin.psi.JetNamedFunction
+import org.jetbrains.kotlin.psi.JetProperty
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.serialization.DescriptorSerializer
+import org.jetbrains.kotlin.serialization.PackageData
+import org.jetbrains.kotlin.serialization.SerializationUtil
+import org.jetbrains.kotlin.serialization.deserialization.NameResolver
+import org.jetbrains.kotlin.serialization.jvm.BitEncoding
+import org.jetbrains.org.objectweb.asm.Opcodes
+import org.jetbrains.org.objectweb.asm.Type
+import java.util.*
+
+
+public class MultifileClassPartCodegen(
+        v: ClassBuilder,
+        file: JetFile,
+        private val filePartType: Type,
+        private val multifileClassFqName: FqName,
+        partContext: FieldOwnerContext<*>,
+        state: GenerationState
+) : MemberCodegen<JetFile>(state, null, partContext, file, v){
+    override fun generateDeclaration() {
+        v.defineClass(element, Opcodes.V1_6,
+                      Opcodes.ACC_SYNTHETIC,
+                      filePartType.internalName,
+                      null,
+                      "java/lang/Object",
+                      ArrayUtil.EMPTY_STRING_ARRAY)
+        v.visitSource(element.name, null)
+
+        generatePropertyMetadataArrayFieldIfNeeded(filePartType)
+    }
+
+    override fun generateBody() {
+        for (declaration in element.declarations) {
+            if (declaration is JetNamedFunction || declaration is JetProperty) {
+                genFunctionOrProperty(declaration);
+            }
+        }
+
+        if (state.classBuilderMode == ClassBuilderMode.FULL) {
+            generateInitializers({ createOrGetClInitCodegen(); });
+        }
+    }
+
+    override fun generateKotlinAnnotation() {
+        if (state.classBuilderMode != ClassBuilderMode.FULL) {
+            return
+        }
+
+        val members = ArrayList<DeclarationDescriptor>()
+        for (declaration in element.declarations) {
+            when (declaration) {
+                is JetNamedFunction -> {
+                    val functionDescriptor = bindingContext.get(BindingContext.FUNCTION, declaration)
+                    members.add(functionDescriptor ?: throw AssertionError("Function ${declaration.name} is not bound in ${element.name}"))
+                }
+                is JetProperty -> {
+                    val property = bindingContext.get(BindingContext.VARIABLE, declaration)
+                    members.add(property ?: throw AssertionError("Property ${declaration.name} is not bound in ${element.name}"))
+                }
+            }
+        }
+
+        val bindings = v.serializationBindings
+
+        val serializer = DescriptorSerializer.createTopLevel(JvmSerializerExtension(bindings, state.typeMapper))
+        val packageProto = serializer.packagePartProto(members).build()
+
+        if (packageProto.memberCount == 0) return
+
+        val strings = serializer.stringTable
+        val nameResolver = NameResolver(strings.serializeSimpleNames(), strings.serializeQualifiedNames())
+        val data = PackageData(nameResolver, packageProto)
+
+        val av = v.newAnnotation(AsmUtil.asmDescByFqNameWithoutInnerClasses(JvmAnnotationNames.KOTLIN_MULTIFILE_CLASS_PART), true)
+        av.visit(JvmAnnotationNames.ABI_VERSION_FIELD_NAME, JvmAbi.VERSION)
+        av.visit(JvmAnnotationNames.MULTIFILE_CLASS_NAME_FIELD_NAME, multifileClassFqName.shortName().asString())
+        val dataArray = av.visitArray(JvmAnnotationNames.DATA_FIELD_NAME)
+        for (string in BitEncoding.encodeBytes(SerializationUtil.serializePackageData(data))) {
+            dataArray.visit(null, string)
+        }
+        dataArray.visitEnd()
+        av.visitEnd()
+    }
+}

compiler/backend/src/org/jetbrains/kotlin/codegen/PackageCodegen.java

@@ -39,6 +39,7 @@ import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor;
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor;
 import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor;
 import org.jetbrains.kotlin.diagnostics.DiagnosticUtils;
+import org.jetbrains.kotlin.fileClasses.JvmFileClassInfo;
 import org.jetbrains.kotlin.load.java.JvmAbi;
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames;
 import org.jetbrains.kotlin.load.kotlin.PackagePartClassUtils;
@@ -335,7 +336,6 @@ public class PackageCodegen {
             }
         }
 
-
         if (!generatePackagePart || !state.getGenerateDeclaredClassFilter().shouldGeneratePackagePart(file)) return null;
 
         String name = packagePartType.getInternalName();

compiler/backend/src/org/jetbrains/kotlin/codegen/context/CodegenContext.java

@@ -189,6 +189,24 @@ public abstract class CodegenContext<T extends DeclarationDescriptor> {
         return new PackageFacadeContext(descriptor, this, delegateTo);
     }
 
+    @NotNull
+    public FieldOwnerContext<PackageFragmentDescriptor> intoMultifileClassPart(
+            @NotNull PackageFragmentDescriptor descriptor,
+            @NotNull Type multifileClassType,
+            @NotNull Type filePartType
+    ) {
+        return new MultifileClassPartContext(descriptor, this, multifileClassType, filePartType);
+    }
+
+    @NotNull
+    public FieldOwnerContext<PackageFragmentDescriptor> intoMultifileClass(
+            @NotNull PackageFragmentDescriptor descriptor,
+            @NotNull Type multifileClassType,
+            @NotNull Type filePartType
+    ) {
+        return new MultifileClassContext(descriptor, this, multifileClassType, filePartType);
+    }
+
     @NotNull
     public ClassContext intoClass(ClassDescriptor descriptor, OwnerKind kind, GenerationState state) {
         return new ClassContext(state.getTypeMapper(), descriptor, kind, this, null);

compiler/backend/src/org/jetbrains/kotlin/codegen/context/MultifileClassContext.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen.context;
+
+import org.jetbrains.kotlin.codegen.OwnerKind;
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor;
+import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor;
+import org.jetbrains.org.objectweb.asm.Type;
+
+public class MultifileClassContext extends FieldOwnerContext<PackageFragmentDescriptor> {
+    private final Type multifileClassType;
+    private final Type filePartType;
+
+    public MultifileClassContext(
+            PackageFragmentDescriptor descriptor,
+            CodegenContext parent,
+            Type multifileClassType,
+            Type filePartType
+    ) {
+        super(descriptor, OwnerKind.PACKAGE, parent, null, null, null);
+        this.multifileClassType = multifileClassType;
+        this.filePartType = filePartType;
+    }
+
+    public Type getMultifileClassType() {
+        return multifileClassType;
+    }
+
+    public Type getFilePartType() {
+        return filePartType;
+    }
+}

compiler/backend/src/org/jetbrains/kotlin/codegen/context/MultifileClassPartContext.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen.context;
+
+import org.jetbrains.kotlin.codegen.OwnerKind;
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor;
+import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor;
+import org.jetbrains.org.objectweb.asm.Type;
+
+public class MultifileClassPartContext extends FieldOwnerContext<PackageFragmentDescriptor> {
+    private final Type multifileClassType;
+    private final Type filePartType;
+
+    public MultifileClassPartContext(
+            PackageFragmentDescriptor descriptor,
+            CodegenContext parent,
+            Type multifileClassType,
+            Type filePartType
+    ) {
+        super(descriptor, OwnerKind.PACKAGE, parent, null, null, null);
+        this.multifileClassType = multifileClassType;
+        this.filePartType = filePartType;
+    }
+
+    public Type getMultifileClassType() {
+        return multifileClassType;
+    }
+
+    public Type getFilePartType() {
+        return filePartType;
+    }
+}

compiler/backend/src/org/jetbrains/kotlin/codegen/state/GenerationState.kt

@@ -52,6 +52,7 @@ public class GenerationState jvmOverloads constructor(
         public val generateDeclaredClassFilter: GenerationState.GenerateClassFilter = GenerationState.GenerateClassFilter.GENERATE_ALL,
         disableInline: Boolean = false,
         disableOptimization: Boolean = false,
+        public val packageFacadesAsMultifileClasses: Boolean = false,
         public val diagnostics: DiagnosticSink = DiagnosticSink.DO_NOTHING,
         public val packagesWithObsoleteParts: Collection<FqName> = emptySet(),
         // for PackageCodegen in incremental compilation mode

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.java

@@ -69,6 +69,9 @@ public class K2JVMCompilerArguments extends CommonCompilerArguments {
     @Argument(value = "Xno-optimize", description = "Disable optimizations")
     public boolean noOptimize;
 
+    @Argument(value = "Xmultifile-package-facades", description = "Compile package facade classes as multifile classes")
+    public boolean packageFacadesAsMultifileClasses;
+
     @Argument(value = "Xreport-perf", description = "Report detailed performance statistics")
     public boolean reportPerf;
 

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/K2JVMCompiler.kt

@@ -272,6 +272,7 @@ public open class K2JVMCompiler : CLICompiler<K2JVMCompilerArguments>() {
             configuration.put(JVMConfigurationKeys.DISABLE_PARAM_ASSERTIONS, arguments.noParamAssertions)
             configuration.put(JVMConfigurationKeys.DISABLE_INLINE, arguments.noInline)
             configuration.put(JVMConfigurationKeys.DISABLE_OPTIMIZATION, arguments.noOptimize)
+            configuration.put(JVMConfigurationKeys.PACKAGE_FACADES_AS_MULTIFILE_CLASSES, arguments.packageFacadesAsMultifileClasses);
         }
 
         private fun getClasspath(paths: KotlinPaths, arguments: K2JVMCompilerArguments): List<File> {

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/KotlinToJVMBytecodeCompiler.java

@@ -392,6 +392,7 @@ public class KotlinToJVMBytecodeCompiler {
                 GenerationState.GenerateClassFilter.GENERATE_ALL,
                 configuration.get(JVMConfigurationKeys.DISABLE_INLINE, false),
                 configuration.get(JVMConfigurationKeys.DISABLE_OPTIMIZATION, false),
+                configuration.get(JVMConfigurationKeys.PACKAGE_FACADES_AS_MULTIFILE_CLASSES, false),
                 diagnosticHolder,
                 packagesWithObsoleteParts,
                 targetId,

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/config/JVMConfigurationKeys.java

@@ -42,6 +42,8 @@ public class JVMConfigurationKeys {
             CompilerConfigurationKey.create("disable inline");
     public static final CompilerConfigurationKey<Boolean> DISABLE_OPTIMIZATION =
             CompilerConfigurationKey.create("disable optimization");
+    public static final CompilerConfigurationKey<Boolean> PACKAGE_FACADES_AS_MULTIFILE_CLASSES =
+            CompilerConfigurationKey.create("compile package facades as multifile classes");
 
     public static final CompilerConfigurationKey<IncrementalCompilationComponents> INCREMENTAL_COMPILATION_COMPONENTS =
             CompilerConfigurationKey.create("incremental cache provider");

compiler/frontend.java/src/org/jetbrains/kotlin/fileClasses/JvmFileClassInfo.kt

@@ -22,30 +22,23 @@ import org.jetbrains.kotlin.psi.JetFile
 public interface JvmFileClassInfo {
     public val fileClassFqName: FqName
     public val facadeClassFqName: FqName
-    public val kind: Kind
-
-    public enum class Kind {
-        FILE_CLASS,
-        MULTIFILE_CLASS_PART
-        ;
-    }
+    public val isWithJvmName: Boolean
+    public val isMultifileClass: Boolean
 }
 
-public class JvmFileFacadeInfo(
-        override val fileClassFqName: FqName
+public class JvmSimpleFileClassInfo(
+        override val fileClassFqName: FqName,
+        override val isWithJvmName: Boolean
 ) : JvmFileClassInfo {
-    override val facadeClassFqName: FqName
-        get() = fileClassFqName
-    override val kind: JvmFileClassInfo.Kind
-        get() = JvmFileClassInfo.Kind.FILE_CLASS
+    override val facadeClassFqName: FqName get() = fileClassFqName
+    override val isMultifileClass: Boolean get() = false
 }
 
-public class JvmMultifileFacadePartInfo(
+public class JvmMultifileClassPartInfo(
         override val fileClassFqName: FqName,
         override val facadeClassFqName: FqName
 ) : JvmFileClassInfo {
-    override val kind: JvmFileClassInfo.Kind
-        get() = JvmFileClassInfo.Kind.MULTIFILE_CLASS_PART
-
+    override val isWithJvmName: Boolean get() = true
+    override val isMultifileClass: Boolean get() = true
 }
 

compiler/frontend.java/src/org/jetbrains/kotlin/fileClasses/JvmFileClassUtil.kt

@@ -30,7 +30,8 @@ public object JvmFileClassUtil {
     public val JVM_NAME: FqName = FqName("kotlin.jvm.JvmName")
     public val JVM_NAME_SHORT: String = JVM_NAME.shortName().asString()
 
-    // TODO @JvmMultifileClass
+    public val JVM_MULTIFILE_CLASS: FqName = FqName("kotlin.jvm.JvmMultifileClass")
+    public val JVM_MULTIFILE_CLASS_SHORT = JVM_MULTIFILE_CLASS.shortName().asString()
 
     public @jvmStatic fun getFileClassInfo(file: JetFile, jvmFileClassAnnotations: ParsedJmvFileClassAnnotations?): JvmFileClassInfo =
             if (jvmFileClassAnnotations != null)
@@ -40,13 +41,13 @@ public object JvmFileClassUtil {
 
     public @jvmStatic fun getFileClassInfoForAnnotation(file: JetFile, jvmFileClassAnnotations: ParsedJmvFileClassAnnotations): JvmFileClassInfo =
             if (jvmFileClassAnnotations.multipleFiles)
-                JvmMultifileFacadePartInfo(getHiddenPartFqName(file, jvmFileClassAnnotations),
-                                           getFacadeFqName(file, jvmFileClassAnnotations))
+                JvmMultifileClassPartInfo(getHiddenPartFqName(file, jvmFileClassAnnotations),
+                                          getFacadeFqName(file, jvmFileClassAnnotations))
             else
-                JvmFileFacadeInfo(getFacadeFqName(file, jvmFileClassAnnotations))
+                JvmSimpleFileClassInfo(getFacadeFqName(file, jvmFileClassAnnotations), true)
 
     public @jvmStatic fun getDefaultFileClassInfo(file: JetFile): JvmFileClassInfo =
-            JvmFileFacadeInfo(PackagePartClassUtils.getPackagePartFqName(file.packageFqName, file.name))
+            JvmSimpleFileClassInfo(PackagePartClassUtils.getPackagePartFqName(file.packageFqName, file.name), false)
 
     public @jvmStatic fun getFacadeFqName(file: JetFile, jvmFileClassAnnotations: ParsedJmvFileClassAnnotations): FqName =
             file.packageFqName.child(Name.identifier(jvmFileClassAnnotations.name))
@@ -59,31 +60,35 @@ public object JvmFileClassUtil {
 
     public @jvmStatic fun parseJvmFileClass(annotations: Annotations): ParsedJmvFileClassAnnotations? {
         val jvmName = annotations.findAnnotation(JVM_NAME)
-        // TODO @JvmMultifileClass
-        return if (jvmName != null) parseJvmFileClass(jvmName) else null
+        val jvmMultifileClass = annotations.findAnnotation(JVM_MULTIFILE_CLASS)
+        return jvmName?.let {
+            parseJvmFileClass(it, jvmMultifileClass)
+        }
     }
 
-    public @jvmStatic fun parseJvmFileClass(jvmName: AnnotationDescriptor): ParsedJmvFileClassAnnotations {
+    public @jvmStatic fun parseJvmFileClass(jvmName: AnnotationDescriptor, jvmMultifileClass: AnnotationDescriptor?): ParsedJmvFileClassAnnotations {
         val name = jvmName.allValueArguments.values().firstOrNull()?.let { (it as? StringValue)?.value }
-        return ParsedJmvFileClassAnnotations(name!!, false)
+        val isMultifileClassPart = jvmMultifileClass != null
+        return ParsedJmvFileClassAnnotations(name!!, isMultifileClassPart)
     }
 
     public @jvmStatic fun getFileClassInfoNoResolve(file: JetFile): JvmFileClassInfo =
             getFileClassInfo(file, parseJvmNameOnFileNoResolve(file))
 
     public @jvmStatic fun parseJvmNameOnFileNoResolve(file: JetFile): ParsedJmvFileClassAnnotations? =
-            findJvmNameOnFileNoResolve(file)?.let { parseJvmNameOnFileNoResolve(it) }
-
-    public @jvmStatic fun findJvmNameOnFileNoResolve(file: JetFile): JetAnnotationEntry? =
-            file.fileAnnotationList?.annotationEntries?.firstOrNull {
-                it.calleeExpression?.constructorReferenceExpression?.getReferencedName() == JVM_NAME_SHORT
+            findAnnotationEntryOnFileNoResolve(file, JVM_NAME_SHORT)?.let { annotationEntry ->
+                val nameExpr = annotationEntry.valueArguments.firstOrNull()?.getArgumentExpression() ?: return null
+                val name = getLiteralStringFromRestrictedConstExpression(nameExpr)
+                val isMultifileClassPart = findAnnotationEntryOnFileNoResolve(file, JVM_MULTIFILE_CLASS_SHORT) != null
+                name?.let {
+                    ParsedJmvFileClassAnnotations(it, isMultifileClassPart)
+                }
             }
 
-    public @jvmStatic fun parseJvmNameOnFileNoResolve(annotationEntry: JetAnnotationEntry): ParsedJmvFileClassAnnotations? {
-        val nameExpr = annotationEntry.valueArguments.firstOrNull()?.getArgumentExpression() ?: return null
-        val name = getLiteralStringFromRestrictedConstExpression(nameExpr)
-        return name?.let { ParsedJmvFileClassAnnotations(it, false) }
-    }
+    public @jvmStatic fun findAnnotationEntryOnFileNoResolve(file: JetFile, shortName: String): JetAnnotationEntry? =
+            file.fileAnnotationList?.annotationEntries?.firstOrNull {
+                it.calleeExpression?.constructorReferenceExpression?.getReferencedName() == shortName
+            }
 
     private @jvmStatic fun getLiteralStringFromRestrictedConstExpression(argumentExpression: JetExpression?): String? {
         val stringTemplate = argumentExpression as? JetStringTemplateExpression ?: return null

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/JvmDeclarationOrigin.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.psi.JetClassOrObject
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.resolve.jvm.diagnostics.JvmDeclarationOriginKind.*
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils
 
 public enum class MemberKind { FIELD, METHOD }
@@ -39,13 +40,16 @@ public enum class JvmDeclarationOriginKind {
     DELEGATION_TO_TRAIT_IMPL,
     DELEGATION,
     BRIDGE,
+    MULTIFILE_CLASS,
+    MULTIFILE_CLASS_PART,
     SYNTHETIC // this means that there's no proper descriptor for this jvm declaration
 }
 
 public class JvmDeclarationOrigin(
         public val originKind: JvmDeclarationOriginKind,
         public val element: PsiElement?,
-        public val descriptor: DeclarationDescriptor?
+        public val descriptor: DeclarationDescriptor?,
+        public val multifileClassFqName: FqName? = null
 ) {
     companion object {
         public val NO_ORIGIN: JvmDeclarationOrigin = JvmDeclarationOrigin(OTHER, null, null)
@@ -67,6 +71,11 @@ public fun Bridge(descriptor: DeclarationDescriptor, element: PsiElement? = Desc
 public fun PackageFacade(descriptor: PackageFragmentDescriptor): JvmDeclarationOrigin = JvmDeclarationOrigin(PACKAGE_FACADE, null, descriptor)
 public fun PackagePart(file: JetFile, descriptor: PackageFragmentDescriptor): JvmDeclarationOrigin = JvmDeclarationOrigin(PACKAGE_PART, file, descriptor)
 
+public fun MultifileClass(descriptor: PackageFragmentDescriptor, multifileClassFqName: FqName): JvmDeclarationOrigin =
+        JvmDeclarationOrigin(MULTIFILE_CLASS, null, descriptor, multifileClassFqName)
+public fun MultifileClassPart(file: JetFile, descriptor: PackageFragmentDescriptor, multifileClassFqName: FqName): JvmDeclarationOrigin =
+        JvmDeclarationOrigin(MULTIFILE_CLASS_PART, file, descriptor, multifileClassFqName)
+
 public fun TraitImpl(element: JetClassOrObject, descriptor: ClassDescriptor): JvmDeclarationOrigin = JvmDeclarationOrigin(TRAIT_IMPL, element, descriptor)
 public fun DelegationToTraitImpl(element: PsiElement?, descriptor: FunctionDescriptor): JvmDeclarationOrigin =
         JvmDeclarationOrigin(DELEGATION_TO_TRAIT_IMPL, element, descriptor)

compiler/light-classes/src/org/jetbrains/kotlin/asJava/KotlinJavaFileStubProvider.java

@@ -214,7 +214,7 @@ public class KotlinJavaFileStubProvider<T extends WithFileStubAndExtraDiagnostic
 
                     @Override
                     public void generate(@NotNull GenerationState state, @NotNull Collection<JetFile> files) {
-                        PackageCodegen codegen = state.getFactory().forFacade(facadeFqName, files);
+                        PackageCodegen codegen = state.getFactory().forFacadeLightClass(facadeFqName, files);
                         codegen.generate(CompilationErrorHandler.THROW_EXCEPTION);
                         state.getFactory().asList();
                     }
@@ -415,6 +415,7 @@ public class KotlinJavaFileStubProvider<T extends WithFileStubAndExtraDiagnostic
                     /*generateClassFilter=*/stubGenerationStrategy.getGenerateClassFilter(),
                     /*disableInline=*/false,
                     /*disableOptimization=*/false,
+                    /*packageFacadesAsMultifileClasses=*/false,
                     forExtraDiagnostics
             );
             KotlinCodegenFacade.prepareForCompilation(state);

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

@@ -67,6 +67,7 @@ public class CodegenTestUtil {
                 GenerationState.GenerateClassFilter.GENERATE_ALL,
                 configuration.get(JVMConfigurationKeys.DISABLE_INLINE, false),
                 configuration.get(JVMConfigurationKeys.DISABLE_OPTIMIZATION, false),
+                configuration.get(JVMConfigurationKeys.PACKAGE_FACADES_AS_MULTIFILE_CLASSES, false),
                 forExtraDiagnostics
         );
         KotlinCodegenFacade.compileCorrectFiles(state, CompilationErrorHandler.THROW_EXCEPTION);

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/JvmAnnotationNames.java

@@ -31,6 +31,8 @@ public final class JvmAnnotationNames {
     public static final FqName KOTLIN_CLASS = KotlinClass.CLASS_NAME.getFqNameForClassNameWithoutDollars();
     public static final FqName KOTLIN_PACKAGE = new FqName("kotlin.jvm.internal.KotlinPackage");
     public static final FqName KOTLIN_FILE_FACADE = new FqName("kotlin.jvm.internal.KotlinFileFacade");
+    public static final FqName KOTLIN_MULTIFILE_CLASS = new FqName("kotlin.jvm.internal.KotlinMultifileClass");
+    public static final FqName KOTLIN_MULTIFILE_CLASS_PART = new FqName("kotlin.jvm.internal.KotlinMultifileClassPart");
     public static final FqName KOTLIN_CALLABLE = new FqName("kotlin.jvm.internal.KotlinCallable");
 
     public static final FqName KOTLIN_SIGNATURE = new FqName("kotlin.jvm.KotlinSignature");
@@ -38,6 +40,8 @@ public final class JvmAnnotationNames {
 
     public static final String ABI_VERSION_FIELD_NAME = "abiVersion";
     public static final String KIND_FIELD_NAME = "kind";
+    public static final String FILE_PART_CLASS_NAMES_FIELD_NAME = "filePartClassNames";
+    public static final String MULTIFILE_CLASS_NAME_FIELD_NAME = "multifileClassName";
     public static final String DATA_FIELD_NAME = "data";
     public static final Name DEFAULT_ANNOTATION_MEMBER_NAME = Name.identifier("value");
     public static final Name TARGET_ANNOTATION_MEMBER_NAME = Name.identifier("allowedTargets");

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/header/KotlinClassHeader.kt

@@ -25,7 +25,9 @@ public class KotlinClassHeader(
         public val version: Int,
         public val annotationData: Array<String>?,
         public val classKind: KotlinClass.Kind?,
-        public val syntheticClassKind: KotlinSyntheticClass.Kind?
+        public val syntheticClassKind: KotlinSyntheticClass.Kind?,
+        public val filePartClassNames: Array<String>?,
+        public val multifileClassName: String?
 ) {
     public val isCompatibleAbiVersion: Boolean get() = AbiVersionUtil.isAbiVersionCompatible(version)
 
@@ -33,6 +35,8 @@ public class KotlinClassHeader(
         CLASS,
         PACKAGE_FACADE,
         FILE_FACADE,
+        MULTIFILE_CLASS,
+        MULTIFILE_CLASS_PART,
         SYNTHETIC_CLASS
     }
 
@@ -46,4 +50,6 @@ public class KotlinClassHeader(
 public fun KotlinClassHeader.isCompatibleClassKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.CLASS
 public fun KotlinClassHeader.isCompatiblePackageFacadeKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.PACKAGE_FACADE
 public fun KotlinClassHeader.isCompatibleFileFacadeKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.FILE_FACADE
+public fun KotlinClassHeader.isCompatibleMultifileClassKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.MULTIFILE_CLASS
+public fun KotlinClassHeader.isCompatibleMultifileClassPartKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.MULTIFILE_CLASS_PART
 public fun KotlinClassHeader.isCompatibleSyntheticClassKind(): Boolean = isCompatibleAbiVersion && kind == KotlinClassHeader.Kind.SYNTHETIC_CLASS

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/header/ReadKotlinClassHeaderAnnotationVisitor.java

@@ -37,11 +37,12 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
     private static final Map<JvmClassName, KotlinClassHeader.Kind> HEADER_KINDS = new HashMap<JvmClassName, KotlinClassHeader.Kind>();
     private static final Map<JvmClassName, KotlinClassHeader.Kind> OLD_DEPRECATED_ANNOTATIONS_KINDS = new HashMap<JvmClassName, KotlinClassHeader.Kind>();
 
-    private int version = AbiVersionUtil.INVALID_VERSION;
     static {
         HEADER_KINDS.put(KotlinClass.CLASS_NAME, CLASS);
         HEADER_KINDS.put(JvmClassName.byFqNameWithoutInnerClasses(KOTLIN_PACKAGE), PACKAGE_FACADE);
         HEADER_KINDS.put(JvmClassName.byFqNameWithoutInnerClasses(KOTLIN_FILE_FACADE), FILE_FACADE);
+        HEADER_KINDS.put(JvmClassName.byFqNameWithoutInnerClasses(KOTLIN_MULTIFILE_CLASS), MULTIFILE_CLASS);
+        HEADER_KINDS.put(JvmClassName.byFqNameWithoutInnerClasses(KOTLIN_MULTIFILE_CLASS_PART), MULTIFILE_CLASS_PART);
         HEADER_KINDS.put(KotlinSyntheticClass.CLASS_NAME, SYNTHETIC_CLASS);
 
         initOldAnnotations();
@@ -58,6 +59,9 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
         OLD_DEPRECATED_ANNOTATIONS_KINDS.put(JvmClassName.byFqNameWithoutInnerClasses(OLD_KOTLIN_TRAIT_IMPL), SYNTHETIC_CLASS);
     }
 
+    private int version = AbiVersionUtil.INVALID_VERSION;
+    private String multifileClassName = null;
+    private String[] filePartClassNames = null;
     private String[] annotationData = null;
     private KotlinClassHeader.Kind headerKind = null;
     private KotlinClass.Kind classKind = null;
@@ -75,16 +79,24 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
         }
 
         if (!AbiVersionUtil.isAbiVersionCompatible(version)) {
-            return new KotlinClassHeader(headerKind, version, null, classKind, syntheticClassKind);
+            return new KotlinClassHeader(headerKind, version, null, classKind, syntheticClassKind, null, null);
         }
 
-        if ((headerKind == CLASS || headerKind == PACKAGE_FACADE || headerKind == FILE_FACADE) && annotationData == null) {
+        if (shouldHaveData() && annotationData == null) {
             // This means that the annotation is found and its ABI version is compatible, but there's no "data" string array in it.
             // We tell the outside world that there's really no annotation at all
             return null;
         }
 
-        return new KotlinClassHeader(headerKind, version, annotationData, classKind, syntheticClassKind);
+        return new KotlinClassHeader(headerKind, version, annotationData, classKind, syntheticClassKind, filePartClassNames, multifileClassName);
+    }
+
+    private boolean shouldHaveData() {
+        return headerKind == CLASS ||
+               headerKind == PACKAGE_FACADE ||
+               headerKind == FILE_FACADE ||
+               headerKind == MULTIFILE_CLASS ||
+               headerKind == MULTIFILE_CLASS_PART;
     }
 
     @Nullable
@@ -136,15 +148,38 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
 
         @Override
         public void visit(@Nullable Name name, @Nullable Object value) {
-            if (name != null && name.asString().equals(ABI_VERSION_FIELD_NAME)) {
-                version = value instanceof Integer ? (Integer) value : AbiVersionUtil.INVALID_VERSION;
+            if (name != null) {
+                if (name.asString().equals(ABI_VERSION_FIELD_NAME)) {
+                    version = value instanceof Integer ? (Integer) value : AbiVersionUtil.INVALID_VERSION;
+                }
+                else if (name.asString().equals(MULTIFILE_CLASS_NAME_FIELD_NAME)) {
+                    multifileClassName = value instanceof String ? (String) value : null;
+                }
             }
         }
 
         @Override
         @Nullable
         public AnnotationArrayArgumentVisitor visitArray(@NotNull Name name) {
-            return name.asString().equals(DATA_FIELD_NAME) ? stringArrayVisitor() : null;
+            if (name.asString().equals(DATA_FIELD_NAME)) {
+                return dataArrayVisitor();
+            }
+            else if (name.asString().equals(FILE_PART_CLASS_NAMES_FIELD_NAME)) {
+                return filePartClassNamesVisitor();
+            }
+            else {
+                return null;
+            }
+        }
+
+        @NotNull
+        private AnnotationArrayArgumentVisitor filePartClassNamesVisitor() {
+            return new CollectStringArrayAnnotationVisitor() {
+                @Override
+                protected void visitEnd(String[] data) {
+                    filePartClassNames = data;
+                }
+            };
         }
 
         @Override
@@ -158,24 +193,11 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
         }
 
         @NotNull
-        private AnnotationArrayArgumentVisitor stringArrayVisitor() {
-            final List<String> strings = new ArrayList<String>(1);
-            return new AnnotationArrayArgumentVisitor() {
+        private AnnotationArrayArgumentVisitor dataArrayVisitor() {
+            return new CollectStringArrayAnnotationVisitor() {
                 @Override
-                public void visit(@Nullable Object value) {
-                    if (value instanceof String) {
-                        strings.add((String) value);
-                    }
-                }
-
-                @Override
-                public void visitEnum(@NotNull ClassId enumClassId, @NotNull Name enumEntryName) {
-                }
-
-                @Override
-                public void visitEnd() {
-                    //noinspection SSBasedInspection
-                    annotationData = strings.toArray(new String[strings.size()]);
+                protected void visitEnd(String[] data) {
+                    annotationData = data;
                 }
             };
         }
@@ -183,6 +205,33 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
         @Override
         public void visitEnd() {
         }
+
+        private abstract class CollectStringArrayAnnotationVisitor implements AnnotationArrayArgumentVisitor {
+            private final List<String> strings;
+
+            public CollectStringArrayAnnotationVisitor() {
+                this.strings = new ArrayList<String>();
+            }
+
+            @Override
+            public void visit(@Nullable Object value) {
+                if (value instanceof String) {
+                    strings.add((String) value);
+                }
+            }
+
+            @Override
+            public void visitEnum(@NotNull ClassId enumClassId, @NotNull Name enumEntryName) {
+            }
+
+            @Override
+            public void visitEnd() {
+                //noinspection SSBasedInspection
+                visitEnd(strings.toArray(new String[strings.size()]));
+            }
+
+            protected abstract void visitEnd(String[] data);
+        }
     }
 
     private class ClassHeaderReader extends HeaderAnnotationArgumentVisitor {

core/runtime.jvm/src/kotlin/jvm/internal/KotlinMultifileClass.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlin.jvm.internal;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface KotlinMultifileClass {
+    int abiVersion();
+
+    String[] filePartClassNames();
+    String[] data();
+}

core/runtime.jvm/src/kotlin/jvm/internal/KotlinMultifileClassPart.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlin.jvm.internal;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface KotlinMultifileClassPart {
+    int abiVersion();
+
+    String multifileClassName();
+    String[] data();
+}

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/DecompiledUtils.kt

@@ -70,7 +70,8 @@ public fun isKotlinInternalCompiledFile(file: VirtualFile): Boolean {
     }
     val header = KotlinBinaryClassCache.getKotlinBinaryClass(file)?.getClassHeader() ?: return false
     return (header.kind == KotlinClassHeader.Kind.SYNTHETIC_CLASS && header.syntheticClassKind != KotlinSyntheticClass.Kind.PACKAGE_PART) ||
-           (header.kind == KotlinClassHeader.Kind.CLASS && header.classKind != null && header.classKind != KotlinClass.Kind.CLASS)
+           (header.kind == KotlinClassHeader.Kind.CLASS && header.classKind != null && header.classKind != KotlinClass.Kind.CLASS) ||
+           (header.kind == KotlinClassHeader.Kind.MULTIFILE_CLASS_PART)
 }
 
 public fun isKotlinJavaScriptInternalCompiledFile(file: VirtualFile): Boolean =

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/ClsStubBuilderContext.kt

@@ -83,7 +83,7 @@ private fun ClsStubBuilderContext.child(typeParameterList: List<ProtoBuf.TypePar
     )
 }
 
-private fun ClsStubBuilderContext.child(nameResolver: NameResolver): ClsStubBuilderContext {
+internal fun ClsStubBuilderContext.child(nameResolver: NameResolver): ClsStubBuilderContext {
     return ClsStubBuilderContext(
             this.components,
             nameResolver,

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/KotlinClsStubBuilder.kt

@@ -28,11 +28,10 @@ import org.jetbrains.kotlin.idea.decompiler.textBuilder.DirectoryBasedDataFinder
 import org.jetbrains.kotlin.idea.decompiler.textBuilder.LoggingErrorReporter
 import org.jetbrains.kotlin.load.java.JvmAnnotationNames
 import org.jetbrains.kotlin.load.kotlin.KotlinBinaryClassCache
-import org.jetbrains.kotlin.load.kotlin.header.isCompatibleClassKind
-import org.jetbrains.kotlin.load.kotlin.header.isCompatibleFileFacadeKind
-import org.jetbrains.kotlin.load.kotlin.header.isCompatiblePackageFacadeKind
-import org.jetbrains.kotlin.load.kotlin.header.isCompatibleSyntheticClassKind
+import org.jetbrains.kotlin.load.kotlin.header.*
+import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.JetFile
 import org.jetbrains.kotlin.serialization.jvm.JvmProtoBufUtil
 
@@ -81,10 +80,35 @@ public open class KotlinClsStubBuilder : ClsStubBuilder() {
                 val context = components.createContext(packageData.getNameResolver(), packageFqName)
                 createFileFacadeStub(packageData.getPackageProto(), classId.asSingleFqName(), context)
             }
+            header.isCompatibleMultifileClassKind() -> {
+                val packageData = JvmProtoBufUtil.readPackageDataFrom(annotationData)
+                val context = components.createContext(packageData.nameResolver, packageFqName)
+                val partHeaders = readMultifileClassPartHeaders(file, header, packageFqName)
+                partHeaders?.let {
+                    createMultifileClassStub(it, classId.asSingleFqName(), context)
+                }
+            }
             else -> throw IllegalStateException("Should have processed " + file.getPath() + " with header $header")
         }
     }
 
+    private fun readMultifileClassPartHeaders(file: VirtualFile, header: KotlinClassHeader, packageFqName: FqName): List<KotlinClassHeader>? {
+        val result = arrayListOf<KotlinClassHeader>()
+        val partsFinder = DirectoryBasedClassFinder(file.parent!!, packageFqName)
+        val partNames = header.filePartClassNames
+        if (partNames != null) {
+            for (partName in partNames) {
+                val partClass = partsFinder.findKotlinClass(ClassId.topLevel(packageFqName.child(Name.identifier(partName))))
+                if (partClass == null) {
+                    LOG.error("Missing part class: $packageFqName.$partName")
+                    return null
+                }
+                result.add(partClass.classHeader)
+            }
+        }
+        return result
+    }
+
     private fun createStubBuilderComponents(file: VirtualFile, packageFqName: FqName): ClsStubBuilderComponents {
         val classFinder = DirectoryBasedClassFinder(file.getParent()!!, packageFqName)
         val classDataFinder = DirectoryBasedDataFinder(classFinder, LOG)
@@ -93,6 +117,6 @@ public open class KotlinClsStubBuilder : ClsStubBuilder() {
     }
 
     companion object {
-        val LOG = Logger.getInstance(javaClass<KotlinClsStubBuilder>())
+        val LOG = Logger.getInstance(KotlinClsStubBuilder::class.java)
     }
 }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/clsStubBuilding.kt

@@ -20,9 +20,9 @@ import com.intellij.psi.PsiElement
 import com.intellij.psi.stubs.StubElement
 import com.intellij.util.io.StringRef
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
-import org.jetbrains.kotlin.descriptors.annotations.AnnotationUseSiteTarget
 import org.jetbrains.kotlin.lexer.JetModifierKeywordToken
 import org.jetbrains.kotlin.lexer.JetTokens
+import org.jetbrains.kotlin.load.kotlin.header.KotlinClassHeader
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.serialization.ProtoBuf
 import org.jetbrains.kotlin.serialization.ProtoBuf.Callable.CallableKind
 import org.jetbrains.kotlin.serialization.deserialization.AnnotatedCallableKind
 import org.jetbrains.kotlin.serialization.deserialization.ProtoContainer
+import org.jetbrains.kotlin.serialization.jvm.JvmProtoBufUtil
 
 fun createTopLevelClassStub(classId: ClassId, classProto: ProtoBuf.Class, context: ClsStubBuilderContext): KotlinFileStubImpl {
     val fileStub = createFileStub(classId.getPackageFqName())
@@ -71,6 +72,25 @@ fun createFileFacadeStub(
     return fileStub
 }
 
+fun createMultifileClassStub(
+        partHeaders: List<KotlinClassHeader>,
+        facadeFqName: FqName,
+        c: ClsStubBuilderContext
+): KotlinFileStubImpl {
+    val packageFqName = facadeFqName.parent()
+    val fileStub = KotlinFileStubImpl.forFileFacadeStub(facadeFqName, packageFqName.isRoot)
+    setupFileStub(fileStub, packageFqName)
+    val multifileClassContainer = ProtoContainer(null, facadeFqName.parent())
+    for (partHeader in partHeaders) {
+        val partData = JvmProtoBufUtil.readPackageDataFrom(partHeader.annotationData!!)
+        val partContext = c.child(partData.nameResolver)
+        for (partMember in partData.packageProto.memberList) {
+            createCallableStub(fileStub, partMember, partContext, multifileClassContainer)
+        }
+    }
+    return fileStub
+}
+
 fun createIncompatibleAbiVersionFileStub() = createFileStub(FqName.ROOT)
 
 fun createFileStub(packageFqName: FqName): KotlinFileStubImpl {

idea/src/org/jetbrains/kotlin/idea/internal/KotlinBytecodeToolWindow.java

@@ -239,6 +239,7 @@ public class KotlinBytecodeToolWindow extends JPanel implements Disposable {
                                         generateClassFilter,
                                         !enableInline,
                                         !enableOptimization,
+                                        /*packageFacadesAsMultifileClasses=*/false,
                                         sink);
             KotlinCodegenFacade.compileCorrectFiles(state, CompilationErrorHandler.THROW_EXCEPTION);
         }

libraries/stdlib/src/kotlin/jvm/JvmPlatformAnnotations.kt

@@ -50,6 +50,14 @@ public annotation class JvmStatic
 @MustBeDocumented
 public annotation class JvmName(public val name: String)
 
+/**
+ * Instructs the Kotlin compiler to generate a multifile class with this file as one o
+ */
+target(AnnotationTarget.FILE)
+@Retention(AnnotationRetention.RUNTIME)
+@MustBeDocumented
+public annotation class JvmMultifileClass
+
 /**
  * Instructs the Kotlin compiler to generate a public backing field for this property.
  */