JVM IR: write inherited multifile parts flag to kotlin.Metadata

This flag is unused at the moment, but might be used one day to support
proper incremental compilation for multifile classes.

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

@@ -10,8 +10,12 @@ import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.backend.jvm.lower.MultifileFacadeFileEntry
 import org.jetbrains.kotlin.backend.jvm.lower.buildAssertionsDisabledField
 import org.jetbrains.kotlin.backend.jvm.lower.hasAssertionsDisabledField
-import org.jetbrains.kotlin.codegen.*
+import org.jetbrains.kotlin.codegen.DescriptorAsmUtil
+import org.jetbrains.kotlin.codegen.VersionIndependentOpcodes
+import org.jetbrains.kotlin.codegen.addRecordComponent
 import org.jetbrains.kotlin.codegen.inline.*
+import org.jetbrains.kotlin.codegen.writeKotlinMetadata
+import org.jetbrains.kotlin.config.JvmAnalysisFlags
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
@@ -194,9 +198,6 @@ class ClassCodegen private constructor(
         )
 
     private fun generateKotlinMetadataAnnotation() {
-        // TODO: if `-Xmultifile-parts-inherit` is enabled, write the corresponding flag for parts and facades to [Metadata.extraInt].
-        val extraFlags = context.backendExtension.generateMetadataExtraFlags(state.abiStability)
-
         val facadeClassName = context.multifileFacadeForPart[irClass.attributeOwnerId]
         val metadata = irClass.metadata
         val entry = irClass.fileParent.fileEntry
@@ -208,6 +209,14 @@ class ClassCodegen private constructor(
             entry is MultifileFacadeFileEntry -> KotlinClassHeader.Kind.MULTIFILE_CLASS
             else -> KotlinClassHeader.Kind.SYNTHETIC_CLASS
         }
+
+        val isMultifileClassOrPart = kind == KotlinClassHeader.Kind.MULTIFILE_CLASS || kind == KotlinClassHeader.Kind.MULTIFILE_CLASS_PART
+
+        var extraFlags = context.backendExtension.generateMetadataExtraFlags(state.abiStability)
+        if (isMultifileClassOrPart && state.languageVersionSettings.getFlag(JvmAnalysisFlags.inheritMultifileParts)) {
+            extraFlags = extraFlags or JvmAnnotationNames.METADATA_MULTIFILE_PARTS_INHERIT_FLAG
+        }
+
         writeKotlinMetadata(visitor, state, kind, extraFlags) {
             if (metadata != null) {
                 metadataSerializer.serialize(metadata)?.let { (proto, stringTable) ->
@@ -229,9 +238,7 @@ class ClassCodegen private constructor(
             }
 
             if (irClass in context.classNameOverride) {
-                val isFileClass = kind == KotlinClassHeader.Kind.MULTIFILE_CLASS ||
-                        kind == KotlinClassHeader.Kind.MULTIFILE_CLASS_PART ||
-                        kind == KotlinClassHeader.Kind.FILE_FACADE
+                val isFileClass = isMultifileClassOrPart || kind == KotlinClassHeader.Kind.FILE_FACADE
                 assert(isFileClass) { "JvmPackageName is not supported for classes: ${irClass.render()}" }
                 it.visit(JvmAnnotationNames.METADATA_PACKAGE_NAME_FIELD_NAME, irClass.fqNameWhenAvailable!!.parent().asString())
             }