Introduce KlibMetadataHeaderFlags

This class lists possible flags for KlibMetadataProtoBuf.Header, and
helps avoid using magic constants in the source code.

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

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.backend.common.serialization.isSerializableExpectCla
 import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
+import org.jetbrains.kotlin.library.metadata.KlibMetadataHeaderFlags
 import org.jetbrains.kotlin.library.metadata.KlibMetadataProtoBuf
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.deserialization.BinaryVersion
@@ -255,7 +256,7 @@ fun serializeKlibHeader(
     header.moduleName = moduleDescriptor.name.asString()
 
     if (languageVersionSettings.isPreRelease()) {
-        header.flags = 1
+        header.flags = KlibMetadataHeaderFlags.PRE_RELEASE
     }
 
     fragmentNames.forEach {

compiler/util-klib-metadata/src/KlibMetadataProtoBuf.proto

@@ -25,7 +25,7 @@ option optimize_for = LITE_RUNTIME;
 message Header {
   required string module_name = 1;
   /*
-    0x1 = preRelease
+    Possible values are listed in KlibMetadataHeaderFlags class.
   */
   optional int32 flags = 2;
   optional org.jetbrains.kotlin.metadata.StringTable strings = 4;

compiler/util-klib-metadata/src/org/jetbrains/kotlin/library/metadata/KlibDeserializedContainerSource.kt

@@ -20,7 +20,7 @@ class KlibDeserializedContainerSource private constructor(
 
     constructor(header: Header, configuration: DeserializationConfiguration, packageFqName: FqName) : this(
         configuration.reportErrorsOnPreReleaseDependencies &&
-                (header.flags and 1) != 0,
+                (header.flags and KlibMetadataHeaderFlags.PRE_RELEASE) != 0,
         "Package '$packageFqName'"
     )
 

compiler/util-klib-metadata/src/org/jetbrains/kotlin/library/metadata/KlibMetadataHeaderFlags.kt

@@ -0,0 +1,13 @@
+/*
+ * 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 org.jetbrains.kotlin.library.metadata
+
+/**
+ * Possible values for [KlibMetadataProtoBuf.Header] flags field.
+ */
+object KlibMetadataHeaderFlags {
+    const val PRE_RELEASE = 0x1
+}