[KLIB] Use -Xmetadata-klib to produce metadata KLIBs

With this change a new `-Xmetadata-klib` CLI flag becomes the
preferable way to instruct K2MetadataCompiler to produce metadata
KLIBs. The old `-Xexpect-actual-linker` flag still works for
K2MetadataCompiler, but that would last just for a short transition
period until the necessary changes are made in the Gradle plugin.

The K2NativeCompiler does not work anymore with `-Xexpect-actual-linker`
and respects only the `-Xmetadata-klib` flag. This is not an
issue since the Gradle plugin anyway supplies both flags for Native
metadata compilations.

^KT-61136

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonCompilerArguments.kt

@@ -818,7 +818,7 @@ abstract class CommonCompilerArguments : CommonToolArguments() {
                 )
             }
             put(AnalysisFlags.optIn, useExperimentalFqNames + optIn?.toList().orEmpty())
-            put(AnalysisFlags.skipExpectedActualDeclarationChecker, expectActualLinker)
+            put(AnalysisFlags.skipExpectedActualDeclarationChecker, expectActualLinker || metadataKlib) // TODO (KT-61136): drop `expectActualLinker` later, after the appropriate changes in the Gradle plugin
             put(AnalysisFlags.explicitApiVersion, apiVersion != null)
             put(AnalysisFlags.allowResultReturnType, allowResultReturnType)
             ExplicitApiMode.fromString(explicitApi)?.also { put(AnalysisFlags.explicitApiMode, it) } ?: collector.report(

compiler/cli/src/org/jetbrains/kotlin/cli/metadata/K2MetadataCompiler.kt

@@ -101,7 +101,8 @@ class K2MetadataCompiler : CLICompiler<K2MetadataCompilerArguments>() {
         val environment =
             KotlinCoreEnvironment.createForProduction(rootDisposable, configuration, EnvironmentConfigFiles.METADATA_CONFIG_FILES)
 
-        val mode = if(arguments.expectActualLinker) "KLib" else "metadata"
+        // TODO (KT-61136): drop `expectActualLinker` later, after the appropriate changes in the Gradle plugin
+        val mode = if (arguments.expectActualLinker || arguments.metadataKlib) "KLib" else "metadata"
 
         val sourceFiles = environment.getSourceFiles()
         performanceManager.notifyCompilerInitialized(sourceFiles.size, environment.countLinesOfCode(sourceFiles), "$mode mode for $moduleName module")
@@ -120,7 +121,8 @@ class K2MetadataCompiler : CLICompiler<K2MetadataCompilerArguments>() {
             val useFir = configuration.getBoolean(CommonConfigurationKeys.USE_FIR)
             val metadataSerializer = when {
                 useFir -> FirMetadataSerializer(configuration, environment)
-                arguments.expectActualLinker -> K2MetadataKlibSerializer(configuration, environment)
+                // TODO (KT-61136): drop `expectActualLinker` later, after the appropriate changes in the Gradle plugin
+                arguments.expectActualLinker || arguments.metadataKlib -> K2MetadataKlibSerializer(configuration, environment)
                 else -> MetadataSerializer(configuration, environment, dependOnOldBuiltIns = true)
             }
             metadataSerializer.analyzeAndSerialize()

compiler/tests/org/jetbrains/kotlin/jvm/compiler/AbstractCompileKotlinAgainstCustomBinariesTest.kt

@@ -686,14 +686,14 @@ abstract class AbstractCompileKotlinAgainstCustomBinariesTest : AbstractKotlinCo
     fun testAnonymousObjectTypeMetadataKlib() {
         val klibLibrary = compileCommonLibrary(
             libraryName = "library",
-            listOf("-Xexpect-actual-linker"),
+            listOf("-Xmetadata-klib"),
         )
         compileKotlin(
             "anonymousObjectTypeMetadata.kt",
             tmpdir,
             listOf(klibLibrary),
             K2MetadataCompiler(),
-            listOf("-Xexpect-actual-linker")
+            listOf("-Xmetadata-klib")
         )
     }