[Gradle] Mark "main" metadata compilation as non-klib in all cases

Metadata compilation with name "main" isn't used in Hierarchical
Multiplatform. It used to compile commonMain source set to legacy
metadata artifacts. With Hierarchical MPP common source sets start
to compile to klib metadata.

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/targets/metadata/KotlinMetadataTargetConfigurator.kt

@@ -69,11 +69,12 @@ class KotlinMetadataTargetConfigurator :
             KotlinBuildStatsService.getInstance()?.report(BooleanMetrics.ENABLED_HMPP, true)
 
             target.compilations.withType(KotlinCommonCompilation::class.java).getByName(KotlinCompilation.MAIN_COMPILATION_NAME).run {
+                // Force the default 'main' compilation to produce *.kotlin_metadata regardless of the klib feature flag.
+                forceCompilationToKotlinMetadata = true
+
                 // Capture it here to use in onlyIf spec. Direct usage causes serialization of target attempt when configuration cache is enabled
                 val isCompatibilityMetadataVariantEnabled = target.project.isCompatibilityMetadataVariantEnabled
                 if (isCompatibilityMetadataVariantEnabled) {
-                    // Force the default 'main' compilation to produce *.kotlin_metadata regardless of the klib feature flag.
-                    forceCompilationToKotlinMetadata = true
                     // Add directly dependsOn sources for Legacy Compatibility Metadata variant
                     // it isn't necessary for KLib compilations
                     // see [KotlinCompilationSourceSetInclusion.AddSourcesWithoutDependsOnClosure]

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/KotlinMetadataTargetCompilationsTest.kt

@@ -11,10 +11,12 @@ import org.gradle.api.NamedDomainObjectContainer
 import org.jetbrains.kotlin.gradle.dsl.metadataTarget
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinCommonCompilation
 import org.jetbrains.kotlin.gradle.targets.metadata.awaitMetadataCompilationsCreated
 import org.jetbrains.kotlin.gradle.util.buildProjectWithMPP
 import org.jetbrains.kotlin.gradle.util.runLifecycleAwareTest
 import kotlin.test.Test
+import kotlin.test.assertEquals
 import kotlin.test.fail
 
 class KotlinMetadataTargetCompilationsTest {
@@ -55,6 +57,29 @@ class KotlinMetadataTargetCompilationsTest {
         }
     }
 
+    @Test
+    fun `test - metadata compilations - isKlibCompilation`() {
+        val project = buildProjectWithMPP()
+        val kotlin = project.multiplatformExtension
+        kotlin.jvm()
+        kotlin.linuxX64()
+        kotlin.linuxArm64()
+
+        project.runLifecycleAwareTest {
+            val target = kotlin.metadataTarget
+            val metadataCompilations = target.awaitMetadataCompilationsCreated() // returns common + shared native
+                .filterIsInstance<KotlinCommonCompilation>()
+                .associate { it.name to it.isKlibCompilation }
+
+            val expectedCommonMetadataCompilations = mapOf(
+                "main" to false,
+                "commonMain" to true
+            )
+
+            assertEquals(expectedCommonMetadataCompilations, metadataCompilations)
+        }
+    }
+
     private fun NamedDomainObjectContainer<KotlinCompilation<*>>.assertExists(name: String) {
         if (name !in names) fail("Missing '$name' compilation")
     }