[Gradle] Make sure that rootSoftwareComponent is always added

Even when createDefaultMultiplatformPublications=false and maven-publish
is applied it is required to create all publication-specific entities
such as tasks, configurations, components etc. In order to let users
to compose publications on their own.

^KT-62877 Verification Pending

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/Publishing.kt

@@ -38,15 +38,14 @@ internal val Project.kotlinMultiplatformRootPublication: Future<MavenPublication
     get() = kotlinMultiplatformRootPublicationImpl
 
 internal val MultiplatformPublishingSetupAction = KotlinProjectSetupCoroutine {
-    if (!project.kotlinPropertiesProvider.createDefaultMultiplatformPublications) {
-        kotlinMultiplatformRootPublicationImpl.complete(null)
-        return@KotlinProjectSetupCoroutine
-    }
-
     if (isPluginApplied("maven-publish")) {
-        project.extensions.configure(PublishingExtension::class.java) { publishing ->
-            createRootPublication(project, publishing).also(kotlinMultiplatformRootPublicationImpl::complete)
-            createTargetPublications(project, publishing)
+        if (project.kotlinPropertiesProvider.createDefaultMultiplatformPublications) {
+            project.extensions.configure(PublishingExtension::class.java) { publishing ->
+                createRootPublication(project, publishing).also(kotlinMultiplatformRootPublicationImpl::complete)
+                createTargetPublications(project, publishing)
+            }
+        } else {
+            kotlinMultiplatformRootPublicationImpl.complete(null)
         }
         project.components.add(project.multiplatformExtension.rootSoftwareComponent)
     } else {

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

@@ -19,6 +19,7 @@ import org.gradle.api.publish.maven.MavenPublication
 import org.gradle.testfixtures.ProjectBuilder
 import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
 import org.jetbrains.kotlin.gradle.plugin.mpp.internal
+import org.jetbrains.kotlin.gradle.util.*
 import org.jetbrains.kotlin.gradle.util.addBuildEventsListenerRegistryMock
 import org.jetbrains.kotlin.gradle.util.disableLegacyWarning
 import org.jetbrains.kotlin.util.capitalizeDecapitalize.toLowerCaseAsciiOnly
@@ -227,6 +228,46 @@ class MppPublicationTest {
         }
     }
 
+    @Test
+    fun `test creation of default publications can be disabled`() {
+        val project = buildProject { }
+        project.propertiesExtension.set("kotlin.internal.mpp.createDefaultMultiplatformPublications", "false")
+        project.plugins.apply("kotlin-multiplatform")
+        project.plugins.apply("maven-publish")
+
+        project.kotlin {
+            jvm()
+            linuxArm64()
+        }
+
+        project.evaluate()
+
+        val publishing = project.extensions.getByType(PublishingExtension::class.java)
+        val actualPublications = publishing.publications.names
+        if (actualPublications.isNotEmpty()) fail("Expected no default publications to be created")
+
+        // Even though creation of default publications are disabled
+        // it is still important that components and everything else needed for publishing are still present
+        val components = project.components.names
+        assertEquals(setOf("kotlin"), components)
+
+        val expectedSourcesJarTasks = setOf("sourcesJar", "metadataSourcesJar", "jvmSourcesJar", "linuxArm64SourcesJar")
+        val missingSourcesJarTasks = expectedSourcesJarTasks - project.tasks.names
+        if (missingSourcesJarTasks.isNotEmpty()) fail("Following sources jar tasks are not created: $missingSourcesJarTasks")
+
+        val expectedConfigurations = setOf(
+            "jvmApiElements",
+            "jvmApiElements-published",
+            "jvmRuntimeElements",
+            "jvmRuntimeElements-published",
+            "jvmSourcesElements",
+            "jvmSourcesElements-published",
+            "metadataApiElements",
+        )
+        val missingConfigurations = expectedConfigurations - project.configurations.names
+        if (missingConfigurations.isNotEmpty()) fail("Following configurations are not created: $missingConfigurations")
+    }
+
     private fun SoftwareComponent.attributesOfUsageContext(usageContextName: String): AttributeContainer {
         this as SoftwareComponentInternal
         return usages.first { it.name == usageContextName }.attributes