Don't set Kotlin platform attribute for the default configuration

Also, fix empty configurations created for targets that have no runtime
outputs (metadata ones, especially), which could get chosen by Gradle
during dependency variant-aware resolution of a `project(...)`
dependency.

See also: d13ca38

With the attribute set, an input configuration that does not require the
Gradle's USAGE attribute but requires Kotlin platform metadata, will
fail to resolve because the attributes set on the consumable
output configurations are not subsets of each other, as follows:

> Cannot choose between the following variants of project :lib:
  - metadataApiElements
  - metadataDefault
  - metadataRuntimeElements
  All of them match the consumer attributes:
    - Variant 'metadataApiElements':
      - Found org.gradle.usage 'java-api' but wasn't required.
      - Required org.jetbrains.kotlin.platform.type 'common' and found
        compatible value 'common'.
    - Variant 'metadataDefault':
      - Required org.jetbrains.kotlin.platform.type 'common' and found
        compatible value 'common'.
    - Variant 'metadataRuntimeElements':
      - Found org.gradle.usage 'java-runtime-jars' but wasn't required.
      - Required org.jetbrains.kotlin.platform.type 'common' and found
        compatible value 'common'.

Issue #KT-26383 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/NewMultiplatformIT.kt

@@ -2,7 +2,6 @@
  * Copyright 2010-2018 JetBrains s.r.o. 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.gradle
 
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinMultiplatformPlugin
@@ -399,6 +398,38 @@ class NewMultiplatformIT : BaseGradleIT() {
         }
     }
 
+    @Test
+    fun testResolveMppProjectDependencyToMetadata() {
+        val libProject = Project("sample-lib", gradleVersion, "new-mpp-lib-and-app")
+        val appProject = Project("sample-app", gradleVersion, "new-mpp-lib-and-app")
+
+        val pathPrefix = "metadataDependency: "
+
+        with(appProject) {
+            setupWorkingDir()
+            libProject.setupWorkingDir()
+
+            libProject.projectDir.copyRecursively(projectDir.resolve(libProject.projectDir.name))
+            projectDir.resolve("settings.gradle").appendText("\ninclude '${libProject.projectDir.name}'")
+            gradleBuildScript().modify {
+                it.replace("'com.example:sample-lib:1.0'", "project(':${libProject.projectDir.name}')") +
+                        "\n" + """
+                        task('printMetadataFiles') {
+                           doFirst {
+                               configurations.getByName('commonMainImplementation$METADATA_CONFIGURATION_NAME_SUFFIX')
+                                   .files.each { println '$pathPrefix' + it.name }
+                           }
+                        }
+                        """.trimIndent()
+            }
+
+            build("printMetadataFiles") {
+                assertSuccessful()
+                assertContains(pathPrefix + "sample-lib-metadata-1.0.jar")
+            }
+        }
+    }
+
     @Test
     fun testPublishingOnlySupportedNativeTargets() = with(Project("sample-lib", gradleVersion, "new-mpp-lib-and-app")) {
         val (publishedVariant, nonPublishedVariant) = when {

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinTargetConfigurator.kt

@@ -173,7 +173,7 @@ abstract class AbstractKotlinTargetConfigurator<KotlinTargetType : KotlinTarget>
 
         val runtimeOnlyConfiguration = configurations.maybeCreate(mainCompilation.runtimeOnlyConfigurationName)
 
-        configurations.maybeCreate(target.apiElementsConfigurationName).apply {
+        val apiElementsConfiguration = configurations.maybeCreate(target.apiElementsConfigurationName).apply {
             description = "API elements for main."
             isVisible = false
             isCanBeResolved = false
@@ -187,20 +187,21 @@ abstract class AbstractKotlinTargetConfigurator<KotlinTargetType : KotlinTarget>
             usesPlatformOf(target)
         }
 
+        if (mainCompilation is KotlinCompilationToRunnableFiles) {
             val runtimeElementsConfiguration = configurations.maybeCreate(target.runtimeElementsConfigurationName).apply {
                 description = "Elements of runtime for main."
                 isVisible = false
                 isCanBeConsumed = true
                 isCanBeResolved = false
                 attributes.attribute<Usage>(USAGE_ATTRIBUTE, project.usageByName(Usage.JAVA_RUNTIME_JARS))
-            if (mainCompilation is KotlinCompilationToRunnableFiles) {
                 val runtimeConfiguration = configurations.maybeCreate(mainCompilation.deprecatedRuntimeConfigurationName)
                 extendsFrom(implementationConfiguration, runtimeOnlyConfiguration, runtimeConfiguration)
-            }
                 usesPlatformOf(target)
             }
-
+            defaultConfiguration.extendsFrom(runtimeElementsConfiguration)
-        defaultConfiguration.extendsFrom(runtimeElementsConfiguration).usesPlatformOf(target)
+        } else {
+            defaultConfiguration.extendsFrom(apiElementsConfiguration)
+        }
 
         if (createTestCompilation) {
             val testCompilation = target.compilations.getByName(KotlinCompilation.TEST_COMPILATION_NAME)