Support published MPP consumption with PM2.0 projects

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

@@ -35,6 +35,9 @@ internal fun Project.createKotlinExtension(extensionClass: KClass<out KotlinTopL
 internal val Project.topLevelExtension: KotlinTopLevelExtension
     get() = extensions.getByName(KOTLIN_PROJECT_EXTENSION_NAME) as KotlinTopLevelExtension
 
+internal val Project.topLevelExtensionOrNull: KotlinTopLevelExtension?
+    get() = extensions.findByName(KOTLIN_PROJECT_EXTENSION_NAME) as KotlinTopLevelExtension?
+
 internal val Project.kotlinExtensionOrNull: KotlinProjectExtension?
     get() = extensions.findByName(KOTLIN_PROJECT_EXTENSION_NAME) as? KotlinProjectExtension
 

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

@@ -36,6 +36,7 @@ import org.jetbrains.kotlin.gradle.logging.kotlinDebug
 import org.jetbrains.kotlin.gradle.model.builder.KotlinModelBuilder
 import org.jetbrains.kotlin.gradle.plugin.mpp.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinCompilationData
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.isMain
 import org.jetbrains.kotlin.gradle.scripting.internal.ScriptingGradleSubplugin
 import org.jetbrains.kotlin.gradle.targets.js.dsl.KotlinJsBinaryMode
 import org.jetbrains.kotlin.gradle.targets.js.ir.*
@@ -283,14 +284,14 @@ internal class Kotlin2JsSourceSetProcessor(
                     val baseName = if (kotlinCompilation.isMain()) {
                         project.name
                     } else {
-                        "${project.name}_${kotlinCompilation.name}"
+                        "${project.name}_${kotlinCompilation.compilationPurpose}"
                     }
                     kotlinTaskInstance.kotlinOptions.freeCompilerArgs += "$MODULE_NAME=${project.klibModuleName(baseName)}"
                 }
             }
 
             val subpluginEnvironment: SubpluginEnvironment = SubpluginEnvironment.loadSubplugins(project, kotlinPluginVersion)
-            if (kotlinCompilation is KotlinCompilation<*>) {
+            if (kotlinCompilation is KotlinCompilation<*>) { // FIXME support compiler plugins with PM20
                 subpluginEnvironment.addSubpluginOptions(project, kotlinCompilation)
             }
         }

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

@@ -86,9 +86,6 @@ abstract class KotlinBasePluginWrapper : Plugin<Project> {
         kotlinGradleBuildServices.detectKotlinPluginLoadedInMultipleProjects(project, kotlinPluginVersion)
 
         project.createKotlinExtension(projectExtensionClass).apply {
-            if (this is KotlinPm20ProjectExtension)
-                this.project = project // refactor this code to remove the specific plugin class?
-
             coreLibrariesVersion = kotlinPluginVersion
 
             fun kotlinSourceSetContainer(factory: NamedDomainObjectFactory<KotlinSourceSet>) =

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

@@ -11,10 +11,6 @@ import org.gradle.api.tasks.Nested
 import org.gradle.api.tasks.OutputFile
 import org.gradle.api.tasks.TaskAction
 import java.io.File
-import javax.xml.transform.OutputKeys
-import javax.xml.transform.TransformerFactory
-import javax.xml.transform.dom.DOMSource
-import javax.xml.transform.stream.StreamResult
 
 open class GenerateProjectStructureMetadata : DefaultTask() {
     @get:Internal
@@ -25,14 +21,14 @@ open class GenerateProjectStructureMetadata : DefaultTask() {
         get() = lazyKotlinProjectStructureMetadata.value
 
     @get:OutputFile
-    val resultXmlFile: File
+    val resultFile: File
         get() = project.buildDir.resolve("kotlinProjectStructureMetadata/$MULTIPLATFORM_PROJECT_METADATA_JSON_FILE_NAME")
 
     @TaskAction
     fun generateMetadataXml() {
-        resultXmlFile.parentFile.mkdirs()
+        resultFile.parentFile.mkdirs()
         val resultString = kotlinProjectStructureMetadata.toJson()
-        resultXmlFile.writeText(resultString)
+        resultFile.writeText(resultString)
     }
 }
 

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

@@ -7,13 +7,15 @@ package org.jetbrains.kotlin.gradle.plugin.mpp
 
 import org.gradle.api.Named
 import org.gradle.api.Project
+import org.gradle.api.artifacts.Configuration
 import org.gradle.api.artifacts.Dependency
 import org.gradle.api.artifacts.ModuleDependency
 import org.gradle.api.artifacts.ProjectDependency
+import org.gradle.api.artifacts.result.ResolvedComponentResult
+import org.gradle.api.artifacts.result.ResolvedDependencyResult
 import org.gradle.api.attributes.Attribute
 import org.gradle.api.attributes.AttributeContainer
-import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
-import org.jetbrains.kotlin.gradle.dsl.KotlinSingleTargetExtension
+import org.jetbrains.kotlin.gradle.dsl.*
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtensionOrNull
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
@@ -28,45 +30,56 @@ class ProjectStructureMetadataModuleBuilder {
     private val modulesCache = mutableMapOf<KotlinModuleIdentifier, KotlinModule>()
 
     private fun buildModuleFromProjectStructureMetadata(
-        moduleIdentifier: KotlinModuleIdentifier,
+        component: ResolvedComponentResult,
         metadata: KotlinProjectStructureMetadata
-    ): KotlinModule =
-        BasicKotlinModule(moduleIdentifier).apply {
-            metadata.sourceSetNamesByVariantName.keys.forEach { variantName ->
-                fragments.add(BasicKotlinModuleVariant(this@apply, variantName))
-            }
-            fun fragment(sourceSetName: String): BasicKotlinModuleFragment {
-                if (fragments.none { it.fragmentName == sourceSetName })
-                    fragments.add(BasicKotlinModuleFragment(this@apply, sourceSetName))
-                return fragmentByName(sourceSetName)
-            }
-            metadata.sourceSetNamesByVariantName.forEach { (variantName, sourceSets) ->
-                val variant = fragmentByName(variantName)
-                sourceSets.forEach { sourceSetName ->
-                    variant.directRefinesDependencies.add(fragment(sourceSetName))
+    ): KotlinModule {
+        return ExternalImportedKotlinModule(
+            BasicKotlinModule(component.toModuleIdentifier()).apply {
+                metadata.sourceSetNamesByVariantName.keys.forEach { variantName ->
+                    fragments.add(BasicKotlinModuleVariant(this@apply, variantName))
                 }
-            }
-            metadata.sourceSetModuleDependencies.forEach { (sourceSetName, dependencies) ->
-                val fragment = fragment(sourceSetName)
-                dependencies.forEach { dependency ->
-                    fragment.declaredModuleDependencies.add(
-                        KotlinModuleDependency(MavenModuleIdentifier(dependency.groupId.orEmpty(), dependency.moduleId, null /* TODO */))
-                    )
+                fun fragment(sourceSetName: String): BasicKotlinModuleFragment {
+                    if (fragments.none { it.fragmentName == sourceSetName })
+                        fragments.add(BasicKotlinModuleFragment(this@apply, sourceSetName))
+                    return fragmentByName(sourceSetName)
+                }
+                metadata.sourceSetNamesByVariantName.forEach { (variantName, sourceSets) ->
+                    val variant = fragmentByName(variantName)
+                    sourceSets.forEach { sourceSetName ->
+                        variant.directRefinesDependencies.add(fragment(sourceSetName))
+                    }
+                }
+                metadata.sourceSetModuleDependencies.forEach { (sourceSetName, dependencies) ->
+                    val fragment = fragment(sourceSetName)
+                    dependencies.forEach { dependency ->
+                        fragment.declaredModuleDependencies.add(
+                            KotlinModuleDependency(
+                                MavenModuleIdentifier(
+                                    dependency.groupId.orEmpty(),
+                                    dependency.moduleId,
+                                    null /* TODO */
+                                )
+                            )
+                        )
+                    }
                 }
-            }
 
-            metadata.sourceSetsDependsOnRelation.forEach { (depending, dependencies) ->
-                val dependingFragment = fragment(depending)
-                dependencies.forEach { dependency ->
-                    dependingFragment.directRefinesDependencies.add(fragment(dependency))
+                metadata.sourceSetsDependsOnRelation.forEach { (depending, dependencies) ->
+                    val dependingFragment = fragment(depending)
+                    dependencies.forEach { dependency ->
+                        dependingFragment.directRefinesDependencies.add(fragment(dependency))
+                    }
                 }
-            }
-        }
+            },
+            metadata
+        )
+    }
 
-    fun getModule(moduleIdentifier: KotlinModuleIdentifier, projectStructureMetadata: KotlinProjectStructureMetadata): KotlinModule {
-        return modulesCache.getOrPut(moduleIdentifier) {
+    fun getModule(component: ResolvedComponentResult, projectStructureMetadata: KotlinProjectStructureMetadata): KotlinModule {
+        val moduleId = component.toModuleIdentifier()
+        return modulesCache.getOrPut(moduleId) {
             buildModuleFromProjectStructureMetadata(
-                moduleIdentifier,
+                component,
                 projectStructureMetadata
             )
         }
@@ -107,7 +120,12 @@ private fun detectModules(targets: Iterable<KotlinTarget>, sourceSets: Iterable<
 
 @Suppress("unused")
 class GradleProjectModuleBuilder(private val addInferredSourceSetVisibilityAsExplicit: Boolean) {
+    private fun getModulesFromPm20Project(project: Project) = project.pm20Extension.modules.toList()
+
     fun buildModulesFromProject(project: Project): List<KotlinModule> {
+        if (project.topLevelExtension is KotlinPm20ProjectExtension)
+            return getModulesFromPm20Project(project)
+
         val extension = project.multiplatformExtensionOrNull
             ?: project.kotlinExtension
             ?: return emptyList()
@@ -217,15 +235,6 @@ class GradleProjectModuleBuilder(private val addInferredSourceSetVisibilityAsExp
     }
 }
 
-
-private fun <T : Any> attributeString(container: AttributeContainer, attributeKey: Attribute<T>): String {
-    val value = container.getAttribute(attributeKey)
-    return when (value) {
-        is Named -> value.name
-        else -> value.toString()
-    }
-}
-
 internal fun Dependency.toModuleDependency(
     project: Project
 ): KotlinModuleDependency {
@@ -266,21 +275,7 @@ class GradleModuleVariantResolver(val project: Project) : ModuleVariantResolver
         // This implementation can only resolve variants for the current project's KotlinModule
         require(module.representsProject(project))
 
-        val targets =
-            project.multiplatformExtensionOrNull?.targets ?: listOf((project.kotlinExtension as KotlinSingleTargetExtension).target)
-
-        val compilation =
-            targets.filterIsInstance<AbstractKotlinTarget>()
-                .flatMap { it.kotlinComponents.filterIsInstance<KotlinVariant>() }
-                .flatMap { it.usages }
-                .firstOrNull { it.name == requestingVariant.fragmentName }
-                ?.compilation
-                ?: targets.asSequence().flatMap { it.compilations.asSequence() }.single {
-                    it.defaultSourceSetName == requestingVariant.fragmentName
-                } // TODO: generalize the mapping PM2.0 <-> MPP
-                ?: return VariantResolution.Unknown(requestingVariant, dependencyModule)
-
-        val compileClasspath = project.configurations.getByName(compilation.compileDependencyConfigurationName)
+        val compileClasspath = getCompileDependenciesConfigurationForVariant(project, requestingVariant)
 
         // TODO optimize O(n) search, store the mapping
         val component = compileClasspath.incoming.resolutionResult.allComponents.find { it.id.matchesModule(dependencyModule) }
@@ -288,7 +283,9 @@ class GradleModuleVariantResolver(val project: Project) : ModuleVariantResolver
 
         val dependencyModuleId = ModuleIds.fromComponent(project, component)
         // FIXME check composite builds, it's likely that resolvedVariantProvider fails on them?
-        val variantName = resolvedVariantProvider.getResolvedVariantName(dependencyModuleId, compileClasspath)
+        val variantName =
+            resolvedVariantProvider.getResolvedVariantName(dependencyModuleId, compileClasspath)
+                ?.let(::kotlinVariantNameFromPublishedVariantName)
 
         val resultVariant = dependencyModule.variants.singleOrNull { it.fragmentName == variantName }
 
@@ -297,4 +294,31 @@ class GradleModuleVariantResolver(val project: Project) : ModuleVariantResolver
         else
             VariantResolution.VariantMatch(requestingVariant, dependencyModule, resultVariant)
     }
+
+    private fun getCompileDependenciesConfigurationForVariant(project: Project, requestingVariant: KotlinModuleVariant): Configuration =
+        when (project.topLevelExtension) {
+            is KotlinMultiplatformExtension, is KotlinSingleTargetExtension -> {
+                val targets =
+                    project.multiplatformExtensionOrNull?.targets ?: listOf((project.kotlinExtension as KotlinSingleTargetExtension).target)
+
+                val compilation =
+                    targets.filterIsInstance<AbstractKotlinTarget>()
+                        .flatMap { it.kotlinComponents.filterIsInstance<KotlinVariant>() }
+                        .flatMap { it.usages }
+                        .firstOrNull { it.name == requestingVariant.fragmentName }
+                        ?.compilation
+
+                        ?: targets.asSequence().flatMap { it.compilations.asSequence() }.single {
+                            it.defaultSourceSetName == requestingVariant.fragmentName
+                        } // TODO: generalize the mapping PM2.0 <-> MPP
+
+                        ?: error("could not find a compilation that produces the variant $requestingVariant in $project")
+
+                project.configurations.getByName(compilation.compileDependencyConfigurationName)
+            }
+            is KotlinPm20ProjectExtension -> {
+                project.configurations.getByName((requestingVariant as KotlinGradleVariant).compileDependencyConfigurationName)
+            }
+            else -> error("could not find the compile dependencies configuration for variant $requestingVariant")
+        }
 }

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

@@ -13,8 +13,12 @@ import org.gradle.api.artifacts.result.ResolvedComponentResult
 import org.gradle.api.artifacts.result.ResolvedDependencyResult
 import org.gradle.api.attributes.Attribute
 import org.gradle.api.file.FileCollection
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
+import org.jetbrains.kotlin.gradle.dsl.topLevelExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinPm20ProjectExtension
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.toModuleIdentifier
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope
 import org.jetbrains.kotlin.gradle.plugin.sources.sourceSetDependencyConfigurationByScope
 import org.jetbrains.kotlin.gradle.targets.metadata.ALL_COMPILE_METADATA_CONFIGURATION_NAME
@@ -207,7 +211,7 @@ internal class GranularMetadataTransformation(
             resolveViaAvailableAt = false // we will process the available-at module as a dependency later in the queue
         )
 
-        val resolvedToProject: Project? = (mppDependencyMetadataExtractor as? ProjectMppDependencyMetadataExtractor)?.dependencyProject
+        val resolvedToProject: Project? = module.toProjectOrNull(project)
 
         val projectStructureMetadata = mppDependencyMetadataExtractor?.getProjectStructureMetadata()
             ?: return MetadataDependencyResolution.KeepOriginalDependency(module, resolvedToProject)
@@ -254,25 +258,33 @@ internal class GranularMetadataTransformation(
             transitiveDependenciesToVisit, mppDependencyMetadataExtractor
         )
     }
+}
 
-    private class ChooseVisibleSourceSetsImpl(
-        dependency: ResolvedComponentResult,
-        projectDependency: Project?,
-        projectStructureMetadata: KotlinProjectStructureMetadata,
-        allVisibleSourceSetNames: Set<String>,
-        visibleSourceSetNamesExcludingDependsOn: Set<String>,
-        visibleTransitiveDependencies: Set<ResolvedDependencyResult>,
-        private val metadataExtractor: MppDependencyMetadataExtractor
-    ) : MetadataDependencyResolution.ChooseVisibleSourceSets(
-        dependency,
-        projectDependency,
-        projectStructureMetadata,
-        allVisibleSourceSetNames,
-        visibleSourceSetNamesExcludingDependsOn,
-        visibleTransitiveDependencies
-    ) {
-        override fun getExtractableMetadataFiles(baseDir: File): ExtractableMetadataFiles =
-            metadataExtractor.getExtractableMetadataFiles(visibleSourceSetNamesExcludingDependsOn, baseDir)
+internal class ChooseVisibleSourceSetsImpl(
+    dependency: ResolvedComponentResult,
+    projectDependency: Project?,
+    projectStructureMetadata: KotlinProjectStructureMetadata,
+    allVisibleSourceSetNames: Set<String>,
+    visibleSourceSetNamesExcludingDependsOn: Set<String>,
+    visibleTransitiveDependencies: Set<ResolvedDependencyResult>,
+    private val metadataExtractor: MppDependencyMetadataExtractor
+) : MetadataDependencyResolution.ChooseVisibleSourceSets(
+    dependency,
+    projectDependency,
+    projectStructureMetadata,
+    allVisibleSourceSetNames,
+    visibleSourceSetNamesExcludingDependsOn,
+    visibleTransitiveDependencies
+) {
+    override fun getExtractableMetadataFiles(baseDir: File): ExtractableMetadataFiles =
+        metadataExtractor.getExtractableMetadataFiles(visibleSourceSetNamesExcludingDependsOn, baseDir)
+}
+
+internal fun ResolvedComponentResult.toProjectOrNull(currentProject: Project): Project? {
+    val identifier = id
+    return when {
+        identifier is ProjectComponentIdentifier && identifier.build.isCurrentBuild -> currentProject.project(identifier.projectPath)
+        else -> null
     }
 }
 
@@ -345,7 +357,7 @@ internal fun requestedDependencies(
 }
 
 
-private abstract class MppDependencyMetadataExtractor(val project: Project, val dependency: ResolvedComponentResult) {
+internal abstract class MppDependencyMetadataExtractor(val project: Project, val dependency: ResolvedComponentResult) {
     abstract fun getProjectStructureMetadata(): KotlinProjectStructureMetadata?
 
     abstract fun getExtractableMetadataFiles(
@@ -366,9 +378,19 @@ private class ProjectMppDependencyMetadataExtractor(
         visibleSourceSetNames: Set<String>,
         baseDir: File
     ): ExtractableMetadataFiles {
-        val result = dependencyProject.multiplatformExtension.targets.getByName(KotlinMultiplatformPlugin.METADATA_TARGET_NAME).compilations
-            .filter { it.name in visibleSourceSetNames }
-            .associate { it.defaultSourceSet.name to it.output.classesDirs }
+        val result = when (val projectExtension = dependencyProject.topLevelExtension) {
+            is KotlinMultiplatformExtension -> projectExtension.targets.getByName(KotlinMultiplatformPlugin.METADATA_TARGET_NAME).compilations
+                .filter { it.name in visibleSourceSetNames }.associate { it.defaultSourceSet.name to it.output.classesDirs }
+            is KotlinPm20ProjectExtension -> {
+                val moduleId = dependency.toModuleIdentifier()
+                val module = projectExtension.modules.single { it.moduleIdentifier == moduleId }
+                val metadataCompilationRegistry = projectExtension.metadataCompilationRegistryByModuleId.getValue(moduleId)
+                visibleSourceSetNames.associateWith {
+                    metadataCompilationRegistry.byFragment(module.fragments.getByName(it)).output.classesDirs
+                }
+            }
+            else -> error("unexpected top-level Kotlin extension $projectExtension")
+        }
 
         return object : ExtractableMetadataFiles() {
             override fun getMetadataFilesPerSourceSet(doProcessFiles: Boolean): Map<String, FileCollection> = result
@@ -502,32 +524,45 @@ private open class JarArtifactMppDependencyMetadataExtractor(
     }
 }
 
-private fun getMetadataExtractor(
+internal fun getMetadataExtractor(
     project: Project,
-    module: ResolvedComponentResult,
+    resolvedComponentResult: ResolvedComponentResult,
     configuration: Configuration,
     resolveViaAvailableAt: Boolean
 ): MppDependencyMetadataExtractor? {
     val resolvedMppVariantsProvider = ResolvedMppVariantsProvider.get(project)
-    val moduleIdentifier = ModuleIds.fromComponent(project, module)
+    val moduleIdentifier = ModuleIds.fromComponent(project, resolvedComponentResult)
+    // TODO check how this code works with multi-capability resolutions
+
+    var resolvedViaAvailableAt = false
+
     val metadataArtifact = resolvedMppVariantsProvider.getResolvedArtifactByPlatformModule(
         moduleIdentifier,
         configuration
-    ) ?: if (resolveViaAvailableAt) resolvedMppVariantsProvider.getHostSpecificMetadataArtifactByRootModule(
-        moduleIdentifier,
-        configuration
-    ) else null
+    ) ?: if (resolveViaAvailableAt) {
+        resolvedMppVariantsProvider.getHostSpecificMetadataArtifactByRootModule(
+            moduleIdentifier,
+            configuration
+        )?.also {
+            resolvedViaAvailableAt = true
+        }
+    } else null
 
-    val moduleId = module.id
+    val actualComponent = if (resolvedViaAvailableAt) {
+        resolvedComponentResult.dependencies.filterIsInstance<ResolvedDependencyResult>().singleOrNull()?.selected
+            ?: resolvedComponentResult
+    } else resolvedComponentResult
+
+    val moduleId = actualComponent.id
     return when {
         moduleId is ProjectComponentIdentifier -> when {
             moduleId.build.isCurrentBuild ->
-                ProjectMppDependencyMetadataExtractor(project, module, project.project(moduleId.projectPath))
+                ProjectMppDependencyMetadataExtractor(project, actualComponent, project.project(moduleId.projectPath))
             metadataArtifact != null ->
-                IncludedBuildMetadataExtractor(project, module, metadataArtifact)
+                IncludedBuildMetadataExtractor(project, actualComponent, metadataArtifact)
             else -> null
         }
-        metadataArtifact != null -> JarArtifactMppDependencyMetadataExtractor(project, module, metadataArtifact)
+        metadataArtifact != null -> JarArtifactMppDependencyMetadataExtractor(project, actualComponent, metadataArtifact)
         else -> null
     }
 }

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

@@ -10,10 +10,16 @@ import com.google.gson.JsonObject
 import com.google.gson.JsonParser
 import com.google.gson.stream.JsonWriter
 import org.gradle.api.Project
+import org.gradle.api.provider.Provider
 import org.gradle.api.tasks.Input
 import org.gradle.api.tasks.Internal
 import org.gradle.api.tasks.Nested
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtensionOrNull
+import org.jetbrains.kotlin.gradle.dsl.topLevelExtension
+import org.jetbrains.kotlin.gradle.dsl.topLevelExtensionOrNull
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinGradleModule
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinPm20ProjectExtension
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.refinesClosure
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope
 import org.jetbrains.kotlin.gradle.plugin.sources.withAllDependsOnSourceSets
 import org.jetbrains.kotlin.gradle.plugin.sources.sourceSetDependencyConfigurationByScope
@@ -27,10 +33,40 @@ import org.w3c.dom.NodeList
 import java.io.StringWriter
 import javax.xml.parsers.DocumentBuilderFactory
 
-data class ModuleDependencyIdentifier(
-    val groupId: String?,
-    val moduleId: String
-)
+// FIXME support module classifiers for PM2.0 or drop this class in favor of KotlinModuleIdentifier
+open class ModuleDependencyIdentifier(
+    open val groupId: String?,
+    open val moduleId: String
+) {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is ModuleDependencyIdentifier) return false
+
+        if (groupId != other.groupId) return false
+        if (moduleId != other.moduleId) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = groupId?.hashCode() ?: 0
+        result = 31 * result + moduleId.hashCode()
+        return result
+    }
+
+    operator fun component1(): String? = groupId
+    operator fun component2(): String = moduleId
+}
+
+class ChangingModuleDependencyIdentifier(
+    val groupIdProvider: () -> String?,
+    val moduleIdProvider: () -> String
+) : ModuleDependencyIdentifier(groupIdProvider(), moduleIdProvider()) {
+    override val groupId: String?
+        get() = groupIdProvider()
+    override val moduleId: String
+        get() = moduleIdProvider()
+}
 
 sealed class SourceSetMetadataLayout(
     @get:Input
@@ -96,6 +132,12 @@ data class KotlinProjectStructureMetadata(
 }
 
 internal fun buildKotlinProjectStructureMetadata(project: Project): KotlinProjectStructureMetadata? {
+    val topLevelExtensionOrNull = project.topLevelExtensionOrNull
+    if (topLevelExtensionOrNull is KotlinPm20ProjectExtension) {
+        // FIXME: get module by ID, don't just take the main module
+        return buildProjectStructureMetadata(topLevelExtensionOrNull.main)
+    }
+
     val sourceSetsWithMetadataCompilations =
         project.multiplatformExtensionOrNull?.targets?.getByName(KotlinMultiplatformPlugin.METADATA_TARGET_NAME)?.compilations?.associate {
             it.defaultSourceSet to it
@@ -142,6 +184,37 @@ internal fun buildKotlinProjectStructureMetadata(project: Project): KotlinProjec
     )
 }
 
+internal fun buildProjectStructureMetadata(module: KotlinGradleModule): KotlinProjectStructureMetadata {
+    val kotlinVariantToGradleVariantNames = module.variants.associate { it.name to it.gradleVariantNames }
+
+    fun <T> expandVariantKeys(map: Map<String, T>) =
+        map.entries.flatMap { (key, value) ->
+            kotlinVariantToGradleVariantNames[key].orEmpty().plus(key).map { it to value }
+        }.toMap()
+
+    val kotlinFragmentsPerKotlinVariant =
+        module.variants.associate { variant -> variant.name to variant.refinesClosure.map { it.name }.toSet() }
+    val fragmentRefinesRelation =
+        module.fragments.associate { it.name to it.directRefinesDependencies.map { it.name }.toSet() }
+
+    // FIXME: support native implementation-as-api-dependencies
+    val fragmentDependencies =
+        module.fragments.associate { fragment ->
+            fragment.name to fragment.declaredModuleDependencies.map {
+                ModuleIds.lossyFromModuleIdentifier(module.project, it.moduleIdentifier)
+            }.toSet()
+        }
+
+    return KotlinProjectStructureMetadata(
+        expandVariantKeys(kotlinFragmentsPerKotlinVariant),
+        fragmentRefinesRelation,
+        module.fragments.associate { it.name to SourceSetMetadataLayout.KLIB },
+        fragmentDependencies,
+        emptySet(),
+        isPublishedAsRoot = true
+    )
+}
+
 internal fun <Serializer> KotlinProjectStructureMetadata.serialize(
     serializer: Serializer,
     node: Serializer.(name: String, Serializer.() -> Unit) -> Unit,

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

@@ -84,9 +84,13 @@ abstract class KotlinSoftwareComponent(
         return _usages
     }
 
-
     val sourcesArtifacts: Set<PublishArtifact> by lazy {
-        val sourcesJarTask = sourcesJarTask(project, lazy { project.kotlinExtension.sourceSets.toSet() }, null, name.toLowerCase())
+        val sourcesJarTask = sourcesJarTask(
+            project,
+            lazy { project.kotlinExtension.sourceSets.associate { it.name to it.kotlin } },
+            null,
+            name.toLowerCase()
+        )
         val sourcesJarArtifact = project.artifacts.add(Dependency.ARCHIVES_CONFIGURATION, sourcesJarTask) { sourcesJarArtifact ->
             sourcesJarArtifact.classifier = "sources"
         }

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

@@ -10,8 +10,18 @@ import org.gradle.api.artifacts.Dependency
 import org.gradle.api.artifacts.ProjectDependency
 import org.gradle.api.artifacts.component.*
 import org.gradle.api.artifacts.result.ResolvedComponentResult
+import org.gradle.api.publish.maven.MavenPublication
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformExtension
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtensionOrNull
+import org.jetbrains.kotlin.gradle.dsl.topLevelExtension
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinPm20ProjectExtension
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.currentBuildId
+import org.jetbrains.kotlin.gradle.utils.getValue
+import org.jetbrains.kotlin.project.model.KotlinModuleIdentifier
+import org.jetbrains.kotlin.project.model.LocalModuleIdentifier
+import org.jetbrains.kotlin.project.model.MavenModuleIdentifier
+import java.lang.IllegalArgumentException
 
 internal object ModuleIds {
     fun fromDependency(dependency: Dependency) = when (dependency) {
@@ -60,4 +70,57 @@ internal object ModuleIds {
 
     private fun idOfRootModuleByProjectPath(thisProject: Project, projectPath: String): ModuleDependencyIdentifier =
         idOfRootModule(thisProject.project(projectPath))
+
+    // FIXME use capabilities to point to auxiliary modules
+    fun lossyFromModuleIdentifier(thisProject: Project, moduleIdentifier: KotlinModuleIdentifier): ModuleDependencyIdentifier {
+        when (moduleIdentifier) {
+            is LocalModuleIdentifier -> {
+                check(moduleIdentifier.buildId == thisProject.currentBuildId().name)
+                val dependencyProject = thisProject.project(moduleIdentifier.projectId)
+                val getRootPublication: () -> MavenPublication? = when (val topLevelExtension = dependencyProject.topLevelExtension) {
+                    is KotlinMultiplatformExtension -> {
+                        { topLevelExtension.rootSoftwareComponent.publicationDelegate }
+                    }
+                    is KotlinPm20ProjectExtension -> {
+                        { topLevelExtension.rootPublication }
+                    }
+                    else -> error("unexpected top-level extension $topLevelExtension")
+                }
+                val coordinatesProvider = MultiplatformRootPublicationCoordinatesProvider(dependencyProject, getRootPublication)
+                return ChangingModuleDependencyIdentifier({ coordinatesProvider.group }, { coordinatesProvider.name })
+            }
+            is MavenModuleIdentifier -> {
+                return ModuleDependencyIdentifier(moduleIdentifier.group, moduleIdentifier.name)
+            }
+            else -> error("unexpected module identifier $moduleIdentifier")
+        }
+    }
+}
+
+interface PublishedModuleCoordinatesProvider {
+    val group: String
+    val name: String
+    val version: String
+    val capabilities: Iterable<String>
+}
+
+class MultiplatformRootPublicationCoordinatesProvider(
+    project: Project,
+    val getPublication: () -> MavenPublication?
+) : PublishedModuleCoordinatesProvider {
+
+    override val group: String by project.provider {
+        getPublication()?.groupId ?: project.group.toString()
+    }
+
+    override val name: String by project.provider {
+        getPublication()?.artifactId ?: project.group.toString()
+    }
+
+    override val version: String by project.provider {
+        getPublication()?.artifactId ?: project.version.toString()
+    }
+
+    override val capabilities: Iterable<String>
+        get() = emptyList()
 }

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

@@ -123,7 +123,7 @@ internal class SourceSetVisibilityProvider(
     }
 }
 
-private fun kotlinVariantNameFromPublishedVariantName(resolvedToVariantName: String): String =
+internal fun kotlinVariantNameFromPublishedVariantName(resolvedToVariantName: String): String =
     originalVariantNameFromPublished(resolvedToVariantName) ?: resolvedToVariantName
 
 private fun Project.resolvableConfigurationFromCompilationByScope(

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

@@ -11,10 +11,12 @@ import org.gradle.api.tasks.*
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.TransformKotlinGranularMetadataForFragment
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope.*
 import org.jetbrains.kotlin.gradle.plugin.sources.withAllDependsOnSourceSets
 import org.jetbrains.kotlin.gradle.targets.metadata.ALL_COMPILE_METADATA_CONFIGURATION_NAME
 import org.jetbrains.kotlin.gradle.targets.metadata.KotlinMetadataTargetConfigurator
+import org.jetbrains.kotlin.gradle.targets.metadata.ResolvedMetadataFilesProvider
 import org.jetbrains.kotlin.gradle.targets.metadata.dependsOnClosureWithInterCompilationDependencies
 import org.jetbrains.kotlin.gradle.utils.getValue
 import java.io.File
@@ -100,9 +102,9 @@ open class TransformKotlinGranularMetadata
             .associateWith { it.getExtractableMetadataFiles(outputsDir) }
 
     @get:Internal
-    internal val filesByResolution: Map<out MetadataDependencyResolution, FileCollection>
+    internal val filesByResolution: Map<MetadataDependencyResolution, FileCollection>
         get() = extractableFilesByResolution.mapValues { (_, value) ->
-            project.files(value.getMetadataFilesPerSourceSet(false).values)
+            project.files(value.getMetadataFilesPerSourceSet(false).values).builtBy(this)
         }
 
     private val extractableFiles by project.provider { extractableFilesByResolution.values }
@@ -117,3 +119,11 @@ open class TransformKotlinGranularMetadata
         extractableFiles.forEach { it.getMetadataFilesPerSourceSet(doProcessFiles = true) }
     }
 }
+
+internal class SourceSetResolvedMetadataProvider(
+    taskProvider: TaskProvider<out TransformKotlinGranularMetadata>
+) : ResolvedMetadataFilesProvider {
+    override val buildDependencies: Iterable<TaskProvider<*>> = listOf(taskProvider)
+    override val metadataResolutions: Iterable<MetadataDependencyResolution> by taskProvider.map { it.metadataDependencyResolutions }
+    override val metadataFilesByResolution: Map<MetadataDependencyResolution, FileCollection> by taskProvider.map { it.filesByResolution }
+}

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

@@ -236,6 +236,12 @@ abstract class AbstractKotlinCompilation<T : KotlinCommonOptions>(
             } else files()
         }
 
+    override val friendPaths: Iterable<FileCollection>
+        get() = mutableListOf<FileCollection>().also { allCollections ->
+            associateWithTransitiveClosure.forEach { allCollections.add(it.output.classesDirs) }
+            allCollections.add(friendArtifacts)
+        }
+
     override val moduleName: String
         get() = KotlinCompilationsModuleGroups.getModuleLeaderCompilation(this).takeIf { it != this }?.ownModuleName() ?: ownModuleName
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/DependencyGraphResolver.kt

@@ -10,22 +10,33 @@ import org.gradle.api.artifacts.Configuration
 import org.gradle.api.artifacts.result.ResolvedComponentResult
 import org.gradle.api.artifacts.result.ResolvedDependencyResult
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
+import org.jetbrains.kotlin.gradle.dsl.topLevelExtension
 import org.jetbrains.kotlin.gradle.plugin.mpp.resolvableMetadataConfiguration
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope
 import org.jetbrains.kotlin.project.model.*
 
-class GradleKotlinDependencyGraphResolver(
-    private val project: Project,
-    private val moduleResolver: ModuleDependencyResolver,
-    private val fragmentsResolver: ModuleFragmentsResolver
-) : KotlinDependencyGraphResolver {
+internal fun resolvableMetadataConfiguration(
+    module: KotlinGradleModule
+) = module.project.configurations.getByName(module.resolvableMetadataConfigurationName)
 
-    private val configurationToResolve: Configuration
-        get() = resolvableMetadataConfiguration(
+internal fun configurationToResolveMetadataDependencies(project: Project, requestingModule: KotlinModule): Configuration =
+    when (project.topLevelExtension) {
+        is KotlinPm20ProjectExtension -> resolvableMetadataConfiguration(requestingModule as KotlinGradleModule)
+        else -> resolvableMetadataConfiguration(
             project,
             project.kotlinExtension.sourceSets, // take dependencies from all source sets; TODO introduce consistency scopes?
             KotlinDependencyScope.compileScopes
         )
+    }
+
+
+class GradleKotlinDependencyGraphResolver(
+    private val project: Project,
+    private val moduleResolver: ModuleDependencyResolver
+) : KotlinDependencyGraphResolver {
+
+    private fun configurationToResolve(requestingModule: KotlinModule): Configuration =
+        configurationToResolveMetadataDependencies(project, requestingModule)
 
     override fun resolveDependencyGraph(requestingModule: KotlinModule): DependencyGraphResolution {
         if (!requestingModule.representsProject(project))
@@ -40,11 +51,17 @@ class GradleKotlinDependencyGraphResolver(
             return nodeByModuleId.getOrPut(id) {
                 val module = if (isRoot)
                     requestingModule
-                else moduleResolver.resolveDependency(component.toModuleDependency())
+                else moduleResolver.resolveDependency(requestingModule, component.toModuleDependency())
                     .takeIf { component !in excludeLegacyMetadataModulesFromResult }
-                    ?: buildStubModule(component, component.variants.singleOrNull()?.displayName ?: "default")
+                    ?: buildSyntheticModule(component, component.variants.singleOrNull()?.displayName ?: "default")
 
-                val resolvedComponentDependencies = component.dependencies
+                val componentContainingTransitiveDependencies =
+                    (module as? ExternalImportedKotlinModule)
+                        ?.takeIf { it.hasLegacyMetadataModule }
+                        ?.let { (component.dependencies.singleOrNull() as? ResolvedDependencyResult)?.selected }
+                    ?: component
+
+                val resolvedComponentDependencies = componentContainingTransitiveDependencies.dependencies
                     .filterIsInstance<ResolvedDependencyResult>()
                     .flatMap { dependency -> dependency.requested.toModuleIdentifiers().map { id -> id to dependency.selected } }
                     .toMap()
@@ -61,7 +78,7 @@ class GradleKotlinDependencyGraphResolver(
 
         return DependencyGraphResolution.DependencyGraph(
             requestingModule,
-            nodeFromComponent(configurationToResolve.incoming.resolutionResult.root, isRoot = true)
+            nodeFromComponent(configurationToResolve(requestingModule).incoming.resolutionResult.root, isRoot = true)
         )
     }
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/DependencyResolution.kt

@@ -13,8 +13,7 @@ import org.gradle.api.artifacts.result.ResolvedDependencyResult
 import org.gradle.api.capabilities.Capability
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
-import org.jetbrains.kotlin.gradle.plugin.mpp.ProjectStructureMetadataModuleBuilder
-import org.jetbrains.kotlin.gradle.plugin.mpp.GradleProjectModuleBuilder
+import org.jetbrains.kotlin.gradle.plugin.mpp.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.getProjectStructureMetadata
 import org.jetbrains.kotlin.gradle.plugin.mpp.resolvableMetadataConfiguration
 import org.jetbrains.kotlin.gradle.plugin.sources.KotlinDependencyScope
@@ -27,15 +26,11 @@ class GradleModuleDependencyResolver(
     private val projectModuleBuilder: GradleProjectModuleBuilder
 ) : ModuleDependencyResolver {
 
-    private val configurationToResolve: Configuration
-        get() = resolvableMetadataConfiguration(
-            project,
-            project.kotlinExtension.sourceSets, // take dependencies from all source sets; TODO introduce consistency scopes?
-            listOf(KotlinDependencyScope.API_SCOPE, KotlinDependencyScope.IMPLEMENTATION_SCOPE, KotlinDependencyScope.COMPILE_ONLY_SCOPE)
-        )
+    private fun configurationToResolve(requestingModule: KotlinModule): Configuration =
+        configurationToResolveMetadataDependencies(project, requestingModule)
 
-    override fun resolveDependency(moduleDependency: KotlinModuleDependency): KotlinModule? {
-        val allComponents = configurationToResolve.incoming.resolutionResult.allComponents
+    override fun resolveDependency(requestingModule: KotlinModule, moduleDependency: KotlinModuleDependency): KotlinModule? {
+        val allComponents = configurationToResolve(requestingModule).incoming.resolutionResult.allComponents
         // TODO: optimize O(n) search, store the resolved components with dependency keys?
         val component = allComponents.find { it.id.matchesModuleDependency(moduleDependency) }
         val id = component?.id
@@ -48,8 +43,9 @@ class GradleModuleDependencyResolver(
                 projectModuleBuilder.buildModulesFromProject(project.project(id.projectPath))
                     .find { it.moduleIdentifier.moduleClassifier == classifier }
             id is ModuleComponentIdentifier -> {
-                val metadata = getProjectStructureMetadata(project, component, configurationToResolve) ?: return null
-                projectStructureMetadataModuleBuilder.getModule(id.toModuleIdentifier(classifier), metadata)
+                val metadata = getProjectStructureMetadata(project, component, configurationToResolve(requestingModule)) ?: return null
+                val result = projectStructureMetadataModuleBuilder.getModule(component, metadata)
+                result
             }
             else -> null
         }
@@ -110,9 +106,9 @@ class FragmentDependenciesDiscovery(
             val component = resolvedComponentQueue.removeFirst()
             visited.add(component)
 
-            val module = moduleResolver.resolveDependency(component.toModuleDependency())
+            val module = moduleResolver.resolveDependency(fragment.containingModule, component.toModuleDependency())
                 .takeIf { component !in excludeLegacyMetadataModulesFromResult }
-                ?: buildStubModule(component, component.variants.singleOrNull()?.displayName ?: "default")
+                ?: buildSyntheticModule(component, component.variants.singleOrNull()?.displayName ?: "default")
 
             val transitiveDepsToVisit = when (val fragmentsResolution = fragmentsResolver.getChosenFragments(fragment, module)) {
                 is FragmentResolution.ChosenFragments ->
@@ -126,9 +122,7 @@ class FragmentDependenciesDiscovery(
 
             // With legacy publication scheme, the root MPP module may have a single 'dependency' (available-at) to the metadata module
             val isMetadataModulePublishedSeparately =
-                getProjectStructureMetadata(project, component, configurationToResolve)
-                    ?.let { !it.isPublishedAsRoot }
-                    ?: false
+                (module is ExternalImportedKotlinModule) && module.hasLegacyMetadataModule
             val singleDependencyComponentOrNull = (component.dependencies.singleOrNull() as? ResolvedDependencyResult)?.selected
             if (isMetadataModulePublishedSeparately && singleDependencyComponentOrNull != null) {
                 newTransitiveDeps.add(singleDependencyComponentOrNull)
@@ -144,9 +138,9 @@ class FragmentDependenciesDiscovery(
 
 // refactor extract to a separate class/interface
 // TODO think about multi-variant stub modules for non-Kotlin modules which got more than one chosen variant
-internal fun buildStubModule(resolvedComponentResult: ResolvedComponentResult, singleVariantName: String): KotlinModule {
+internal fun buildSyntheticModule(resolvedComponentResult: ResolvedComponentResult, singleVariantName: String): ExternalSyntheticKotlinModule {
     val moduleDependency = resolvedComponentResult.toModuleDependency()
-    return BasicKotlinModule(moduleDependency.moduleIdentifier).apply {
+    return ExternalSyntheticKotlinModule(BasicKotlinModule(moduleDependency.moduleIdentifier).apply {
         BasicKotlinModuleVariant(this@apply, singleVariantName).apply {
             fragments.add(this)
             this.declaredModuleDependencies.addAll(
@@ -155,7 +149,20 @@ internal fun buildStubModule(resolvedComponentResult: ResolvedComponentResult, s
                     .map { it.selected.toModuleDependency() }
             )
         }
-    }
+    })
+}
+
+internal class ExternalSyntheticKotlinModule(private val moduleData: BasicKotlinModule) : KotlinModule by moduleData {
+    override fun toString(): String = "synthetic $moduleData"
+}
+
+internal class ExternalImportedKotlinModule(
+    private val moduleData: BasicKotlinModule,
+    val projectStructureMetadata: KotlinProjectStructureMetadata
+) : KotlinModule by moduleData {
+    val hasLegacyMetadataModule = !projectStructureMetadata.isPublishedAsRoot
+
+    override fun toString(): String = "imported $moduleData"
 }
 
 class VariantDependencyDiscovery(

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/FragmentGranularMetadataResolver.kt

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2010-2021 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.gradle.plugin.mpp.pm20
+
+import org.gradle.api.Project
+import org.gradle.api.artifacts.result.ResolvedDependencyResult
+import org.jetbrains.kotlin.gradle.plugin.mpp.*
+import org.jetbrains.kotlin.gradle.plugin.mpp.ChooseVisibleSourceSetsImpl
+import org.jetbrains.kotlin.gradle.plugin.mpp.MetadataDependencyResolution
+import org.jetbrains.kotlin.gradle.plugin.mpp.getMetadataExtractor
+import org.jetbrains.kotlin.gradle.plugin.mpp.getProjectStructureMetadata
+import org.jetbrains.kotlin.project.model.*
+import org.jetbrains.kotlin.utils.addToStdlib.flattenTo
+import java.util.ArrayDeque
+
+internal class FragmentGranularMetadataResolver(
+    val requestingFragment: KotlinGradleFragment,
+    val refinesParentResolvers: Lazy<Iterable<FragmentGranularMetadataResolver>>
+) {
+    val resolutions: Iterable<MetadataDependencyResolution> by lazy {
+        doResolveMetadataDependencies()
+    }
+
+    private val project: Project
+        get() = requestingFragment.containingModule.project
+
+    private val parentResultsByModuleIdentifier: Map<KotlinModuleIdentifier, List<MetadataDependencyResolution>> by lazy {
+        refinesParentResolvers.value.flatMap { it.resolutions }.groupBy { it.dependency.toModuleIdentifier() }
+    }
+
+    private val metadataModuleBuilder = ProjectStructureMetadataModuleBuilder()
+    private val projectModuleBuilder = GradleProjectModuleBuilder(true)
+    private val moduleResolver = GradleModuleDependencyResolver(project, metadataModuleBuilder, projectModuleBuilder)
+    private val variantResolver = GradleModuleVariantResolver(project)
+    private val fragmentResolver = DefaultModuleFragmentsResolver(variantResolver)
+    private val dependencyGraphResolver = GradleKotlinDependencyGraphResolver(project, moduleResolver)
+
+    private fun doResolveMetadataDependencies(): Iterable<MetadataDependencyResolution> {
+        val configurationToResolve = configurationToResolveMetadataDependencies(project, requestingFragment.containingModule)
+        val resolvedComponentsByModuleId =
+            configurationToResolve.incoming.resolutionResult.allComponents.associateBy { it.toModuleIdentifier() }
+        val resolvedDependenciesByModuleId =
+            configurationToResolve.incoming.resolutionResult.allDependencies.filterIsInstance<ResolvedDependencyResult>()
+                .flatMap { dependency -> dependency.requested.toModuleIdentifiers().map { id -> id to dependency } }.toMap()
+
+        val dependencyGraph = dependencyGraphResolver.resolveDependencyGraph(requestingFragment.containingModule)
+
+        if (dependencyGraph is DependencyGraphResolution.Unknown)
+            error("unexpected failure in dependency graph resolution for $requestingFragment in $project")
+
+        dependencyGraph as DependencyGraphResolution.DependencyGraph
+        val fragmentsToInclude = requestingFragment.refinesClosure
+        val requestedDependencies = dependencyGraph.root.dependenciesByFragment.filterKeys { it in fragmentsToInclude }.values.flatten()
+
+        val visited = mutableSetOf<DependencyGraphNode>()
+        val fragmentResolutionQueue = ArrayDeque<DependencyGraphNode>().apply {
+            addAll(requestedDependencies)
+        }
+
+        val results = mutableSetOf<MetadataDependencyResolution>()
+
+        while (fragmentResolutionQueue.isNotEmpty()) {
+            val dependencyNode = fragmentResolutionQueue.removeFirst()
+            visited.add(dependencyNode)
+
+            val dependencyModule = dependencyNode.module
+
+            val fragmentVisibility = fragmentResolver.getChosenFragments(requestingFragment, dependencyModule)
+            val visibleFragments = (fragmentVisibility as? FragmentResolution.ChosenFragments)?.visibleFragments?.toList().orEmpty()
+            val variantResolutions =
+                (fragmentVisibility as? FragmentResolution.ChosenFragments)?.variantResolutions?.associateBy { it.requestingVariant }
+
+            val visibleTransitiveDependencies =
+                dependencyNode.dependenciesByFragment.filterKeys { it in visibleFragments }.values.flattenTo(mutableSetOf())
+
+            //FIXME host-specific fragments
+
+            fragmentResolutionQueue.addAll(visibleTransitiveDependencies.filter { it !in visited })
+
+            val resolvedComponentResult = resolvedComponentsByModuleId.getValue(dependencyModule.moduleIdentifier)
+            val isResolvedAsProject = resolvedComponentResult.toProjectOrNull(project)
+            val result = when (dependencyModule) {
+                is ExternalSyntheticKotlinModule -> {
+                    MetadataDependencyResolution.KeepOriginalDependency(resolvedComponentResult, isResolvedAsProject)
+                }
+                else -> run {
+                    val projectStructureMetadata = (dependencyModule as? ExternalImportedKotlinModule)?.projectStructureMetadata
+                        ?: checkNotNull(getProjectStructureMetadata(project, resolvedComponentResult, configurationToResolve))
+
+                    // FIXME host-specific metadata!!!
+
+                    val metadataSourceComponent = when {
+                        dependencyModule is ExternalImportedKotlinModule && dependencyModule.hasLegacyMetadataModule ->
+                            resolvedComponentResult.dependencies.filterIsInstance<ResolvedDependencyResult>().singleOrNull()?.selected
+                                ?: resolvedComponentResult
+                        else -> resolvedComponentResult
+                    }
+
+                    val parentResolutionsForDependency =
+                        parentResultsByModuleIdentifier[metadataSourceComponent.toModuleIdentifier()].orEmpty()
+                    val fragmentsVisibleByParents =
+                        parentResolutionsForDependency.filterIsInstance<ChooseVisibleSourceSetsImpl>()
+                            .flatMapTo(mutableSetOf()) { it.allVisibleSourceSetNames }
+                    val visibleFragmentNames = visibleFragments.map { it.fragmentName }.toSet()
+
+                    ChooseVisibleSourceSetsImpl(
+                        metadataSourceComponent,
+                        isResolvedAsProject,
+                        projectStructureMetadata,
+                        visibleFragmentNames,
+                        visibleFragmentNames.minus(fragmentsVisibleByParents),
+                        visibleTransitiveDependencies.map { resolvedDependenciesByModuleId.getValue(it.module.moduleIdentifier) }.toSet(),
+                        checkNotNull(getMetadataExtractor(project, resolvedComponentResult, configurationToResolve, true))
+                    )
+                }
+            }
+            results.add(result)
+            fragmentResolutionQueue.addAll(visibleTransitiveDependencies.filterNot(visited::contains))
+        }
+
+        val resultSourceComponents = results.mapTo(mutableSetOf()) { it.dependency }
+        resolvedComponentsByModuleId.values.minus(resultSourceComponents).forEach {
+            results.add(MetadataDependencyResolution.ExcludeAsUnrequested(it, it.toProjectOrNull(project)))
+        }
+
+        return results
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/GradlePlugin.kt

@@ -5,16 +5,35 @@
 
 package org.jetbrains.kotlin.gradle.plugin.mpp.pm20
 
-import org.gradle.api.NamedDomainObjectContainer
-import org.gradle.api.NamedDomainObjectProvider
-import org.gradle.api.Plugin
-import org.gradle.api.Project
+import org.gradle.api.*
+import org.gradle.api.attributes.Usage
 import org.gradle.api.plugins.JavaBasePlugin
+import org.gradle.api.publish.maven.MavenPublication
+import org.gradle.api.tasks.TaskProvider
+import org.gradle.jvm.tasks.Jar
 import org.gradle.util.GradleVersion
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformCommonOptions
 import org.jetbrains.kotlin.gradle.dsl.KotlinTopLevelExtension
 import org.jetbrains.kotlin.gradle.dsl.pm20Extension
 import org.jetbrains.kotlin.gradle.internal.customizeKotlinDependencies
+import org.jetbrains.kotlin.gradle.plugin.KotlinCommonSourceSetProcessor
+import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
+import org.jetbrains.kotlin.gradle.plugin.getKotlinPluginVersion
+import org.jetbrains.kotlin.gradle.plugin.mpp.*
+import org.jetbrains.kotlin.gradle.plugin.mpp.MULTIPLATFORM_PROJECT_METADATA_JSON_FILE_NAME
+import org.jetbrains.kotlin.gradle.plugin.mpp.addSourcesToKotlinCompileTask
+import org.jetbrains.kotlin.gradle.plugin.mpp.buildKotlinProjectStructureMetadata
+import org.jetbrains.kotlin.gradle.plugin.usageByName
+import org.jetbrains.kotlin.gradle.targets.metadata.createGenerateProjectStructureMetadataTask
+import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
+import org.jetbrains.kotlin.gradle.tasks.registerTask
+import org.jetbrains.kotlin.gradle.tasks.withType
+import org.jetbrains.kotlin.gradle.utils.addExtendsFromRelation
 import org.jetbrains.kotlin.gradle.utils.checkGradleCompatibility
+import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
+import org.jetbrains.kotlin.project.model.KotlinModuleFragment
+import org.jetbrains.kotlin.project.model.KotlinModuleIdentifier
+import java.util.concurrent.Callable
 
 abstract class KotlinPm20GradlePlugin : Plugin<Project> {
     override fun apply(project: Project) {
@@ -43,21 +62,17 @@ abstract class KotlinPm20GradlePlugin : Plugin<Project> {
             modules.create(KotlinGradleModule.TEST_MODULE_NAME)
             main { makePublic() }
         }
+        setupMetadataCompilationAndDependencyResolution(project)
     }
 
-    private fun setupMetadataCompilation() {
-        // TODO dependency transformations in tasks
-        // TODO classpath configurations
-        // TODO compilation data -> tasks
-        // TODO project structure metadata -> metadata artifact
-        // TODO task outputs -> metadata artifact
-        // TODO export the metadata artifact in consumable configurations
+    private fun setupMetadataCompilationAndDependencyResolution(project: Project) {
+        project.pm20Extension.modules.all { module ->
+            configureMetadataResolutionAndBuild(module)
+        }
     }
 }
 
-open class KotlinPm20ProjectExtension : KotlinTopLevelExtension() {
-    internal lateinit var project: Project
-
+open class KotlinPm20ProjectExtension(project: Project) : KotlinTopLevelExtension(project) {
     val modules: NamedDomainObjectContainer<KotlinGradleModule> by lazy {
         project.objects.domainObjectContainer(
             KotlinGradleModule::class.java,
@@ -79,6 +94,11 @@ open class KotlinPm20ProjectExtension : KotlinTopLevelExtension() {
 
     fun main(configure: KotlinGradleModule.() -> Unit = { }) = main.apply(configure)
     fun test(configure: KotlinGradleModule.() -> Unit = { }) = test.apply(configure)
+
+    internal val metadataCompilationRegistryByModuleId: MutableMap<KotlinModuleIdentifier, MetadataCompilationRegistry> =
+        mutableMapOf()
+
+    internal var rootPublication: MavenPublication? = null
 }
 
 val KotlinGradleModule.jvm: KotlinJvmVariant

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinCompilationData.kt

@@ -9,9 +9,11 @@ import org.gradle.api.Project
 import org.gradle.api.file.FileCollection
 import org.gradle.api.file.SourceDirectorySet
 import org.jetbrains.kotlin.gradle.dsl.KotlinCommonOptions
+import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilationOutput
 import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
 import org.jetbrains.kotlin.gradle.plugin.LanguageSettingsBuilder
+import org.jetbrains.kotlin.gradle.plugin.mpp.isMain
 
 interface KotlinCompilationData<T : KotlinCommonOptions> {
     val project: Project
@@ -34,4 +36,11 @@ interface KotlinCompilationData<T : KotlinCommonOptions> {
     val ownModuleName: String
 
     val kotlinOptions: T
+
+    val friendPaths: Iterable<FileCollection>
+}
+
+fun KotlinCompilationData<*>.isMain(): Boolean = when (this) {
+    is KotlinCompilation<*> -> isMain()
+    else -> compilationPurpose == KotlinGradleModule.MAIN_MODULE_NAME
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinFragmentMetadataCompilationData.kt

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2010-2021 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.gradle.plugin.mpp.pm20
+
+import org.gradle.api.DefaultTask
+import org.gradle.api.Project
+import org.gradle.api.file.FileCollection
+import org.gradle.api.file.SourceDirectorySet
+import org.gradle.api.plugins.BasePluginConvention
+import org.gradle.api.tasks.TaskProvider
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformCommonOptions
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformCommonOptionsImpl
+import org.jetbrains.kotlin.gradle.dsl.pm20Extension
+import org.jetbrains.kotlin.gradle.plugin.KotlinCompilationOutput
+import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
+import org.jetbrains.kotlin.gradle.plugin.LanguageSettingsBuilder
+import org.jetbrains.kotlin.gradle.plugin.mpp.DefaultKotlinCompilationOutput
+import org.jetbrains.kotlin.gradle.plugin.mpp.filterModuleName
+import org.jetbrains.kotlin.gradle.plugin.sources.DefaultLanguageSettingsBuilder
+import org.jetbrains.kotlin.gradle.targets.metadata.ResolvedMetadataFilesProvider
+import org.jetbrains.kotlin.gradle.targets.metadata.createTransformedMetadataClasspath
+import org.jetbrains.kotlin.gradle.utils.getValue
+import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
+
+internal class KotlinFragmentMetadataCompilationData(
+    override val project: Project,
+    val fragment: KotlinGradleFragment,
+    private val module: KotlinGradleModule,
+    private val compileAllTask: TaskProvider<DefaultTask>,
+    val metadataCompilationRegistry: MetadataCompilationRegistry,
+    private val resolvedMetadataFiles: Lazy<Iterable<ResolvedMetadataFilesProvider>>
+) : KotlinCompilationData<KotlinMultiplatformCommonOptions> {
+
+    override val owner
+        get() = project.pm20Extension
+
+    override val compilationPurpose: String
+        get() = fragment.fragmentName
+
+    override val compilationClassifier: String
+        get() = lowerCamelCaseName(module.name, "metadata")
+
+    override val kotlinSourceDirectoriesByFragmentName: Map<String, SourceDirectorySet>
+        get() = mapOf(fragment.fragmentName to fragment.kotlinSourceRoots)
+
+    override val compileKotlinTaskName: String
+        get() = lowerCamelCaseName("compile", fragment.disambiguateName(""), "KotlinMetadata")
+
+    override val compileAllTaskName: String
+        get() = compileAllTask.name
+
+    override val compileDependencyFiles: FileCollection by project.provider {
+        createTransformedMetadataClasspath(
+            project,
+            resolvableMetadataConfiguration(fragment.containingModule),
+            lazy { fragment.refinesClosure.minus(fragment).map { metadataCompilationRegistry.byFragment(it).output.classesDirs } },
+            resolvedMetadataFiles
+        )
+    }
+
+    override val output: KotlinCompilationOutput = DefaultKotlinCompilationOutput(
+        project,
+        project.provider { project.buildDir.resolve("processedResources/${fragment.disambiguateName("metadata")}") }
+    )
+
+    override val languageSettings: LanguageSettingsBuilder = DefaultLanguageSettingsBuilder() // FIXME apply settings
+
+    override val platformType: KotlinPlatformType
+        get() = KotlinPlatformType.common
+
+    override val moduleName: String
+        get() { // FIXME deduplicate with ownModuleName
+            val baseName = project.convention.findPlugin(BasePluginConvention::class.java)?.archivesBaseName
+                ?: project.name
+            val suffix = if (module.moduleClassifier == null) "" else "_${module.moduleClassifier}"
+            return filterModuleName("$baseName$suffix")
+        }
+
+    override val ownModuleName: String
+        get() = moduleName
+
+    override val kotlinOptions: KotlinMultiplatformCommonOptions = // FIXME expose for configuration
+        KotlinMultiplatformCommonOptionsImpl()
+
+    override val friendPaths: Iterable<FileCollection>
+        get() = metadataCompilationRegistry.run {
+            fragment.refinesClosure.minus(fragment)
+                .map {
+                    metadataCompilationRegistry.byFragment(it).output.classesDirs
+                }
+        }
+}
+
+internal class MetadataCompilationRegistry {
+    private val compilationDataPerFragment = mutableMapOf<KotlinGradleFragment, KotlinFragmentMetadataCompilationData>()
+
+    fun register(fragment: KotlinGradleFragment, compilationData: KotlinFragmentMetadataCompilationData) {
+        compilationDataPerFragment[fragment]?.let { error("compilation data for fragment $fragment already registered") }
+        compilationDataPerFragment[fragment] = compilationData
+        withAllCallbacks.forEach { it.invoke(compilationData) }
+    }
+
+    fun byFragment(fragment: KotlinGradleFragment): KotlinFragmentMetadataCompilationData =
+        compilationDataPerFragment.getValue(fragment)
+
+    private val withAllCallbacks = mutableListOf<(KotlinFragmentMetadataCompilationData) -> Unit>()
+
+    fun withAll(action: (KotlinFragmentMetadataCompilationData) -> Unit) {
+        compilationDataPerFragment.forEach { action(it.value) }
+        withAllCallbacks += action
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinGradleFragment.kt

@@ -16,11 +16,13 @@ import org.jetbrains.kotlin.gradle.plugin.HasKotlinDependencies
 import org.jetbrains.kotlin.gradle.plugin.KotlinDependencyHandler
 import org.jetbrains.kotlin.gradle.plugin.LanguageSettingsBuilder
 import org.jetbrains.kotlin.gradle.plugin.mpp.DefaultKotlinDependencyHandler
+import org.jetbrains.kotlin.gradle.plugin.mpp.toModuleDependency
 import org.jetbrains.kotlin.gradle.plugin.sources.DefaultLanguageSettingsBuilder
 import org.jetbrains.kotlin.gradle.utils.addExtendsFromRelation
 import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
 import org.jetbrains.kotlin.project.model.KotlinModuleDependency
 import org.jetbrains.kotlin.project.model.KotlinModuleFragment
+import org.jetbrains.kotlin.project.model.refinesClosure
 import javax.inject.Inject
 
 open class KotlinGradleFragment @Inject constructor(
@@ -31,6 +33,8 @@ open class KotlinGradleFragment @Inject constructor(
     override fun getName(): String = fragmentName
 
     // TODO pull up to KotlinModuleFragment
+    // FIXME apply to compilation
+    // FIXME check for consistency
     val languageSettings: LanguageSettingsBuilder = DefaultLanguageSettingsBuilder()
 
     protected val project: Project
@@ -80,7 +84,7 @@ open class KotlinGradleFragment @Inject constructor(
         get() = _directRefinesDependencies.map { it.get() }
 
     override val declaredModuleDependencies: Iterable<KotlinModuleDependency>
-        get() = TODO("Not yet implemented")
+        get() = project.configurations.getByName(apiConfigurationName).allDependencies.map { it.toModuleDependency(project) } // FIXME impl
 
     override val kotlinSourceRoots: SourceDirectorySet by lazy {
         project.objects.sourceDirectorySet(
@@ -104,7 +108,12 @@ open class KotlinGradleFragment @Inject constructor(
     companion object {
         const val COMMON_FRAGMENT_NAME = "common"
     }
+
+    override fun toString(): String = "fragment $fragmentName in $containingModule"
 }
 
 internal fun KotlinModuleFragment.disambiguateName(simpleName: String) =
     lowerCamelCaseName(fragmentName, containingModule.moduleIdentifier.moduleClassifier ?: KotlinGradleModule.MAIN_MODULE_NAME, simpleName)
+
+val KotlinGradleFragment.refinesClosure: Set<KotlinGradleFragment>
+    get() = (this as KotlinModuleFragment).refinesClosure.map { it as KotlinGradleFragment }.toSet()

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinGradleModule.kt

@@ -12,9 +12,8 @@ import org.gradle.api.NamedDomainObjectSet
 import org.gradle.api.Project
 import org.jetbrains.kotlin.gradle.plugin.HasKotlinDependencies
 import org.jetbrains.kotlin.gradle.plugin.KotlinDependencyHandler
-import org.jetbrains.kotlin.project.model.KotlinModule
-import org.jetbrains.kotlin.project.model.KotlinModuleIdentifier
-import org.jetbrains.kotlin.project.model.LocalModuleIdentifier
+import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
+import org.jetbrains.kotlin.project.model.*
 import javax.inject.Inject
 
 open class KotlinGradleModule(
@@ -87,7 +86,15 @@ open class KotlinGradleModule(
 
     override val runtimeOnlyConfigurationName: String
         get() = common.runtimeOnlyConfigurationName
+
+    override fun toString(): String = "$moduleIdentifier (Gradle)"
 }
 
+internal val KotlinGradleModule.resolvableMetadataConfigurationName: String
+    get() = lowerCamelCaseName(name, "DependenciesMetadata")
+
 internal val KotlinGradleModule.isMain
     get() = moduleIdentifier.moduleClassifier == null
+
+fun KotlinGradleModule.variantsContainingFragment(fragment: KotlinModuleFragment): Iterable<KotlinGradleVariant> =
+    variants.filter { fragment in it.refinesClosure }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinGradleModuleFactory.kt

@@ -20,7 +20,7 @@ open class KotlinGradleModuleFactory(private val project: Project) : NamedDomain
     }
 
     protected open fun registerDefaultCommonFragment(module: KotlinGradleModule) {
-        module.fragments.create(KotlinGradleFragment.COMMON_FRAGMENT_NAME, KotlinGradleFragment::class.java)
+        module.fragments.register(KotlinGradleFragment.COMMON_FRAGMENT_NAME, KotlinGradleFragment::class.java)
     }
 
     protected open fun addDefaultRefinementDependencyOnCommon(module: KotlinGradleModule) {

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinJvmVariant.kt

@@ -58,6 +58,13 @@ class KotlinJvmVariantCompilationData(val variant: KotlinJvmVariant) : KotlinCom
     override val platformType: KotlinPlatformType
         get() = variant.platformType
 
+    override val friendPaths: Iterable<FileCollection>
+        // TODO for now, all output classes of the module are considered friends, even those not on the classpath
+        get() {
+            // FIXME support compiling against the JARs
+            return variant.containingModule.project.pm20Extension.modules.flatMap { it.variants.map { it.compilationOutputs.classesDirs } }
+        }
+
     override val moduleName: String
         get() = // TODO accurate module names that don't rely on all variants having a main counterpart
             variant.containingModule.project.pm20Extension.modules

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/TransformKotlinGranularMetadataForFragment.kt

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2010-2021 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.gradle.plugin.mpp.pm20
+
+import org.gradle.api.DefaultTask
+import org.gradle.api.file.FileCollection
+import org.gradle.api.model.ObjectFactory
+import org.gradle.api.tasks.*
+import org.jetbrains.kotlin.gradle.plugin.mpp.ExtractableMetadataFiles
+import org.jetbrains.kotlin.gradle.plugin.mpp.MetadataDependencyResolution
+import org.jetbrains.kotlin.gradle.targets.metadata.ResolvedMetadataFilesProvider
+import org.jetbrains.kotlin.gradle.utils.getValue
+import java.io.File
+import javax.inject.Inject
+
+internal open class TransformKotlinGranularMetadataForFragment
+@Inject constructor(
+    @get:Internal
+    @field:Transient
+    val fragment: KotlinGradleFragment,
+    //FIXME annotations
+    private val transformation: FragmentGranularMetadataResolver
+) : DefaultTask() {
+
+    @get:OutputDirectory
+    val outputsDir: File by project.provider {
+        project.buildDir.resolve("kotlinFragmentDependencyMetadata").resolve(fragment.disambiguateName(""))
+    }
+
+    @Suppress("unused") // Gradle input
+    @get:InputFiles
+    @get:PathSensitive(PathSensitivity.RELATIVE)
+    internal val allSourceSetsMetadataConfiguration: FileCollection by lazy {
+        project.files(resolvableMetadataConfiguration(fragment.containingModule))
+    }
+
+    @Suppress("unused") // Gradle input
+    @get:Input
+    internal val inputFragmentsAndVariants: Map<String, Iterable<String>> by project.provider {
+        val participatingFragments = fragment.refinesClosure
+        participatingFragments.associateWith { it.containingModule.variantsContainingFragment(it) }
+            .entries.associate { (fragment, variants) ->
+                fragment.name to variants.map { it.fragmentName }.sorted()
+            }
+    }
+
+    @Suppress("unused") // Gradle input
+    @get:Input
+    internal val inputVariantDependencies: Map<String, Set<List<String?>>> by project.provider {
+        val participatingFragments = fragment.refinesClosure
+        val participatingCompilations = participatingFragments.flatMap { it.containingModule.variantsContainingFragment(it) }
+        participatingCompilations.associate { variant ->
+            variant.fragmentName to project.configurations.getByName(variant.compileDependencyConfigurationName)
+                .allDependencies.map { listOf(it.group, it.name, it.version) }.toSet()
+        }
+    }
+
+    @get:Internal
+    @delegate:Transient // exclude from Gradle instant execution state
+    internal val metadataDependencyResolutions: Iterable<MetadataDependencyResolution> by project.provider {
+        transformation.resolutions
+    }
+
+    private val extractableFilesByResolution: Map<out MetadataDependencyResolution, ExtractableMetadataFiles>
+        get() = metadataDependencyResolutions
+            .filterIsInstance<MetadataDependencyResolution.ChooseVisibleSourceSets>()
+            .associateWith { it.getExtractableMetadataFiles(outputsDir) }
+
+    @get:Internal
+    internal val filesByResolution: Map<MetadataDependencyResolution, FileCollection>
+        get() = extractableFilesByResolution.mapValues { (_, value) ->
+            project.files(value.getMetadataFilesPerSourceSet(false).values).builtBy(this)
+        }
+
+    private val extractableFiles by project.provider { extractableFilesByResolution.values }
+
+    @TaskAction
+    fun transformMetadata() {
+        if (outputsDir.isDirectory) {
+            outputsDir.deleteRecursively()
+        }
+        outputsDir.mkdirs()
+
+        extractableFiles.forEach { it.getMetadataFilesPerSourceSet(doProcessFiles = true) }
+    }
+}
+
+internal class FragmentResolvedMetadataProvider(
+    taskProvider: TaskProvider<out TransformKotlinGranularMetadataForFragment>
+) : ResolvedMetadataFilesProvider {
+    override val buildDependencies: Iterable<TaskProvider<*>> = listOf(taskProvider)
+    override val metadataResolutions: Iterable<MetadataDependencyResolution> by taskProvider.map { it.metadataDependencyResolutions }
+    override val metadataFilesByResolution: Map<MetadataDependencyResolution, FileCollection> by taskProvider.map { it.filesByResolution }
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/abstractVariants.kt

@@ -12,7 +12,7 @@ import org.gradle.api.tasks.bundling.AbstractArchiveTask
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilationOutput
 import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
 import org.jetbrains.kotlin.gradle.plugin.mpp.DefaultKotlinCompilationOutput
-import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.util.fromPlatform
+import org.jetbrains.kotlin.gradle.plugin.mpp.publishedConfigurationName
 import org.jetbrains.kotlin.gradle.tasks.withType
 import org.jetbrains.kotlin.project.model.KotlinAttributeKey
 import org.jetbrains.kotlin.project.model.KotlinModuleVariant
@@ -26,7 +26,7 @@ abstract class KotlinGradleVariant(
     abstract val platformType: KotlinPlatformType
 
     override val variantAttributes: Map<KotlinAttributeKey, String>
-        get() = mapOf(KotlinPlatformTypeAttribute to KotlinPlatformTypeAttribute.fromPlatform(platformType)) // TODO user attributes
+        get() = mapOf(KotlinPlatformTypeAttribute to kotlinPlatformTypeAttributeFromPlatform(platformType)) // TODO user attributes
 
     // TODO generalize with KotlinCompilation?
     val compileDependencyConfigurationName: String
@@ -48,8 +48,15 @@ abstract class KotlinGradleVariant(
     // TODO generalize exposing outputs: what if a variant has more than one such configurations or none?
     val apiElementsConfigurationName: String
         get() = disambiguateName("apiElements")
+
+    open val gradleVariantNames: Set<String>
+        get() = listOf(apiElementsConfigurationName, publishedConfigurationName(apiElementsConfigurationName)).toSet()
+
+    override fun toString(): String = "variant $fragmentName in $containingModule"
 }
 
+private fun kotlinPlatformTypeAttributeFromPlatform(platformType: KotlinPlatformType) = platformType.name
+
 // TODO: rewrite with the artifacts API
 internal val KotlinGradleVariant.defaultSourceArtifactTaskName: String
     get() = disambiguateName("sourcesJar")
@@ -71,4 +78,8 @@ abstract class KotlinGradleVariantWithRuntimeDependencies(
     // TODO generalize exposing outputs: what if a variant has more than one such configurations or none?
     val runtimeElementsConfigurationName: String
         get() = disambiguateName("runtimeElements")
+
+    override val gradleVariantNames: Set<String>
+        get() = super.gradleVariantNames +
+                listOf(runtimeElementsConfigurationName, publishedConfigurationName(runtimeElementsConfigurationName))
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/fragmentsMetadataCompilation.kt

@@ -0,0 +1,198 @@
+/*
+ * Copyright 2010-2021 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.gradle.plugin.mpp.pm20
+
+import org.gradle.api.DefaultTask
+import org.gradle.api.Project
+import org.gradle.api.attributes.Usage
+import org.gradle.api.tasks.TaskProvider
+import org.gradle.jvm.tasks.Jar
+import org.jetbrains.kotlin.gradle.dsl.KotlinMultiplatformCommonOptions
+import org.jetbrains.kotlin.gradle.dsl.pm20Extension
+import org.jetbrains.kotlin.gradle.plugin.KotlinCommonSourceSetProcessor
+import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
+import org.jetbrains.kotlin.gradle.plugin.getKotlinPluginVersion
+import org.jetbrains.kotlin.gradle.plugin.mpp.*
+import org.jetbrains.kotlin.gradle.plugin.mpp.MULTIPLATFORM_PROJECT_METADATA_JSON_FILE_NAME
+import org.jetbrains.kotlin.gradle.plugin.mpp.addSourcesToKotlinCompileTask
+import org.jetbrains.kotlin.gradle.plugin.mpp.buildKotlinProjectStructureMetadata
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.disambiguateName
+import org.jetbrains.kotlin.gradle.plugin.usageByName
+import org.jetbrains.kotlin.gradle.targets.metadata.createGenerateProjectStructureMetadataTask
+import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
+import org.jetbrains.kotlin.gradle.tasks.registerTask
+import org.jetbrains.kotlin.gradle.tasks.withType
+import org.jetbrains.kotlin.gradle.utils.addExtendsFromRelation
+import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
+import org.jetbrains.kotlin.project.model.KotlinModuleFragment
+import java.util.concurrent.Callable
+
+internal fun configureMetadataResolutionAndBuild(module: KotlinGradleModule) {
+    val project = module.project
+    createResolvableMetadataConfigurationForModule(module)
+
+    val metadataCompilationRegistry = MetadataCompilationRegistry()
+    project.pm20Extension.metadataCompilationRegistryByModuleId[module.moduleIdentifier] =
+        metadataCompilationRegistry
+
+    configureMetadataCompilationsAndCreateRegistry(module, metadataCompilationRegistry)
+
+    configureMetadataJarTask(module, metadataCompilationRegistry)
+    generateAndExportProjectStructureMetadata(module)
+}
+
+private fun generateAndExportProjectStructureMetadata(
+    module: KotlinGradleModule
+) {
+    val project = module.project
+    val projectStructureMetadata = project.createGenerateProjectStructureMetadataTask(module.moduleClassifier)
+    project.tasks.withType<Jar>().named(metadataJarName(module)).configure { jar ->
+        jar.from(projectStructureMetadata.map { it.resultFile }) { spec ->
+            spec.into("META-INF")
+                .rename { MULTIPLATFORM_PROJECT_METADATA_JSON_FILE_NAME }
+        }
+    }
+    GlobalProjectStructureMetadataStorage.registerProjectStructureMetadata(project) {
+        checkNotNull(buildKotlinProjectStructureMetadata(project))
+    }
+}
+
+private fun createResolvableMetadataConfigurationForModule(module: KotlinGradleModule) {
+    val project = module.project
+    project.configurations.create(module.resolvableMetadataConfigurationName).apply {
+        isCanBeConsumed = false
+        isCanBeResolved = true
+        attributes.attribute(Usage.USAGE_ATTRIBUTE, project.usageByName(KotlinUsages.KOTLIN_METADATA))
+        module.fragments.all { fragment ->
+            project.addExtendsFromRelation(name, fragment.apiConfigurationName)
+            project.addExtendsFromRelation(name, fragment.implementationConfigurationName)
+        }
+    }
+}
+
+private fun configureMetadataCompilationsAndCreateRegistry(
+    module: KotlinGradleModule,
+    metadataCompilationRegistry: MetadataCompilationRegistry
+) {
+    val project = module.project
+    val metadataResolutionByFragment = mutableMapOf<KotlinGradleFragment, FragmentGranularMetadataResolver>()
+    module.fragments.all { fragment ->
+        val transformation = FragmentGranularMetadataResolver(fragment, lazy {
+            fragment.refinesClosure.minus(fragment).map {
+                metadataResolutionByFragment.getValue(it)
+            }
+        })
+        metadataResolutionByFragment[fragment] = transformation
+        createExtractMetadataTask(project, fragment, transformation)
+    }
+    val compileAllTask = project.registerTask<DefaultTask>(lowerCamelCaseName(module.moduleClassifier, "metadataClasses"))
+    module.fragments.all { fragment ->
+        createMetadataCompilation(fragment, compileAllTask, metadataCompilationRegistry)
+    }
+}
+
+private fun configureMetadataJarTask(
+    module: KotlinGradleModule,
+    registry: MetadataCompilationRegistry
+) {
+    val project = module.project
+    val allMetadataJar = project.registerTask<Jar>(metadataJarName(module)) { task ->
+        task.archiveAppendix.set("metadata")
+        task.from()
+    }
+    registry.withAll { compilationData ->
+        allMetadataJar.configure { jar ->
+            jar.from(compilationData.output.allOutputs) { spec ->
+                spec.into(compilationData.fragment.fragmentName)
+            }
+        }
+    }
+}
+
+private fun metadataJarName(module: KotlinGradleModule) =
+    lowerCamelCaseName(module.moduleClassifier, "metadataJar")
+
+private fun createMetadataCompilation(
+    fragment: KotlinGradleFragment,
+    compileAllTask: TaskProvider<DefaultTask>,
+    metadataCompilationRegistry: MetadataCompilationRegistry
+): KotlinCompilationData<out KotlinMultiplatformCommonOptions> {
+    val module = fragment.containingModule
+    val project = module.project
+
+    val metadataCompilationData =
+        KotlinFragmentMetadataCompilationData(
+            project,
+            fragment,
+            module,
+            compileAllTask,
+            metadataCompilationRegistry,
+            lazy {
+                fragment.refinesClosure.map {
+                    FragmentResolvedMetadataProvider(
+                        project.tasks.withType<TransformKotlinGranularMetadataForFragment>()
+                            .named(transformFragmentMetadataTaskName(it))
+                    )
+                }
+            }
+        )
+    metadataCompilationRegistry.register(fragment, metadataCompilationData)
+
+    addSourcesToKotlinCompileTask(
+        project,
+        metadataCompilationData.compileKotlinTaskName,
+        /*FIXME*/ emptyList(),
+        { fragment.kotlinSourceRoots },
+        lazyOf(true)
+    )
+
+    KotlinCommonSourceSetProcessor(
+        metadataCompilationData,
+        KotlinTasksProvider(),
+        project.getKotlinPluginVersion() ?: "undefined"
+    ).run()
+
+    return metadataCompilationData
+}
+
+private fun createExtractMetadataTask(
+    project: Project,
+    fragment: KotlinGradleFragment,
+    transformation: FragmentGranularMetadataResolver
+) {
+    project.tasks.register(
+        transformFragmentMetadataTaskName(fragment),
+        TransformKotlinGranularMetadataForFragment::class.java,
+        fragment,
+        transformation
+    ).configure { task ->
+        task.dependsOn(Callable {
+            fragment.refinesClosure.mapNotNull { refined ->
+                if (refined !== fragment)
+                    project.tasks.named(transformFragmentMetadataTaskName(refined))
+                else null
+            }
+        })
+    }
+}
+
+// FIXME: use this function once more than one platform is supported
+private fun disableMetadataCompilationIfNotYetSupported(
+    metadataCompilationData: KotlinFragmentMetadataCompilationData
+) {
+    val fragment = metadataCompilationData.fragment
+    val platforms = fragment.containingModule.variantsContainingFragment(fragment).map { it.platformType }.toSet()
+    if (platforms != setOf(KotlinPlatformType.native) && platforms.size == 1
+        || platforms == setOf(KotlinPlatformType.jvm, KotlinPlatformType.androidJvm)
+    ) {
+        fragment.containingModule.project.tasks.named(metadataCompilationData.compileKotlinTaskName).configure {
+            it.enabled = false
+        }
+    }
+}
+
+private fun transformFragmentMetadataTaskName(fragment: KotlinModuleFragment) =
+    lowerCamelCaseName("resolve", fragment.disambiguateName("Metadata"))

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/modelClasses.kt

@@ -5,36 +5,18 @@
 
 package org.jetbrains.kotlin.gradle.plugin.mpp.pm20
 
-import org.gradle.api.*
-import org.gradle.api.file.FileCollection
-import org.gradle.api.file.SourceDirectorySet
-import org.gradle.api.plugins.BasePluginConvention
 import org.gradle.api.tasks.TaskProvider
 import org.gradle.jvm.tasks.Jar
-import org.jetbrains.kotlin.gradle.dsl.KotlinCommonOptions
-import org.jetbrains.kotlin.gradle.dsl.KotlinJvmOptions
-import org.jetbrains.kotlin.gradle.dsl.KotlinJvmOptionsImpl
-import org.jetbrains.kotlin.gradle.dsl.pm20Extension
-import org.jetbrains.kotlin.gradle.plugin.*
-import org.jetbrains.kotlin.gradle.plugin.mpp.*
+import org.jetbrains.kotlin.gradle.plugin.Kotlin2JvmSourceSetProcessor
+import org.jetbrains.kotlin.gradle.plugin.getKotlinPluginVersion
+import org.jetbrains.kotlin.gradle.plugin.mpp.addSourcesToKotlinCompileTask
 import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
 import org.jetbrains.kotlin.gradle.tasks.locateOrRegisterTask
 import org.jetbrains.kotlin.gradle.utils.dashSeparatedName
-import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
-import org.jetbrains.kotlin.project.model.*
+import org.jetbrains.kotlin.project.model.refinesClosure
 import org.jetbrains.kotlin.project.model.utils.variantsContainingFragment
 import java.util.concurrent.Callable
 
-//region Fragment
-
-//endregion Fragment
-
-//region Variant
-
-
-
-
-
 open class KotlinJvmVariantFactory(module: KotlinGradleModule) :
     AbstractKotlinGradleVariantWithRuntimeDependenciesFactory<KotlinJvmVariant>(module) {
     override fun instantiateFragment(name: String) = KotlinJvmVariant(module, name)

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

@@ -15,13 +15,13 @@ import org.gradle.api.plugins.BasePlugin
 import org.gradle.api.tasks.TaskProvider
 import org.gradle.api.tasks.bundling.Jar
 import org.gradle.api.tasks.bundling.Zip
-import org.jetbrains.kotlin.gradle.dsl.KotlinCommonOptions
+import org.jetbrains.kotlin.gradle.dsl.*
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
-import org.jetbrains.kotlin.gradle.dsl.multiplatformExtensionOrNull
 import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.*
 import org.jetbrains.kotlin.gradle.plugin.mpp.CompilationSourceSetUtil.compilationsBySourceSets
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinPm20ProjectExtension
 import org.jetbrains.kotlin.gradle.plugin.sources.*
 import org.jetbrains.kotlin.gradle.plugin.statistics.KotlinBuildStatsService
 import org.jetbrains.kotlin.gradle.targets.native.internal.*
@@ -38,7 +38,8 @@ internal const val ALL_COMPILE_METADATA_CONFIGURATION_NAME = "allSourceSetsCompi
 internal const val ALL_RUNTIME_METADATA_CONFIGURATION_NAME = "allSourceSetsRuntimeDependenciesMetadata"
 
 internal val Project.isKotlinGranularMetadataEnabled: Boolean
-    get() = PropertiesProvider(rootProject).enableGranularSourceSetsMetadata == true
+    get() = project.topLevelExtension is KotlinPm20ProjectExtension ||
+            PropertiesProvider(rootProject).enableGranularSourceSetsMetadata == true
 
 internal val Project.isCompatibilityMetadataVariantEnabled: Boolean
     get() = PropertiesProvider(this).enableCompatibilityMetadataVariant == true
@@ -231,7 +232,7 @@ class KotlinMetadataTargetConfigurator(kotlinPluginVersion: String) :
         val generateMetadata = project.createGenerateProjectStructureMetadataTask()
 
         allMetadataJar.configure {
-            it.from(generateMetadata.map { it.resultXmlFile }) { spec ->
+            it.from(generateMetadata.map { it.resultFile }) { spec ->
                 spec.into("META-INF").rename { MULTIPLATFORM_PROJECT_METADATA_JSON_FILE_NAME }
             }
         }
@@ -437,91 +438,28 @@ class KotlinMetadataTargetConfigurator(kotlinPluginVersion: String) :
     ): FileCollection {
         val project = compilation.target.project
 
-        // Adjust metadata compilation to support source set hierarchies, i.e. use both the outputs of dependsOn source set compilation
-        // and their dependencies metadata transformed for compilation:
-        return project.files(
-            project.provider {
-                val sourceSet = compilation.defaultSourceSet
+        val sourceSet = compilation.defaultSourceSet
 
-                val transformationTaskHolders = sourceSet.withAllDependsOnSourceSets().mapNotNull { hierarchySourceSet ->
-                    project.locateTask<TransformKotlinGranularMetadata>(transformGranularMetadataTaskName(hierarchySourceSet.name))
-                }
-
-                val allResolutionsByComponentId: Map<ComponentIdentifier, List<MetadataDependencyResolution>> =
-                    mutableMapOf<ComponentIdentifier, MutableList<MetadataDependencyResolution>>().apply {
-                        transformationTaskHolders.forEach {
-                            val resolutions = it.get().metadataDependencyResolutions
-                            resolutions.forEach { resolution ->
-                                getOrPut(resolution.dependency.id) { mutableListOf() }.add(resolution)
-                            }
-                        }
-                    }
-
-                val transformedFilesByResolution: Map<MetadataDependencyResolution, FileCollection> =
-                    transformationTaskHolders.flatMap { it.get().filesByResolution.toList() }.toMap()
-
-                val dependsOnCompilationOutputs = sourceSet.resolveAllDependsOnSourceSets().mapNotNull { hierarchySourceSet ->
-                    val dependencyCompilation = project.getMetadataCompilationForSourceSet(hierarchySourceSet)
-                    dependencyCompilation?.output?.classesDirs
-                }
-
-                val artifactView = fromFiles.incoming.artifactView { view ->
-                    view.componentFilter { id ->
-                        allResolutionsByComponentId[id].let { resolutions ->
-                            resolutions == null || resolutions.any { it !is MetadataDependencyResolution.ExcludeAsUnrequested }
-                        }
-                    }
-                }
-
-                mutableSetOf<Any /* File | FileCollection */>().apply {
-                    addAll(dependsOnCompilationOutputs)
-                    artifactView.artifacts.forEach { artifact ->
-                        val resolutions = allResolutionsByComponentId[artifact.id.componentIdentifier]
-                        if (resolutions == null) {
-                            add(artifact.file)
-                        } else {
-                            val chooseVisibleSourceSets =
-                                resolutions.filterIsInstance<MetadataDependencyResolution.ChooseVisibleSourceSets>()
-
-                            if (chooseVisibleSourceSets.isNotEmpty()) {
-                                // Wrap the list into a FileCollection, as some older Gradle version failed to resolve the classpath
-                                add(project.files(chooseVisibleSourceSets.map { transformedFilesByResolution.getValue(it) }))
-                            } else if (resolutions.any { it is MetadataDependencyResolution.KeepOriginalDependency }) {
-                                add(artifact.file)
-                            } // else: all dependency transformations exclude this dependency as unrequested; don't add any files
-                        }
-                    }
-
-                    // Add a build dependency on the granular metadata transformations of the dependency source sets
-                    add(project.files().builtBy(transformationTaskHolders))
-                }
+        val dependsOnCompilationOutputs = lazy {
+            sourceSet.withAllDependsOnSourceSets().mapNotNull { hierarchySourceSet ->
+                val dependencyCompilation = project.getMetadataCompilationForSourceSet(hierarchySourceSet)
+                dependencyCompilation?.output?.classesDirs.takeIf { hierarchySourceSet != sourceSet }
             }
-        )
-        /*
-        val transformedFilesByOriginalFiles = project.provider {
-            transformationTaskHolders
-                .flatMap { it.get().filesByOriginalFiles.toList() }
-                .groupBy({ it.first }, valueTransform = { it.second })
         }
 
-        val builtBySet = mutableSetOf<FileCollection>()
-        val resultFiles = project.files(Callable {
-            val originalFiles = fromFiles.toSet()
-            val filesToAdd = mutableSetOf<File>()
-            val filesToExclude = mutableSetOf<File>()
-
-            transformedFilesByOriginalFiles.get().forEach { (original, replacement) ->
-                if (original.all { it in originalFiles }) {
-                    builtBySet.addAll(replacement)
-                    filesToAdd += replacement.flatMap { it.files }
-                    filesToExclude += original
-                }
+        val resolvedMetadataFilesProviders = lazy {
+            val transformationTaskHolders = sourceSet.withAllDependsOnSourceSets().mapNotNull { hierarchySourceSet ->
+                project.locateTask<TransformKotlinGranularMetadata>(transformGranularMetadataTaskName(hierarchySourceSet.name))
             }
+            transformationTaskHolders.map { SourceSetResolvedMetadataProvider(it) }
+        }
 
-            originalFiles - filesToExclude + filesToAdd
-        })
-        return resultFiles.builtBy(builtBySet)
-         */
+        return createTransformedMetadataClasspath(
+            project,
+            fromFiles,
+            dependsOnCompilationOutputs,
+            resolvedMetadataFilesProviders
+        )
     }
 
     private fun createCommonMainElementsConfiguration(target: KotlinMetadataTarget) {
@@ -545,11 +483,69 @@ class KotlinMetadataTargetConfigurator(kotlinPluginVersion: String) :
             project.artifacts.add(name, project.tasks.getByName(target.legacyArtifactsTaskName))
         }
     }
+}
 
-    private fun Project.createGenerateProjectStructureMetadataTask(): TaskProvider<GenerateProjectStructureMetadata> =
-        project.registerTask("generateProjectStructureMetadata") { task ->
-            task.lazyKotlinProjectStructureMetadata = lazy { checkNotNull(buildKotlinProjectStructureMetadata(project)) }
+internal fun Project.createGenerateProjectStructureMetadataTask(moduleClassifier: String? = null): TaskProvider<GenerateProjectStructureMetadata> =
+    project.registerTask(lowerCamelCaseName("generate", moduleClassifier, "ProjectStructureMetadata")) { task ->
+        task.lazyKotlinProjectStructureMetadata = lazy { checkNotNull(buildKotlinProjectStructureMetadata(project)) }
+    }
+
+internal interface ResolvedMetadataFilesProvider {
+    val buildDependencies: Iterable<TaskProvider<*>>
+    val metadataResolutions: Iterable<MetadataDependencyResolution>
+    val metadataFilesByResolution: Map<MetadataDependencyResolution, FileCollection>
+}
+
+internal fun createTransformedMetadataClasspath(
+    project: Project,
+    fromFiles: Configuration,
+    parentCompiledMetadataFiles: Lazy<Iterable<FileCollection>>,
+    metadataResolutionProviders: Lazy<Iterable<ResolvedMetadataFilesProvider>>
+): FileCollection {
+    return project.files(
+        project.provider {
+            val allResolutionsByComponentId: Map<ComponentIdentifier, List<MetadataDependencyResolution>> =
+                mutableMapOf<ComponentIdentifier, MutableList<MetadataDependencyResolution>>().apply {
+                    metadataResolutionProviders.value.forEach {
+                        it.metadataResolutions.forEach { resolution ->
+                            getOrPut(resolution.dependency.id) { mutableListOf() }.add(resolution)
+                        }
+                    }
+                }
+
+            val transformedFilesByResolution: Map<MetadataDependencyResolution, FileCollection> =
+                metadataResolutionProviders.value.flatMap { it.metadataFilesByResolution.toList() }.toMap()
+
+            val artifactView = fromFiles.incoming.artifactView { view ->
+                view.componentFilter { id ->
+                    allResolutionsByComponentId[id].let { resolutions ->
+                        resolutions == null || resolutions.any { it !is MetadataDependencyResolution.ExcludeAsUnrequested }
+                    }
+                }
+            }
+
+            mutableSetOf<Any /* File | FileCollection */>().apply {
+                addAll(metadataResolutionProviders.value.map { project.files().builtBy(it.buildDependencies) })
+                addAll(parentCompiledMetadataFiles.value)
+                artifactView.artifacts.forEach { artifact ->
+                    val resolutions = allResolutionsByComponentId[artifact.id.componentIdentifier]
+                    if (resolutions == null) {
+                        add(artifact.file)
+                    } else {
+                        val chooseVisibleSourceSets =
+                            resolutions.filterIsInstance<MetadataDependencyResolution.ChooseVisibleSourceSets>()
+
+                        if (chooseVisibleSourceSets.isNotEmpty()) {
+                            // Wrap the list into a FileCollection, as some older Gradle version failed to resolve the classpath
+                            add(project.files(chooseVisibleSourceSets.map { transformedFilesByResolution.getValue(it) }))
+                        } else if (resolutions.any { it is MetadataDependencyResolution.KeepOriginalDependency }) {
+                            add(artifact.file)
+                        } // else: all dependency transformations exclude this dependency as unrequested; don't add any files
+                    }
+                }
+            }
         }
+    )
 }
 
 internal fun isSharedNativeSourceSet(project: Project, sourceSet: KotlinSourceSet): Boolean {
@@ -560,9 +556,7 @@ internal fun isSharedNativeSourceSet(project: Project, sourceSet: KotlinSourceSe
 }
 
 internal fun dependsOnClosureWithInterCompilationDependencies(project: Project, sourceSet: KotlinSourceSet): Set<KotlinSourceSet> =
-    sourceSet.getSourceSetHierarchy().toMutableSet().apply {
-        /** exclude self from the results of [getSourceSetHierarchy] */
-        remove(sourceSet)
+    sourceSet.resolveAllDependsOnSourceSets().toMutableSet().apply {
         addAll(getVisibleSourceSetsFromAssociateCompilations(project, sourceSet))
     }
 

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

@@ -34,6 +34,8 @@ import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
 import org.jetbrains.kotlin.gradle.plugin.KotlinTarget
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinCommonCompilation
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.KotlinFragmentMetadataCompilationData
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.refinesClosure
 import org.jetbrains.kotlin.gradle.utils.getValue
 import org.jetbrains.kotlin.gradle.plugin.sources.resolveAllDependsOnSourceSets
 import org.jetbrains.kotlin.incremental.ChangedFiles
@@ -60,7 +62,9 @@ open class KotlinCompileCommon : AbstractKotlinCompile<K2MetadataCompilerArgumen
 
         args.moduleName = this@KotlinCompileCommon.moduleName
 
-        if ((taskData.compilation as? KotlinCommonCompilation)?.isKlibCompilation == true) {
+        if ((taskData.compilation as? KotlinCommonCompilation)?.isKlibCompilation == true ||
+            taskData.compilation is KotlinFragmentMetadataCompilationData
+        ) {
             args.expectActualLinker = true
         }
 
@@ -97,6 +101,14 @@ open class KotlinCompileCommon : AbstractKotlinCompile<K2MetadataCompilerArgumen
                 val defaultKotlinSourceSet: KotlinSourceSet = compilation.defaultSourceSet
                 outputPathsFromMetadataCompilationsOf(defaultKotlinSourceSet.resolveAllDependsOnSourceSets())
             }
+            is KotlinFragmentMetadataCompilationData -> {
+                val fragment = compilation.fragment
+                project.files(
+                    fragment.refinesClosure.minus(fragment).map {
+                        compilation.metadataCompilationRegistry.byFragment(it).output.classesDirs
+                    }
+                )
+            }
             else -> error("unexpected compilation type") // FIXME support PM20 variant
         }
     }

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

@@ -307,15 +307,7 @@ abstract class AbstractKotlinCompile<T : CommonCompilerArguments>() : AbstractKo
 
     @get:Internal // takes part in the compiler arguments
     val friendPaths: FileCollection = project.files(
-        project.provider {
-            taskData.compilation.run {
-                if (this !is AbstractKotlinCompilation<*>) return@run project.files() // FIXME support PM20
-                mutableListOf<FileCollection>().also { allCollections ->
-                    associateWithTransitiveClosure.forEach { allCollections.add(it.output.classesDirs) }
-                    allCollections.add(friendArtifacts)
-                }
-            }
-        }
+        project.provider { taskData.compilation.friendPaths }
     )
 
     private val kotlinLogger by lazy { GradleKotlinLogger(logger) }

libraries/tools/kotlin-project-model/src/main/kotlin/DependencyResolution.kt

@@ -9,7 +9,7 @@ package org.jetbrains.kotlin.project.model
 // TODO think about state management: unresolved -> (known dependency graph?) ... -> completely resolved
 //      it seems to be important to learn whether or not the model is final
 interface ModuleDependencyResolver {
-    fun resolveDependency(moduleDependency: KotlinModuleDependency): KotlinModule?
+    fun resolveDependency(requestingModule: KotlinModule, moduleDependency: KotlinModuleDependency): KotlinModule?
 }
 
 // TODO merge with ModuleDependencyResolver?
@@ -34,4 +34,6 @@ sealed class DependencyGraphResolution(val requestingModule: KotlinModule) {
 class DependencyGraphNode(
     val module: KotlinModule,
     val dependenciesByFragment: Map<KotlinModuleFragment, Iterable<DependencyGraphNode>>
-)
+) {
+    override fun toString(): String = "node ${module}"
+}

libraries/tools/kotlin-project-model/src/main/kotlin/KotlinAttributes.kt

@@ -17,6 +17,7 @@ open class KotlinAttributeKey(
 
 object KotlinPlatformTypeAttribute : KotlinAttributeKey("org.jetbrains.kotlin.platform.type") {
     const val JVM = "jvm"
+    const val ANDROID_JVM = "androidJvm"
     const val JS = "js"
     const val NATIVE = "native"
 }

libraries/tools/kotlin-project-model/src/main/kotlin/KotlinModule.kt

@@ -45,7 +45,7 @@ interface KotlinModule {
     // TODO: isSynthetic?
 }
 
-class BasicKotlinModule(
+open class BasicKotlinModule(
     override val moduleIdentifier: KotlinModuleIdentifier
 ) : KotlinModule {
     override val fragments = mutableListOf<BasicKotlinModuleFragment>()