Coerce commonTest to common in HMPP

Otherwise, Android import won't add dependency from androidTest to
commoonTest. See KT-38744 for details

^KT-38744 Fixed

idea/kotlin-gradle-tooling/src/KotlinMPPGradleModelBuilder.kt

@@ -20,6 +20,8 @@ import org.gradle.api.provider.Provider
 import org.gradle.api.tasks.Exec
 import org.gradle.api.tasks.TaskProvider
 import org.jetbrains.kotlin.gradle.KotlinMPPGradleModel.Companion.NO_KOTLIN_NATIVE_HOME
+import org.jetbrains.kotlin.gradle.KotlinSourceSet.Companion.COMMON_MAIN_SOURCE_SET_NAME
+import org.jetbrains.kotlin.gradle.KotlinSourceSet.Companion.COMMON_TEST_SOURCE_SET_NAME
 import org.jetbrains.plugins.gradle.DefaultExternalDependencyId
 import org.jetbrains.plugins.gradle.model.*
 import org.jetbrains.plugins.gradle.tooling.ErrorMessageBuilder
@@ -58,7 +60,7 @@ class KotlinMPPGradleModelBuilder : ModelBuilderService {
         val sourceSets = buildSourceSets(dependencyResolver, project, dependencyMapper) ?: return null
         val sourceSetMap = sourceSets.map { it.name to it }.toMap()
         val targets = buildTargets(projectTargets, sourceSetMap, dependencyResolver, project, dependencyMapper) ?: return null
-        computeSourceSetsDeferredInfo(sourceSetMap, targets, isHMPPEnabled(project))
+        computeSourceSetsDeferredInfo(sourceSetMap, targets, isHMPPEnabled(project), shouldCoerceRootSourceSetToCommon(project))
         val coroutinesState = getCoroutinesState(project)
         reportUnresolvedDependencies(targets)
         val kotlinNativeHome = KotlinNativeHomeEvaluator.getKotlinNativeHome(project) ?: NO_KOTLIN_NATIVE_HOME
@@ -94,6 +96,10 @@ class KotlinMPPGradleModelBuilder : ModelBuilderService {
         return (project.findProperty("kotlin.mpp.enableGranularSourceSetsMetadata") as? String)?.toBoolean() ?: false
     }
 
+    private fun shouldCoerceRootSourceSetToCommon(project: Project): Boolean {
+        return (project.findProperty("kotlin.mpp.coerceRootSourceSetsToCommon") as? String)?.toBoolean() ?: true
+    }
+
     private fun isNativeDependencyPropagationEnabled(project: Project): Boolean {
         return (project.findProperty("kotlin.native.enableDependencyPropagation") as? String)?.toBoolean() ?: true
     }
@@ -771,7 +777,8 @@ class KotlinMPPGradleModelBuilder : ModelBuilderService {
     private fun computeSourceSetsDeferredInfo(
         sourceSets: Map<String, KotlinSourceSetImpl>,
         targets: Collection<KotlinTarget>,
-        isHMPPEnabled: Boolean
+        isHMPPEnabled: Boolean,
+        coerceRootSourceSetsToCommon: Boolean
     ) {
         // includes only compilations where source set is listed
         val compiledSourceSetToCompilations = LinkedHashMap<KotlinSourceSet, MutableSet<KotlinCompilation>>()
@@ -810,12 +817,32 @@ class KotlinMPPGradleModelBuilder : ModelBuilderService {
                 val platforms = compilations.map { it.platform }
                 sourceSet.actualPlatforms.addSimplePlatforms(platforms)
             }
-            if ((!isHMPPEnabled) && sourceSet.actualPlatforms.platforms.size != 1) {
+
+            if (sourceSet.shouldCoerceToCommon(isHMPPEnabled, coerceRootSourceSetsToCommon)) {
                 sourceSet.actualPlatforms.addSimplePlatforms(listOf(KotlinPlatform.COMMON))
             }
         }
     }
 
+    private fun KotlinSourceSetImpl.shouldCoerceToCommon(isHMPPEnabled: Boolean, coerceRootSourceSetsToCommon: Boolean): Boolean {
+        val isRoot = name == COMMON_MAIN_SOURCE_SET_NAME || name == COMMON_TEST_SOURCE_SET_NAME
+
+        // never makes sense to coerce single-targeted source-sets
+        if (actualPlatforms.platforms.size == 1) return false
+
+        return when {
+            // pre-HMPP has only single-targeted source sets and COMMON
+            !isHMPPEnabled -> true
+
+            // in HMPP, we might want to coerce source sets to common, but only root ones, and only
+            // when the corresponding setting is turned on
+            isHMPPEnabled && isRoot && coerceRootSourceSetsToCommon -> true
+
+            // in all other cases, in HMPP we shouldn't coerce anything
+            else -> false
+        }
+    }
+
     private class DependencyAdjuster(
         private val configuration: Configuration,
         private val scope: String,