[kotlin-test] Post-process capabilities in leaf framework artifacts' .module files KT-61969

Gradle copies capabilities from the variants of the root artifacts
to the variants of leaf artifacts which leads to capability conflict
when both root and leaf artifacts are present in a configuration during
variant-based dependency resolution

libraries/kotlin.test/build.gradle.kts

@@ -1,5 +1,6 @@
 @file:Suppress("UNUSED_VARIABLE")
-
+import com.google.gson.GsonBuilder
+import com.google.gson.JsonObject
 import org.gradle.api.publish.internal.PublicationInternal
 import org.gradle.jvm.tasks.Jar
 import org.jetbrains.kotlin.gradle.plugin.KotlinPlatformType
@@ -516,3 +517,30 @@ publishing {
         }
     }
 }
+
+
+tasks.withType<GenerateModuleMetadata> {
+    val publication = publication.get() as MavenPublication
+    // alter capabilities of leaf JVM framework artifacts published by "available-at" coordinates
+    if (jvmTestFrameworks.map { it.lowercase() }.any { publication.artifactId.endsWith(it) }) {
+        fun capability(group: String, name: String, version: String) =
+            mapOf("group" to group, "name" to name, "version" to version)
+
+        val defaultCapability = publication.let { capability(it.groupId, it.artifactId, it.version) }
+        val implCapability = implCapability.split(":").let { (g, n, v) -> capability(g, n, v) }
+        val capabilities = listOf(defaultCapability, implCapability)
+
+        doLast {
+            val output = outputFile.get().asFile
+            val gson = GsonBuilder().setPrettyPrinting().create()
+            val moduleJson = output.bufferedReader().use { gson.fromJson(it, JsonObject::class.java) }
+            val variants = moduleJson.getAsJsonArray("variants")
+            variants.forEach { variant ->
+                variant as JsonObject
+                variant.remove("capabilities")
+                variant.add("capabilities", gson.toJsonTree(capabilities))
+            }
+            output.bufferedWriter().use { writer -> gson.toJson(moduleJson, writer) }
+        }
+    }
+}