Report warning for several modules with same name on module path

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/ClasspathRootsResolver.kt

@@ -154,8 +154,16 @@ internal class ClasspathRootsResolver(
         }
 
         for (module in modules) {
-            // TODO: report a diagnostic if a module with this name was already added
-            javaModuleFinder.addUserModule(module)
+            val existing = javaModuleFinder.findModule(module.name)
+            if (existing == null) {
+                javaModuleFinder.addUserModule(module)
+            }
+            else if (module.moduleRoot != existing.moduleRoot) {
+                val jar = VfsUtilCore.getVirtualFileForJar(module.moduleRoot) ?: module.moduleRoot
+                val existingPath = (VfsUtilCore.getVirtualFileForJar(existing.moduleRoot) ?: existing.moduleRoot).path
+                report(STRONG_WARNING, "The root is ignored because a module with the same name '${module.name}' " +
+                                       "has been found earlier on the module path at: $existingPath", jar)
+            }
         }
 
         if (javaModuleFinder.allObservableModules.none()) return

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/modules/CliJavaModuleFinder.kt

@@ -26,13 +26,8 @@ import org.jetbrains.kotlin.resolve.jvm.modules.JavaModuleInfo
 internal class CliJavaModuleFinder(private val jrtFileSystem: VirtualFileSystem?) : JavaModuleFinder {
     private val userModules = linkedMapOf<String, JavaModule>()
 
-    /**
-     * @return true if the module was added successfully, false otherwise
-     */
-    fun addUserModule(module: JavaModule): Boolean {
-        if (module.name in userModules) return false
-        userModules[module.name] = module
-        return true
+    fun addUserModule(module: JavaModule) {
+        userModules.putIfAbsent(module.name, module)
     }
 
     val allObservableModules: Sequence<JavaModule>