Warn on duplicate library inclusion.

backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2Native.kt

@@ -72,8 +72,7 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
         }
 
         if (arguments.freeArgs.isEmpty() && !arguments.isUsefulWithoutFreeArgs) {
-            val messageCollector = configuration.getNotNull(CLIConfigurationKeys.MESSAGE_COLLECTOR_KEY)
-            messageCollector.report(ERROR, "You have not specified any compilation arguments. No output has been produced.")
+            configuration.report(ERROR, "You have not specified any compilation arguments. No output has been produced.")
         }
 
         // TODO: catch Errors and IllegalStateException.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanConfig.kt

@@ -24,6 +24,9 @@ import org.jetbrains.kotlin.backend.konan.util.File
 import org.jetbrains.kotlin.backend.konan.util.profile
 import org.jetbrains.kotlin.backend.konan.util.removeSuffixIfPresent
 import org.jetbrains.kotlin.backend.konan.util.suffixIfNot
+import org.jetbrains.kotlin.cli.common.CLIConfigurationKeys
+import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity
+import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity.*
 import org.jetbrains.kotlin.config.CommonConfigurationKeys
 import org.jetbrains.kotlin.config.CompilerConfiguration
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
@@ -69,7 +72,9 @@ class KonanConfig(val project: Project, val configuration: CompilerConfiguration
     private val repositories = configuration.getList(KonanConfigKeys.REPOSITORIES) ?: emptyList()
     private val resolver = KonanLibrarySearchPathResolver(repositories, distribution.klib, distribution.localKonanDir)
     private val librariesFound: List<File> by lazy {
-        libraryNames.map{it -> resolver.resolve(it)}
+        val resolvedLibraries = libraryNames.map{it -> resolver.resolve(it)}
+        checkLibraryDuplicates(resolvedLibraries)
+        resolvedLibraries
     }
 
     internal val libraries: List<KonanLibraryReader> by lazy {
@@ -106,4 +111,14 @@ class KonanConfig(val project: Project, val configuration: CompilerConfiguration
 
         loadedDescriptors
     }
+
+    private fun checkLibraryDuplicates(resolvedLibraries: List<File>) {
+        val duplicates = resolvedLibraries.groupBy { it.absolutePath } .values.filter { it.size > 1 }
+        duplicates.forEach {
+            configuration.report(STRONG_WARNING, "library included more than once: ${it.first().absolutePath}")
+        }
+    }
 }
+
+fun CompilerConfiguration.report(priority: CompilerMessageSeverity, message: String) 
+    = this.getNotNull(CLIConfigurationKeys.MESSAGE_COLLECTOR_KEY).report(priority, message)