Allow running compiler only for libraries (#1508)

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

@@ -24,7 +24,7 @@ import org.jetbrains.kotlin.backend.konan.util.profile
 import org.jetbrains.kotlin.cli.common.CLICompiler
 import org.jetbrains.kotlin.cli.common.CLITool
 import org.jetbrains.kotlin.cli.common.ExitCode
-import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity.ERROR
+import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity.*
 import org.jetbrains.kotlin.cli.jvm.compiler.EnvironmentConfigFiles
 import org.jetbrains.kotlin.cli.jvm.compiler.KotlinCoreEnvironment
 import org.jetbrains.kotlin.config.CompilerConfiguration
@@ -49,15 +49,21 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
             return ExitCode.OK
         }
 
-        if (arguments.freeArgs.isEmpty() && !arguments.isUsefulWithoutFreeArgs) {
-            configuration.report(ERROR, "You have not specified any compilation arguments. No output has been produced.")
-        }
-
         val environment = KotlinCoreEnvironment.createForProduction(rootDisposable,
             configuration, EnvironmentConfigFiles.NATIVE_CONFIG_FILES)
         val project = environment.project
         val konanConfig = KonanConfig(project, configuration)
 
+        val enoughArguments = arguments.freeArgs.isNotEmpty() || arguments.isUsefulWithoutFreeArgs
+        if (!enoughArguments) {
+            configuration.report(ERROR, "You have not specified any compilation arguments. No output has been produced.")
+        }
+
+        if (konanConfig.linkOnly) {
+            configuration.report(WARNING, "You have not specified any source files. " +
+                    "Only libraries will be used to produce the output binary.")
+        }
+
         try {
             runTopLevelPhases(konanConfig, environment)
         } catch (e: KonanCompilationException) {
@@ -78,7 +84,7 @@ class K2Native : CLICompiler<K2NativeCompilerArguments>() {
     }
 
     val K2NativeCompilerArguments.isUsefulWithoutFreeArgs: Boolean
-        get() = this.listTargets || this.listPhases || this.checkDependencies
+        get() = this.listTargets || this.listPhases || this.checkDependencies || this.libraries?.isNotEmpty() ?: false
 
     fun Array<String>?.toNonNullList(): List<String> {
         return this?.asList<String>() ?: listOf<String>()