kotlin-maven-plugin: avoid adding sourceroots to read-only freeArgs list

libraries/tools/kotlin-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/KotlinCompileMojoBase.java

@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.maven;
@@ -231,9 +220,11 @@ public abstract class KotlinCompileMojoBase<A extends CommonCompilerArguments> e
             A arguments,
             List<File> sourceRoots
     ) throws MojoExecutionException {
+        ArrayList<String> freeArgs = new ArrayList<>(arguments.getFreeArgs());
         for (File sourceRoot : sourceRoots) {
-            arguments.getFreeArgs().add(sourceRoot.getPath());
+            freeArgs.add(sourceRoot.getPath());
         }
+        arguments.setFreeArgs(freeArgs);
         return compiler.exec(messageCollector, Services.EMPTY, arguments);
     }