Maven: eliminate warning classpath entry doesn't exist. Fix integration test

libraries/tools/kotlin-maven-plugin/src/it/simple/expected.log

@@ -1,8 +1,6 @@
 [INFO] Kotlin Compiler version @snapshot@
 [INFO] Compiling Kotlin sources from [/src/main/kotlin]
 [INFO] Classes directory is /target/classes
-[INFO] Classpath: /target/classes
-[INFO] Classes directory is /target/classes
 [INFO] Using kotlin annotations from /local-repo/org/jetbrains/kotlin/kotlin-jdk-annotations/0.1-SNAPSHOT/kotlin-jdk-annotations-0.1-SNAPSHOT.jar
 [INFO] PERF: INIT: Compiler initialized in LLL ms
 [INFO] PERF: ANALYZE: 1 files (2 lines) in LLL ms

libraries/tools/kotlin-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/K2JVMCompileMojo.java

@@ -19,6 +19,8 @@ package org.jetbrains.kotlin.maven;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.util.ArrayUtil;
 import com.sampullara.cli.Args;
+import kotlin.KotlinPackage;
+import kotlin.jvm.functions.Function1;
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugin.logging.Log;
@@ -85,7 +87,6 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
 
     @Override
     protected void configureSpecificCompilerArguments(@NotNull K2JVMCompilerArguments arguments) throws MojoExecutionException {
-        getLog().info("Classes directory is " + output);
         arguments.destination = output;
 
         // don't include runtime, it should be in maven dependencies
@@ -96,7 +97,7 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
             arguments.module = module;
         }
 
-        ArrayList<String> classpathList = new ArrayList<String>(classpath);
+        List<String> classpathList = filterClassPath(classpath);
 
         if (!classpathList.isEmpty()) {
             String classPathString = join(classpathList, File.pathSeparator);
@@ -123,6 +124,15 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
         }
     }
 
+    protected List<String> filterClassPath(List<String> classpath) {
+        return KotlinPackage.filter(classpath, new Function1<String, Boolean>() {
+            @Override
+            public Boolean invoke(String s) {
+                return new File(s).exists() || new File(project.getBasedir(), s).exists();
+            }
+        });
+    }
+
     protected String getFullAnnotationsPath(Log log, List<String> annotations) {
         String jdkAnnotation = getJdkAnnotations().getPath();