Add test

pmd-core/src/main/java/net/sourceforge/pmd/internal/util/ClasspathClassLoader.java

@@ -116,8 +116,9 @@ public class ClasspathClassLoader extends URLClassLoader {
 
         URL url = findResource(name);
         if (url == null) {
-            // note this will actually call back into findResource, but
-            // we can't avoid this as the super call
+            // note this will actually call back into this.findResource, but
+            // we can't avoid this as the super implementation uses JDK internal
+            // stuff that we can't copy down here.
             return super.getResource(name);
         }
         return url;

pmd-java/src/test/java/net/sourceforge/pmd/lang/java/symbols/ClassLoadingChildFirstTest.java

@@ -0,0 +1,55 @@
+/*
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.lang.java.symbols;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasProperty;
+import static org.hamcrest.Matchers.hasSize;
+
+import java.net.URL;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import net.sourceforge.pmd.PMDConfiguration;
+import net.sourceforge.pmd.internal.util.ClasspathClassLoader;
+import net.sourceforge.pmd.lang.java.types.JClassType;
+import net.sourceforge.pmd.lang.java.types.TypeSystem;
+
+/**
+ * @author Clément Fournier
+ */
+class ClassLoadingChildFirstTest {
+
+
+    /**
+     * In this test I packed a jar with a custom version of {@link Void}.
+     * The test asserts that when putting that jar on the auxclasspath,
+     * a {@link TypeSystem} prefers that custom class to the one on the
+     * bootstrap classpath. The functionality under test is actually in
+     * {@link ClasspathClassLoader}.
+     */
+    @Test
+    void testClassLoading() {
+        String jarPath = getClass().getPackage().getName().replace('.', '/') + "/custom_java_lang.jar";
+        URL url = Thread.currentThread().getContextClassLoader().getResource(jarPath);
+        Path file = Paths.get(url.getPath());
+
+        PMDConfiguration config = new PMDConfiguration();
+        config.prependAuxClasspath(file.toAbsolutePath().toString());
+
+        TypeSystem typeSystem = TypeSystem.usingClassLoaderClasspath(config.getClassLoader());
+
+        JClassType voidClass = typeSystem.BOXED_VOID;
+        List<JMethodSymbol> declaredMethods = voidClass.getSymbol().getDeclaredMethods();
+        assertThat(declaredMethods, hasSize(1));
+        assertThat(declaredMethods.get(0), hasProperty("simpleName", equalTo("customMethodOnJavaLangVoid")));
+
+    }
+
+}