Improve functionality of the classloader task when applied to the core loader

src/main/org/apache/tools/ant/Project.java

@@ -185,10 +185,9 @@ protected Boolean initialValue() {
         };
 
     /**
-     * The Ant core classloader--may be <code>null</code> if using
-     * parent classloader.
+     * The Ant core classloader
      */
-    private ClassLoader coreLoader = null;
+    private AntClassLoader coreLoader = null;
 
     /** Records the latest task to be executed on a thread. */
     private final Map<Thread,Task> threadTasks =
@@ -302,7 +301,8 @@ public void initSubProject(final Project subProject) {
      */
     public void init() throws BuildException {
         initProperties();
-
+        if (coreLoader == null)
+            setCoreLoader(null);
         ComponentHelper.getComponentHelper(this).initDefaultDefinitions();
     }
 
@@ -361,18 +361,31 @@ public AntClassLoader createClassLoader(
     /**
      * Set the core classloader for the project. If a <code>null</code>
      * classloader is specified, the parent classloader should be used.
+     * <p>
+     * <em>Since Ant 1.9.5</em>, if the argument is not a
+     * non-<code>null</code> instance of {@link AntClassLoader}, then
+     * an ant class loader will be constructed around the specified
+     * class loader. This ensures that the core class loader is always
+     * an ant class loader which can be modified using the
+     * &lt;classloader&gt; task.
      *
      * @param coreLoader The classloader to use for the project.
      *                   May be <code>null</code>.
      */
     public void setCoreLoader(final ClassLoader coreLoader) {
-        this.coreLoader = coreLoader;
+        if (coreLoader == null || coreLoader instanceof AntClassLoader == false)
+            this.coreLoader = createClassLoader(coreLoader, null);
+        else
+            this.coreLoader = (AntClassLoader)coreLoader;
     }
 
     /**
      * Return the core classloader to use for this project.
-     * This may be <code>null</code>, indicating that
-     * the parent classloader should be used.
+     * <p>
+     * <em>Since Ant 1.9.5</em> the returned loader will always be a
+     * non-<code>null</code> instance of {@link AntClassLoader}.
+     * In older versions, this might be <code>null</code>,
+     * indicating that the parent classloader should be used.
      *
      * @return the core classloader to use for this project.
      *

src/main/org/apache/tools/ant/taskdefs/Classloader.java

@@ -161,17 +161,26 @@ public Path createClasspath() {
      */
     public void execute() {
         try {
-            // Gump friendly - don't mess with the core loader if only classpath
-            if ("only".equals(getProject().getProperty("build.sysclasspath"))
-                && (name == null || SYSTEM_LOADER_REF.equals(name))) {
-                log("Changing the system loader is disabled "
-                    + "by build.sysclasspath=only", Project.MSG_WARN);
-                return;
+            String loaderName;
+            Object obj;
+            if (name == null || SYSTEM_LOADER_REF.equals(name)) {
+                if ("only".equals(getProject()
+                                  .getProperty("build.sysclasspath"))) {
+                    // Gump friendly - don't mess with the core loader
+                    // if only the system classpath is to be used
+                    log("Changing the system loader is disabled "
+                        + "by build.sysclasspath=only", Project.MSG_WARN);
+                    return;
+                }
+                name = null;
+                loaderName = SYSTEM_LOADER_REF;
+                obj = getProject().getCoreLoader();
+            }
+            else {
+                loaderName = name;
+                obj = getProject().getReference(loaderName);
             }
 
-            String loaderName = (name == null) ? SYSTEM_LOADER_REF : name;
-
-            Object obj = getProject().getReference(loaderName);
             if (reset) {
                 // Are any other references held ? Can we 'close' the loader
                 // so it removes the locks on jars ?

src/tests/antunit/taskdefs/classloader-test.xml

@@ -0,0 +1,87 @@
+<?xml version="1.0"?>
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You 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.
+-->
+
+<project name="classloader-test" default="antunit" xmlns:au="antlib:org.apache.ant.antunit">
+  <import file="../antunit-base.xml" />
+
+  <target name="setUp">
+    <mkdir dir="${input}" />
+    <macrodef name="antCore">
+      <!--
+          Execute ant similar to how the launcher script does it,
+          but make sure to only include the core ant.jar in the library list.
+          That way we can see whether loading extra modules works as expected.
+      -->
+      <attribute name="target" />
+      <sequential>
+        <java classname="org.apache.tools.ant.launch.Launcher"
+              outputproperty="test.output"
+              fork="true"
+              failonerror="false">
+          <classpath>
+            <pathelement location="${ant.library.dir}/ant-launcher.jar" />
+          </classpath>
+          <sysproperty key="ant.home" value="${ant.home}" />
+          <sysproperty key="ant.library.dir" value="${input}" />
+          <arg value="-lib" />
+          <arg value="${ant.library.dir}/ant.jar" />
+          <arg value="-cp" />
+          <arg value="" />
+          <arg value="-f" />
+          <arg value="${ant.file}" />
+          <arg value="-Dorig.library.dir=${ant.library.dir}" />
+          <arg value="@{target}" />
+        </java>
+      </sequential>
+    </macrodef>
+  </target>
+
+  <available file="${ant.library.dir}/ant-junit.jar"
+             property="test.have.junit" />
+
+  <target name="testCannotLoadTask" if="test.have.junit">
+    <!-- Make sure we DON'T have <junit> available by default -->
+    <antCore target="runCannotLoadTask" />
+    <au:assertTrue message="Expected line not found:&#10;${test.output}">
+      <contains string="${test.output}"
+                substring="JUnitTask was not found" />
+    </au:assertTrue>
+  </target>
+
+  <target name="runCannotLoadTask">
+    <junit/>
+  </target>
+
+  <target name="testTweakCoreLoader" if="test.have.junit">
+    <!-- <junit> becomes available if we tweak the core class loader -->
+    <antCore target="runTweakCoreLoader" />
+    <au:assertTrue message="Expected line not found:&#10;${test.output}">
+      <!-- This error message is generated by the <junit> task,
+           so that task itself must have been loaded successfully -->
+      <contains string="${test.output}"
+                substring="must include junit.jar" />
+    </au:assertTrue>
+  </target>
+
+  <target name="runTweakCoreLoader">
+    <echo message="${orig.library.dir}/ant-junit.jar"/>
+    <classloader classpath="${orig.library.dir}/ant-junit.jar"/>
+    <junit/>
+  </target>
+
+</project>