ant/docs/ant2/features.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!--
   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.
-->
<html>
  <head>
    <meta http-equiv="Content-Language" content="en-us">
    <title>Ant2 feature list</title>

      <style type="text/css">
        .comment {
          COLOR: #900000;
	  BACKGROUND: #ffa;
        }
      </style>

  </head>

  <body bgcolor="#FFFFFF">

    <p class="comment">If something looks like this, this is either a
    request for input or a &quot;REVISIT&quot; marker or similar.</p>

    <h1>Ant2 Goals</h1>

    <p>Even though Ant2 is expected to be incompatible with the
    current Ant1 series, it still has the same goals. Ant is a Java
    based build tool and this remains the main focus of it. The
    original goals of simplicity, understandability and extensibility
    still stand and Ant2 will try to achieve them even better than
    Ant1 does.</p>

    <h2>Simplicity and Understandability</h2>

    <p>These two goals are closely related. Ant build files shall be
    easy to read and understand - at the same time it should be easy
    to write a custom Ant task and to use the utility classes that
    Ant2 provides.</p>

    <p>Ant2 shall be more consistent than Ant1 is - this means:</p>

    <ul>

      <li>core tasks will use the same attribute names for common
      functionality</li>

      <li>similar tasks will be unified to use similar forms.</li>

      <li>different implementations for the same functionality will be
      hidden behind facade tasks.</li>

      <li>properties and data types will be unified so that they share
      the same namespace and inheritance rules. <i
      class="comment">Need to talk about how ${} expansion works for
      filesets and so on.</i></li>

    </ul>

    <p>Furthermore some things will have to become more explicit:</p>

    <ul>

      <li>remove all magic properties</li>

      <li>make build file writers explicitly state which
      filters/filtersets a copy task will use</li>

      <li>add scoping rules for properties so that not all of them
      will be inherited by sub-builds, only those that have been
      specified explicitly. <i class="comment">Fill in details once
      they've been sorted out.</i></li>

    </ul>

    <p>The front-ends for Ant2 shall be smart enough to automatically
    detect the required libraries (like <code>tools.jar</code>), the
    use of native scripts shall be kept to a minimum.</p>

    <p>Build file writers can attach a message to targets that will be
    presented to the user if that target is going to be skipped (based
    on the if/unless attribute of the target).</p>

    <p>Even though Ant installation already is quite simple in Ant1
    (extract the archive and set two environment variables),
    alternative ways to install Ant like using 
    <a href="http://java.sun.com/products/javawebstart/">Webstart</a> or
    a "self-extracting" JAR file will be explored.</p>

    <h2>Extensibility</h2>

    <p>Ant2 like Ant1 uses build files written in XML as its main
    input, but it will not be restricted to it. The core of Ant2 will
    work on an object model of Project/Target/Task that is independent
    of any external representation.</p> 

    <p>As an extension of the current <code>&lt;taskdef&gt;</code>
    concept, tasks can be bundled into task libraries (together with
    data types and other utility classes). These task libraries are
    special JAR archives that somehow describe the contained tasks to
    Ant. Ant will automatically know all tasks contained in task
    libraries that have been placed into a special directory - in
    addition task libraries can be referenced and used in a build file
    explicitly. <i class="comment">Fill in details once they've been
    sorted out.</i></p>

    <p>It has become apparent, that several &quot;aspects&quot; of
    tasks are so common that task writers find themselves duplicating
    code all over again - things like classpath handling or &quot;do
    we stop the build if this task fails?&quot; functionality for
    example. Ant2 will provide a way to let the user attach an
    &quot;aspect handler&quot; to a project - all attributes that live
    in a certain namespace are going to be passed to this handler. <i
    class="comment">Need to talk about TaskContext here.</i></p>

    <p>Ant2 will farm out common functionality from tasks into utility
    classes so that task writers can benefit from a tested and stable
    framework - they shouldn't need to deal with existing tasks
    directly (like some tasks &quot;abuse&quot; the
    <code>&lt;touch&gt;</code> task in Ant1).</p>

    <p>Ant2 will provide a way to define tasks that itself can have
    tasks as child elements without knowing all defined tasks at
    compile time.  Discussions on ant-dev usually talk about
    &quot;container tasks&quot; in this context.</p>

    <p>The only way to &quot;include&quot; common XML snippets so far
    has been the usage of external SYSTEM entities, a mechanism that
    is tied to DTDs and doesn't mix well with alternative
    approaches like XML Schema.  Ant2 will provide a built-in include
    mechanism.</p>

    <h1>New/Modified Features</h1>

    <p>Ant2 will run the build process fully dynamically, which means
    that task won't be instantiated before they are actually being run
    and <code>${}</code> expansion will see the very latest value of a
    property. It will be possible to reassign values of properties via
    a built-in task.</p>

    <h2>Compatibility with Ant1</h2>

    <p>Ant2 is going to break Ant1 in several ways:</p>

    <ul>

      <li>Tasks written for Ant1 won't work in Ant2 as the API of
      Ant's core and the names of utility classes are going to
      change. There will probably be adaptors and utility classes to
      ease the transition for task writers.</li>

      <li>Build files written for Ant1 will probably not be valid in
      Ant2 or at least not yield the same results. It is expected that
      Ant2 will come with a tool to translate Ant1 build files into
      equivalent Ant2 versions</li>

      <li>magic properties like <code>build.compiler</code> may
      disappear and be replaced by a different customization
      concept.</li>

      <li>Ant2 is going to require a JDK version 1.2 or above and a
      JAXP compliant parser version 1.1 or above.</li>

      <li>If you specify more than one target in another target's
      depends attribute, Ant1 will execute these targets from left to
      right (as long as the dependency tree permits it) - Ant2 will
      not guarantee this behavior but will allow build file writers to
      specify the order explicitly.</li>

      <li>Dereferencing a non existent property a via ${a} will result
      in a build failure.</li>

    </ul>

    <h2>Support Integration of Ant Into Other Tools</h2>

    <p>Ant2 will have a clear separation between the front-end that is
    responsible for user interactions, the object model that
    represents the project to build and the part of Ant that runs the
    build process itself <i class="comment">Name that TaskEngine,
    ProjectEngine, ExecutionEngine or what?</i>. This separation is
    expected to ease the integration of Ant (or parts of it) into
    other products.</p>

    <p>Ant2 itself will include a command line front-end and Antidote
    will become the GUI front-end to it. Other front-ends like a
    servlet front-end are expected <i class="comment">outside of
    Ant's core</i> as well.</p>

    <p>In addition to this separation, the following features should
    help people who want to integrate Ant into their products:</p>

    <ul>

      <li>It will be possible to cancel a running build process.</li>

      <li>Ant will detach from <code>System.err/.out/.in</code>
      completely and communicate with the front-end via a well defined
      API.  The front-end will have to handle user input for tasks
      that need it (tasks that ask for a password for example).</li>

      <li>Tasks will provide some way to identify their attributes
      from the outside. <i class="default">fill in details</i></li>

    </ul>

    <h2>More Control for Users and Build File Writers</h2>

    <p>Ant2 will use a <code>BuildListener</code> concept similar to
    the one of Ant1 but may provide a richer set of events. It will be
    possible to attach and detach listeners to a build process from
    within the build file and to modify the behavior of attached
    listeners.</p>

    <p>In Ant1 users have little control over how things work.  There
    are a couple of magic properties to make Ant chose a preferred
    compiler or modify the CLASSPATH, but they are barely documented.
    If users want to set these properties for every build process,
    they have to learn the undocumented tricks of the
    <code>ANT_OPTS</code> environment variable or the
    <code>~/.antrc</code> file.</p>

    <p>Ant2 will have a well defined system to specify user
    preferences.  This system will not only let user chose their
    compiler but also give them a chance to provide default values for
    attributes (say you always want the <code>debug</code> attribute
    of the <code>javac</code> task to be true - unless it has been
    disabled explicitly). <i class="comment">Need to give details once
    they've been sorted out.</i></p>

    <h2>Documentation System</h2>

    <p>All tasks will be documented in XML files using a common DTD <i
    class="comment">Still need to define it</i> - task libraries are
    expected to include the documentation using this DTD inside the
    library itself.</p>

    <h2>Better Subbuild Handling</h2>

    <p class="comment">Is there something beyond &quot;should become
    better&quot; right now?</p>

    <h2>Data Types</h2>

    <p>Ant1 supports a limited set of data types (fileset, patternset
    and path) and at least up to Ant 1.3 it is not possible to
    register custom data types without writing a task that does this.
    Ant2 will provide a built-in mechanism to define new data
    types.</p>

    <p>Existing data-types will be improved, the files in a fileset
    can be chosen based on more than just pattern matching for example
    (modification time or permissions for example).  Ant2 will have
    built-in tasks for set operations.</p>

    <p>Data types and properties will share the same name space and
    follow the same scoping and precedence rules. 
    <i class="comment">${} again.</i></p>

    <h2>Multi-Threading of Tasks Within a Target</h2>

    <p>It will be possible to run several tasks in parallel - these
    tasks will belong to the same target and all tasks will be joined
    at the end of the target.</p>

    <h2>Internationalization</h2>

    <p>Ant2 itself will provide internationalized (error) messages and
    provide utility classes to help task writers to do the same.  
    <i class="comment">These utility classes may very well come from a
    different (Jakarta) project</i>.</p>

    <p>Ant's primary language and the language of the build file
    will continue to be English.</p>

    <h1>Rejected Features</h1>

    <p>This is list is not complete, it just highlights some of the
    rejected features and tries to explain why they've been
    rejected.  Two very common reasons to reject something were, that
    the request has been too vague or the same functionality could
    already be provided by some other accepted new feature.</p>

    <p>For a complete listing of all requested features, see <a
    href="requested-features.html">requested-features.html</a>. The
    discussion on all topics can be followed in the <a
    href="http://marc.theaimsgroup.com/?l=ant-dev&r=1&w=2">archives
    for ant-dev</a> in threads starting from 2001-03-21 - the subject
    lines contained either <code>[VOTE]</code> or
    <code>[DISC]</code>.</p>

    <h2>Simple Flow-Control</h2>

    <p>People asking for these kind of things have often heard the
    standard "Ant shall not become yet another scripting language, Ant
    shall not fall into the same traps make/Perl did ..." response
    from the committers and some long-term ant-dev people.</p>

    <p>The long version of that answer is:</p>

    <ul>
      <li>There are lots of open source scripting languages, there is
      no need to define a new one.</li>

      <li>Ant has been created to be a build tool.  While you can use
      it for a whole lot of other things, this is not Ant's primary
      focus (and it shouldn't be).  Most use-cases that ask for
      flow-control are out of Ant's scope.</li>

      <li>Ant already provides the requested functionality for many
      common situations.  The execon and apply tasks can be used to
      iterate over a set of files as the (planed for Ant2) javaon and
      anton tasks will do.</li>

      <li>Providing flow-control inside Ant's core would increase the
      complexity of this core.  This would make it difficult for new
      contributors to understand how Ant works and increase the
      maintenance cost for Ant at the same time.  The goal of the Ant
      developers is to push as much complexity and functionality out
      of Ant's core into the tasks as possible.</li>
    </ul>

    <p>That being said, Ant2 will make it easy to write iteration or
    conditional tasks via the new container task concept.  We expect
    foreach, switch and if tasks to be written, but they will probably
    not become core parts of the Ant distribution.</p>

    <h2>Advanced Conditionals for if/unless Attributes</h2>

    <p>The argument here is the same as for flow-control.  We are
    talking about complexity that can be pushed from the core to tasks
    - and that is what will be done.  Instead of additional power for
    the if/unless attributes, Ant2 will have a new task that can set
    properties based on the values of other properties or logical
    combinations of other conditions, something like (making up
    syntax):</p>

<pre>
&lt;condition name=&quot;javamail-complete&quot;&gt;
  &lt;and&gt;
    &lt;available class=&quot;javax.mail.Transport&quot;/&gt;
    &lt;available class=&quot;javax.activation.DataHandler&quot;/&gt;
  &lt;/and&gt;
&lt;/condition&gt;
</pre>

    <p>will become possible</p>

    <h2>Multi-Threaded Execution of Targets</h2>

    <p>The general feeling was, that the combination of target
    dependencies and multi-threading would soon become too complex,
    especially since Ant2 will allow people to explicitly enforce the
    order in which (independent) targets will be executed.</p>

    <p>This issue will be explored again later, it has not been
    rejected for all time being, but it is out of scope for
    Ant&nbsp;2.0</p>

    <h1>Ideas for New Tasks and Tools</h1>

    <p>Please refer to <a
    href="requested-features.html">requested-features.html</a> in the
    section &quot;I. Things that don't affect the core but are
    requests for new tasks or enhancements to existing tasks.&quot;
    for this.</p>

  </body>
</html>