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<title>AspectJ 1.9.20 Readme</title>
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<div align="right"><small>&copy; Copyright 2023 Contributors. All rights reserved.</small></div>

<h1>AspectJ 1.9.20.1</h1>

<p>
  This is a bugfix release for 1.9.20, fixing two problems:
  <ul>
    <li>
      <a href="https://github.com/eclipse-aspectj/aspectj/issues/257">Regression bug 257</a> introduced in 1.9.20 would
      match negated type patterns like <tt>!void</tt> or <tt>!String[]</tt> incorrectly.
    </li>
    <li>
      <a href="https://github.com/spring-projects/spring-framework/issues/27761">Spring issue 27761</a> describes a
      problem where AspectJ, when used by Spring AOP, in rare cases falsely considered bridge methods for overridden
      generic methods for matching, leading to falsely negative matching results. See also
      <a href="https://github.com/eclipse-aspectj/aspectj/issues/256">AspectJ tracker issue 256</a>).
    </li>
  </ul>
</p>
<p>
  The list of issues addressed for 1.9.20.1 can be found
  <a href="https://github.com/eclipse/org.aspectj/issues?q=is%3Aissue+is%3Aclosed++milestone%3A1.9.20.1">here</a>.
</p>

<h1>AspectJ 1.9.20</h1>

<p>
  Please note that Bugzilla for issue management is deprecated and new issues should be filed as
  <a href="https://github.com/eclipse/org.aspectj/issues/new">GitHub issues</a>.
  The list of issues addressed for 1.9.20 can be found here:
  <ul>
    <li><a href="https://github.com/eclipse/org.aspectj/issues?q=is%3Aissue+is%3Aclosed++milestone%3A1.9.20">GitHub 1.9.20</a></li>
    <li><a href="https://bugs.eclipse.org/bugs/buglist.cgi?bug_status=RESOLVED&bug_status=VERIFIED&bug_status=CLOSED&f0=OP&f1=OP&f3=CP&f4=CP&j1=OR&list_id=16866879&product=AspectJ&query_format=advanced&target_milestone=1.9.20">Bugzilla 1.9.20</a></li>
  </ul>
</p>

<h2>New features</h2>

<p>
  AspectJ 1.9.20 supports <a href="https://openjdk.java.net/projects/jdk/20/">Java 20</a> and its final, preview and
  incubator features, such as:
</p>
<ul>
  <li>Record patterns (preview)</li>
  <li>Virtual threads (preview)</li>
  <li>Pattern matching for <tt>switch</tt> (preview 3)</li>
  <li>Structured concurrency (incubator)</li>
</ul>

<p>
  Please note that the upstream Eclipse Java Compiler (ECJ) which the AspectJ Compiler (AJC) is a fork of still has some
  open issues concerning Java 20 preview feature support, see the list in
  <a href="https://github.com/eclipse/org.aspectj/issues/184#issuecomment-1272254940">this comment</a>. AJC therefore
  inherits the same problems for the specific cases described in the linked issues.
</p>

<h2>Improvements</h2>

<ul>
  <li>
    Since Java 9 and the introduction of the Java Module System, the upstream Eclipse Java Compiler (ECJ) and Eclipse
    Java Development Tools (JDT) had gone through some internal changes, enabling both the compiler and the IDE to
    handle new Java language features. In AspectJ, some of those internal changes have not been properly upgraded for
    quite a while, but this is now fixed. However, it might <b>require you to recompile your aspects and
    projects/classes using them.</b> Otherwise, you might get problems in Eclipse IDE or under certain circumstances
    even when running newly compiled aspects in older AspectJ versions and vice versa. You are on the safe side if you
    simply rebuild your projects. We are sorry for the inconvenience, but we have to follow upstream ECJ and JDT
    changes.
  </li>
  <li>
    Along with fixing <a href="https://github.com/eclipse-aspectj/aspectj/issues/24">GitHub bug 24</a>, the syntax for
    array type matching has been improved considerably. You can find some examples
    <a href="https://github.com/eclipse-aspectj/aspectj/tree/master/tests/bugs1920/github_24">here</a>.
  </li>
</ul>

<h2>Code examples</h2>

<p>
  You can find some sample code in the AspectJ test suite under the respective AspectJ version in which the features
  were first supported (possibly as JVM preview features):
</p>
<ul>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features198/java17">
      Pattern matching for switch (preview 1)
    </a>
  </li>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features199/java18">
      Pattern matching for switch (preview 2)
    </a>
  </li>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features1919/java19">
      Pattern matching for switch (preview 3), record patterns (preview 1)
    </a>
  </li>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features1920/java20">
      Pattern matching for switch (preview 4), record patterns (preview 2)
    </a>
  </li>
  <li>
    Please note that presently there is no specific sample code for virtual threads and structured concurrency in the
    AspectJ code base, because these are just new APIs, no Java language features. You can find sample code for these
    concurrency features elsewhere, e.g. in the corresponding JEPs. In AspectJ, they should just work transparently
    like any other Java API.
  </li>
</ul>

<h2>Other changes and bug fixes</h2>

<ul>
  <li>
    About a dozen bugs have been fixed, some of them quite old. See "list of issues addressed" further above and follow
    the link to GitHub to find out if your issue is among them.
  </li>
</ul>

<h2>AspectJ usage hints</h2>

<h3>AspectJ compiler build system requirements</h3>

<p>
  Since 1.9.7, the AspectJ compiler <tt>ajc</tt> (contained in the <tt>aspectjtools</tt> library) no longer works on
  JDKs 8 to 10. The minimum compile-time requirement is now JDK 11 due to upstream changes in the Eclipse Java Compiler
  (subset of JDT Core), which AspectJ is a fork of. You can still compile to legacy target versions as low as Java 1.3
  when compiling plain Java code or using plain Java ITD constructs which do not require the AspectJ runtime
  <tt>aspectjrt</tt>, but the compiler itself needs JDK 11+. Just like in previous AspectJ versions, both the runtime
  <tt>aspectjrt</tt> and the load-time weaver <tt>aspectjweaver</tt> still only require JRE 8+.
</p>

<h3>Use LTW on Java 16+</h3>

<p>
  Please note that if you want to use load-time weaving on Java 16+, the weaving agent collides with
  <a href="https://openjdk.java.net/jeps/396">JEP 396 (Strongly Encapsulate JDK Internals by Default)</a> and related
  subsequent JEPs. Therefore, you need to set the JVM parameter <tt>--add-opens java.base/java.lang=ALL-UNNAMED</tt> in
  order to enable aspect weaving. This is due to the fact that the weaver uses internal APIs for which we have not found
  an adequate replacement yet when defining classes in different classloaders.
</p>

<h3>Compile with Java preview features</h3>

<p>
  For features marked as preview on a given JDK, you need to compile with <tt>ajc --enable-preview</tt> and run with
  <tt>java --enable-preview</tt> on that JDK.
</p>
<p>
  Please note that you cannot run code compiled with preview features on any other JDK than the one used for
  compilation. For example, records compiled with preview on JDK 15 cannot be used on JDK 16 without recompilation. This
  is a JVM limitation unrelated to AspectJ. Also, e.g. sealed classes are preview-1 on JDK 15 and preview-2 on JDK 16.
  You still need to recompile, no matter what.
</p>

<hr>

<p>
  <b>Available:</b> 1.9.20 on 16-Aug-2023
</p>

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