org.aspectj/docs/dist/doc/README-1.9.19.adoc

== AspectJ 1.9.19

_© Copyright 2022 Contributors. All rights reserved._

== AspectJ 1.9.19

_© Copyright 2022 Contributors. All rights reserved._

_Release info: 1.9.19 available 21-Dec-2022_

Please note that Bugzilla for issue management is deprecated and new issues should be filed as
https://github.com/eclipse/org.aspectj/issues/new[GitHub issues]. The list of issues addressed for 1.9.19 can be found
here:

* https://github.com/eclipse/org.aspectj/issues?q=is%3Aissue+is%3Aclosed++milestone%3A1.9.19[GitHub 1.9.19]
* 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=1.9.19[Bugzilla 1.9.19]

=== New features

AspectJ 1.9.19 supports https://openjdk.java.net/projects/jdk/19/[Java 19] and its final, preview and incubator
features, such as:

* Record patterns (preview)
* Virtual threads (preview)
* Pattern matching for `switch` (preview 3)
* Structured concurrency (incubator)

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 19 preview feature support, see the list in
https://github.com/eclipse/org.aspectj/issues/184#issuecomment-1272254940[this comment]. AJC therefore inherits the same
problems for the specific cases described in the linked issues.

=== Improvements

* Improve condy (constant dynamic) support. Together with some custom compilation or weaving options, this helps to
  avoid a problem when using JaCoCo together with AspectJ, see
  https://github.com/eclipse/org.aspectj/issues/170#issuecomment-1214163297[this comment in #170] for more details.

=== Code examples

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):

* https://github.com/eclipse/org.aspectj/tree/master/tests/features198/java17[Pattern matching for switch (preview 1)]
* https://github.com/eclipse/org.aspectj/tree/master/tests/features199/java18[Pattern matching for switch (preview 2)]
* https://github.com/eclipse/org.aspectj/tree/master/tests/features1919/java19[Pattern matching for switch (preview 3),
  record patterns (preview 1)]
* 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.

=== Other changes and bug fixes

* Fix (or rather work around) an old bug occurring when compiling or weaving code using ITD to declare annotations with
  `SOURCE` retention on types, methods, constructors or fields. While declaring such annotations does not make sense to
  begin with, at least the AspectJ weaver or compiler should handle the situation gracefully, which now it does by
  simply ignoring errors caused by it. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=366085[Bugzilla #366085] and
  https://github.com/eclipse/org.aspectj/pull/196[pull request #196]. Better than this workaround would be for the
  compiler or weaver to actually print a warning when meeting source level annotations in declare statements. Hence,
  follow-up issue https://github.com/eclipse/org.aspectj/issues/201[#201] was created.
* Remove legacy AspectJ Browser code and documentation.
* Thanks to Andrey Turbanov for several clean code contributions.

=== AspectJ usage hints

==== AspectJ compiler build system requirements

Since 1.9.8, the AspectJ compiler `ajc` (contained in the `aspectjtools` 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 `aspectjrt`, but the
compiler itself needs JDK 11+. Just like in previous AspectJ versions, both the runtime `aspectjrt` and the load-time
weaver `aspectjweaver` still only require JRE 8+.

==== Use LTW on Java 16+

Please note that if you want to use load-time weaving on Java 16+, the weaving agent collides with
https://openjdk.java.net/jeps/396[JEP 396 (Strongly Encapsulate JDK Internals by Default)]. Therefore, you need to set
the JVM parameter `--add-opens java.base/java.lang=ALL-UNNAMED` 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.

==== Compile with Java preview features

For features marked as preview on a given JDK, you need to compile with `ajc --enable-preview` and run with
`java --enable-preview` on that JDK.

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.