org.aspectj/docs/release/README-1.8.3.adoc

= AspectJ 1.8.3

_© Copyright 2014 Contributors. All rights reserved._

The full list of resolved issues in 1.8.3 is available
https://bugs.eclipse.org/bugs/buglist.cgi?query_format=advanced;bug_status=RESOLVED;bug_status=VERIFIED;bug_status=CLOSED;product=AspectJ;target_milestone=1.8.3;[here]

_Release info: 1.8.3 available 22-Oct-2014_

== Notable changes

=== Conditional aspect activation with @RequiredTypes - https://bugs.eclipse.org/bugs/show_bug.cgi?id=436653[Issue 436653]

AspectJ is sometimes used to create aspect libraries. These libraries
contain a number of aspects often covering a variety of domains. The
library might typically be available as a jar and contains a single
aop.xml file that names all the aspects. The library is then consumed by
some application. However, the application may not need to use all those
aspects but because they are listed in the aop.xml they will be
'active'. Now the pointcuts in those unused aspects may not match
anything in the application and could be considered harmless but the
pointcuts and the aspects themselves may have references to types in
other libraries that the application does not have around. This can lead
to unhelpful "can't find type" messages and currently requires the user
to add unnecessary entries to their build dependencies just to keep the
unused aspects happy.

With AspectJ 1.8.3 it is now possible to express a constraint on an
aspect. The @RequiredTypes annotation specifies one or more fully
qualified types that must be discoverable on the classpath in order for
the aspect to activate. Using this there is no need to add those
extraneous dependencies to an applications build classpath.

Example:

[source, java]
....
import org.aspectj.lang.annotation.*;

@RequiredTypes("com.foo.Bar")
public aspect Foo {
  before(): execution(@com.foo.Bar * *(..)) {}
}
....

If the above aspect is listed in an aop.xml for loadtime weaving or
passed on the aspectpath for compile time weaving, if the type
'com.foo.Bar' is not accessible on the classpath then the aspect will be
turned off and the pointcut will have no effect. There will be no
attempt made to match it and so no unhelpful "can't find type" messages.

=== cflow and the pre-initialization joinpoint changes due to Java 7 verifier modifications - https://bugs.eclipse.org/bugs/show_bug.cgi?id=443477[Issue 443477]

There has been a change in the Java7 verifier in a recent patch release
of Java7 (update 67) that causes a verify error for usage of a
particular AspectJ construct. The problem occurs if you are using cflow
and it hits the preinitialization join point. The pattern of code
generated in that case causes the verifyerror. In this release of
AspectJ we have taken the 'quick' approach to solving this, namely to
avoid advising preinitialization with the cflow construct. This problem
appears to come up when the aspect is non-optimal anyway and hitting
preinitialization was never really intended by the pointcut writer. For
example:

[source, java]
....
execution(* foo(..)) && cflow(within(Bar))
....

The use of cflow and within there will actually hit *a lot* of
joinpoints, many of which the user probably didn't mean to. It feels
like we actually need a warning to indicate the pointcut is probably
suboptimal. What the user probably meant was something more like this:

[source, java]
....
execution(* foo(..)) && cflow(execution(* Bar.*(..))
....

or

[source, java]
....
execution(* foo(..)) && cflow(within(Bar) && execution(* *(..)))
....

But even if they did want the less optimal form of cflow there still
seems little use in applying it to pre-initialization - that is your cue
to raise an AspectJ bug with a realistic use case inside that proves
this an invalid assumption :)

=== around advice and lambdas - https://bugs.eclipse.org/bugs/show_bug.cgi?id=445395[Issue 445395]

For optimal performance, where possible, AspectJ tries to inline around
advice when it applies at a joinpoint. There are few characteristics of
a joinpoint match that can prevent this but we do try to inline where we
can (the inlining can be manually turned off via -XnoInline).

Inlining of around advice basically means copying the advice
instructions into the target class. This causes a problem when the
advice uses lambdas. Lambda usage is currently implemented in java
compilers by generating invokedynamic bytecode instructions that
reference bootstrap methods created in the class and a helper method
generated in the class containing the lambda code. When the
invokedynamic is encountered at runtime, some magic happens and the
bootstrap method is used to generate a class on the fly that calls the
particular lambda method. All this 'extra stuff' breaks the basic
inlining algorithm that simply copies the advice bytecode into the
target. Effectively the inlining process needs to become much more
sophisticated and copy the bootstrap methods and the lambda helper
methods, avoiding clashes with existing bootstrap/helpers in the target.

Prior to AspectJ 1.8.3 when the inlining failed you would get a horrible
class cast exception that mentions constant pool entries (because the
bootstrap method hadn't been copied over to the target). Temporarily in
1.8.3 we are turning off inlining of around advice containing lambdas,
which will at least avoid the failure, with the longer term goal of
improving the inlining process to do all the necessary extra work.