Upon special request by Andy Clement, I included 'lib' as a child module
in the parent POM again, making several modules which refer to
downloaded library files dependent the 'lib' module. I am not sure I
caught all of them, but I hope so.

Now after cloning the project and configuring the token for reading from
GitHub Packages (sorry!), you can just run a Maven build for the main
project and no longer need to fail the first build, read the Maven
Enforcer message and run 'cd lib && mvn compile' as a first step. This
convenience comes at the price of a more complex POM and two new
profiles:

  - Profile 'provision-libs' is auto-activated by the absence of a
    marker file, kicking off the library provisioning process and
    creating same marker file at the end, if successful. Therefore,
    during subsequent builds libraries will not be re-provisioned,
    because the marker file exists and Maven skips all download and
    (un)zip steps, which saves build time and bandwidth. Otherwise
    offline builds would not work either.

  - Profile 'clean-libs' needs to be activated manually, because by
    default 'mvn clean' will not erase provisioned libraries. In most
    cases, even after a clean a developer does not want to re-provision
    all libraries if they have not changed (e.g. new JDT Core build).
    But if you do wish too erase the libraries and the marker file, just
    call 'cd lib && mvn -P clean-libs clean'.

Please note: The Maven Enforcer build step, which additionally checks
for existence of other files, still exists and was moved from the parent
POM to 'libs'. No matter if provisioning was just done or skipped
because the main marker file exists, a quick heuristic check for that
list of files is done during each build, failing the build with a
comprehensive message if an inconsistency was found. The error message
says which files are missing and tells the user:

  "There is an inconsistency in module subdirectory 'lib'. Please run
  'mvn --projects lib -P clean-libs clean compile'. This should take
  care of cleaning and freshly downloading all necessary libraries to
  that directory, where some tests expect them to be."

This should cover the topic.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Some runtime dependencies are reported as unused in Maven Dependency
Plugin goal 'dependency:analyze', but actually they are needed. I
noticed by chance when running RunTheseBeforeYouCommitTests in IntelliJ
IDEA for the first time after a while and dependency modules could not
find classes.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

If 'name' is identical to 'artifactId' and 'packaging' has the default
value 'jar', we can just remove those tags from the POM.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

In module 'tests', our tests need Ant launcher. Hence, dependency
ant:ant-launcher was re-added to the POM (with test scope this time)
and Maven Dependency plugin configured to regard it as a used
dependency and not falsely report it as unused.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Notably, this change involves a partial revert of @4a5660b3, because we
are not using JUnit Jupiter yet but still JUnit 4 tests. See discussion
under commit at https://github.com/eclipse/org.aspectj/commit/4a5660b3.

Many other warnings - concerning both used undeclared and unused
declared dependencies - were eliminated by adding or removing the
corresponding dependencies from the POMs. Furthermore, I tried to make
sure that some clearly test-scoped dependencies are now actually
declared as such, so as to avoid unwanted transitivity bleeding into
compile scope and maybe unwanted classes ending up in uber JARs via
Maven Shade or Maven Assembly.

TODO: I am not so sure why modules other than 'run-all-unit-tests' would
depend on test JARs. I hope I broke nothing essential there. As of
today, the other modules where I found '<type>test-jar</type>'
dependencies are:
  - ajde
  - testing
  - testing-drivers
  - tests
  - weaver

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Now there is no system-scoped dependency left anymore in the Maven
build, i.e. the corresponding warnings are gone and we can focus on the
actual build log.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

This means that instead of a system-scoped dependency we now have a
regular one.

The 'libx' module also downloads binary and source JARs redundantly into
the libraries directory in order to be found there by other scripts and
tests.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Get rid of system paths. Instead, rely on JDT Core Shadows to deploy
both binary and source JARs to GitHub Packages. The former module
directory was deleted completely. Instead, the JARs are redundantly
copied into 'libs/jdtcore-aj' in order to be found there by tests and
other Ant scripts.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

There are only two direct dependencies used in AspectJ code:
  - Commons Digester (module 'testing')
  - Commons Logging (module 'org.aspectj.matcher')

I declared those two and experimentally removed all the other
system-scoped dependencies, as it should be. Let's see if the build
works with transitive dependencies.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Due to JEP 260 (Encapsulate Most Internal APIs), aspect weaving on
Java 16 now requires '--add-opens java.base/java.lang=ALL-UNNAMED' on
the command line. Otherwise there will be illegal access exceptions for
some internal API calls AspectJ needs, most prominently when trying to
define classes in other packages or modules.

This had to be done on several levels:

  - Maven Surefire: running tests in a JVM directly forked by Surefire.
    In order to make this backwards compatible, I added two profiles
    with JDK-level-dependent auto-activation, one 8-15 and one 16+. In
    the latter a property containing the JVM parameter is defined, in
    the former it is empty, i.e. the JVM is started without the
    parameter. In Java 8 the parameter did not even exist, in Java 9+ we
    could use it, but we need to test how users use AspectJ.

  - RunSpec: Whenever an XML test is declared to use '<run>', we need to
    determine the current JVM version and again dynamically add the
    parameter when forking the target JVM.

  - AntSpec: Whenever an XML test is declared to use '<ant>', we need to
    determine the current JVM version dynamically add two properties
    usable from within Ant scripts: 'aj.addOpensKey' and
    'aj.addOpensValue'. Unfortunately, Ant needs to use two '<argLine>'
    parameters, because the two parts of the option are separated by a
    space character.

  - Ant scripts: When triggered by an AntSpec, each Ant target using LTW
    needs to manually set
      <jvmarg value="${aj.addOpensKey}"/>
      <jvmarg value="${aj.addOpensValue}"/>
    for each '<java>' task. It was quite tedious to find all(?) of them.

TODO: In the AspectJ 1.9.7 release notes we need to document that this
parameter is now needed for LTW.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Keep only ASM 2.0 binary because it is still used in UnweavableTest
which uses an old ASM API, e.g. with a ClassWriter constructor which no
longer exists.

Also add JarJar 1.3 library because it is needed by an Ant task in
lib/asm/build.xml.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

Signed-off-by: Lars Grefer <eclipse@larsgrefer.de>