Use the 'io.freefair.aspectj' gradle plugin

[larsgrefer]

After I've migrated (or removed) the other gradle plugins in #7077 #7173 and #7174 the AspectJ plugin was the last remaining one. Instead of migrating the current groovy based plugin to java, I just used the AspectJ gradle plugin I've already written last year.

[rwinch]

Thanks for the PR @larsgrefer! We'd love to rely on proper AspectJ Gradle plugin. However, it appears this PR broke the build. Can you take a look at that?

[larsgrefer]

@rwinch The build is fixed now.

[rwinch]

Is there a reason that we need to move the source code into a different source folder? I'd prefer to keep the code in the src/main/java folder.

[larsgrefer]

The io.freefair.aspectj plugin uses src/main/aspectj as source root for the code to be compiled by ajc by default. (The same way like src/main/groovy would contain code for groovyc and src/main/kotlin would contain the code compiled by kotlinc).

If you like, this can be changed in the build script:

sourceSets.main.aspectj.srcDir "src/main/java"

Another option would be the io.freefair.aspectj.post-compile-weaving plugin.
This plugin leaves the actual compilation to javac (or groovyc, kotlinc, ...) and only performs the weaving as bytecode-to-bytecode transformation (by passing the compiler output into ajc's --inpath)

[rwinch]

I think I'd like to use sourceSets.main.aspectj.srcDir "src/main/java". My reasoning is that while it makes sense from a Gradle plugin perspective that aspectj code is place in it's own source folder it feels a bit invasive.

Spring allows switching between proxy and compile time aspects with just configuration. It is a bit disruptive to switch the folder that the annotated Java code is in.

[larsgrefer]

I think I'd like to use sourceSets.main.aspectj.srcDir "src/main/java". My reasoning is that while it makes sense from a Gradle plugin perspective that aspectj code is place in it's own source folder it feels a bit invasive.

For the aspects project this is actually the only option because its aspect is an *.aj file, which has to be compiled by ajc.

For samples/javaconfig/aspectj and samples/xml/aspectj I've chosen the post-compile-weaving approach because it's even less invasive and provides better integration:

• The post-compile-weaving plugin can also weave groovy, scala and kotlin classes
• Since the acutal compilation is perfomed by javac, additional tooling like lombok could be used without problems.

[rwinch]

Thanks for the PR @larsgrefer! This is now merged into master