Ensure that the -parameters compiler flag is included in boot applications built with Gradle

[kashike]

#9831

[philwebb]

Thanks for the pull-request! I'm wondering if always applying the -parameters flag is the right call. The problem that I can foresee is that someone specifically doesn't want -parameters and they now have no way to achieve that.

The configureUtf8Encoding method was quite nice because if the user did set an encode it would back off. I don't see an easy way to do this with -parameters.

@wilkinsona any suggestions?

[wilkinsona]

There are a couple of things we could do:

1. Set it up front (rather than deferring it to afterEvaluate) and allow the user to override it by setting the args back to an empty list.
2. Set it in afterEvaluate but only if the compiler args are empty

[kashike]

Let me know if the changes I've made are what you're looking for.

[wilkinsona]

@kashike Thanks for the update. Sorry, looks like I've created some confusion. My two suggestions were intended as two different options. We need to decide which one we prefer and just implement that one.

I think I'm leaning towards 1 as it's quite flexible:

1. You get -parameters by default
2. It's easy to add additional args
3. You can override it by setting an empty list or a list that doesn't include -parameters

After more thought, the second suggestion may not work. If we set -parameters when the list is empty I'm not sure how you'd indicate that you don't want it. Perhaps with null but I'm not sure I like that or if it would even be permitted.

In summary, the first option is the best I can come up with. It'd be great to have some tests that cover the three scenarios I've listed above showing that default, additional args, and overridden args all work.

We should also update the docs to mention that -parameters is set as one of the reactions to the Java plugin being applied. That's something we can take care of as part of the merge, though, so please don't feel obliged to do it.

[kashike]

No problem, @wilkinsona. I've made some changes, which I think are what you've suggested - let me know.

[wilkinsona]

@kashike Thank you for making your first contribution to Spring Boot. I've merged this into master.