@Option to enable export feature for PitestTask

[Vampire]

Since Gradle 4.6 you can add custom command-line flags for tasks using the @Option annotation.
It would be nice if the PitestTask had such an option that enables the EXPORT feature, so that you can decide on each run easily whether you want the mutants to be dumped on disk or not without having to edit the build script or implementing the logic using a project property in each build individually.

[szpak]

For reference: https://docs.gradle.org/4.6/userguide/custom_tasks.html#sec:declaring_and_using_command_line_options

[szpak]

I tried to implement it in a natural way - with an ability to override features property, but I ran into Gradle limitations. Mostly gradle/gradle#10517, but also gradle/gradle#4311 and gradle/gradle#10518.

I don't know if I would like to implement any "hack" to just allow to enable EXPORT. In hindsight, I should rethink introduction of Property API (#105) as due to limitations the old mechanism had to stay for part of the values (no real gain for the others), it blocks some features and it took too much time to implement...

Btw, unfortunately, the other plugin for configuration overriding also doesn't support collections: nebula-plugins/gradle-override-plugin#3

[Vampire]

Just in case you don't know, Spock has a @PendingFeature annotation, that you can use instead of @Ignore.
That will report the test as skipped as long as the tests fail and once all iterations of the feature are successful, the feature is deemed implemented and the test begins to fail, so that the @PendingFeature annotation can be removed.

I don't know if I would like to implement any "hack" to just allow to enable EXPORT.

Actually I wouldn't consider this a hack, but exactly what I wanted.
I don't want an option that overrides all features.
I have in my build script disabled -FLOGCALL for now, but I could have other features configured.
I really would like to be able to just add to that the +EXPORT feature instead of replacing the list of features.

[szpak]

Yes, I know @PendingFeature and I intended to use it :).

I implemented --additionalFeatures=+EXPORT. Please take a look at the new commit and provide feedback based on the latest uploaded 1.4.6-SNAPSHOT.

[Vampire]

I didn't test it yet, but from what I see in the commit, it looks nice, thanks :-)