Add and apply Checkstyle config.

[blackwinter]

Based on https://github.com/metafacture/metafacture-fix/blob/master/config/checkstyle/checkstyle.xml (metafacture/metafacture-fix#11).

We need those (annoying) checks from metafacture-fix here :-)

Originally posted by @fsteeg in #387 (comment)

This would be part 2 (see #388 for part 1).

Notes:

• Checks have been disabled for test sources; maybe they should be enabled at a later stage?
• Suppressed rules (checkstyle-disable-line) should be evaluated; maybe adjust the Checkstyle config.
• Most obvious nuisances: MagicNumber, MissingCtor, ReturnCount
• metafacture/metafacture-fix@d70d5d3 introduced suppression via annotations in addition to comments; maybe we should stick to one method.

[blackwinter]

Oh well, looks like I've touched virtually every single Java file there is: 496/499 🤯

[dr0i]

Uh, this is a lot of change ... hard to check everything. After my scanning I think it's good.

Checks have been disabled for test sources ...

Very good - so it's clear with one glimpse that the code (style) changes didn't change the outcome of the tests (there are some tests changed - but it's just adding a newline before package declaration).

... ; maybe they should be enabled at a later stage?

+1

[blackwinter]

Uh, this is a lot of change ... hard to check everything.

Yes, sorry about that! But if it's any consolation, it was also a lot to write ;)

After my scanning I think it's good.

Thanks!

there are some tests changed - but it's just adding a newline before package declaration

I only applied very few automatic changes to the test sources.

[fsteeg]

Phew, awesome, many thanks for setting this up! 🎉

Oddly, I had to run ./gradlew editorconfigFormat locally once (but resulting in no changes on git diff) to get rid of violation errors (whitespace/newline issues).

[blackwinter]

Thanks for the review!

Oddly, I had to run ./gradlew editorconfigFormat locally once (but resulting in no changes on git diff) to get rid of violation errors (whitespace/newline issues).

So you had local (unversioned) files that were checked? Would you want those to get excluded/ignored?

[fsteeg]

So you had local (unversioned) files that were checked? Would you want those to get excluded/ignored?

No, no unversioned files. Maybe related to line endings managed by git internally (core.autocrlf)? No problem though, mostly a note in case anyone has the same issue locally.