[WIP] Add ANTLR4 support

[matthiasbalke]

This PR adds support for formatting ANTLR4 grammars using Antlr4Formatter and Gradle.

Checklist:

• add formatter step to lib
• add gradle extension including unit tests
• add maven extension
• add FormatterStep to readme matrix
• add example how to configure gradle-plugin readme
• add gradle-plugin Changelog entry
• add example how to configure maven-plugin
• add maven-plugin Changelog entry
• externalized defaults for gradle and maven into lib
• test antlr4 + license headers with antlr grammars, lexers and parsers
• test antlr4 + generic formatter steps
• review by spotless team

[matthiasbalke]

Just found something which seems to be a huge bug (antlr/Antlr4Formatter#25) in Antlr4Formatter. The bug seems to be removing parts of the grammar while formatting.

So please review the spotless integration but
do not merge the PR yet!

[nedtwigg]

Looks great! Exemplary "add a language" PR. PaddedCell can be used to remedy idempotence problems, but it doesn't fix removing meaningful content :)

[matthiasbalke]

Looks great! Exemplary "add a language" PR.

Thanks! 😊

[JLLeitschuh]

This is awesome. I love how pluggable Spotless is. Does this have automatic maven support for it or does more work need to be done to add that in the future?

Another quick comment:
Looking at the antlr4formatter Github Project: https://github.com/antlr/Antlr4Formatter/graphs/contributors

It seems like it has very little activity and very little interactivity from the community. I just want to make sure that we aren't adding a framework to spotless that is at risk of not being maintained going forward (bit rot). Just something to consider @nedtwigg. It's not immediately a disqualifier for me, but I just want to let everyone think about it.

[matthiasbalke]

This pr brings maven and gradle support. I know this project didn't have a lot of support. That's why I started to support it in December. Also I don't know about any other antlr4 formatter project. If you know one I be happy to take a look. Also the project is done by some of the official antlr4 guys, that is why I put my efforts there.

[nedtwigg]

adding a framework to spotless that is at risk of not being maintained going forward

Everything is at risk of not being maintained :) I'm very much in favor of merging in support for marginal and esoteric formatters, so long as they don't require changes to our core, which this does not.

[nedtwigg]

Looks like we're almost there! Let me know if you need anything from me.

[nedtwigg]

I expect to publish a new release sometime this week. Do you think you'll get a chance to polish this up in that timeframe? If so I'm happy to wait to include this, else I'm just as happy to publish this whenever you get around to it :)

[nedtwigg]

I'll lend a hand here.

[nedtwigg]

If you force-push your branch to this location:
https://github.com/diffplug/spotless/tree/antlr4

then it will keep all the commits and discussion except for the recent rebase attempt. Thanks for your tenacity, I think it will be the oldest PR to actually get merged that I have ever worked with!

[matthiasbalke]

I don't quite understand, how force-pushing my work to the new branch, should remove the rebase attempt? Actually I merged the upstream/master into my local branch, so the branch name rebase is missleading ;) But if you want, I will polish the history later, when the build is back to green. Does that sound good?

The biggest problem I have right now, is that I'm having issues building spotless locally (Windows 10 and Ubuntu 20.04 using OpenJDK8). Do you have any idea, what I might do wrong?

$ ./gradlew test  

FAILURE: Build failed with an exception.

* Where:
Build file '/home/balke/repositories/spotless/ide/build.gradle' line: 11

* What went wrong:
A problem occurred evaluating project ':ide'.
> A problem occurred configuring project ':lib'.
   > java.lang.NullPointerException (no error message)

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 1s

And yeah I took me some time to get back to this, but I would love to get this merged too! Thanks for beeing so supportive.

[nedtwigg]

Our primary branch is now main, not master. And because of that confusion, your PR was changing 237 files due to copyright header, which is not correct. I just did something very rude, and force-pushed over yours, but hopefully now you can see what I meant. I backed up your branch before force-pushing at matthias-backup, so if you really want to go back to that, you can. But I can't merge something that changed 100s of files, too hard to review.

[nedtwigg]

I think now all of the test failures are about the expected input/output of the step, not related to infrastructure. I'll let you take it from here.

[nedtwigg]

Now that this PR is nice and fixed-up, it's going to get merge-conflict clobbered again pretty soon, in ~week. I'm happy to work with you in realtime on https://gitter.im/diffplug/spotless if you have any hiccups. I think it's extremely close.

[matthiasbalke]

@nedtwigg I just double checked the format with the ANLR4 grammar itself and the format is as expected now!

Thanks again for all the support!

This PR is finally ready to be merged.

[nedtwigg]

Congrats on reaching a productive checkpoint on your long journey :D. I plan on releasing this (along with a bunch of other stuff) in a day or two.