[core] Antlr visitor rules

[lsoncini]

This pull request depends on #1698.

Before submitting a PR, please check that:

• The PR is submitted against master. The PMD team will merge back to support branches as needed.
• ./mvnw clean verify passes. This will build and test PMD, execute PMD and checkstyle rules. Check this for more info

PR Description:

This pull request adds the necessary classes to implement antlr-based abstract rules and generic implementations of both RuleChainVisitor (AntlrRuleChainVisitor) and RuleViolationFactory (AntlrRuleViolationFactory).

We also added AbstractSwiftRule to serve as an example to show how to implement AbstractAntlrVisitor for a specific language and modified the ant-file antlr4.xml to make antlr's autogenerated BaseVisitors extend AbstractAntlrVisitor.

Team Raptor.

[pmd-test]

	1 Message
📖	No java rules are changed!

Generated by 🚫 Danger

[oowekyala]

This is an interesting change, it introduces some nice ideas that I think we can take further to reduce the complexity of language implementations (outside of this PR)

[oowekyala]

@matifraga I think, the comments I made can be handled at a later stage, as they indeed are not limited to Antlr rules. I'll open a couple of tickets to track them. This PR seems otherwise perfectly fine to me and I think it can be merged.

[adangel]

@lsoncini @matifraga @tomidelucca
I've merged now your PRs to PMD 7. I don't know, if anything works, since I didn't see a unit test 😃

I added the ANTLR support on the wiki here: https://github.com/pmd/pmd/wiki/PMD-7.0.0#language-specific-improvements to track the progress a bit and see, what's still ahead.

Here are the points I see next:

• Create a sample rule for swift
• XPath support for Antlr based grammars
• Unit tests for Antlr support
• Documentation

[matifraga]

Thanks @adangel ! Sorry about unit testing, we will unit test the classes we introduced already. We do have a working rule for Swift already, we will send a PR soon.

Regarding XPath our first attempt making a rule didn't work out, we are currently digging the code to find out why. We will also document with examples all that is needed to add a new rule using antlr as we did with the CPD feature.

cc/ @lsoncini @tomidelucca @jsotuyod

[adangel]

Don't worry. I just wanted to make sure, you guys have this on your radar...