Decent Antlr4 tool/gen support - Gradle

[Steve Ebersole]

Gradle ships with a plugin for Antlr support.  They made the decision to try to support all versions (2, 3 and 4) of Antlr in a single plugin however, which leads to a few problems.  Additionally, Antlr's Tool itself causes numerous problems trying to integrate it into build tool (I've helped write both the Maven and Gradle support for Antlr).

I have asked the Gradle team about splitting up their single plugin into multiple version-specific ones, but they are not interested.  They say (and I can't blame them) that the best solution is for the Gradle team to maintain such a version-specific plugin.  There are a number of attempts to write a Antlr4-specific Gradle plugin, but they all suffer from various short-comings.

As I transition Hibernate to use Antlr 4 this lack of decent build support causes us trouble.  I need to solve these problems so I can actually get our build working.  I already have a working solution which required writing a custom plugin.  My solution, however, misses some Antlr features that I will need shortly (token vocabs and import grammars) that I did not need initially.

So I need to make a decision regarding how generally applicable I make this solution, versus just hard-coding the specifics for our build (which is what I have today).  Really this comes down to whether this is something the Antlr team would be interested in accepting and maintaining.  If not, I'll just hack away for specifically what I need.  But if you are willing to accept it and take on maintaining it, I have a few questions to really be able to move forward - around these Antlr Tool shortcomings, mainly relating to parsing the grammar files such as building a GrammarAST tree, getting access to certain info and getting the Tool to operate on the GrammarAST trees I just built.