How to build an ANTLR grammar with Gradle in a multi-platform project?

Question

So I have been struggling all afternoon with getting some Gradle build to work for a Kotlin multiplatform project that involves an ANTLR grammar. What I'm trying to do is to have a parser generated by ANTLR from a shared grammar for both a Kotlin (or Java if that doesn't work) and JavaScript target. Based on this I'd like to write some library around the parser that can be used from the JVM and JavaScript.

So I have set up a Kotlin multi-platform project because that seemed like a nice way of killing two birds with one stone (here is a repo https://github.com/derkork/project.txt). I created a source set commonAntlr where I placed the grammar file under commonAntlr/antlr/project_txt.g4. According to the documentation of the ANTLR plugin this is how stuff should be set up. I also apply the antlr plugin at the top (here is the build.gradle.kts - https://github.com/derkork/project.txt/blob/master/build.gradle.kts).

Now I run gradle build in the hopes that the ANTLR plugin will at least try to generate some nice Java code for me from the grammar using the default settings. Alas, it does not. The ANTLR plugin does not even get started, which is what I can tell from the output. The build later fails with some obscure JavaScript problem, but that looks unrelated and I'd like to skip over it for now.

Now my Gradle-foo isn't exactly strong (I have only used it in extremely simple projects, most of my experience is in Maven), and I have the distinct feeling I'm missing something here. However the documentation of the plugin just says

To use the ANTLR plugin, include the following in your build script:

plugins { antlr }

Which I did. Since I get zero output, I have a feeling that I need to do a bit more for this to work. I have read a lot of the Gradle documentation up and down to find out how plugins work in general and I found that they add tasks to the build and also add some dependencies so that tasks are invoked when you try to build certain things. However I don't really understand how plugins work together with source sets and how you can tell Gradle "would you please run the generateGrammarSource task for this source set" (or if it even works like this).

So if some of the Gradle gods could enlighten me on this, this would be much appreciated :)

Giovanni Ciatto Giovanni Ciatto · Accepted Answer · 2020-01-30T10:25:53

I have met a similar issue: https://gitlab.com/pika-lab/tuprolog/2p-in-kotlin/tree/feature/parser

My solution -- which is still a work in progress -- consists in decomposing the problem. I reasonable solution in my opinion is to create a Kotlin/JVM project (say parser-jvm) where to put the generated Java code + any JVM specific facility, and a Kotlin/JS project where to put the generated JS code + any JS specific facility (say parser-js). The next step is to create a Kotlin/MPP (say parser-common) project whose JVM implementation depends on parser-jvm and whose JS implementation depends on parser-js.

My approach is actually working for JVM while I'm experiencing some issues for JS, which are mostly caused by this issue.

The main drawback of this approach is that some Gradle coding is required to setup ANTLR with Kotlin/JS. I already faced this problem in my build.gradle and I'm quite satisfied with the result and the overall architecture of the project. However, I believe that my proposal is far less troublesome than configuring a Kotlin/MPP project to work with ANTLR.

How to build an ANTLR grammar with Gradle in a multi-platform project?

1 Answers