Support Palantir-Java-Format for Java (500USD Bounty)

[lihaoyi]

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From the maintainer Li Haoyi: I'm putting a 500USD bounty on this issue, payable by bank transfer on a merged PR implementing this.

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Palantir-Java-Format is a common Java autoformatter, and we should support it as a contrib/ module to better support Java projects. We should support all common configuration options to allow usage on JavaModules and ScalaModules (which can contain Java sources). It should broadly work the same way ScalaFmt works for Scala (https://mill-build.org/mill/0.11.12/Scala_Module_Config.html#_reformatting_your_code) This needs to come with a reasonable set of unit tests, docs, and at least one example test that can be included in the documentation.

May be able to adapt something from https://github.com/sbt/sbt-java-formatter

[lefou]

I'd prefer palantir, either directly or via spotless, which could provide a lot of other formatters too.

• https://github.com/palantir/palantir-java-format
• https://github.com/diffplug/spotless

[lihaoyi]

Sure! Maybe it should be via spotless then?

[lihaoyi]

Let's go with palantir-java-format for now. At a glance Spotless seems a lot more heavyweight, and maybe can come in a follow up, but palantir-java-format should suit the immediate need of "we need a java formatter" and hopefully be easier to implement

[lefou]

I experiemented with it in the past but got some class access issues due to not using the module classloader. So, if you're a Scala dev not so deep into Java, expect some difficulties.

[lihaoyi]

yeah I assume there'll be stumbling blocks but I assume they'll be work-around-able. If it can work in eclipse/intellij/gradle/spotless it should be doable inside Mill; worst come to worst we can run it in a separate subprocess. But that's for whoever picks up the bounty to figure out!