React to the checkstyle plugin in Gradle projects

[quaff]

It would be nice if io.spring.javaformat gradle plugin add dependency io.spring.javaformat:spring-javaformat-checkstyle to checkstyle configuration.

Given:

plugins {
	java
	checkstyle
	id("io.spring.javaformat").version("0.0.45")
}

Then:

dependencies {
	checkstyle("io.spring.javaformat:spring-javaformat-checkstyle:0.0.45")
}

should be optional.

[wilkinsona]

I've had this at the back of my mind for a while and I do think it would be useful, but I've never done anything about it as it's not as straightforward as it first appears to be. A few things that we'd have to keep in mind:

• Adding a dependency to the checkstyle configuration replaces the default dependency on com.puppycrawl.tools:checkstyle. We'd probably need to add it back again and consider the checkstyle.toolVersion property when doing so
• Some users may want this plugin's formatting but not want its Checkstyle integration. They'd need a way to disable the automatic configuration of Checkstyle. A property, configured in gradle.properties, would be the easiest. A DSL would be nicer but this is complicated as it requires the dependency to be added lazily once the user's had a chance to configure things using the DSL
• Can we somehow configure things so that our pre-canned checkstyle.xml is used by default?

[wilkinsona]

3 isn't possible as there's no way to tell if the user wants to use the default config location. We can do 1 and 2 though.

[wilkinsona]

See #453 for an alternative to 3 that allows a user to opt into using Java Format's default Checkstyle config.