Enable json in maven plugin

[blacelle]

Following #1445

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Please DO NOT FORCE PUSH. Don't worry about messy history, it's easier to do code review if we can tell what happened after the review, and force pushing breaks that.

Please make sure that your PR allows edits from maintainers. Sometimes its faster for us to just fix something than it is to describe how to fix it.

After creating the PR, please add a commit that adds a bullet-point under the [Unreleased] section of CHANGES.md, plugin-gradle/CHANGES.md, and plugin-maven/CHANGES.md which includes:

• a summary of the change
• either
  • a link to the issue you are resolving (for small changes)
  • a link to the PR you just created (for big changes likely to have discussion)

If your change only affects a build plugin, and not the lib, then you only need to update the plugin-foo/CHANGES.md for that plugin.

If your change affects lib in an end-user-visible way (fixing a bug, updating a version) then you need to update CHANGES.md for both the lib and all build plugins. Users of a build plugin shouldn't have to refer to lib to see changes that affect them.

This makes it easier for the maintainers to quickly release your changes :)

[nedtwigg]

Great PR! Needs

• an entry in plugin-maven/CHANGES.md
• at least one test for Gson and one test Simple

[nedtwigg]

Oh, also run spotlessApply and commit the result ;-)

[nedtwigg]

Great PR, thanks!

[blacelle]

@nedtwigg Would it be reasonable to add '**/*.json' as default include? (It is unclear to me why some formats has a default while other do not (which I feel there is some rationale default include)).

[nedtwigg]

Would it be reasonable to add '**/*.json' as default include?

We used to have a lot of **/*.blah default includes, and it turned out to be a mistake. You have a toy project, the **/* works really well. People with real projects actually adopt it, and those wildcards become meaningfully slow.

why some formats has a default while other do not

There are some cases where a standard is common enough that most users won't need to change it. e.g. src/main/java/**/*.java. But unless it's really standard and contained to a specific folder then it's better for it to be manually specified.

The great underappreciated value of needing to manually specify the target is that it's self-documenting. Someone new joins the project, is confused by what's getting formatted, searches "spotless" in their project. And right there, they can see how to change it. If the target hasn't been set, the default is an invisible mystery.

Invisible mysteries are nice, but only when they work, so it's important to only set a default if it's almost definitely right. We got this wrong earlier in Spotless' life.

[nedtwigg]

Published in plugin-maven 2.30.0.