Add Prettier to Maven plugin

[source-knights]

This PR adds Prettier to the Maven plugin.

The only limitation (which is also for the Gradle plugin, is that Spotless uses J2V8. As development for J2V8 for non android envs is stopped (for Windows since J2V8 4.6.0 and Unix 4.8.0), therefore Prettier is limited to <= v1.19.0 as newer versions use ES6 feature and that would need a newer J2V8 version.

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 -SNAPSHOT section of 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 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 the 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 :)

[source-knights]

Happy eastern :-)

[source-knights]

Link to the issue stating the discontinuation of J2V8 for non android envs: eclipsesource/J2V8#279

[nedtwigg]

Amazing, thanks very much! I made some comments. If you get stuck fixing the tests let me know and I will try to take a look.

[source-knights]

Thx for the comments, I think I addressed all. Still fighting with the failing build, as that does not happen locally.

[source-knights]

Hey finally green... and I don't think I committed anything to fix that ;)

[nedtwigg]

Published in plugin-maven 1.30.0

[nedtwigg]

in the docs

Specify either simple prettier version (1.19.0 is max supported, which is also default) or whole devDependencies

But it looks to me like our default is actually 1.16.4

spotless/lib/src/main/java/com/diffplug/spotless/npm/PrettierFormatterStep.java

Lines 40 to 42 in 608af5c

	public static final Map<String, String> defaultDevDependencies() {
	return defaultDevDependenciesWithPrettier("1.16.4");
	}

Did you perhaps mean to commit something that didn't make it? Also, wanted to double-check that 1.19.0 is really the max supported, was that what you found in testing? See #556

[source-knights]

@nedtwigg Oh yes, good spot. That's a leftover in the doc from a point, where I wanted to up the default to max supported. But I decided against this to not change existing behaviour for people using the gradle plugin and keep it in sync with that.

1.19.0 is in fact the last prettier version working with current spotless. As explained, that is due to the used J2V8. The newer prettier from version 2.0.0 uses ES6 features in the JS, e.g. (...args). J2V8 can't use that and errors then, showing something like:

com.eclipsesource.v8.V8ScriptExecutionException: C:\Users\XYZ\AppData\Local\Temp\junit5133972595801156893\target\spotless-node-modules-prettier-format\node_modules\prettier\index.js:1938: SyntaxError: Unexpected token ...

[nedtwigg]

I decided against this to not change existing behaviour for people using the gradle plugin and keep it in sync with that.

Roger. No obligation to fix, but just FYI, our policy on default versions is that we always bump the default to latest and note it in the changelog. New users of Spotless get the best formatters available, existing users of Spotless who prefer the old version can easily pin it.

[nedtwigg]

We don't have any formal system for finding new versions either, it's just if somebody is working on that component or bothers to make a PR.