Validation mode to check if file is correctly formatted

[JLLeitschuh]

This would be useful in CI systems where you would want the build to fail if the user hasn't formatted their code before the CI system runs.

[jbduncan]

FWIW, Spotless (which supports google-java-format) already allows the user to do this. :)

[JLLeitschuh]

We are using maven in our build at the moment (trying to move to gradle but transition is slow).
Anything we can do in our world?
I was thinking about doing a checksum diff as a simple fix unless there is a better solution out there.

[Stephan202]

We have a format.sh script that wraps the Maven plugin, and a Dangerfile containing the following (this is executed by Travis CI, only for PR builds):

# Run the formatter and check whether this introduces any changes. 
if !system('./format.sh && git diff --exit-code --name-status')
  fail 'There are formatting errors, please run `./format.sh`.' 
end

[jbduncan]

@JLLeitschuh Interesting you mention Maven, as we (@nedtwigg and I) are in the middle of writing version 3.0 of Spotless, and one of the things @nedtwigg has been working on recently is splitting out the "core" of Spotless into its own lib so that it can eventually be used in non-Gradle contexts.

However, I don't know if he has any definite plans to support a Maven plugin, so if you're interested, I'd suggest you ask him on the issue he's made to track the spotless-lib efforts. (diffplug/spotless#56)

[JLLeitschuh]

I honestly don't plan on supporting our maven build for that much longer either.
I'm in the process of rewriting our build using gradle groovy and gradle script kotlin however being a startup with many other things going on simeltaneously I've got a lot of moving targets.

You've been a lot of help.
Do you mind sharing the contents of your ./format.sh @Stephan202 ? Is it just the call out to the google-java-format jar??

[Stephan202]

@JLLeitschuh: there's some other (actually unused) stuff in there, but the no-arg invocation boils down to:

mvn -B -T 1.0C com.github.PicnicSupermarket:googleformatter-maven-plugin:format

Where the referenced plugin is a Jitpack'ed version of this branch, forked off talios/googleformatter-maven-plugin. (I recommend using the latest version instead. Reason I haven't upgraded our script yet is that I need to make sure we have precisely matching versions of the IDEA and Eclipse plugins. For that I am waiting on #80.)

[mernst]

The run-google-java-format project has a check-google-java-format.py script that checks whether a file is properly formatted. The project's README file tells how to integrate with make, ant, gradle, git pre-commit hooks, and gives some advice about running google-java-format for the first time.

[sormuras]

I still think, a validation mode is a useful core addition.

[alexkleiman]

I agree that this would be very useful as a core feature. I imagine that nearly everybody using google-java-format within a large organization maintains some sort of CI system to enforce that code is formatted properly. In any organization with more than a handful of developers, it is essential to ensure that every developer always submits code formatted to google-java-format's standards. Otherwise, there is no way to maintain a codebase's formatting without constantly causing merge conflicts for developers whenever a reformatting event takes place.

For these reasons, I view a validation mode as a hard requirement for use of google-java-format in a large organization. Because this is a requirement for use of google-java-format at scale, it makes sense as a core feature.

[sormuras]

FWIW, you may use https://jitpack.io to get a compiled version of google-java-format with integrated validation mode:

https://jitpack.io/#sormuras/google-java-format/validate-SNAPSHOT

If you want to just download the all-deps JAR, you can grab it here: https://jitpack.io/com/github/sormuras/google-java-format/google-java-format/validate-SNAPSHOT/google-java-format-validate-SNAPSHOT-all-deps.jar

I'll try to keep the validate branch as up-to-date as possible.