Fork removeUnusedImports() and googleJavaFormat() to support later JLS than the JRE used for the build

[marcphilipp]

EDIT by @nedtwigg: summarizing the current situation, easy workaround, and a hard-to-implement potential fix:

If you use googleJavaFormat() or removeUnusedImports(), and you also use cutting edge java language features such as the Java 15 text blocks, then you must also run your build on JRE 15+ (same for language features in any other release, e.g. must use JRE 14+ to use Java 14 language features, etc.). This is because google-java-format selects which JLS specification to use based on which version of JVM it is running on.

The easy solution is to run your build with a JVM at least as new as the code you are formatting. The hard solution is to add a feature to Spotless which allows forking a more modern JVM just to run formatting. Happy to take a PR for this feature, but we have no plans to implement the feature ourselves.

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When trying to use removeUnusedImports with a Java file that contains a Java 15 text block, the following exception is thrown:
https://ge.junit.org/s/5jcvukwcdcckg/console-log?task=:junit-jupiter-engine:spotlessJava

Config:
https://github.com/junit-team/junit5/blob/4dd6981ece3a5d5275844ba6d9b4fa7ab60bf0af/build.gradle.kts#L134-L154

[sormuras]

I guess, an outdated GJF is bundled. Perhaps an upgrade to 1.9 does help?

https://github.com/google/google-java-format/releases

[jbduncan]

When using the googleJavaFormat() step, by default we import 1.7 if the JDK that Spotless is running on is JDK >=8, or 1.9 if it's JDK >=11. This is because GJF 1.8+ now requires JDK 11. However, I don't know how we deal with removeUnusedImports(), as I don't have an IDE in front of me at the moment...

@nedtwigg Do you happen to know which version we use for removeUnusedImports()? Regardless, I can think of a few potential fixes:

• Import GJF 1.7/1.9 depending on the JDK
• Allow the user to choose which version of GJF to use
• Find an alternative to GJF that's Java 8-compatible. Maybe Eclipse has something here? But I recall @fvgh saying that it requires JDK 11 now...

Any thoughts on this?

[nedtwigg]

We do use the latest 1.9 when run on Java 11+. But, gjf picks formatting rules based on the JVM it's running on. So if you want to format Java 15 constructs, you need to run the build on Java 15.

[marcphilipp]

Does gjf run in the build VM or a forked one?

[nedtwigg]

The build VM. Not forked. Happy to take a PR which adds that feature though.

[marcphilipp]

For the time being, I made it optional depending on the Java version the build is running on.

[nedtwigg]

This issue was first, but I'm going to close it as a dupe of #724, because that issue is more general-purpose.