Xtext Maven plugin should specify required Java version

[rosczja]

We wanted to upgrade our projects to Maven 3.9.12 and noticed an issue with Xtext Maven plugin. Our projects use Java 11 and Xtext 2.37, which would build just fine with Maven 3.9.11. The newer Maven versions will enforce the required Java version set in a plugins descriptor. For Xtext 2.37 it is seems to be autodetected and set to Java 17. Which did not seem right, because our projects build with Java 11 just fine.

I would like to suggest to add the "requiredJavaVersion" property of the "maven-plugin-plugin" configuration to a dedicated value instead of the default value "auto". So in future it is always clear what Java version is required by the Xtext Maven plugin.

[cdietrich]

did you check #3603
which properties do you have set?

am also not sure when the maven plugin initially learned about maven.compiler(source/target)

cc @HannesWell

[rosczja]

no @cdietrich , I meant the property should be set in the pom.xml of the Xtext maven plugin. Our projects do use maven.compiler.release.

Extract from the Xtext Maven plugin plugin.xml:

plugin>
  <name>Xtext Maven Plugin</name>
  <description>Xtext is a framework for development of programming languages and domain-specific languages. With Xtext you define your language using a powerful grammar language. As a result you get a full infrastructure, including parser, linker, typechecker, compiler as well as editing support for Eclipse, LSP and your favorite web browser.</description>
  <groupId>org.eclipse.xtext</groupId>
  <artifactId>xtext-maven-plugin</artifactId>
  <version>2.37.0</version>
  <goalPrefix>xtext</goalPrefix>
  <isolatedRealm>false</isolatedRealm>
  <inheritedByDefault>true</inheritedByDefault>
  <requiredJavaVersion>17</requiredJavaVersion>
  <requiredMavenVersion>3.6.0</requiredMavenVersion>

[cdietrich]

do you know how the autodetect works?

[rosczja]

Not in detail, no. Checking the source code it takes the Java version from the annotated class version:
https://github.com/apache/maven-plugin-tools/blob/master/maven-plugin-tools-annotations/src/main/java/org/apache/maven/tools/plugin/extractor/annotations/JavaAnnotationsMojoDescriptorExtractor.java#L206

Which does not seem to make sense for Xtext 2.37, right? Because if the class version was 17, it would not run with Java 11.

[cdietrich]

maybe you have something that clutters the classpath?
did you check running with -X

[rosczja]

Ok @cdietrich , I guess I did not make myself clear, sorry. We have one project which uses Xtext 2.37 to generate Java code from a DSL file. If we build this project with Java 11 and Maven 3.9.11 everything works as expected.

But if we try to build the same project without any changes with Java 11 and Maven 3.9.12, Maven fails the build, because the Xtext Maven plugin requires Java 17.

Quote from the Maven 3.9.12 release notes (https://maven.apache.org/docs/3.9.12/release-notes.html):
"Verify the Java version requirements for plugins before execution and provide a clear error message if the requirement is not met"

So for whatever reason the Xtext Maven plugin 2.37 states in its plugin descriptor that it requires Java 17, but actually works just fine with Java 11.

So for future versions of the Xtext Maven plugin I suggest to make the "requiredJavaVersion" explicit and not rely on auto detection.

[LorenzoBettini]

@rosczja would you like to propose a PR?

[rosczja]

If having that "feature" makes sense to you @LorenzoBettini , then yes I can propose a PR