Tycho 3 and Java toolchain

[LorenzoBettini]

If we switch to Tycho 3 we must use Java 17.

If we want to use Java 11 for building and testing there are basically two options:

• configure Jenkins so that, when running on Java 11, the tycho-version property is overridden on the command line
• use Maven toolchain as suggested in compiler release option #2210 (comment)

[cdietrich]

my main question about toolchains is:

• how can they easily be setup (maybe we need a template to adjust)
• how can i tell: run now with j11, run now with j17 .... (as i can do with setting JAVA_HOME now)

[HannesWell]

• configure Jenkins so that, when running on Java 11, the tycho-version property is overridden on the command line

I believe that this option is too complex and would basically limit you to use only what's available in Tycho 2.7.

• use Maven toolchain as suggested in compiler release option #2210 (comment)

That's probably the better option forward.

* how can i tell: run now with j11, run now with j17 .... (as i can do with setting JAVA_HOME now)

For plain Maven project (with packaging-type jar) this magic should happen in the maven-toolchain-plugin:
https://maven.apache.org/guides/mini/guide-using-toolchains.html#using-toolchains-in-your-project

From #2210 (comment)

@HannesWell I created a dedicated issue. If, in the meantime, could you please point me to the relevant parts needed for the toolchain? I saw the XML file and it's simple, but I don't see in the SWT repository how to activate a specific toolchain. Moreover, who provides the locations for the actual JDK installations? If you have time, please comment on the other issue.

Tycho can auto-magically selects the corresponding Toolchain based on the BREE/osgi.ee requirement of a bundle, when using the tycho-compiler-plugin:useJDK configuration parameter.

Regarding the locations of the actual JVM, please see: https://github.com/actions/setup-java/#install-multiple-jdks

The setup-java action can even create a toolchains file on the fly, but I have not yet checked if that is suitable:
https://github.com/actions/setup-java/#using-maven-toolchains
But if it is, it is maybe sufficient to just specify the multiple java-version and everything else works automagically.

In Jenkins you could do something like the following. You only have to ensure that the env-variable names match the names used in the toolchain.xml

withEnv([
'JAVA_HOME_11_X86=' +tool(type:'jdk', name:'temurin-jdk11-latest'),
'JAVA_HOME_17_X86=' +tool(type:'jdk', name:'temurin-jdk17-latest')
]) {
  ... <Maven build steps>
}

[LorenzoBettini]

@HannesWell but the Maven documentation mentions that you need to use a maven toolchain plugin, and I haven't found that in the SWT repository.

Please, remember that in some projects (packaging jar) the tycho-compiler-plugin is not used and the default maven-compiler-plugin is used.

[HannesWell]

@HannesWell but the Maven documentation mentions that you need to use a maven toolchain plugin, and I haven't found that in the SWT repository.

That's probably because in the SWT repo there are not jar-typed projects.

Please, remember that in some projects (packaging jar) the tycho-compiler-plugin is not used and the default maven-compiler-plugin is used.

Then for xtext we probably need to configure both, tycho-compiler-plugin:useJDK and the maven-toolchain-plugin. I have not yet used the latter myself so cannot yet provide any more details in that regard yet.

In general it is often a good idea to only require toolchains in the CI activated in a corresponding Maven profile. This allows local builds without the need to set up toolchains on a computer. Then just the release option of the compiler is used, which is often not that bad. Using toolchains you can just be more confident.

@LorenzoBettini do you plan to provide a PR to do the migration to Tycho 3? Alternativly I can offer to work that out?

[LorenzoBettini]

@HannesWell I cannot work on that right now. If you are willing to work on that I can follow.

Of course, first, you can only try on GitHub Actions, then we'll deal with Jenkins.

First, let's hear from @cdietrich : do you think we can give it a try?

[cdietrich]

sure. give it a try.

[HannesWell]

sure. give it a try.

Great, I have started to work on it. I'll provide a draft as soon.
If #2214 is merged before that would avoid some unrelated changes. :)

[LorenzoBettini]

@HannesWell #2214 has been merged

[HannesWell]

Created #2223 with the current state of the work, which should be quite complete besides the failures that have to be fixed.