Multirelease support: imports in editor cannot be resolved

[tomaswolf]

Thanks for providing multirelease support in JDT. (m2e should also get updates...) The new feature works for compiling, but in an open Java editor, references to imports or classes from java.lang cannot be resolved.

Eclipse version:

Version: 2025-09 (4.37.0)
Build id: 20250905-1456

org.eclipse.jdt.core 3.43.0.v20250820-1501
org.eclipse.jdt.ui 3.35.100.v20250905-1111
org.eclipse.m2e.jdt 2.4.101.20250727-0653

To reproduce:

1. Import the "mrproject" maven project from mrproject.zip into the workspace.
2. Reset the project's default compliance to 1.8 (Package explorer context menu→Properties→Java Compiler; uncheck "Use compliance from execution environment" and set "Compiler compliance level" to 1.8, then apply.) Importing the maven project unfortunately resets that to 15.
3. Now the project should show no errors in the package explorer.
4. Open src/main/java15/com/example/MultiReleaseClass.java.
5. The editor cannot resolve java.lang.System:

[tomaswolf]

Related to #4275.

[laeubi]

@tomaswolf sorry I have missed this issue, I'm currently looking into this.

[laeubi]

@tomaswolf I testes this now and interestingly it only happens with Java 1.8 ... if I select e.g. Java 9 it works. So something seems special here ...

[laeubi]

@tomaswolf should be fixed with:

• Take release level into account when check for java9 #4529

[laeubi]

Importing the maven project unfortunately resets that to 15.

This is something independent from MR support, but of course much more visible as one uses multiple executions of compiler mojo.

I created a PR here to fix that:

• Only consider the default-compile execution when update JDT settings eclipse-m2e/m2e-core#2050