xml-apis dependency causes build failure in JDT when migrating to JDK 11

[Treehopper]

I checked if it would be possible to migrate to JDK, and ran into this issue: https://bugs.eclipse.org/bugs/show_bug.cgi?id=536928
I learned that JDT is correctly reporting an error, whereas the Maven build incorrectly passes because of this JDK bug: https://bugs.openjdk.java.net/browse/JDK-8215739

I'd suggest to migrate to 11 now, and remove the xml-apis dependency.
Apart from the benefits of a modern JDK, I'd argue that more such problems will accumulate over time, making migration only harder in the future.

[fbricon]

What do you mean by migrate to JDK 11? The project can build and run fine with JDK 11, produce a distribution perfectly working with Java 8

[Treehopper]

I can confirm your observation. I'm compiling it with 14 myself.
This is less an immediate issue, and more of a "timebomb".

Steps to reproduce the issue:

• set maven-compiler-plugin configuration to use source and target 11
• $ mvn clean compile #=> works because of bug JDK-8215739
• remove existing .classpath files
• import projects into eclipse (e.g. via m2e)
  => compile errors: "The package javax.xml.* is accessible from more than one module: javax.xml, "

Some day JDK-8215739 will be fixed, possibly in a patch-release of the JDK, then also the Maven build for this project breaks.

The immediate issue is that JDK 11 is simply more fun to work with. :-)

[fbricon]

Unfortunately, "more fun to work with" is not a compelling reason to require Java 11 at the moment, given that a majority of users are still stuck with Java 8.
I'm not to worried about the migration to Java 11, once we reach that point though, it'll be a matter of removing one dependency.
So I'll keep this issue on the backburner, hopefully not for too long, until we decide it's time to move on.

[datho7561]

See eclipse-lsp4j/lsp4j#547. Once we move to lsp4j 0.13.0, we will need to support Java 11 properly.