Provide support for Java 21

[snjeza]

Fixes redhat-developer/vscode-java#3292
Requires redhat-developer/vscode-java#3314
Test vsix - VS Code 1.24.5

[fbricon]

Please add some unnamed classes/ instance main method test cases.

It seems to me completion doesn't work at all in a instance main method example, e.g.:

public void main() {
  Syste|
}

[fbricon]

the main snippet should now be allowed in an empty class

[fbricon]

well JEP445 is not supported yet eclipse-jdt/eclipse.jdt.core#1106

*sigh*

[rgrunber]

Has anyone been able to get String templates ( https://openjdk.org/jeps/430 ) working ? STR doesn't seem to be recognized.

[fbricon]

All preview features are currently missing eclipse-jdt/eclipse.jdt.core#890

[rgrunber]

Are we ok to merge as-is for releasing by Thursday ? As far as I could tell I was able to configure a Java 21 JVM with this change.

[snjeza]

We could use https://download.eclipse.org/eclipse/updates/4.30-I-builds/ instead of https://download.eclipse.org/eclipse/updates/4.29-P-builds/. See eclipse-jdt/eclipse.jdt.ui#806
@fbricon @rgrunber Do you agree?

[rgrunber]

After discussion, we've decided to hold off on this for after the 1.28.0 JDT-LS release. Once we release we can adopt the 4.30-I-builds.

[snjeza]

After discussion, we've decided to hold off on this for after the 1.28.0 JDT-LS release. Once we release we can adopt the 4.30-I-builds.

@rgrunber I have updated the PR.

[akurtakov]

So I've uncovered today that ecj actually supports instance main methods (protected void main() in a class)- aka compiles them fine (no restrictions on that) and they are executed just fine on the console via java --enable-preview ClassName.

[rgrunber]

The code to programmatically run/debug isn't handled by JDT-LS. It would be under https://github.com/microsoft/java-debug . The only problem I see is that locating the main class is done through the JDT search engine. I think that if the source parser can't recognize an unnamed classes without throwing syntax errors, then it also won't be able to index that content. It would still rely on language support being adopted.

@snjeza It looks like we'll need to manually add commons.codec (required by m2e) to the target platform. It appears to have been removed in https://download.eclipse.org/eclipse/updates/4.30-I-builds/I20230923-1800/plugins/ .

[ERROR] Cannot resolve dependencies of product languageServer.product:
[ERROR]   eclipse-plugin artifact with ID "org.apache.commons.codec" and version matching "0.0.0" was not found in the target platform

[snjeza]

It looks like we'll need to manually add commons.codec (required by m2e) to the target platform. It appears to have been removed in https://download.eclipse.org/eclipse/updates/4.30-I-builds/I20230923-1800/plugins/ .

@rgrunber I have removed it. I have added it from https://download.eclipse.org/eclipse/updates/4.29/

[snjeza]

@rgrunber I have updated the PR.

[snjeza]

test this please

[aghasemi]

All preview features are currently missing eclipse-jdt/eclipse.jdt.core#890

Thanks for the information. Will they be available on the final release?