Java 21 pattern matching on records seems not working, gives false error "incorrect number of nested patterns"

[liufuyang]

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello from Java!");
        printAngleFromXAxis(new Point(1, 1));
    }

    static void printAngleFromXAxis(Object obj) {
        if (obj instanceof Point(double x1, double y1)) {
            System.out.println(Math.toDegrees(Math.atan2(y1, x1)));
        }
    }
}

record Point(double x, double y) {}

This piece of Java code compiles in Java 21.

But with the language server, I got a weird error saying:

incorrect number of nested patterns
required: double,double,double,double
found: double,double(compiler.err.incorrect.number.of.nested.patterns)

---

By the way, @georgewfraser, thanks for making this nice tool. Just wondering, will you still have time to improve it? There seem to be many good PRs are also hanging there for some time :)

[alepekhin]

It works in vim for me. You probably use VS Code extention that is not corresponding the latest code in this project.

[liufuyang]

I think I am using this language server.

I opened my editor again and seems the error is gone up on opening.

But I tried to remove the printAngleFromXAxis and add it back via undo, then this error show up again.

Maybe you could try that as well?

[liufuyang]

Oh sorry, you mean I didn't use the latest code? Then is there a simple way to use the latest version on VSCode? The VSExtention is not updated anymore perhaps?

The VsCode extension page shows version of 0.2.47

[alepekhin]

Sorry, I was too fast. I confirm it does not process records properly

[liufuyang]

@alepekhin Thanks, seems still not working with Java25. Firstly open the file it does not show the error, but if just doing some change on the line and revert, this error shows up.

I also tried to paste some Java 25 compatible code such as:

static void test(Object obj) {
    if (obj instanceof int i) {
        System.out.println("It's an int: " + i);
    }
}

And it also gives some errors:

So perhaps this language server has not updated to use new features of Java25?

[liufuyang]

@alepekhin Oh, sorry, I just saw your updated comments.

One more question perhaps you know is that, are you also mentaining this repo? I wonder if the repo's owner is still actively maintaining this.

I appreciate that it is a light weight language server and could be userful in many cases, but it just needs a bit more polishing, such as issue mentioned here and there seems many good PRs waiting to be landed.

Also, it confused me (probably inclduing many new users out there) is that it has a dependency of bazel command available on the path to make this tool work (at least with VsCode), and I think that is why it has a very low plugin score on VsCode side, is because it is hard to know why it fails as a new user and seldomly people have bazel on their classpath.

A simple doc update, or perferabbly to remove the bazel dependency if possible, can help a lot. But I am not sure who else other than the author can still merge code to this repo nowadays.

@alepekhin so perhaps you have more insights?

[alepekhin]

Only maintainer can merge PR to this project.
I have a fork of it at my Gihub account where I can do everything I want.
Try the branch
https://github.com/alepekhin/java-language-server/tree/with_all_PR_merged
where some PR from this project are merged and a lot of improvements added by me.
Write an issue there if you want anything else.

[liufuyang]

Aha, I see, thanks a lot. I can try check it out, especially after I could figure out how to use a local-built one with VsCode (shouldn't be hard, I guess?).

@georgewfraser Have you thought about adding one or two more active maintainers in this opensource repo? :)

[alepekhin]

I think you can just copy built app to vscode extensions like
java-language-server$ cp -r * ~/.vscode/extensions/georgewfraser.vscode-javac-0.2.47/

[liufuyang]

Appreciated it, I can give it a try later when I have time :)

[nya3jp]

It's nice to file a separate issue for discussing project maintenance. Some portion of my team relies on this language server and I'm interested in the maintenance plan.

[liufuyang]

Indeed, @nya3jp maybe you want to create one for that? I am interested in looking deeper into this repo as well, as my work touches on using eclipse jdt parser internally, so I am looking at this one as something potentially we could use, especially if it can be well maintained.

[nya3jp]

I filed #340 to discuss project maintenance. Thanks!

[liufuyang]

@alepekhin Hi there, I was about the test your changes, but seems you have removed your branch?
https://github.com/alepekhin/java-language-server/tree/with_all_PR_merged

Anyway, as I cloned your repo earlier, so I locally have that branch and I needed to go back a few commits to test your fix, the error indeed is gone, but the language server seems a bit slow to show other issues if I do some edit on the of code that doing pattern matthing.

Still... would be nice to see this project getting proper maintenance later. With a few things unpolished here, the plugin seems to be much less useful.

[alepekhin]

@liufuyang Hi

• it was very rough attempt to solve the problem that makes the server slow. We have to find another approach
• some tests, working in master branch, were failed and I decided to drop all my branches. May be later I will reconsider my work more carefully
• for now I will work with main branch. The single thing I had to add is a link to java in dist folder

ln -s ~/bin/jdk-25 dist/linux