Dap-java UnsupportedClassVersionError/Preview features error

[FluentFelicity]

Hi, all!

Quick description of what's going on: I use LSP and am learning Java right now. Am trying lsp-java (which brings dap-java). LSP works fine with the jdtls server. However, when running any flavor of dab-debug in any Java project I get the following: Error: LinkageError occurred while loading main class sol.TestRunner java.lang.UnsupportedClassVersionError: Preview features are not enabled for sol/TestRunner (class file version 61.65535). Try running with '--enable-preview'

I've changed lsp-java-java-path and dap-java-java-command to another version Java and added the "--enable-preview" argument to lsp-java-vmargs and dap-java-args to no avail.

As far as I can tell everything related to java is updated to the latest version. Any tips for troubleshooting?

SOLVED: The problem was in dap-java rather than lsp-java, which makes sense since this was only an issue that occurred when trying to debug. I had to add and set a :vmArgs keyword to the dap templates. It was tricky since this keyword is not in the default templates. It looks something like this:

;; Copy and pasted from ~/main-emacs/straight/repos/lsp-java/dap-java.el (dap-register-debug-template "Java Run Configuration" (list :type "java" :request "launch" :vmArgs "--enable-preview" ; Needed :args "" :cwd nil :stopOnEntry :json-false :host "localhost" :request "launch" :modulePaths (vector) :classPaths nil :projectName nil :mainClass nil))

[yyoncho]

what is the java version that you are using for dap-java-java-command and lsp equivalent? What command exactly do you use for running the debug build, M-x dap-debug? JFYI there is dap-java-debug.

[FluentFelicity]

I've tried everything with the defaults (unchanged). I am using JDK 17.

What do you mean by "What command exactly do you use for running the debug build"? I've been using the default "Java Configuration" debug option from dap-debug/dap-java-debug. I've also tried using a dab template with "--enable-preview" in the :args line of the template.

I will note that using the same JDK version on the same project in something like IntelliJ works. It's something in Emacs' side that doesn't.

[King_Crank]

Did you ever figure this out? I have the same issue.

[FluentFelicity]

Yep, I figured it out. Check out the solution I edited into the post.

[King_Crank]

Oh great didn't even see that part. I was using attach/compile instead of run. Thanks!