How to properly use TeaVMRunner?

[matetokodi]

I would like to turn a simple java class (bytecode) file into a simple wasm-gc binary file; As far as I understand TeaVMRunner is the tool I need to use for this, but if not please point me in the correct direction;
I don't quite understand how to give it the parameters properly.
I am also not super familiar with the java world, so I apologise in advance.

At first I built it with the command in the readme (./gradlew publishToMavenLocal), but then I'm not sure why java does not pick it up from the classpath automatically

$ java org.teavm.cli.TeaVMRunner
Error: Could not find or load main class org.teavm.cli.TeaVMRunner
Caused by: java.lang.ClassNotFoundException: org.teavm.cli.TeaVMRunner

Then I tried running it with just IntelliJ IDEA, which after some fiddling worked
(I needed to comment out the lines renaming the apache commons cli utils in settings.gradle.kts, otherwise it would not build

Error: Unable to initialize main class org.teavm.cli.TeaVMRunner
Caused by: java.lang.NoClassDefFoundError: org/apache/commons/cli/ParseException
Error: Unable to initialize main class org.teavm.cli.TeaVMRunner

Caused by: java.lang.NoClassDefFoundError: org/apache/commons/cli/ParseException


Execution failed for task ':tools:cli:org.teavm.cli.TeaVMRunner.main()'.
> Process 'command '/usr/lib/jvm/java-25-openjdk/bin/java'' finished with non-zero exit value 1

)

But with it building, I cannot figure out how to properly give it the correct parameters.
In the IntelliJ run configuration, I tried giving it various options:

--targetdir /mnt/cupcake/Projects/teavm/output/fannkuch -t wasm --classpath /mnt/cupcake/Projects/fannkuch-redux-javat/out/production/fannkuch-redux-java/ --entry-point main com.example.fannkuchredux

The help text says that I need a qualified main class
usage: java org.teavm.cli.TeaVMRunner [OPTIONS] [qualified.main.Class]

and as far as I understand com.example.fannkuchredux should be it, however I'm not sure how that is supposed to be picked up, I assume from the CLASSPATH, thats why I also included the --classpath option pointing it to where the class file that I want to turn into wasm is.
I also included that same directory in the project classpath in the IntelliJ run configuration, to be sure, but no dice :(
I also tried _start as the entry-point.

The main error I get is:

> Task :tools:cli:org.teavm.cli.TeaVMRunner.main() FAILED
INFO: Running TeaVM
Analyzing classes...java.lang.NullPointerException: Cannot invoke "org.teavm.model.ClassReader.getFields()" because the return value of "org.teavm.dependency.ClassDependency.getClassReader()" is null
	at org.teavm.backend.wasm.WasmTarget.contributeDependencies(WasmTarget.java:418)
	at org.teavm.vm.TeaVM.build(TeaVM.java:421)
	at org.teavm.tooling.TeaVMTool.generate(TeaVMTool.java:540)
	at org.teavm.cli.TeaVMRunner.build(TeaVMRunner.java:457)
	at org.teavm.cli.TeaVMRunner.buildNonInteractive(TeaVMRunner.java:442)
	at org.teavm.cli.TeaVMRunner.runAll(TeaVMRunner.java:405)
	at org.teavm.cli.TeaVMRunner.main(TeaVMRunner.java:182)

Execution failed for task ':tools:cli:org.teavm.cli.TeaVMRunner.main()'.
> Process 'command '/usr/lib/jvm/java-25-openjdk/bin/java'' finished with non-zero exit value 254

I'd appreciate some pointers towards the right direction, and to know what exactly I'm doing wrong.

[konsoletyper]

I would like to turn a simple java class (bytecode) file into a simple wasm-gc binary file

It's not possible. TeaVM does not work on per-class basis. You need to convert entire application, i.e. your class and all its dependencies.

As far as I understand TeaVMRunner is the tool I need to use for this

No, you need either Gradle or Maven. You can also use TeaVMTool, but it's primarily for the case you are writing a plugin for another build system (e.g. sbt or bazel, etc.). So I suggest you to start with Gradle. You are not supposed to use TeaVMRunner

Error: Unable to initialize main class org.teavm.cli.TeaVMRunner
Caused by: java.lang.NoClassDefFoundError: org/apache/commons/cli/ParseException
Error: Unable to initialize main class org.teavm.cli.TeaVMRunner

Perhaps you don't provide all necessary jar files to java.

-t wasm

Oh, I just realized that TeaVMRunner does not support an option to generate Wasm GC.

The main error I get is:

Please, stop doing this. If you want to start using TeaVM, you can read this: https://teavm.org/docs/intro/getting-started.html

[matetokodi]

TeaVM does not work on per-class basis. You need to convert entire application, i.e. your class and all its dependencies.

I apologize, by simple class file I meant that the whole application is just a single class file, with no or minimal imports.

I would like to have a self contained wasm file, which I would run without a browser, using just a simple wasm runtime; That is why at first I did not go for the things described in the getting started guide, and I would have liked to avoid creating a separate java project; and TeaVMRunner kind-of seemed like it would do what I wanted, but evidently not.

But now that I've gotten things generating with gradle, the normal way, a few questions:
Is there a way of generating the wasm to not require the js glue?
I've looked inside, and the wasm code imports functions from the js side (e.g teavm::takeStackTrace), which are defined in the js file that is also generated.
I did also try disabling the generation of the js bits, but the wasm still wanted to import them, the js was just not generated in that case.

    js {
         addedToWebApp = false
    }

Or is generating standalone wasm not a supported use-case? (Based on the documentation so far I would guess this is the case, but I wanted to try my luck anyways.)

Thank you!

[konsoletyper]

Is there a way of generating the wasm to not require the js glue?

No, for Wasm GC backend this was never the goal to support any non-browser environments. For classical Wasm I created a WASI backend, but nobody shown any interest. If you want to, you can patch TeaVM to not depend on JS as a proof of concept, but this won't work out of the box

[matetokodi]

I see. What would the patching it to not depend on JS entail roughly? (I am not familiar with the codebase at all)

[konsoletyper]

You can start from looking into WasmGCTarget and org.teavm.backend.wasm.transformation.gc.EntryPointTransformation

[konsoletyper]

Another option. I'll try to find some time within next two weeks to create such patch for you. It would be super experimental, with everything hard-coded, but still viable solution for testing.