Add return_call example for WASM

[pepelsbey]

Description

Adds example for return_call, tail call version of the call. I took it from the explainer.

But there’s a catch: the playground shows an error when I try to run the code. There might be two reasons for that:

• I don’t fully understand what I’m doing (first time looking at WASM)
• Playground doesn’t support return_call, see the error below

Motivation

To support enabled tail calls in Firefox 121.

Additional details

> Error: parseWat failed:
3:6: error: opcode not allowed: return_call
    (return_call $fac-aux (local.get $x) (i32.const 1))
     ^^^^^^^^^^^
10:10: error: opcode not allowed: return_call
        (return_call $fac-aux
         ^^^^^^^^^^^

Related issues and pull requests

mdn/content#30333

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[pepelsbey]

@eqrion could you please have a look?

[pepelsbey]

@yurydelendik thank you! However, the code still won’t run if pasted into the playground we have on the call page, for example:

> Error: parseWat failed:
3:6: error: opcode not allowed: return_call
    (return_call $fac-aux (local.get $x) (i64.const 1))
     ^^^^^^^^^^^
10:10: error: opcode not allowed: return_call
        (return_call $fac-aux
         ^^^^^^^^^^^

Do you have an idea if it’s the problem with the playground?

[yurydelendik]

Do you have an idea if it’s the problem with the playground?

I have a little insight into how playground works. The WebAssembly engine does not know about WAT and text representation. The transformation to bytecode is happening somewhere else. That something perhaps needs to be updated with new wasm specifications support.

[yurydelendik]

If not mistaken, parseWat is API function from wabt JS library. Is https://github.com/mdn/bob/blob/main/editor/js/editable-wat.ts executed on the main page?

There is a reference to "wabt": "^1.0.29", which is https://github.com/AssemblyScript/wabt.js . The package is not updated for long time and probably missing new specifications.

[pepelsbey]

The package is not updated for long time and probably missing new specifications.

Thank you for investigating! I’ll reach out to platform engineers about this.