cross-compiling to wasm32-wasi

[cymqqqq]

🐛 Bug Reports

When reporting a bug, please provide the following information. If this is not a bug report you can just discard this template.

🌍 Environment

• Your operating system and version:
• Your python version:
• How did you install python (e.g. apt or pyenv)? Did you use a virtualenv?:
• Your Rust version (rustc --version):
• Your PyO3 version:
• Have you tried using latest PyO3 main (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")?:

💥 Reproducing

Please provide a minimal working example. This means both the Rust code and the Python.

Please also write what exact flags are required to reproduce your results.
ubuntu 20.04
py3.7
install python by apt. Did you use a virtualenv? No.
rust version 1.42
pyo3 version 0.13.2
yes, tried git = "https://github.com/PyO3/pyo3" when I build my demo code, an error comes: error: failed to run custom build command for pyo3 v0.13.2`

Caused by:
process didn't exit successfully: /home/azureuser/rustpy/target/release/build/pyo3-c4d90697e291dc3a/build-script-build (exit code: 1)
--- stderr
Error: NotPresent
warning: build failed, waiting for other jobs to finish...
error: build failed
Error: Compiling your crate to WebAssembly failed
Caused by: failed to execute cargo build: exited with exit code: 101
full command: "cargo" "build" "--all-targets" "--release" "--target" "wasm32-wasi"

[davidhewitt]

Hi @cymqqqq can you please share your demo code?

[cymqqqq]

ok, here is my demo code:
use pyo3::prelude::;
use pyo3::{prelude::, types::{IntoPyDict, PyModule}};
use wasm_bindgen::prelude::*;
#[wasm_bindgen]
Python::with_gil(|py| {
let activators = PyModule::from_code(py, r#"
def relu(x):
"""see https://en.wikipedia.org/wiki/Rectifier_(neural_networks)"""
return max(0.0, x)

            def leaky_relu(x, slope=0.01):
                return x if x >= 0 else x * slope
                    "#, "activators.py", "activators")?;

                    let relu_result: f64 = activators.getattr("relu")?.call1((-1.0,))?.extract()?;
                        assert_eq!(relu_result, 0.0);

                            let kwargs = [("slope", 0.2)].into_py_dict(py);
                                let lrelu_result: f64 = activators
                                            .getattr("leaky_relu")?.call((-1.0,), Some(kwargs))?
                                                    .extract()?;
                                    assert_eq!(lrelu_result, -0.2);

})

[cymqqqq]

just copy the code from https://pyo3.rs/main/python_from_rust.html

[davidhewitt]

@cymqqqq so what's going on here is that you're trying to cross-compile to the wasm target. To do this successfully you must direct PyO3 to the lib directory of a wasm Python build, so that PyO3 can read its information to configure the build.

However I am unsure whether building a wasm Python extension is possible. There is some prior discussion at #1221 .

The bug Error: NotPresent seems to have been related to some broken code which was recently removed in #1521. (Thanks @ravenexp!) So if you use the current main branch you should get more helpful error messages.

[cymqqqq]

OK. thanks for answering:-)

[abbec]

We also have some small fixes in #1605 that at least makes it work to cross-compile pyo3 to WASI for our case (given that you have already cross-compiled Python itself).

[davidhewitt]

As we now sort of support wasm32-wasi (we check the crate has no compilation errors, though we don't actually try to test with wasm32 Python, I'm going to close this issue.

If anyone with knowledge of how to build a Python interpreter for wasm wants to contribute a full CI job, that would be cool!