Add support for wasm32-unknown-emscripten via Pyodide

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## Unreleased
+### Added
+- Add support for extension modules built for wasm32-unknown-emscripten with Pyodide.
+
 ### Changed
 - Locate cdylib artifacts by handling messages from cargo instead of searching target dir (fixes build on MSYS2). [#267](https://github.com/PyO3/setuptools-rust/pull/267)
 - Fix RustBin build without wheel. [#273](https://github.com/PyO3/setuptools-rust/pull/273)

setuptools_rust/build.py

@@ -3,7 +3,6 @@
 import glob
 import json
 import os
-import pkg_resources
 import platform
 import shutil
 import subprocess
@@ -20,6 +19,7 @@
 from pathlib import Path
 from typing import Dict, Iterable, List, NamedTuple, Optional, Set, Tuple, cast
 
+import pkg_resources
 from setuptools.command.build import build as CommandBuild  # type: ignore[import]
 from setuptools.command.build_ext import build_ext as CommandBuildExt
 from setuptools.command.build_ext import get_abi3_suffix
@@ -200,6 +200,12 @@ def build_extension(
                 # the cdylib, see https://github.com/rust-lang/cargo/issues/10143
                 rustflags.append("-Ctarget-feature=-crt-static")
 
+            elif (rustc_cfgs.get("target_arch"), rustc_cfgs.get("target_os")) == (
+                "wasm32",
+                "emscripten",
+            ):
+                rustc_args.append(["-C", f"link-args=-sSIDE_MODULE=2 -sWASM_BIGINT"])
+
             command = [
                 self.cargo,
                 "rustc",