Add Pyodide support for Rust extensions

.github/workflows/build.yaml

@@ -97,3 +97,37 @@ jobs:
         with:
           name: dist-${{matrix.os}}
           path: dist
+
+  pyodide:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Setup Python
+        uses: actions-ext/python/setup@6e1b91a408ea89f49bc8aff8724f83826f7b5446
+        with:
+          version: "3.14"
+
+      - name: Setup Rust
+        uses: actions-ext/rust/setup@main
+
+      - name: Install dependencies
+        run: |
+          make develop
+          uv pip install pyodide-build==0.39.0
+          rustup target add wasm32-unknown-emscripten
+
+      - name: Build Pyodide fixture
+        run: |
+          mkdir -p dist/pyodide
+          pyodide build hatch_rs/tests/test_project_pyodide --outdir dist/pyodide --no-isolation --skip-dependency-check
+
+      - name: Test in Pyodide
+        run: |
+          pyodide venv .venv-pyodide
+          .venv-pyodide/bin/pip install dist/pyodide/*.whl
+          .venv-pyodide/bin/python -c "from pyodide_project.pyodide_project import answer; assert answer() == 42"

.gitignore

@@ -142,6 +142,7 @@ hatch_rs/labextension
 
 # Emscripten SDK (locally installed)
 emsdk
+.pyodide_build
 
 # Mac
 .DS_Store

README.md

@@ -155,5 +155,26 @@ test-command = "python -c \"import project\""
 When cross-building outside cibuildwheel, set `wheel-platform-tag` only if the
 final wheel platform tag is known, for example `manylinux_2_28_x86_64`.
 
+### Pyodide
+
+Pyodide builds are detected from `CARGO_BUILD_TARGET=wasm32-unknown-emscripten`.
+The hook collects Cargo's `.wasm` cdylib, gives it CPython's Emscripten extension
+suffix, and uses `PYODIDE_ABI_VERSION` for the `pyemscripten` wheel platform tag.
+No project-specific build hook is required.
+
+```toml
+[tool.hatch.build.hooks.hatch-rs]
+module = "project"
+path = "."
+
+[tool.cibuildwheel.pyodide]
+xbuild-tools = ["cargo", "rustc", "rustup"]
+test-command = "python -c 'import project.project'"
+```
+
+Rust 1.95 or newer is required to emit an Emscripten shared library for a
+`cdylib` automatically. `wheel-platform-tag` remains available as an explicit
+override when building outside Pyodide's configured environment.
+
 > [!NOTE]
 > This library was generated using [copier](https://copier.readthedocs.io/en/stable/) from the [Base Python Project Template repository](https://github.com/python-project-templates/base).

hatch_rs/structs.py

@@ -41,7 +41,7 @@
 InstallScheme = Literal["package", "shared-data", "shared-scripts", "validate-only"]
 Language = Literal["c", "c++"]
 Binding = Literal["cpython", "pybind11", "nanobind", "generic"]
-Platform = Literal["linux", "darwin", "win32"]
+Platform = Literal["linux", "darwin", "win32", "emscripten"]
 
 
 @dataclass(frozen=True)
@@ -149,6 +149,8 @@ def _normalize_platform(platform: str) -> str:
         return "darwin"
     if normalized.startswith(("linux", "manylinux", "musllinux")):
         return "linux"
+    if normalized.startswith(("emscripten", "pyemscripten")):
+        return "emscripten"
     return normalized
 
 
@@ -181,6 +183,8 @@ def _explicit_target(target: str, *, platform: str, machine: str) -> ResolvedTar
         return ResolvedTarget(platform="darwin", machine=_target_machine(target), triple=target)
     if "-linux-" in target:
         return ResolvedTarget(platform="linux", machine=_target_machine(target), triple=target)
+    if target.endswith("-emscripten"):
+        return ResolvedTarget(platform="emscripten", machine=_target_machine(target), triple=target)
     return ResolvedTarget(platform=platform, machine=machine, triple=target)
 
 
@@ -198,6 +202,8 @@ def shared_library_name(library: str, *, platform: str | None = None) -> str:
         return f"lib{library}.dylib"
     if platform == "linux":
         return f"lib{library}.so"
+    if platform == "emscripten":
+        return f"{library}.wasm"
     raise ValueError(f"Unsupported platform: {platform}")
 
 
@@ -209,12 +215,21 @@ def executable_name(name: str, *, platform: str | None = None) -> str:
     return name
 
 
-def python_extension_name(source_stem: str, *, abi3: bool = False, platform: str | None = None) -> str:
+def python_extension_name(
+    source_stem: str,
+    *,
+    abi3: bool = False,
+    platform: str | None = None,
+    python_version: tuple[int, int] | None = None,
+) -> str:
     """Render the Python extension filename for a Cargo cdylib artifact stem."""
     platform = _normalize_platform(platform or environ.get("HATCH_RUST_PLATFORM", sys_platform))
     module_name = source_stem.removeprefix("lib")
     if platform == "win32":
         return f"{module_name}.pyd"
+    if platform == "emscripten":
+        major, minor = python_version or (version_info.major, version_info.minor)
+        return f"{module_name}.cpython-{major}{minor}-wasm32-emscripten.so"
     if abi3:
         return f"{module_name}.abi3.so"
     return f"{module_name}.so"
@@ -224,6 +239,7 @@ def _resolve_target(target: str | None = None, *, platform: str | None = None, m
     raw_platform = platform or environ.get("HATCH_RUST_PLATFORM", sys_platform)
     platform = _normalize_platform(raw_platform)
     machine = _normalize_machine(machine or environ.get("HATCH_RUST_MACHINE", platform_machine()))
+    target = target or environ.get("CARGO_BUILD_TARGET")
 
     if target:
         return _explicit_target(target, platform=platform, machine=machine)
@@ -292,6 +308,13 @@ def _wheel_platform(resolved_target: ResolvedTarget, platform_tag: str | None) -
             raise _unsupported_machine("macOS wheel", resolved_target.machine, darwin_arches) from error
     if resolved_target.platform == "linux":
         return _linux_wheel_platform(resolved_target, platform_tag)
+    if resolved_target.platform == "emscripten":
+        if platform_tag:
+            return platform_tag
+        abi_version = environ.get("PYODIDE_ABI_VERSION")
+        if not abi_version:
+            raise ValueError("PYODIDE_ABI_VERSION or wheel-platform-tag is required for Emscripten wheel tags.")
+        return f"pyemscripten_{abi_version}_wasm32"
     raise ValueError(f"Unsupported platform for wheel tag: {resolved_target.platform}")
 
 
@@ -308,7 +331,7 @@ def wheel_tag(
     """Render a wheel tag for the resolved Rust target using packaging.tags."""
     resolved = resolved_target or _resolve_target(target, platform=platform, machine=machine)
     version = python_version or (version_info.major, version_info.minor)
-    abis = ["abi3"] if abi3 else None
+    abis = [f"cp{version[0]}{version[1]}"] if resolved.platform == "emscripten" else (["abi3"] if abi3 else None)
     return str(next(cpython_tags(python_version=version, abis=abis, platforms=[_wheel_platform(resolved, platform_tag)])))
 
 
@@ -319,6 +342,8 @@ def _artifact_patterns(platform: str) -> tuple[str, ...]:
         return ("*.so",)
     if platform == "darwin":
         return ("*.dylib",)
+    if platform == "emscripten":
+        return ("*.wasm",)
     raise ValueError(f"Unsupported platform machine: {platform_machine()}")
 
 

hatch_rs/tests/test_project_pyodide/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "hatch-rs-test-pyodide"
+version = "0.1.0"
+edition = "2024"
+publish = false
+
+[lib]
+name = "pyodide_project"
+path = "src/lib.rs"
+crate-type = ["cdylib"]
+
+[dependencies]
+pyo3 = { version = "0.29.0", features = ["abi3", "extension-module"] }
+
+[profile.release]
+panic = "abort"

hatch_rs/tests/test_project_pyodide/pyodide_project/__init__.py

@@ -0,0 +1 @@
+"""Pyodide integration-test package."""

hatch_rs/tests/test_project_pyodide/pyproject.toml

@@ -0,0 +1,16 @@
+[build-system]
+requires = ["hatchling>=1.20"]
+build-backend = "hatchling.build"
+
+[project]
+name = "hatch-rs-test-pyodide"
+version = "0.1.0"
+requires-python = ">=3.14"
+
+[tool.hatch.build.targets.wheel]
+packages = ["pyodide_project"]
+
+[tool.hatch.build.hooks.hatch-rs]
+abi3 = true
+module = "pyodide_project"
+path = "."

hatch_rs/tests/test_project_pyodide/src/lib.rs

@@ -0,0 +1,12 @@
+use pyo3::prelude::*;
+
+#[pyfunction]
+fn answer() -> u8 {
+    42
+}
+
+#[pymodule]
+fn pyodide_project(module: &Bound<'_, PyModule>) -> PyResult<()> {
+    module.add_function(wrap_pyfunction!(answer, module)?)?;
+    Ok(())
+}