ci: Add a build for wasm

This adds a `pyproject.toml` config for it, so you can replicate locally
with cibuildwheel.

Author: QuLogic

.github/workflows/wasm.yml

@@ -0,0 +1,58 @@
+---
+name: Build wasm wheels
+
+on:
+  # Save CI by only running this on release branches or tags.
+  push:
+    branches:
+      - main
+      - v[0-9]+.[0-9]+.x
+    tags:
+      - v*
+  # Also allow running this action on PRs if requested by applying the
+  # "Run cibuildwheel" label.
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
+
+permissions:
+  contents: read
+
+jobs:
+  build_wasm:
+    if: >-
+      github.event_name == 'push' ||
+      github.event_name == 'pull_request' && (
+        (
+          github.event.action == 'labeled' &&
+          github.event.label.name == 'CI: Run cibuildwheel'
+        ) ||
+        contains(github.event.pull_request.labels.*.name,
+                 'CI: Run cibuildwheel')
+      )
+    name: Build wasm
+    runs-on: ubuntu-24.04
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@v5
+        name: Install Python
+        with:
+          python-version: '3.12'
+
+      - name: Build wheels for wasm
+        uses: pypa/cibuildwheel@7940a4c0e76eb2030e473a5f864f291f63ee879b  # v2.21.3
+        env:
+          CIBW_PLATFORM: "pyodide"
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: cibw-wheels-${{ runner.os }}-${{ matrix.cibw_archs }}
+          path: ./wheelhouse/*.whl
+          if-no-files-found: error

pyproject.toml

@@ -318,3 +318,17 @@ testpaths = ["lib"]
 addopts = [
     "--import-mode=importlib",
 ]
+
+# This build is just for testing right now.
+[tool.cibuildwheel.pyodide]
+build-frontend = "build; args: --exports whole_archive"
+test-requires = "pytest"
+test-command = "pytest -p no:cacheprovider --pyargs matplotlib --maxfail=50 -v"
+[tool.cibuildwheel.pyodide.config-settings]
+install-args = "--tags=data,python-runtime,runtime,tests"
+[tool.cibuildwheel.pyodide.environment]
+# Exceptions are needed for pybind11:
+# https://github.com/pybind/pybind11/pull/5298
+CFLAGS = "-fexceptions"
+CXXFLAGS = "-fexceptions"
+LDFLAGS = "-fexceptions"