ci: Add a build for wasm

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

Author: QuLogic

.github/labeler.yml

@@ -1,7 +1,9 @@
 ---
 "CI: Run cibuildwheel":
   - changed-files:
-      - any-glob-to-any-file: ['.github/workflows/cibuildwheel.yml']
+      - any-glob-to-any-file:
+          - '.github/workflows/cibuildwheel.yml'
+          - '.github/workflows/wasm.yml'
 "CI: Run cygwin":
   - changed-files:
       - any-glob-to-any-file: ['.github/workflows/cygwin.yml']

.github/workflows/nightlies.yml

@@ -31,28 +31,28 @@ jobs:
         run: |
           PROJECT_REPO="matplotlib/matplotlib"
           BRANCH="main"
-          WORKFLOW_NAME="cibuildwheel.yml"
           ARTIFACT_PATTERN="cibw-wheels-*"
 
-          gh run --repo "${PROJECT_REPO}" \
-             list --branch "${BRANCH}" \
-                  --workflow "${WORKFLOW_NAME}" \
-                  --json event,status,conclusion,databaseId > runs.json
-          RUN_ID=$(
-            jq --compact-output \
-              '[
-                .[] |
-                # Filter on "push" events to main (merged PRs) ...
-                select(.event == "push") |
-                # that have completed successfully ...
-                select(.status == "completed" and .conclusion == "success")
-               ] |
-              # and get ID of latest build of wheels.
-              sort_by(.databaseId) | reverse | .[0].databaseId' runs.json
-          )
-          gh run --repo "${PROJECT_REPO}" view "${RUN_ID}"
-          gh run --repo "${PROJECT_REPO}" \
-             download "${RUN_ID}" --pattern "${ARTIFACT_PATTERN}"
+          for WORKFLOW_NAME in cibuildwheel.yml wasm.yml; do
+            gh run --repo "${PROJECT_REPO}" \
+               list --branch "${BRANCH}" \
+                    --workflow "${WORKFLOW_NAME}" \
+                    --json event,status,conclusion,databaseId > runs.json
+            RUN_ID=$(
+              jq --compact-output \
+                '[
+                  .[] |
+                  # Filter on "push" events to main (merged PRs) ...
+                  select(.event == "push") |
+                  # that have completed successfully ...
+                  select(.status == "completed" and .conclusion == "success")
+                 ] |
+                # and get ID of latest build of wheels.
+                sort_by(.databaseId) | reverse | .[0].databaseId' runs.json
+            )
+            gh run --repo "${PROJECT_REPO}" view "${RUN_ID}"
+            gh run --repo "${PROJECT_REPO}" download "${RUN_ID}" --pattern "${ARTIFACT_PATTERN}"
+          done
 
           mkdir dist
           mv ${ARTIFACT_PATTERN}/*.whl dist/

.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@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065  # v5.6.0
+        name: Install Python
+        with:
+          python-version: '3.13'
+
+      - name: Build wheels for wasm
+        uses: pypa/cibuildwheel@faf86a6ed7efa889faf6996aa23820831055001a  # v2.23.3
+        env:
+          CIBW_PLATFORM: "pyodide"
+
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02  # v4.6.2
+        with:
+          name: cibw-wheels-wasm
+          path: ./wheelhouse/*.whl
+          if-no-files-found: error

pyproject.toml

@@ -340,3 +340,23 @@ testpaths = ["lib"]
 addopts = [
     "--import-mode=importlib",
 ]
+
+[tool.cibuildwheel.pyodide]
+test-requires = "pytest"
+test-command = [
+    # Wheels are built without test images, so copy them into the testing directory.
+    "basedir=$(python -c 'import pathlib, matplotlib; print(pathlib.Path(matplotlib.__file__).parent.parent)')",
+    "cp -a {package}/lib/matplotlib/tests/data $basedir/matplotlib/tests/",
+    """
+    for subdir in matplotlib mpl_toolkits/axes_grid1 mpl_toolkits/axisartist mpl_toolkits/mplot3d; do
+        cp -a {package}/lib/${subdir}/tests/baseline_images $basedir/${subdir}/tests/
+    done""",
+    # Test installed, not repository, copy as we aren't using an editable install.
+    "pytest -p no:cacheprovider --pyargs matplotlib mpl_toolkits.axes_grid1 mpl_toolkits.axisartist mpl_toolkits.mplot3d",
+]
+[tool.cibuildwheel.pyodide.environment]
+# Exceptions are needed for pybind11:
+# https://github.com/pybind/pybind11/pull/5298
+CFLAGS = "-fexceptions"
+CXXFLAGS = "-fexceptions"
+LDFLAGS = "-fexceptions"