From e804200d4141d09d103c4e3eab263a99bebc62d7 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 4 Jun 2024 16:45:34 -0700
Subject: [PATCH 01/12] TST: Fix condition for test_tmpconfigdir_warning

This checks `os.geteuid`, but this is only available on Unix, not
Emscripten or WASM.
---
 lib/matplotlib/tests/test_matplotlib.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/matplotlib/tests/test_matplotlib.py b/lib/matplotlib/tests/test_matplotlib.py
index 37b41fafdb78..3b55b526dbe0 100644
--- a/lib/matplotlib/tests/test_matplotlib.py
+++ b/lib/matplotlib/tests/test_matplotlib.py
@@ -18,9 +18,9 @@ def test_parse_to_version_info(version_str, version_tuple):
     assert matplotlib._parse_to_version_info(version_str) == version_tuple
 
 
-@pytest.mark.skipif(sys.platform == "win32",
+@pytest.mark.skipif(sys.platform not in ["linux", "darwin"],
                     reason="chmod() doesn't work as is on Windows")
-@pytest.mark.skipif(sys.platform != "win32" and os.geteuid() == 0,
+@pytest.mark.skipif(sys.platform in ["linux", "darwin"] and os.geteuid() == 0,
                     reason="chmod() doesn't work as root")
 def test_tmpconfigdir_warning(tmp_path):
     """Test that a warning is emitted if a temporary configdir must be used."""

From ee446a02f81c3588a3377496e395336ac4aa0c34 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 4 Jun 2024 17:15:43 -0700
Subject: [PATCH 02/12] Ignore threading errors when preparing font cache

In Enscripten/WASM, this module can be imported, but doesn't work, so we
can't fall back to `dummy_threading` at import-time as we used to do.
---
 lib/matplotlib/font_manager.py | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
index 9aa8dccde444..f922f13e5e78 100644
--- a/lib/matplotlib/font_manager.py
+++ b/lib/matplotlib/font_manager.py
@@ -1092,9 +1092,12 @@ def __init__(self, size=None, weight='normal'):
         self.ttflist = []
 
         # Delay the warning by 5s.
-        timer = threading.Timer(5, lambda: _log.warning(
-            'Matplotlib is building the font cache; this may take a moment.'))
-        timer.start()
+        try:
+            timer = threading.Timer(5, lambda: _log.warning(
+                'Matplotlib is building the font cache; this may take a moment.'))
+            timer.start()
+        except RuntimeError:
+            timer = None
         try:
             for fontext in ["afm", "ttf"]:
                 for path in [*findSystemFonts(paths, fontext=fontext),
@@ -1107,7 +1110,8 @@ def __init__(self, size=None, weight='normal'):
                         _log.info("Failed to extract font properties from %s: "
                                   "%s", path, exc)
         finally:
-            timer.cancel()
+            if timer:
+                timer.cancel()
 
     def addfont(self, path):
         """

From 522c318c8f5ce4bd7e8b695ad0707592c120d691 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 4 Jun 2024 17:28:28 -0700
Subject: [PATCH 03/12] Don't attempt to load system fonts on Emscripten

The file system is either sandboxed or there are simply no other fonts,
so limit ourselves to our pre-shipped fonts.
---
 lib/matplotlib/font_manager.py            | 3 +++
 lib/matplotlib/tests/test_font_manager.py | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
index f922f13e5e78..cac7ea4eba1b 100644
--- a/lib/matplotlib/font_manager.py
+++ b/lib/matplotlib/font_manager.py
@@ -287,6 +287,9 @@ def findSystemFonts(fontpaths=None, fontext='ttf'):
         if sys.platform == 'win32':
             installed_fonts = _get_win32_installed_fonts()
             fontpaths = []
+        elif sys.platform == 'emscripten':
+            installed_fonts = []
+            fontpaths = []
         else:
             installed_fonts = _get_fontconfig_fonts()
             if sys.platform == 'darwin':
diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
index d15b892b3eea..d9c03c8465af 100644
--- a/lib/matplotlib/tests/test_font_manager.py
+++ b/lib/matplotlib/tests/test_font_manager.py
@@ -20,7 +20,7 @@
 from matplotlib.testing import subprocess_run_helper, subprocess_run_for_testing
 
 
-has_fclist = shutil.which('fc-list') is not None
+has_fclist = sys.platform != 'emscripten' and shutil.which('fc-list') is not None
 
 
 def test_font_priority():

From 94c0924edfe652363bceb7bdcc5e6812aeadbf06 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Thu, 26 Sep 2024 06:14:03 -0400
Subject: [PATCH 04/12] ft2font: Explicitly cast dimensions when creating
 Python buffer

On WASM, which is wholly 32-bit, casting unsigned int to signed long is
a narrowing conversion, which it seems to treat as an error. The Agg
buffer cannot be over `(1<<23)` in width or height, so this cast is
safe even with the smaller sizes.
---
 src/_backend_agg_wrapper.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/_backend_agg_wrapper.cpp b/src/_backend_agg_wrapper.cpp
index 269e2aaa9ee5..2bad7f4d0b9f 100644
--- a/src/_backend_agg_wrapper.cpp
+++ b/src/_backend_agg_wrapper.cpp
@@ -250,12 +250,12 @@ PYBIND11_MODULE(_backend_agg, m, py::mod_gil_not_used())
 
         .def_buffer([](RendererAgg *renderer) -> py::buffer_info {
             std::vector<py::ssize_t> shape {
-                renderer->get_height(),
-                renderer->get_width(),
+                static_cast<py::ssize_t>(renderer->get_height()),
+                static_cast<py::ssize_t>(renderer->get_width()),
                 4
             };
             std::vector<py::ssize_t> strides {
-                renderer->get_width() * 4,
+                static_cast<py::ssize_t>(renderer->get_width() * 4),
                 4,
                 1
             };

From f2a3abc8a1decf1ca5dffb3d6dcf149c76092e53 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 5 Nov 2024 04:33:59 -0500
Subject: [PATCH 05/12] wasm: Skip more subprocess & thread tests

---
 lib/matplotlib/animation.py               | 2 ++
 lib/matplotlib/dviread.py                 | 4 ++--
 lib/matplotlib/testing/__init__.py        | 5 ++++-
 lib/matplotlib/testing/decorators.py      | 2 ++
 lib/matplotlib/tests/test_animation.py    | 4 ++++
 lib/matplotlib/tests/test_dviread.py      | 3 ++-
 lib/matplotlib/tests/test_figure.py       | 5 +++++
 lib/matplotlib/tests/test_font_manager.py | 2 ++
 lib/matplotlib/texmanager.py              | 8 ++++----
 9 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/lib/matplotlib/animation.py b/lib/matplotlib/animation.py
index a0236a6956cb..1fc39560801b 100644
--- a/lib/matplotlib/animation.py
+++ b/lib/matplotlib/animation.py
@@ -360,6 +360,8 @@ def bin_path(cls):
     @classmethod
     def isAvailable(cls):
         """Return whether a MovieWriter subclass is actually available."""
+        if sys.platform == 'emscripten':
+            return False
         return shutil.which(cls.bin_path()) is not None
 
 
diff --git a/lib/matplotlib/dviread.py b/lib/matplotlib/dviread.py
index bd21367ce73d..6d6d66e56944 100644
--- a/lib/matplotlib/dviread.py
+++ b/lib/matplotlib/dviread.py
@@ -1070,7 +1070,7 @@ def find_tex_file(filename):
 
     try:
         lk = _LuatexKpsewhich()
-    except FileNotFoundError:
+    except (FileNotFoundError, OSError):
         lk = None  # Fallback to directly calling kpsewhich, as below.
 
     if lk:
@@ -1090,7 +1090,7 @@ def find_tex_file(filename):
             path = (cbook._check_and_log_subprocess(['kpsewhich', filename],
                                                     _log, **kwargs)
                     .rstrip('\n'))
-        except (FileNotFoundError, RuntimeError):
+        except (FileNotFoundError, OSError, RuntimeError):
             path = None
 
     if path:
diff --git a/lib/matplotlib/testing/__init__.py b/lib/matplotlib/testing/__init__.py
index 19113d399626..4731848aa6b1 100644
--- a/lib/matplotlib/testing/__init__.py
+++ b/lib/matplotlib/testing/__init__.py
@@ -88,6 +88,9 @@ def subprocess_run_for_testing(command, env=None, timeout=60, stdout=None,
     pytest.xfail
         If platform is Cygwin and subprocess reports a fork() failure.
     """
+    if sys.platform == 'emscripten':
+        import pytest
+        pytest.skip('emscripten does not support subprocesses')
     if capture_output:
         stdout = stderr = subprocess.PIPE
     try:
@@ -175,7 +178,7 @@ def _has_tex_package(package):
     try:
         mpl.dviread.find_tex_file(f"{package}.sty")
         return True
-    except FileNotFoundError:
+    except (FileNotFoundError, OSError):
         return False
 
 
diff --git a/lib/matplotlib/testing/decorators.py b/lib/matplotlib/testing/decorators.py
index 6f1af7debdb3..82900fa7d4e8 100644
--- a/lib/matplotlib/testing/decorators.py
+++ b/lib/matplotlib/testing/decorators.py
@@ -138,6 +138,8 @@ def copy_baseline(self, baseline, extension):
             try:
                 if 'microsoft' in uname().release.lower():
                     raise OSError  # On WSL, symlink breaks silently
+                if sys.platform == 'emscripten':
+                    raise OSError
                 os.symlink(orig_expected_path, expected_fname)
             except OSError:  # On Windows, symlink *may* be unavailable.
                 shutil.copyfile(orig_expected_path, expected_fname)
diff --git a/lib/matplotlib/tests/test_animation.py b/lib/matplotlib/tests/test_animation.py
index d026dae59533..a47c92ed648a 100644
--- a/lib/matplotlib/tests/test_animation.py
+++ b/lib/matplotlib/tests/test_animation.py
@@ -278,6 +278,8 @@ def test_no_length_frames(anim):
     anim.save('unused.null', writer=NullMovieWriter())
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten',
+                    reason='emscripten does not support subprocesses')
 def test_movie_writer_registry():
     assert len(animation.writers._registered) > 0
     mpl.rcParams['animation.ffmpeg_path'] = "not_available_ever_xxxx"
@@ -546,6 +548,8 @@ def test_disable_cache_warning(anim):
 def test_movie_writer_invalid_path(anim):
     if sys.platform == "win32":
         match_str = r"\[WinError 3] .*'\\\\foo\\\\bar\\\\aardvark'"
+    elif sys.platform == "emscripten":
+        match_str = r"\[Errno 44] .*'/foo"
     else:
         match_str = r"\[Errno 2] .*'/foo"
     with pytest.raises(FileNotFoundError, match=match_str):
diff --git a/lib/matplotlib/tests/test_dviread.py b/lib/matplotlib/tests/test_dviread.py
index 7b7ff151be18..2aa3abe12e4b 100644
--- a/lib/matplotlib/tests/test_dviread.py
+++ b/lib/matplotlib/tests/test_dviread.py
@@ -1,6 +1,7 @@
 import json
 from pathlib import Path
 import shutil
+import sys
 
 import matplotlib.dviread as dr
 import pytest
@@ -60,7 +61,7 @@ def test_PsfontsMap(monkeypatch):
         fontmap[b'%']
 
 
-@pytest.mark.skipif(shutil.which("kpsewhich") is None,
+@pytest.mark.skipif(sys.platform == "emscripten" or shutil.which("kpsewhich") is None,
                     reason="kpsewhich is not available")
 def test_dviread():
     dirpath = Path(__file__).parent / 'baseline_images/dviread'
diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
index edf5ea05f119..d71dca15e7c3 100644
--- a/lib/matplotlib/tests/test_figure.py
+++ b/lib/matplotlib/tests/test_figure.py
@@ -3,6 +3,7 @@
 import io
 import pickle
 import platform
+import sys
 from threading import Timer
 from types import SimpleNamespace
 import warnings
@@ -1605,6 +1606,8 @@ def test_add_axes_kwargs():
     plt.close()
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten',
+                    reason='emscripten does not support threads')
 def test_ginput(recwarn):  # recwarn undoes warn filters at exit.
     warnings.filterwarnings("ignore", "cannot show the figure")
     fig, ax = plt.subplots()
@@ -1627,6 +1630,8 @@ def multi_presses():
     np.testing.assert_allclose(fig.ginput(3), [(.3, .4), (.5, .6)])
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten',
+                    reason='emscripten does not support threads')
 def test_waitforbuttonpress(recwarn):  # recwarn undoes warn filters at exit.
     warnings.filterwarnings("ignore", "cannot show the figure")
     fig = plt.figure()
diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
index d9c03c8465af..21e1c16075fa 100644
--- a/lib/matplotlib/tests/test_font_manager.py
+++ b/lib/matplotlib/tests/test_font_manager.py
@@ -228,6 +228,8 @@ def _model_handler(_):
     plt.close()
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten',
+                    reason='emscripten does not support subprocesses')
 @pytest.mark.skipif(not hasattr(os, "register_at_fork"),
                     reason="Cannot register at_fork handlers")
 def test_fork():
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
index a374bfba8cab..85417be32fb0 100644
--- a/lib/matplotlib/texmanager.py
+++ b/lib/matplotlib/texmanager.py
@@ -247,10 +247,6 @@ def _run_checked_subprocess(cls, command, tex, *, cwd=None):
             report = subprocess.check_output(
                 command, cwd=cwd if cwd is not None else cls._texcache,
                 stderr=subprocess.STDOUT)
-        except FileNotFoundError as exc:
-            raise RuntimeError(
-                f'Failed to process string with tex because {command[0]} '
-                'could not be found') from exc
         except subprocess.CalledProcessError as exc:
             raise RuntimeError(
                 '{prog} was not able to process the following string:\n'
@@ -263,6 +259,10 @@ def _run_checked_subprocess(cls, command, tex, *, cwd=None):
                     tex=tex.encode('unicode_escape'),
                     exc=exc.output.decode('utf-8', 'backslashreplace'))
                 ) from None
+        except (FileNotFoundError, OSError) as exc:
+            raise RuntimeError(
+                f'Failed to process string with tex because {command[0]} '
+                'could not be found') from exc
         _log.debug(report)
         return report
 

From 2e4450c63d27787cbb30e2a84c676763fb2294cd Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Mon, 22 Aug 2022 18:43:28 -0400
Subject: [PATCH 06/12] Use old stride_windows implementation on 32-bit builds

This was originally for i686 on Fedora, but is now applicable to WASM,
which is 32-bit. The older implementation doesn't OOM.
---
 lib/matplotlib/mlab.py | 39 +++++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/lib/matplotlib/mlab.py b/lib/matplotlib/mlab.py
index 8326ac186e31..bdaa34b73427 100644
--- a/lib/matplotlib/mlab.py
+++ b/lib/matplotlib/mlab.py
@@ -49,6 +49,7 @@
 
 import functools
 from numbers import Number
+import sys
 
 import numpy as np
 
@@ -210,6 +211,30 @@ def detrend_linear(y):
     return y - (b*x + a)
 
 
+def _stride_windows(x, n, noverlap=0):
+    if noverlap >= n:
+        raise ValueError('noverlap must be less than n')
+    if n < 1:
+        raise ValueError('n cannot be less than 1')
+
+    x = np.asarray(x)
+
+    if n == 1 and noverlap == 0:
+        return x[np.newaxis]
+    if n > x.size:
+        raise ValueError('n cannot be greater than the length of x')
+
+    # np.lib.stride_tricks.as_strided easily leads to memory corruption for
+    # non integer shape and strides, i.e. noverlap or n. See #3845.
+    noverlap = int(noverlap)
+    n = int(n)
+
+    step = n - noverlap
+    shape = (n, (x.shape[-1]-noverlap)//step)
+    strides = (x.strides[0], step*x.strides[0])
+    return np.lib.stride_tricks.as_strided(x, shape=shape, strides=strides)
+
+
 def _spectral_helper(x, y=None, NFFT=None, Fs=None, detrend_func=None,
                      window=None, noverlap=None, pad_to=None,
                      sides=None, scale_by_freq=None, mode=None):
@@ -304,8 +329,11 @@ def _spectral_helper(x, y=None, NFFT=None, Fs=None, detrend_func=None,
         raise ValueError(
             "The window length must match the data's first dimension")
 
-    result = np.lib.stride_tricks.sliding_window_view(
-        x, NFFT, axis=0)[::NFFT - noverlap].T
+    if sys.maxsize > 2**32:  # NumPy version on 32-bit OOMs.
+        result = np.lib.stride_tricks.sliding_window_view(
+            x, NFFT, axis=0)[::NFFT - noverlap].T
+    else:
+        result = _stride_windows(x, NFFT, noverlap=noverlap)
     result = detrend(result, detrend_func, axis=0)
     result = result * window.reshape((-1, 1))
     result = np.fft.fft(result, n=pad_to, axis=0)[:numFreqs, :]
@@ -313,8 +341,11 @@ def _spectral_helper(x, y=None, NFFT=None, Fs=None, detrend_func=None,
 
     if not same_data:
         # if same_data is False, mode must be 'psd'
-        resultY = np.lib.stride_tricks.sliding_window_view(
-            y, NFFT, axis=0)[::NFFT - noverlap].T
+        if sys.maxsize > 2**32:  # NumPy version on 32-bit OOMs.
+            resultY = np.lib.stride_tricks.sliding_window_view(
+                y, NFFT, axis=0)[::NFFT - noverlap].T
+        else:
+            resultY = _stride_windows(y, NFFT, noverlap=noverlap)
         resultY = detrend(resultY, detrend_func, axis=0)
         resultY = resultY * window.reshape((-1, 1))
         resultY = np.fft.fft(resultY, n=pad_to, axis=0)[:numFreqs, :]

From 2f92b80bd11a718a090e176b13fdc1f867b83a16 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 5 Nov 2024 06:14:35 -0500
Subject: [PATCH 07/12] Skip tests that OOM on WASM

---
 lib/matplotlib/tests/test_agg.py   | 2 ++
 lib/matplotlib/tests/test_image.py | 1 +
 2 files changed, 3 insertions(+)

diff --git a/lib/matplotlib/tests/test_agg.py b/lib/matplotlib/tests/test_agg.py
index 59387793605a..2a2a97f074aa 100644
--- a/lib/matplotlib/tests/test_agg.py
+++ b/lib/matplotlib/tests/test_agg.py
@@ -1,4 +1,5 @@
 import io
+import sys
 
 import numpy as np
 from numpy.testing import assert_array_almost_equal
@@ -279,6 +280,7 @@ def test_draw_path_collection_error_handling():
         fig.canvas.draw()
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten', reason='Too large for emscripten VM')
 def test_chunksize_fails():
     # NOTE: This test covers multiple independent test scenarios in a single
     #       function, because each scenario uses ~2GB of memory and we don't
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
index 24a0ab929bbf..f82aad388f6d 100644
--- a/lib/matplotlib/tests/test_image.py
+++ b/lib/matplotlib/tests/test_image.py
@@ -1507,6 +1507,7 @@ def test_rc_interpolation_stage():
             mpl.rcParams["image.interpolation_stage"] = val
 
 
+@pytest.mark.skipif(sys.platform == 'emscripten', reason='Figure too large for WASM')
 # We check for the warning with a draw() in the test, but we also need to
 # filter the warning as it is emitted by the figure test decorator
 @pytest.mark.filterwarnings(r'ignore:Data with more than .* '

From 9099e9e788137669bde138cfcd94134ca6547a85 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Wed, 6 Nov 2024 05:20:05 -0500
Subject: [PATCH 08/12] Skip tests that expect LinAlgError on WASM

---
 lib/matplotlib/tests/test_mlab.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/matplotlib/tests/test_mlab.py b/lib/matplotlib/tests/test_mlab.py
index 3b0d2529b5f1..3496027bb2f6 100644
--- a/lib/matplotlib/tests/test_mlab.py
+++ b/lib/matplotlib/tests/test_mlab.py
@@ -1,3 +1,5 @@
+import sys
+
 from numpy.testing import (assert_allclose, assert_almost_equal,
                            assert_array_equal, assert_array_almost_equal_nulp)
 import numpy as np
@@ -873,6 +875,8 @@ def test_single_dataset_element(self):
         with pytest.raises(ValueError):
             mlab.GaussianKDE([42])
 
+    @pytest.mark.skipif(sys.platform == 'emscripten',
+                        reason="WASM doesn't support floating-point exceptions")
     def test_silverman_multidim_dataset(self):
         """Test silverman's for a multi-dimensional array."""
         x1 = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
@@ -886,6 +890,8 @@ def test_silverman_singledim_dataset(self):
         y_expected = 0.76770389927475502
         assert_almost_equal(mygauss.covariance_factor(), y_expected, 7)
 
+    @pytest.mark.skipif(sys.platform == 'emscripten',
+                        reason="WASM doesn't support floating-point exceptions")
     def test_scott_multidim_dataset(self):
         """Test scott's output for a multi-dimensional array."""
         x1 = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

From 7a30cf3fe874d410fe759424b4f46a6e9b57bc65 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Wed, 6 Nov 2024 00:25:44 -0500
Subject: [PATCH 09/12] ci: Add a build for wasm

This adds a `pyproject.toml` config for it, so you can replicate locally
with cibuildwheel.
---
 .github/workflows/wasm.yml | 58 ++++++++++++++++++++++++++++++++++++++
 pyproject.toml             | 14 +++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 .github/workflows/wasm.yml

diff --git a/.github/workflows/wasm.yml b/.github/workflows/wasm.yml
new file mode 100644
index 000000000000..dc854a353588
--- /dev/null
+++ b/.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
diff --git a/pyproject.toml b/pyproject.toml
index 48a174731440..0771404fbf10 100644
--- a/pyproject.toml
+++ b/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"
+[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"

From f1b6047c54681f4768b2aae0f2e631a9c7aabd95 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Wed, 6 Nov 2024 01:20:52 -0500
Subject: [PATCH 10/12] Open symbol visibility for FreeType on wasm

---
 subprojects/packagefiles/freetype-2.6.1-meson/meson.build | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/subprojects/packagefiles/freetype-2.6.1-meson/meson.build b/subprojects/packagefiles/freetype-2.6.1-meson/meson.build
index 9a5180ef7586..1fd4bc44e7b5 100644
--- a/subprojects/packagefiles/freetype-2.6.1-meson/meson.build
+++ b/subprojects/packagefiles/freetype-2.6.1-meson/meson.build
@@ -179,11 +179,17 @@ ft_config_headers += [configure_file(input: 'include/freetype/config/ftoption.h.
   output: 'ftoption.h',
   configuration: conf)]
 
+if cc.get_id() == 'emscripten'
+  kwargs = {}
+else
+  kwargs = {'gnu_symbol_visibility': 'inlineshidden'}
+endif
+
 libfreetype = static_library('freetype', base_sources,
   include_directories: incbase,
   dependencies: deps,
   c_args: c_args,
-  gnu_symbol_visibility: 'inlineshidden',
+  kwargs: kwargs
 )
 
 freetype_dep = declare_dependency(

From 52579fa157b2539ec3647fe5dc9dd92bba598609 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Thu, 7 Nov 2024 18:53:55 -0500
Subject: [PATCH 11/12] TST: Avoid using os.devnull for path tests

On wasm, this file doesn't support seeking, which is sometimes necessary
depending on file type.
---
 lib/matplotlib/tests/test_backend_pdf.py | 5 ++---
 lib/matplotlib/tests/test_image.py       | 4 ++--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/lib/matplotlib/tests/test_backend_pdf.py b/lib/matplotlib/tests/test_backend_pdf.py
index c816c4715ae2..f220a70788a6 100644
--- a/lib/matplotlib/tests/test_backend_pdf.py
+++ b/lib/matplotlib/tests/test_backend_pdf.py
@@ -1,7 +1,6 @@
 import datetime
 import decimal
 import io
-import os
 from pathlib import Path
 
 import numpy as np
@@ -307,8 +306,8 @@ def test_text_urls_tex():
             assert annot.Rect[1] == decimal.Decimal('0.7') * 72
 
 
-def test_pdfpages_fspath():
-    with PdfPages(Path(os.devnull)) as pdf:
+def test_pdfpages_fspath(tmp_path):
+    with PdfPages(tmp_path / 'unused.pdf') as pdf:
         pdf.savefig(plt.figure())
 
 
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
index f82aad388f6d..6135bb7dd167 100644
--- a/lib/matplotlib/tests/test_image.py
+++ b/lib/matplotlib/tests/test_image.py
@@ -193,8 +193,8 @@ def test_imsave_rgba_origin(origin):
 
 
 @pytest.mark.parametrize("fmt", ["png", "pdf", "ps", "eps", "svg"])
-def test_imsave_fspath(fmt):
-    plt.imsave(Path(os.devnull), np.array([[0, 1]]), format=fmt)
+def test_imsave_fspath(fmt, tmp_path):
+    plt.imsave(tmp_path / f'unused.{fmt}', np.array([[0, 1]]), format=fmt)
 
 
 def test_imsave_color_alpha():

From 98a8b8c07094dd3b21ac4907ce0255b3fe4f4c65 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Thu, 7 Nov 2024 19:23:36 -0500
Subject: [PATCH 12/12] Add wasm build to cibuildwheel label

---
 .github/labeler.yml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/.github/labeler.yml b/.github/labeler.yml
index 75adfed57f43..77b79146b47f 100644
--- a/.github/labeler.yml
+++ b/.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']