feat: pyemscripten platform tag (PEP 783), 314.0a1, pyodide-eol flag, and maintenance updates (#2812)

* Use `pyodide config get emscripten_dir`

* Update constraints

* Updates for `pyemscripten` platform tag

* Weird constraints stuff...

* Revert "Weird constraints stuff..."

This reverts commit 4bd785de872269c0b27362ee800f17288b2b4789.

* Add some special constraints for pyodide

* Wheel pyemscripten collision

* Put delocate back in constraints (not needed tho)

* Drop Pyodide 0.27.7 (cp312-pyodide_wasm32)

* Add Pyodide 314.0.0a1 (cp314-pyodide_wasm32)

* Delete no-longer-needed Pyodide 312 constraints

* Update Pyodide 313 and 314 constraints

* Add back prerelease stuff and update tests

* Fix `test_pyodide_on_windows`

* Update and fix tests some more

* Also enable pyodide-prerelease in GHA sample build

* Update tests yet again (`SINGLE_PYTHON_VERSION` changes)

* Add a Pyodide-specific maintenance guide

* Add suggestions from Hood and Gyeongjae

Co-Authored-By: Hood Chatham <roberthoodchatham@gmail.com>
Co-Authored-By: Gyeongjae Choi <def6488@gmail.com>

* Add "Last updated: May 2026" to Pyodide document

* Add a Pyodide EOL filter

* Fix typo

* Update maintenance docs about EoL Pyodide

* Add Pyodide 312 constraints back

* Update Pyodide 313 and 314 constraints

* Remove "experimental" note about Pyodide

* Remove another experimental Pyodide sentence

* Add docs about the `pyodide-eol` enable option

---------

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
Co-authored-by: Gyeongjae Choi <def6488@gmail.com>
Co-authored-by: Henry Schreiner <henryfs@princeton.edu>

cibuildwheel/platforms/pyodide.py

@@ -94,20 +94,19 @@ def ensure_node(major_version: str) -> Path:
     return path
 
 
-def install_emscripten(
-    env: dict[str, str], version: str, xbuildenv_cache_path: Path, pyodide_version: str
-) -> Path:
+def install_emscripten(env: dict[str, str], version: str, xbuildenv_cache_path: Path) -> Path:
     """Install Emscripten via pyodide-build, which also applies Pyodide-specific patches."""
-    emcc_path = (
-        xbuildenv_cache_path / pyodide_version / "emsdk" / "upstream" / "emscripten" / "emcc"
+    emscripten_dir = Path(
+        call("pyodide", "config", "get", "emscripten_dir", env=env, capture_stdout=True).strip()
     )
     with FileLock(CIBW_CACHE_PATH / "emscripten.lock"):
-        if emcc_path.exists():
-            return emcc_path
+        if emscripten_dir.exists():
+            return emscripten_dir
         call(
             "pyodide",
             "xbuildenv",
             "install-emscripten",
+            "--force",
             "--version",
             version,
             "--path",
@@ -115,8 +114,8 @@ def install_emscripten(
             env=env,
             cwd=CIBW_CACHE_PATH,
         )
-    assert emcc_path.exists()
-    return emcc_path
+    assert emscripten_dir.exists()
+    return emscripten_dir
 
 
 def get_all_xbuildenv_version_info(env: dict[str, str]) -> list[PyodideXBuildEnvInfo]:
@@ -315,9 +314,9 @@ def setup_python(
     log.step(
         f"Installing Emscripten {emscripten_version} and applying Pyodide-specific patches ..."
     )
-    emcc_path = install_emscripten(env, emscripten_version, xbuildenv_cache_path, pyodide_version)
+    emscripten_dir = install_emscripten(env, emscripten_version, xbuildenv_cache_path)
 
-    env["PATH"] = os.pathsep.join([str(emcc_path.parent), env["PATH"]])
+    env["PATH"] = os.pathsep.join([str(emscripten_dir), env["PATH"]])
 
     return env