Cap cython<3 (#4001)

I added tools/constraints.txt and set it into the PIP_CONSTRAINT environment variable.

Makefile.envs

@@ -53,6 +53,8 @@ export PYODIDE_BASE_URL?=./
 # Brotli compression.
 export PYODIDE_ZIP_COMPRESSION_LEVEL?=6
 
+export PIP_CONSTRAINT=$(PYODIDE_ROOT)/tools/constraints.txt
+
 # For packages that depend on numpy.
 # TODO: maybe move this somewhere else?
 export NUMPY_LIB=$(HOSTSITEPACKAGES)/numpy/

pyodide-build/pyodide_build/build_env.py

@@ -37,6 +37,7 @@ BUILD_VARS: set[str] = {
     "PATH",
     "PKG_CONFIG_PATH",
     "PLATFORM_TRIPLET",
+    "PIP_CONSTRAINT",
     "PYMAJOR",
     "PYMICRO",
     "PYMINOR",

pyodide-build/pyodide_build/create_xbuildenv.py

@@ -57,6 +57,7 @@ def _copy_wasm_libs(
         Path("dist/pyodide-lock.json"),
         Path("dist/python"),
         Path("dist/python_stdlib.zip"),
+        Path("tools/constraints.txt"),
     ]
     to_copy.extend(
         x.relative_to(pyodide_root) for x in (pyodide_root / "dist").glob("pyodide.*")

tools/constraints.txt

@@ -0,0 +1,4 @@
+cython<3
+# Remove the following when mypy releases a new version
+# https://github.com/python/mypy/pull/14788
+types-setuptools<67.4.0.2