Allow globally forcing C file regeneration by setting the env var...

Allow globally forcing C file regeneration by setting the env var CYTHON_FORCE_REGEN=1, e.g. from external build systems.

CHANGES.rst

@@ -24,6 +24,9 @@ Features added
 * ``cythonize()`` and the corresponding CLI command now regenerate the output files
   also when they already exist but were generated by a different Cython version.
 
+* The environment variable ``CYTHON_FORCE_REGEN=1`` can be used to force ``cythonize``
+  to regenerate the output files regardless of modification times and changes.
+
 * The generated C code now compiles in CPython 3.11a4.
   (Github issue :issue:`4500`)
 

Cython/Build/Dependencies.py

@@ -883,7 +883,7 @@ def create_extension_list(patterns, exclude=None, ctx=None, aliases=None, quiet=
 
 
 # This is the user-exposed entry point.
-def cythonize(module_list, exclude=None, nthreads=0, aliases=None, quiet=False, force=False, language=None,
+def cythonize(module_list, exclude=None, nthreads=0, aliases=None, quiet=False, force=None, language=None,
               exclude_failures=False, show_all_warnings=False, **options):
     """
     Compile a set of source modules into C/C++ files and return a list of distutils
@@ -976,6 +976,9 @@ def cythonize(module_list, exclude=None, nthreads=0, aliases=None, quiet=False,
         pythran_options.cplus = True
         pythran_options.np_pythran = True
 
+    if force is None:
+        force = os.environ.get("CYTHON_FORCE_REGEN") == "1"  # allow global overrides for build systems
+
     c_options = CompilationOptions(**options)
     cpp_options = CompilationOptions(**options); cpp_options.cplus = True
     ctx = Context.from_options(c_options)

tests/build/cythonize_newer_files.srctree

@@ -7,6 +7,7 @@ PYTHON test.py
 ######## test.py ########
 
 import os.path
+import time
 
 from Cython.Utils import GENERATED_BY_MARKER_BYTES, clear_function_caches, clear_method_caches
 from Cython.Build.Dependencies import cythonize, DependencyTree
@@ -85,3 +86,11 @@ with open("a.c", "rb") as f:
 # now up to date
 fresh_cythonize("*.pyx")
 assert mtime < new_mtime < other_cython_mtime <= latest_mtime == getmtime("a.c")
+
+# force regeneration with environment variable
+os.environ["CYTHON_FORCE_REGEN"] = "1"
+time.sleep(0.1)
+
+assert latest_mtime == getmtime("a.c")
+fresh_cythonize("*.pyx")
+assert latest_mtime < getmtime("a.c")