Fix Generated C depends on the host interpreter

doc/source/whatsnew.rst

@@ -9,6 +9,8 @@ v2.2.0.dev0
   built against a libffi other than the one provided by the macOS SDK — that
   is, the iOS/tvOS/watchOS wheels, or a macOS build using a Homebrew libffi.
   (`#265`_).
+* The C source generated by ``cffi-gen-src`` and ``ffibuilder.emit_c_code()``
+  no longer depends on the interpreter running the generator.
 
 .. _`#265`: https://github.com/python-cffi/cffi/pull/265
 

src/cffi/_cffi_include.h

@@ -13,24 +13,19 @@
    In that case, we guess what pyconfig.h will do to the macros above,
    and check our guess after the #include.
 
-   Note that on Windows, with CPython 3.x, you need >= 3.5 and virtualenv
-   version >= 16.0.0.  With older versions of either, you don't get a
-   copy of PYTHON3.DLL in the virtualenv.  We can't check the version of
-   CPython *before* we even include pyconfig.h.  ffi.set_source() puts
-   a ``#define _CFFI_NO_LIMITED_API'' at the start of this file if it is
-   running on Windows < 3.5, as an attempt at fixing it, but that's
-   arguably wrong because it may not be the target version of Python.
-   Still better than nothing I guess.  As another workaround, you can
-   remove the definition of Py_LIMITED_API here.
-
    See also 'py_limited_api' in cffi/setuptools_ext.py.
 */
 #if !defined(_CFFI_USE_EMBEDDING) && !defined(Py_LIMITED_API)
+#  include <patchlevel.h>   /* for PY_VERSION_HEX; self-contained */
 #  ifdef _MSC_VER
 #    if !defined(_DEBUG) && !defined(Py_DEBUG) && !defined(Py_TRACE_REFS) && !defined(Py_REF_DEBUG) && !defined(_CFFI_NO_LIMITED_API)
 #      if !defined(Py_GIL_DISABLED)
 #        define Py_LIMITED_API
-#      else
+#      elif PY_VERSION_HEX >= 0x030f0000
+         /* the free-threaded build supports the limited API (the abi3t
+            stable ABI) since 3.15.  Note that on Windows pyconfig.h does
+            not define Py_GIL_DISABLED; build backends targeting the
+            free-threaded build pass it on the compiler command line. */
 #        define Py_LIMITED_API 0x030f0000
 #      endif
 #    endif
@@ -56,7 +51,9 @@
 #    if !defined(Py_DEBUG) && !defined(Py_TRACE_REFS) && !defined(Py_REF_DEBUG) && !defined(_CFFI_NO_LIMITED_API)
 #      if !defined(Py_GIL_DISABLED)
 #        define Py_LIMITED_API
-#      else
+#      elif PY_VERSION_HEX >= 0x030f0000
+         /* the free-threaded build supports the limited API (the abi3t
+            stable ABI) since 3.15 */
 #        define Py_LIMITED_API 0x030f0000
 #      endif
 #    endif

src/cffi/recompiler.py

@@ -1,4 +1,4 @@
-import io, os, sys, sysconfig
+import io, os, sys
 from . import ffiplatform, model
 from .error import VerificationError
 from .cffi_opcode import *
@@ -7,11 +7,6 @@
 VERSION_EMBEDDED = 0x2701
 VERSION_CHAR16CHAR32 = 0x2801
 
-FREE_THREADED_BUILD = sysconfig.get_config_var("Py_GIL_DISABLED")
-USE_LIMITED_API = ((sys.platform != 'win32' or sys.version_info < (3, 0) or
-                   sys.version_info >= (3, 5)) and
-                   # free-threaded build doesn't support the stable ABI until Python 3.15
-                   (not FREE_THREADED_BUILD or sys.version_info >= (3, 15)))
 
 class GlobalExpr:
     def __init__(self, name, address, type_op, size=0, check_value=0):
@@ -306,8 +301,6 @@ def write_c_source_to_f(self, f, preamble):
         prnt = self._prnt
         if self.ffi._embedding is not None:
             prnt('#define _CFFI_USE_EMBEDDING')
-        if not USE_LIMITED_API:
-            prnt('#define _CFFI_NO_LIMITED_API')
         #
         # first the '#include' (actually done by inlining the file's content)
         lines = self._rel_readlines('_cffi_include.h')

src/cffi/setuptools_ext.py

@@ -82,17 +82,12 @@ def _set_py_limited_api(Extension, kwds):
     it doesn't so far, creating troubles.  That's why we check
     for "not hasattr(sys, 'gettotalrefcount')" (the 2.7 compatible equivalent
     of 'd' not in sys.abiflags). (http://bugs.python.org/issue28401)
-
-    On Windows, with CPython <= 3.4, it's better not to use py_limited_api
-    because virtualenv *still* doesn't copy PYTHON3.DLL on these versions.
-    Recently (2020) we started shipping only >= 3.5 wheels, though.  So
-    we'll give it another try and set py_limited_api on Windows >= 3.5.
     """
     from cffi._shimmed_dist_utils import log
-    from cffi import recompiler
 
     if ('py_limited_api' not in kwds and not hasattr(sys, 'gettotalrefcount')
-            and recompiler.USE_LIMITED_API):
+            and (not sysconfig.get_config_var("Py_GIL_DISABLED")
+                 or sys.version_info >= (3, 15))):
         import setuptools
         try:
             setuptools_major_version = int(setuptools.__version__.partition('.')[0])

testing/cffi1/test_cffi_gen_src.py

@@ -211,3 +211,16 @@ def test_import_is_inert():
     assert proc.returncode == 0, proc.stderr
     assert proc.stdout == ""
     assert proc.stderr == ""
+
+
+def test_output_independent_of_generating_interpreter(tmp_path):
+    # runs on free-threaded and GIL-enabled CI alike; the output must be
+    # the same on both, with the limited-API decision left to
+    # _cffi_include.h at compile time
+    pyfile = tmp_path / "_squared_build.py"
+    pyfile.write_text(SIMPLE_SCRIPT)
+    out = tmp_path / "squared.c"
+    proc = _run([sys.executable, "-m", "cffi.gen_src"],
+                "exec-python", str(pyfile), str(out))
+    assert proc.returncode == 0, proc.stderr
+    assert "#define _CFFI_NO_LIMITED_API" not in out.read_text().splitlines()

testing/cffi1/test_recompiler.py

@@ -2595,3 +2595,15 @@ def test_large_enum():
         relements[biglist[i]] = i
     assert e.elements == elements
     assert e.relements == relements
+
+def test_emit_c_code_is_interpreter_independent():
+    # the emitted source must be a pure function of the FFI object, with
+    # no #defines derived from the interpreter running the generator
+    import io
+    ffi = FFI()
+    ffi.cdef("int ff_interp_indep(int);")
+    ffi.set_source("_CFFI_interp_indep",
+                   "int ff_interp_indep(int x) { return x; }")
+    f = io.StringIO()
+    ffi.emit_c_code(f)
+    assert "#define _CFFI_NO_LIMITED_API" not in f.getvalue().splitlines()