bpo-39562: Prevent collision of future and compiler flags

Doc/whatsnew/3.9.rst

@@ -832,6 +832,10 @@ Changes in the Python API
  inherit from it should have this method defined.
  (Contributed by Kyle Stanley in :issue:`34037`.)
 
+* The constant values of future flags in the :mod:`__future__` module
+ is updated in order to prevent collision with compiler flags. Previously
+ ``PyCF_ALLOW_TOP_LEVEL_AWAIT`` was clashing with ``CO_FUTURE_DIVISION``.
+ (Contributed by Batuhan Taskaya in :issue:`39562`)
 
 CPython bytecode changes
 ------------------------

Include/code.h

@@ -88,19 +88,19 @@ typedef struct {
 #define CO_ITERABLE_COROUTINE 0x0100
 #define CO_ASYNC_GENERATOR 0x0200
 
-/* These are no longer used. */
-#if 0
-#define CO_GENERATOR_ALLOWED 0x1000
-#endif
-#define CO_FUTURE_DIVISION 0x2000
-#define CO_FUTURE_ABSOLUTE_IMPORT 0x4000 /* do absolute imports by default */
-#define CO_FUTURE_WITH_STATEMENT 0x8000
-#define CO_FUTURE_PRINT_FUNCTION 0x10000
-#define CO_FUTURE_UNICODE_LITERALS 0x20000
-
-#define CO_FUTURE_BARRY_AS_BDFL 0x40000
-#define CO_FUTURE_GENERATOR_STOP 0x80000
-#define CO_FUTURE_ANNOTATIONS 0x100000
+/* bpo-39562: These constant values are changed in Python 3.9
+ to prevent collision with compiler flags. CO_FUTURE_ and PyCF_
+ constants must be kept unique. PyCF_ constants can use bits from
+ 0x0100 to 0x10000. CO_FUTURE_ constants use bits starting at 0x20000. */
+#define CO_FUTURE_DIVISION 0x20000
+#define CO_FUTURE_ABSOLUTE_IMPORT 0x40000 /* do absolute imports by default */
+#define CO_FUTURE_WITH_STATEMENT 0x80000
+#define CO_FUTURE_PRINT_FUNCTION 0x100000
+#define CO_FUTURE_UNICODE_LITERALS 0x200000
+
+#define CO_FUTURE_BARRY_AS_BDFL 0x400000
+#define CO_FUTURE_GENERATOR_STOP 0x800000
+#define CO_FUTURE_ANNOTATIONS 0x1000000
 
 /* This value is found in the co_cell2arg array when the associated cell
  variable does not correspond to an argument. */

Include/compile.h

@@ -18,12 +18,18 @@ PyAPI_FUNC(PyCodeObject *) PyNode_Compile(struct _node *, const char *);
  CO_FUTURE_UNICODE_LITERALS | CO_FUTURE_BARRY_AS_BDFL | \
  CO_FUTURE_GENERATOR_STOP | CO_FUTURE_ANNOTATIONS)
 #define PyCF_MASK_OBSOLETE (CO_NESTED)
+
+/* bpo-39562: CO_FUTURE_ and PyCF_ constants must be kept unique.
+ PyCF_ constants can use bits from 0x0100 to 0x10000.
+ CO_FUTURE_ constants use bits starting at 0x20000. */
 #define PyCF_SOURCE_IS_UTF8 0x0100
 #define PyCF_DONT_IMPLY_DEDENT 0x0200
 #define PyCF_ONLY_AST 0x0400
 #define PyCF_IGNORE_COOKIE 0x0800
 #define PyCF_TYPE_COMMENTS 0x1000
 #define PyCF_ALLOW_TOP_LEVEL_AWAIT 0x2000
+#define PyCF_COMPILE_MASK (PyCF_ONLY_AST | PyCF_ALLOW_TOP_LEVEL_AWAIT | \
+ PyCF_TYPE_COMMENTS | PyCF_DONT_IMPLY_DEDENT)
 
 #ifndef Py_LIMITED_API
 typedef struct {

Lib/__future__.py

@@ -68,14 +68,14 @@
 # this module.
 CO_NESTED = 0x0010 # nested_scopes
 CO_GENERATOR_ALLOWED = 0 # generators (obsolete, was 0x1000)
-CO_FUTURE_DIVISION = 0x2000 # division
-CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
-CO_FUTURE_WITH_STATEMENT = 0x8000 # with statement
-CO_FUTURE_PRINT_FUNCTION = 0x10000 # print function
-CO_FUTURE_UNICODE_LITERALS = 0x20000 # unicode string literals
-CO_FUTURE_BARRY_AS_BDFL = 0x40000
-CO_FUTURE_GENERATOR_STOP = 0x80000 # StopIteration becomes RuntimeError in generators
-CO_FUTURE_ANNOTATIONS = 0x100000 # annotations become strings at runtime
+CO_FUTURE_DIVISION = 0x20000 # division
+CO_FUTURE_ABSOLUTE_IMPORT = 0x40000 # perform absolute imports by default
+CO_FUTURE_WITH_STATEMENT = 0x80000 # with statement
+CO_FUTURE_PRINT_FUNCTION = 0x100000 # print function
+CO_FUTURE_UNICODE_LITERALS = 0x200000 # unicode string literals
+CO_FUTURE_BARRY_AS_BDFL = 0x400000
+CO_FUTURE_GENERATOR_STOP = 0x800000 # StopIteration becomes RuntimeError in generators
+CO_FUTURE_ANNOTATIONS = 0x1000000 # annotations become strings at runtime
 
 class _Feature:
  def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):

Lib/test/test_future.py

@@ -1,5 +1,7 @@
 # Test various flavors of legal and illegal future statements
 
+import __future__
+import ast
 import unittest
 from test import support
 from textwrap import dedent
@@ -75,6 +77,21 @@ def test_badfuture10(self):
  from test import badsyntax_future10
  self.check_syntax_error(cm.exception, "badsyntax_future10", 3)
 
+ def test_ensure_flags_dont_clash(self):
+ # bpo-39562: test that future flags and compiler flags doesn't clash
+
+ # obtain future flags (CO_FUTURE_***) from the __future__ module
+ flags = {
+ f"CO_FUTURE_{future.upper()}": getattr(__future__, future).compiler_flag
+ for future in __future__.all_feature_names
+ }
+ # obtain some of the exported compiler flags (PyCF_***) from the ast module
+ flags |= {
+ flag: getattr(ast, flag)
+ for flag in dir(ast) if flag.startswith("PyCF_")
+ }
+ self.assertCountEqual(set(flags.values()), flags.values())
+
  def test_parserhack(self):
  # test that the parser.c::future_hack function works as expected
  # Note: although this test must pass, it's not testing the original

Python/bltinmodule.c

@@ -739,7 +739,7 @@ builtin_compile_impl(PyObject *module, PyObject *source, PyObject *filename,
  }
 
  if (flags &
- ~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_DONT_IMPLY_DEDENT | PyCF_ONLY_AST | PyCF_TYPE_COMMENTS))
+ ~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_COMPILE_MASK))
  {
  PyErr_SetString(PyExc_ValueError,
  "compile(): unrecognised flags");