PEP 743: Make the macro a simple boolean (#4595)

* Remove the version value.
* Rename the macro to Py_OMIT_LEGACY_API

Co-authored-by: Petr Viktorin <[email protected]>

Author: vstinner

peps/pep-0743.rst

@@ -1,24 +1,23 @@
 PEP: 743
-Title: Add Py_COMPAT_API_VERSION to the Python C API
+Title: Add Py_OMIT_LEGACY_API to the Python C API
 Author: Victor Stinner <[email protected]>,
         Petr Viktorin <[email protected]>,
 PEP-Delegate: C API Working Group
 Discussions-To: https://discuss.python.org/t/pep-743-add-py-compat-api-version-to-the-python-c-api-take-2/59323
 Status: Draft
 Type: Standards Track
 Created: 11-Mar-2024
-Python-Version: 3.14
+Python-Version: 3.15
 
 .. highlight:: c
 
 
 Abstract
 ========
 
-Add ``Py_COMPAT_API_VERSION`` C macro that hides some deprecated and
+Add ``Py_OMIT_LEGACY_API`` C macro that hides deprecated and
 soft-deprecated symbols, allowing users to opt out of using API with known
 issues that other API solves.
-The macro is versioned, allowing users to update (or not) on their own pace.
 
 Also, add namespaced alternatives for API without the ``Py_`` prefix,
 and soft-deprecate the original names.
@@ -81,7 +80,7 @@ It might be be sufficient to leave this to third-party linters.
 For that we'd need a good way to expose a list of (soft-)deprecated
 API to such linters.
 While adding that, we can -- rather easily -- do the linter's job directly
-in CPython headers, avoiding the neel for an extra tool.
+in CPython headers, avoiding the need for an extra tool.
 Unlike Python, C makes it rather easy to limit available API -- for a whole
 project or for each individual source file -- by having users define
 an “opt-in” macro.
@@ -91,11 +90,6 @@ available API to a subset that compiles to stable ABI. (In hindsight, we should
 have used a different macro name for that particular kind of limiting, but it's
 too late to change that now.)
 
-To prevent working code from breaking as we identify more “undesirable” API
-and add safer alternatives to it, the opt-in macro should be *versioned*.
-Users can choose a version they need based on their compatibility requirements,
-and update it at their own pace.
-
 To be clear, this mechanism is *not* a replacement for deprecation.
 Deprecation is for API that prevents new features or optimizations, or
 presents a security risk or maintenance burden.
@@ -126,7 +120,7 @@ third-party libraries.
 Specification
 =============
 
-We introduce a ``Py_COMPAT_API_VERSION`` macro.
+We introduce a ``Py_OMIT_LEGACY_API`` macro.
 If this macro is defined before ``#include <Python.h>``, some API definitions
 -- as described below -- will be omitted from the Python header files.
 
@@ -142,17 +136,11 @@ of CPython, and is finalized in each 3.x.0 Beta 1 release.
 In rare cases, entries can be removed (i.e. made available for use) at any
 time.
 
-The macro should be defined to a version in the format used by
-``PY_VERSION_HEX``, with the “micro”, “release” and “serial” fields
-set to zero.
-For example, to omit API deemed undesirable in 3.14.0b1, users should define
-``Py_COMPAT_API_VERSION`` to ``0x030e0000``.
-
 
 Requirements for omitted API
 ----------------------------
 
-An API that is omitted with ``Py_COMPAT_API_VERSION`` must:
+An API that is omitted with ``Py_OMIT_LEGACY_API`` must:
 
 - be soft-deprecated (see :pep:`387`);
 - for all known use cases of the API, have a documented alternative
@@ -164,15 +152,15 @@ An API that is omitted with ``Py_COMPAT_API_VERSION`` must:
 - be approved by the C API working group. (The WG may give blanket approvals
   for groups of related API; see *Initial set* below for examples.)
 
-Note that ``Py_COMPAT_API_VERSION`` is meant for API that can be trivially
+Note that ``Py_OMIT_LEGACY_API`` is meant for API that can be trivially
 replaced by a better alternative.
 API without a replacement should generally be deprecated instead.
 
 
 Location
 --------
 
-All API definitions omitted by ``Py_COMPAT_API_VERSION`` will be moved to
+All API definitions omitted by ``Py_OMIT_LEGACY_API`` will be moved to
 a new header, ``Include/legacy.h``.
 
 This is meant to help linter authors compile lists, so they can flag the API
@@ -200,8 +188,7 @@ Exceptions are possible if there is a good reason for them.
 Initial set
 -----------
 
-The following API will be omitted with ``Py_COMPAT_API_VERSION`` set to
-``0x030e0000`` (3.14) or greater:
+The following API will be omitted with ``Py_OMIT_LEGACY_API`` set:
 
 - Omit API returning borrowed references:
 
@@ -289,7 +276,7 @@ The following API will be omitted with ``Py_COMPAT_API_VERSION`` set to
 
   The header file ``structmember.h``, which is not included from ``<Python.h>``
   and must be included separately, will ``#error`` if
-  ``Py_COMPAT_API_VERSION`` is defined.
+  ``Py_OMIT_LEGACY_API`` is defined.
   This affects the following API:
 
   ====================================  ==============================
@@ -346,7 +333,7 @@ The following API will be omitted with ``Py_COMPAT_API_VERSION`` set to
 
 If any of these proposed replacements, or associated documentation,
 are not added in time for 3.14.0b1, they'll be omitted with later versions
-of ``Py_COMPAT_API_VERSION``.
+of ``Py_OMIT_LEGACY_API``.
 (We expect this for macros generated by ``configure``: ``HAVE_*``, ``WITH_*``,
 ``ALIGNOF_*``, ``SIZEOF_*``, and several without a common prefix.)
 
@@ -357,20 +344,18 @@ Implementation
 TBD
 
 
-Open issues
-===========
-
-The name ``Py_COMPAT_API_VERSION`` was taken from the earlier PEP;
-it doesn't fit this version.
-
-
 Backwards Compatibility
 =======================
 
 The macro is backwards compatible.
 Developers can introduce and update the macro on their own pace, potentially
 for one source file at a time.
 
+Future versions of CPython may add more API to the set that
+``Py_OMIT_LEGACY_API`` hides, breaking user code.
+The fix is to undefine the macro (which is safe to do) or rework the
+code.
+
 
 Discussions
 ===========