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Bug 1897178 - mercurial fails to build with Python 3.10: Py_TYPE=/Py_SIZE= needs to be replaced with Py_SET_TYPE/Py_SET_SIZE
Summary: mercurial fails to build with Python 3.10: Py_TYPE=/Py_SIZE= needs to be repl...
Alias: None
Product: Fedora
Classification: Fedora
Component: mercurial
Version: rawhide
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
Assignee: Neal Becker
QA Contact: Fedora Extras Quality Assurance
Depends On:
Blocks: PYTHON3.10
TreeView+ depends on / blocked
Reported: 2020-11-12 14:13 UTC by Tomáš Hrnčiar
Modified: 2020-12-04 22:11 UTC (History)
10 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2020-11-18 19:47:46 UTC
Type: Bug

Attachments (Terms of Use)

Description Tomáš Hrnčiar 2020-11-12 14:13:07 UTC
mercurial fails to build with Python 3.10.0a2.

mercurial/cext/pathencode.c:178:18: error: lvalue required as decrement operand
  178 |   Py_SIZE(newobj)--;
      |                  ^~
mercurial/cext/pathencode.c: In function 'hashmangle':
mercurial/cext/pathencode.c:681:15: error: lvalue required as left operand of assignment
  681 |  Py_SIZE(ret) = destlen;
      |               ^
mercurial/cext/pathencode.c: In function 'pathencode':
mercurial/cext/pathencode.c:793:19: error: lvalue required as decrement operand
  793 |    Py_SIZE(newobj)--;
      |                   ^~
contrib/python-zstandard/c-ext/bufferutil.c:761:39: error: lvalue required as left operand of assignment
  761 |  Py_TYPE(&ZstdBufferWithSegmentsType) = &PyType_Type;
      |                                       ^
contrib/python-zstandard/c-ext/bufferutil.c:769:35: error: lvalue required as left operand of assignment
  769 |  Py_TYPE(&ZstdBufferSegmentsType) = &PyType_Type;
      |                                   ^
contrib/python-zstandard/c-ext/bufferutil.c:777:34: error: lvalue required as left operand of assignment
  777 |  Py_TYPE(&ZstdBufferSegmentType) = &PyType_Type;
      |                                  ^
contrib/python-zstandard/c-ext/bufferutil.c:785:49: error: lvalue required as left operand of assignment
  785 |  Py_TYPE(&ZstdBufferWithSegmentsCollectionType) = &PyType_Type;

Since Py_TYPE() is changed to the inline static function, Py_TYPE(obj) = new_type must be replaced with Py_SET_TYPE(obj, new_type): see Py_SET_TYPE() (available since Python 3.9). For backward compatibility, this macro can be used:

#if PY_VERSION_HEX < 0x030900A4
#  define Py_SET_TYPE(obj, type) ((Py_TYPE(obj) = (type)), (void)0)

bpo-39573: Convert Py_REFCNT() and Py_SIZE() macros to static inline functions. They cannot be used as l-value anymore: use Py_SET_REFCNT() and Py_SET_SIZE() to set an object reference count and size. This change is backward incompatible on purpose, to prepare the C API for an opaque PyObject structure.

For the build logs, see:

For all our attempts to build mercurial with Python 3.10, see:

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.10:

Let us know here if you have any questions.

Python 3.10 will be included in Fedora 35. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.10.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.

Comment 1 Miro Hrončok 2020-11-18 17:57:11 UTC
The change was reverted in Python 3.10, because it caused too much trouble (the amount of affected Fedora packages was too big). Keeping this open for now, unit  anew alpha version is out to test it out.

This comment is mass posted in all relevant bugzillas. If you already worked upstream to fix the problem, please let them know about the revert.

Comment 2 Miro Hrončok 2020-11-18 19:47:46 UTC
I've patched Python 3.10 in our testing copr to include the revert. This package built fine. Sorry for the noise.

Comment 3 Victor Stinner 2020-12-04 22:11:21 UTC
I proposed a patch to Mercurial:

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