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GeezerVison is showing github.com — gh-120593: Fix const qualifier in _PyLong_CompactValue() by vstinner · Pull Request #121053 · python/cpython

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@vstinner

@vstinner vstinner commented Jun 26, 2024 •
edited by bedevere-app Bot
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Remove the const qualifier of the argument of functions:

  • _PyLong_IsCompact()
  • _PyLong_CompactValue()

Py_TYPE() argument is not const.

Fix the compiler warning:

  Include/cpython/longintrepr.h: In function ‘_PyLong_CompactValue’: Include/pyport.h:19:31: error: cast discards ‘const’ qualifier from pointer target type [-Werror=cast-qual]
  (...) 
  Include/cpython/longintrepr.h:133:30: note: in expansion of macro ‘Py_TYPE’ assert(PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_LONG_SUBCLASS));
  • Issue: pyatomic_gcc.h with GCC discards const qualifier  #120593

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@vstinner
pythongh-120593: Fix const qualifier in _PyLong_CompactValue()
a742884 
Remove the const qualifier of the argument of functions:

* _PyLong_IsCompact()
* _PyLong_CompactValue()

Py_TYPE() argument is not const.

Fix the compiler warning:

  Include/cpython/longintrepr.h: In function ‘_PyLong_CompactValue’:
  Include/pyport.h:19:31: error: cast discards ‘const’ qualifier from
  pointer target type [-Werror=cast-qual]
    (...)
  Include/cpython/longintrepr.h:133:30: note: in expansion of macro
  ‘Py_TYPE’
    assert(PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_LONG_SUBCLASS));
@vstinner vstinner added the skip news label Jun 26, 2024
@bedevere-app bedevere-app Bot mentioned this pull request Jun 26, 2024
pyatomic_gcc.h with GCC discards const qualifier #120593
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@bedevere-app bedevere-app Bot added the awaiting core review label Jun 26, 2024
@vstinner

vstinner commented Jun 26, 2024

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The important part is to respect the -Werror=cast-qual flag (avoid compiler warnings) in the public Python C API.

In Python implementation and the internal C API, we don't have to worry about this flag, since we don't use it.
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@vstinner vstinner added the needs backport to 3.13 only security fixes label Jun 26, 2024
@vstinner
vstinner merged commit e51e880 into python:main Jun 26, 2024
@vstinner
vstinner deleted the long_compact branch June 26, 2024 18:11
@miss-islington-app

miss-islington-app Bot commented Jun 26, 2024

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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting core review label Jun 26, 2024
@miss-islington-app

miss-islington-app Bot commented Jun 26, 2024

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Sorry, @vstinner, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker e51e880e75d79687b54a71351266e29ee349b4b8 3.13
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@miss-islington-app miss-islington-app Bot assigned vstinner Jun 26, 2024
@vstinner vstinner removed the needs backport to 3.13 only security fixes label Jun 26, 2024
@vstinner

vstinner commented Jun 26, 2024 •
edited
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The backport to Python 3.13 is not needed.
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mrahtz pushed a commit to mrahtz/cpython that referenced this pull request Jun 30, 2024
@vstinner @mrahtz
pythongh-120593: Fix const qualifier in _PyLong_CompactValue() (pytho…
f003fd6 
…n#121053)

Remove the const qualifier of the argument of functions:

* _PyLong_IsCompact()
* _PyLong_CompactValue()

Py_TYPE() argument is not const.

Fix the compiler warning:

  Include/cpython/longintrepr.h: In function ‘_PyLong_CompactValue’:
  Include/pyport.h:19:31: error: cast discards ‘const’ qualifier from
  pointer target type [-Werror=cast-qual]
    (...)
  Include/cpython/longintrepr.h:133:30: note: in expansion of macro
  ‘Py_TYPE’
    assert(PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_LONG_SUBCLASS));
@markshannon

markshannon commented Jul 15, 2024 •
edited
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The const modifier is correct.
Please don't remove them, they add some much needed type safety to our C code.
If Py_TYPE() argument is not const, then fix that, don't weaken the types of other code.
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estyxx pushed a commit to estyxx/cpython that referenced this pull request Jul 17, 2024
@vstinner @estyxx
pythongh-120593: Fix const qualifier in _PyLong_CompactValue() (pytho…
bbf3d03 
…n#121053)

Remove the const qualifier of the argument of functions:

* _PyLong_IsCompact()
* _PyLong_CompactValue()

Py_TYPE() argument is not const.

Fix the compiler warning:

  Include/cpython/longintrepr.h: In function ‘_PyLong_CompactValue’:
  Include/pyport.h:19:31: error: cast discards ‘const’ qualifier from
  pointer target type [-Werror=cast-qual]
    (...)
  Include/cpython/longintrepr.h:133:30: note: in expansion of macro
  ‘Py_TYPE’
    assert(PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_LONG_SUBCLASS));
@vstinner

vstinner commented Jul 27, 2024

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The const modifier is correct. Please don't remove them, they add some much needed type safety to our C code.

Ok, I restored the const modified with PR gh-122367.

If Py_TYPE() argument is not const, then fix that, don't weaken the types of other code.

I tried hard to use const PyObject*, but it went badly: #91768 I'm not convinced that it helps the compiler to optimize.

In my PR, I just restored the code to avoid Py_TYPE().
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@vstinner @markshannon
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