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In C++, Python 3.11 C API introduces new compiler warnings/errors #92135

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vstinner opened this issue May 2, 2022 · 2 comments
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In C++, Python 3.11 C API introduces new compiler warnings/errors #92135

vstinner opened this issue May 2, 2022 · 2 comments
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type-bug An unexpected behavior, bug, or error

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@vstinner
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vstinner commented May 2, 2022

To fix C++ compiler warnings about "old-style casts", I recently modified the Python C API to use C++ reinterpret_cast<> and static_cast<>: #91959

Previously, "old-style cast" like (PyObject*)expr didn't emit a compiler warning if expr was const. Now with the new cast, C++ compilers emit warnings: see #91959 (comment)

const_cast<> can be used to fix this issue.

Note: PEP 670 was accepted with the condition: converting macros to functions must not introduce new compiler warnings (so no new compile errors neither). But most functions modified in Python 3.11 (to use C++ casts) were already static inline functions in Python 3.10.
@vstinner vstinner added the type-bug An unexpected behavior, bug, or error label May 2, 2022
@vstinner vstinner mentioned this issue May 2, 2022
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vstinner commented May 2, 2022

Documentation:

@vstinner vstinner mentioned this issue May 2, 2022
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vstinner added a commit that referenced this issue May 2, 2022
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gh-92135: Fix _Py_reinterpret_cast() for const (#92138)
0313970 
Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when
casting a constant expression to a non constant type: use
const_cast<> in C++.

* In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than
  reinterpret_cast<>.
* Add tests to the _testcppext C++ extension.
* test_cppext no longer captures stdout in verbose mode.
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vstinner commented May 2, 2022

Fixed by #92138

@vstinner vstinner closed this as completed May 2, 2022
vstinner added a commit that referenced this issue May 3, 2022
@vstinner
gh-92135: Rename _Py_reinterpret_cast() to _Py_CAST() (#92230)
fbd5539 
Rename also _Py_static_cast() to _Py_STATIC_CAST().
tiran added a commit to tiran/cpython that referenced this issue May 5, 2022
@tiran
pythongh-92135: test_cppext requires subprocess
6b7635f
tiran added a commit that referenced this issue May 5, 2022
@tiran
gh-92135: test_cppext requires subprocess (GH-92349)
bb35d65
@tacaswell tacaswell mentioned this issue May 14, 2022
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