gh-131510: Deprecate PyUnicodeObject structs, revert memory layout #130697
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Deprecate `PyASCIIObject`, `PyCompactUnicodeObject`, `PyUnicodeObject` structs, and the `PyUnicode_IS_COMPACT` macro. Schedule removal for 3.16, the shortest non-exceptional deprecation period per PEP-387. The structs are blocking development of the free-threaded build (bitfields can't be used atomically) and of possible UTF-8-focused string representations. In non-free-threaded builds, revert `PyASCIIObject` to the binary layout used in 3.13. For free-threaded builds, use `alignas` instead of padding to ensure alignment. All relevant compilers support `alignas`, as do the C11 & C++11 standards, but they may need different spelling or compiler options for it.
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I'll look at the compile errors later. (Thank you GHA; I can't easily do a matrix build locally.) |
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| && (defined(__GNUC__) || defined(__clang__)) | ||
| # define _Py_ALIGN_AS(V) __attribute__((aligned(V))) | ||
| # else | ||
| # define _Py_ALIGN_AS(V) alignas(V) |
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This will be used if __cplusplus < 201103L and neither __GNUC__ nor __clang__ are defined.
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That's unknown compilers that aren't in C++11+-standard mode.
IMO, the best we can do is hope that they do support this part of C++11.
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What if it is an old Microsoft compiler? Then we could use __declspec(align(V)).
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It's not yet time to deprecate these. I'll send a new PR for the memory layout revert. |
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(Draft for discussion with the C API WG.)
Deprecate
PyASCIIObject,PyCompactUnicodeObject,PyUnicodeObjectstructs, and thePyUnicode_IS_COMPACTmacro.Schedule removal for 3.16, the shortest non-exceptional deprecation period per PEP-387. The structs are blocking development of the free-threaded build (bitfields can't be used atomically) and of possible UTF-8-focused string representations.
Add an example of what I'd like to see in porting notes for a deprecation.
In non-free-threaded builds, revert
PyASCIIObjectto be ABI-compatible with in 3.13.For free-threaded builds, use
alignasinstead of padding to ensure alignment.All relevant compilers support
alignas, as do the C11 & C++11 standards, but they may need different spelling or compiler options for it.Introduce
_Py_ALIGN_ASfor this.📚 Documentation preview 📚: https://cpython-previews--130697.org.readthedocs.build/