[smart_holder] Fix handling of const unique_ptr<T, D> & (do not disown).
#5332
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added 9 commits
August 23, 2024 12:13
…`rtrn_unique_ptr_cref()` to make the current behavior obvious.
…th MSVC, NVHPC, ICC
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PREPARATION for: PR pybind#5332 — Fix handling of const unique_ptr<T, D> & (do not disown). Splitting out so that the functional changes under PR pybind#5332 will be more obvious.
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PREPARATION for: PR pybind#5332 — Fix handling of const unique_ptr<T, D> & (do not disown). Splitting out so that the functional changes under PR pybind#5332 will be more obvious. The only functional change under this PR is that ``` assert(custom_deleter_ptr != nullptr); ``` is replaced with: ``` if (custom_deleter_ptr == nullptr) { throw std::runtime_error( std::string("smart_holder::extract_deleter() precondition failure (") + context + ")."); } ```
rwgk
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Aug 25, 2024
rwgk
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Aug 25, 2024
PREPARATION for: PR pybind#5332 — Fix handling of const unique_ptr<T, D> & (do not disown). Splitting out so that the functional changes under PR pybind#5332 will be more obvious. The only functional change under this PR is that ``` assert(custom_deleter_ptr != nullptr); ``` is replaced with: ``` if (custom_deleter_ptr == nullptr) { throw std::runtime_error( std::string("smart_holder::extract_deleter() precondition failure (") + context + ")."); } ```
rwgk
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Aug 25, 2024
PREPARATION for: PR #5332 — Fix handling of const unique_ptr<T, D> & (do not disown). Splitting out so that the functional changes under PR #5332 will be more obvious. The only functional change under this PR is that ``` assert(custom_deleter_ptr != nullptr); ``` is replaced with: ``` if (custom_deleter_ptr == nullptr) { throw std::runtime_error( std::string("smart_holder::extract_deleter() precondition failure (") + context + ")."); } ```
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August 25, 2024 08:59
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Description
Before this PR, passing a Python object as a C++
const unique_ptr<T, D> &involved building a temporary (non-const)unique_ptr<T, D>, which was then passed as aconst unique_ptr<T, D> &. The Python object was disowned when the temporaryunique_ptr<T, D>was built. This was unintentional and counter-intuitive (although bug-compatible with PyCLIF; probably also unintentional).This PR introduces a different mechanism, specifically for
const unique_ptr<T, D> &: a temporary (still non-const)unique_ptr<T, D>is built, but the Python object is not disowned, and the temporaryunique_ptris meant to never expire (this would only be possible if the passed-to C++ code applied aconst_cast, to then disown the non-constunique_ptr). When thetype_castergoes out of scope, the new implementation checks if the temporaryunique_ptrdid in fact not expire (otherwise aFATALexception is thrown), then.release()s it before deleting theunique_ptrobject. Conveniently, this can be achieved by managing the temporaryunique_ptrwith ashared_ptrand a custom deleter.I (rwgk) strongly considered the alternative of using a
static_assert()to make it impossible to pass a Python object as aconst unique_ptr<T, D> &, but the new implementation is sufficiently small, it's less trouble than backing out all existing test code that would break. There could also be existing client code in the wild that may need workarounds. Having the revised feature is convenient and not very costly (amount of code; complexity).@rhaschke FYI
Suggested changelog entry: