AI Issue analysis

[henryiii]

Ran with my explore issue skill.

🤖 AI text below 🤖

All ten batches are complete — 103 issues triaged, with repros compiled against master headers wherever the report included usable code. Here's the synthesis.

Summary

Of 103 candidate issues (all 32 bug/regression-labeled + ~70 [BUG]-titled/crash-keyword issues): 42 verified as real bugs still present on master (26 of those reproduced live on this machine), ~20 confirmed or strongly likely fixed (close candidates), 7 needs-info, and the rest usage errors, environment problems, or documented behavior.

Verified bugs — reproduced locally on master

Crashes / memory corruption

Issue	What happens
#3514	Hard segfault with diamond/virtual inheritance — unsafe static_cast to virtual base in class_::add_base
#3902	PYBIND11_OVERRIDE breaks with multiple-inheritance trampolines (static_cast<const cname*>(this) pointer offset); pure-virtual abort
#4365	Same family: missing MI pointer adjustment in the shared_ptr downcast path (duplicate of #3514; repro PR #4374 still open)
#5473	py::init factory + py::call_guard<gil_scoped_release> under threads aborts with "Tried to deallocate unregistered instance!" — the guard spans register_instance, which runs without the GIL
#2245	Silent data corruption: std::vector<const char*> from ['abc','defg'] yields 'defg|defg' — dangling pointers into the recycled per-element string caster buffer
#5637	std::optional<std::reference_wrapper<Eigen::MatrixXd>> arg dangles (caster temporary dies before the call) — garbage values here, segfault on Linux
#3776	Second scoped_interpreter + re-import of an externally built module now fails worse than reported: internals_pp_manager reentrant-call ImportError, no make_iterator needed

Wrong results / broken dispatch

Issue	What happens
#2786	Overflowing py::cast<py::int_> → unchecked PyLong_AsLong, escapes as SystemError
#2336 / #4099	Casting an unregistered type returns a null handle with an error set instead of throwing cast_error (same root cause, could be one fix)
#5283	Eigen sparse caster ignores noconvert — float32 csr_matrix silently dispatches to a bool overload
#5405 / #3357	get_type_override misses overrides: C++-bound mixin methods rejected via is_cpp_function() (and cached!); recursive dispatch fails via the frame-name check
#6080	PYBIND11_OVERRIDE called from native C++ (no dispatcher frame) can't do implicit return conversion — no loader_life_support frame
#5558	PySequence_Check-based vector conversion lets iteration exceptions escape the dispatcher instead of trying the next overload
#4236	def_property returning a numpy view never applies reference_internal keep-alive (policy demoted to move) — parent freed, garbage data
#6025	Objects from __new__ are never register_instanced, so later py::cast(T*) builds a fresh base-typed object (subclass lost)
#3062	Pickle round-trip slices unregistered derived types (vtable lost), no fail-fast
#2742	Returning new std::vector<T> with stl.h leaks the pointer (possibly by-design → docs fix)
#5895	Signed/unsigned noconvert inconsistency for __index__-only objects (as_unsigned requires a real PyLong); float half already fixed by #5879
#2059 / #2722	__qualname__ = pybind11_detail_function_record_v1... instead of Class.method; unbound methods are unhashable instancemethods
#5600	cProfile loses all frames around bound-method calls on 3.12/3.13 (CPython 3.14 masks it)
#5428	format_descriptor<long double> is 'g' even where sizeof(long double)==sizeof(double); comment contradicts behavior

Compile-time

• #5983 — any class with value_type = void (CGAL) fails is_move_constructible static_assert; recursive_container_traits recurses blindly into value_type
• #4018 / #2147 — PYBIND11_NUMPY_DTYPE: commas in template args break the macro; const members fail (is_fmt_numeric lacks remove_cv — reproduced as ImportError: invalid buffer descriptor)
• #5622 — PYBIND11_OVERRIDE_PURE with Eigen::Map return can't instantiate (deleted caster members)
• #5765 — std::array<int, 102400> takes 133 s to compile (index_sequence pack expansion; proposed std::copy fast path never merged)
• #5635 — returning a null Eigen::MatrixXd* raises PyCapsule_New called with null pointer instead of None

Build system / CMake (all confirmed against current tools/)

• #6043 — CMake 4.1 CMP0190 regression from fix: cross-compilation updates #5829 silently disables Emscripten/Pyodide cross-compile detection; author-confirmed with an unlanded patch
• #5813 / #5472 / #6063 — one shared root: if(NOT Python_FOUND...) in pybind11NewTools.cmake:20 skips finding Development.Module/Development.Embed when the parent already found Python partially → python_add_library unknown / pybind11::embed missing Python::Python
• #6060 — -fno-fat-lto-objects appended for all GNU compilers makes every LTO probe fail on macOS gcc
• #5937 — unconditional SYSTEM includes in add_subdirectory mode let an installed pybind11 shadow the vendored one; no opt-out
• #5467 — Windows-Debug half still live (pythonXY_d.lib vs _DEBUG undef → LNK1104; your own CI works around it in .appveyor.yml)

Smaller / cosmetic: #6102 (complex annotation omits complex — one-line fix), #5847 (numpy.bool hint invalid on numpy <2), #5819/#5431 (sparse caster: no sort_indices, spurious mutable_data() on read-only arrays), #5421 (remaining free-threading races on implicit_casts/simple_type — partial fix only).

Fixed — close candidates

Verified fixed on master (fixing commit identified; repro passes where testable):

• #1111 static-property docstrings — Added write only property functions for issue #1142 #1144 (2017!)
• #2601 chrono null-localtime crash — fix: add null pointer check with std::localtime #2846
• #2765 py::cast thread safety — Use thread_local for loader_life_support to improve performance #5830 thread-local loader_life_support
• #3336 def_buffer terminate — fix: properly translate C++ exception to Python exception when creating Python buffer from wrapped object #5324 (now BufferError with __cause__)
• #4459 atexit/finalize ordering — feat: support for sub-interpreters #5564
• #5005 requested tests already exist (fix: Revert pfect args make iterator #4234)
• #5046 keep_alive-on-property now a hard compile error — Don't allow keep_alive or call_guard on properties #5533
• #5290 / #5359 cross-DSO exception catching — Define (non-empty) PYBIND11_EXPORT_EXCEPTION only under macOS. #4298 (v2.10.1)
• #5316 internals double-init — Add per-interpreter storage for gil_safe_call_once_and_store #5933/Revert internals destruction and add test for internals recreation #5972
• #5341 Clang 3.4 lambda deduction — code replaced by fix(free-threading): fix data race when using shared variables #5494
• #5382 / #5626 / #5467(half) — FindPython by default (feat(cmake): FindPython by default #5553)
• #5393 include_guard regression — fix(cmake): regression in include guard #5691
• #5420 internals ABI pin — PYBIND11_INTERNALS_VERSION 12 + #error
• #5479 virtual-inheritance crash — fix: detect virtual inheritance in add_base to prevent pointer offset crash #6017 (exact posted code runs clean)
• #5499 3.14 pickling — fix: support Python 3.14 #5646/fix: use original dict #5658/fix: prepare for 3.14 beta 2 #5697 (all assertions pass on 3.14.6)
• #5716 greedy vector overload — fix(types): updated STL casters and py::buffer to use collections.abc #5566 (repro now picks the right overload)
• #5991 / #5993 exit segfaults — fix: strdup "self" arg in def_property_static, partially revert #6010 (gh-5976) #6015/gh-5991: Fix segfault during finalization related to function_record #6010 and Harden PYBIND11_MODULE_PYINIT and get_internals() against crashes during module init #6018 hardening; reporters already confirmed on master

Needs-info (7): #5377, #5417, #5872, #5956, #6037, #6046 (retest on master likely resolves — #6018 targets that exact path), plus #4467's FreeBSD twin — three of these look like pytest-randomly/test-order artifacts, worth one canned "try -p no:randomly" reply.

Everything is preserved per-batch with file/line evidence and fixing commits in scratchpad/results-batch{A..J}.md; several compiled repros live in scratchpad/batch*/. Data downloaded today; open issues only.

If you want, I can draft close-comments for the fixed group, or pick off one of the small confirmed fixes (#6102 is a one-liner; the pybind11NewTools.cmake:20 guard fixes three issues at once).