Fix ambiguous str(handle) constructor for object-derived types (#5949)

* Fix ambiguous `str(handle)` constructor for object-derived types

Templatize `str(handle h)` with SFINAE to exclude types derived from
`object`, resolving ambiguity with `str(const object&)` when calling
`py::str()` on types like `kwargs`, `dict`, etc.

The template now only accepts `handle` or `PyObject*`, while all
`object`-derived types use the `str(const object&)` overload.

* fix(tests): CIBW test fixes from b-pass→vectorcall branch

- Install multiple-interpreter test modules into wheel (CMakeLists.txt)
  The mod_per_interpreter_gil, mod_shared_interpreter_gil, and
  mod_per_interpreter_gil_with_singleton modules were being built
  but not installed into the wheel when using scikit-build-core.

- Pin numpy 2.4.0 for Python 3.14 CI tests (requirements.txt)
  NumPy 2.4.0 is the first version with official Python 3.14 wheels.

- Add IOS platform constant to tests/env.py

- Skip subinterpreter tests on iOS (test_multiple_interpreters.py)
  Subinterpreters are not supported in the iOS simulator environment.

- Enable pytest timeout of 120s for CIBW tests (pyproject.toml)
  Provides a safety net to catch hanging tests before CI job timeout.

- Disable pytest-timeout for Pyodide (no signal.setitimer)
  Pyodide runs in WebAssembly without POSIX signals.

- Add -v flag for verbose pytest output in CIBW tests

include/pybind11/pytypes.h

@@ -1690,7 +1690,13 @@ public:
         Return a string representation of the object. This is analogous to
         the ``str()`` function in Python.
     \endrst */
-    explicit str(handle h) : object(raw_str(h.ptr()), stolen_t{}) {
+    // Templatized to avoid ambiguity with str(const object&) for object-derived types.
+    template <typename T,
+              detail::enable_if_t<!std::is_base_of<object, detail::remove_cvref_t<T>>::value
+                                      && std::is_constructible<handle, T>::value,
+                                  int>
+              = 0>
+    explicit str(T &&h) : object(raw_str(handle(std::forward<T>(h)).ptr()), stolen_t{}) {
         if (!m_ptr) {
             throw error_already_set();
         }

tests/CMakeLists.txt

@@ -602,6 +602,12 @@ if(NOT PYBIND11_CUDA_TESTS)
     endif()
   endforeach()
 
+  if(SKBUILD)
+    foreach(mod IN LISTS PYBIND11_MULTIPLE_INTERPRETERS_TEST_MODULES)
+      install(TARGETS "${mod}" LIBRARY DESTINATION .)
+    endforeach()
+  endif()
+
   if(PYBIND11_TEST_SMART_HOLDER)
     foreach(mod IN LISTS PYBIND11_MULTIPLE_INTERPRETERS_TEST_MODULES)
       target_compile_definitions(

tests/env.py

@@ -5,6 +5,7 @@ import sys
 import sysconfig
 
 ANDROID = sys.platform.startswith("android")
+IOS = sys.platform.startswith("ios")
 LINUX = sys.platform.startswith("linux")
 MACOS = sys.platform.startswith("darwin")
 WIN = sys.platform.startswith("win32") or sys.platform.startswith("cygwin")

tests/pyproject.toml

@@ -27,7 +27,9 @@ PYBIND11_FINDPYTHON = true
 
 [tool.cibuildwheel]
 test-sources = ["tests", "pyproject.toml"]
-test-command = "python -m pytest -o timeout=0 -p no:cacheprovider tests"
+test-command = "python -m pytest -v -o timeout=120 -p no:cacheprovider tests"
+# Pyodide doesn't have signal.setitimer, so pytest-timeout can't work with timeout > 0
+pyodide.test-command = "python -m pytest -v -o timeout=0 -p no:cacheprovider tests"
 environment.PIP_ONLY_BINARY = "numpy"
 environment.PIP_PREFER_BINARY = "1"
 

tests/requirements.txt

@@ -10,6 +10,7 @@ numpy~=1.22.2; platform_python_implementation=="CPython" and python_version=="3.
 numpy~=1.26.0; platform_python_implementation=="CPython" and python_version>="3.11" and python_version<"3.13" and platform_machine!="ARM64"
 numpy~=2.3.0; platform_python_implementation=="CPython" and python_version>="3.11" and platform_machine=="ARM64"
 numpy~=2.2.0; platform_python_implementation=="CPython" and python_version=="3.13" and platform_machine!="ARM64"
+numpy==2.4.0; platform_python_implementation=="CPython" and python_version>="3.14"
 pytest>=6
 pytest-timeout
 scipy~=1.5.4; platform_python_implementation=="CPython" and python_version<"3.10"

tests/test_multiple_interpreters.py

@@ -9,8 +9,12 @@ import textwrap
 
 import pytest
 
+import env
 import pybind11_tests
 
+if env.IOS:
+    pytest.skip("Subinterpreters not supported on iOS", allow_module_level=True)
+
 # 3.14.0b3+, though sys.implementation.supports_isolated_interpreters is being added in b4
 # Can be simplified when we drop support for the first three betas
 CONCURRENT_INTERPRETERS_SUPPORT = (

tests/test_pytypes.cpp

@@ -1211,4 +1211,6 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("check_type_is", [](const py::object &x) -> py::typing::TypeIs<RealNumber> {
         return py::isinstance<RealNumber>(x);
     });
+
+    m.def("const_kwargs_ref_to_str", [](const py::kwargs &kwargs) { return py::str(kwargs); });
 }

tests/test_pytypes.py

@@ -1367,3 +1367,8 @@ def test_arg_return_type_hints(doc, backport_typehints):
         backport_typehints(doc(m.check_type_guard))
         == "check_type_guard(arg0: list[object]) -> typing.TypeGuard[list[float]]"
     )
+
+
+def test_const_kwargs_ref_to_str():
+    assert m.const_kwargs_ref_to_str() == "{}"
+    assert m.const_kwargs_ref_to_str(a=1) == "{'a': 1}"