Merge branch 'v2.13' into stable

.clang-tidy

@@ -57,10 +57,12 @@ Checks: |
   readability-string-compare,
   readability-suspicious-call-argument,
   readability-uniqueptr-delete-release,
+  -bugprone-chained-comparison,
   -bugprone-easily-swappable-parameters,
   -bugprone-exception-escape,
   -bugprone-reserved-identifier,
   -bugprone-unused-raii,
+  -performance-enum-size,
 
 CheckOptions:
 - key:             modernize-use-equals-default.IgnoreMacros

.github/workflows/ci.yml

@@ -340,6 +340,12 @@ jobs:
           - clang: 16
             std: 20
             container_suffix: "-bullseye"
+          - clang: 17
+            std: 20
+            container_suffix: "-bookworm"
+          - clang: 18
+            std: 20
+            container_suffix: "-bookworm"
 
     name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
     container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
@@ -501,7 +507,9 @@ jobs:
           - { gcc: 7, std: 17 }
           - { gcc: 8, std: 14 }
           - { gcc: 8, std: 17 }
+          - { gcc: 9, std: 20 }
           - { gcc: 10, std: 17 }
+          - { gcc: 10, std: 20 }
           - { gcc: 11, std: 20 }
           - { gcc: 12, std: 20 }
           - { gcc: 13, std: 20 }

.github/workflows/emscripten.yaml

@@ -0,0 +1,30 @@
+name: WASM
+
+on:
+  workflow_dispatch:
+  pull_request:
+    branches:
+    - master
+    - stable
+    - v*
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-wasm-emscripten:
+    name: Pyodide wheel
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: true
+        fetch-depth: 0
+
+    - uses: pypa/cibuildwheel@v2.20
+      env:
+        PYODIDE_BUILD_EXPORTS: whole_archive
+      with:
+        package-dir: tests
+        only: cp312-pyodide_wasm32

.github/workflows/format.yml

@@ -41,7 +41,7 @@ jobs:
     # in .github/CONTRIBUTING.md and update as needed.
     name: Clang-Tidy
     runs-on: ubuntu-latest
-    container: silkeh/clang:15-bullseye
+    container: silkeh/clang:18-bookworm
     steps:
     - uses: actions/checkout@v4
 

.github/workflows/pip.yml

@@ -102,7 +102,7 @@ jobs:
     - uses: actions/download-artifact@v4
 
     - name: Generate artifact attestation for sdist and wheel
-      uses: actions/attest-build-provenance@173725a1209d09b31f9d30a3890cf2757ebbff0d # v1.1.2
+      uses: actions/attest-build-provenance@310b0a4a3b0b78ef57ecda988ee04b132db73ef8 # v1.4.1
       with:
         subject-path: "*/pybind11*"
 

.pre-commit-config.yaml

@@ -25,14 +25,14 @@ repos:
 
 # Clang format the codebase automatically
 - repo: https://github.com/pre-commit/mirrors-clang-format
-  rev: "v18.1.5"
+  rev: "v18.1.8"
   hooks:
   - id: clang-format
     types_or: [c++, c, cuda]
 
 # Ruff, the Python auto-correcting linter/formatter written in Rust
 - repo: https://github.com/astral-sh/ruff-pre-commit
-  rev: v0.4.7
+  rev: v0.5.6
   hooks:
   - id: ruff
     args: ["--fix", "--show-fixes"]
@@ -40,7 +40,7 @@ repos:
 
 # Check static types with mypy
 - repo: https://github.com/pre-commit/mirrors-mypy
-  rev: "v1.10.0"
+  rev: "v1.11.1"
   hooks:
   - id: mypy
     args: []
@@ -79,7 +79,7 @@ repos:
 
 # Also code format the docs
 - repo: https://github.com/adamchainz/blacken-docs
-  rev: "1.16.0"
+  rev: "1.18.0"
   hooks:
   - id: blacken-docs
     additional_dependencies:
@@ -142,14 +142,14 @@ repos:
 
 # PyLint has native support - not always usable, but works for us
 - repo: https://github.com/PyCQA/pylint
-  rev: "v3.2.2"
+  rev: "v3.2.6"
   hooks:
   - id: pylint
     files: ^pybind11
 
 # Check schemas on some of our YAML files
 - repo: https://github.com/python-jsonschema/check-jsonschema
-  rev: 0.28.4
+  rev: 0.29.1
   hooks:
   - id: check-readthedocs
   - id: check-github-workflows

CMakeLists.txt

@@ -154,6 +154,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/internals.h
     include/pybind11/detail/type_caster_base.h
     include/pybind11/detail/typeid.h
+    include/pybind11/detail/value_and_holder.h
     include/pybind11/attr.h
     include/pybind11/buffer_info.h
     include/pybind11/cast.h

docs/advanced/cast/eigen.rst

@@ -259,7 +259,7 @@ copying to take place:
         "small"_a            // <- This one can be copied if needed
     );
 
-With the above binding code, attempting to call the the ``some_method(m)``
+With the above binding code, attempting to call the ``some_method(m)``
 method on a ``MyClass`` object, or attempting to call ``some_function(m, m2)``
 will raise a ``RuntimeError`` rather than making a temporary copy of the array.
 It will, however, allow the ``m2`` argument to be copied into a temporary if

docs/changelog.rst

@@ -15,6 +15,98 @@ IN DEVELOPMENT
 
 Changes will be summarized here periodically.
 
+New Features:
+
+* Support for Python 3.7 was removed. (Official end-of-life: 2023-06-27).
+  `#5191 <https://github.com/pybind/pybind11/pull/5191>`_
+
+* stl.h ``list|set|map_caster`` were made more user friendly: it is no longer
+  necessary to explicitly convert Python iterables to ``tuple()``, ``set()``,
+  or ``map()`` in many common situations.
+  `#4686 <https://github.com/pybind/pybind11/pull/4686>`_
+
+* Support for CMake older than 3.15 removed. CMake 3.15-3.30 supported.
+  `#5304 <https://github.com/pybind/pybind11/pull/5304>`_
+
+Version 2.13.4 (August 14, 2024)
+--------------------------------
+
+Bug fixes:
+
+* Fix paths with spaces, including on Windows.
+  (Replaces regression from `#5302 <https://github.com/pybind/pybind11/pull/5302>`_)
+  `#4874 <https://github.com/pybind/pybind11/pull/4874>`_
+
+Documentation:
+
+* Remove repetitive words.
+  `#5308 <https://github.com/pybind/pybind11/pull/5308>`_
+
+
+Version 2.13.3 (August 13, 2024)
+--------------------------------
+
+Bug fixes:
+
+* Quote paths from pybind11-config
+  `#5302 <https://github.com/pybind/pybind11/pull/5302>`_
+
+
+* Fix typo in Emscripten support when in config mode (CMake)
+  `#5301 <https://github.com/pybind/pybind11/pull/5301>`_
+
+
+Version 2.13.2 (August 13, 2024)
+--------------------------------
+
+New Features:
+
+* A ``pybind11::detail::type_caster_std_function_specializations`` feature was added, to support specializations for
+  ``std::function``'s with return types that require custom to-Python conversion behavior (to primary use case is to catch and
+  convert exceptions).
+  `#4597 <https://github.com/pybind/pybind11/pull/4597>`_
+
+
+Changes:
+
+
+* Use ``PyMutex`` instead of ``std::mutex`` for internal locking in the free-threaded build.
+  `#5219 <https://github.com/pybind/pybind11/pull/5219>`_
+
+* Add a special type annotation for C++ empty tuple.
+  `#5214 <https://github.com/pybind/pybind11/pull/5214>`_
+
+* When compiling for WebAssembly, add the required exception flags (CMake 3.13+).
+  `#5298 <https://github.com/pybind/pybind11/pull/5298>`_
+
+Bug fixes:
+
+* Make ``gil_safe_call_once_and_store`` thread-safe in free-threaded CPython.
+  `#5246 <https://github.com/pybind/pybind11/pull/5246>`_
+
+* A missing ``#include <algorithm>`` in pybind11/typing.h was added to fix build errors (in case user code does not already depend
+  on that include).
+  `#5208 <https://github.com/pybind/pybind11/pull/5208>`_
+
+* Fix regression introduced in #5201 for GCC<10.3 in C++20 mode.
+  `#5205 <https://github.com/pybind/pybind11/pull/5205>`_
+
+
+.. fix(cmake)
+
+* Remove extra = when assigning flto value in the case for Clang in CMake.
+  `#5207 <https://github.com/pybind/pybind11/pull/5207>`_
+
+
+Tests:
+
+* Adding WASM testing to our CI (Pyodide / Emscripten via scikit-build-core).
+  `#4745 <https://github.com/pybind/pybind11/pull/4745>`_
+
+* clang-tidy (in GitHub Actions) was updated from clang 15 to clang 18.
+  `#5272 <https://github.com/pybind/pybind11/pull/5272>`_
+
+
 Version 2.13.1 (June 26, 2024)
 ------------------------------
 

docs/compiling.rst

@@ -25,7 +25,7 @@ A Python extension module can be created with just a few lines of code:
     find_package(pybind11 CONFIG REQUIRED)
 
     pybind11_add_module(example example.cpp)
-    install(TARGET example DESTINATION .)
+    install(TARGETS example DESTINATION .)
 
 (You use the ``add_subdirectory`` instead, see the example in :ref:`cmake`.) In
 this example, the code is located in a file named :file:`example.cpp`.  Either
@@ -388,7 +388,7 @@ that will be respected instead of the built-in flag search.
 
 The ``OPT_SIZE`` flag enables size-based optimization equivalent to the
 standard ``/Os`` or ``-Os`` compiler flags and the ``MinSizeRel`` build type,
-which avoid optimizations that that can substantially increase the size of the
+which avoid optimizations that can substantially increase the size of the
 resulting binary. This flag is particularly useful in projects that are split
 into performance-critical parts and associated bindings. In this case, we can
 compile the project in release mode (and hence, optimize performance globally),
@@ -719,7 +719,7 @@ customizable pybind11-based wrappers by parsing C++ header files.
 
 [litgen]_ is an automatic python bindings generator with a focus on generating
 documented and discoverable bindings: bindings will nicely reproduce the documentation
-found in headers. It is is based on srcML (srcml.org), a highly scalable, multi-language
+found in headers. It is based on srcML (srcml.org), a highly scalable, multi-language
 parsing tool with a developer centric approach. The API that you want to expose to python
 must be C++14 compatible (but your implementation can use more modern constructs).
 

docs/limitations.rst

@@ -50,10 +50,6 @@ clean, well written patch would likely be accepted to solve them.
   One consequence is that containers of ``char *`` are currently not supported.
   `#2245 <https://github.com/pybind/pybind11/issues/2245>`_
 
-- The ``cpptest`` does not run on Windows with Python 3.8 or newer, due to DLL
-  loader changes. User code that is correctly installed should not be affected.
-  `#2560 <https://github.com/pybind/pybind11/issue/2560>`_
-
 Python 3.9.0 warning
 ^^^^^^^^^^^^^^^^^^^^
 

docs/requirements.txt

@@ -16,9 +16,9 @@ breathe==4.35.0 \
     --hash=sha256:5165541c3c67b6c7adde8b3ecfe895c6f7844783c4076b6d8d287e4f33d62386 \
     --hash=sha256:52c581f42ca4310737f9e435e3851c3d1f15446205a85fbc272f1f97ed74f5be
     # via -r requirements.in
-certifi==2024.2.2 \
+certifi==2024.7.4 \
-    --hash=sha256:0569859f95fc761b18b45ef421b1290a0f65f147e92a1e5eb3e635f9a5e4e66f \
+    --hash=sha256:5a1e7645bc0ec61a09e26c36f6106dd4cf40c6db3a1fb6352b0244e7fb057c7b \
-    --hash=sha256:dc383c07b76109f368f6106eee2b593b04a011ea4d55f652c6ca24a754d1cdd1
+    --hash=sha256:c198e21b1289c2ab85ee4e67bb4b4ef3ead0892059901a8d5b622f24a1101e90
     # via requests
 charset-normalizer==3.3.2 \
     --hash=sha256:06435b539f889b1f6f4ac1758871aae42dc3a8c0e24ac9e60c2384973ad73027 \

include/pybind11/cast.h

@@ -740,6 +740,13 @@ class type_caster<std::pair<T1, T2>> : public tuple_caster<std::pair, T1, T2> {}
 template <typename... Ts>
 class type_caster<std::tuple<Ts...>> : public tuple_caster<std::tuple, Ts...> {};
 
+template <>
+class type_caster<std::tuple<>> : public tuple_caster<std::tuple> {
+public:
+    // PEP 484 specifies this syntax for an empty tuple
+    static constexpr auto name = const_name("tuple[()]");
+};
+
 /// Helper class which abstracts away certain actions. Users can provide specializations for
 /// custom holders, but it's only necessary if the type has a non-standard interface.
 template <typename T>
@@ -787,11 +794,11 @@ protected:
         }
     }
 
-    bool load_value(value_and_holder &&v_h) {
+    void load_value(value_and_holder &&v_h) {
         if (v_h.holder_constructed()) {
             value = v_h.value_ptr();
             holder = v_h.template holder<holder_type>();
-            return true;
+            return;
         }
         throw cast_error("Unable to cast from non-held to held instance (T& to Holder<T>) "
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)

include/pybind11/detail/common.h

@@ -11,11 +11,11 @@
 
 #define PYBIND11_VERSION_MAJOR 2
 #define PYBIND11_VERSION_MINOR 13
-#define PYBIND11_VERSION_PATCH 1
+#define PYBIND11_VERSION_PATCH 4
 
 // Similar to Python's convention: https://docs.python.org/3/c-api/apiabiversion.html
 // Additional convention: 0xD = dev
-#define PYBIND11_VERSION_HEX 0x020D0100
+#define PYBIND11_VERSION_HEX 0x020D0400
 
 // Define some generic pybind11 helper macros for warning management.
 //
@@ -462,6 +462,22 @@ PYBIND11_WARNING_POP
                 return "Hello, World!";
             });
         }
+
+    The third macro argument is optional (available since 2.13.0), and can be used to
+    mark the extension module as safe to run without the GIL under a free-threaded CPython
+    interpreter. Passing this argument has no effect on other interpreters.
+
+    .. code-block:: cpp
+
+        PYBIND11_MODULE(example, m, py::mod_gil_not_used()) {
+            m.doc() = "pybind11 example module safe to run without the GIL";
+
+            // Add bindings here
+            m.def("foo", []() {
+                return "Hello, Free-threaded World!";
+            });
+        }
+
 \endrst */
 #define PYBIND11_MODULE(name, variable, ...)                                                      \
     static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name)            \
@@ -538,7 +554,7 @@ enum class return_value_policy : uint8_t {
         object without taking ownership similar to the above
         return_value_policy::reference policy. In contrast to that policy, the
         function or property's implicit this argument (called the parent) is
-        considered to be the the owner of the return value (the child).
+        considered to be the owner of the return value (the child).
         pybind11 then couples the lifetime of the parent to the child via a
         reference relationship that ensures that the parent cannot be garbage
         collected while Python is still using the child. More advanced

include/pybind11/detail/init.h

@@ -128,11 +128,13 @@ void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
         // the holder and destruction happens when we leave the C++ scope, and the holder
         // class gets to handle the destruction however it likes.
         v_h.value_ptr() = ptr;
-        v_h.set_instance_registered(true);          // To prevent init_instance from registering it
+        v_h.set_instance_registered(true); // Trick to prevent init_instance from registering it
-        v_h.type->init_instance(v_h.inst, nullptr); // Set up the holder
+        // DANGER ZONE BEGIN: exceptions will leave v_h in an invalid state.
+        v_h.type->init_instance(v_h.inst, nullptr);                        // Set up the holder
         Holder<Class> temp_holder(std::move(v_h.holder<Holder<Class>>())); // Steal the holder
         v_h.type->dealloc(v_h); // Destroys the moved-out holder remains, resets value ptr to null
         v_h.set_instance_registered(false);
+        // DANGER ZONE END.
 
         construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(*ptr));
     } else {

include/pybind11/detail/internals.h

@@ -148,20 +148,35 @@ struct override_hash {
 
 using instance_map = std::unordered_multimap<const void *, instance *>;
 
+#ifdef Py_GIL_DISABLED
+// Wrapper around PyMutex to provide BasicLockable semantics
+class pymutex {
+    PyMutex mutex;
+
+public:
+    pymutex() : mutex({}) {}
+    void lock() { PyMutex_Lock(&mutex); }
+    void unlock() { PyMutex_Unlock(&mutex); }
+};
+
 // Instance map shards are used to reduce mutex contention in free-threaded Python.
 struct instance_map_shard {
-    std::mutex mutex;
     instance_map registered_instances;
+    pymutex mutex;
     // alignas(64) would be better, but causes compile errors in macOS before 10.14 (see #5200)
-    char padding[64 - (sizeof(std::mutex) + sizeof(instance_map)) % 64];
+    char padding[64 - (sizeof(instance_map) + sizeof(pymutex)) % 64];
 };
 
+static_assert(sizeof(instance_map_shard) % 64 == 0,
+              "instance_map_shard size is not a multiple of 64 bytes");
+#endif
+
 /// Internal data structure used to track registered instances and types.
 /// Whenever binary incompatible changes are made to this structure,
 /// `PYBIND11_INTERNALS_VERSION` must be incremented.
 struct internals {
 #ifdef Py_GIL_DISABLED
-    std::mutex mutex;
+    pymutex mutex;
 #endif
     // std::type_index -> pybind11's type information
     type_map<type_info *> registered_types_cpp;
@@ -538,7 +553,7 @@ PYBIND11_NOINLINE internals &get_internals() {
         }
 #endif
         internals_ptr->istate = tstate->interp;
-        state_dict[PYBIND11_INTERNALS_ID] = capsule(internals_pp);
+        state_dict[PYBIND11_INTERNALS_ID] = capsule(reinterpret_cast<void *>(internals_pp));
         internals_ptr->registered_exception_translators.push_front(&translate_exception);
         internals_ptr->static_property_type = make_static_property_type();
         internals_ptr->default_metaclass = make_default_metaclass();
@@ -614,7 +629,7 @@ inline local_internals &get_local_internals() {
 }
 
 #ifdef Py_GIL_DISABLED
-#    define PYBIND11_LOCK_INTERNALS(internals) std::unique_lock<std::mutex> lock((internals).mutex)
+#    define PYBIND11_LOCK_INTERNALS(internals) std::unique_lock<pymutex> lock((internals).mutex)
 #else
 #    define PYBIND11_LOCK_INTERNALS(internals)
 #endif
@@ -651,7 +666,7 @@ inline auto with_instance_map(const void *ptr,
     auto idx = static_cast<size_t>(hash & internals.instance_shards_mask);
 
     auto &shard = internals.instance_shards[idx];
-    std::unique_lock<std::mutex> lock(shard.mutex);
+    std::unique_lock<pymutex> lock(shard.mutex);
     return cb(shard.registered_instances);
 #else
     (void) ptr;
@@ -667,7 +682,7 @@ inline size_t num_registered_instances() {
     size_t count = 0;
     for (size_t i = 0; i <= internals.instance_shards_mask; ++i) {
         auto &shard = internals.instance_shards[i];
-        std::unique_lock<std::mutex> lock(shard.mutex);
+        std::unique_lock<pymutex> lock(shard.mutex);
         count += shard.registered_instances.size();
     }
     return count;

include/pybind11/detail/type_caster_base.h

@@ -14,6 +14,7 @@
 #include "descr.h"
 #include "internals.h"
 #include "typeid.h"
+#include "value_and_holder.h"
 
 #include <cstdint>
 #include <iterator>
@@ -259,67 +260,6 @@ PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
     });
 }
 
-struct value_and_holder {
-    instance *inst = nullptr;
-    size_t index = 0u;
-    const detail::type_info *type = nullptr;
-    void **vh = nullptr;
-
-    // Main constructor for a found value/holder:
-    value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
-        : inst{i}, index{index}, type{type},
-          vh{inst->simple_layout ? inst->simple_value_holder
-                                 : &inst->nonsimple.values_and_holders[vpos]} {}
-
-    // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
-    value_and_holder() = default;
-
-    // Used for past-the-end iterator
-    explicit value_and_holder(size_t index) : index{index} {}
-
-    template <typename V = void>
-    V *&value_ptr() const {
-        return reinterpret_cast<V *&>(vh[0]);
-    }
-    // True if this `value_and_holder` has a non-null value pointer
-    explicit operator bool() const { return value_ptr() != nullptr; }
-
-    template <typename H>
-    H &holder() const {
-        return reinterpret_cast<H &>(vh[1]);
-    }
-    bool holder_constructed() const {
-        return inst->simple_layout
-                   ? inst->simple_holder_constructed
-                   : (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
-    }
-    // NOLINTNEXTLINE(readability-make-member-function-const)
-    void set_holder_constructed(bool v = true) {
-        if (inst->simple_layout) {
-            inst->simple_holder_constructed = v;
-        } else if (v) {
-            inst->nonsimple.status[index] |= instance::status_holder_constructed;
-        } else {
-            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
-        }
-    }
-    bool instance_registered() const {
-        return inst->simple_layout
-                   ? inst->simple_instance_registered
-                   : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
-    }
-    // NOLINTNEXTLINE(readability-make-member-function-const)
-    void set_instance_registered(bool v = true) {
-        if (inst->simple_layout) {
-            inst->simple_instance_registered = v;
-        } else if (v) {
-            inst->nonsimple.status[index] |= instance::status_instance_registered;
-        } else {
-            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
-        }
-    }
-};
-
 // Container for accessing and iterating over an instance's values/holders
 struct values_and_holders {
 private:
@@ -488,7 +428,7 @@ PYBIND11_NOINLINE void instance::allocate_layout() {
 // NOLINTNEXTLINE(readability-make-member-function-const)
 PYBIND11_NOINLINE void instance::deallocate_layout() {
     if (!simple_layout) {
-        PyMem_Free(nonsimple.values_and_holders);
+        PyMem_Free(reinterpret_cast<void *>(nonsimple.values_and_holders));
     }
 }
 

include/pybind11/detail/value_and_holder.h

@@ -0,0 +1,77 @@
+// Copyright (c) 2016-2024 The Pybind Development Team.
+// All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#pragma once
+
+#include "common.h"
+
+#include <cstddef>
+#include <typeinfo>
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+struct value_and_holder {
+    instance *inst = nullptr;
+    size_t index = 0u;
+    const detail::type_info *type = nullptr;
+    void **vh = nullptr;
+
+    // Main constructor for a found value/holder:
+    value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
+        : inst{i}, index{index}, type{type},
+          vh{inst->simple_layout ? inst->simple_value_holder
+                                 : &inst->nonsimple.values_and_holders[vpos]} {}
+
+    // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
+    value_and_holder() = default;
+
+    // Used for past-the-end iterator
+    explicit value_and_holder(size_t index) : index{index} {}
+
+    template <typename V = void>
+    V *&value_ptr() const {
+        return reinterpret_cast<V *&>(vh[0]);
+    }
+    // True if this `value_and_holder` has a non-null value pointer
+    explicit operator bool() const { return value_ptr() != nullptr; }
+
+    template <typename H>
+    H &holder() const {
+        return reinterpret_cast<H &>(vh[1]);
+    }
+    bool holder_constructed() const {
+        return inst->simple_layout
+                   ? inst->simple_holder_constructed
+                   : (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_holder_constructed(bool v = true) {
+        if (inst->simple_layout) {
+            inst->simple_holder_constructed = v;
+        } else if (v) {
+            inst->nonsimple.status[index] |= instance::status_holder_constructed;
+        } else {
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
+        }
+    }
+    bool instance_registered() const {
+        return inst->simple_layout
+                   ? inst->simple_instance_registered
+                   : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_instance_registered(bool v = true) {
+        if (inst->simple_layout) {
+            inst->simple_instance_registered = v;
+        } else if (v) {
+            inst->nonsimple.status[index] |= instance::status_instance_registered;
+        } else {
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
+        }
+    }
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/eigen/tensor.h

@@ -469,9 +469,6 @@ struct type_caster<Eigen::TensorMap<Type, Options>,
                 parent_object = reinterpret_borrow<object>(parent);
                 break;
 
-            case return_value_policy::take_ownership:
-                delete src;
-                // fallthrough
             default:
                 // move, take_ownership don't make any sense for a ref/map:
                 pybind11_fail("Invalid return_value_policy for Eigen Map type, must be either "

include/pybind11/functional.h

@@ -9,12 +9,55 @@
 
 #pragma once
 
+#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS
+
 #include "pybind11.h"
 
 #include <functional>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
+PYBIND11_NAMESPACE_BEGIN(type_caster_std_function_specializations)
+
+// ensure GIL is held during functor destruction
+struct func_handle {
+    function f;
+#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
+    // This triggers a syntax error under very special conditions (very weird indeed).
+    explicit
+#endif
+        func_handle(function &&f_) noexcept
+        : f(std::move(f_)) {
+    }
+    func_handle(const func_handle &f_) { operator=(f_); }
+    func_handle &operator=(const func_handle &f_) {
+        gil_scoped_acquire acq;
+        f = f_.f;
+        return *this;
+    }
+    ~func_handle() {
+        gil_scoped_acquire acq;
+        function kill_f(std::move(f));
+    }
+};
+
+// to emulate 'move initialization capture' in C++11
+struct func_wrapper_base {
+    func_handle hfunc;
+    explicit func_wrapper_base(func_handle &&hf) noexcept : hfunc(hf) {}
+};
+
+template <typename Return, typename... Args>
+struct func_wrapper : func_wrapper_base {
+    using func_wrapper_base::func_wrapper_base;
+    Return operator()(Args... args) const {
+        gil_scoped_acquire acq;
+        // casts the returned object as a rvalue to the return type
+        return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
+    }
+};
+
+PYBIND11_NAMESPACE_END(type_caster_std_function_specializations)
 
 template <typename Return, typename... Args>
 struct type_caster<std::function<Return(Args...)>> {
@@ -77,40 +120,8 @@ public:
             // See PR #1413 for full details
         }
 
-        // ensure GIL is held during functor destruction
+        value = type_caster_std_function_specializations::func_wrapper<Return, Args...>(
-        struct func_handle {
+            type_caster_std_function_specializations::func_handle(std::move(func)));
-            function f;
-#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
-            // This triggers a syntax error under very special conditions (very weird indeed).
-            explicit
-#endif
-                func_handle(function &&f_) noexcept
-                : f(std::move(f_)) {
-            }
-            func_handle(const func_handle &f_) { operator=(f_); }
-            func_handle &operator=(const func_handle &f_) {
-                gil_scoped_acquire acq;
-                f = f_.f;
-                return *this;
-            }
-            ~func_handle() {
-                gil_scoped_acquire acq;
-                function kill_f(std::move(f));
-            }
-        };
-
-        // to emulate 'move initialization capture' in C++11
-        struct func_wrapper {
-            func_handle hfunc;
-            explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
-            Return operator()(Args... args) const {
-                gil_scoped_acquire acq;
-                // casts the returned object as a rvalue to the return type
-                return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
-            }
-        };
-
-        value = func_wrapper(func_handle(std::move(func)));
         return true;
     }
 

include/pybind11/gil_safe_call_once.h

@@ -8,6 +8,10 @@
 #include <cassert>
 #include <mutex>
 
+#ifdef Py_GIL_DISABLED
+#    include <atomic>
+#endif
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 // Use the `gil_safe_call_once_and_store` class below instead of the naive
@@ -82,7 +86,12 @@ public:
 private:
     alignas(T) char storage_[sizeof(T)] = {};
     std::once_flag once_flag_ = {};
-    bool is_initialized_ = false;
+#ifdef Py_GIL_DISABLED
+    std::atomic_bool
+#else
+    bool
+#endif
+        is_initialized_{false};
     // The `is_initialized_`-`storage_` pair is very similar to `std::optional`,
     // but the latter does not have the triviality properties of former,
     // therefore `std::optional` is not a viable alternative here.

include/pybind11/numpy.h

@@ -901,7 +901,11 @@ public:
 
     template <typename T>
     array(ShapeContainer shape, StridesContainer strides, const T *ptr, handle base = handle())
-        : array(pybind11::dtype::of<T>(), std::move(shape), std::move(strides), ptr, base) {}
+        : array(pybind11::dtype::of<T>(),
+                std::move(shape),
+                std::move(strides),
+                reinterpret_cast<const void *>(ptr),
+                base) {}
 
     template <typename T>
     array(ShapeContainer shape, const T *ptr, handle base = handle())
@@ -1986,7 +1990,7 @@ private:
         // Pointers to values the function was called with; the vectorized ones set here will start
         // out as array_t<T> pointers, but they will be changed them to T pointers before we make
         // call the wrapped function.  Non-vectorized pointers are left as-is.
-        std::array<void *, N> params{{&args...}};
+        std::array<void *, N> params{{reinterpret_cast<void *>(&args)...}};
 
         // The array of `buffer_info`s of vectorized arguments:
         std::array<buffer_info, NVectorized> buffers{

include/pybind11/stl/filesystem.h

@@ -33,6 +33,13 @@
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
+#ifdef PYPY_VERSION
+#    define PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(...) (__VA_ARGS__)
+#else
+#    define PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(...)                                   \
+        (reinterpret_cast<void *>(__VA_ARGS__))
+#endif
+
 #if defined(PYBIND11_HAS_FILESYSTEM) || defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)
 template <typename T>
 struct path_caster {
@@ -72,7 +79,8 @@ public:
         }
         PyObject *native = nullptr;
         if constexpr (std::is_same_v<typename T::value_type, char>) {
-            if (PyUnicode_FSConverter(buf, &native) != 0) {
+            if (PyUnicode_FSConverter(buf, PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(&native))
+                != 0) {
                 if (auto *c_str = PyBytes_AsString(native)) {
                     // AsString returns a pointer to the internal buffer, which
                     // must not be free'd.
@@ -80,7 +88,8 @@ public:
                 }
             }
         } else if constexpr (std::is_same_v<typename T::value_type, wchar_t>) {
-            if (PyUnicode_FSDecoder(buf, &native) != 0) {
+            if (PyUnicode_FSDecoder(buf, PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(&native))
+                != 0) {
                 if (auto *c_str = PyUnicode_AsWideCharString(native, nullptr)) {
                     // AsWideCharString returns a new string that must be free'd.
                     value = c_str; // Copies the string.

include/pybind11/stl_bind.h

@@ -180,7 +180,7 @@ void vector_modifiers(
                         v.end());
                 try {
                     v.shrink_to_fit();
-                } catch (const std::exception &) {
+                } catch (const std::exception &) { // NOLINT(bugprone-empty-catch)
                     // Do nothing
                 }
                 throw;

include/pybind11/typing.h

@@ -14,6 +14,8 @@
 #include "cast.h"
 #include "pytypes.h"
 
+#include <algorithm>
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(typing)
 
@@ -98,7 +100,10 @@ class Never : public none {
     using none::none;
 };
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(__cpp_nontype_template_parameter_class)                                               \
+    && (/* See #5201 */ !defined(__GNUC__)                                                        \
+        || (__GNUC__ > 10 || (__GNUC__ == 10 && __GNUC_MINOR__ >= 3)))
+#    define PYBIND11_TYPING_H_HAS_STRING_LITERAL
 template <size_t N>
 struct StringLiteral {
     constexpr StringLiteral(const char (&str)[N]) { std::copy_n(str, N, name); }
@@ -222,7 +227,7 @@ struct handle_type_name<typing::Never> {
     static constexpr auto name = const_name("Never");
 };
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
 template <typing::StringLiteral... Literals>
 struct handle_type_name<typing::Literal<Literals...>> {
     static constexpr auto name = const_name("Literal[")

pybind11/__main__.py

@@ -2,12 +2,35 @@
 from __future__ import annotations
 
 import argparse
+import re
 import sys
 import sysconfig
 
 from ._version import __version__
 from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
+# This is the conditional used for os.path being posixpath
+if "posix" in sys.builtin_module_names:
+    from shlex import quote
+elif "nt" in sys.builtin_module_names:
+    # See https://github.com/mesonbuild/meson/blob/db22551ed9d2dd7889abea01cc1c7bba02bf1c75/mesonbuild/utils/universal.py#L1092-L1121
+    # and the original documents:
+    # https://docs.microsoft.com/en-us/cpp/c-language/parsing-c-command-line-arguments and
+    # https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/
+    UNSAFE = re.compile("[ \t\n\r]")
+
+    def quote(s: str) -> str:
+        if s and not UNSAFE.search(s):
+            return s
+
+        # Paths cannot contain a '"' on Windows, so we don't need to worry
+        # about nuanced counting here.
+        return f'"{s}\\"' if s.endswith("\\") else f'"{s}"'
+else:
+
+    def quote(s: str) -> str:
+        return s
+
 
 def print_includes() -> None:
     dirs = [
@@ -22,7 +45,7 @@ def print_includes() -> None:
         if d and d not in unique_dirs:
             unique_dirs.append(d)
 
-    print(" ".join("-I" + d for d in unique_dirs))
+    print(" ".join(quote(f"-I{d}") for d in unique_dirs))
 
 
 def main() -> None:
@@ -54,9 +77,9 @@ def main() -> None:
     if args.includes:
         print_includes()
     if args.cmakedir:
-        print(get_cmake_dir())
+        print(quote(get_cmake_dir()))
     if args.pkgconfigdir:
-        print(get_pkgconfig_dir())
+        print(quote(get_pkgconfig_dir()))
 
 
 if __name__ == "__main__":

pybind11/_version.py

@@ -8,5 +8,5 @@ def _to_int(s: str) -> int | str:
         return s
 
 
-__version__ = "2.13.1"
+__version__ = "2.13.4"
 version_info = tuple(_to_int(s) for s in __version__.split("."))

tests/CMakeLists.txt

@@ -88,7 +88,12 @@ set(PYBIND11_TEST_FILTER
 if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
   # We're being loaded directly, i.e. not via add_subdirectory, so make this
   # work as its own project and load the pybind11Config to get the tools we need
-  find_package(pybind11 REQUIRED CONFIG)
+
+  if(SKBUILD)
+    add_subdirectory(.. pybind11_src)
+  else()
+    find_package(pybind11 REQUIRED CONFIG)
+  endif()
 endif()
 
 if(NOT CMAKE_BUILD_TYPE AND NOT DEFINED CMAKE_CONFIGURATION_TYPES)
@@ -153,6 +158,7 @@ set(PYBIND11_TEST_FILES
     test_tagbased_polymorphic
     test_thread
     test_type_caster_pyobject_ptr
+    test_type_caster_std_function_specializations
     test_union
     test_unnamed_namespace_a
     test_unnamed_namespace_b
@@ -489,6 +495,9 @@ foreach(target ${test_targets})
       endforeach()
     endif()
   endif()
+  if(SKBUILD)
+    install(TARGETS ${target} LIBRARY DESTINATION .)
+  endif()
 endforeach()
 
 # Provide nice organisation in IDEs

tests/constructor_stats.h

@@ -190,7 +190,7 @@ public:
                     t1 = &p.first;
                 }
             }
-        } catch (const std::out_of_range &) {
+        } catch (const std::out_of_range &) { // NOLINT(bugprone-empty-catch)
         }
         if (!t1) {
             throw std::runtime_error("Unknown class passed to ConstructorStats::get()");

tests/extra_python_package/test_files.py

@@ -58,6 +58,7 @@ detail_headers = {
     "include/pybind11/detail/internals.h",
     "include/pybind11/detail/type_caster_base.h",
     "include/pybind11/detail/typeid.h",
+    "include/pybind11/detail/value_and_holder.h",
 }
 
 eigen_headers = {

tests/pyproject.toml

@@ -0,0 +1,21 @@
+# Warning: this is currently used for pyodide, and is not a general out-of-tree
+# builder for the tests (yet). Specifically, wheels can't be built from SDists.
+
+[build-system]
+requires = ["scikit-build-core"]
+build-backend = "scikit_build_core.build"
+
+[project]
+name = "pybind11_tests"
+version = "0.0.1"
+dependencies = ["pytest", "pytest-timeout", "numpy", "scipy"]
+
+[tool.scikit-build]
+# Hide a warning while we also support CMake < 3.15
+cmake.version = ">=3.15"
+
+[tool.scikit-build.cmake.define]
+PYBIND11_FINDPYTHON = true
+
+[tool.cibuildwheel]
+test-command = "pytest -o timeout=0 -p no:cacheprovider {project}/tests/test_*.py"

tests/test_async.py

@@ -1,10 +1,15 @@
 from __future__ import annotations
 
+import sys
+
 import pytest
 
 asyncio = pytest.importorskip("asyncio")
 m = pytest.importorskip("pybind11_tests.async_module")
 
+if sys.platform.startswith("emscripten"):
+    pytest.skip("Can't run a new event_loop in pyodide", allow_module_level=True)
+
 
 @pytest.fixture()
 def event_loop():

tests/test_builtin_casters.py

@@ -368,6 +368,8 @@ def test_tuple(doc):
     """
     )
 
+    assert doc(m.empty_tuple) == """empty_tuple() -> tuple[()]"""
+
     assert m.rvalue_pair() == ("rvalue", "rvalue")
     assert m.lvalue_pair() == ("lvalue", "lvalue")
     assert m.rvalue_tuple() == ("rvalue", "rvalue", "rvalue")

tests/test_callbacks.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import sys
 import time
 from threading import Thread
 
@@ -153,6 +154,7 @@ def test_python_builtins():
     assert m.test_sum_builtin(sum, []) == 0
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_async_callbacks():
     # serves as state for async callback
     class Item:
@@ -176,6 +178,7 @@ def test_async_callbacks():
     assert sum(res) == sum(x + 3 for x in work)
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_async_async_callbacks():
     t = Thread(target=test_async_callbacks)
     t.start()

tests/test_eigen_tensor.inl

@@ -147,33 +147,39 @@ void init_tensor_module(pybind11::module &m) {
 
     m.def(
         "take_fixed_tensor",
-
         []() {
             Eigen::aligned_allocator<
                 Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>>
                 allocator;
-            return new (allocator.allocate(1))
+            static auto *obj = new (allocator.allocate(1))
                 Eigen::TensorFixedSize<double, Eigen::Sizes<3, 5, 2>, Options>(
                     get_fixed_tensor<Options>());
+            return obj; // take_ownership will fail.
         },
         py::return_value_policy::take_ownership);
 
     m.def(
         "take_tensor",
-        []() { return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>()); },
+        []() {
+            static auto *obj = new Eigen::Tensor<double, 3, Options>(get_tensor<Options>());
+            return obj; // take_ownership will fail.
+        },
         py::return_value_policy::take_ownership);
 
     m.def(
         "take_const_tensor",
         []() -> const Eigen::Tensor<double, 3, Options> * {
-            return new Eigen::Tensor<double, 3, Options>(get_tensor<Options>());
+            static auto *obj = new Eigen::Tensor<double, 3, Options>(get_tensor<Options>());
+            return obj; // take_ownership will fail.
         },
         py::return_value_policy::take_ownership);
 
     m.def(
         "take_view_tensor",
         []() -> const Eigen::TensorMap<Eigen::Tensor<double, 3, Options>> * {
-            return new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+            static auto *obj
+                = new Eigen::TensorMap<Eigen::Tensor<double, 3, Options>>(get_tensor<Options>());
+            return obj; // take_ownership will fail.
         },
         py::return_value_policy::take_ownership);
 

tests/test_exceptions.py

@@ -75,7 +75,7 @@ def test_cross_module_exceptions(msg):
 
 # TODO: FIXME
 @pytest.mark.xfail(
-    "env.MACOS and (env.PYPY or pybind11_tests.compiler_info.startswith('Homebrew Clang'))",
+    "env.MACOS and (env.PYPY or pybind11_tests.compiler_info.startswith('Homebrew Clang')) or sys.platform.startswith('emscripten')",
     raises=RuntimeError,
     reason="See Issue #2847, PR #2999, PR #4324",
 )

tests/test_gil_scoped.py

@@ -71,24 +71,28 @@ def test_cross_module_gil_inner_pybind11_acquired():
     m.test_cross_module_gil_inner_pybind11_acquired()
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_cross_module_gil_nested_custom_released():
     """Makes sure that the GIL can be nested acquired/released by another module
     from a GIL-released state using custom locking logic."""
     m.test_cross_module_gil_nested_custom_released()
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_cross_module_gil_nested_custom_acquired():
     """Makes sure that the GIL can be nested acquired/acquired by another module
     from a GIL-acquired state using custom locking logic."""
     m.test_cross_module_gil_nested_custom_acquired()
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_cross_module_gil_nested_pybind11_released():
     """Makes sure that the GIL can be nested acquired/released by another module
     from a GIL-released state using pybind11 locking logic."""
     m.test_cross_module_gil_nested_pybind11_released()
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_cross_module_gil_nested_pybind11_acquired():
     """Makes sure that the GIL can be nested acquired/acquired by another module
     from a GIL-acquired state using pybind11 locking logic."""
@@ -103,6 +107,7 @@ def test_nested_acquire():
     assert m.test_nested_acquire(0xAB) == "171"
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_multi_acquire_release_cross_module():
     for bits in range(16 * 8):
         internals_ids = m.test_multi_acquire_release_cross_module(bits)
@@ -204,7 +209,7 @@ def _run_in_threads(test_fn, num_threads, parallel):
         thread.join()
 
 
-# TODO: FIXME, sometimes returns -11 (segfault) instead of 0 on macOS Python 3.9
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 @pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
 def test_run_in_process_one_thread(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread.
@@ -214,7 +219,7 @@ def test_run_in_process_one_thread(test_fn):
     assert _run_in_process(_run_in_threads, test_fn, num_threads=1, parallel=False) == 0
 
 
-# TODO: FIXME on macOS Python 3.9
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 @pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
 def test_run_in_process_multiple_threads_parallel(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread multiple times in parallel.
@@ -224,7 +229,7 @@ def test_run_in_process_multiple_threads_parallel(test_fn):
     assert _run_in_process(_run_in_threads, test_fn, num_threads=8, parallel=True) == 0
 
 
-# TODO: FIXME on macOS Python 3.9
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 @pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
 def test_run_in_process_multiple_threads_sequential(test_fn):
     """Makes sure there is no GIL deadlock when running in a thread multiple times sequentially.
@@ -234,7 +239,7 @@ def test_run_in_process_multiple_threads_sequential(test_fn):
     assert _run_in_process(_run_in_threads, test_fn, num_threads=8, parallel=False) == 0
 
 
-# TODO: FIXME on macOS Python 3.9
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 @pytest.mark.parametrize("test_fn", ALL_BASIC_TESTS_PLUS_INTENTIONAL_DEADLOCK)
 def test_run_in_process_direct(test_fn):
     """Makes sure there is no GIL deadlock when using processes.

tests/test_iostream.py

@@ -1,8 +1,11 @@
 from __future__ import annotations
 
+import sys
 from contextlib import redirect_stderr, redirect_stdout
 from io import StringIO
 
+import pytest
+
 from pybind11_tests import iostream as m
 
 
@@ -270,6 +273,7 @@ def test_redirect_both(capfd):
     assert stream2.getvalue() == msg2
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_threading():
     with m.ostream_redirect(stdout=True, stderr=False):
         # start some threads

tests/test_modules.cpp

@@ -90,32 +90,32 @@ TEST_SUBMODULE(modules, m) {
         try {
             py::class_<Dupe1>(dm, "Dupe1");
             failures.append("Dupe1 class");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
         try {
             dm.def("Dupe1", []() { return Dupe1(); });
             failures.append("Dupe1 function");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
         try {
             py::class_<Dupe3>(dm, "dupe1_factory");
             failures.append("dupe1_factory");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
         try {
             py::exception<Dupe3>(dm, "Dupe2");
             failures.append("Dupe2");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
         try {
             dm.def("DupeException", []() { return 30; });
             failures.append("DupeException1");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
         try {
             py::class_<DupeException>(dm, "DupeException");
             failures.append("DupeException2");
-        } catch (std::runtime_error &) {
+        } catch (std::runtime_error &) { // NOLINT(bugprone-empty-catch)
         }
 
         return failures;

tests/test_numpy_dtypes.cpp

@@ -266,6 +266,8 @@ py::array_t<int32_t, 0> test_array_ctors(int i) {
             return fill(arr_t(buf_ndim1_null));
         case 44:
             return fill(py::array(buf_ndim1_null));
+        default:
+            break;
     }
     return arr_t();
 }

tests/test_opaque_types.cpp

@@ -65,7 +65,7 @@ TEST_SUBMODULE(opaque_types, m) {
 
     m.def("return_unique_ptr", []() -> std::unique_ptr<StringList> {
         auto *result = new StringList();
-        result->push_back("some value");
+        result->emplace_back("some value");
         return std::unique_ptr<StringList>(result);
     });
 

tests/test_pytypes.cpp

@@ -109,7 +109,7 @@ void m_defs(py::module_ &m) {
 
 } // namespace handle_from_move_only_type_with_operator_PyObject
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
 namespace literals {
 enum Color { RED = 0, BLUE = 1 };
 
@@ -905,7 +905,7 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("annotate_optional_to_object",
           [](py::typing::Optional<int> &o) -> py::object { return o; });
 
-#if defined(__cpp_nontype_template_parameter_class)
+#if defined(PYBIND11_TYPING_H_HAS_STRING_LITERAL)
     py::enum_<literals::Color>(m, "Color")
         .value("RED", literals::Color::RED)
         .value("BLUE", literals::Color::BLUE);
@@ -919,8 +919,8 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("annotate_listT_to_T",
           [](const py::typing::List<typevar::TypeVarT> &l) -> typevar::TypeVarT { return l[0]; });
     m.def("annotate_object_to_T", [](const py::object &o) -> typevar::TypeVarT { return o; });
-    m.attr("if_defined__cpp_nontype_template_parameter_class") = true;
+    m.attr("defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL") = true;
 #else
-    m.attr("if_defined__cpp_nontype_template_parameter_class") = false;
+    m.attr("defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL") = false;
 #endif
 }

tests/test_pytypes.py

@@ -1025,7 +1025,7 @@ def test_optional_object_annotations(doc):
 
 
 @pytest.mark.skipif(
-    not m.if_defined__cpp_nontype_template_parameter_class,
+    not m.defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL,
     reason="C++20 feature not available.",
 )
 def test_literal(doc):
@@ -1036,7 +1036,7 @@ def test_literal(doc):
 
 
 @pytest.mark.skipif(
-    not m.if_defined__cpp_nontype_template_parameter_class,
+    not m.defined_PYBIND11_TYPING_H_HAS_STRING_LITERAL,
     reason="C++20 feature not available.",
 )
 def test_typevar(doc):

tests/test_tagbased_polymorphic.cpp

@@ -74,6 +74,7 @@ std::vector<std::unique_ptr<Animal>> create_zoo() {
     // simulate some new type of Dog that the Python bindings
     // haven't been updated for; it should still be considered
     // a Dog, not just an Animal.
+    // NOLINTNEXTLINE(clang-analyzer-optin.core.EnumCastOutOfRange)
     ret.emplace_back(new Dog("Ginger", Dog::Kind(150)));
 
     ret.emplace_back(new Chihuahua("Hertzl"));

tests/test_thread.py

@@ -1,7 +1,10 @@
 from __future__ import annotations
 
+import sys
 import threading
 
+import pytest
+
 from pybind11_tests import thread as m
 
 
@@ -24,6 +27,7 @@ class Thread(threading.Thread):
             raise self.e
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_implicit_conversion():
     a = Thread(m.test)
     b = Thread(m.test)
@@ -34,6 +38,7 @@ def test_implicit_conversion():
         x.join()
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_implicit_conversion_no_gil():
     a = Thread(m.test_no_gil)
     b = Thread(m.test_no_gil)

tests/test_type_caster_std_function_specializations.cpp

@@ -0,0 +1,46 @@
+#include <pybind11/functional.h>
+#include <pybind11/pybind11.h>
+
+#include "pybind11_tests.h"
+
+namespace py = pybind11;
+
+namespace {
+
+struct SpecialReturn {
+    int value = 99;
+};
+
+} // namespace
+
+namespace pybind11 {
+namespace detail {
+namespace type_caster_std_function_specializations {
+
+template <typename... Args>
+struct func_wrapper<SpecialReturn, Args...> : func_wrapper_base {
+    using func_wrapper_base::func_wrapper_base;
+    SpecialReturn operator()(Args... args) const {
+        gil_scoped_acquire acq;
+        SpecialReturn result;
+        try {
+            result = hfunc.f(std::forward<Args>(args)...).template cast<SpecialReturn>();
+        } catch (error_already_set &) {
+            result.value += 1;
+        }
+        result.value += 100;
+        return result;
+    }
+};
+
+} // namespace type_caster_std_function_specializations
+} // namespace detail
+} // namespace pybind11
+
+TEST_SUBMODULE(type_caster_std_function_specializations, m) {
+    py::class_<SpecialReturn>(m, "SpecialReturn")
+        .def(py::init<>())
+        .def_readwrite("value", &SpecialReturn::value);
+    m.def("call_callback_with_special_return",
+          [](const std::function<SpecialReturn()> &func) { return func(); });
+}

tests/test_type_caster_std_function_specializations.py

@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+from pybind11_tests import type_caster_std_function_specializations as m
+
+
+def test_callback_with_special_return():
+    def return_special():
+        return m.SpecialReturn()
+
+    def raise_exception():
+        raise ValueError("called raise_exception.")
+
+    assert return_special().value == 99
+    assert m.call_callback_with_special_return(return_special).value == 199
+    assert m.call_callback_with_special_return(raise_exception).value == 200

tests/test_virtual_functions.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import sys
+
 import pytest
 
 import env  # noqa: F401
@@ -435,6 +437,7 @@ def test_inherited_virtuals():
     assert obj.say_everything() == "BT -7"
 
 
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
 def test_issue_1454():
     # Fix issue #1454 (crash when acquiring/releasing GIL on another thread in Python 2.7)
     m.test_gil()

tools/pybind11Common.cmake

@@ -2,7 +2,7 @@
 
 Adds the following targets::
 
-    pybind11::pybind11 - link to headers and pybind11
+    pybind11::pybind11 - link to Python headers and pybind11::headers
     pybind11::module - Adds module links
     pybind11::embed - Adds embed links
     pybind11::lto - Link time optimizations (only if CMAKE_INTERPROCEDURAL_OPTIMIZATION is not set)
@@ -75,6 +75,32 @@ set_property(
   APPEND
   PROPERTY INTERFACE_LINK_LIBRARIES pybind11::pybind11)
 
+# -------------- emscripten requires exceptions enabled -------------
+# _pybind11_no_exceptions is a private mechanism to disable this addition.
+# Please open an issue if you need to use it; it will be removed if no one
+# needs it.
+if(CMAKE_SYSTEM_NAME MATCHES Emscripten AND NOT _pybind11_no_exceptions)
+  if(CMAKE_VERSION VERSION_LESS 3.13)
+    message(WARNING "CMake 3.13+ is required to build for Emscripten. Some flags will be missing")
+  else()
+    if(is_config)
+      set(_tmp_config_target pybind11::pybind11_headers)
+    else()
+      set(_tmp_config_target pybind11_headers)
+    endif()
+
+    set_property(
+      TARGET ${_tmp_config_target}
+      APPEND
+      PROPERTY INTERFACE_LINK_OPTIONS -fexceptions)
+    set_property(
+      TARGET ${_tmp_config_target}
+      APPEND
+      PROPERTY INTERFACE_COMPILE_OPTIONS -fexceptions)
+    unset(_tmp_config_target)
+  endif()
+endif()
+
 # --------------------------- link helper ---------------------------
 
 add_library(pybind11::python_link_helper IMPORTED INTERFACE ${optional_global})
@@ -329,13 +355,13 @@ function(_pybind11_generate_lto target prefer_thin_lto)
 
     if(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le" OR CMAKE_SYSTEM_PROCESSOR MATCHES "mips64")
       # Do nothing
-    elseif(CMAKE_SYSTEM_PROCESSOR MATCHES emscripten)
+    elseif(CMAKE_SYSTEM_NAME MATCHES Emscripten)
       # This compile is very costly when cross-compiling, so set this without checking
       set(PYBIND11_LTO_CXX_FLAGS "-flto${thin}${cxx_append}")
       set(PYBIND11_LTO_LINKER_FLAGS "-flto${thin}${linker_append}")
     elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
       _pybind11_return_if_cxx_and_linker_flags_work(
-        HAS_FLTO_THIN "-flto${thin}${cxx_append}" "-flto=${thin}${linker_append}"
+        HAS_FLTO_THIN "-flto${thin}${cxx_append}" "-flto${thin}${linker_append}"
         PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
     endif()
     if(NOT HAS_FLTO_THIN)

tools/pybind11Config.cmake.in

@@ -84,7 +84,7 @@ you can either use the basic targets, or use the FindPython tools:
 
   # Python method:
   Python_add_library(MyModule2 src2.cpp)
-  target_link_libraries(MyModule2 pybind11::headers)
+  target_link_libraries(MyModule2 PUBLIC pybind11::headers)
   set_target_properties(MyModule2 PROPERTIES
                                   INTERPROCEDURAL_OPTIMIZATION ON
                                   CXX_VISIBILITY_PRESET ON