Merge branch 'master' into sh_merge_master

.github/ISSUE_TEMPLATE/bug-report.md

@@ -1,28 +0,0 @@
----
-name: Bug Report
-about: File an issue about a bug
-title: "[BUG] "
----
-
-
-Make sure you've completed the following steps before submitting your issue -- thank you!
-
-1. Make sure you've read the [documentation][]. Your issue may be addressed there.
-2. Search the [issue tracker][] to verify that this hasn't already been reported. +1 or comment there if it has.
-3. Consider asking first in the [Gitter chat room][].
-4. Include a self-contained and minimal piece of code that reproduces the problem. If that's not possible, try to make the description as clear as possible.
-    a. If possible, make a PR with a new, failing test to give us a starting point to work on!
-
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist and the template text in parentheses below.*
-
-## Issue description
-
-(Provide a short description, state the expected behavior and what actually happens.)
-
-## Reproducible example code
-
-(The code should be minimal, have no external dependencies, isolate the function(s) that cause breakage. Submit matched and complete C++ and Python snippets that can be easily compiled and run to diagnose the issue.)

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,45 @@
+name: Bug Report
+description: File an issue about a bug
+title: "[BUG]: "
+labels: [triage]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Maintainers will only make a best effort to triage PRs. Please do your best to make the issue as easy to act on as possible, and only open if clearly a problem with pybind11 (ask first if unsure).
+  - type: checkboxes
+    id: steps
+    attributes:
+      label: Required prerequisites
+      description: Make sure you've completed the following steps before submitting your issue -- thank you!
+      options:
+        - label: Make sure you've read the [documentation](https://pybind11.readthedocs.io). Your issue may be addressed there.
+          required: true
+        - label: Search the [issue tracker](https://github.com/pybind/pybind11/issues) and [Discussions](https:/pybind/pybind11/discussions) to verify that this hasn't already been reported. +1 or comment there if it has.
+          required: true
+        - label: Consider asking first in the [Gitter chat room](https://gitter.im/pybind/Lobby) or in a [Discussion](https:/pybind/pybind11/discussions/new).
+          required: false
+
+  - type: textarea
+    id: description
+    attributes:
+      label: Problem description
+      placeholder: >-
+        Provide a short description, state the expected behavior and what
+        actually happens. Include relevant information like what version of
+        pybind11 you are using, what system you are on, and any useful commands
+        / output.
+    validations:
+      required: true
+
+  - type: textarea
+    id: code
+    attributes:
+      label: Reproducible example code
+      placeholder: >-
+        The code should be minimal, have no external dependencies, isolate the
+        function(s) that cause breakage. Submit matched and complete C++ and
+        Python snippets that can be easily compiled and run to diagnose the
+        issue. If possible, make a PR with a new, failing test to give us a
+        starting point to work on!
+      render: text

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
 blank_issues_enabled: false
 contact_links:
+  - name: Ask a question
+    url: https://github.com/pybind/pybind11/discussions/new
+    about: Please ask and answer questions here, or propose new ideas.
   - name: Gitter room
     url: https://gitter.im/pybind/Lobby
     about: A room for discussing pybind11 with an active community

.github/ISSUE_TEMPLATE/feature-request.md

@@ -1,16 +0,0 @@
----
-name: Feature Request
-about: File an issue about adding a feature
-title: "[FEAT] "
----
-
-
-Make sure you've completed the following steps before submitting your issue -- thank you!
-
-1. Check if your feature has already been mentioned / rejected / planned in other issues.
-2. If those resources didn't help, consider asking in the [Gitter chat room][] to see if this is interesting / useful to a larger audience and possible to implement reasonably,
-4. If you have a useful feature that passes the previous items (or not suitable for chat), please fill in the details below.
-
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist.*

.github/ISSUE_TEMPLATE/question.md

@@ -1,21 +0,0 @@
----
-name: Question
-about: File an issue about unexplained behavior
-title: "[QUESTION] "
----
-
-If you have a question, please check the following first:
-
-1. Check if your question has already been answered in the [FAQ][] section.
-2. Make sure you've read the [documentation][]. Your issue may be addressed there.
-3. If those resources didn't help and you only have a short question (not a bug report), consider asking in the [Gitter chat room][]
-4. Search the [issue tracker][], including the closed issues, to see if your question has already been asked/answered. +1 or comment if it has been asked but has no answer.
-5. If you have a more complex question which is not answered in the previous items (or not suitable for chat), please fill in the details below.
-6. Include a self-contained and minimal piece of code that illustrates your question. If that's not possible, try to make the description as clear as possible.
-
-[FAQ]: http://pybind11.readthedocs.io/en/latest/faq.html
-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
-
-*After reading, remove this checklist.*

.github/workflows/ci.yml

@@ -860,3 +860,34 @@ jobs:
 
     - name: Run all checks
       run: cmake --build build -t check
+
+  mingw:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+    - uses: msys2/setup-msys2@v2
+      with:
+        install: >-
+          mingw-w64-x86_64-gcc
+          mingw-w64-x86_64-python-pip
+          mingw-w64-x86_64-cmake
+          mingw-w64-x86_64-make
+          mingw-w64-x86_64-python-pytest
+          mingw-w64-x86_64-eigen3
+          mingw-w64-x86_64-boost
+          mingw-w64-x86_64-catch
+
+    - uses: actions/checkout@v1
+
+    - name: Configure
+      # LTO leads to many undefined reference like
+      # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
+      run: cmake -G "MinGW Makefiles" -S . -B build
+
+    - name: Build
+      run: cmake --build build -j 2
+
+    - name: Python tests
+      run: cmake --build build --target pytest

.github/workflows/ci_sh_def.yml

@@ -884,3 +884,34 @@ jobs:
 
     - name: Run all checks
       run: cmake --build build -t check
+
+  mingw:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+    - uses: msys2/setup-msys2@v2
+      with:
+        install: >-
+          mingw-w64-x86_64-gcc
+          mingw-w64-x86_64-python-pip
+          mingw-w64-x86_64-cmake
+          mingw-w64-x86_64-make
+          mingw-w64-x86_64-python-pytest
+          mingw-w64-x86_64-eigen3
+          mingw-w64-x86_64-boost
+          mingw-w64-x86_64-catch
+
+    - uses: actions/checkout@v1
+
+    - name: Configure
+      # LTO leads to many undefined reference like
+      # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
+      run: cmake -G "MinGW Makefiles" -S . -B build -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
+
+    - name: Build
+      run: cmake --build build -j 2
+
+    - name: Python tests
+      run: cmake --build build --target pytest

.github/workflows/ci_sh_def.yml.patch

@@ -1,5 +1,5 @@
---- ci.yml	2021-07-11 00:44:59.934547958 -0700
+--- ci.yml	2021-07-30 11:29:33.606510028 -0700
-+++ ci_sh_def.yml	2021-07-11 00:45:29.964628911 -0700
++++ ci_sh_def.yml	2021-07-30 11:36:51.284724775 -0700
 @@ -1,4 +1,16 @@
 -name: CI-SH-AVL
 +# PLEASE KEEP THIS GROUP OF FILES IN SYNC AT ALL TIMES:
@@ -132,3 +132,12 @@
  
      steps:
      - uses: actions/checkout@v2
+@@ -884,7 +908,7 @@
+     - name: Configure
+       # LTO leads to many undefined reference like
+       # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
+-      run: cmake -G "MinGW Makefiles" -S . -B build
++      run: cmake -G "MinGW Makefiles" -S . -B build -DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"
+ 
+     - name: Build
+       run: cmake --build build -j 2

README.rst

@@ -3,7 +3,7 @@
 
 **pybind11 — Seamless operability between C++11 and Python**
 
-|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |CI| |Build status|
+|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |GitHub Discussions| |CI| |Build status|
 
 |Repology| |PyPI package| |Conda-forge| |Python Versions|
 
@@ -180,3 +180,5 @@ to the terms and conditions of this license.
    :target: https://repology.org/project/python:pybind11/versions
 .. |Python Versions| image:: https://img.shields.io/pypi/pyversions/pybind11.svg
    :target: https://pypi.org/project/pybind11/
+.. |GitHub Discussions| image:: https://img.shields.io/static/v1?label=Discussions&message=Ask&color=blue&logo=github
+   :target: https://github.com/pybind/pybind11/discussions

include/pybind11/cast.h

@@ -406,7 +406,11 @@ template <typename StringType, bool IsView = false> struct string_caster {
 
         const auto *buffer = reinterpret_cast<const CharT *>(PYBIND11_BYTES_AS_STRING(utfNbytes.ptr()));
         size_t length = (size_t) PYBIND11_BYTES_SIZE(utfNbytes.ptr()) / sizeof(CharT);
-        if (UTF_N > 8) { buffer++; length--; } // Skip BOM for UTF-16/32
+        // Skip BOM for UTF-16/32
+        if (PYBIND11_SILENCE_MSVC_C4127(UTF_N > 8)) {
+            buffer++;
+            length--;
+        }
         value = StringType(buffer, length);
 
         // If we're loading a string_view we need to keep the encoded Python object alive:
@@ -521,7 +525,7 @@ public:
         // out how long the first encoded character is in bytes to distinguish between these two
         // errors.  We also allow want to allow unicode characters U+0080 through U+00FF, as those
         // can fit into a single char value.
-        if (StringCaster::UTF_N == 8 && str_len > 1 && str_len <= 4) {
+        if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 8) && str_len > 1 && str_len <= 4) {
             auto v0 = static_cast<unsigned char>(value[0]);
             // low bits only: 0-127
             // 0b110xxxxx - start of 2-byte sequence
@@ -546,7 +550,7 @@ public:
         // UTF-16 is much easier: we can only have a surrogate pair for values above U+FFFF, thus a
         // surrogate pair with total length 2 instantly indicates a range error (but not a "your
         // string was too long" error).
-        else if (StringCaster::UTF_N == 16 && str_len == 2) {
+        else if (PYBIND11_SILENCE_MSVC_C4127(StringCaster::UTF_N == 16) && str_len == 2) {
             one_char = static_cast<CharT>(value[0]);
             if (one_char >= 0xD800 && one_char < 0xE000)
                 throw value_error("Character code point not in range(0x10000)");
@@ -804,7 +808,7 @@ struct pyobject_caster {
         // For Python 2, without this implicit conversion, Python code would
         // need to be cluttered with six.ensure_text() or similar, only to be
         // un-cluttered later after Python 2 support is dropped.
-        if (std::is_same<T, str>::value && isinstance<bytes>(src)) {
+        if (PYBIND11_SILENCE_MSVC_C4127(std::is_same<T, str>::value) && isinstance<bytes>(src)) {
             PyObject *str_from_bytes = PyUnicode_FromEncodedObject(src.ptr(), "utf-8", nullptr);
             if (!str_from_bytes) throw error_already_set();
             value = reinterpret_steal<type>(str_from_bytes);

include/pybind11/detail/common.h

@@ -89,13 +89,27 @@
 #  endif
 #endif
 
+#if !defined(PYBIND11_EXPORT_EXCEPTION)
+#  ifdef __MINGW32__
+// workaround for:
+// error: 'dllexport' implies default visibility, but xxx has already been declared with a different visibility
+#    define PYBIND11_EXPORT_EXCEPTION
+#  else
+#    define PYBIND11_EXPORT_EXCEPTION PYBIND11_EXPORT
+#  endif
+#endif
+
 #if defined(_MSC_VER)
 #  define PYBIND11_NOINLINE __declspec(noinline)
 #else
 #  define PYBIND11_NOINLINE __attribute__ ((noinline))
 #endif
 
-#if defined(PYBIND11_CPP14)
+#if defined(__MINGW32__)
+// For unknown reasons all PYBIND11_DEPRECATED member trigger a warning when declared
+// whether it is used or not
+#  define PYBIND11_DEPRECATED(reason)
+#elif defined(PYBIND11_CPP14)
 #  define PYBIND11_DEPRECATED(reason) [[deprecated(reason)]]
 #else
 #  define PYBIND11_DEPRECATED(reason) __attribute__((deprecated(reason)))
@@ -121,7 +135,8 @@
 #    define HAVE_ROUND 1
 #  endif
 #  pragma warning(push)
-#  pragma warning(disable: 4510 4610 4512 4005)
+// C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
+#  pragma warning(disable: 4505)
 #  if defined(_DEBUG) && !defined(Py_DEBUG)
 #    define PYBIND11_DEBUG_MARKER
 #    undef _DEBUG
@@ -740,7 +755,7 @@ PYBIND11_NAMESPACE_END(detail)
 #  pragma warning(disable: 4275) // warning C4275: An exported class was derived from a class that wasn't exported. Can be ignored when derived from a STL class.
 #endif
 /// C++ bindings of builtin Python exceptions
-class PYBIND11_EXPORT builtin_exception : public std::runtime_error {
+class PYBIND11_EXPORT_EXCEPTION builtin_exception : public std::runtime_error {
 public:
     using std::runtime_error::runtime_error;
     /// Set the error using the Python C API
@@ -751,7 +766,7 @@ public:
 #endif
 
 #define PYBIND11_RUNTIME_EXCEPTION(name, type) \
-    class PYBIND11_EXPORT name : public builtin_exception { public: \
+    class PYBIND11_EXPORT_EXCEPTION name : public builtin_exception { public: \
         using builtin_exception::builtin_exception; \
         name() : name("") { } \
         void set_error() const override { PyErr_SetString(type, what()); } \
@@ -926,5 +941,16 @@ inline constexpr void workaround_incorrect_msvc_c4100(Args &&...) {}
 #    define PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(...)
 #endif
 
+#if defined(_MSC_VER) // All versions (as of July 2021).
+
+// warning C4127: Conditional expression is constant
+constexpr inline bool silence_msvc_c4127(bool cond) { return cond; }
+
+#    define PYBIND11_SILENCE_MSVC_C4127(...) detail::silence_msvc_c4127(__VA_ARGS__)
+
+#else
+#    define PYBIND11_SILENCE_MSVC_C4127(...) __VA_ARGS__
+#endif
+
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

include/pybind11/detail/init.h

@@ -98,7 +98,7 @@ template <typename Class>
 void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     no_nullptr(ptr);
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr)) {
         // We're going to try to construct an alias by moving the cpp type.  Whether or not
         // that succeeds, we still need to destroy the original cpp pointer (either the
         // moved away leftover, if the alias construction works, or the value itself if we
@@ -141,7 +141,7 @@ void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
     auto *ptr = holder_helper<Holder<Class>>::get(holder);
     no_nullptr(ptr);
     // If we need an alias, check that the held pointer is actually an alias instance
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr))
         throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
                          "is not an alias instance");
 
@@ -158,7 +158,7 @@ void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     static_assert(std::is_move_constructible<Cpp<Class>>::value,
         "pybind11::init() return-by-value factory function requires a movable class");
-    if (Class::has_alias && need_alias)
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias)
         construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
     else
         v_h.value_ptr() = new Cpp<Class>(std::move(result));
@@ -183,7 +183,7 @@ void construct(value_and_holder &v_h, std::unique_ptr<Cpp<Class>, D> &&unq_ptr,
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     auto *ptr = unq_ptr.get();
     no_nullptr(ptr);
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr))
         throw type_error("pybind11::init(): construction failed: returned std::unique_ptr pointee "
                          "is not an alias instance");
     // Here and below: if the new object is a trampoline, the shared_from_this mechanism needs
@@ -219,7 +219,7 @@ void construct(value_and_holder &v_h, std::shared_ptr<Cpp<Class>> &&shd_ptr, boo
     PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
     auto *ptr = shd_ptr.get();
     no_nullptr(ptr);
-    if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
+    if (PYBIND11_SILENCE_MSVC_C4127(Class::has_alias) && need_alias && !is_alias<Class>(ptr))
         throw type_error("pybind11::init(): construction failed: returned std::shared_ptr pointee "
                          "is not an alias instance");
     auto smhldr = type_caster<Cpp<Class>>::template smart_holder_from_shared_ptr(shd_ptr);

include/pybind11/detail/pragma_warning_block.h

@@ -1,14 +1,7 @@
 #pragma once
 
-#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
+#if defined(__GNUG__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
-#  pragma warning(push)
-#  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#  pragma warning(disable: 4505) // warning C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
-#elif defined(__GNUG__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
 #  pragma GCC diagnostic push
 #  pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
 #  pragma GCC diagnostic ignored "-Wattributes"
-#  if __GNUC__ >= 7
-#    pragma GCC diagnostic ignored "-Wnoexcept-type"
-#  endif
 #endif

include/pybind11/pybind11.h

@@ -41,6 +41,18 @@
 #  include <cxxabi.h>
 #endif
 
+/* https://stackoverflow.com/questions/46798456/handling-gccs-noexcept-type-warning
+   This warning is about ABI compatibility, not code health.
+   It is only actually needed in a couple places, but apparently GCC 7 "generates this warning if
+   and only if the first template instantiation ... involves noexcept" [stackoverflow], therefore
+   it could get triggered from seemingly random places, depending on user code.
+   No other GCC version generates this warning.
+ */
+#if defined(__GNUC__) && __GNUC__ == 7
+#    pragma GCC diagnostic push
+#    pragma GCC diagnostic ignored "-Wnoexcept-type"
+#endif
+
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -151,7 +163,7 @@ protected:
         auto rec = unique_rec.get();
 
         /* Store the capture object directly in the function record if there is enough space */
-        if (sizeof(capture) <= sizeof(rec->data)) {
+        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(capture) <= sizeof(rec->data))) {
             /* Without these pragmas, GCC warns that there might not be
                enough space to use the placement new operator. However, the
                'if' statement above ensures that this is the case. */
@@ -2481,8 +2493,10 @@ inline function get_overload(const T *this_ptr, const char *name) {
 
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
 
-#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
+#if defined(__GNUC__) && __GNUC__ == 7
-#  pragma warning(pop)
+#    pragma GCC diagnostic pop // -Wnoexcept-type
-#elif defined(__GNUG__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
+#endif
+
+#if defined(__GNUG__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
 #  pragma GCC diagnostic pop
 #endif

include/pybind11/pytypes.h

@@ -327,7 +327,7 @@ PYBIND11_NAMESPACE_END(detail)
 /// thrown to propagate python-side errors back through C++ which can either be caught manually or
 /// else falls back to the function dispatcher (which then raises the captured error back to
 /// python).
-class PYBIND11_EXPORT error_already_set : public std::runtime_error {
+class PYBIND11_EXPORT_EXCEPTION error_already_set : public std::runtime_error {
 public:
     /// Constructs a new exception from the current Python error indicator, if any.  The current
     /// Python error indicator will be cleared.
@@ -1191,7 +1191,7 @@ PYBIND11_NAMESPACE_BEGIN(detail)
 // unsigned type: (A)-1 != (B)-1 when A and B are unsigned types of different sizes).
 template <typename Unsigned>
 Unsigned as_unsigned(PyObject *o) {
-    if (sizeof(Unsigned) <= sizeof(unsigned long)
+    if (PYBIND11_SILENCE_MSVC_C4127(sizeof(Unsigned) <= sizeof(unsigned long))
 #if PY_VERSION_HEX < 0x03000000
         || PyInt_Check(o)
 #endif
@@ -1212,7 +1212,7 @@ public:
     template <typename T,
               detail::enable_if_t<std::is_integral<T>::value, int> = 0>
     int_(T value) {
-        if (sizeof(T) <= sizeof(long)) {
+        if (PYBIND11_SILENCE_MSVC_C4127(sizeof(T) <= sizeof(long))) {
             if (std::is_signed<T>::value)
                 m_ptr = PyLong_FromLong((long) value);
             else

pybind11/setup_helpers.py

@@ -59,8 +59,7 @@ except ImportError:
 import distutils.errors
 import distutils.ccompiler
 
-
+WIN = sys.platform.startswith("win32") and "mingw" not in sysconfig.get_platform()
-WIN = sys.platform.startswith("win32") and sysconfig.get_platform() != "mingw"
 PY2 = sys.version_info[0] < 3
 MACOS = sys.platform.startswith("darwin")
 STD_TMPL = "/std:c++{}" if WIN else "-std=c++{}"

tests/test_exceptions.h

@@ -4,7 +4,7 @@
 
 // shared exceptions for cross_module_tests
 
-class PYBIND11_EXPORT shared_exception : public pybind11::builtin_exception {
+class PYBIND11_EXPORT_EXCEPTION shared_exception : public pybind11::builtin_exception {
 public:
     using builtin_exception::builtin_exception;
     explicit shared_exception() : shared_exception("") {}

tools/pybind11Common.cmake

@@ -302,13 +302,18 @@ function(_pybind11_return_if_cxx_and_linker_flags_work result cxxflags linkerfla
 endfunction()
 
 function(_pybind11_generate_lto target prefer_thin_lto)
+  if(MINGW)
+    message(STATUS "${target} disabled (problems with undefined symbols for MinGW for now)")
+    return()
+  endif()
+
   if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
     set(cxx_append "")
     set(linker_append "")
     if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT APPLE)
       # Clang Gold plugin does not support -Os; append -O3 to MinSizeRel builds to override it
       set(linker_append ";$<$<CONFIG:MinSizeRel>:-O3>")
-    elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+    elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND NOT MINGW)
       set(cxx_append ";-fno-fat-lto-objects")
     endif()