"anonymous types declared in an anonymous union are an extension [-Wnested-anon-types]"

[anntzer]

Issue description

Compiling a file that includes pybind11/detail/common.h (it is private but obviously included by other public headers) with clang -Wpedantic triggers the warning

In file included from src/main.cpp:1:
In file included from /usr/include/python3.6m/pybind11/pybind11.h:43:
In file included from /usr/include/python3.6m/pybind11/attr.h:13:
In file included from /usr/include/python3.6m/pybind11/cast.h:13:
In file included from /usr/include/python3.6m/pybind11/pytypes.h:12:
/usr/include/python3.6m/pybind11/detail/common.h:386:9: warning: anonymous types declared in an anonymous union are an extension [-Wnested-anon-types]
        struct 

Reproducible example code

Add #include <pybind11/detail/common.h> to python_example and compile with

CC=clang CFLAGS=-Wpedantic CXX=clang setup.py build_ext

[Psirus]

I've run into this as well. Since I'm using the provided CMake macros (thank you for this, btw), I would be fine with a solution like this:

diff --git a/tools/pybind11Tools.cmake b/tools/pybind11Tools.cmake
index a7c471a..b8bfb1c 100644
--- a/tools/pybind11Tools.cmake
+++ b/tools/pybind11Tools.cmake
@@ -130,7 +130,7 @@ function(pybind11_add_module target_name)
 
   add_library(${target_name} ${lib_type} ${exclude_from_all} ${ARG_UNPARSED_ARGUMENTS})
 
-  target_include_directories(${target_name}
+  target_include_directories(${target_name} SYSTEM
     PRIVATE ${PYBIND11_INCLUDE_DIR}  # from project CMakeLists.txt
     PRIVATE ${pybind11_INCLUDE_DIR}  # from pybind11Config
     PRIVATE ${PYTHON_INCLUDE_DIRS})

[wjakob]

I'm not a big fan of this approach -- it would be better to suppress this warning as is already done for others. The include files should be warning-free without any special compiler flags.

[Psirus]

Was just a suggestion in case getting the headers warning free was too intrusive. Obviously I'd prefer a solution that works for everyone as well.

[Psirus]

So rather

diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 82f8a48..ad152f3 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -38,6 +38,9 @@
 #  if __GNUC__ >= 7
 #    pragma GCC diagnostic ignored "-Wnoexcept-type"
 #  endif
+#elif defined(__clang__)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wnested-anon-types"
 #endif
 
 #include "attr.h"
@@ -1979,4 +1982,6 @@ NAMESPACE_END(PYBIND11_NAMESPACE)
 /* Leave ignored warnings on */
 #elif defined(__GNUG__) && !defined(__clang__)
 #  pragma GCC diagnostic pop
+#elif defined(__clang__)
+#  pragma clang diagnostic pop
 #endif

Should I open a PR for that?

[wjakob]

Thank you -- yes, please do.

[jagerman]

Fixed by #1248