[smart_holder] Add test_namespace_visibility (#4050)

* Add test_namespace_visibility

To probe environment/toolchain/platform-specific behavior under the exact same conditions as normal tests.

(An earlier version of this code was used to inform PR #4043.)

* Disable flake8 in ubench/holder_comparison_*.py, to suppress new & useless diagnostics.

* Disable namespace_visibility_1s.cpp (tosee if that resolves the MSVC and CUDA `test_cross_module_exception_translator` failures).

* Turn off flake8 completely for ubench (the Strip unnecessary `# noqa`s action un-helpfully removed the added noqa).

* Disable test_namespace_visibility completely. Just keep the two .cpp files, only setting the module docstring and doing nothing else.

* Rename test_namespace_visibility.py to test_exc_namespace_visibility.py, so that it is imported by pytest before test_exceptions.py

* Add `set_property(SOURCE namespace_visibility_1s.cpp PROPERTY LANGUAGE CUDA)`

* Add reference to PR #4054

* Complete the documentation (comments in test_exc_namespace_visibility.py).

* Rename namespace_visibility.h to namespace_visibility.inl, as suggested by @charlesbeattie

tests/CMakeLists.txt

@@ -148,6 +148,7 @@ set(PYBIND11_TEST_FILES
     test_eigen
     test_enum
     test_eval
+    test_exc_namespace_visibility.py
     test_exceptions
     test_factory_constructors
     test_gil_scoped
@@ -236,6 +237,8 @@ tests_extra_targets("test_exceptions.py" "cross_module_interleaved_error_already
 tests_extra_targets("test_gil_scoped.py" "cross_module_gil_utils")
 tests_extra_targets("test_class_sh_module_local.py"
                     "class_sh_module_local_0;class_sh_module_local_1;class_sh_module_local_2")
+tests_extra_targets("test_exc_namespace_visibility.py"
+                    "namespace_visibility_1;namespace_visibility_2")
 
 set(PYBIND11_EIGEN_REPO
     "https://gitlab.com/libeigen/eigen.git"
@@ -426,8 +429,14 @@ if(PYBIND11_CUDA_TESTS)
 endif()
 
 foreach(target ${test_targets})
-  set(test_files ${PYBIND11_TEST_FILES})
-  if(NOT "${target}" STREQUAL "pybind11_tests")
+  if("${target}" STREQUAL "pybind11_tests")
+    set(test_files ${PYBIND11_TEST_FILES})
+  elseif("${target}" STREQUAL "namespace_visibility_1")
+    set(test_files namespace_visibility_1s.cpp)
+    if(PYBIND11_CUDA_TESTS)
+      set_property(SOURCE namespace_visibility_1s.cpp PROPERTY LANGUAGE CUDA)
+    endif()
+  else()
     set(test_files "")
   endif()
 

tests/namespace_visibility.inl

@@ -0,0 +1,31 @@
+// Copyright (c) 2022 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 <cstddef>
+
+#ifdef __GNUG__
+#    define PYBIND11_NS_VIS_U /* unspecified */
+#    define PYBIND11_NS_VIS_H __attribute__((visibility("hidden")))
+#else
+#    define PYBIND11_NS_VIS_U
+#    define PYBIND11_NS_VIS_H
+#endif
+
+#define PYBIND11_NS_VIS_FUNC                                                                      \
+    inline std::ptrdiff_t func() {                                                                \
+        static std::ptrdiff_t value = 0;                                                          \
+        return reinterpret_cast<std::ptrdiff_t>(&value);                                          \
+    }
+
+#define PYBIND11_NS_VIS_DEFS                                                                      \
+    m.def("ns_vis_uuu_func", pybind11_ns_vis_uuu::func);                                          \
+    m.def("ns_vis_uuh_func", pybind11_ns_vis_uuh::func);                                          \
+    m.def("ns_vis_uhu_func", pybind11_ns_vis_uhu::func);                                          \
+    m.def("ns_vis_uhh_func", pybind11_ns_vis_uhh::func);                                          \
+    m.def("ns_vis_huu_func", pybind11_ns_vis_huu::func);                                          \
+    m.def("ns_vis_huh_func", pybind11_ns_vis_huh::func);                                          \
+    m.def("ns_vis_hhu_func", pybind11_ns_vis_hhu::func);                                          \
+    m.def("ns_vis_hhh_func", pybind11_ns_vis_hhh::func);

tests/namespace_visibility_1.cpp

@@ -0,0 +1,24 @@
+#include "pybind11/pybind11.h"
+#include "namespace_visibility.inl"
+
+// clang-format off
+namespace pybind11_ns_vis_uuu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uuh PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhh PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huu PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhu PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+//                        ^                   ^
+//                 bit used .............. here
+// clang-format on
+
+void namespace_visibility_1s(pybind11::module_ &m);
+
+PYBIND11_MODULE(namespace_visibility_1, m) {
+    PYBIND11_NS_VIS_DEFS
+
+    auto sm = m.def_submodule("submodule");
+    namespace_visibility_1s(sm);
+}

tests/namespace_visibility_1s.cpp

@@ -0,0 +1,17 @@
+#include "pybind11/pybind11.h"
+#include "namespace_visibility.inl"
+
+// clang-format off
+namespace pybind11_ns_vis_uuu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uuh PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhu PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huh PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhu PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+//                         ^                  ^
+//                  bit used ............. here
+// clang-format on
+
+void namespace_visibility_1s(pybind11::module_ &m) { PYBIND11_NS_VIS_DEFS }

tests/namespace_visibility_2.cpp

@@ -0,0 +1,17 @@
+#include "pybind11/pybind11.h"
+#include "namespace_visibility.inl"
+
+// clang-format off
+namespace pybind11_ns_vis_uuu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uuh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_uhh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_huh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhu PYBIND11_NS_VIS_U { PYBIND11_NS_VIS_FUNC }
+namespace pybind11_ns_vis_hhh PYBIND11_NS_VIS_H { PYBIND11_NS_VIS_FUNC }
+//                          ^                 ^
+//                   bit used ............ here
+// clang-format on
+
+PYBIND11_MODULE(namespace_visibility_2, m) { PYBIND11_NS_VIS_DEFS }

tests/test_exc_namespace_visibility.py

@@ -0,0 +1,67 @@
+# This is not really a unit test, but probing environment/toolchain/platform-specific
+# behavior under the exact same conditions as normal tests.
+# The results are useful to understanding the effects of, e.g., removing
+# `-fvisibility=hidden` or `__attribute__((visibility("hidden")))`, or linking
+# extensions statically with the core Python interpreter.
+
+# NOTE
+# ====
+# The "exc_" in "test_exc_namespace_visibility.py" is a workaround, to avoid a
+# test_cross_module_exception_translator (test_exceptions.py) failure. This
+# test has to be imported (by pytest) before test_exceptions.py; pytest sorts
+# lexically. See https://github.com/pybind/pybind11/pull/4054 for more information.
+
+import itertools
+
+import namespace_visibility_1
+import namespace_visibility_2
+import pytest
+
+# Please take a quick look at namespace_visibility.h first, to see what is being probed.
+#
+# EXPECTED is for -fvisibility=hidden or equivalent, as recommended in the docs.
+EXPECTED_ALL_UNIQUE_POINTERS_OBSERVED = "AAC:AAc:AaC:Aac:aAC:aAc:aaC:aac"
+#                                        ^^^
+#          namespace_visibility_1 pointer|||
+# namespace_visibility_1.submodule pointer|| (identical letters means same pointer)
+#            namespace_visibility_2 pointer|
+# Upper-case: namespace visibility unspecified
+# Lower-case: namespace visibility hidden
+# This test probes all 2**3 combinations of u/h ** number-of-sub/modules.
+#
+# Also observed:
+# AAA:AAc:AaC:Aac:aAC:aAc:aaC:aac  -fvisibility=default Linux
+# AAA:AAc:AaA:Aac:aAC:aAc:aaC:aac  -fvisibility=default macOS
+# AAA:AAa:AaA:Aaa:aAA:aAa:aaA:aaa  everything linked statically
+
+
+def test_namespace_visibility():
+    modules = (
+        namespace_visibility_1,
+        namespace_visibility_1.submodule,
+        namespace_visibility_2,
+    )
+    unique_pointer_labels = "ABC"
+    unique_pointers_observed = []
+    # u = visibility unspecified
+    # h = visibility hidden
+    for visibility in itertools.product(*([("u", "h")] * len(modules))):
+        # See functions in namespace_visibility_*.cpp
+        func = "ns_vis_" + "".join(visibility) + "_func"
+        ptrs = []
+        uq_ptrs_obs = ""
+        for vis, m in zip(visibility, modules):
+            ptr = getattr(m, func)()
+            ptrs.append(ptr)
+            lbl = unique_pointer_labels[ptrs.index(ptr)]
+            if vis == "h":
+                # Encode u/h info as upper/lower case to make the final result
+                # as compact as possible.
+                lbl = lbl.lower()
+            uq_ptrs_obs += lbl
+        unique_pointers_observed.append(uq_ptrs_obs)
+    all_unique_pointers_observed = ":".join(unique_pointers_observed)
+    if all_unique_pointers_observed != EXPECTED_ALL_UNIQUE_POINTERS_OBSERVED:
+        pytest.skip(
+            f"UNUSUAL all_unique_pointers_observed: {all_unique_pointers_observed}"
+        )