From 3ea37002b10600bef7849f827844e9897ca01c3a Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Tue, 28 Jun 2022 07:05:23 -0700
Subject: [PATCH] Eliminate need for
 `PYBIND11_DETAIL_TYPE_CASTER_ACCESS_TRANSLATION_UNIT_LOCAL` macro.

Copying code first developed by @amauryfa. I tried this at an earlier stage, but by itself this was insufficient. In the meantime I added in the TU-local mechanisms: trying again.

Passes local testing:
```
DISABLED std::system_error: ODR VIOLATION DETECTED: pybind11::detail::type_caster<mrc_ns::type_mrc>: SourceLocation1="/usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_odr_guard_1.cpp:18", SourceLocation2="/usr/local/google/home/rwgk/forked/pybind11/tests/test_type_caster_odr_guard_2.cpp:19"
C++ Info: Debian Clang 13.0.1 C++17 __pybind11_internals_v4_clang_libstdcpp_cxxabi1002_sh_def__
=========================================================== test session starts ============================================================
platform linux -- Python 3.9.12, pytest-6.2.3, py-1.10.0, pluggy-0.13.1 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /usr/local/google/home/rwgk/forked/pybind11/tests, configfile: pytest.ini
collected 6 items

test_type_caster_odr_guard_1.py::test_type_mrc_to_python PASSED
test_type_caster_odr_guard_1.py::test_type_mrc_from_python PASSED
test_type_caster_odr_guard_1.py::test_type_caster_odr_registry_values PASSED
test_type_caster_odr_guard_1.py::test_type_caster_odr_violation_detected_counter PASSED
test_type_caster_odr_guard_2.py::test_type_mrc_to_python PASSED
test_type_caster_odr_guard_2.py::test_type_mrc_from_python PASSED

============================================================ 6 passed in 0.01s =============================================================
```
---
 include/pybind11/detail/type_caster_odr_guard.h | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/pybind11/detail/type_caster_odr_guard.h b/include/pybind11/detail/type_caster_odr_guard.h
index 12472b3b7..c77e6e5b0 100644
--- a/include/pybind11/detail/type_caster_odr_guard.h
+++ b/include/pybind11/detail/type_caster_odr_guard.h
@@ -143,6 +143,19 @@ struct get_type_caster_source_file_line<
 template <typename IntrinsicType, typename TypeCasterType>
 struct type_caster_odr_guard : TypeCasterType {
     static tu_local_no_data_always_false translation_unit_local;
+
+    type_caster_odr_guard() {
+        if (translation_unit_local) {
+        }
+    }
+
+    template <typename CType, typename... Arg>
+    static handle cast(CType &&src, return_value_policy policy, handle parent, Arg &&...arg) {
+        if (translation_unit_local) {
+        }
+        return TypeCasterType::cast(
+            std::forward<CType>(src), policy, parent, std::forward<Arg>(arg)...);
+    }
 };
 
 template <typename IntrinsicType, typename TypeCasterType>
@@ -163,8 +176,6 @@ PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
         static constexpr auto source_file_line                                                    \
             = ::pybind11::detail::tu_local_const_name(__FILE__ ":" PYBIND11_TOSTRING(__LINE__));
 
-#    define PYBIND11_DETAIL_TYPE_CASTER_ACCESS_TRANSLATION_UNIT_LOCAL(...)                        \
-        if (::pybind11::detail::make_caster<__VA_ARGS__>::translation_unit_local) {               \
-        }
+#    define PYBIND11_DETAIL_TYPE_CASTER_ACCESS_TRANSLATION_UNIT_LOCAL(...)
 
 #endif