From f6e543b15ec0aaf39c494936440f91a16f161c9a Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Thu, 16 Jan 2020 00:20:44 +0000
Subject: [PATCH] Adding a default virtual destructor to Animal type in
 test_tagbased_polymorphic.cpp.
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With this change, and cast.h as-is in master, test_tagbased_polymorphic.cpp fails to compile with the error message below.
With the cast.h change in pull/2016, building and testing succeeds.

cd pybind11/build/tests && /usr/bin/c++  -DPYBIND11_TEST_BOOST -DPYBIND11_TEST_EIGEN -Dpybind11_tests_EXPORTS -Ipybind11/include -I/usr/include/python3.7m -isystem /usr/include/eigen3  -Os -DNDEBUG -fPIC -fvisibility=hidden   -std=c++2a -flto -fno-fat-lto-objects -Wall -Wextra -Wconversion -Wcast-qual -Wdeprecated -o CMakeFiles/pybind11_tests.dir/test_tagbased_polymorphic.cpp.o -c pybind11/tests/test_tagbased_polymorphic.cpp
In file included from pybind11/include/pybind11/attr.h:13,
                 from pybind11/include/pybind11/pybind11.h:44,
                 from pybind11/tests/pybind11_tests.h:2,
                 from pybind11/tests/test_tagbased_polymorphic.cpp:10:
pybind11/include/pybind11/cast.h: In instantiation of ‘static std::pair<const void*, const pybind11::detail::type_info*> pybind11::detail::type_caster_base<type>::src_and_type(const itype*) [with type = Animal; pybind11::detail::type_caster_base<type>::itype = Animal]’:
pybind11/include/pybind11/cast.h:906:31:   required from ‘static pybind11::handle pybind11::detail::type_caster_base<type>::cast_holder(const itype*, const void*) [with type = Animal; pybind11::detail::type_caster_base<type>::itype = Animal]’
pybind11/include/pybind11/cast.h:1566:51:   required from ‘static pybind11::handle pybind11::detail::move_only_holder_caster<type, holder_type>::cast(holder_type&&, pybind11::return_value_policy, pybind11::handle) [with type = Animal; holder_type = std::unique_ptr<Animal>]’
pybind11/include/pybind11/stl.h:175:69:   required from ‘static pybind11::handle pybind11::detail::list_caster<Type, Value>::cast(T&&, pybind11::return_value_policy, pybind11::handle) [with T = std::vector<std::unique_ptr<Animal> >; Type = std::vector<std::unique_ptr<Animal> >; Value = std::unique_ptr<Animal>]’
pybind11/include/pybind11/pybind11.h:159:43:   required from ‘void pybind11::cpp_function::initialize(Func&&, Return (*)(Args ...), const Extra& ...) [with Func = std::vector<std::unique_ptr<Animal> > (*&)(); Return = std::vector<std::unique_ptr<Animal> >; Args = {}; Extra = {pybind11::name, pybind11::scope, pybind11::sibling}]’
pybind11/include/pybind11/pybind11.h:64:9:   required from ‘pybind11::cpp_function::cpp_function(Return (*)(Args ...), const Extra& ...) [with Return = std::vector<std::unique_ptr<Animal> >; Args = {}; Extra = {pybind11::name, pybind11::scope, pybind11::sibling}]’
pybind11/include/pybind11/pybind11.h:819:22:   required from ‘pybind11::module& pybind11::module::def(const char*, Func&&, const Extra& ...) [with Func = std::vector<std::unique_ptr<Animal> > (*)(); Extra = {}]’
pybind11/tests/test_tagbased_polymorphic.cpp:141:36:   required from here
pybind11/include/pybind11/cast.h:880:61: error: ambiguous template instantiation for ‘struct pybind11::polymorphic_type_hook<Animal, void>’
         const void *vsrc = polymorphic_type_hook<itype>::get(src, instance_type);
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
pybind11/include/pybind11/cast.h:844:8: note: candidates are: ‘template<class itype> struct pybind11::polymorphic_type_hook<itype, typename std::enable_if<std::is_polymorphic<_Tp>::value, void>::type> [with itype = Animal]’
 struct polymorphic_type_hook<itype, detail::enable_if_t<std::is_polymorphic<itype>::value>>
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pybind11/tests/test_tagbased_polymorphic.cpp:115:12: note:                 ‘template<class itype> struct pybind11::polymorphic_type_hook<itype, typename std::enable_if<std::is_base_of<Animal, itype>::value, void>::type> [with itype = Animal]’
     struct polymorphic_type_hook<itype, detail::enable_if_t<std::is_base_of<Animal, itype>::value>>
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from pybind11/include/pybind11/attr.h:13,
                 from pybind11/include/pybind11/pybind11.h:44,
                 from pybind11/tests/pybind11_tests.h:2,
                 from pybind11/tests/test_tagbased_polymorphic.cpp:10:
pybind11/include/pybind11/cast.h:880:61: error: incomplete type ‘pybind11::polymorphic_type_hook<Animal, void>’ used in nested name specifier
         const void *vsrc = polymorphic_type_hook<itype>::get(src, instance_type);
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
---
 tests/test_tagbased_polymorphic.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tests/test_tagbased_polymorphic.cpp b/tests/test_tagbased_polymorphic.cpp
index 272e460c9..dcc005126 100644
--- a/tests/test_tagbased_polymorphic.cpp
+++ b/tests/test_tagbased_polymorphic.cpp
@@ -12,6 +12,12 @@
 
 struct Animal
 {
+    // Make this type also a "standard" polymorphic type, to confirm that
+    // specializing polymorphic_type_hook using enable_if_t still works
+    // (https://github.com/pybind/pybind11/pull/2016/).
+    virtual ~Animal() = default;
+
+    // Enum for tag-based polymorphism.
     enum class Kind {
         Unknown = 0,
         Dog = 100, Labrador, Chihuahua, LastDog = 199,