Adjust to behavior change due to pybind/pybind11#4586 (smart_holder b…

…ranch).

The behavior change made it possible to exercise the `reference_internal` vs `copy` behavior more thoroughly, which then led to a surprise discovery. See SURPRISE comment in tests/test_class_sh_property_stl.py

tests/test_class_sh_property_stl.cpp

@@ -3,6 +3,7 @@
 
 #include "pybind11_tests.h"
 
+#include <cstddef>
 #include <vector>
 
 namespace test_class_sh_property_stl {
@@ -20,6 +21,11 @@ struct FieldHolder {
 struct VectorFieldHolder {
     std::vector<FieldHolder> vec_fld_hld;
     VectorFieldHolder() { vec_fld_hld.push_back(FieldHolder{Field{300}}); }
+    void reset_at(std::size_t index, int wrapped_int) {
+        if (index < vec_fld_hld.size()) {
+            vec_fld_hld[index].fld.wrapped_int = wrapped_int;
+        }
+    }
 };
 
 } // namespace test_class_sh_property_stl
@@ -37,6 +43,7 @@ TEST_SUBMODULE(class_sh_property_stl, m) {
 
     py::classh<VectorFieldHolder>(m, "VectorFieldHolder")
         .def(py::init<>())
+        .def("reset_at", &VectorFieldHolder::reset_at)
         .def_readwrite("vec_fld_hld_ref", &VectorFieldHolder::vec_fld_hld)
         .def_readwrite("vec_fld_hld_cpy",
                        &VectorFieldHolder::vec_fld_hld,

tests/test_class_sh_property_stl.py

@@ -1,17 +1,31 @@
-import pytest
-
 from pybind11_tests import class_sh_property_stl as m
 
 
-def test_vec_fld_hld_ref():
-    vfh = m.VectorFieldHolder()
-    vfh0 = vfh.vec_fld_hld_ref[0]
-    with pytest.raises(RuntimeError) as exc_info:
-        vfh0.fld
-    assert str(exc_info.value) == "Non-owning holder (loaded_as_shared_ptr)."
+def test_cpy_after_ref():
+    h = m.VectorFieldHolder()
+    c1 = h.vec_fld_hld_cpy
+    c2 = h.vec_fld_hld_cpy
+    assert repr(c2) != repr(c1)
+    r1 = h.vec_fld_hld_ref
+    assert repr(r1) != repr(c2)
+    assert repr(r1) != repr(c1)
+    r2 = h.vec_fld_hld_ref
+    assert repr(r2) == repr(r1)
+    c3 = h.vec_fld_hld_cpy
+    assert repr(c3) == repr(r1)  # SURPRISE!
+
+
+def test_persistent_holder():
+    h = m.VectorFieldHolder()
+    c0 = h.vec_fld_hld_cpy[0]  # Must be first. See test_cpy_after_ref().
+    r0 = h.vec_fld_hld_ref[0]  # Must be second.
+    assert c0.fld.wrapped_int == 300
+    assert r0.fld.wrapped_int == 300
+    h.reset_at(0, 400)
+    assert c0.fld.wrapped_int == 300
+    assert r0.fld.wrapped_int == 400
 
 
-def test_vec_fld_hld_cpy():
-    vfh = m.VectorFieldHolder()
-    vfh0 = vfh.vec_fld_hld_cpy[0]
-    assert vfh0.fld.wrapped_int == 300
+def test_temporary_holder_keep_alive():
+    r0 = m.VectorFieldHolder().vec_fld_hld_ref[0]
+    assert r0.fld.wrapped_int == 300