Add class doc string to native_enum (#5617)

* add class doc string to native_enum

* adapt doc argument name

* fix test, make class enum doc None by default

* fix other python versions?

* make clang-tidy happy

* rename 'enum_doc' to 'class_doc'

* update documentation

* [skip ci] Polish changed documentation (mostly done by ChatGPT).

---------

Co-authored-by: Bryn Lloyd <12702862+dyollb@users.noreply.github.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>

docs/classes.rst

@@ -556,7 +556,7 @@ The binding code for this example looks as follows:
         .def_readwrite("type", &Pet::type)
         .def_readwrite("attr", &Pet::attr);
 
-    py::native_enum<Pet::Kind>(pet, "Kind")
+    py::native_enum<Pet::Kind>(pet, "Kind", "enum.Enum")
         .value("Dog", Pet::Kind::Dog)
         .value("Cat", Pet::Kind::Cat)
         .export_values()
@@ -593,16 +593,20 @@ once. To achieve this, ``py::native_enum`` acts as a buffer to collect the
 name/value pairs. The ``.finalize()`` call uses the accumulated name/value
 pairs to build the arguments for constructing a native Python enum type.
 
-The ``py::native_enum`` constructor supports a third optional
-``native_type_name`` string argument, with default value ``"enum.Enum"``.
-Other types can be specified like this:
+The ``py::native_enum`` constructor takes a third argument,
+``native_type_name``, which specifies the fully qualified name of the Python
+base class to use — e.g., ``"enum.Enum"`` or ``"enum.IntEnum"``. A fourth
+optional argument, ``class_doc``, provides the docstring for the generated
+class.
+
+For example:
 
 .. code-block:: cpp
 
-    py::native_enum<Pet::Kind>(pet, "Kind", "enum.IntEnum")
+    py::native_enum<Pet::Kind>(pet, "Kind", "enum.IntEnum", "Constant specifying the kind of pet")
 
-Any fully-qualified Python name can be specified. The only requirement is
-that the named type is similar to
+You may use any fully qualified Python name for ``native_type_name``.
+The only requirement is that the named type is similar to
 `enum.Enum <https://docs.python.org/3/library/enum.html#enum.Enum>`_
 in these ways:
 

include/pybind11/detail/native_enum_data.h

@@ -29,10 +29,12 @@ public:
     native_enum_data(const object &parent_scope,
                      const char *enum_name,
                      const char *native_type_name,
+                     const char *class_doc,
                      const std::type_index &enum_type_index)
         : enum_name_encoded{enum_name}, native_type_name_encoded{native_type_name},
           enum_type_index{enum_type_index}, parent_scope(parent_scope), enum_name{enum_name},
-          native_type_name{native_type_name}, export_values_flag{false}, finalize_needed{false} {}
+          native_type_name{native_type_name}, class_doc(class_doc), export_values_flag{false},
+          finalize_needed{false} {}
 
     void finalize();
 
@@ -70,10 +72,11 @@ private:
     object parent_scope;
     str enum_name;
     str native_type_name;
+    std::string class_doc;
 
 protected:
     list members;
-    list docs;
+    list member_docs;
     bool export_values_flag : 1; // Attention: It is best to keep the bools together.
 
 private:
@@ -191,7 +194,10 @@ inline void native_enum_data::finalize() {
             parent_scope.attr(member_name) = py_enum[member_name];
         }
     }
-    for (auto doc : docs) {
+    if (!class_doc.empty()) {
+        py_enum.attr("__doc__") = class_doc.c_str();
+    }
+    for (auto doc : member_docs) {
         py_enum[doc[int_(0)]].attr("__doc__") = doc[int_(1)];
     }
     global_internals_native_enum_type_map_set_item(enum_type_index, py_enum.release().ptr());

include/pybind11/native_enum.h

@@ -24,9 +24,10 @@ public:
 
     native_enum(const object &parent_scope,
                 const char *name,
-                const char *native_type_name = "enum.Enum")
+                const char *native_type_name,
+                const char *class_doc = "")
         : detail::native_enum_data(
-              parent_scope, name, native_type_name, std::type_index(typeid(EnumType))) {
+              parent_scope, name, native_type_name, class_doc, std::type_index(typeid(EnumType))) {
         if (detail::get_local_type_info(typeid(EnumType)) != nullptr
             || detail::get_global_type_info(typeid(EnumType)) != nullptr) {
             pybind11_fail(
@@ -53,7 +54,7 @@ public:
         disarm_finalize_check("value after finalize");
         members.append(make_tuple(name, static_cast<Underlying>(value)));
         if (doc) {
-            docs.append(make_tuple(name, doc));
+            member_docs.append(make_tuple(name, doc));
         }
         arm_finalize_check(); // There was no exception.
         return *this;

tests/test_native_enum.cpp

@@ -76,7 +76,7 @@ PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
 TEST_SUBMODULE(native_enum, m) {
     using namespace test_native_enum;
 
-    py::native_enum<smallenum>(m, "smallenum", "enum.IntEnum")
+    py::native_enum<smallenum>(m, "smallenum", "enum.IntEnum", "doc smallenum")
         .value("a", smallenum::a)
         .value("b", smallenum::b)
         .value("c", smallenum::c)
@@ -89,7 +89,7 @@ TEST_SUBMODULE(native_enum, m) {
         .value("blue", color::blue)
         .finalize();
 
-    py::native_enum<altitude>(m, "altitude")
+    py::native_enum<altitude>(m, "altitude", "enum.Enum")
         .value("high", altitude::high)
         .value("low", altitude::low)
         .finalize();
@@ -189,7 +189,7 @@ TEST_SUBMODULE(native_enum, m) {
         py::native_enum<fake>(m, "fake_double_registration_native_enum", "enum.IntEnum")
             .value("x", fake::x)
             .finalize();
-        py::native_enum<fake>(m, "fake_double_registration_native_enum");
+        py::native_enum<fake>(m, "fake_double_registration_native_enum", "enum.Enum");
     });
 
     m.def("native_enum_name_clash", [](py::module_ &m) {

tests/test_native_enum.py

@@ -108,6 +108,12 @@ def test_export_values():
     assert m.exv1 is m.export_values.exv1
 
 
+def test_class_doc():
+    pure_native = enum.IntEnum("pure_native", (("mem", 0),))
+    assert m.smallenum.__doc__ == "doc smallenum"
+    assert m.color.__doc__ == pure_native.__doc__
+
+
 def test_member_doc():
     pure_native = enum.IntEnum("pure_native", (("mem", 0),))
     assert m.member_doc.mem0.__doc__ == "docA"