Add float type caster and revert type hint changes to int_ and float_ (#5839)

* Revert type hint changes to int_ and float_

These two types do not support casting from int-like and float-like types.

* Fix tests

* Add a custom py::float_ caster

The default py::object caster only works if the object is an instance of the type.
py::float_ should accept python int objects as well as float.
This caster will pass through float as usual and cast int to float.
The caster handles the type name so the custom one is not required.

* style: pre-commit fixes

* Fix name

* Fix variable

* Try satisfying the formatter

* Rename test function

* Simplify type caster

* Fix reference counting issue

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: gentlegiantJGC

include/pybind11/cast.h

@@ -1401,7 +1401,7 @@ struct handle_type_name<buffer> {
 };
 template <>
 struct handle_type_name<int_> {
-    static constexpr auto name = io_name("typing.SupportsInt", "int");
+    static constexpr auto name = const_name("int");
 };
 template <>
 struct handle_type_name<iterable> {
@@ -1413,7 +1413,7 @@ struct handle_type_name<iterator> {
 };
 template <>
 struct handle_type_name<float_> {
-    static constexpr auto name = io_name("typing.SupportsFloat", "float");
+    static constexpr auto name = const_name("float");
 };
 template <>
 struct handle_type_name<function> {
@@ -1534,6 +1534,21 @@ struct pyobject_caster {
 template <typename T>
 class type_caster<T, enable_if_t<is_pyobject<T>::value>> : public pyobject_caster<T> {};
 
+template <>
+class type_caster<float_> : public pyobject_caster<float_> {
+public:
+    bool load(handle src, bool /* convert */) {
+        if (isinstance<float_>(src)) {
+            value = reinterpret_borrow<float_>(src);
+        } else if (isinstance<int_>(src)) {
+            value = float_(reinterpret_borrow<int_>(src));
+        } else {
+            return false;
+        }
+        return true;
+    }
+};
+
 // Our conditions for enabling moving are quite restrictive:
 // At compile time:
 // - T needs to be a non-const, non-pointer, non-reference type

tests/test_pytypes.cpp

@@ -209,6 +209,7 @@ TEST_SUBMODULE(pytypes, m) {
     m.def("get_tuple_from_iterable", [](const py::iterable &iter) { return py::tuple(iter); });
     // test_float
     m.def("get_float", [] { return py::float_(0.0f); });
+    m.def("float_roundtrip", [](py::float_ f) { return f; });
     // test_list
     m.def("list_no_args", []() { return py::list{}; });
     m.def("list_ssize_t", []() { return py::list{(py::ssize_t) 0}; });

tests/test_pytypes.py

@@ -61,6 +61,13 @@ def test_iterable(doc):
 
 def test_float(doc):
     assert doc(m.get_float) == "get_float() -> float"
+    assert doc(m.float_roundtrip) == "float_roundtrip(arg0: float) -> float"
+    f1 = m.float_roundtrip(5.5)
+    assert isinstance(f1, float)
+    assert f1 == 5.5
+    f2 = m.float_roundtrip(5)
+    assert isinstance(f2, float)
+    assert f2 == 5.0
 
 
 def test_list(capture, doc):
@@ -917,7 +924,7 @@ def test_inplace_rshift(a, b):
 def test_tuple_nonempty_annotations(doc):
     assert (
         doc(m.annotate_tuple_float_str)
-        == "annotate_tuple_float_str(arg0: tuple[typing.SupportsFloat, str]) -> None"
+        == "annotate_tuple_float_str(arg0: tuple[float, str]) -> None"
     )
 
 
@@ -930,7 +937,7 @@ def test_tuple_empty_annotations(doc):
 def test_tuple_variable_length_annotations(doc):
     assert (
         doc(m.annotate_tuple_variable_length)
-        == "annotate_tuple_variable_length(arg0: tuple[typing.SupportsFloat, ...]) -> None"
+        == "annotate_tuple_variable_length(arg0: tuple[float, ...]) -> None"
     )
 
 
@@ -989,7 +996,7 @@ def test_type_annotation(doc):
 def test_union_annotations(doc):
     assert (
         doc(m.annotate_union)
-        == "annotate_union(arg0: list[str | typing.SupportsInt | object], arg1: str, arg2: typing.SupportsInt, arg3: object) -> list[str | int | object]"
+        == "annotate_union(arg0: list[str | int | object], arg1: str, arg2: int, arg3: object) -> list[str | int | object]"
     )