From a4dd41a18e1ed854dfd77d898ea42ea847a08ce3 Mon Sep 17 00:00:00 2001
From: Michael Carlstrom <rmc@carlstrom.com>
Date: Sun, 30 Jun 2024 12:52:37 -0400
Subject: [PATCH] feat(types) Adds special Case for empty C++ tuple type
 annotation (#5214)

* add special case and unit test

* add newline
---
 include/pybind11/cast.h       | 7 +++++++
 tests/test_builtin_casters.py | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 624b8ebac..e41ad2abf 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -740,6 +740,13 @@ class type_caster<std::pair<T1, T2>> : public tuple_caster<std::pair, T1, T2> {}
 template <typename... Ts>
 class type_caster<std::tuple<Ts...>> : public tuple_caster<std::tuple, Ts...> {};
 
+template <>
+class type_caster<std::tuple<>> : public tuple_caster<std::tuple> {
+public:
+    // PEP 484 specifies this syntax for an empty tuple
+    static constexpr auto name = const_name("tuple[()]");
+};
+
 /// Helper class which abstracts away certain actions. Users can provide specializations for
 /// custom holders, but it's only necessary if the type has a non-standard interface.
 template <typename T>
diff --git a/tests/test_builtin_casters.py b/tests/test_builtin_casters.py
index 9aa5926e9..b37aacff1 100644
--- a/tests/test_builtin_casters.py
+++ b/tests/test_builtin_casters.py
@@ -368,6 +368,8 @@ def test_tuple(doc):
     """
     )
 
+    assert doc(m.empty_tuple) == """empty_tuple() -> tuple[()]"""
+
     assert m.rvalue_pair() == ("rvalue", "rvalue")
     assert m.lvalue_pair() == ("lvalue", "lvalue")
     assert m.rvalue_tuple() == ("rvalue", "rvalue", "rvalue")