From 27941eeb1eaaec73a722b8c1d959aa01ec956368 Mon Sep 17 00:00:00 2001
From: Marcin Wojdyr <wojdyr@gmail.com>
Date: Fri, 4 Oct 2024 15:34:57 +0200
Subject: [PATCH] optional_caster::from_python: reset value on None (fixes
 #747)

---
 include/nanobind/stl/detail/nb_optional.h | 5 +++--
 tests/test_stl.cpp                        | 4 ++++
 tests/test_stl.py                         | 1 +
 tests/test_stl_ext.pyi.ref                | 2 ++
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/nanobind/stl/detail/nb_optional.h b/include/nanobind/stl/detail/nb_optional.h
index 78365c97..deda2189 100644
--- a/include/nanobind/stl/detail/nb_optional.h
+++ b/include/nanobind/stl/detail/nb_optional.h
@@ -21,9 +21,10 @@ struct optional_caster {
     NB_TYPE_CASTER(Optional, optional_name(Caster::Name))
 
     bool from_python(handle src, uint8_t flags, cleanup_list* cleanup) noexcept {
-        if (src.is_none())
-            // default-constructed value is already empty
+        if (src.is_none()) {
+            value.reset();
             return true;
+        }
 
         Caster caster;
         if (!caster.from_python(src, flags_for_local_caster<T>(flags), cleanup) ||
diff --git a/tests/test_stl.cpp b/tests/test_stl.cpp
index bd75db5c..834ccd46 100644
--- a/tests/test_stl.cpp
+++ b/tests/test_stl.cpp
@@ -464,6 +464,10 @@ NB_MODULE(test_stl_ext, m) {
         return x;
     });
 
+    m.def("vector_optional_str", [](const std::vector<std::optional<std::string>>& x) {
+        return x;
+    });
+
     m.def("pass_wstr", [](std::wstring ws) { return ws; });
 
     // uncomment to see compiler error:
diff --git a/tests/test_stl.py b/tests/test_stl.py
index bb2d4e1e..f5fc46f0 100644
--- a/tests/test_stl.py
+++ b/tests/test_stl.py
@@ -782,6 +782,7 @@ def test69_complex_array():
 def test70_vec_char():
     assert isinstance(t.vector_str("123"), str)
     assert isinstance(t.vector_str(["123", "345"]), list)
+    assert t.vector_optional_str(["abc", None]) == ["abc", None]
 
 
 def test71_null_input():
diff --git a/tests/test_stl_ext.pyi.ref b/tests/test_stl_ext.pyi.ref
index 72a0f5fe..e62b4749 100644
--- a/tests/test_stl_ext.pyi.ref
+++ b/tests/test_stl_ext.pyi.ref
@@ -233,6 +233,8 @@ def vec_return_copyable() -> list[Copyable]: ...
 
 def vec_return_movable() -> list[Movable]: ...
 
+def vector_optional_str(arg: Sequence[str | None], /) -> list[str | None]: ...
+
 @overload
 def vector_str(arg: Sequence[str], /) -> list[str]: ...