Also apply ambiguous conversion workaround to str()

Author: jagerman

include/pybind11/pytypes.h

@@ -1090,8 +1090,10 @@ class str : public object {
     str(const std::string &s) : str(s.data(), s.size()) { }
 
 #ifdef PYBIND11_HAS_STRING_VIEW
+    // enable_if is needed to avoid "ambiguous conversion" errors (see PR #3521).
+    template <typename T, detail::enable_if_t<std::is_same<T, std::string_view>::value, int> = 0>
     // NOLINTNEXTLINE(google-explicit-constructor)
-    str(std::string_view s) : str(s.data(), s.size()) { }
+    str(T s) : str(s.data(), s.size()) { }
 
 # ifdef PYBIND11_HAS_U8STRING
     // reinterpret_cast here is safe (C++20 guarantees char8_t has the same size/alignment as char)

tests/test_builtin_casters.cpp

@@ -167,6 +167,8 @@ TEST_SUBMODULE(builtin_casters, m) {
     };
     m.def("bytes_from_type_with_both_operator_string_and_string_view",
           []() { return py::bytes(TypeWithBothOperatorStringAndStringView()); });
+    m.def("str_from_type_with_both_operator_string_and_string_view",
+          []() { return py::str(TypeWithBothOperatorStringAndStringView()); });
 #endif
 
     // test_integer_casting

tests/test_builtin_casters.py

@@ -215,6 +215,7 @@ def test_string_view(capture):
         assert m.string_view_memoryview() == "Have some 🎂".encode()
 
     assert m.bytes_from_type_with_both_operator_string_and_string_view() == b"success"
+    assert m.str_from_type_with_both_operator_string_and_string_view() == "success"
 
 
 def test_integer_casting():