fix: extra parens matter?

Author: henryiii

include/pybind11/pybind11.h

@@ -1966,8 +1966,8 @@ struct iterator_state {
 };
 
 // Note: these helpers take the iterator by non-const reference because some
-// iterators in the wild can't be dereferenced when const.
-template <typename Iterator, typename ResultType = decltype(*std::declval<Iterator>())>
+// iterators in the wild can't be dereferenced when const. C++ needs the extra parens in decltype.
+template <typename Iterator, typename ResultType = decltype((*std::declval<Iterator>()))>
 struct iterator_access {
     using result_type = ResultType;
     // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
@@ -1976,15 +1976,15 @@ struct iterator_access {
     }
 };
 
-template <typename Iterator, typename ResultType = decltype((*std::declval<Iterator>()).first) >
+template <typename Iterator, typename ResultType = decltype(((*std::declval<Iterator>()).first)) >
 struct iterator_key_access {
     using result_type = ResultType;
     result_type operator()(Iterator &it) const {
         return (*it).first;
     }
 };
 
-template <typename Iterator, typename ResultType = decltype((*std::declval<Iterator>()).second)>
+template <typename Iterator, typename ResultType = decltype(((*std::declval<Iterator>()).second))>
 struct iterator_value_access {
     using result_type = ResultType;
     result_type operator()(Iterator &it) const {

tests/test_sequences_and_iterators.cpp

@@ -321,7 +321,17 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
         .def("nonzero_values", [](const IntPairs& s) {
             return py::make_value_iterator(NonZeroIterator<std::pair<int, int>>(s.begin()), NonZeroSentinel());
         }, py::keep_alive<0, 1>())
-        // test iterator with keep_alive (doesn't work, but tests compile)
+        .def("simple_iterator", [](IntPairs& self) {
+            return py::make_iterator(self);
+        }, py::keep_alive<0, 1>())
+        .def("simple_keys", [](IntPairs& self) {
+            return py::make_key_iterator(self);
+        }, py::keep_alive<0, 1>())
+        .def("simple_values", [](IntPairs& self) {
+            return py::make_value_iterator(self);
+        }, py::keep_alive<0, 1>())
+
+        // test iterator with keep_alive (doesn't work so not used at runtime, but tests compile)
         .def("make_iterator_keep_alive", [](IntPairs& self) {
             return py::make_iterator(self, py::keep_alive<0, 1>());
         }, py::keep_alive<0, 1>())

tests/test_sequences_and_iterators.py

@@ -21,10 +21,6 @@ def test_generalized_iterators():
     assert list(m.IntPairs([(1, 2), (2, 0), (0, 3), (4, 5)]).nonzero()) == [(1, 2)]
     assert list(m.IntPairs([(0, 3), (1, 2), (3, 4)]).nonzero()) == []
 
-    # keep_alive can't be attached
-    with pytest.raises(RuntimeError):
-        m.IntPairs([(1, 2), (3, 4), (0, 5)]).make_iterator_keep_alive()
-
     assert list(m.IntPairs([(1, 2), (3, 4), (0, 5)]).nonzero_keys()) == [1, 3]
     assert list(m.IntPairs([(1, 2), (2, 0), (0, 3), (4, 5)]).nonzero_keys()) == [1]
     assert list(m.IntPairs([(0, 3), (1, 2), (3, 4)]).nonzero_keys()) == []
@@ -45,6 +41,16 @@ def test_generalized_iterators():
             next(it)
 
 
+def test_generalized_iterators_simple():
+    assert list(m.IntPairs([(1, 2), (3, 4), (0, 5)]).simple_iterator()) == [
+        (1, 2),
+        (3, 4),
+        (0, 5),
+    ]
+    assert list(m.IntPairs([(1, 2), (3, 4), (0, 5)]).simple_keys()) == [1, 3, 0]
+    assert list(m.IntPairs([(1, 2), (3, 4), (0, 5)]).simple_values()) == [2, 4, 5]
+
+
 def test_iterator_referencing():
     """Test that iterators reference rather than copy their referents."""
     vec = m.VectorNonCopyableInt()