Enable passing `absl::Span<bool>` and `absl::Span<const bool>`

PiperOrigin-RevId: 590290022

pybind11_abseil/absl_casters.h

@@ -387,7 +387,7 @@ namespace internal {
 template <typename T>
 static constexpr bool is_buffer_interface_compatible_type =
     detail::is_same_ignoring_cvref<T, PyObject*>::value ||
-    std::is_arithmetic<T>::value ||
+    std::is_arithmetic<std::remove_cv_t<T>>::value ||
     std::is_same<T, std::complex<float>>::value ||
     std::is_same<T, std::complex<double>>::value;
 
@@ -405,7 +405,8 @@ std::tuple<bool, absl::Span<T>> LoadSpanFromBuffer(handle src) {
   if (PyObject_GetBuffer(src.ptr(), &view, flags) == 0) {
     auto cleanup = absl::MakeCleanup([&view] { PyBuffer_Release(&view); });
     if (view.ndim == 1 && view.strides[0] == sizeof(T) &&
-        buffer_info(&view, /*ownview=*/false).item_type_is_equivalent_to<T>()) {
+        buffer_info(&view, /*ownview=*/false)
+            .item_type_is_equivalent_to<std::remove_cv_t<T>>()) {
       return {true, absl::MakeSpan(static_cast<T*>(view.buf), view.shape[0])};
     }
   } else {
@@ -421,6 +422,29 @@ constexpr std::tuple<bool, absl::Span<T>> LoadSpanFromBuffer(handle /*src*/) {
   return {false, absl::Span<T>()};
 }
 
+template <typename T,
+          typename std::enable_if<
+              !std::is_same<std::remove_cv_t<T>, bool>::value, int>::type = 0>
+std::tuple<bool, absl::Span<T>> LoadSpanOpaqueVector(handle src) {
+  // Attempt to unwrap an opaque std::vector.
+  using value_type = std::remove_cv_t<T>;
+  type_caster_base<std::vector<value_type>> caster;
+  if (caster.load(src, false)) {
+    return {true,
+            absl::MakeSpan(static_cast<std::vector<value_type>&>(caster))};
+  }
+  return {false, absl::Span<T>()};
+}
+
+template <typename T,
+          typename std::enable_if<
+              std::is_same<std::remove_cv_t<T>, bool>::value, int>::type = 0>
+std::tuple<bool, absl::Span<T>> LoadSpanOpaqueVector(handle src) {
+  // std::vector<bool> is special and cannot directly be converted to a Span
+  // (see https://en.cppreference.com/w/cpp/container/vector_bool).
+  return {false, absl::Span<T>()};
+}
+
 // Helper to determine whether T is a span.
 template <typename T>
 struct is_absl_span : std::false_type {};
@@ -433,7 +457,7 @@ template <typename T>
 struct type_caster<absl::Span<T>> {
  public:
   // The type referenced by the span, with const removed.
-  using value_type = typename std::remove_cv<T>::type;
+  using value_type = std::remove_cv_t<T>;
   static_assert(!is_absl_span<value_type>::value,
                 "Nested absl spans are not supported.");
 
@@ -479,19 +503,17 @@ struct type_caster<absl::Span<T>> {
     std::tie(loaded, value_) = LoadSpanFromBuffer<T>(src);
     if (loaded) return true;
 
-    // Attempt to unwrap an opaque std::vector.
-    type_caster_base<std::vector<value_type>> caster;
-    if (caster.load(src, false)) {
-      value_ = get_value(caster);
-      return true;
-    }
+    std::tie(loaded, value_) = LoadSpanOpaqueVector<T>(src);
+    if (loaded) return true;
 
-    // Attempt to convert a native sequence. If the is_base_of_v check passes,
+    // Attempt to convert a native sequence. If the is_base_of check passes,
     // the elements do not require converting and pointers do not reference a
     // temporary object owned by the element caster. Pointers to converted
     // types are not allowed because they would result a dangling reference
     // when the element caster is destroyed.
     if (convert && std::is_const<T>::value &&
+        // See comment for ephemeral_storage_type below.
+        !std::is_same<T, const bool>::value &&
         (!std::is_pointer<T>::value ||
          std::is_base_of<type_caster_generic, make_caster<T>>::value)) {
       list_caster_.emplace();
@@ -512,12 +534,28 @@ struct type_caster<absl::Span<T>> {
   }
 
  private:
-  template <typename Caster>
+  // Unfortunately using std::vector as ephemeral_storage_type creates
+  // complications for std::vector<bool>
+  // (https://en.cppreference.com/w/cpp/container/vector_bool).
+  using ephemeral_storage_type = std::vector<value_type>;
+
+  template <
+      typename Caster, typename VT = value_type,
+      typename std::enable_if<!std::is_same<VT, bool>::value, int>::type = 0>
   absl::Span<T> get_value(Caster& caster) {
-    return absl::MakeSpan(static_cast<std::vector<value_type>&>(caster));
+    return absl::MakeSpan(static_cast<ephemeral_storage_type&>(caster));
+  }
+
+  // This template specialization is needed to avoid compilation errors.
+  // The conditions in load() make this code unreachable.
+  template <
+      typename Caster, typename VT = value_type,
+      typename std::enable_if<std::is_same<VT, bool>::value, int>::type = 0>
+  absl::Span<T> get_value(Caster&) {
+    throw std::runtime_error("Expected to be unreachable.");
   }
 
-  using ListCaster = list_caster<std::vector<value_type>, value_type>;
+  using ListCaster = list_caster<ephemeral_storage_type, value_type>;
   absl::optional<ListCaster> list_caster_;
   absl::Span<T> value_;
 };

pybind11_abseil/tests/absl_example.cc

@@ -279,6 +279,18 @@ std::string PassSpanPyObjectPtr(absl::Span<PyObject*> input_span) {
   return result;
 }
 
+std::string PassSpanBool(absl::Span<bool> input_span) {
+  std::string result;
+  for (const auto& i : input_span) result += (i ? "t" : "f");
+  return result;
+}
+
+std::string PassSpanConstBool(absl::Span<const bool> input_span) {
+  std::string result;
+  for (const auto& i : input_span) result += (i ? "T" : "F");
+  return result;
+}
+
 struct ObjectForSpan {
   explicit ObjectForSpan(int v) : value(v) {}
   int value;
@@ -404,6 +416,8 @@ PYBIND11_MODULE(absl_example, m) {
   m.def("sum_span_const_complex128",
         &SumSpanComplex<const std::complex<double>>, arg("input_span"));
   m.def("pass_span_pyobject_ptr", &PassSpanPyObjectPtr, arg("span"));
+  m.def("pass_span_bool", &PassSpanBool, arg("span"));
+  m.def("pass_span_const_bool", &PassSpanConstBool, arg("span"));
 
   // Span of objects.
   class_<ObjectForSpan>(m, "ObjectForSpan")

pybind11_abseil/tests/absl_test.py

@@ -312,7 +312,7 @@ def make_read_only_numpy_array():
   return values
 
 
-def make_srided_numpy_array(stride):
+def make_strided_numpy_array(stride):
   return np.zeros(10, dtype=np.int32)[::stride]
 
 
@@ -373,10 +373,10 @@ class AbslNumericSpanTest(parameterized.TestCase):
 
   @parameterized.named_parameters(
       ('float_numpy', np.zeros(5, dtype=float)),
-      ('two_d_numpy', np.zeros(
-          (5, 5), dtype=np.int32)), ('read_only', make_read_only_numpy_array()),
-      ('strided_skip', make_srided_numpy_array(2)),
-      ('strided_reverse', make_srided_numpy_array(-1)),
+      ('two_d_numpy', np.zeros((5, 5), dtype=np.int32)),
+      ('read_only', make_read_only_numpy_array()),
+      ('strided_skip', make_strided_numpy_array(2)),
+      ('strided_reverse', make_strided_numpy_array(-1)),
       ('non_supported_type', np.zeros(5, dtype=np.unicode_)),
       ('native_list', [0] * 5))
   def test_fill_span_fails_from(self, values):
@@ -397,6 +397,28 @@ class AbslNumericSpanTest(parameterized.TestCase):
     arr = np.array([-3, 'four', 5.0], dtype=object)
     self.assertEqual(absl_example.pass_span_pyobject_ptr(arr), '-3four5.0')
 
+  @parameterized.parameters(
+      ([], ''),
+      ([False], 'f'),
+      ([True], 't'),
+      ([False, True, True, False], 'fttf'),
+  )
+  def test_pass_span_bool(self, bools, expected):
+    arr = np.array(bools, dtype=bool)
+    s = absl_example.pass_span_bool(arr)
+    self.assertEqual(s, expected)
+
+  @parameterized.parameters(
+      ([], ''),
+      ([False], 'F'),
+      ([True], 'T'),
+      ([False, True, True, False], 'FTTF'),
+  )
+  def test_pass_span_const_bool(self, bools, expected):
+    arr = np.array(bools, dtype=bool)
+    s = absl_example.pass_span_const_bool(arr)
+    self.assertEqual(s, expected)
+
 
 def make_native_list_of_objects():
   return [absl_example.ObjectForSpan(3), absl_example.ObjectForSpan(5)]