array: fix base handling

numpy arrays aren't currently properly setting base: by setting `->base`
directly, the base doesn't follow what numpy expects and documents (that
is, following chained array bases to the root array).

This fixes the behaviour by using numpy's PyArray_SetBaseObject to set
the base instead, and then updates the tests to reflect the fixed
behaviour.

include/pybind11/numpy.h

@@ -154,6 +154,7 @@ struct npy_api {
     int (*PyArray_GetArrayParamsFromObject_)(PyObject *, PyObject *, char, PyObject **, int *,
     int (*PyArray_GetArrayParamsFromObject_)(PyObject *, PyObject *, char, PyObject **, int *,
                                              Py_ssize_t *, PyObject **, PyObject *);
                                              Py_ssize_t *, PyObject **, PyObject *);
     PyObject *(*PyArray_Squeeze_)(PyObject *);
     PyObject *(*PyArray_Squeeze_)(PyObject *);
+    int (*PyArray_SetBaseObject_)(PyObject *, PyObject *);
 private:
 private:
     enum functions {
     enum functions {
         API_PyArray_Type = 2,
         API_PyArray_Type = 2,
@@ -168,7 +169,8 @@ private:
         API_PyArray_DescrConverter = 174,
         API_PyArray_DescrConverter = 174,
         API_PyArray_EquivTypes = 182,
         API_PyArray_EquivTypes = 182,
         API_PyArray_GetArrayParamsFromObject = 278,
         API_PyArray_GetArrayParamsFromObject = 278,
-        API_PyArray_Squeeze = 136
+        API_PyArray_Squeeze = 136,
+        API_PyArray_SetBaseObject = 282
     };
     };
 
 
     static npy_api lookup() {
     static npy_api lookup() {
@@ -194,6 +196,7 @@ private:
         DECL_NPY_API(PyArray_EquivTypes);
         DECL_NPY_API(PyArray_EquivTypes);
         DECL_NPY_API(PyArray_GetArrayParamsFromObject);
         DECL_NPY_API(PyArray_GetArrayParamsFromObject);
         DECL_NPY_API(PyArray_Squeeze);
         DECL_NPY_API(PyArray_Squeeze);
+        DECL_NPY_API(PyArray_SetBaseObject);
 #undef DECL_NPY_API
 #undef DECL_NPY_API
         return api;
         return api;
     }
     }
@@ -365,7 +368,7 @@ public:
             pybind11_fail("NumPy: unable to create array!");
             pybind11_fail("NumPy: unable to create array!");
         if (ptr) {
         if (ptr) {
             if (base) {
             if (base) {
-                detail::array_proxy(tmp.ptr())->base = base.inc_ref().ptr();
+                api.PyArray_SetBaseObject_(tmp.ptr(), base.inc_ref().ptr());
             } else {
             } else {
                 tmp = reinterpret_steal<object>(api.PyArray_NewCopy_(tmp.ptr(), -1 /* any order */));
                 tmp = reinterpret_steal<object>(api.PyArray_NewCopy_(tmp.ptr(), -1 /* any order */));
             }
             }
@@ -632,8 +635,8 @@ public:
         return *(static_cast<T*>(array::mutable_data()) + byte_offset(size_t(index)...) / itemsize());
         return *(static_cast<T*>(array::mutable_data()) + byte_offset(size_t(index)...) / itemsize());
     }
     }
 
 
-    /// Ensure that the argument is a NumPy array of the correct dtype.
-    /// In case of an error, nullptr is returned and the Python error is cleared.
+    /// Ensure that the argument is a NumPy array of the correct dtype (and if not, try to convert
+    /// it).  In case of an error, nullptr is returned and the Python error is cleared.
     static array_t ensure(handle h) {
     static array_t ensure(handle h) {
         auto result = reinterpret_steal<array_t>(raw_array_t(h.ptr()));
         auto result = reinterpret_steal<array_t>(raw_array_t(h.ptr()));
         if (!result)
         if (!result)

tests/test_numpy_array.py

@@ -165,7 +165,9 @@ def test_make_c_f_array():
 def test_wrap():
 def test_wrap():
     from pybind11_tests.array import wrap
     from pybind11_tests.array import wrap
 
 
-    def assert_references(a, b):
+    def assert_references(a, b, base=None):
+        if base is None:
+            base = a
         assert a is not b
         assert a is not b
         assert a.__array_interface__['data'][0] == b.__array_interface__['data'][0]
         assert a.__array_interface__['data'][0] == b.__array_interface__['data'][0]
         assert a.shape == b.shape
         assert a.shape == b.shape
@@ -177,7 +179,7 @@ def test_wrap():
         assert a.flags.updateifcopy == b.flags.updateifcopy
         assert a.flags.updateifcopy == b.flags.updateifcopy
         assert np.all(a == b)
         assert np.all(a == b)
         assert not b.flags.owndata
         assert not b.flags.owndata
-        assert b.base is a
+        assert b.base is base
         if a.flags.writeable and a.ndim == 2:
         if a.flags.writeable and a.ndim == 2:
             a[0, 0] = 1234
             a[0, 0] = 1234
             assert b[0, 0] == 1234
             assert b[0, 0] == 1234
@@ -201,13 +203,13 @@ def test_wrap():
     a2 = wrap(a1)
     a2 = wrap(a1)
     assert_references(a1, a2)
     assert_references(a1, a2)
 
 
-    a1 = a1.transpose()
-    a2 = wrap(a1)
-    assert_references(a1, a2)
+    a1t = a1.transpose()
+    a2 = wrap(a1t)
+    assert_references(a1t, a2, a1)
 
 
-    a1 = a1.diagonal()
-    a2 = wrap(a1)
-    assert_references(a1, a2)
+    a1d = a1.diagonal()
+    a2 = wrap(a1d)
+    assert_references(a1d, a2, a1)
 
 
 
 
 @pytest.requires_numpy
 @pytest.requires_numpy