BUG: Distinguish exact vs. equivalent dtype for C type aliases.

numpy/array_api/tests/test_asarray.py

@@ -0,0 +1,45 @@
+import numpy as np
+
+
+def test_dtype_identity():
+    """Confirm the intended behavior for ``asarray`` results.
+
+    The result of ``asarray()`` should have the dtype provided through the
+    keyword argument, when used. This forces unique array handles to be
+    produced for unique np.dtype objects, but (for equivalent dtypes), the
+    underlying data (the base object) is shared with the original array object.
+
+    Ref https://github.com/numpy/numpy/issues/1468
+    """
+    int_array = np.array([1, 2, 3], dtype='i')
+    assert np.asarray(int_array) is int_array
+
+    # The character code resolves to the singleton dtype object provided
+    # by the numpy package.
+    assert np.asarray(int_array, dtype='i') is int_array
+
+    # Derive a dtype from n.dtype('i'), but add a metadata object to force
+    # the dtype to be distinct.
+    unequal_type = np.dtype('i', metadata={'spam': True})
+    annotated_int_array = np.asarray(int_array, dtype=unequal_type)
+    assert annotated_int_array is not int_array
+    assert annotated_int_array.base is int_array
+
+    # These ``asarray()`` calls may produce a new view or a copy,
+    # but never the same object.
+    long_int_array = np.asarray(int_array, dtype='l')
+    assert long_int_array is not int_array
+    assert np.asarray(int_array, dtype='q') is not int_array
+    assert np.asarray(long_int_array, dtype='q') is not long_int_array
+    assert long_int_array is not np.asarray(int_array, dtype='l')
+    assert long_int_array.base is np.asarray(int_array, dtype='l').base
+
+    equivalent_requirement = np.dtype('i', metadata={'spam': True})
+    annotated_int_array_alt = np.asarray(annotated_int_array,
+                                         dtype=equivalent_requirement)
+    # The descriptors are equivalent, but we have created
+    # distinct dtype instances.
+    assert unequal_type == equivalent_requirement
+    assert unequal_type is not equivalent_requirement
+    assert annotated_int_array_alt is not annotated_int_array
+    assert annotated_int_array_alt.dtype is equivalent_requirement

numpy/core/src/multiarray/multiarraymodule.c

@@ -1627,12 +1627,31 @@ _array_fromobject_generic(
                 goto finish;
             }
         }
-        /* One more chance */
+        /* One more chance for faster exit if user specified the dtype. */
         oldtype = PyArray_DESCR(oparr);
         if (PyArray_EquivTypes(oldtype, type)) {
             if (copy != NPY_COPY_ALWAYS && STRIDING_OK(oparr, order)) {
                 Py_INCREF(op);
-                ret = oparr;
+                if (oldtype == type) {
+                    ret = oparr;
+                }
+                else {
+                    /* Create a new PyArrayObject from the caller's
+                     * PyArray_Descr. Use the reference `op` as the base
+                     * object. */
+                    Py_INCREF(type);
+                    ret = (PyArrayObject *)PyArray_NewFromDescrAndBase(
+                            Py_TYPE(op),
+                            type,
+                            PyArray_NDIM(oparr),
+                            PyArray_DIMS(oparr),
+                            PyArray_STRIDES(oparr),
+                            PyArray_DATA(oparr),
+                            PyArray_FLAGS(oparr),
+                            op,
+                            op
+                            );
+                }
                 goto finish;
             }
             else {

numpy/ma/tests/test_core.py

@@ -5387,7 +5387,7 @@ def test_ufunc_with_out_varied():
 
 
 def test_astype_mask_ordering():
-    descr = [('v', int, 3), ('x', [('y', float)])]
+    descr = np.dtype([('v', int, 3), ('x', [('y', float)])])
     x = array([
         [([1, 2, 3], (1.0,)),  ([1, 2, 3], (2.0,))],
         [([1, 2, 3], (3.0,)),  ([1, 2, 3], (4.0,))]], dtype=descr)