BUG: Ensure PyArray_FromScalar always returns the requested dtype

Fixes gh-15467, where `np.array(np.float64(1), dtype=np.longdouble).dtype.type is np.longdouble` is `False` on windows.

2 files changed, 42 insertions, 1 deletions

diff --git a/numpy/core/src/multiarray/scalarapi.c b/numpy/core/src/multiarray/scalarapi.c
index f3c440dc6..844c1d9cb 100644
--- a/numpy/core/src/multiarray/scalarapi.c
+++ b/numpy/core/src/multiarray/scalarapi.c
@@ -342,7 +342,14 @@ finish:
     if (PyArray_EquivTypes(outcode, typecode)) {
         if (!PyTypeNum_ISEXTENDED(typecode->type_num)
                 || (outcode->elsize == typecode->elsize)) {
-            Py_DECREF(typecode); Py_DECREF(outcode);
+            /*
+             * Since the type is equivalent, and we haven't handed the array
+             * to anyone yet, let's fix the dtype to be what was requested,
+             * even if it is equivalent to what was passed in.
+             */
+            Py_SETREF(((PyArrayObject_fields *)r)->descr, outcode);
+            Py_DECREF(typecode);
+
             return (PyObject *)r;
         }
     }
diff --git a/numpy/core/tests/test_scalar_ctors.py b/numpy/core/tests/test_scalar_ctors.py
index 7645a0853..ec4735b8a 100644
--- a/numpy/core/tests/test_scalar_ctors.py
+++ b/numpy/core/tests/test_scalar_ctors.py
@@ -79,3 +79,37 @@ class TestFromInt:
 
     def test_uint64_from_negative(self):
         assert_equal(np.uint64(-2), np.uint64(18446744073709551614))
+
+
+int_types = [np.byte, np.short, np.intc, np.int_, np.longlong]
+uint_types = [np.ubyte, np.ushort, np.uintc, np.uint, np.ulonglong]
+float_types = [np.half, np.single, np.double, np.longdouble]
+cfloat_types = [np.csingle, np.cdouble, np.clongdouble]
+
+
+class TestArrayFromScalar:
+    """ gh-15467 """
+
+    def _do_test(self, t1, t2):
+        x = t1(2)
+        arr = np.array(x, dtype=t2)
+        # type should be preserved exactly
+        if t2 is None:
+            assert arr.dtype.type is t1
+        else:
+            assert arr.dtype.type is t2
+
+    @pytest.mark.parametrize('t1', int_types + uint_types)
+    @pytest.mark.parametrize('t2', int_types + uint_types + [None])
+    def test_integers(self, t1, t2):
+        return self._do_test(t1, t2)
+
+    @pytest.mark.parametrize('t1', float_types)
+    @pytest.mark.parametrize('t2', float_types + [None])
+    def test_reals(self, t1, t2):
+        return self._do_test(t1, t2)
+
+    @pytest.mark.parametrize('t1', cfloat_types)
+    @pytest.mark.parametrize('t2', cfloat_types + [None])
+    def test_complex(self, t1, t2):
+        return self._do_test(t1, t2)