BUG: fix fromfile behavior when reading sub-array dtypes

Restore previous behavior of fromfile, by ensuring the original dtype is
used for reading, instead of the type of the created array which may
have sub-arrays collapsed.

Reverts parts of 454c5b5e9a76809a4ab60bda30aa048ec37ee11e

2 files changed, 31 insertions, 5 deletions

diff --git a/numpy/core/src/multiarray/ctors.c b/numpy/core/src/multiarray/ctors.c
index ba5121306..77ee3efdd 100644
--- a/numpy/core/src/multiarray/ctors.c
+++ b/numpy/core/src/multiarray/ctors.c
@@ -3580,6 +3580,7 @@ array_fromfile_binary(FILE *fp, PyArray_Descr *dtype, npy_intp num, size_t *nrea
 {
     PyArrayObject *r;
     npy_off_t start, numbytes;
+    int elsize;
 
     if (num < 0) {
         int fail = 0;
@@ -3606,16 +3607,21 @@ array_fromfile_binary(FILE *fp, PyArray_Descr *dtype, npy_intp num, size_t *nrea
         }
         num = numbytes / dtype->elsize;
     }
+
+    /*
+     * Array creation may move sub-array dimensions from the dtype to array
+     * dimensions, so we need to use the original element size when reading.
+     */
+    elsize = dtype->elsize;
+
     r = (PyArrayObject *)PyArray_NewFromDescr(&PyArray_Type, dtype, 1, &num,
                                               NULL, NULL, 0, NULL);
     if (r == NULL) {
         return NULL;
     }
-    /* In some cases NewFromDescr can replace the dtype, so fetch new one */
-    dtype = PyArray_DESCR(r);
 
     NPY_BEGIN_ALLOW_THREADS;
-    *nread = fread(PyArray_DATA(r), dtype->elsize, num, fp);
+    *nread = fread(PyArray_DATA(r), elsize, num, fp);
     NPY_END_ALLOW_THREADS;
     return r;
 }
@@ -3642,14 +3648,19 @@ array_from_text(PyArray_Descr *dtype, npy_intp num, char *sep, size_t *nread,
 
     size = (num >= 0) ? num : FROM_BUFFER_SIZE;
 
+    /*
+     * Array creation may move sub-array dimensions from the dtype to array
+     * dimensions, so we need to use the original dtype when reading.
+     */
+    Py_INCREF(dtype);
+
     r = (PyArrayObject *)
         PyArray_NewFromDescr(&PyArray_Type, dtype, 1, &size,
                              NULL, NULL, 0, NULL);
     if (r == NULL) {
+        Py_DECREF(dtype);
         return NULL;
     }
-    /* In some cases NewFromDescr can replace the dtype, so fetch new one */
-    dtype = PyArray_DESCR(r);
 
     clean_sep = swab_separator(sep);
     if (clean_sep == NULL) {
@@ -3710,6 +3721,7 @@ array_from_text(PyArray_Descr *dtype, npy_intp num, char *sep, size_t *nread,
         if (PyErr_Occurred()) {
             /* If an error is already set (unlikely), do not create new one */
             Py_DECREF(r);
+            Py_DECREF(dtype);
             return NULL;
         }
         /* 2019-09-12, NumPy 1.18 */
@@ -3721,6 +3733,7 @@ array_from_text(PyArray_Descr *dtype, npy_intp num, char *sep, size_t *nread,
     }
 
 fail:
+    Py_DECREF(dtype);
     if (err == 1) {
         PyErr_NoMemory();
     }
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 88db357b2..9b124f603 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -5023,6 +5023,19 @@ class TestIO(object):
             self.test_tofile_sep()
             self.test_tofile_format()
 
+    def test_fromfile_subarray_binary(self):
+        # Test subarray dtypes which are absorbed into the shape
+        x = np.arange(24, dtype="i4").reshape(2, 3, 4)
+        x.tofile(self.filename)
+        res = np.fromfile(self.filename, dtype="(3,4)i4")
+        assert_array_equal(x, res)
+
+        x_str = x.tobytes()
+        with assert_warns(DeprecationWarning):
+            # binary fromstring is deprecated
+            res = np.fromstring(x_str, dtype="(3,4)i4")
+            assert_array_equal(x, res)
+
 
 class TestFromBuffer(object):
     @pytest.mark.parametrize('byteorder', ['<', '>'])