Fixes setting of writable flag for views and writing to read-only arr…

…ays with `out` keyword (#1527)

* Fixes bugs with `writable` flag setting

`writable` flag was not being set correctly for indexing, real views, imaginary views, tranposes, and where shape is set directly

Also fixes cases where flag could be overridden by functions with `out` kwarg

* Adds a test for writable flag view behavior

* Removes assumption that new array is writable

Now flags are set based on input regardless of whether a new array is writable
per review feedback

* Adds _copy_writable for copying the writable flag between arrays

* Correct typos in _copy_writable

* Fixes clip writing to read-only out arrays when min and max are none

dpctl/tensor/_clip.py

@@ -262,6 +262,9 @@ def _clip_none(x, val, out, order, _binary_fn):
                 f"output array must be of usm_ndarray type, got {type(out)}"
             )
 
+        if not out.flags.writable:
+            raise ValueError("provided `out` array is read-only")
+
         if out.shape != res_shape:
             raise ValueError(
                 "The shape of input and output arrays are inconsistent. "
@@ -437,6 +440,9 @@ def clip(x, /, min=None, max=None, out=None, order="K"):
                     f"{type(out)}"
                 )
 
+            if not out.flags.writable:
+                raise ValueError("provided `out` array is read-only")
+
             if out.shape != x.shape:
                 raise ValueError(
                     "The shape of input and output arrays are "
@@ -600,6 +606,9 @@ def clip(x, /, min=None, max=None, out=None, order="K"):
                     f"{type(out)}"
                 )
 
+            if not out.flags.writable:
+                raise ValueError("provided `out` array is read-only")
+
             if out.shape != res_shape:
                 raise ValueError(
                     "The shape of input and output arrays are "

dpctl/tensor/_elementwise_common.py

@@ -202,6 +202,9 @@ def __call__(self, x, out=None, order="K"):
                     f"output array must be of usm_ndarray type, got {type(out)}"
                 )
 
+            if not out.flags.writable:
+                raise ValueError("provided `out` array is read-only")
+
             if out.shape != x.shape:
                 raise ValueError(
                     "The shape of input and output arrays are inconsistent. "
@@ -601,6 +604,9 @@ def __call__(self, o1, o2, out=None, order="K"):
                     f"output array must be of usm_ndarray type, got {type(out)}"
                 )
 
+            if not out.flags.writable:
+                raise ValueError("provided `out` array is read-only")
+
             if out.shape != res_shape:
                 raise ValueError(
                     "The shape of input and output arrays are inconsistent. "

dpctl/tensor/_linear_algebra_functions.py

@@ -738,6 +738,9 @@ def matmul(x1, x2, out=None, dtype=None, order="K"):
                 f"output array must be of usm_ndarray type, got {type(out)}"
             )
 
+        if not out.flags.writable:
+            raise ValueError("provided `out` array is read-only")
+
         if out.shape != res_shape:
             raise ValueError(
                 "The shape of input and output arrays are inconsistent. "

dpctl/tensor/_usmarray.pyx

@@ -60,6 +60,9 @@ cdef object _as_zero_dim_ndarray(object usm_ary):
     view.shape = tuple()
     return view
 
+cdef int _copy_writable(int lhs_flags, int rhs_flags):
+    "Copy the WRITABLE flag to lhs_flags from rhs_flags"
+    return (lhs_flags & ~USM_ARRAY_WRITABLE) | (rhs_flags & USM_ARRAY_WRITABLE)
 
 cdef class usm_ndarray:
     """ usm_ndarray(shape, dtype=None, strides=None, buffer="device", \
@@ -546,7 +549,7 @@ cdef class usm_ndarray:
                 PyMem_Free(self.shape_)
             if (self.strides_):
                 PyMem_Free(self.strides_)
-            self.flags_ = contig_flag
+            self.flags_ = (contig_flag | (self.flags_ & USM_ARRAY_WRITABLE))
             self.nd_ = new_nd
             self.shape_ = shape_ptr
             self.strides_ = strides_ptr
@@ -725,13 +728,13 @@ cdef class usm_ndarray:
             buffer=self.base_,
             offset=_meta[2]
         )
-        res.flags_ |= (self.flags_ & USM_ARRAY_WRITABLE)
         res.array_namespace_ = self.array_namespace_
 
         adv_ind = _meta[3]
         adv_ind_start_p = _meta[4]
 
         if adv_ind_start_p < 0:
+            res.flags_ = _copy_writable(res.flags_, self.flags_)
             return res
 
         from ._copy_utils import _extract_impl, _nonzero_impl, _take_multi_index
@@ -749,6 +752,7 @@ cdef class usm_ndarray:
             if not matching:
                 raise IndexError("boolean index did not match indexed array in dimensions")
             res = _extract_impl(res, key_, axis=adv_ind_start_p)
+            res.flags_ = _copy_writable(res.flags_, self.flags_)
             return res
 
         if any(ind.dtype == dpt_bool for ind in adv_ind):
@@ -758,10 +762,13 @@ cdef class usm_ndarray:
                     adv_ind_int.extend(_nonzero_impl(ind))
                 else:
                     adv_ind_int.append(ind)
-            return _take_multi_index(res, tuple(adv_ind_int), adv_ind_start_p)
-
-        return _take_multi_index(res, adv_ind, adv_ind_start_p)
+            res = _take_multi_index(res, tuple(adv_ind_int), adv_ind_start_p)
+            res.flags_ = _copy_writable(res.flags_, self.flags_)
+            return res
 
+        res = _take_multi_index(res, adv_ind, adv_ind_start_p)
+        res.flags_ = _copy_writable(res.flags_, self.flags_)
+        return res
 
     def to_device(self, target, stream=None):
         """ to_device(target_device)
@@ -1040,8 +1047,7 @@ cdef class usm_ndarray:
             buffer=self.base_,
             offset=_meta[2],
         )
-        # set flags and namespace
-        Xv.flags_ |= (self.flags_ & USM_ARRAY_WRITABLE)
+        # set namespace
         Xv.array_namespace_ = self.array_namespace_
 
         from ._copy_utils import (
@@ -1225,7 +1231,7 @@ cdef usm_ndarray _real_view(usm_ndarray ary):
         offset=offset_elems,
         order=('C' if (ary.flags_ & USM_ARRAY_C_CONTIGUOUS) else 'F')
     )
-    r.flags_ |= (ary.flags_ & USM_ARRAY_WRITABLE)
+    r.flags_ = _copy_writable(r.flags_, ary.flags_)
     r.array_namespace_ = ary.array_namespace_
     return r
 
@@ -1257,7 +1263,7 @@ cdef usm_ndarray _imag_view(usm_ndarray ary):
         offset=offset_elems,
         order=('C' if (ary.flags_ & USM_ARRAY_C_CONTIGUOUS) else 'F')
     )
-    r.flags_ |= (ary.flags_ & USM_ARRAY_WRITABLE)
+    r.flags_ = _copy_writable(r.flags_, ary.flags_)
     r.array_namespace_ = ary.array_namespace_
     return r
 
@@ -1277,7 +1283,7 @@ cdef usm_ndarray _transpose(usm_ndarray ary):
         order=('F' if (ary.flags_ & USM_ARRAY_C_CONTIGUOUS) else 'C'),
         offset=ary.get_offset()
     )
-    r.flags_ |= (ary.flags_ & USM_ARRAY_WRITABLE)
+    r.flags_ = _copy_writable(r.flags_, ary.flags_)
     return r
 
 
@@ -1294,7 +1300,7 @@ cdef usm_ndarray _m_transpose(usm_ndarray ary):
         order=('F' if (ary.flags_ & USM_ARRAY_C_CONTIGUOUS) else 'C'),
         offset=ary.get_offset()
     )
-    r.flags_ |= (ary.flags_ & USM_ARRAY_WRITABLE)
+    r.flags_ = _copy_writable(r.flags_, ary.flags_)
     return r
 
 

dpctl/tests/test_usm_ndarray_ctor.py

@@ -129,6 +129,25 @@ def test_usm_ndarray_flags_bug_gh_1334():
     assert r.flags["F"] and r.flags["C"]
 
 
+def test_usm_ndarray_writable_flag_views():
+    get_queue_or_skip()
+    a = dpt.arange(10, dtype="f4")
+    a.flags["W"] = False
+
+    a.shape = (5, 2)
+    assert not a.flags.writable
+    assert not a.T.flags.writable
+    assert not a.mT.flags.writable
+    assert not a.real.flags.writable
+    assert not a[0:3].flags.writable
+
+    a = dpt.arange(10, dtype="c8")
+    a.flags["W"] = False
+
+    assert not a.real.flags.writable
+    assert not a.imag.flags.writable
+
+
 @pytest.mark.parametrize(
     "dtype",
     [