FIX error when deserialzing a Tree instance from a read only buffer (scikit-learn#25585)

Author: OmarManzoor

sklearn/tree/_tree.pyx

@@ -708,11 +708,9 @@ cdef class Tree:
         if self._resize_c(self.capacity) != 0:
             raise MemoryError("resizing tree to %d" % self.capacity)
 
-        cdef Node[::1] node_memory_view = node_ndarray
-        cdef DOUBLE_t[:, :, ::1] value_memory_view = value_ndarray
-        nodes = memcpy(self.nodes, &node_memory_view[0],
+        nodes = memcpy(self.nodes, cnp.PyArray_DATA(node_ndarray),
                        self.capacity * sizeof(Node))
-        value = memcpy(self.value, &value_memory_view[0, 0, 0],
+        value = memcpy(self.value, cnp.PyArray_DATA(value_ndarray),
                        self.capacity * self.value_stride * sizeof(double))
 
     cdef int _resize(self, SIZE_t capacity) nogil except -1:

sklearn/tree/tests/test_tree.py

@@ -2406,3 +2406,22 @@ def test_splitter_serializable(Splitter):
     splitter_back = pickle.loads(splitter_serialize)
     assert splitter_back.max_features == max_features
     assert isinstance(splitter_back, Splitter)
+
+
+def test_tree_deserialization_from_read_only_buffer(tmpdir):
+    """Check that Trees can be deserialized with read only buffers.
+
+    Non-regression test for gh-25584.
+    """
+    pickle_path = str(tmpdir.join("clf.joblib"))
+    clf = DecisionTreeClassifier(random_state=0)
+    clf.fit(X_small, y_small)
+
+    joblib.dump(clf, pickle_path)
+    loaded_clf = joblib.load(pickle_path, mmap_mode="r")
+
+    assert_tree_equal(
+        loaded_clf.tree_,
+        clf.tree_,
+        "The trees of the original and loaded classifiers are not equal.",
+    )