fix: proposal for #2947 (#3191)

* fix: cast numpy integers to integers in ak.from_buffers (fixes #2947)

* Add test for 3502225e9246ce0197d6143c9d94c9e1aeec88b8

* style: pre-commit fixes

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/awkward/operations/ak_from_buffers.py

@@ -136,6 +136,9 @@ def _impl(
     elif isinstance(form, dict):
         form = ak.forms.from_dict(form)
 
+    if isinstance(length, np.integer):
+        length = int(length)
+
     if not (is_integer(length) and length >= 0):
         raise TypeError("'length' argument must be a non-negative integer")
 

tests/test_2947_to_list_numpy_integer.py

@@ -0,0 +1,18 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/awkward/blob/main/LICENSE
+from __future__ import annotations
+
+import numpy as np
+
+import awkward as ak
+
+
+def test():
+    """Check that to_list() does not break when the array is built from buffers
+    with a length of type np.int64.
+    """
+    awk = ak.Array(np.ones((7, 0)))
+    form, length, container = ak.to_buffers(ak.to_packed(awk))
+    awk_from_buf = ak.from_buffers(form, np.int64(length), container)
+    lst = awk_from_buf.to_list()
+
+    assert len(lst) == length