fix(databricks): keep the default memtable volume name a single identifier

ibis/backends/databricks/__init__.py

@@ -7,6 +7,7 @@
 import getpass
 import json
 import os
+import re
 import sys
 import tempfile
 from typing import TYPE_CHECKING, Any
@@ -638,7 +639,10 @@ def _ensure_path_for_memtable(self, name: str) -> str:
     def _generate_volume_path(self) -> str:
         """Has runtime effects: prompts the user for a password, and fetches the current database and catalog from the backend."""
         short_version = "".join(map(str, sys.version_info[:3]))
-        volume_name = f"{getpass.getuser()}-py={short_version}-pid={os.getpid()}"
+        # a volume name is a single identifier, so a `.` in the username would
+        # split it into another level of the catalog.schema.volume name
+        user = re.sub(r"[^\w-]", "_", getpass.getuser())
+        volume_name = f"{user}-py={short_version}-pid={os.getpid()}"
         return f"/Volumes/{self._backend.current_catalog}/{self._backend.current_database}/{volume_name}"
 
     def _create_volume(self, path: str) -> None:

ibis/backends/databricks/tests/test_memtable.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import pytest
+
+pytest.importorskip("databricks.sql")
+
+from ibis.backends.databricks import MemtableManager
+
+
+class _FakeBackend:
+    current_catalog = "cat"
+    current_database = "db"
+
+
+@pytest.mark.parametrize(
+    ("user", "expected"),
+    [
+        ("first.last", "first_last"),
+        ("first last", "first_last"),
+        ("plain-user_1", "plain-user_1"),
+    ],
+)
+def test_volume_path_is_a_single_name(monkeypatch, user, expected):
+    monkeypatch.setattr("getpass.getuser", lambda: user)
+
+    path = MemtableManager(_FakeBackend(), None).get_volume_path()
+
+    prefix, volume = path.rsplit("/", 1)
+    assert prefix == "/Volumes/cat/db"
+    assert volume.startswith(f"{expected}-py=")
+    assert "." not in volume