Python: add 'is absolute' check to disk file hash service storage path

To connect to SQLite, the path to the SQLite file needs to be absolute,
otherwise it cannot be converted to a URI. This is now explicitly
checked, to make this requirement explicit, and to produce a nicer error
message.

I've thought of just making the path absolute in the Disk File Hash
Service itself (instead of raising an error). However, that introduces
the assumption that the path is relative to the current working
directory, which might be incorrect. So IMO it's better to make the
caller responsible for this.

Pull Request: https://projects.blender.org/blender/blender/pulls/153592

scripts/modules/_bpy_internal/disk_file_hash_service/backend_sqlite.py

@@ -53,6 +53,7 @@ class SQLiteBackend:
 
     def __init__(self, storage_path: Path) -> None:
         assert not storage_path.is_dir(), "SQLite back-end expects a directory + file prefix as storage path"
+        assert storage_path.is_absolute(), "SQLite back-end needs an absolute storage path"
 
         self._storage_path = storage_path
         self.dbfile_path = storage_path.with_name("{}_v{}.sqlite".format(storage_path.stem, DB_SCHEMA_VERSION))
@@ -82,7 +83,14 @@ class SQLiteBackend:
         self._execute_pragmas_on_connect(self.db_conn_rw)
 
         # Open a read-only connection.
-        uri = self.dbfile_path.as_uri() + "?mode=ro"
+        try:
+            uri = self.dbfile_path.as_uri() + "?mode=ro"
+        except ValueError as ex:
+            # The ValueError from as_uri() doesn't contain the actual path. Note that
+            # this shouldn't happen, unless the assert from the __init__ function was
+            # disabled (which is possible via a Python CLI argument).
+            raise ValueError("{!s}: {!s}".format(ex, self.dbfile_path))
+
         # Once we upgrade to Python 3.12+, pass `autocommit=False` instead of `isolation_level=None`.
         self.db_conn_ro = sqlite3.connect(uri, uri=True, timeout=DB_TIMEOUT_MSEC / 1000, isolation_level=None)
         if _DEBUG_QUERIES: