fix: return a writable copy from get_rule_config

src/legenddataflowscripts/utils/cfgtools.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import copy
 from collections.abc import Iterable, Mapping
 from pathlib import Path
 
@@ -133,14 +134,15 @@ def get_rule_config(configs_path, rule_name, timestamp, datatype):
 
     Wraps ``TextDB(...).on(...)["snakemake_rules"][rule_name]`` so that a
     missing key names the rule, timestamp, datatype and config path instead
-    of raising a bare :class:`KeyError`.
+    of raising a bare :class:`KeyError`. Returns a writable deep copy, since
+    ``TextDB.on()`` results are shared and read-only.
     """
     if not Path(configs_path).is_dir():
         msg = f"config directory {configs_path} does not exist"
         raise FileNotFoundError(msg)
     configs = TextDB(configs_path, lazy=True).on(timestamp, category=datatype)
     try:
-        return configs["snakemake_rules"][rule_name]
+        return copy.deepcopy(configs["snakemake_rules"][rule_name])
     except KeyError as err:
         msg = (
             f"config resolved from {configs_path} for timestamp {timestamp} "

tests/test_utils_helpers.py

@@ -155,6 +155,12 @@ def test_get_rule_config(configs_tree):
     config = get_rule_config(configs_tree, "tier_tcm", "20230201T000000Z", "cal")
     assert config["inputs"]["config"] == "c.yaml"
 
+    # writable, and edits don't leak into the next call
+    config["inputs"]["config"] = "other.yaml"
+    config["inputs"].setdefault("extra", []).append(1)
+    again = get_rule_config(configs_tree, "tier_tcm", "20230201T000000Z", "cal")
+    assert again["inputs"] == {"config": "c.yaml"}
+
     with pytest.raises(KeyError, match=r"no snakemake_rules\.tier_dsp entry"):
         get_rule_config(configs_tree, "tier_dsp", "20230201T000000Z", "cal")