fix: copy caller-supplied paths instead of aliasing

donfig/config_obj.py

@@ -415,7 +415,9 @@ def __init__(
                 *[os.path.join(prefix, "etc", name) for prefix in site.PREFIXES],
                 os.path.join(os.path.expanduser("~"), ".config", name),
             ]
-
+        else:
+            # copy so the env-var append below never mutates the caller's list
+            paths = list(paths)
         if env_prefix is None:
             env_prefix = f"{name.upper()}_"
         if env is None:

donfig/tests/test_config.py

@@ -606,6 +606,21 @@ def test__get_paths(monkeypatch):
         assert len(paths) == len(set(paths))
 
 
+def test_paths_not_mutated(monkeypatch):
+    monkeypatch.setenv("MYPKG_CONFIG", "foo-bar")
+    paths = ["/etc/mypkg"]
+    config = Config("mypkg", paths=paths)
+    assert config.paths == ["/etc/mypkg", "foo-bar"]
+    # the caller's list is copied on init, not aliased
+    assert paths == ["/etc/mypkg"]
+
+
+def test_paths_accepts_any_sequence(monkeypatch):
+    monkeypatch.setenv("MYPKG_CONFIG", "foo-bar")
+    config = Config("mypkg", paths=("/etc/mypkg",))
+    assert config.paths == ["/etc/mypkg", "foo-bar"]
+
+
 def test_serialization():
     config = Config(CONFIG_NAME)
     config.set(one_key="one_value")