refactor(config): log the duplicate-key warning without the python warning prefix

tests/core/test_config_duplicate_keys.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-import warnings
+import logging
 from pathlib import Path
 
 import pytest
@@ -17,22 +17,25 @@ def test_duplicate_key_lines_follows_aliases_without_looping(compose) -> None:
     assert duplicate_key_lines(compose(ALIASES)) == [(2, 3), (7, 8)]
 
 
-def test_load_yaml_warns_with_lines_and_keeps_the_later_copy(tmp_path: Path) -> None:
+def test_load_yaml_warns_once_with_lines_and_keeps_the_later_copy(
+    tmp_path: Path, caplog: pytest.LogCaptureFixture
+) -> None:
     path = tmp_path / "unshackle.yaml"
     path.write_text("credentials:\n  EXAMPLE: first-secret\n  EXAMPLE: second-secret\n", encoding="utf-8")
-    with pytest.warns(UserWarning) as caught:
+    with caplog.at_level(logging.WARNING, logger="config"):
         data = load_yaml(path)
+        load_yaml(path)
     assert data == {"credentials": {"EXAMPLE": "second-secret"}}
-    message = str(caught[0].message)
-    assert message == f"{path}: duplicate key on lines 2 and 3. Unshackle uses the later one."
-    assert "EXAMPLE" not in message and "secret" not in message
+    assert caplog.messages == [f"{path}: duplicate key on lines 2 and 3. Unshackle uses the later one."]
+    assert "EXAMPLE" not in caplog.text and "secret" not in caplog.text
 
 
-def test_config_from_yaml_warns_on_a_duplicate_key(tmp_path: Path) -> None:
+def test_config_from_yaml_warns_on_a_duplicate_key(tmp_path: Path, caplog: pytest.LogCaptureFixture) -> None:
     path = tmp_path / "unshackle.yaml"
     path.write_text("tag: first\ntag: second\n", encoding="utf-8")
-    with pytest.warns(UserWarning, match="duplicate key on lines 1 and 2"):
+    with caplog.at_level(logging.WARNING, logger="config"):
         assert Config.from_yaml(path).tag == "second"
+    assert "duplicate key on lines 1 and 2" in caplog.text
 
 
 @pytest.mark.parametrize(
@@ -40,9 +43,11 @@ def test_config_from_yaml_warns_on_a_duplicate_key(tmp_path: Path) -> None:
     ["a: 1\nb: [1, 2]\n", "", "a: &a\n  x: 1\nb: &b\n  y: 2\nc:\n  <<: *a\n  <<: *b\n"],
     ids=["valid", "empty", "two-merges"],
 )
-def test_load_yaml_matches_safe_load_without_a_warning(tmp_path: Path, text: str) -> None:
+def test_load_yaml_matches_safe_load_without_a_warning(
+    tmp_path: Path, text: str, caplog: pytest.LogCaptureFixture
+) -> None:
     path = tmp_path / "config.yaml"
     path.write_text(text, encoding="utf-8")
-    with warnings.catch_warnings():
-        warnings.simplefilter("error")
+    with caplog.at_level(logging.WARNING, logger="config"):
         assert load_yaml(path) == yaml.safe_load(text)
+    assert not caplog.records

unshackle/core/config.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import logging
 import re
 import warnings
 from pathlib import Path
@@ -411,6 +412,9 @@ def duplicate_key_message(name: str, pairs: list[tuple[int, int]], line: int = 0
     return f"{name}: duplicate key on {where}. Unshackle uses the later one."
 
 
+_warned: set[str] = set()
+
+
 def load_yaml(path: Path) -> Any:
     """yaml.safe_load a file, and warn with the lines of each duplicate key, which PyYAML takes silently."""
     loader = yaml.SafeLoader(path.read_text(encoding="utf8"))
@@ -418,8 +422,9 @@ def load_yaml(path: Path) -> Any:
         node = loader.get_single_node()
         if node is None:
             return None
-        if pairs := duplicate_key_lines(node):
-            warnings.warn(duplicate_key_message(str(path), pairs), stacklevel=2)
+        if (pairs := duplicate_key_lines(node)) and (message := duplicate_key_message(str(path), pairs)) not in _warned:
+            _warned.add(message)
+            logging.getLogger("config").warning(message)
         return loader.construct_document(node)
     finally:
         loader.dispose()