fix: Treat a repeated override file path in different case as a repeat on Windows

The builder dropped repeated paths by exact string match, so on Windows
a path listed twice in different case survived as two paths, and every
key of that file failed as a duplicate of itself under the default fail
handling. Paths are now compared with os.path.normcase, which ignores
case on Windows and compares exactly elsewhere. The first spelling keeps
its place in the order.

Author: kinyoklion

ldclient/integrations/overrides.py

@@ -27,6 +27,7 @@
 """
 
 import math
+import os
 import threading
 from typing import List, Optional, Union
 
@@ -158,9 +159,17 @@ def build(self, config: DataSourceBuilderConfig) -> OverrideSource:  # pylint: d
             poll_interval = self.MINIMUM_POLL_INTERVAL
 
         # A path listed more than once would make every entry of that file a duplicate of itself,
-        # so the repeats are dropped and the first occurrence keeps its place in the order.
+        # so the repeats are dropped and the first occurrence keeps its place in the order. Paths
+        # are compared the way the platform compares file names: without regard to case on
+        # Windows, exactly elsewhere.
         all_paths = abs_file_paths(self.__paths)
-        paths = list(dict.fromkeys(all_paths))
+        paths: List[str] = []
+        seen = set()
+        for path in all_paths:
+            key = os.path.normcase(path)
+            if key not in seen:
+                seen.add(key)
+                paths.append(path)
         if len(paths) != len(all_paths):
             log.warning("The file-based override source lists the same file more than once; the repeats are ignored")
 

ldclient/testing/integrations/test_file_override_source.py

@@ -3,6 +3,7 @@
 absent files, change detection in both modes, failure retention, and its Info log.
 """
 import logging
+import ntpath
 import os
 import threading
 import time
@@ -135,6 +136,24 @@ def test_builder_drops_a_repeated_path_and_warns(caplog):
     assert any('more than once' in r.getMessage() for r in caplog.records)
 
 
+def test_builder_treats_a_path_repeated_in_different_case_as_a_repeat_only_where_file_names_ignore_case():
+    source = FileOverrideSourceBuilder(['/a.json', '/A.json']).build(SDKConfig('SDK_KEY'))
+    assert isinstance(source, _FileOverrideSource)
+    if os.name == 'nt':
+        assert source._paths == [os.path.abspath('/a.json')]
+    else:
+        assert source._paths == [os.path.abspath('/a.json'), os.path.abspath('/A.json')]
+
+
+def test_builder_drops_a_path_repeated_in_different_case_on_windows(monkeypatch):
+    # Windows file names ignore case, so two spellings of one path name the same file. The path
+    # comparison of Windows is used here on any platform.
+    monkeypatch.setattr(os.path, 'normcase', ntpath.normcase)
+    source = FileOverrideSourceBuilder(['/a.json', '/b.json', '/A.json']).build(SDKConfig('SDK_KEY'))
+    assert isinstance(source, _FileOverrideSource)
+    assert source._paths == [os.path.abspath('/a.json'), os.path.abspath('/b.json')]
+
+
 def test_builder_polls_by_default(tmp_path):
     path = os.path.join(str(tmp_path), 'overrides.json')
     source = FileOverrideSourceBuilder([path]).build(SDKConfig('SDK_KEY'))