fix(data-classes): keep CaseInsensitiveDict on copy and merge (#8537)

* fix(data-classes): keep CaseInsensitiveDict on copy and merge

* test(data-classes): cover non-mapping operands in CaseInsensitiveDict merge

---------

Co-authored-by: Leandro Damascena <lcdama@amazon.pt>

Author: chiruu12

aws_lambda_powertools/utilities/data_classes/common.py

@@ -63,6 +63,27 @@ def update(self, data=None, **kwargs):
             super().update((k.lower(), v) for k, v in data)
         super().update((k.lower(), v) for k, v in kwargs.items())
 
+    def copy(self):
+        return CaseInsensitiveDict(self)
+
+    def __or__(self, other):
+        if not isinstance(other, Mapping):
+            return NotImplemented
+        new = self.copy()
+        new.update(other)
+        return new
+
+    def __ror__(self, other):
+        if not isinstance(other, Mapping):
+            return NotImplemented
+        new = CaseInsensitiveDict(other)
+        new.update(self)
+        return new
+
+    def __ior__(self, other):
+        self.update(other)
+        return self
+
     def __contains__(self, k):
         return super().__contains__(k.lower())
 

tests/unit/data_classes/required_dependencies/test_common.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pytest
+
 from aws_lambda_powertools.utilities.data_classes.common import CaseInsensitiveDict
 
 
@@ -17,3 +19,41 @@ def test_case_insensitive_dict_update_with_kwargs():
     assert headers["AB"] == "1"
     assert headers["user_agent"] == "test"
     assert len(headers) == 3
+
+
+def test_case_insensitive_dict_copy_keeps_case_insensitive_lookup():
+    headers = CaseInsensitiveDict({"Content-Type": "application/json"})
+    copied = headers.copy()
+
+    assert isinstance(copied, CaseInsensitiveDict)
+    assert copied.get("Content-Type") == "application/json"
+
+    copied["X-Trace-Id"] = "abc"
+    assert "x-trace-id" not in headers
+
+
+def test_case_insensitive_dict_merge_operators():
+    headers = CaseInsensitiveDict({"Content-Type": "application/json"})
+
+    merged = headers | {"X-Trace-Id": "abc"}
+    assert isinstance(merged, CaseInsensitiveDict)
+    assert merged["x-trace-id"] == "abc"
+    assert merged["CONTENT-TYPE"] == "application/json"
+
+    merged = {"X-Trace-Id": "abc"} | headers
+    assert isinstance(merged, CaseInsensitiveDict)
+    assert merged["X-TRACE-ID"] == "abc"
+
+    headers |= {"X-Trace-Id": "abc"}
+    assert headers["x-trace-id"] == "abc"
+    assert list(headers) == ["content-type", "x-trace-id"]
+
+
+def test_case_insensitive_dict_merge_rejects_non_mapping():
+    headers = CaseInsensitiveDict({"Content-Type": "application/json"})
+
+    with pytest.raises(TypeError):
+        headers | [("X-Trace-Id", "abc")]
+
+    with pytest.raises(TypeError):
+        [("X-Trace-Id", "abc")] | headers