fix(parameters): honor auto transform in batched get_parameters_by_name (#8436)

transform="auto" infers the transform method from the parameter name suffix, but _transform_and_cache_get_parameters_response called transform_value() without key=name. The batched GetParameters path therefore inferred from an empty string and silently fell back to the identity transform, returning raw strings instead of parsed values.

Parameters routed to the single GetParameter path (decrypt=True) already pass the key via BaseProvider.get(), so a single get_parameters_by_name call could return a parsed dict for some parameters and a raw string for others.

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

Author: MohammedAlkindi

aws_lambda_powertools/utilities/parameters/ssm.py

@@ -654,7 +654,12 @@ def _transform_and_cache_get_parameters_response(
 
             # NOTE: If transform is set, we do it before caching to reduce number of operations
             if transform:
-                value = transform_value(value=value, transform=transform, raise_on_transform_error=raise_on_error)  # type: ignore[assignment]
+                value = transform_value(
+                    value=value,
+                    transform=transform,
+                    raise_on_transform_error=raise_on_error,
+                    key=name,
+                )  # type: ignore[assignment]
 
             _cache_key = (name, transform)
             self.add_to_cache(key=_cache_key, value=value, max_age=options["max_age"])

tests/functional/parameters/_boto3/test_utilities_parameters.py

@@ -1142,6 +1142,34 @@ def test_ssm_provider_get_parameters_by_name_do_not_raise_on_failure_transform(m
         stubber.deactivate()
 
 
+def test_ssm_provider_get_parameters_by_name_auto_transform_infers_from_parameter_name(mock_name, mock_value, config):
+    # GIVEN transform="auto" and a parameter name suffixed with ".json"
+    # (auto-transform must infer the transform method from the parameter name, not its value)
+    success = f"/dev/{mock_name}.json"
+    fail = "/does_not_exist"  # stub model doesn't support all-success yet
+    params = {success: {}, fail: {}}
+    param_names = list(params.keys())
+    expected_value = {"value": mock_value}
+    stub_params = {success: json.dumps(expected_value)}
+
+    expected_stub_response = build_get_parameters_stub(params=stub_params, invalid_parameters=[fail])
+    expected_stub_params = {"Names": param_names}
+
+    provider = parameters.SSMProvider(boto_config=config)
+    stubber = stub.Stubber(provider.client)
+    stubber.add_response("get_parameters", expected_stub_response, expected_stub_params)
+    stubber.activate()
+
+    try:
+        ret = provider.get_parameters_by_name(parameters=params, transform="auto", raise_on_error=False)
+
+        stubber.assert_no_pending_responses()
+        # THEN the value should be parsed as JSON, not returned as a raw string
+        assert ret[success] == expected_value
+    finally:
+        stubber.deactivate()
+
+
 def test_ssm_provider_get_parameters_by_name_do_not_raise_on_failure_with_decrypt(mock_name, config):
     # GIVEN one parameter requires decryption and an arbitrary SDK error occurs
     param = f"/{mock_name}"