From 7c78178210960607ef24a8b64ecc39d6c54293bb Mon Sep 17 00:00:00 2001
From: Anthony Volk <14987227+anth-volk@users.noreply.github.com>
Date: Tue, 1 Sep 2026 19:38:35 +0400
Subject: [PATCH] Reject misplaced uprating rounding metadata

---
 ...eject-misplaced-uprating-rounding.fixed.md |  1 +
 policyengine_core/parameters/helpers.py       | 17 ++++++
 .../parameters/operations/test_uprating.py    | 56 +++++++++++++++++++
 3 files changed, 74 insertions(+)
 create mode 100644 changelog.d/reject-misplaced-uprating-rounding.fixed.md

diff --git a/changelog.d/reject-misplaced-uprating-rounding.fixed.md b/changelog.d/reject-misplaced-uprating-rounding.fixed.md
new file mode 100644
index 00000000..6fbae3f5
--- /dev/null
+++ b/changelog.d/reject-misplaced-uprating-rounding.fixed.md
@@ -0,0 +1 @@
+Parameter loading now rejects uprating rounding rules placed where they would be silently ignored.
diff --git a/policyengine_core/parameters/helpers.py b/policyengine_core/parameters/helpers.py
index 8435bf46..ab0af7b6 100644
--- a/policyengine_core/parameters/helpers.py
+++ b/policyengine_core/parameters/helpers.py
@@ -90,10 +90,27 @@ def _validate_parameter(parameter, data, data_type=None, allowed_keys=None):
             parameter.file_path,
         )
 
+    if isinstance(data, dict):
+        _validate_uprating_rounding_metadata(parameter, data.get("metadata"))
+
     if allowed_keys is not None and isinstance(data, dict):
         _warn_on_unknown_keys(parameter, data, allowed_keys)
 
 
+def _validate_uprating_rounding_metadata(parameter, metadata):
+    if not isinstance(metadata, dict):
+        return
+    if "uprating" not in metadata or "rounding" not in metadata:
+        return
+
+    raise ParameterParsingError(
+        "Invalid uprating metadata for '{}': `rounding` must be nested inside "
+        "`uprating`; placing both keys at the same level causes the rounding "
+        "rule to be ignored.".format(parameter.name),
+        parameter.file_path,
+    )
+
+
 def _warn_on_unknown_keys(parameter, data, allowed_keys):
     """Warn about keys placed alongside the recognized parameter keys.
 
diff --git a/tests/core/parameters/operations/test_uprating.py b/tests/core/parameters/operations/test_uprating.py
index dcd4eaf7..74aee22e 100644
--- a/tests/core/parameters/operations/test_uprating.py
+++ b/tests/core/parameters/operations/test_uprating.py
@@ -344,6 +344,62 @@ def test_parameter_uprating_with_rounding():
     assert interpolated.to_be_uprated("2018-01-01") == 4
 
 
+@pytest.mark.parametrize(
+    "data",
+    [
+        {
+            "parameter": {
+                "values": {"2025-01-01": 1},
+                "metadata": {
+                    "uprating": "uprater",
+                    "rounding": {"interval": 1, "type": "upwards"},
+                },
+            },
+        },
+        {
+            "scale": {
+                "metadata": {
+                    "uprating": "uprater",
+                    "rounding": {"interval": 1, "type": "upwards"},
+                },
+                "brackets": [
+                    {
+                        "threshold": {"2025-01-01": 0},
+                        "rate": {"2025-01-01": 0.1},
+                    },
+                ],
+            },
+        },
+        {
+            "scale": {
+                "brackets": [
+                    {
+                        "threshold": {"2025-01-01": 0},
+                        "rate": {"2025-01-01": 0.1},
+                        "metadata": {
+                            "uprating": "uprater",
+                            "rounding": {
+                                "interval": 1,
+                                "type": "upwards",
+                            },
+                        },
+                    },
+                ],
+            },
+        },
+    ],
+)
+def test_parameter_uprating_rejects_rounding_beside_uprating(data):
+    from policyengine_core.errors import ParameterParsingError
+    from policyengine_core.parameters import ParameterNode
+
+    with pytest.raises(
+        ParameterParsingError,
+        match="`rounding` must be nested inside `uprating`",
+    ):
+        ParameterNode(data=data)
+
+
 def test_parameter_uprating_with_self():
     from policyengine_core.parameters import ParameterNode