Filter JSON instead of diff

Instead of trying to filter out doc strings after running the diff, adjust the input to the diff to get the same effect.  This is a little less fragile.

python/lsst/daf/butler_migrate/_dimensions_json_utils.py

@@ -21,7 +21,6 @@
 
 import difflib
 import json
-from typing import Literal
 
 import yaml
 from lsst.resources import ResourcePath
@@ -67,9 +66,7 @@ def load_historical_dimension_universe_json(universe_version: int) -> str:
     return json.dumps(dimensions)
 
 
-def compare_json_strings(
-    expected: str, actual: str, diff_style: Literal["unified", "ndiff"] = "unified"
-) -> str | None:
+def compare_json_strings(expected: str, actual: str) -> str | None:
     """Compare two JSON strings and return a human-readable description of
     the differences.
 
@@ -79,8 +76,6 @@ def compare_json_strings(
         JSON-encoded string to use as the basis for comparison.
     actual : `str`
         JSON-encoded string to compare with the expected value.
-    diff_style : "unified" | "ndiff"
-        What type of diff to return.
 
     Returns
     -------
@@ -95,12 +90,7 @@ def compare_json_strings(
     if expected == actual:
         return None
 
-    if diff_style == "unified":
-        diff = difflib.unified_diff(expected.splitlines(), actual.splitlines(), lineterm="")
-    elif diff_style == "ndiff":
-        diff = difflib.ndiff(expected.splitlines(), actual.splitlines())
-    else:
-        raise ValueError(f"Unknown {diff_style=}")
+    diff = difflib.unified_diff(expected.splitlines(), actual.splitlines(), lineterm="")
     return "\n".join(diff)
 
 

python/lsst/daf/butler_migrate/butler_attributes.py

@@ -22,7 +22,6 @@
 from __future__ import annotations
 
 import json
-import re
 from collections.abc import Callable, Iterable
 from typing import Any, cast
 
@@ -251,24 +250,28 @@ def _is_expected_dimensions_json_mismatch(expected_json: str, actual_json: str)
     # don't match the current dimension universe because of how dimension
     # universes were patched in earlier migrations.
 
-    diff = compare_json_strings(expected_json, actual_json, diff_style="ndiff")
-    if diff is None:
-        return True
+    diff = compare_json_strings(
+        _strip_doc_properties_from_json(expected_json), _strip_doc_properties_from_json(actual_json)
+    )
+    return diff is None
 
-    return all(_is_expected_diff_line(line) for line in diff.splitlines())
 
+def _strip_doc_properties_from_json(json_string: str) -> str:
+    # Remove any properties named 'doc' from objects in the given JSON string.
+    dictionary = json.loads(json_string)
+    stripped = _strip_doc_properties_from_dict(dictionary)
+    return json.dumps(stripped)
 
-def _is_expected_diff_line(line: str) -> bool:
-    # ndiff prefix for matching lines and "hint" lines.
-    if line.startswith("  ") or line.startswith("? "):
-        return True
 
-    # Lines containing only docstring changes.
-    if re.match(r'^[-+]\s+"doc":', line):
-        return True
+def _strip_doc_properties_from_dict(dictionary: dict[str, object]) -> dict[str, object]:
+    # Recursively remove any properties named 'doc' from the given dict or any
+    # dicts in its values.
+    stripped: dict[str, object] = {}
+    for key, value in dictionary.items():
+        if key != "doc":
+            if isinstance(value, dict):
+                stripped[key] = _strip_doc_properties_from_dict(value)
+            else:
+                stripped[key] = value
 
-    # Empty line.
-    if line.strip() == "":
-        return True
-
-    return False
+    return stripped

tests/test_dimensions_json.py

@@ -329,23 +329,25 @@ def test_validate_dimensions_json(self) -> None:
             attribs.validate_dimensions_json(universe)
 
     def test_ignore_expected_dimension_json_mismatch(self) -> None:
-        original = '{"a": 1, "doc": "good"}'
+        original = '{"a": 1, "b": {"doc": "good"}}'
         self.assertTrue(butler_attributes._is_expected_dimensions_json_mismatch(original, original))
         # Mismatched doc but everything else OK
         self.assertTrue(
-            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"a": 1, "doc": "bad"}')
+            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"a": 1, "b": {"doc": "bad"}}')
         )
         # Order doesn't matter
         self.assertTrue(
-            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"doc": "bad", "a": 1}')
+            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"b": {"doc": "bad"}, "a": 1}')
         )
         # Mismatched non-doc value
         self.assertFalse(
-            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"a": 2, "doc": "good"}')
+            butler_attributes._is_expected_dimensions_json_mismatch(
+                original, '{"a": 2, "b": {"doc": "good"}}'
+            )
         )
         # Mismatched value and doc
         self.assertFalse(
-            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"a": 2, "doc": "bad"}')
+            butler_attributes._is_expected_dimensions_json_mismatch(original, '{"a": 2, "b": {"doc": "bad"}}')
         )