ref(backup): Do deepcopy before validation

Previously, all validation mutated the inputs in-place. This was
performant (no need to make deep copies of two potentially large JSON
blobs), but potentially bug prone if not held carefully, since the
validation itself mutated the inputs via JSONScrubbingComparators. This
means that the post-comparison input objects MUST NOT be re-used, since
they are meaningfully different from the inputs that were declared
valid.

Instead, we now do deepcopies under the hood, leaving the originally
passed-in inputs untouched.

Issue: getsentry/team-ospo#156

src/sentry/runner/commands/backup.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
+from copy import deepcopy
 from datetime import datetime, timedelta, timezone
 from difflib import unified_diff
 from io import StringIO
@@ -159,10 +160,13 @@ def compare(self, on: InstanceID, left: JSONData, right: JSONData) -> Comparator
 
 
 def validate(
-    expect: JSONData, actual: JSONData, comparators: ComparatorMap = DEFAULT_COMPARATORS
+    expect: JSONData,
+    actual: JSONData,
+    comparators: ComparatorMap = DEFAULT_COMPARATORS,
 ) -> ComparatorFindings:
     """Ensures that originally imported data correctly matches actual outputted data, and produces a
-    list of reasons why not when it doesn't"""
+    list of reasons why not when it doesn't.
+    """
 
     def json_lines(obj: JSONData) -> list[str]:
         """Take a JSONData object and pretty-print it as JSON."""
@@ -176,6 +180,11 @@ def json_lines(obj: JSONData) -> list[str]:
         id = InstanceID(model["model"], model["pk"])
         exp_models[id] = model
 
+    # Because we may be scrubbing data from the objects as we compare them, we may (optionally) make
+    # deep copies to start to avoid potentially mangling the input data.
+    expect = deepcopy(expect)
+    actual = deepcopy(actual)
+
     # Ensure that the actual JSON contains no duplicates - we assume that the expected JSON did not.
     for model in actual:
         id = InstanceID(model["model"], model["pk"])

tests/sentry/backup/test_correctness.py

@@ -20,7 +20,9 @@
 
 
 def import_export_then_validate(
-    tmp_path: Path, fixture_file_name: str, map: ComparatorMap = EMPTY_COMPARATORS_FOR_TESTING
+    tmp_path: Path,
+    fixture_file_name: str,
+    map: ComparatorMap = EMPTY_COMPARATORS_FOR_TESTING,
 ) -> None:
     """Test helper that validates that data imported from a fixture `.json` file correctly matches
     the actual outputted export data."""
@@ -34,11 +36,7 @@ def import_export_then_validate(
         rv = CliRunner().invoke(import_, [str(fixture_file_path)])
         assert rv.exit_code == 0, rv.output
 
-    res = validate(
-        expect,
-        tmp_export_to_file(tmp_path.joinpath("tmp_test_file.json")),
-        map,
-    )
+    res = validate(expect, tmp_export_to_file(tmp_path.joinpath("tmp_test_file.json")), map)
     if res.findings:
         raise ValidationError(res)