feat(backup): Enable shimming deleted fields

src/sentry/backup/imports.py

@@ -47,6 +47,20 @@
     "import_in_global_scope",
 )
 
+# We have to be careful when removing fields from our model schemas, since exports created using
+# the old-but-still-in-the-support-window versions could have those fields set in the data they
+# provide. This dict serves as a map of all fields that have been deleted on HEAD but are still
+# valid in at least one of the versions we support. For example, since our current version
+# support window is two minor versions back, if we delete a field at version 24.5.N, we must
+# include an entry in this map for that field until that version is out of the support window
+# (in this case, we can remove shim once version 24.7.0 is released).
+#
+# NOTE TO FUTURE EDITORS: please keep the `DELETED_FIELDS` dict, and the subsequent `if` clause,
+# around even if the dict is empty, to ensure that there is a ready place to pop shims into. For
+# each entry in this dict, please leave a TODO comment pointed to a github issue for removing
+# the shim, noting in the comment which self-hosted release will trigger the removal.
+DELETED_FIELDS: dict[str, set[str]] = {}
+
 
 class ImportingError(Exception):
     def __init__(self, context: RpcImportError) -> None:
@@ -135,6 +149,21 @@ def _import(
         if decryptor is not None
         else src.read().decode("utf-8")
     )
+
+    if len(DELETED_FIELDS) > 0:
+        # Parse the content JSON and remove and fields that we have marked for deletion in the
+        # function.
+        shimmed_models = set(DELETED_FIELDS.keys())
+        content_as_json = json.loads(content)  # type: ignore
+        for json_model in content_as_json:
+            if json_model["model"] in shimmed_models:
+                fields_to_remove = DELETED_FIELDS[json_model["model"]]
+                for field in fields_to_remove:
+                    json_model["fields"].pop(field, None)
+
+        # Return the content to byte form, as that is what the Django deserializer expects.
+        content = json.dumps(content_as_json)
+
     filters = []
     if filter_by is not None:
         filters.append(filter_by)