Refactor the AnVIL plugin's manifest config

src/azul/plugins/metadata/anvil/__init__.py

@@ -277,6 +277,14 @@ def facets(self) -> Sequence[str]:
     def manifest_config(self) -> ManifestConfig:
         result = defaultdict(dict)
 
+        # This is used to modify the field names from how they are specified in
+        # the field mapping. Keys are field paths in an ES hit, and values are
+        # the desired manifest column name, or None to omit from the manifest.
+        custom_field_names = {
+            ('contents', 'files', 'uuid'): None,
+            ('contents', 'files', 'version'): None,
+        }
+
         def recurse(mapping: MetadataPlugin._FieldMapping, path: FieldPath):
             for path_element, name_or_type in mapping.items():
                 new_path = (*path, path_element)
@@ -285,20 +293,17 @@ def recurse(mapping: MetadataPlugin._FieldMapping, path: FieldPath):
                 elif isinstance(name_or_type, str):
                     if new_path == ('entity_id',):
                         pass
-                    elif new_path == ('contents', 'files', 'uuid'):
-                        # Request the injection of a file URL …
-                        result[path]['file_url'] = 'files.file_url'
-                        # … but suppress the columns for the fields …
-                        result[path][path_element] = None
-                    elif new_path == ('contents', 'files', 'version'):
-                        # … only used by that injection.
-                        result[path][path_element] = None
+                    elif new_path in custom_field_names:
+                        result[path][path_element] = custom_field_names[new_path]
                     else:
                         result[path][path_element] = name_or_type
                 else:
                     assert False, (path, path_element, name_or_type)
 
         recurse(self._field_mapping, ())
+        # Add a file URL column. It isn't an indexed field so isn't in the field
+        # mapping, rather it is dynamically added in during manifest generation.
+        result[('contents', 'files')]['file_url'] = 'files.file_url'
         return result
 
     def verbatim_pfb_schema(self,