syntax_data: {"ast_node_type":"other","tokens":[{"end":66,"kind":"keyword","start":0,"text":"relation,"}]}
source_snippet:                     relation, a.def_id, variances, a.args, b.args,
context_before:                 relate_args_with_variances(
context_after:                     false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle