syntax_data: {"ast_node_type":"other","tokens":[{"end":60,"kind":"keyword","start":0,"text":"opaque_def_id:"}]}
source_snippet:                 opaque_def_id: opaque_ty_def_id.to_def_id(),
context_before:                 fn_def_id: fn_def_id.to_def_id(),
context_after:             }),