syntax_data: {"ast_node_type":"other","tokens":[{"end":48,"kind":"keyword","start":0,"text":"this.fmt_diff_with(old,"}]}
source_snippet:                 this.fmt_diff_with(old, ctxt, f)
context_before:             (MaybeReachable::Reachable(this), MaybeReachable::Reachable(old)) => {
context_after:             }