syntax_data: {"ast_node_type":"other","tokens":[{"end":46,"kind":"keyword","start":0,"text":"metavar_spans:"}]}
source_snippet:             metavar_spans: Default::default(),
context_before:             span_interner: Lock::new(span_encoding::SpanInterner::default()),
context_after:             hygiene_data: Lock::new(hygiene::HygieneData::new(edition)),