syntax_data: {"ast_node_type":"other","tokens":[{"end":99,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // and `parent_opaque_and_semiopaque` == `parent` if the expn contains only (semi-)opaques.
context_before:         // parent itself. E.g. `parent_opaque` == `parent` if the expn chain contains only opaques,
context_after:         let parent_data = &self.syntax_context_data[parent.0 as usize];