syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"self.alloc_ctxt(parent_opaque,"}]}
source_snippet:                 self.alloc_ctxt(parent_opaque, expn_id, transparency),
context_before:                 // Will be the same as `ctxt` if the expn chain contains only opaques.
context_after:                 // Will be the same as `ctxt` if the expn chain contains only (semi-)opaques.