syntax_data: {"ast_node_type":"other","tokens":[{"end":53,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // up represented in MIR _somewhere_.
context_before:                 // patterns containing no bindings, to ensure that the type ends
context_after:                 let base_user_ty = self.canonical_user_type_annotations.push(annotation.clone());