syntax_data: {"ast_node_type":"other","tokens":[{"end":7,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     ///
context_before:     /// the given place has a variant downcast, we invoke the function on all the other variants.
context_after:     /// `tail_elem` allows to support discriminants that are not a place in MIR, but that we track